Jun. 2024, The Royal Society of Chemistry, 2024 Materials Chemistry Horizon Prize
For demonstrating the potential and impact of embedded mechanochemical reactivity on the mechanical limits of cross-linked polymer networks
NSF Center for Molecularly;Optimized Networks

Mar. 2023, American Physical Society, 2023 Polymer Physics Prize　　　　　　　　　　　　　　　
For outstanding contributions to the understanding of mechanical and fracture properties of hydrogels based on novel network architectures and for discovering the concept of double network gels based on internal overstressed sacrificial bonds
Jian Ping Gong

Mar. 2022, Chemical Society of Japan, The 74th Chemical Society of Japan (CSJ) Award　　　　　　　　　　　　　　　
Creation of Diverse Soft Materials with High Toughness by Sacrificial Bond Principle
Jian Ping Gong

May 2021, The Society of Rubber Science and Technology, Japan, Award of the Society of Rubber Science and Technology, Japan (2021)
Development of a polymer complex that achieves both low fuel consumption and high strength toward the realization of resource-saving tires
Katsuhiko Tsunoda;Kohzo Ito;Hideaki Yokoyama;Jian Ping Gong;Kenji Urayama, 24510616

Apr. 2019, Ministry of Education, Culture, Sports, Science and Technology, 2019 The Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology: Prizes for Science and Technology　　　　　　　　　　　　　　　
受賞した研究テーマ「強靭ゲルの創成とその強靭化原理の解明に関する研究
Jian Ping Gong, Others

Mar. 2018, Hokkaido University President's Award for Excellence in Research and Education for AY2017　　　　　　　　　　　　　　　
Jian Ping Gong

Jul. 2014, Royal DSM, The DSM Materials Sciences Award 2014　　　　　　　　　　　　　　　
Jian Ping Gong

Mar. 2014, 平成25年度北海道大学研究総長賞　　　　　　　　　　　　　　　
グン 剣萍

2011, 日本化学会 第28回学術賞　　　　　　　　　　　　　　　
Japan

2011, The Chemical Society of Japan Award for Creative Work for 2011　　　　　　　　　　　　　　　

2006, 高分子学会賞（科学）　　　　　　　　　　　　　　　
Japan

2006, The Award of the Society of Polymer Science, Japan　　　　　　　　　　　　　　　

2001, 2001年Wiley高分子科学賞（物理学分野）　　　　　　　　　　　　　　　
Japan

2001, 2001 Wiley Polymer Science Award (Physics)　　　　　　　　　　　　　　　

Phase separation-induced glass transition under critical miscible conditions
Mayu Watanabe, Dong Shi, Ryuji Kiyama, Kagari Maruyama, Yuichiro Nishizawa, Takayuki Uchihashi, Jian Ping Gong, Takayuki Nonoyama
Materials Advances, 2024, 5, 7140, 7146, Royal Society of Chemistry (RSC), Sep. 2024, [Peer-reviewed]
English, Scientific journal, A polymer material shows phase separation-induced glass transition under critical miscible conditions, where the miscible/immiscible state is altered by temperature variations predicted by temperature-corrected Hansen solubility parameters., 42408869

A multiscale model for the multiaxial anisotropic damage of double-network gels
Lionel Ogouari, Qiang Guo, Fahmi Zaïri, Thanh-Tam Mai, Jian Ping Gong, Kenji Urayama
Mechanics of Materials, 196, 105058, 105058, Elsevier BV, Sep. 2024, [Peer-reviewed], ［Internationally co-authored］
English, Scientific journal

Unique stick–slip crack dynamics of double-network hydrogels under pure-shear loading
Yong Zheng, Yiru Wang, Fucheng Tian, Tasuku Nakajima, Chung-Yuen Hui, Jian Ping Gong
Proceedings of the National Academy of Sciences, 121, 30, Proceedings of the National Academy of Sciences, 17 Jul. 2024, [Peer-reviewed], [Last author, Corresponding author]
English, Scientific journal, In this work, we have found that a prenotched double-network (DN) hydrogel, when subjected to tensile loading in a pure-shear geometry, exhibits intriguing stick–slip crack dynamics. These dynamics synchronize with the oscillation of the damage (yielding) zone at the crack tip. Through manipulation of the loading rate and the predamage level of the brittle network in DN gels, we have clarified that this phenomenon stems from the significant amount of energy dissipation required to form the damage zone at the crack tip, as well as a kinetic contrast between the rapid crack extension through the yielding zone (slip process) and the slow formation of a new yielding zone controlled by the external loading rate (stick process)., 42408869

Real-Space Visualization of Charged Polymer Network of Hydrogel by Double Network Strategy and Mineral Staining
Shinji Noguchi, Ryuji Kiyama, Masahiro Yoshida, Maradhana Agung Marsudi, Naohiro Kashimura, Kiyoharu Tadanaga, Jian Ping Gong, Takayuki Nonoyama
Nano Letters, American Chemical Society (ACS), 09 Jul. 2024
English, Scientific journal

Hydrogel morphogenesis induced by force-controlled growth
Zhi Jian Wang, Ji Lin, Tasuku Nakajima, Jian Ping Gong
Proceedings of the National Academy of Sciences, 121, 27, Proceedings of the National Academy of Sciences, 26 Jun. 2024, [Peer-reviewed], [Last author, Corresponding author], ［Internationally co-authored］
English, Scientific journal, Morphogenesis is one of the most marvelous natural phenomena. The morphological characteristics of biological organs develop through growth, which is often triggered by mechanical force. In this study, we propose a bioinspired strategy for hydrogel morphogenesis through force-controlled chemical reaction and growth under isothermal conditions. We adopted a double network (DN) hydrogel with sacrificial bonds. Applying mechanical force to the gel caused deformation and sacrificial bond rupture. By supplying monomers to the gel, the radicals generated by the bond rupture triggered the formation of a new network inside the deformed gel. This new network conferred plasticity to the elastic gel, allowing it to maintain its deformed shape, along with increased volume and strength. We demonstrated that sheet-shaped DN hydrogels rapidly adopted various three-dimensional shapes at ambient temperature when subjected to forces such as drawing and blowing. This mechanism enables morphogenesis of elastic hydrogels and will promote the application of these materials in biomedical fields and soft machines., 36977687

Pre-yielding and necking process of double network hydrogels revealed by sample geometry effects
Masahiro Yoshida, Ryuji Kiyama, Ye Zhang, Daniel R. King, Takayuki Kurokawa, Jian Ping Gong
Extreme Mechanics Letters, 69, 102163, 102163, Elsevier BV, Jun. 2024, [Peer-reviewed], [Last author, Corresponding author]
English, Scientific journal, 36977687

Design principles for strong and tough hydrogels
Xueyu Li, Jian Ping Gong
Nature Reviews Materials, 9, 380, 398, Springer Science and Business Media LLC, 07 May 2024
English, Scientific journal

Effect of the Activation Force of Mechanophore on Its Activation Selectivity and Efficiency in Polymer Networks
Zhi Jian Wang, Shu Wang, Julong Jiang, Yixin Hu, Tasuku Nakajima, Satoshi Maeda, Stephen L. Craig, Jian Ping Gong
Journal of the American Chemical Society, 146, 19, 13336, 13346, American Chemical Society (ACS), 02 May 2024, [Peer-reviewed], [Last author, Corresponding author], ［Internationally co-authored］
English, Scientific journal, 36977687

Tuning network structures of hydrophobic hydrogels by controlling polymerization solvent
Hailong Fan, Daito Naohara, Wei Li, Xiang Li, Jian Ping Gong
Polymer Chemistry, 15, 20, 2104, 2111, Royal Society of Chemistry (RSC), May 2024, [Peer-reviewed], [Last author, Corresponding author]
English, Scientific journal, Hydrophobic hydrogels with various copolymer sequences and network structures are prepared by tuning the solvent condition of the reaction solution, which exhibit different appearance and properties under the same monomer composition., 36977687

Mapping deformation and dissipation during fracture of soft viscoelastic solid
Yuan Qi, Xueyu Li, Sairam Pamulaparthi Venkata, Xingwei Yang, Tao Lin Sun, Chung-Yuen Hui, Jian Ping Gong, Rong Long
Journal of the Mechanics and Physics of Solids, 186, 105595, 105595, Elsevier BV, May 2024, [Peer-reviewed], ［Internationally co-authored］
English, Scientific journal, 42408869

Color-switching hydrogels as integrated microfluidic pressure sensors
Lucie Ducloué, Md. Anamul Haque, Martyna Goral, Muhammad Ilyas, Jian Ping Gong, Anke Lindner
Scientific Reports, 14, 1, Springer Science and Business Media LLC, 15 Mar. 2024, [Peer-reviewed]
English, Scientific journal, Abstract

Precisely measuring pressure in microfluidic flows is essential for flow control, fluid characterization, and monitoring, but faces specific challenges such as achieving sufficient resolution, non-invasiveness, or ease of use. Here, we demonstrate a fully integrated multiplexed optofluidic pressure sensor, entirely decoupled from the flow path, that enables local pressure measurements along any microfluidic channel without altering its flow geometry. The sensor itself relies on the compression of a soft mechano-actuated hydrogel, changing color in response to a pressure change. The hydrogel is separated from the fluid circulating in the channel by a thin membrane, allowing for the unrestricted use of different types of fluids. Imaging the gel through the transparent PDMS with a color camera provides a direct, easy, and contact-free determination of the fluid pressure at the sensing location for pressures as small as 20mbar with a resolution of around 10mbar. The sensitivity and accessible pressure range can be tuned via the mechanical properties of the sensing unit. The photonic gel can also be used to acquire 2D pressure or deformation maps, taking advantage of the fast response time and fine spatial resolution., 36977687

Tough Hydroxyapatite Hydrogels Based on Bone-like Self-Regulatory Sacrificial Bond Formation
Naohiro Kashimura, Yuki Suzuki, Takayuki Nonoyama, Jian Ping Gong
Chemistry of Materials, 36, 6, 2944, 2952, American Chemical Society (ACS), 05 Mar. 2024, [Peer-reviewed], [Last author, Corresponding author]
English, Scientific journal, Learning from nature is a promising approach to achieving specific functions of synthetic materials. The high material functions, in turn, shed light on the fundamental mechanisms underlying the high performance of biological tissues. For instance, bone is an attractive metabolic tissue with fascinating capabilities from the perspective of both biochemical and biomechanical functionalities. Bone tissue exhibits exceptional mechanical performance as a skeleton, enabling to sustain the locomotion of mammals. In this study, we design coupled reactions for self-regulatory sacrificial bond formation in poly(acrylic acid) hydrogels by introducing biomineral hydroxyapatite (HAp) found in bones. We demonstrate that through five coupled reactions, HAp regulates the Ca2+ bridging to the acidic polymer and toughens the hydrogels in water by the sacrificial bonds effect. This work is expected not only to greatly contribute to the design of tough soft materials but also to give deep insights into the self-regulated bone-toughening mechanisms., 36977687

Spatial Analysis of the Damage Zone in Double Network Hydrogel Using the Microelectrode Technique
Takuya Nishimura, Honglei Guo, Yoshinori Katsuyama, Masahiro Yoshida, Jian Ping Gong, Takayuki Kurokawa
Macromolecules, 57, 4, 1502, 1508, American Chemical Society (ACS), 09 Feb. 2024, [Peer-reviewed]
English, Scientific journal, 42408869

Effect of Predamage on the Fracture Energy of Double-Network Hydrogels
Yong Zheng, Yiru Wang, Tasuku Nakajima, Jian Ping Gong
ACS Macro Letters, 13, 2, 130, 137, American Chemical Society (ACS), 11 Jan. 2024, [Peer-reviewed], [Last author, Corresponding author]
English, Scientific journal, 36977687

Role of hierarchy structure on the mechanical adaptation of self-healing hydrogels under cyclic stretching
Xueyu Li, Kunpeng Cui, Yong Zheng, Ya Nan Ye, Chengtao Yu, Wenqi Yang, Tasuku Nakajima, Jian Ping Gong
Science Advances, 9, 51, American Association for the Advancement of Science (AAAS), 20 Dec. 2023, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, Soft materials with mechanical adaptability have substantial potential for various applications in tissue engineering. Gaining a deep understanding of the structural evolution and adaptation dynamics of soft materials subjected to cyclic stretching gives insight into developing mechanically adaptive materials. Here, we investigate the effect of hierarchy structure on the mechanical adaptation of self-healing hydrogels under cyclic stretching training. A polyampholyte hydrogel, composed of hierarchical structures including ionic bonds, transient and permanent polymer networks, and bicontinuous hard/soft-phase networks, is adopted as a model. Conditions for effective training, mild overtraining, and fatal overtraining are demonstrated in soft materials. We further reveal that mesoscale hard/soft-phase networks dominate the long-term memory effect of training and play a crucial role in the asymmetric dynamics of compliance changes and the symmetric dynamics of hydrogel shape evolution. Our findings provide insights into the design of hierarchical structures for adaptive soft materials.

Azobenzene as a photoswitchable mechanophore
Yiran Li, Bin Xue, Jiahui Yang, Julong Jiang, Jing Liu, Yanyan Zhou, Junsheng Zhang, Mengjiao Wu, Yuan Yuan, Zhenshu Zhu, Zhi Jian Wang, Yulan Chen, Yu Harabuchi, Tasuku Nakajima, Wei Wang, Satoshi Maeda, Jian Ping Gong, Yi Cao
Nature Chemistry, Springer Science and Business Media LLC, 05 Dec. 2023, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 36977687

Thermoresponsive Lamellar Hydrogels with Tunable Turbidity, Structural Color, and Anisotropic Swelling
Yang Han, Yunzhou Guo, Tasuku Nakajima, Jian Ping Gong
ACS Applied Materials & Interfaces, 15, 49, 57687, 57698, American Chemical Society (ACS), 29 Nov. 2023, [Peer-reviewed], [Last author, Corresponding author], [International Magazine]
English, Scientific journal, 36977687

Fractographic mirror law for brittle fracture of nonlinear elastic soft materials
Ryuji Kiyama, Yong Zheng, Takayuki Nonoyama, Jian Ping Gong
Soft Matter, 19, 40, 7724, 7730, Royal Society of Chemistry (RSC), Sep. 2023, [Peer-reviewed], [Corresponding author]
English, Scientific journal, The first fractographic mirror radius analysis for soft hydrogel materials was conducted. The universal −1 power law between fracture stress and mirror radius was established, in contrast to the different power law of linear elastic hard materials., 42408869

Sustainable mechanochemical growth of double-network hydrogels supported by vascular-like perfusion
Gumi Wei, Yumeko Kudo, Takahiro Matsuda, Zhi Jian Wang, Qi Feng Mu, Daniel R. King, Tasuku Nakajima, Jian Ping Gong
Materials Horizons, 2023, 10, 4882, 4891, Royal Society of Chemistry (RSC), Aug. 2023, [Peer-reviewed], [Last author, Corresponding author]
English, Scientific journal, Double-network (DN) gels are unique mechanochemical materials owing to their structures that can be dynamically remodelled during use., 36977687

Mechanical Reinforcement of Lamellar Bilayer Hydrogels by Small Amounts of Co-surfactants
Milena Lama, Jian Ping Gong
ACS Omega, 8, 28, 25185, 25194, American Chemical Society (ACS), 03 Jul. 2023, [Peer-reviewed], [Last author, Corresponding author]
English, Scientific journal, 42408869

Origin of Surface Charge of Double Network Hydrogels Prepared by Sequential Polymerization
Martin Frauenlob, Honglei Guo, Takayuki Kurokawa, Jian Ping Gong
ACS macro letters, 56, 11, 860, 865, 20 Jun. 2023, [Last author, Corresponding author], [International Magazine]
English, Scientific journal, Understanding the physicochemical properties of hydrogel surfaces and their molecular origins is important for their applications. In this paper, we elucidate the molecular origin of surface charges in double-network hydrogels synthesized by two-step sequential polymerization. Synthesis of hydrogels by free-radical polymerization does not fully complete the reaction, leaving a small number of unreacted monomers. When this approach is used to synthesize double network (DN) hydrogels by a two-step sequential polymerization from charged monomers for the first network and neutral monomers for the second network, the unreacted first network monomers are incorporated into the second network. Since the surface of such DN hydrogels is covered with a μm-thick layer of the neutral second network, the incorporation of a small amount of charged monomers into the second network increases the surface charge and, thereby, their repulsive/adhesive properties. Therefore, we propose a method to remove unreacted monomers and modulate the surface charge density of DN hydrogels., 42408869

Swelling Effect on the Yielding, Elasticity, and Fracture of Double-Network Hydrogels with an Inhomogeneous First Network
Yong Zheng, Tasuku Nakajima, Wei Cui, Chung-Yuen Hui, Jian Ping Gong
Macromolecules, 56, 11, 3962, 3972, American Chemical Society (ACS), 17 May 2023, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 36977687

Inverse mechanical-swelling coupling of a highly deformed double-network gel
Chika Imaoka, Tasuku Nakajima, Tsutomu Indei, Masaya Iwata, Wei Hong, Alba Marcellan, Jian Ping Gong
Science Advances, 9, 19, American Association for the Advancement of Science (AAAS), 10 May 2023, [Peer-reviewed], [Last author], ［Internationally co-authored］
English, Scientific journal, Mechanical behaviors of a polymer gel are coupled with its swelling behavior. It has been known that typical hydrogels display extension-induced swelling and drying-induced stiffening, called normal mechanical-swelling coupling. In this study, we experimentally found that highly extended double-network (DN) hydrogels exhibit abnormal inverse mechanical-swelling coupling such as extension-induced deswelling and drying-induced softening. We established theoretical hyperelastic and swelling models that reproduced all the complicated mechanical and swelling trends of the highly deformed DN hydrogels. From these theoretical analyses, it is considered that the inverse mechanical-swelling coupling of a DN gel is derived from the extreme nonlinear elasticity of its first network at its ultimate deformation state. These findings contribute toward the understanding of the mechanics of rubber-like materials up to their ultimate deformation and fracture limit., 36977687

Mechanical Model for Super-Anisotropic Swelling of the Multi-Cylindrical PDGI/PAAm Gels
Tasuku Nakajima, Kei Mito, Jian Ping Gong
Polymers, 15, 7, 1624, 1624, MDPI AG, 24 Mar. 2023, [Peer-reviewed], [Last author, Corresponding author]
English, Scientific journal, MC-PDGI/PAAm gels are cylindrical composite gels containing poly(dodecyl glyceryl itaconate) (PDGI) as a polymerized lipid oriented in a multilayer tubular shape within a polyacrylamide (PAAm) network. The most unique feature of the MC-PDGI/PAAm gel is its super-anisotropic swelling, wherein the diameter of the gel increases, but the length decreases with an increase in the volume of the gel. Through swelling and small-angle X-ray diffraction experiments, we investigated the effects of PDGI lipid bilayers and polymer network on the swelling of the MC-PDGI/PAAm gel, which suggests that the swelling anisotropy of the MC-PDGI/PAAm gel is dominated by the elasticity of the PDGI bilayers. Furthermore, we investigated the equation of state of the gel that roughly reproduced the experimental swelling results. These findings are crucial for realizing the controlled super-anisotropic swelling of MC-PDGI/PAAm gels and their applications as anisotropic actuation devices., 36977687

In Situ and Real-Time Visualization of Mechanochemical Damage in Double-Network Hydrogels by Prefluorescent Probe via Oxygen-Relayed Radical Trapping
Yong Zheng, Julong Jiang, Mingoo Jin, Daiyo Miura, Fei Xue Lu, Koji Kubota, Tasuku Nakajima, Satoshi Maeda, Hajime Ito, Jian Ping Gong
Journal of the American Chemical Society, 145, 13, 7376, 7389, 23 Mar. 2023, [Peer-reviewed], [Last author, Corresponding author], [International Magazine]
English, Scientific journal, Visualization of mechanochemical damages, especially for those in the molecular-scale (e.g., bond scission in polymeric materials), is of great industrial and academic significance. Herein, we report a novel strategy for in situ and real-time visualization of mechanochemical damages in hydrogels by utilizing prefluorescent probes via oxygen-relayed free-radical trapping. Double-network (DN) hydrogels that generate numerous mechanoradicals by homolytic bond scission of the brittle first network at large deformation are used as model materials. Theoretical calculation suggests that mechanoradicals generated by the damage of the first network undergo an oxygen-relayed radical-transfer process which can be detected by the prefluorescent probe through the radical-radical coupling reaction. Such an oxygen-relayed radical-trapping process of the prefluorescent probe exhibits a dramatically enhanced emission, which enables the real-time sensing and visualization of mechanochemical damages in DN hydrogels made from brittle networks of varied chemical structures. To the best of authors' knowledge, this work is the first report utilizing oxygen as a radical-relaying molecule for visualizing mechanoradical damages in polymer materials. Moreover, this new method based on the probe post-loading is simple and does not introduce any chemical structural changes in the materials, outperforming most previous methods that require chemical incorporation of mechanophores into polymer networks., 36977687

脳腫瘍に対する病理研究者としての克服戦略 ハイドロゲルによる髄膜腫幹細胞の探索(Strategies for overcoming the brain tumors presented by pathology researchers Search for meningioma stem cells using hydrogel)　　　　　　　　　　　　　　　
小田 義崇, 津田 真寿美, 湯澤 明夏, 王 磊, 鈴鹿 淳, ハビバ・ウンマ, 種井 善一, モーウリン・クリスチアン, グン 剣萍, 田中 伸哉
日本病理学会会誌, 112, 1, 184, 184, (一社)日本病理学会, Mar. 2023
English

ハイドロゲルを用いた中皮腫幹細胞の創出および治療標的分子の探索　　　　　　　　　　　　　　　
加藤 万里絵, 杉野 弘和, 津田 真寿美, 王 磊, 種井 善一, 小田 義崇, 谷川 聖, グン 剣萍, 田中 伸哉
日本病理学会会誌, 112, 1, 332, 332, (一社)日本病理学会, Mar. 2023
Japanese

Relaxation mechanisms in hydrogels with uniaxially oriented lamellar bilayers
Anaïs Giustiniani, Muhammad Ilyas, Tsutomu Indei, Jian Ping Gong
Polymer, 267, 125686, 125691, Elsevier BV, Feb. 2023, [Peer-reviewed], [Last author, Corresponding author]
English, Scientific journal, 36977687

Squid/synthetic polymer double-network gel: elaborated anisotropy and outstanding fracture toughness characteristics
Shou Ohmura, Tasuku Nakajima, Masahiro Yoshida, Jian Ping Gong
NPG Asia Materials, 15, 2, Springer Science and Business Media LLC, 20 Jan. 2023, [Peer-reviewed]
English, Scientific journal, Abstract

The hierarchical anisotropy of a biotissue plays an essential role in its elaborate functions. To mimic the anisotropy-based functions of biotissues, soft and wet synthetic hydrogels with sophisticated biotissue-like anisotropy have been extensively explored. However, most existing synthetically manufactured anisotropic hydrogels exhibit fundamental anisotropy and poor mechanical toughness characteristics. In this paper, natural/synthetic hybrid double-network (DN) hydrogels with hierarchical anisotropy and high toughness characteristics are reported. These DN gels are prepared directly by using a squid mantle as an anisotropic soft bioproduct for the primary network and polyacrylamide (PAAm) as a synthetic polymer for the secondary network. The obtained squid/PAAm DN gel maintains the complex orientation of the muscle fibers of the squid mantle and exhibits anisotropic, enhanced mechanical properties and excellent fracture resistance due to its unique composite structure. This hybrid strategy provides a general method for preparing hydrogels with elaborated anisotropy and determining functions derived from the anisotropy., 36977687

Rapid induction of reprogramming towards cancer stem cells by hydrogel　　　　　　　　　　　　　　　
田中伸哉, 鈴鹿 淳, 王 磊, 津田真寿美, 龔 剣萍
細胞, 55, 1, 23, 25, Jan. 2023, [Invited]
Japanese, Scientific journal

Geometrical analysis identified morphological features of hydrogel-induced cancer stem cells in synovial sarcoma model cells
Zannatul Ferdous, Jean-Emmanuel Clément, Jian Ping Gong, Shinya Tanaka, Tamiki Komatsuzaki, Masumi Tsuda
Biochemical and Biophysical Research Communications, 642, 41, 49, Elsevier BV, Jan. 2023, [Peer-reviewed], [International Magazine]
English, Scientific journal, Cancer stem cells (CSCs) has been a key target to cure cancer patients completely. Although many CSC markers have been identified, they are frequently cancer type-specific and those expressions are occasionally variable, which becomes an obstacle to elucidate the characteristics of the CSCs. Here we scrutinized the relationship between stemness elevation and geometrical features of single cells. The PAMPS hydrogel was utilized to create the CSCs from mouse myoblast C2C12 and its synovial sarcoma model cells. qRT-PCR analysis confirmed the significant increase in expression levels of Sox2, Nanog, and Oct3/4 on the PAMPS gel, which was higher in the synovial sarcoma model cells. Of note, the morphological heterogeneity was appeared on the PAMPS gel, mainly including flat spreading, elongated spindle, and small round cells, and the Sox2 expression was highest in the small round cells. To examine the role of morphological differences in the elevation of stemness, over 6,400 cells were segmented along with the Sox2 intensity, and 12 geometrical features were extracted at single cell level. A nonlinear mapping of the geometrical features by using uniform manifold approximation and projection (UMAP) clearly revealed the existence of relationship between morphological differences and the stemness elevation, especially for C2C12 and its synovial sarcoma model on the PAMPS gel in which the small round cells possess relatively high Sox2 expression on the PAMPS gel, which supports the strong relationship between morphological changes and the stemness elevation. Taken together, these geometrical features can be useful for morphological profiling of CSCs to classify and distinguish them for understanding of their role in disease progression and drug discovery.

Effect of Salt on Dynamic Mechanical Behaviors of Polyampholyte Hydrogels
Xueyu Li, Feng Luo, Tao Lin Sun, Kunpeng Cui, Reina Watanabe, Tasuku Nakajima, Jian Ping Gong
Macromolecules, American Chemical Society (ACS), 16 Dec. 2022, [Peer-reviewed], [Last author, Corresponding author], ［Internationally co-authored］
English, Scientific journal, 36977687

ERK MAP Kinase Signaling Regulates RAR Signaling to Confer Retinoid Resistance on Breast Cancer Cells
Akira Hirota, Jean-Emmanuel Clément, Satoshi Tanikawa, Takayuki Nonoyama, Tamiki Komatsuzaki, Jian Ping Gong, Shinya Tanaka, Masamichi Imajo
Cancers, 14, 23, 5890, 5890, MDPI AG, 29 Nov. 2022, [Peer-reviewed], [International Magazine]
English, Scientific journal, Retinoic acid (RA) and its synthetic derivatives, retinoids, have been established as promising anticancer agents based on their ability to regulate cell proliferation and survival. Clinical trials, however, have revealed that cancer cells often acquire resistance to retinoid therapy. Therefore, elucidation of underlying mechanisms of retinoid resistance has been considered key to developing more effective use of retinoids in cancer treatment. In this study, we show that constitutive activation of ERK MAP kinase signaling, which is often caused by oncogenic mutations in RAS or RAF genes, suppresses RA receptor (RAR) signaling in breast cancer cells. We show that activation of the ERK pathway suppresses, whereas its inhibition promotes, RA-induced transcriptional activation of RAR and the resultant upregulation of RAR-target genes in breast cancer cells. Importantly, ERK inhibition potentiates the tumor-suppressive activity of RA in breast cancer cells. Moreover, we also reveal that suppression of RAR signaling and activation of ERK signaling are associated with poor prognoses in breast cancer patients and represent hallmarks of specific subtypes of breast cancers, such as basal-like, HER2-enriched and luminal B. These results indicate that ERK-dependent suppression of RAR activity underlies retinoid resistance and is associated with cancer subtypes and patient prognosis in breast cancers.

Computational Exploration of Polymer Mechanochemistry: Quantitation of Activation Force and Systematic Discovery of Reaction Sites Utilizing Two Forces
Julong Jiang, Koji Kubota, Mingoo Jin, Zhi Jian Wang, Tasuku Nakajima, Hajime Ito, Jian Ping Gong, Satoshi Maeda
American Chemical Society (ACS), 23 Nov. 2022
A series of mechanophores were studied computationally by employing the AFIR (Artificial Force Induced Reaction) method, which applies an artificial force on the molecule to trigger reactions, and meanwhile with a tensile force to simulate a mechanochemical reaction. The calculation results were both qualitatively and quantitatively consistent to those reported experimentally, indicating that the AFIR is a reliable approach to studying mechanochemical reactions. It was then applied to the study of retro-Diels-Alder reactions for the theoretical predictions of activation force levels which are currently unavailable. Moreover, it also helped to reveal the favored geometry for the enhancement of force effect. Later, the AFIR method was employed to study the mechanodegradation of generic polymers. The substituents effect and the polymer tacticity in strengthening the mechanical responsiveness, were highlighted by our study. Given the importance of cross-linker molecules in the double-network (DN) hydrogels, a fully automatic search of mechanochemical transformation pathways of a commonly used cross-linker molecule, N,N'-methylenebisacrylamide (MBAA), was also performed by the AFIR method. Through the work described in this article, we demonstrated that, in the field of polymer mechanochemistry, the AFIR method utilizing two forces is a simple but effective tool to give accurate predictions of activation force levels at any given timescale. In the meantime, the mechanistic study of mechanochemical reactions shown in this article is believed to provide insightful suggestions for the further design and application of mechanophores.

Nanoscale TEM Imaging of Hydrogel Network Architecture
Ryuji Kiyama, Masahiro Yoshida, Takayuki Nonoyama, Tomáš Sedlačík, Hiroshi Jinnai, Takayuki Kurokawa, Tasuku Nakajima, Jian Ping Gong
Advanced Materials, 35, 1, 2208902, 2208902, Wiley, 09 Nov. 2022, [Peer-reviewed], [Last author, Corresponding author]
English, Scientific journal, 36977687

Load transfer between permanent and dynamic networks due to stress gradients in nonlinear viscoelastic hydrogels
Jikun Wang, Kunpeng Cui, Bangguo Zhu, Jian Ping Gong, Chung-Yuen Hui, Alan T. Zehnder
Extreme Mechanics Letters, 101928, 101928, Elsevier BV, Nov. 2022, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 36977687

How double dynamics affects the large deformation and fracture behaviors of soft materials
Kunpeng Cui, Jian Ping Gong
Journal of Rheology, 66, 6, 1093, 1111, Society of Rheology, 01 Nov. 2022, [Peer-reviewed], [Invited], [Corresponding author]
English, Scientific journal, Numerous mechanically strong and tough soft materials comprising of polymer networks have been developed over the last two decades, motivated by new high-tech applications in engineering and bio-related fields. These materials are characterized by their dynamic complexities and large deformation behaviors. In this Review, we focus on how chain dynamics affects the large deformation and fracture behaviors of soft materials. To favor readers without a rheology background, first we review the linear rheology behaviors of several simple networks. We show that, by playing with the physical entanglement, chemical cross-linking, and physical association of the building polymers, a very rich panel of dynamic responses can be obtained. Then, we show examples of how chain dynamics affects the deformation and fracture behaviors of dually cross-linked hydrogels having chemical cross-linkers and physical bonds. We also provide examples on the unique deformation behavior of physical double-network gels made from triblock polymers. Thereafter, examples of the influence of chain dynamics on the crack initiation and growth behaviors are presented. We show that even for chemically cross-linked double-network hydrogels that exhibit elastic behaviors in a common deformation window, the chain dynamics influences the damage zone size at the crack tip. Finally, we conclude this Review by proposing several directions for future research., 11782741

Force-triggered rapid microstructure growth on hydrogel surface for on-demand functions
Qifeng Mu, Kunpeng Cui, Zhi Jian Wang, Takahiro Matsuda, Wei Cui, Hinako Kato, Shotaro Namiki, Tomoko Yamazaki, Martin Frauenlob, Takayuki Nonoyama, Masumi Tsuda, Shinya Tanaka, Tasuku Nakajima, Jian Ping Gong
Nature Communications, 13, 1, Springer Science and Business Media LLC, 20 Oct. 2022, [Peer-reviewed], [Corresponding author]
English, Scientific journal, Abstract

Living organisms share the ability to grow various microstructures on their surface to achieve functions. Here we present a force stamp method to grow microstructures on the surface of hydrogels based on a force-triggered polymerisation mechanism of double-network hydrogels. This method allows fast spatial modulation of the morphology and chemistry of the hydrogel surface within seconds for on-demand functions. We demonstrate the oriented growth of cells and directional transportation of water droplets on the engineered hydrogel surfaces. This force-triggered method to chemically engineer the hydrogel surfaces provides a new tool in addition to the conventional methods using light or heat, and will promote the wide application of hydrogels in various fields., 36977687

Rate-Independent Self-Healing Double Network Hydrogels Using a Thixotropic Sacrificial Network
Tomoki Yasui, Yong Zheng, Tasuku Nakajima, Eiji Kamio, Hideto Matsuyama, Jian Ping Gong
Macromolecules, 55, 21, 9547, 9557, American Chemical Society (ACS), 18 Oct. 2022, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 11782740

Gluing blood into gel by electrostatic interaction using a water-soluble polymer as an embolic agent
Zhiping Jin, Hailong Fan, Toshiya Osanai, Takayuki Nonoyama, Takayuki Kurokawa, Hideki Hyodoh, Kotaro Matoba, Akiko Takeuchi, Jian Ping Gong, Miki Fujimura
Proceedings of the National Academy of Sciences, 119, 42, e2206685119, Proceedings of the National Academy of Sciences, 18 Oct. 2022, [Peer-reviewed], [International Magazine]
English, Scientific journal, Liquid embolic agents are widely used for the endovascular embolization of vascular conditions. However, embolization based on phase transition is limited by the adhesion of the microcatheter to the embolic agent, use of an organic solvent, unintentional catheter retention, and other complications. By mimicking thrombus formation, a water-soluble polymer that rapidly glues blood into a gel without triggering coagulation was developed. The polymer, which consists of cationic and aromatic residues with adjacent sequences, shows electrostatic adhesion with negatively charged blood substances in a physiological environment, while common polycations cannot. Aqueous polymer solutions are injectable through clinical microcatheters and needles. The formed blood gel neither adhered to the catheter nor blocked the port. Postoperative computed tomography imaging showed that the polymer can block the rat femoral artery in vivo and remain at the injection site without nontarget embolization. This study provides an alternative for the development of waterborne embolic agents., 11782740

Mechanism of temperature-induced asymmetric swelling and shrinking kinetics in self-healing hydrogels
Kunpeng Cui, Chengtao Yu, Ya Nan Ye, Xueyu Li, Jian Ping Gong
Proceedings of the National Academy of Sciences, 119, 36, e2207422119, Proceedings of the National Academy of Sciences, 06 Sep. 2022, [Peer-reviewed], [Corresponding author]
English, Scientific journal, Understanding the physical principle that governs the stimuli-induced swelling and shrinking kinetics of hydrogels is indispensable for their applications. Here, we show that the shrinking and swelling kinetics of self-healing hydrogels could be intrinsically asymmetric. The structure frustration, formed by the large difference in the heat and solvent diffusions, remarkably slows down the shrinking kinetics. The plateau modulus of viscoelastic gels is found to be a key parameter governing the formation of structure frustration and, in turn, the asymmetric swelling and shrinking kinetics. This work provides fundamental understandings on the temperature-triggered transient structure formation in self-healing hydrogels. Our findings will find broad use in diverse applications of self-healing hydrogels, where cooperative diffusion of water and gel network is involved. Our findings should also give insight into the molecular diffusion in biological systems that possess macromolecular crowding environments similar to self-healing hydrogels., 11782741

ハイドロゲルを用いた髄膜腫がん幹細胞マーカーの検索(Identification of novel stemness marker of meningioma by using hydrogel)　　　　　　　　　　　　　　　
小田 義崇, 津田 真寿美, 湯澤 明夏, 王 磊, 谷川 聖, 種井 善一, グン 剣萍, 田中 伸哉
日本癌学会総会記事, 81回, P, 2111, (一社)日本癌学会, Sep. 2022
English

Rapid Induction of Reprogramming Towards Cancer Stem Cells by Hydrogel as HARP Phenomenon　　　　　　　　　　　　　　　
田中伸哉, 鈴鹿 淳, 王 磊, 津田真寿美, 龔 剣萍
BIO INDUSTRY, 39, 8, 40, 46, Aug. 2022, [Invited]
Japanese, Scientific journal

Surfactant induced bilayer-micelle transition for emergence of functions in anisotropic hydrogel
Md Anamul Haque, Takayuki Kurokawa, Tasuku Nakajima, Gen Kamita, Jian Ping Gong, Zannatul Fatema
Journal of Materials Chemistry B, 10, 41, 8386, 8397, Royal Society of Chemistry (RSC), 23 Jun. 2022, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］
English, Scientific journal, Tuning the self-assembled structures in amorphous hydrogels will enrich the functionality of hydrogels. In this study, we tuned the structure of a photonic hydrogel, which consists of polymeric lamellar bilayers..., 11782741

Synthesis of degradable double network gels using a hydrolysable cross-linker
Takanori Yokoi, Akinori Kuzuya, Tasuku Nakajima, Takayuki Kurokawa, Jian Ping Gong, Yuichi Ohya
Polymer Chemistry, 13, 25, 3756, 3762, Royal Society of Chemistry (RSC), 02 Jun. 2022, [Peer-reviewed]
English, Scientific journal, Double network (DN) gels have remarkably high mechanical strength and toughness and can be potentially applied in biomedical applications such as cartilage regeneration. However, most DN gels synthesised by usual...

Role of Dynamic Bonds on Fatigue Threshold of Tough Hydrogels
Xueyu Li, Jian Ping Gong
Proceedings of the National Academy of Sciences, 119, 20, e2200678119, 12 May 2022, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 11782740

Evaluation of biological responses to micro-particles derived from a double network hydrogel
Gen Matsumae, Mohamad Alaa Terkawi, Takayuki Nonoyama, Takayuki Kurokawa, Daisuke Takahashi, Tomohiro Shimizu, Ken Kadoya, Jian Ping Gong, Kazunori Yasuda, Norimasa Iwasaki
Biomaterials Science, 10, 9, 2182, 2187, Royal Society of Chemistry (RSC), 16 Mar. 2022, [Peer-reviewed], [International Magazine]
English, Scientific journal, Double network hydrogels have been proven to be a substitute biomaterial for cartilage. For further applications as articular cartilages, it is essential to understand the biological reactions that might be initiated by their micro-particles., 11782740

細胞外基質の電位変化に伴うJCウイルス増殖の制御　　　　　　　　　　　　　　　
谷川 聖, 野々山 貴行, 津田 真寿美, 王 磊, 種井 善一, Gong Jian Ping, 田中 伸哉
日本病理学会会誌, 111, 1, 263, 263, (一社)日本病理学会, Mar. 2022
Japanese

細胞外基質の電位変化に伴うJCウイルス増殖の制御　　　　　　　　　　　　　　　
谷川 聖, 野々山 貴行, 津田 真寿美, 王 磊, 種井 善一, Gong Jian Ping, 田中 伸哉
日本病理学会会誌, 111, 1, 263, 263, (一社)日本病理学会, Mar. 2022
Japanese

Engineering of an electrically charged hydrogel implanted into a traumatic brain injury model for stepwise neuronal tissue reconstruction
Satoshi Tanikawa, Yuki Ebisu, Tomáš Sedlačík, Shingo Semba, Takayuki Nonoyama, Akira Hirota, Taiga Takahashi, Kazushi Yamaguchi, Masamichi Imajo, Hinako Kato, Takuya Nishimura, Zen-ichi Tanei, Masumi Tsuda, Tomomi Nemoto, Jian Ping Gong, Shinya Tanaka
Scientific Reports, 13, 2233, Cold Spring Harbor Laboratory, 19 Feb. 2022, [Peer-reviewed]
English, Scientific journal, Abstract

Neural regeneration is extremely difficult to achieve. In traumatic brain injuries, the loss of brain parenchyma volume hinders neural regeneration. In this study, neuronal tissue engineering was performed by using electrically charged hydrogels composed of cationic and anionic monomers in a 1:1 ratio (C1A1 hydrogel), which served as an effective scaffold for the attachment of neural stem cells (NSCs). In the 3D environment of porous C1A1 hydrogels engineered by the cryogelation technique, NSCs differentiated into neuroglial cells. The C1A1 porous hydrogel was implanted into brain defects in a mouse traumatic damage model. The VEGF-immersed C1A1 porous hydrogel promoted host-derived vascular network formation together with the infiltration of macrophages/microglia and astrocytes into the gel. Furthermore, the stepwise transplantation of GFP-labeled NSCs supported differentiation to glial and neuronal cells. Therefore, this two-step method for neural regeneration may become a new approach for therapeutic brain tissue reconstruction after brain damage in the future.

One Sentence Summary

Brain tissue reconstruction using charged hydrogel and stepwise NCS injection

Azo-Crosslinked Double-Network Hydrogels Enabling Highly Efficient Mechanoradical Generation
Zhi Jian Wang, Julong Jiang, Qifeng Mu, Satoshi Maeda, Tasuku Nakajima, Jian Ping Gong
Journal of the American Chemical Society, 144, 7, 3154, 3161, American Chemical Society (ACS), 11 Feb. 2022, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 11782740

Quantitative determination of cation–π interactions between metal ions and aromatic groups in aqueous media by a hydrogel Donnan potential method
Hailong Fan, Honglei Guo, Takayuki Kurokawa, Jian Ping Gong
Physical Chemistry Chemical Physics, 24, 10, 6126, 6132, Royal Society of Chemistry (RSC), Feb. 2022, [Peer-reviewed], [Corresponding author]
English, Scientific journal, The binding ratios of various metal ions to aromatic groups by cation–π interactions in aqueous media have been quantitatively calculated by using Donnan potential measurements., 11782740

Facile preparation of cellulose hydrogel with Achilles tendon-like super strength through aligning hierarchical fibrous structure
Yun Zhou Guo, Tasuku Nakajima, Md. Tariful Islam Mredha, Hong Lei Guo, Kunpeng Cui, Yong Zheng, Wei Cui, Takayuki Kurokawa, Jian Ping Gong
Chemical Engineering Journal, 428, 132040, 132040, Elsevier BV, Jan. 2022, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］
English, Scientific journal, 11782740

Unique crack propagation of double network hydrogels under high stretch
Ye Zhang, Kazuki Fukao, Takahiro Matsuda, Tasuku Nakajima, Katsuhiko Tsunoda, Takayuki Kurokawa, Jian Ping Gong
Extreme Mechanics Letters, 51, 101588, 101588, Elsevier BV, 18 Dec. 2021, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 24510616

In Situ Evaluation of the Polymer Concentration Distribution of Microphase-Separated Polyelectrolyte Hydrogels by the Microelectrode Technique
Takuya Nishimura, Honglei Guo, Ryuji Kiyama, Yoshinori Katsuyama, Jian Ping Gong, Takayuki Kurokawa
Macromolecules, 54, 23, 10776, 10785, American Chemical Society (ACS), 14 Dec. 2021, [Peer-reviewed]
English, Scientific journal, The heterogeneous structure that exists in virtually all hydrogels has a significant influence on the resulting strength and toughness. While the internal structure has been observed with electron microscopy, it is difficult to measure the in situ local polymer concentration in the native swollen state. In this study, a modified microelectrode technique (MET) was employed to measure the Donnan potential of a heterogeneous hydrogel with a phase-separated structure. With this method, we succeeded in observing quantitative in situ polymer concentrations ranging from 10.2 mu mol/L to several hundred mmol/L. From the obtained concentration profiles, we could successfully evaluate the internal phase-separated structure with a resolution of less than 0.8 mu m. Using MET, we could estimate the average activity coefficient of the hydrogel, and we found a difference in concentration between the dense and sparse phases. We demonstrate that MET is a powerful method that can locally and quantitatively measure the polyelectrolyte concentration distribution within hydrogels. Furthermore, this method can be applied to cells and organs in vivo due to their similarities with polyelectrolytes. Enabling the in situ determination of the internal structures of biomaterials could have important implications toward the characterization of damaged and diseased tissues on the local scale., 11782740

How chain dynamics affects crack initiation in double-network gels
Yong Zheng, Takahiro Matsuda, Tasuku Nakajima, Wei Cui, Ye Zhang, Chung-Yuen Hui, Takayuki Kurokawa, Jian Ping Gong
Proceedings of the National Academy of Sciences, 118, 49, e2111880118, e2111880118, Proceedings of the National Academy of Sciences, 07 Dec. 2021, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］
English, Scientific journal, Double-network gels are a class of tough soft materials comprising two elastic networks with contrasting structures. The formation of a large internal damage zone ahead of the crack tip by the rupturing of the brittle network accounts for the large crack resistance of the materials. Understanding what determines the damage zone is the central question of the fracture mechanics of double-network gels. In this work, we found that at the onset of crack propagation, the size of necking zone, in which the brittle network breaks into fragments and the stretchable network is highly stretched, distinctly decreases with the increase of the solvent viscosity, resulting in a reduction in the fracture toughness of the material. This is in sharp contrast to the tensile behavior of the material that does not change with the solvent viscosity. This result suggests that the dynamics of stretchable network strands, triggered by the rupture of the brittle network, plays a role. To account for this solvent viscosity effect on the crack initiation, a delayed blunting mechanism regarding the polymer dynamics effect is proposed. The discovery on the role of the polymer dynamic adds an important missing piece to the fracture mechanism of this unique material., 11782740

Bioinspired Underwater Adhesives
Hailong Fan, Jian Ping Gong
Advanced Materials, 33, 44, 2102983, 2102983, Wiley, 02 Nov. 2021, [Peer-reviewed], [Invited], [Corresponding author]
English, Scientific journal

Revisiting the Origins of the Fracture Energy of Tough Double-Network Hydrogels with Quantitative Mechanochemical Characterization of the Damage Zone
Takahiro Matsuda, Runa Kawakami, Tasuku Nakajima, Yukiko Hane, Jian Ping Gong
Macromolecules, 54, 22, 10331, 10339, American Chemical Society (ACS), 01 Nov. 2021, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 11782740

Hydroxyapatite‐hybridized double‐network hydrogel surface enhances differentiation of bone marrow‐derived mesenchymal stem cells to osteogenic cells
Takuma Kaibara, Lei Wang, Masumi Tsuda, Takayuki Nonoyama, Takayuki Kurokawa, Norimasa Iwasaki, Jian Ping Gong, Shinya Tanaka, Kazunori Yasuda
Journal of Biomedical Materials Research Part A, 110, 4, 747, 760, Wiley, 28 Oct. 2021, [Peer-reviewed], [International Magazine]
English, Scientific journal, Recently, we have developed a hydroxyapatite (HAp)-hybridized double-network (DN) hydrogel (HAp/DN gel), which can robustly bond to the bone tissue in the living body. The purpose of this study is to clarify whether the HAp/DN gel surface can differentiate the bone marrow-derived mesenchymal stem cells (MSCs) to osteogenic cells. We used the MSCs which were harvested from the rabbit bone marrow and cultured on the polystyrene (PS) dish using the autogenous serum-supplemented medium. First, we confirmed the properties of MSCs by evaluating colony forming unit capacity, expression of MSC markers using flow cytometry, and multidifferential capacity. Secondly, polymerase chain reaction analysis demonstrated that the HAp/DN gel surface significantly enhanced mRNA expression of the eight osteogenic markers (TGF-β1, BMP-2, Runx2, Col-1, ALP, OPN, BSP, and OCN) in the cultured MSCs at 7 days than the PS surfaces (p < 0.0001), while the DN gel and HAp surfaces provided no or only a slight effect on the expression of these markers except for Runx2. Additionally, the alkaline phosphatase activity was significantly higher in the cells cultured on the HAp/DN gel surface than in the other three material surfaces (p < 0.0001). Thirdly, when the HAp/DN gel plug was implanted into the rabbit bone marrow, MSC marker-positive cells were recruited in the tissue generated around the plug at 3 days, and Runx2 and OCN were highly expressed in these cells. In conclusion, this study demonstrated that the HAp/DN gel surface can differentiate the MSCs into osteogenic cells., 11782740

Structure Frustration Enables Thermal History-Dependent Responsive Behavior in Self-Healing Hydrogels
Chengtao Yu, Kunpeng Cui, Honglei Guo, Ya Nan Ye, Xueyu Li, Jian Ping Gong
Macromolecules, 54, 21, 9927, 9936, American Chemical Society (ACS), 28 Oct. 2021, [Peer-reviewed], [Corresponding author]
English, Scientific journal, Biological soft tissues usually execute their functions via nonequilibrium and dynamic structural transformations. By contrast, functional hydrogels are mainly constructed by implementing static and equilibrium structures in the polymer network. Here, using polyampholyte hydrogel as a model system, we demonstrated that the nonequilibrium structure transformation in self-healing hydrogels enables the gels with many new features, including thermal history dependence, quick and asymmetric thermal response (instant transparent-to-turbid transition but slow turbid-to-transparent transition), tunable cloud point, tunable recovery time, and tiny changes in sample size and mechanical performance. These features make them distinct to conventional thermoresponsive hydrogels based on thermodynamic equilibrium and endow them with a new type of promising thermoresponsive materials. We revealed the structure change and studied the role of the thermal protocol on this thermoresponsive behavior by combining ultraviolet spectrum, small-angle X-ray scattering, theology, and mechanical measurements. We also presented two conceptual applications of this thermoresponsive hydrogel in thermal imaging and security paper. We believe that this work will inspire future research on creating functional hydrogels via nonequilibrium structure transformations., 11782740

Toughening hydrogels through force-triggered chemical reactions that lengthen polymer strands
Zi Wang, Xujun Zheng, Tetsu Ouchi, Tatiana B. Kouznetsova, Haley K. Beech, Sarah Av-Ron, Takahiro Matsuda, Brandon H. Bowser, Shu Wang, Jeremiah A. Johnson, Julia A. Kalow, Bradley D. Olsen, Jian Ping Gong, Michael Rubinstein, Stephen L. Craig
Science, 374, 6564, 193, 196, American Association for the Advancement of Science (AAAS), 08 Oct. 2021, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 11782740

ハイドロゲルを用いた新規髄膜腫治療標的分子の検討(Analysis of novel therapeutic target for meningioma using hydrogel)　　　　　　　　　　　　　　　
小田 義崇, 津田 真寿美, 湯澤 明夏, 王 磊, Umma Habiba, 杉野 弘和, 種井 善一, グン 剣萍, 田中 伸哉
日本病理学会会誌, 110, 2, 110, 110, (一社)日本病理学会, Oct. 2021
English

Rapid reprogramming of tumour cells into cancer stem cells on double-network hydrogel　　　　　　　　　　　　　　　
田中伸哉, 鈴鹿淳, 津田真寿美, 龔 剣萍, 高阪真路, 間野博行
実験医学, 39, 14, 2255, 2259, Sep. 2021, [Invited]
Japanese, Scientific journal

Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism
Wei Cui, Yiwan Huang, Liang Chen, Yong Zheng, Yoshiyuki Saruwatari, Chung-Yuen Hui, Takayuki Kurokawa, Daniel R. King, Jian Ping Gong
Matter, 4, 11, 3646, 3661, Elsevier BV, Sep. 2021, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］
English, Scientific journal, 11782740

Facile tuning of hydrogel properties by manipulating cationic-aromatic monomer sequences
Hailong Fan, Yirong Cai, Jian Ping Gong
Science China Chemistry, 64, 9, 1560, 1568, Springer Science and Business Media LLC, Sep. 2021, [Corresponding author]
English, Scientific journal, 11782740

Fast in vivo fixation of double network hydrogel to bone by monetite surface hybridization
Takayuki NONOYAMA, Lei WANG, Ryuji KIYAMA, Naohiro KASHIMURA, Kazunori YASUDA, Shinya TANAKA, Takayuki KUROKAWA, Jian Ping GONG
Journal of the Ceramic Society of Japan, 129, 9, 584, 589, Ceramic Society of Japan, 01 Sep. 2021, [Peer-reviewed], [Last author]
English, Scientific journal, Double network (DN) hydrogels, possessing biocompatibility, low sliding friction, high strength and toughness, are promising as artificial cartilages for next-generation joint disease treatment. For such application, a fast and robust fixation of DN hydrogel to bone tissue in vivo is indispensable. However, bonding the DN hydrogel that contains similar to 90 wt % of water to bone is a grand challenge since glues do not work on hydrated surfaces. Recently, we reported that a DN hydrogel of its subsurface hybridized with low crystalline hydroxyapatite (HAp) can achieve robust fixation to bone after 4 weeks implantation in rabbit knees, owing to the HAp-induced osteogenesis penetration into the hydrogel matrix. For clinical application, achieving a quick fixation at the early stage of implantation remains as a next subject. In this study, instead of HAp, we hybridized calcium monohydrogen phosphate (monetite), which is a HAp precursor calcium phosphate salt, in the subsurface of the DN hydrogel and we observed an increase in the pushout resistance of the DN hydrogel to bone after 1 week implantation, prior to the HAp-induced osteogenesis penetration. In physiological environment, the monetite hybridized in the subsurface of the DN gel spontaneously dissolved to calcium and phosphate ions and then recrystallized to more stable HAp. We consider that the HAp formed in the boundary between the gel and the bone forms physical interlocking that significantly enhances the frictional resistance against the pushout force. The fast temporally pre-fixation to the bone by monetite surface hybridization makes one step closer to the clinical application of the DN gels as artificial cartilages. (C) 2021 The Ceramic Society of Japan. All rights reserved., 11782740

Structure and unique functions of anisotropic hydrogels comprising uniaxially aligned lamellar bilayers
Youfeng Yue, Jian Ping Gong
Bulletin of the Chemical Society of Japan, 94, 9, 2221, 2234, The Chemical Society of Japan, 20 Jul. 2021, [Peer-reviewed], [Invited], [Corresponding author]
English, Scientific journal, 11782740

A surface flattening method for characterizing the surface stress, drained Poisson’s ratio and diffusivity of poroelastic gels
Zezhou Liu, Chung-Yuen Hui, Anand Jagota, Jian Ping Gong, Ryuji Kiyama
Soft Matter, 17, 31, 7332, 7340, Royal Society of Chemistry (RSC), Jul. 2021, [Peer-reviewed], ［Internationally co-authored］
English, Scientific journal,

When a poroelastic gel is released from a patterned mold, surface stress drives deformation and solvent migration in the gel and flattens its surface profile in a time-dependent manner. Specifically,...

, 11782740

Improving the strength and toughness of macroscale double networks by exploiting Poisson’s ratio mismatch
Tsuyoshi Okumura, Riku Takahashi, Katsumi Hagita, Daniel R. King, Jian Ping Gong
Scientific Reports, 11, 1, 13280, 13280, Springer Science and Business Media LLC, 24 Jun. 2021, [Peer-reviewed], [Last author]
English, Scientific journal, We propose a new concept that utilizes the difference in Poisson's ratio between component materials as a strengthening mechanism that increases the effectiveness of the sacrificial bond toughening mechanism in macroscale double-network (Macro-DN) materials. These Macro-DN composites consist of a macroscopic skeleton imbedded within a soft elastic matrix. We varied the Poisson's ratio of the reinforcing skeleton by introducing auxetic or honeycomb functional structures that results in Poisson’s ratio mismatch between the skeleton and matrix. During uniaxial tensile experiments, high strength and toughness were achieved due to two events: (1) multiple internal bond fractures of the skeleton (like sacrificial bonds in classic DN gels) and (2) significant, biaxial deformation of the matrix imposed by the functional skeleton. The Macro-DN composite with auxetic skeleton exhibits up to 4.2 times higher stiffness and 4.4 times higher yield force than the sum of the component materials. The significant improvement in mechanical performance is correlated to the large mismatch in Poisson's ratio between component materials, and the enhancement is especially noticeable in the low-stretch regime. The strengthening mechanism reported here based on Poisson's ratio mismatch can be widely used for soft materials regardless of chemical composition and will improve the mechanical properties of elastomer and hydrogel systems., 11782740

Tough Double Network Hydrogel and Its Biomedical Applications
Takayuki Nonoyama, Jian Ping Gong
Annual Review of Chemical and Biomolecular Engineering, 12, 1, 393, 410, Annual Reviews, 07 Jun. 2021, [Peer-reviewed], [Invited], [Lead author, Corresponding author], [International Magazine]
English, Scientific journal, Soft and wet hydrogels have many similarities to biological tissues, though their mechanical fragility had been one of the biggest obstacles in biomedical applications. Studies and developments in double network (DN) hydrogels have elucidated how to create tough gels universally based on sacrificial bond principles and opened a path for biomedical application of hydrogels in regenerative medicine and artificial soft connective tissues, such as cartilage, tendon, and ligament, which endure high tension and compression. This review explores a universal toughening mechanism for and biomedical studies of DN hydrogels. Moreover, because the term sacrificial bonds has been mentioned often in studies of bone tissues, consisting of biomacromolecules and biominerals, recent studies of gel–biomineral composites to understand early-stage osteogenesis and to simulate bony sacrificial bonds are also summarized.

Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 12 is June 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates., 11782740

Ultrapurified Alginate Gel Containing Bone Marrow Aspirate Concentrate Enhances Cartilage and Bone Regeneration on Osteochondral Defects in a Rabbit Model
Liang Xu, Atsushi Urita, Tomohiro Onodera, Ryosuke Hishimura, Takayuki Nonoyama, Masanari Hamasaki, Dawei Liang, Kentaro Homan, Jian Ping Gong, Norimasa Iwasaki
The American Journal of Sports Medicine, 49, 8, 2199, 2210, SAGE Publications, 01 Jun. 2021, [Peer-reviewed]
English, Scientific journal, Ultrapurified alginate (UPAL) gel implantation has been demonstrated as effective in cartilage repair for osteochondral defects; however, cell transplantation within UPAL gels would be required to treat larger defects.

The combination of UPAL gel and bone marrow aspirate concentrate (BMAC) would enhance cartilage repair and subchondral bone repair for large osteochondral defects.

Controlled laboratory study.

A total of 104 osteochondral defects (1 defect per knee) of 52 rabbits were randomly divided into 4 groups (26 defects per group): defects without any treatment (Defect group), defects treated using UPAL gel alone (UPAL group), defects treated using UPAL gel containing allogenic bone marrow mesenchymal stromal cells (UPAL-MSC group), and defects treated using UPAL gel containing BMAC (UPAL-BMAC group). At 4 and 16 weeks postoperatively, macroscopic and histologic evaluations and measurements of repaired subchondral bone volumes of reparative tissues were performed. Collagen orientation and mechanical properties of the reparative tissue were assessed at 16 weeks.

The defects in the UPAL-BMAC group were repaired with hyaline-like cartilage with well-organized collagen structures. The histologic scores at 4 weeks were significantly higher in the UPAL-BMAC group (16.9 ± 2.0) than in the Defect group (4.7 ± 1.9; P < .05), the UPAL group (10.0 ± 3.3; P < .05), and the UPAL-MSC group (12.2 ± 2.9; P < .05). At 16 weeks, the score in the UPAL-BMAC group (24.4 ± 1.7) was significantly higher than those in the Defect group (9.0 ± 3.7; P < .05), the UPAL group (14.2 ± 3.9; P < .05), and the UPAL-MSC group (16.3 ± 3.6; P < .05). At 4 and 16 weeks, the macroscopic evaluations were significantly superior in the UPAL-BMAC group compared with the other groups, and the values of repaired subchondral bone volumes in the UPAL-BMAC group were significantly higher than those in the Defect and UPAL groups. The mechanical properties of the reparative tissues were significantly better in the UPAL-BMAC group than in the other groups.

The implantation of UPAL gel containing BMAC-enhanced hyaline-like cartilage repair and subchondral bone repair of osteochondral defects in a rabbit knee model.

These data support the potential clinical application of 1-step treatment for large osteochondral defects using biomaterial implantation with cell transplantation.

Flower-like Photonic Hydrogel with Superstructure Induced via Modulated Shear Field
Ya Nan Ye, Md Anamul Haque, Akane Inoue, Yoshinori Katsuyama, Takayuki Kurokawa, Jian Ping Gong
ACS Macro Letters, 10, 6, 708, 713, American Chemical Society (ACS), 20 May 2021, [Peer-reviewed], [Corresponding author]
English, Scientific journal, Biological tissues usually have complex superstructures and elaborated functionalities. However, creating superstructures in soft and wet hydrogels is challenging because of the absence of effective approaches to control the molecular orientation. Here we introduce a method to create superstructures in photonic hydrogels comprising lamellar bilayers intercalated in the cross-linked polymer network. The orientation of lamellar bilayers in the photonic gel, which are sensitive to shear, is modulated by applying a gradient shear field on the precursor solution using a customized rheometer. The difference in orientation of lamellar bilayers leads to swelling mismatch in the radial direction, endowing the disk-shape hydrogel with a macroscopic flower-like shape with a central dome and an edge petal, along with a bright photonic color. By characterization of the swelling anisotropy of the radial profile, the shear rate required for the unidirectional orientation of lamellar bilayers was extracted. Moreover, a delayed polymerization experiment was designed to measure the lifetime of aligned lamellar bilayers, which reveals the domain size of lamellar bilayers in the precursor solution. Furthermore, we also demonstrated that the hydrogel flowers could fade and rebloom reversibly in response to external stimuli. This work presents a strategy to develop superstructures in hydrogels and sheds light on designing biomimetic materials with intricately architectural superstructure., 11782740

Quantitative evaluation of macromolecular crowding environment based on translational and rotational diffusion using polarization dependent fluorescence correlation spectroscopy
Johtaro Yamamoto, Akito Matsui, Fusako Gan, Makoto Oura, Riku Ando, Takahiro Matsuda, Jian Ping Gong, Masataka Kinjo
Scientific Reports, 11, 1, 10594, 10594, Springer Science and Business Media LLC, 19 May 2021, [Peer-reviewed], [International Magazine]
English, Scientific journal, Macromolecular crowding (MMC) in cells is a hot topic in biology; therefore, well-characterized measurement standards for the evaluation of the nano-environment in MMC solutions are necessary. We propose to use polarization-dependent fluorescence correlation spectroscopy (Pol-FCS) for evaluation of macromolecular crowding in solutions. Pol-FCS can simultaneously measure the relaxation times of rotational and translational diffusion of fluorescent molecules at the same position, even in living cells with low damage. In this report, the differences in the nano-environment among solutions of small molecules, gels, and MMC solutions were evaluated by comparing their rotational and translational diffusion using Pol-FCS. Moreover, this method could distinguish the phase shift in the polyethylene glycol solution. Finally, we separately evaluated the nano-environment in the cytosol and nucleus of living cells in different cell lines and cell cycles. We expect this evaluation method to be useful in characterizing the nano-environment in MMC studies. In addition, the proposed method may be useful for other nano-environments such as liquid–liquid phase separation.

Hierarchical toughening: A step toward matching the complexity of biological materials　　　　　　　　　　　　　　　
Daniel R. King, Jian Ping Gong
Chem, 7, 5, 1153, 1155, May 2021, [Invited]
English, Scientific journal

Nanophase Separation in Immiscible Double Network Elastomers Induces Synergetic Strengthening, Toughening, and Fatigue Resistance
Yong Zheng, Ryuji Kiyama, Takahiro Matsuda, Kunpeng Cui, Xueyu Li, Wei Cui, Yunzhou Guo, Tasuku Nakajima, Takayuki Kurokawa, Jian Ping Gong
Chemistry of Materials, 33, 9, 3321, 3334, American Chemical Society (ACS), 19 Apr. 2021, [Peer-reviewed], [Corresponding author]
English, Scientific journal, High modulus, toughness, and fatigue resistance are usually difficult to be obtained simultaneously in rubbery materials. Here, we report that by superimposing the nanophase separation structure in double network (DN) elastomers using immiscible polymers, the modulus, fracture energy, and energy release rate of fatigue threshold are enhanced all together by 13, 5, and 5 times, respectively. We reveal that the interplay between the DN structure and the nanophase separation structure brings two effects synergistically: (1) formation of nanoclusters overstresses and homogenizes the sacrificial network, thereby remarkably increasing the modulus and yielding stress and (2) the nanoclusters act as viscoelastic nanofillers dissipating energy and pinning the crack propagation, thereby significantly enhancing toughness and fatigue resistance. This work provides a facile approach to superimpose high-order structures in DN materials for excellent mechanical performance. The clarified synergetic effects should be universal for DN materials made of immiscible polymers. We believe that this work will facilitate more studies on elastomers and gels along this line., 11782740

Molecular mechanism of abnormally large nonsoftening deformation in a tough hydrogel
Ya Nan Ye, Kunpeng Cui, Wei Hong, Xueyu Li, Chengtao Yu, Dominique Hourdet, Tasuku Nakajima, Takayuki Kurokawa, Jian Ping Gong
Proceedings of the National Academy of Sciences, 118, 14, e2014694118, e2014694118, Proceedings of the National Academy of Sciences, 06 Apr. 2021, [Peer-reviewed], [Last author, Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, Tough soft materials usually show strain softening and inelastic deformation. Here, we study the molecular mechanism of abnormally large nonsoftening, quasi-linear but inelastic deformation in tough hydrogels made of hyperconnective physical network and linear polymers as molecular glues to the network. The interplay of hyperconnectivity of network and effective load transfer by molecular glues prevents stress concentration, which is revealed by an affine deformation of the network to the bulk deformation up to sample failure. The suppression of local stress concentration and strain amplification plays a key role in avoiding necking or strain softening and endows the gels with a unique large nonsoftening, quasi-linear but inelastic deformation., 11782740

Effect of mesoscale phase contrast on fatigue-delaying behavior of self-healing hydrogels
Xueyu Li, Kunpeng Cui, Takayuki Kurokawa, Ya Nan Ye, Tao Lin Sun, Chengtao Yu, Costantino Creton, Jian Ping Gong
Science Advances, 7, 16, eabe8210, eabe8210, American Association for the Advancement of Science (AAAS), Apr. 2021
Scientific journal, We investigate the fatigue resistance of chemically cross-linked polyampholyte hydrogels with a hierarchical structure due to phase separation and find that the details of the structure, as characterized by SAXS, control the mechanisms of crack propagation. When gels exhibit a strong phase contrast and a low cross-linking level, the stress singularity around the crack tip is gradually eliminated with increasing fatigue cycles and this suppresses crack growth, beneficial for high fatigue resistance. On the contrary, the stress concentration persists in weakly phase-separated gels, resulting in low fatigue resistance. A material parameter, λ_tran, is identified, correlated to the onset of non-affine deformation of the mesophase structure in a hydrogel without crack, which governs the slow-to-fast transition in fatigue crack growth. The detailed role played by the mesoscale structure on fatigue resistance provides design principles for developing self-healing, tough, and fatigue-resistant soft materials.

Experimental Verification of the Balance between Elastic Pressure and Ionic Osmotic Pressure of Highly Swollen Charged Gels
Tasuku Nakajima, Ken-ichi Hoshino, Honglei Guo, Takayuki Kurokawa, Jian Ping Gong
Gels, 7, 2, 39, 39, MDPI AG, 01 Apr. 2021, [Peer-reviewed], [Invited], [Last author], [International Magazine]
English, Scientific journal, The equilibrium swelling degree of a highly swollen charged gel has been thought to be determined by the balance between its elastic pressure and ionic osmotic pressure. However, the full experimental verification of this balance has not previously been conducted. In this study, we verified the balance between the elastic pressure and ionic osmotic pressure of charged gels using purely experimental methods. We used tetra-PEG gels created using the molecular stent method (St-tetra-PEG gels) as the highly swollen charged gels to precisely and separately control their network structure and charge density. The elastic pressure of the gels was measured through the indentation test, whereas the ionic osmotic pressure was determined by electric potential measurement without any strong assumptions or fittings. We confirmed that the two experimentally determined pressures of the St-tetra-PEG gels were well balanced at their swelling equilibrium, suggesting the validity of the aforementioned relationship. Furthermore, from single-strand level analysis, we investigated the structural requirements of the highly swollen charged gels in which the elasticity and ionic osmosis are balanced at their swelling equilibrium., 11782740

Rapid reprogramming of tumour cells into cancer stem cells on double-network hydrogels
Jun Suzuka, Masumi Tsuda, Lei Wang, Shinji Kohsaka, Karin Kishida, Shingo Semba, Hirokazu Sugino, Sachiyo Aburatani, Martin Frauenlob, Takayuki Kurokawa, Shinya Kojima, Toshihide Ueno, Yoshihiro Ohmiya, Hiroyuki Mano, Kazunori Yasuda, Jian Ping Gong, Shinya Tanaka
Nature Biomedical Engineering, 5, 8, 914, 925, Springer Science and Business Media LLC, 29 Mar. 2021, [Peer-reviewed], [International Magazine]
English, Scientific journal, Cancer recurrence can arise owing to rare circulating cancer stem cells (CSCs) that are resistant to chemotherapies and radiotherapies. Here, we show that a double-network hydrogel can rapidly reprogramme differentiated cancer cells into CSCs. Spheroids expressing elevated levels of the stemness genes Sox2, Oct3/4 and Nanog formed within 24 h of seeding the gel with cells from any of six human cancer cell lines or with brain cancer cells resected from patients with glioblastoma. Human brain cancer cells cultured on the double-network hydrogel and intracranially injected in immunodeficient mice led to higher tumorigenicity than brain cancer cells cultured on single-network gels. We also show that the double-network gel induced the phosphorylation of tyrosine kinases, that gel-induced CSCs from primary brain cancer cells were eradicated by an inhibitor of the platelet-derived growth factor receptor, and that calcium channel receptors and the protein osteopontin were essential for the regulation of gel-mediated induction of stemness in brain cancer cells.

The Fracture of Highly Deformable Soft Materials: A Tale of Two Length Scales
Rong Long, Chung-Yuen Hui, Jian Ping Gong, Eran Bouchbinder
Annual Review of Condensed Matter Physics, 12, 1, 71, 94, Annual Reviews, 10 Mar. 2021, [Peer-reviewed], [Invited]
English, Scientific journal, The fracture of highly deformable soft materials is of great practical importance in a wide range of technological applications, emerging in fields such as soft robotics, stretchable electronics, and tissue engineering. From a basic physics perspective, the failure of these materials poses fundamental challenges due to the strongly nonlinear and dissipative deformation involved. In this review, we discuss the physics of cracks in soft materials and highlight two length scales that characterize the strongly nonlinear elastic and dissipation zones near crack tips in such materials. We discuss physical processes, theoretical concepts, and mathematical results that elucidate the nature of the two length scales and show that the two length scales can classify a wide range of materials. The emerging multiscale physical picture outlines the theoretical ingredients required for the development of predictive theories of the fracture soft materials. We conclude by listing open challenges and future investigation directions.

Expected final online publication date for the Annual Review of Condensed Matter Physics, Volume 12 is March 10, 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates., 11782740

忘却能力を持つ動的記憶素子の構築～人間の脳の動的な記憶・忘却挙動に触発されて～　　　　　　　　　　　　　　　
崔 昆朋, 龔 剣萍
超分子研究会アニュアルレビュー, 41, 12, 13, Mar. 2021, [Invited], [Last author]
Japanese, Scientific journal

新陳代謝して成長するゲル
中島 祐, 龔剣萍
化学と教育, 69, 3, 94, 97, Mar. 2021, [Invited], [Last author]
Japanese, Scientific journal

Constitutive modeling of strain-dependent bond breaking and healing kinetics of chemical polyampholyte (PA) gel
Sairam Pamulaparthi Venkata, Kunpeng Cui, Jingyi Guo, Alan T. Zehnder, Jian Ping Gong, Chung-Yuen Hui
Soft Matter, 17, 15, 4161, 4169, Royal Society of Chemistry (RSC), Mar. 2021, [Peer-reviewed], ［Internationally co-authored］
English, Scientific journal,

A finite strain nonlinear viscoelastic constitutive model is used to study the uniaxial tension behaviour of a chemical polyampholyte (PA) gel.

, 11782740

Ultrahigh‐Water‐Content Photonic Hydrogels with Large Electro‐Optic Responses in Visible to Near‐Infrared Region
Youfeng Yue, Yasuo Norikane, Jian Ping Gong
Advanced Optical Materials, 9, 9, 2002198, 2002198, Wiley, 16 Feb. 2021, [Peer-reviewed], [Last author]
English, Scientific journal, The embedding of photonic crystals within stimuli-responsive hydrogels has attracted tremendous interest because it provides new applications such as optical switches, displays, and sensors. However, the production of electrically tunable photonic hydrogels with a wide range of color tunability, fast electrical response, and high stability for repeated use is still challenging. Here, electrically tunable photonic hydrogels are fabricated using ultrahigh-water-content polyelectrolyte layered hydrogels composed of thousands of bilayer domain structures. The layered hydrogel exhibits versatile color tunability by applying an electric field parallel or perpendicular to the direction of the gel layers. The hydrogel exhibits homogeneous color tuning when a perpendicular electric field is applied, while it shows a large rainbow-like electric-optic response in the visible to near-infrared region when a parallel electric field is applied. Additionally, by a simple method using patterned electrodes, a reflective display showing the designed characters is demonstrated and maintained for hours underwater without an external source of energy. Moreover, the electrically induced optical patterns can be erased, and the responsive photonic hydrogel shows excellent stability for repeated use. We anticipate that this study will provide the foundation for the development of responsive photonic hydrogels with new and large electro-optical effects for future chromatic applications., 11782741

Aggregated structures and their functionalities in hydrogels
Kunpeng Cui, Jian Ping Gong
Aggregate, 2, 2, e33, Wiley, 13 Feb. 2021, [Peer-reviewed], [Invited], [Corresponding author]
English, Scientific journal, 11782740

Constitutive modeling of bond breaking and healing kinetics of physical Polyampholyte (PA) gel
Sairam Pamulaparthi Venkata, Kunpeng Cui, Jingyi Guo, Alan T. Zehnder, Jian Ping Gong, Chung-Yuen Hui
Extreme Mechanics Letters, 43, 101184, 101184, Elsevier BV, Feb. 2021, [Peer-reviewed], ［Internationally co-authored］
English, Scientific journal, 11782740

Barnacle Cement Proteins‐Inspired Tough Hydrogels with Robust, Long‐Lasting, and Repeatable Underwater Adhesion
Hailong Fan, Jiahui Wang, Jian Ping Gong
Advanced Functional Materials, 31, 11, 2009334, 2009334, Wiley, 28 Dec. 2020, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 11782740

骨リモデリングプロセスを利用したハイドロゲルの骨への高強度接着―人工軟骨への応用に向けて　　　　　　　　　　　　　　　
樫村尚宏, 野々山貴行, 龔剣萍
医学のあゆみ, 275, 11, 1203, 1209, 12 Dec. 2020, [Invited], [Last author]
Japanese, Scientific journal

Isotope Microscopic Observation of Osteogenesis Process Forming Robust Bonding of Double Network Hydrogel to Bone.
Takayuki Nonoyama, Lei Wang, Masumi Tsuda, Yuki Suzuki, Ryuji Kiyama, Kazunori Yasuda, Shinya Tanaka, Kousuke Nagata, Ryosuke Fujita, Naoya Sakamoto, Noriyuki Kawasaki, Hisayoshi Yurimoto, Jian Ping Gong
Advanced healthcare materials, 10, 3, 2001731, 16 Nov. 2020, [Peer-reviewed], [Corresponding author], [International Magazine]
English, Scientific journal, Tough double network (DN) hydrogels are promising substitutes of soft supporting tissues such as cartilage and ligaments. For such applications, it is indispensable to robustly fix the hydrogels to bones with medically feasible methods. Recently, robustly bonding the DN hydrogels to defected bones of rabbits in vivo has been proved successful. The low crystalline hydroxyapatite (HAp) of calcium-phosphate-hydroxide salt coated on the surface layer of the DN hydrogels induced spontaneous osteogenesis penetrating into the semi-permeable hydrogels to form a gel/bone composite layer. In this work, the 44 Ca isotope-doped HAp/DN hydrogel is implanted in a defect of rabbit femoral bone and the dynamic osteogenesis process at the gel/bone interface is analyzed by tracing the calcium isotope ratio using isotope microscopy. The synthetic HAp hybridized on the surface layer of DN gel dissolves rapidly in the first two weeks by inflammation, and then the immature bone with a gradient structure starts to form in the gel region, reutilizing the dissolved Ca ions. These results reveal, for the first time, that synthetic HAp is reutilized for osteogenesis. These facts help to understand the lifetime of bone absorbable materials and to elucidate the mechanism of spontaneous, non-toxic, but strong fixation of hydrogels to bones., 11782740

Micromechanical modeling of the multi-axial deformation behavior in double network hydrogels
Rui Xiao, Thanh-Tam Mai, Kenji Urayama, Jian Ping Gong, Shaoxing Qu
International Journal of Plasticity, 137, 102901, 102901, Elsevier BV, Nov. 2020, [Peer-reviewed], ［Internationally co-authored］
English, Scientific journal, © 2020 Elsevier Ltd. The Mullins-type damage behaviors in double network hydrogels have attracted a broad research interest in recent years. However, most of current works focus on characterizing and modeling the uniaxial deformation behaviors of these materials. In this work, we combine experimental and theoretical approaches to investigate the anisotropic damage behaviors of double network hydrogels revealed in multi-axial deformation conditions. We demonstrate that an isotropic damage model based on the eight-chain model and the network alteration theory fails to capture the stress response in multi-axial loading tests. An anisotropic damage theory based on the microsphere model has also been developed, while both the affine and non-affine approaches are adopted to obtain the micro-macro mapping. The results show that the affine microsphere model cannot describe the experimental results in pure shear and unequal biaxial tests. Remarkably, the non-affine microsphere model with three parameters captures all the important features of the experimental observations. This is because the non-affine model accurately predicts the directional damage of the primary cross-linked network. The non-affine microsphere model is also able to describe the damage cross-effect in double network hydrogels. The developed theoretical framework can promote the fundamental understanding of the anisotropic damage behaviors in various types of tough gels.

How surface stress transforms surface profiles and adhesion of rough elastic bodies
Chung-Yuen Hui, Zezhou Liu, Nicolas Bain, Anand Jagota, Eric R. Dufresne, Robert W. Style, Ryuji Kiyama, Jian Ping Gong
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 476, 2243, 20200477, 20200477, The Royal Society, Nov. 2020, [Peer-reviewed], [Last author], ［Internationally co-authored］
English, Scientific journal, The surface of soft solids carries a surface stress that tends to flatten surface profiles. For example, surface features on a soft solid, fabricated by moulding against a stiff-patterned substrate, tend to flatten upon removal from the mould. In this work, we derive a transfer function in an explicit form that, given any initial surface profile, shows how to compute the shape of the corresponding flattened profile. We provide analytical results for several applications including flattening of one-dimensional and two-dimensional periodic structures, qualitative changes to the surface roughness spectrum, and how that strongly influences adhesion., 11782740

Stress Relaxation and Underlying Structure Evolution in Tough and Self-Healing Hydrogels
Kunpeng Cui, Ya Nan Ye, Chengtao Yu, Xueyu Li, Takayuki Kurokawa, Jian Ping Gong
ACS Macro Letters, 9, 11, 1582, 1589, American Chemical Society (ACS), 22 Oct. 2020, [Peer-reviewed], [Corresponding author]
English, Scientific journal, The tough and self-healing hydrogels composed of polyampholytes (PA gels) are drawing great attention due to their multiscale structures and the resultant multiple mechanical properties. This work studies the stress relaxation behavior of PA gels and reveals the underlying multiscale structure evolutions by combining birefringence and small-angle X-ray scattering measurements. The PA gels show a fast and strong stress relaxation that obeys the stress-optical rule, which could be associated with relaxation of chain segment orientation by the breaking of ionic bonds. A slow and weak relaxation of phase structure (similar to 100 nm) is also observed, which tells that the stress redistributes and local strain amplification gradually builds in the phase network at long relaxation times as a result of synergetic breaking of multiple ionic bonds. This work gives insight into exploring the formation of the crack precursor that is important in the fracture and fatigue of self-healing hydrogels., 11782740

Polyzwitterions as a Versatile Building Block of Tough Hydrogels: From Polyelectrolyte Complex Gels to Double-Network Gels
Haiyan Yin, Daniel R. King, Tao Lin Sun, Yoshiyuki Saruwatari, Tasuku Nakajima, Takayuki Kurokawa, Jian Ping Gong
ACS Applied Materials & Interfaces, 12, 44, 50068, 50076, American Chemical Society (ACS), 21 Oct. 2020, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, The high water content of hydrogels makes them important as synthetic biomaterials, and tuning the mechanical properties of hydrogels to match those of natural tissues without changing chemistry is usually difficult. In this study, we have developed a series of hydrogels with varied stiffness, strength, and toughness based on a combination of poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS), a strong acidic polyelectrolyte, and poly-N-(carboxymethyl)-N,N-dimethyl-2-(methacryloyloxy) ethanaminium) (PCDME), a polyzwitterion with a weak acidic moiety. We demonstrate that modifying the true molar ratio, R, of PCDME to PAMPS results in four unique categories of hydrogels with different swelling ratios and Young's moduli. When R < 1, a negatively charged polyelectrolyte gel (PE) is formed; when 1 < R < 3, a tough and viscoelastic polyelectrolyte complex gel (PEC) is formed; when 3 < R < 6.5, a conventional, elastic interpenetrating network gel (IPN) is formed; and when R > 6.5, a tough and stiff double-network gel (DN) is formed. Both the PEC and DN gels exhibit high toughness and fracture stress, up to 1.8 and 1.5 MPa, respectively. Importantly, the PEC gels exhibit strong recovery properties along with high toughness, distinguishing them from DN gels. Without requiring a change in chemistry, we can tune the mechanical response of hydrogels over a wide spectrum, making this a useful system of soft and hydrated biomaterials., 11782740

Chitin-Based Double-Network Hydrogel as Potential Superficial Soft-Tissue-Repairing Materials
Junchao Huang, Martin Frauenlob, Yuki Shibata, Lei Wang, Tasuku Nakajima, Takayuki Nonoyama, Masumi Tsuda, Shinya Tanaka, Takayuki Kurokawa, Jian Ping Gong
Biomacromolecules, 21, 10, 4220, 4230, American Chemical Society (ACS), 27 Sep. 2020, [Peer-reviewed], [Corresponding author], [International Magazine]
English, Scientific journal, Chitin is a biopolymer, which has been proven to be a biomedical material candidate, yet the weak mechanical properties seriously limit their potentials. In this work, a chitin-based double-network (DN) hydrogel has been designed as a potential superficial repairing material. The hydrogel was synthesized through a double-network (DN) strategy composing hybrid regenerated chitin nanofiber (RCN)-poly (ethylene glycol diglycidyl ether) (PEGDE) as the first network and polyacrylamide (PAAm) as the second network. The hybrid RCN-PEGDE/PAAm DN hydrogel was strong and tough, possessing Young's modulus (elasticity) E 0.097 ± 0.020 MPa, fracture stress σf 0.449 ± 0.025 MPa, and work of fracture Wf 5.75 ± 0.35 MJ·m-3. The obtained DN hydrogel was strong enough for surgical requirements in the usage of soft tissue scaffolds. In addition, chitin endowed the DN hydrogel with good bacterial resistance and accelerated fibroblast proliferation, which increased the NIH3T3 cell number by nearly five times within 3 days. Subcutaneous implantation studies showed that the DN hydrogel did not induce inflammation after 4 weeks, suggesting a good biosafety in vivo. These results indicated that the hybrid RCN-PEGDE/PAAm DN hydrogel had great prospect as a rapid soft-tissue-repairing material., 11782740

Crack Tip Field of a Double-Network Gel: Visualization of Covalent Bond Scission through Mechanoradical Polymerization
Takahiro Matsuda, Runa Kawakami, Tasuku Nakajima, Jian Ping Gong
Macromolecules, 53, 20, 8787, 8795, American Chemical Society (ACS), 25 Sep. 2020, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 11782740

Preparation of Tough Double- and Triple-Network Supermacroporous Hydrogels through Repeated Cryogelation
Tomáš Sedlačík, Takayuki Nonoyama, Honglei Guo, Ryuji Kiyama, Tasuku Nakajima, Yoshihiro Takeda, Takayuki Kurokawa, Jian Ping Gong
Chemistry of Materials, 32, 19, 8576, 8586, American Chemical Society (ACS), 04 Sep. 2020, [Peer-reviewed], [Corresponding author]
English, Scientific journal, Copyright © 2020 American Chemical Society. Supermacroporous hydrogels, possessing a spongelike structure and permeability, have drawn significant attention for their bioengineering and biomedical applications. However, their mechanical weakness due to the low-density structure is one of their biggest limitations. This work reports a multistep cryogelation technique, which does not require special equipment, for preparing tough supermacroporous hydrogels on the basis of the double-network (DN) strategy. The produced supermacroporous DN gels possess interconnected pores with pore sizes of 50-230 μm. They also show a compressive modulus of up to ∼100 kPa, which is 2-4 times higher than that of the corresponding supermacroporous single-network (SN) gels, and a compressive strength of up to 1 MPa at 80% compression. The supermacroporous DN cryogels are also stretchable with a work of extension of up to 38 kJ m-3, which is 1-2 orders larger than that of the SN cryogels. Their high stiffness and stretchability distinguish them from other types of cryogels. Supermacroporous triple-network (TN) gels and DN gels composed of different polymer combinations are also prepared. The technique presented herein is suitable for preparing supermacroporous DN gels from various polymers; hence, it is promising in meeting bioengineering and biomedical demands., 11782740

High-Fidelity Hydrogel Thin-Films Processed from Deep Eutectic Solvents
David Delgado, Daniel Rudolf King, KUNPENG CUI, Jian Ping Gong, Kenneth R Shull
ACS Applied Materials & Interfaces, 12, 38, 43191, 43200, American Chemical Society (ACS), 21 Aug. 2020, [Peer-reviewed], ［Internationally co-authored］
English, Scientific journal, 11782740

バイオマテリアルによる肝癌幹細胞の新規誘導法の開発とその解析　　　　　　　　　　　　　　　
谷 道夫, 津田 真寿美, 鈴鹿 淳, 王 磊, 杉野 弘和, 谷川 聖, 石田 雄介, グン 剣萍, 田中 伸哉, 武冨 紹信
日本外科学会定期学術集会抄録集, 120回, DP, 6, (一社)日本外科学会, Aug. 2020
Japanese

バイオマテリアルによる肝癌幹細胞の新規誘導法の開発とその解析　　　　　　　　　　　　　　　
谷 道夫, 津田 真寿美, 鈴鹿 淳, 王 磊, 杉野 弘和, 谷川 聖, 石田 雄介, グン 剣萍, 田中 伸哉, 武冨 紹信
日本外科学会定期学術集会抄録集, 120回, DP, 6, (一社)日本外科学会, Aug. 2020
Japanese

Hydrogels as dynamic memory with forgetting ability
Chengtao Yu, Honglei Guo, Kunpeng Cui, Xueyu Li, Ya Nan Ye, Takayuki Kurokawa, Jian Ping Gong
Proceedings of the National Academy of Sciences, 117, 32, 202006842, 202006842, Proceedings of the National Academy of Sciences, 27 Jul. 2020, [Peer-reviewed], [Corresponding author]
English, Scientific journal, The memory of our brain, stored in soft matter, is dynamic, and it forgets spontaneously to filter unimportant information. By contrast, the existing manmade memory, made from hard materials, is static, and it does not forget without external stimuli. Here we propose a principle for developing dynamic memory from soft hydrogels with temperature-sensitive dynamic bonds. The memorizing–forgetting behavior is achieved based on fast water uptake and slow water release upon thermal stimulus, as well as thermal-history-dependent transparency change of these gels. The forgetting time is proportional to the thermal learning time, in analogy to the behavior of brain. The memory is stable against temperature fluctuation and large stretching; moreover, the forgetting process is programmable. This principle may inspire future research on dynamic memory based on the nonequilibrium process of soft matter., 11782740

Bactericidal effect of cationic hydrogels prepared from hydrophilic polymers
Yuki Shibata, Takayuki Kurokawa, Tomoyasu Aizawa, Jian Ping Gong
Journal of Applied Polymer Science, 137, 48, 49583, 49583, Wiley, 24 Jul. 2020, [Peer-reviewed], [Last author]
English, Scientific journal, 11782740

Phase Separation Behavior in Tough and Self-Healing Polyampholyte Hydrogels
Kunpeng Cui, Ya Nan Ye, Tao Lin Sun, Chengtao Yu, Xueyu Li, Takayuki Kurokawa, Jian Ping Gong
Macromolecules, 53, 13, 5116, 5126, American Chemical Society (ACS), 26 Jun. 2020, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］
English, Scientific journal, 11782740

Fiber‐Reinforced Viscoelastomers Show Extraordinary Crack Resistance That Exceeds Metals
Wei Cui, Daniel R. King, Yiwan Huang, Liang Chen, Tao Lin Sun, Yunzhou Guo, Yoshiyuki Saruwatari, Chung‐Yuen Hui, Takayuki Kurokawa, Jian Ping Gong
Advanced Materials, 32, 31, 1907180, 1907180, Wiley, 25 Jun. 2020, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, Soft fiber-reinforced polymers (FRPs), consisting of rubbery matrices and rigid fabrics, are widely utilized in industry because they possess high specific strength in tension while allowing flexural deformation under bending or twisting. Nevertheless, existing soft FRPs are relatively weak against crack propagation due to interfacial delamination, which substantially increases their risk of failure during use. In this work, a class of soft FRPs that possess high specific strength while simultaneously showing extraordinary crack resistance are developed. The strategy is to synthesize tough viscoelastic matrices from acrylate monomers in the presence of woven fabrics, which generates soft composites with a strong interface and interlocking structure. Such composites exhibit fracture energy, Γ, of up to 2500 kJ m-2 , exceeding the toughest existing materials. Experimental elucidation shows that the fracture energy obeys a simple relation, Γ = W · lT , where W is the volume-weighted average of work of extension at fracture of the two components and lT is the force transfer length that scales with the square root of fiber/matrix modulus ratio. Superior Γ is achieved through a combination of extraordinarily large lT (10-100 mm), resulting from the extremely high fiber/matrix modulus ratios (104 -105 ), and the maximized energy dissipation density, W. The elucidated quantitative relationship provides guidance toward the design of extremely tough soft composites., 11782740

Lamellar Bilayer to Fibril Structure Transformation of Tough Photonic Hydrogel under Elongation
M. Anamul Haque, Kunpeng Cui, Muhammad Ilyas, Takayuki Kurokawa, Alba Marcellan, Annie Brulet, Riku Takahashi, Tasuku Nakajima, J. Ping Gong
Macromolecules, 53, 12, 4711, 4721, American Chemical Society (ACS), 12 Jun. 2020, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］
English, Scientific journal, 11782740

Synthetic PAMPS Gel Induces Chondrogenic Differentiation of ATDC5 Cells via a Novel Protein Reservoir Function
Shingo Semba, Nobuto Kitamura, Masumi Tsuda, Keiko Goto, Sadamu Kurono, Yoshihiro Ohmiya, Takayuki Kurokawa, Jian Ping Gong, Kazunori Yasuda, Shinya Tanaka
Journal of Biomedical Materials Research Part A, 109, 3, 354, 364, 04 Jun. 2020, [Peer-reviewed], [International Magazine]
English, Scientific journal, We previously demonstrated that a synthetic negatively charged poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) gel induced chondrogenic differentiation of ATDC5 cells. In this study, we clarified the underlying molecular mechanism, in particular, focusing on the events that occurred at the interface between the gel and the cells. Gene expression profiling revealed that the expression of extracellular components was enhanced in the ATDC5 cells that were cultured on the PAMPS gel, suggesting that extracellular proteins secreted from the ATDC5 cells might be adsorbed in the PAMPS gel, thereby contributing to the induction of chondrogenic differentiation. Therefore, we created "Treated-PAMPS gel," which adsorbed various proteins secreted from the cultured ATDC5 cells during 7 days. Proteomic analysis identified 27 proteins, including extracellular matrix proteins such as Types I, III, and V collagens and thrombospondin (THBS) in the Treated-PAMPS gel. The Treated-PAMPS gel preferentially induced expression of chondrogenic markers, namely, aggrecan and Type II collagen, in the ATDC5 cells compared with the untreated PAMPS gel. Addition of recombinant THBS1 to the ATDC5 cells significantly enhanced the PAMPS-induced chondrogenic differentiation, whereas knockdown of THBS1 completely abolished this response. In conclusion, we demonstrated that the PAMPS gel has the potential to induce chondrogenic differentiation through novel reservoir functions, and the adsorbed THBS plays a significant role in the induction.

Integrin α4 Mediates ATDC5 Cell Adhesion to Negatively Charged Synthetic Polymer Hydrogel Leading to Chondrogenic Differentiatio
Daiki Hashimoto, Shingo Semba, Masumi Tsuda, Takayuki Kurokawa, Nobuto Kitamura, Kazunori Yasuda, Jian Ping Gong, Shinya Tanaka
Biochemical and Biophysical Research Communications, 528, 1, 120, 126, 23 May 2020, [Peer-reviewed], [International Magazine]
English, Scientific journal, Negatively charged synthetic hydrogels have been known to facilitate various cellular responses including cell adhesion, proliferation, and differentiation; however, the molecular mechanism of hydrogel-dependent control of cell behavior remains unclear. Recently, we reported that negatively charged poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) gel induces chondrogenic differentiation of ATDC5 cells via novel protein reservoir function. In this study, we identified the cell adhesion molecules binding to PAMPS gels that act as mechanoreceptors. First, we performed a pull-down assay by particle gels using cell membrane proteins of ATDC5, and found that multiple membrane proteins bound to the PAMPS gel, whereas the uncharged poly(N,N'-dimethylacrylamide) gel as control did not bind to any membrane proteins. Western blot analysis indicated differential binding of integrin (ITG) isoforms to the PAMPS gel, in which the α4 isoform, but not α5 and αv, efficiently bound to the PAMPS gel. ITG α4 knockdown decreased cell spreading of ATDC5 on PAMPS gels, whereas the enhanced expression increased the behavior. Furthermore, ITG α4 depletion suppressed PAMPS gel-induced expression of bone morphogenic protein (BMP) 4 contributing to chondrogenic differentiation, in concordance with the reduction of ERK activation. These results demonstrated that membrane protein binding to PAMPS gels occurred in a charge-dependent manner, and that ITG α4 plays a crucial role in cell spreading on PAMPS gels and acts as a mechanoreceptor triggering cellular signaling leads to chondrogenic differentiation.

Anisotropic Double Network Hydrogels via Controlled Orientation of a Physical Sacrificial Network
Daniel R. King, Riku Takahashi, Takuma Ikai, Kazuki Fukao, Takayuki Kurokawa, Jian Ping Gong
ACS Applied Polymer Materials, 2, 6, 2350, 2358, 15 May 2020, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 24510616

Double-Network Gels as Polyelectrolyte Gels with Salt-Insensitive Swelling Properties
Tasuku Nakajima, Takaharu Chida, Kei Mito, Taayuki Kurokawa, Jian Ping Gong
Soft Matter, 16, 23, 5487, 5496, 15 May 2020, [Peer-reviewed], [Last author], [International Magazine]
English, Scientific journal, Polyelectrolyte gels exhibit intrinsic salt-sensitive swelling behaviour, which causes size instability in ionic environments. Thus, polyelectrolyte gels that show salt-insensitive swelling have been anticipated for applications in ionic environments, such as medical materials used in vivo. We found that double-network (DN) gels consisting of both a polyelectrolyte network and a non-ionic network are resistant to salt-sensitive swelling. This resistance is attributed to their lower osmotic pressure originating from mobile ions relative to the osmotic pressure of mixing at swelling equilibrium. Our investigation indicated that the two contrasting network structures within the DN gels are vital for achieving these properties, where the structures include a highly prestretched and sparse polyelectrolyte network and a coiled and dense non-ionic network. The salt-insensitivity of the DN gels will lead to their unique applications in ionic environments., 11782740

Hydrogels Toughened by Biominerals as Energy-Dissipative Sacrificial Bonds
Kazuki Fukao, Kazuki Tanaka, Ryuji Kiyama, Takayuki Nonoyama, Jian Ping Gong
Journal of Materials Chemistry B, 8, 24, 5184, 5188, 06 May 2020, [Peer-reviewed], [Corresponding author], [International Magazine]
English, Scientific journal, Inspired by bone tissues, we mineralized low crystalline hydroxyapatite (HAp) particles in double network (DN) hydrogels, and we observed that the HAp minerals toughen the gels. The contribution of dissipated energy from HAp minerals was over 500% higher than that from the polymer during tensile deformation. We elucidated that the amorphous parts in the HAp minerals break at deformation, acting as energy-dissipative sacrificial bonds. This result implies that not only brittle polymer networks but also minerals can provide sacrificial bonds to toughen soft materials., 24510616

Competitive Cation−π Interactions Between Small Cations and Polycations with Phenyl Groups in Poly(Cation−π) Hydrogels
Hailong Fan, Honglei Guo, Jiahui Wang, Jian Ping Gong
Giant, 1, 100005, 100005, Elsevier BV, Apr. 2020, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 11782740

Fabrication of Bioinspired Hydrogels: Challenges and Opportunities
Hailong Fan, Jian Ping Gong
Macromolecules, 53, 8, 2769, 2782, Apr. 2020, [Peer-reviewed], [Invited], [Corresponding author]
English, Scientific journal

人工軟骨を目指した高強度ハイドロゲル－リン酸カルシウムの複合化および骨との接着
Takayuki Nonoyama, Ryuji Kiyama, Kazuki Fukao, Kazunori Yasuda, Takayuki Kurokawa, Jian Ping Gong
Ceramics Japan, 55, 3, 166, 170, 日本セラミックス協会, Mar. 2020, [Invited], [Last author]
Japanese, Scientific journal

Meet the phase-separation polymeric gel　　　　　　　　　　　　　　　
Takayuki Nonoyama, Jian Ping Gong
The Innovation Platform, 1, 73, 74, Mar. 2020, [Invited], [Last author]
English, Scientific journal

Mesoscale Bicontinuous Networks in Self-healing Hydrogels Delay Fatigue Fracture
Xueyu Li, Kunpeng Cui, Tao Lin Sun, Lingpu Meng, Chengtao Yu, Liangbin Li, Costantino Creton, Takayuki Kurokawa, Jian Ping Gong
Proceedings of the National Academy of Sciences, 117, 14, 7606, 7612, Mar. 2020, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, Load-bearing biological tissues, such as muscles, are highly fatigue-resistant, but how the exquisite hierarchical structures of biological tissues contribute to their excellent fatigue resistance is not well understood. In this work, we study antifatigue properties of soft materials with hierarchical structures using polyampholyte hydrogels (PA gels) as a simple model system. PA gels are tough and self-healing, consisting of reversible ionic bonds at the 1-nm scale, a cross-linked polymer network at the 10-nm scale, and bicontinuous hard/soft phase networks at the 100-nm scale. We find that the polymer network at the 10-nm scale determines the threshold of energy release rate G 0 above which the crack grows, while the bicontinuous phase networks at the 100-nm scale significantly decelerate the crack advance until a transition G tran far above G 0 In situ small-angle X-ray scattering analysis reveals that the hard phase network suppresses the crack advance to show decelerated fatigue fracture, and G tran corresponds to the rupture of the hard phase network.

Non-Linear Rheological Study of Hydrogel Sliding Friction in Water and Concentrated Hyaluronan Solution
Satoshi Hirayama, Takayuki Kurokawa, Jian Ping Gong
Tribology International, 147, 106270, Feb. 2020, [Peer-reviewed], [Last author]
English, Scientific journal

Mechanical Behavior of Unidirectional Fiber Reinforced Soft Composites
Chung-Yuen Hui, Zezhou Liu, Stuart Leigh Phoenix, Daniel R. King, Wei Cui, Yiwan Huang, Jian Ping Gong
Extreme Mechanics Letters, 35, 100642, Feb. 2020, [Peer-reviewed], [Last author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, 11782740

Effect of Relative Strength of Two Networks on the Internal Fracture Process of Double Network Hydrogels As Revealed by in Situ Small-Angle X-ray Scattering
Kazuki Fukao, Tasuku Nakajima, Takayuki Nonoyama, Takayuki Kurokawa, Takahiko Kawai, Jian Ping Gong
Macromolecules, 53, 4, 1154, 1163, 31 Jan. 2020, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 24510616

Erratum: Preparation of Tough Double- and Triple-Network Supermacroporous Hydrogels through Repeated Cryogelation (Chem. Mater. (2020) 32:19 (8576−8586) DOI: 10.1021/acs.chemmater.0c02911)
Sedla?{\'i}k, T., Nonoyama, T., Guo, H., Kiyama, R., Nakajima, T., Takeda, Y., Kurokawa, T., Gong, J.P.
Chemistry of Materials, 32, 24, 10737, 10737, 2020
Scientific journal

Effect of void structure on the toughness of double network hydrogels
Tasuku Nakajima, Hidemitsu Furukawa, Yoshimi Tanaka, Takayuki Kurokawa, Jian Ping Gong
Soft Matter, 16, 37, 8618, 8627, Wiley, 2020
Scientific journal

Effect of the constituent networks of double-network gels on their mechanical properties and energy dissipation process
Tasuku Nakajima, Takayuki Kurokawa, Hidemitsu Furukawa, Jian Ping Gong
Soft Matter, 16, 37, 8618, 8627, Royal Society of Chemistry (RSC), 2020, [Peer-reviewed], [Last author]
English, Scientific journal,

The relationship between composition and mechanical properties of tough double-network hydrogels was clarified by systematic experiments and theoretical investigations.

, 11782740

Relaxation Dynamics and Underlying Mechanism of a Thermally Reversible Gel from Symmetric Triblock Copolymer
Ya Nan Ye, Kunpeng Cui, Tsutomu Indei, Tasuku Nakajima, Dominique Hourdet, Takayuki Kurokawa, Jian Ping Gong
Macromolecules, 52, 22, 8651, 8661, American Chemical Society ({ACS}), 26 Nov. 2019, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］
English, Scientific journal, 11782740

Tough Double-Network Gels and Elastomers from the Nonprestretched First Network
Tasuku Nakajima, Yuhei Ozaki, Ryo Namba, Kumi Ota, Yuki Maida, Takahiro Matsuda, Takayuki Kurokawa, Jian Ping Gong
ACS Macro Letters, 8, 11, 1407, 1412, American Chemical Society ({ACS}), 19 Nov. 2019, [Peer-reviewed], [Last author]
English, Scientific journal, 11782740

Instant Thermal Switching from Soft Hydrogel to Rigid Plastics Inspired by Thermophile Proteins
Takayuki Nonoyama, Yong Woo Lee, Kumi Ota, Keigo Fujioka, Wei Hong, Jian Ping Gong
Advanced Materials, 32, 4, 1905878, Nov. 2019, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］
English, Scientific journal, 11782740

Adjacent cationic-aromatic sequences yield strong electrostatic adhesion of hydrogels in seawater
Hailong Fan, Jiahui Wang, Zhen Tao, Junchao Huang, Ping Rao, Takayuki Kurokawa, Jian Ping Gong
NATURE COMMUNICATIONS, 10, 5127, NATURE PUBLISHING GROUP, Nov. 2019, [Peer-reviewed], [Corresponding author]
English, Scientific journal, Electrostatic interaction is strong but usually diminishes in high ionic-strength environments. Biosystems can use this interaction through adjacent cationic-aromatic amino acids sequence of proteins even in a saline medium. Application of such specific sequence to the development of cationic polymer materials adhesive to negatively charged surfaces in saline environments is challenging due to the difficulty in controlling the copolymer sequences. Here, we discover that copolymers with adjacent cation-aromatic sequences can be synthesized through cation-ic complex-aided free-radical polymerization. Sequence controlled hydrogels from diverse cation/aromatic monomers exhibit fast, strong but reversible adhesion to negatively charged surfaces in seawater. Aromatics on copolymers are found to enhance the electrostatic interactions of their adjacent cationic residues to the counter surfaces, even in a high ionic-strength medium that screens the electrostatic interaction for common polyelectrolytes. This work opens a pathway to develop adhesives using saline water., 11782740

Fabrication of Tough Hydrogel Composites from Photoresponsive Polymers to Show Double-Network Effect
Zhen Tao, Hailong Fan, Junchao Huang, Taolin Sun, Takayuki Kurokawa, Jian Ping Gong
ACS APPLIED MATERIALS & INTERFACES, 11, 40, 37139, 37146, AMER CHEMICAL SOC, Oct. 2019, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］
English, Scientific journal, Inspired by the toughening mechanism of double-network (DN) gels, tough hydrogel composites with a sandwich structure were fabricated from photoresponsive polymers. By copolymerization of hydrophilic monomers, 2-ureidoethyl methacrylate (UM), and photoresponsive hydrophobic monomers, (2-nitrobenzyloxycarbonylaminoethyl methacrylate (NBOC)) at high concentrations, physical hydrogels that are soft and highly stretchable are formed due to the hydrophobic associations of NBOC, serving as dynamic crosslinkers. By UV irradiation, the physical crosslinking switches into chemical crosslinking, and the soft physical hydrogels transform into rigid and less stretchable chemical hydrogels. By UV curing the surface layers of the physical hydrogels, we prepared hydrogel composites having a sandwiched structure with two rigid outer layers and a soft inner layer. The molecular-level continuous interfaces and matched swelling ratios between the layers ensure the macroscale hydrogel composites' high strength and toughness with a DN gel effect. The outer layers fracture preferentially at deformation, playing a role like the first network of a DN gel, while the inner layer maintains the integrity, playing a role resembling the second network. The evolution of the fracture morphology of the rigid layers gives useful insight into the internal fracture process of DN gels., 11782740

Toughening Mechanism of Double Network Gels and New Research Trends　　　　　　　　　　　　　　　
Ryuji Kiyama, Jian Ping Gong
Journal of Society of Rubber Science and Technology, Japan, 92, 9, 352, 356, Sep. 2019, [Invited], [Last author]
Japanese, Scientific journal

Effect of Structure Heterogeneity on Mechanical Performance of Physical Polyampholytes Hydrogels
Kunpeng Cui, Ya Nan Ye, Tao Lin Sun, Liang Chen, Xueyu Li, Takayuki Kurokawa, Tasuku Nakajima, Takayuki Nonoyama, Jian Ping Gong
Macromolecules, 52, 19, 7369, 7378, AMER CHEMICAL SOC, Sep. 2019, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］
English, Scientific journal, Recent studies reported a multiscale structure in tough and self-healing hydrogels containing physical associations. For example, a type of tough and self-healing hydrogel from charge-balanced polyampholytes (PA) has a mesoscale bicontinuous double network structure with structural length around 400 nm. This mesoscale network structure plays an essential role in the multistep rupture process, which leads to the high toughness of PA hydrogels. In this work, by using an osmotic stress method, we symmetrically studied how the relative strength of soft and hard networks and the strength of ionic bonds influence the property of PA gels. We found that increasing osmotic stress of the bath solution triggers the structure transition from bicontinuous double network structure to a homogeneous structure, which drives the concurrently opaque-transparent transition in optical property and viscoelastic-glassy transition in mechanical behavior. The gels around the structural transition point were found to possess both high toughness (fracture energy of 7200 J m(-2)) and high stiffness (Young's modulus of 12.9 MPa), which is a synergy of soft network and hard network of the bicontinuous structure. Our work not only provides an approach to tune the structure and property of physical hydrogels through tuning physical association but also gives a demo to investigate their relationships, yet another step forward gives inspiration to design a new type of tough and self-healing materials around the structural transition point., 11782740

Programmed Diffusion Induces Anisotropic Superstructure in Hydrogel with High Mechano-Optical Sensitivity
Laicong Qiao, Cong Du, Jian Ping Gong, Zi Liang Wu, Qiang Zhen
Advanced Materials Technologies, 4, 11, 1900665, Sep. 2019, [Peer-reviewed], ［Internationally co-authored］
English, Scientific journal, 11782740

Internal Damage Evolution in Double-Network Hydrogels Studied by Microelectrode Technique
Honglei Guo, Wei Hong, Takayuki Kurokawa, Takahiro Matsuda, Zi Liang Wu, Tasuku Nakajima, Masakazu Takahata, Taolin Sun, Ping Rao, Jian Ping Gong
Macromoledules, 52, 18, 7114, 7122, Sep. 2019, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］
English, Scientific journal, 11782740

Macroscale Double Networks: Design Criteria for Optimizing Strength and Toughness
Daniel R. King, Tsuyoshi Okumura, Riku Takahashi, Takayuki Kurokawa, Jian Ping Gong
ACS Applied Materials & Interfaces, 11, 38, 35343, 35353, Sep. 2019, [Peer-reviewed], [Corresponding author], [International Magazine]
English, Scientific journal, The double network concept, based on the fracture of sacrificial bonds, has been revolutionary toward the creation of robust soft materials. Based on the essence of double network hydrogels, macroscale, three-dimensional printed rigid sacrificial networks are embedded within silicone rubber stretchable matrices. Preferential fracture of the sacrificial network results in a ∼60 time increase in stiffness and a ∼50% increase in the work of extension compared with the neat matrix. Maximizing yield strength while maintaining multistep internal fracture occurs when the strength of the sacrificial network approaches the strength of the matrix. Upon determining the optimal sacrificial network strength, the sacrificial bond section density can be increased to maximize energy dissipation and toughening efficiencies up to ∼70% of the maximum theoretical toughness are achieved. High toughness and dissipation are achieved because topological interlocking enables significant force transmission to the sacrificial network at smaller length scales than interfacial adhesion, allowing much higher sacrificial bond density. This method is general and can be used with a variety of materials systems, without requiring strong interfacial adhesion, contrasting traditional composite systems. Demonstrating that the double network concept can be used at length scales far beyond the molecular scale will have important implications toward the development of future structural materials., 11782740

鍛えて成長するゲル―破壊による創造の材料科学―　　　　　　　　　　　　　　　
Takahiro Matsuda, Tasuku Nakajima, Jian Ping Gong
現代化学, 581, 53, 57, Aug. 2019, [Invited], [Last author]
Japanese, Scientific journal

Modulation and Characterization of the Double Network Hydrogel Surface-bulk Transition
Martin Frauenlob, Daniel R. King, Honglei Guo, Seiichiro Ishihara, Masumi Tsuda, Takayuki Kurokawa, Hisashi Haga, Shinya Tanaka, Jian Ping Gong
Macromolecules, 52, 17, 6704, 6713, Aug. 2019, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 11782740

Hydrogel/Elastomer Laminates Bonded via Fabric Interphases for Stimuli-Responsive Actuators
Amber M. Hubbard, Wei Cui, Yiwan Huang, Riku Takahashi, Michael D. Dickey, Jan Genzer, Daniel R. King, Jian Ping Gong
Matter, 1, 3, 674, 689, Aug. 2019, [Peer-reviewed], ［Internationally co-authored］
English, Scientific journal, 11782740

Polyelectrolyte Complexation via Viscoelastic Phase Separation Results in Tough and Self-Recovering Porous Hydrogel
Kohei Murakawa, Daniel R. King, Tao Lin Sun, Honglei Guo, Takayuki Kurokawa, Jian Ping Gong
Journal of Materials Chemistry B, 7, 35, 5296, 5305, Aug. 2019, [Peer-reviewed], [Corresponding author], [International Magazine]
English, Scientific journal, Polyelectrolyte complexation between oppositely charged polyelectrolytes forms coacervates in dilute solutions and thin films in concentrated solutions. It is difficult to obtain macroscopically uniform bulk polyelectrolyte complex (PEC) materials, since the two polymers form insoluble complexes quickly at the contact interface during mixing, resulting in heterogeneous aggregates. Here, we succeeded in preparing bulk PEC materials based on desalting-induced polyelectrolyte complexation via viscoelastic phase separation. With a high ionic strength aqueous medium, a homogeneous and concentrated solution containing oppositely charged polyelectrolytes is prepared. Desalting of the counter-ions and co-ions of the solution through semi-permeable membranes induces viscoelastic phase separation of the solution to form a physical hydrogel with open pore structure. Regulating the charge ratio of the two oppositely charged polymers results in significant changes in the porous morphology and mechanical properties. The charge-balanced PEC hydrogels show unique properties including high toughness and self-recovery due to the reversible ionic associations. The porous yet tough properties of bulk PEC hydrogels makes them potential candidates for applications such as cell scaffolds., 11782740

A Multi-axial Theory of Double Network Hydrogels
Vu Ngoc Khiêm, Thanh-Tam Mai, Kenji Urayama, Jian Ping Gong, Mikhail Itskov
Macromolecules, 52, 15, 5937, 5947, Jul. 2019, [Peer-reviewed], ［Internationally co-authored］
English, Scientific journal

Tough Double Network Elastomers Reinforced by the Amorphous Cellulose Network
Joji Murai, Tasuku Nakajima, Takahiro Matsuda, Katsuhiko Tsunoda, Takayuki Nonoyama, Takayuki Kurokawa, Jian Ping Gong
Polymer, 178, 121686, Jul. 2019, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 24510616

Double Network Hydrogels Based on Semi-rigid Polyelectrolyte Physical Networks
Riku Takahashi, Takuma Ikai, Takayuki Kurokawa, Daniel R. King, Jian Ping Gong
Journal of Materials Chemistry B, 7, 41, 6347, 6354, Jul. 2019, [Peer-reviewed], [Invited], [Corresponding author], [International Magazine]
English, Scientific journal, Applying the double network principle to develop tough hydrogels with different polymer chemistries is important for the potential application of hydrogel materials. Synthesis of the two interpenetrated networks with contrasting structure and properties required for double networks usually involves a two-step polymerization process. In this work, we present a new method to synthesize tough double network hydrogels by post-physical crosslinking of linear semi-rigid polyelectrolytes entrapped in a chemically crosslinked neutral network. Owing to their semi-rigid structure, the linear polyelectrolytes form a brittle physical network above their overlap concentration in multi-valent ZrCl2O ion solutions without macroscopic phase separation within the flexible neutral network. The double network hydrogels thus prepared exhibit high modulus (∼1.7 MPa), strength (∼1.3 MPa), fracture strain (∼7.3), and strain energy density (∼5.9 MJ m-3), while containing over 80% water. These materials also exhibit modest self-healing ability (∼51% after 30 minutes), demonstrating an additional benefit of a physical sacrificial network. This method is simpler than the conventional two-step polymerization and could be applied to develop tough hydrogels from rigid polyelectrolytes, including biopolymers such as DNA, HA, and chondroitin sulfate., 24510616

Facile Synthesis of Novel Elastomers with Tunable Dynamics for Toughness, Self-healing and Adhesion
Liang Chen, Tao Lin Sun, Kunpeng Cui, Daniel R. King, Takayuki Kurokawa, Yoshiyuki Saruwatari, Jian Ping Gong
Journal of Materials Chemistry A, 7, 29, 17334, 17344, Jun. 2019, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 24510616

Hydrophobic Hydrogels with Fruit-like Structure and Functions
Hui Guo, Tasuku Nakajima, Dominique Hourdet, Alba Marcellan, Costantino Creton, Wei Hong, Takayuki Kurokawa, Jian Ping Gong
Advanced Materials, 31, 25, 1900702, May 2019, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, Normally, a polymer network swells in a good solvent to form a gel but the gel shrinks in a poor solvent. Here, an abnormal phenomenon is reported: some hydrophobic gels significantly swell in water, reaching water content as high as 99.6 wt%. Such abnormal swelling behaviors in the nonsolvent water are observed universally for various hydrophobic organogels containing omniphilic organic solvents that have a higher affinity to water than to the hydrophobic polymers. The formation of a semipermeable skin layer due to rapid phase separation, and the asymmetric diffusion of water molecules into the gel driven by the high osmotic pressure of the organic solvent-water mixing, are found to be the reasons. As a result, the hydrophobic hydrogels have a fruit-like structure, consisting of hydrophobic skin and water-trapped micropores, to display various unique properties, such as significantly enhanced strength, surface hydrophobicity, and antidrying, despite their extremely high water content. Furthermore, the hydrophobic hydrogels exhibit selective water absorption from concentrated saline solutions and rapid water release at a small pressure like squeezing juices from fruits. These novel functions of hydrophobic hydrogels will find promising applications, e.g., as materials that can automatically take the fresh water from seawater., 11782740

バイオマテリアルによる肝癌幹細胞の新規誘導法　　　　　　　　　　　　　　　
谷 道夫, 津田 真寿美, 鈴鹿 淳, 王 磊, 杉野 弘和, 谷川 聖, 石田 雄介, グン 剣萍, 田中 伸哉, 武冨 紹信
日本外科学会定期学術集会抄録集, 119回, PS, 6, (一社)日本外科学会, Apr. 2019
Japanese

Fabrication of Tough and Stretchable Hybrid Double-Network Elastomers Using Ionic Dissociation of Polyelectrolyte in Nonaqueous Media
Takahiro Matsuda, Tasuku Nakajima, Jian Ping Gong
Chemistry of Materials, 31, 10, 3766, 3776, Apr. 2019, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 24510616

Superior Fracture Resistance of Fiber Reinforced Polyampholyte Hydrogels Achieved by Extraordinarily Large Energy-dissipative Process Zones
Yiwan Huang, Daniel R. King, Wei Cui, Tao Lin Sun, Honglei Guo, Takayuki Kurokawa, Hugh R. Brown, Chung-Yuen Hui, Jian Ping Gong
Journal of Materials Chemistry A, 7, 22, 13431, 13440, Apr. 2019, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］
English, Scientific journal, 24510616

Damage Cross-effect and Anisotropy in Tough Double Network Hydrogels Revealed by Biaxial Stretching
Thanh-Tam Mai, Takahiro Matsuda, Tasuku Nakajima, Jian Ping Gong, Kenji Urayama
Soft Matter, 15, 18, 3719, 3732, Apr. 2019, [Peer-reviewed], [Corresponding author]
English, Scientific journal, 24510616

Tough and Self-healing Supramolecular Hydrogels Composed of Polyampholytes
Kunpeng Cui, Tao Lin Sun, Jian Ping Gong
Polymer Bulletin, 3, 1, 6, Mar. 2019, [Invited], [Last author]
Chinese, Scientific journal

Mechanoresponsive Self-growing Hydrogels Inspired by Muscle Training
Takahiro Matsuda, Runa Kawakami, Ryo Namba, Tasuku Nakajima, Jian Ping Gong
Science, 363, 6426, 504, 508, Feb. 2019, [Peer-reviewed], [Corresponding author]
English, Scientific journal

Osteochondral Autograft Transplantation Technique Augmented by an Ultrapurified Alginate Gel Enhances Osteochondral Repair in a Rabbit Model.
Ryosuke Hishimura, Tomohiro Onodera, Kazutoshi Hontani, Rikiya Baba, Kentaro Homan, Shinji Matsubara, Zenta Joutoku, WooYoung Kim, Takayuki Nonoyama, Takayuki Kurokawa, Jian Ping Gong, Norimasa Iwasaki
The American journal of sports medicine, 47, 2, 468, 478, Feb. 2019, [Peer-reviewed], [International Magazine]
English, Scientific journal, BACKGROUND: One of the most important limitations of osteochondral autograft transplantation (OAT) is the adverse effect on donor sites in the knee. To decrease the number and/or size of osteochondral defects, we devised a method with biomaterial implantation after OAT. HYPOTHESIS: OAT augmented by ultrapurified alginate (UPAL) gel enhances cartilage repair capacity. STUDY DESIGN: Controlled laboratory study. METHODS: Seventy-five osteochondral defects in rabbits were divided into 3 groups: osteochondral defects with OAT alone, defects with OAT augmented by UPAL gel (combined group), and defects without intervention as controls. Macroscopic and histological evaluations of the reparative tissues were performed at 4 and 12 weeks postoperatively. Histological evaluation of graft cartilage degradation was also performed. To evaluate the effects of UPAL gel on graft healing, repaired bone volumes and osseointegration of the graft were evaluated. Collagen orientation and the mechanical properties of the reparative tissue and graft cartilage were also evaluated qualitatively. RESULTS: The macroscopic and histological evaluations of the combined group were significantly superior to the other groups at 12 weeks postoperatively. Regarding degenerative change of the graft, the histological scores of the combined group were significantly higher than those of the OAT-alone group. The values of repaired subchondral bone volumes and osseointegration of the graft were almost identical in both groups. Collagen orientation and the mechanical properties of the reparative tissue and graft cartilage were significantly better in the combined group than in the other groups. CONCLUSION: Administration of UPAL gel in OAT enhanced cartilage repair and protected graft cartilage without inhibiting subchondral bone repair and graft survival. CLINICAL RELEVANCE: OAT augmented by UPAL gel decreases the number and/or size of osteochondral grafts, minimizing the risk of donor site morbidity. This combination technique has the potential to improve clinical outcomes and expand the surgical indications for OAT.

Shearing-induced Contact Pattern Formation in Hydrogels Sliding in Polymer Solution
Shintaro Yashima, Satoshi Hirayama, Takayuki Kurokawa, Thomas Salez, Haruna Takefuji, Wei Hong, Jian Ping Gong
Soft Matter, 15, 9, 1953, 1959, Jan. 2019, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, The contact of a hydrogel during the rotational shearing on a glass surface in concentrated polymer solution was observed in situ. Dynamic contact patterns that rotate in-phase with the rotational shearing of the gel were observed for the first time. The contact patterns with a periodicity in the circumferential direction appeared and became fine with the shearing time. The patterns appeared more quickly at an elevated sliding velocity, polymer concentration, and normal pressure. Furthermore, the softness of the gel also substantially influenced the characteristics of the patterns. The pattern formation was discussed in terms of the non-linear rheology of the polymer solution at the rotational soft interface.

Network elasticity of a model hydrogel as a function of swelling ratio: from shrinking to extreme swelling states
Ken-ichi Hoshino, Tasuku Nakajima, Takahiro Matsuda, Takamasa Sakai, Jian Ping Gong
SOFT MATTER, 14, 47, 9693, 9701, ROYAL SOC CHEMISTRY, Dec. 2018, [Peer-reviewed]
English, Scientific journal, In this work, we intended to investigate the relationship between the swelling ratio Q and Young's modulus E of hydrogels from their contracted state to extreme swelling state and elucidate the underlining molecular mechanism. For this purpose, we used tetra-poly(ethylene glycol) (tetra-PEG) gel, whose network parameters are well known, as the polymer backbone, and we succeeded in tuning the swelling of the gel by a factor of 1500 times while maintaining the topological structure of the network unchanged, using an approach combining a molecular stent method and a PEG dehydration method. A master curve of Q-E, independent of the method of obtaining Q, was obtained. Using the worm-like chain model, the experimentally determined master curve can be well reproduced. We also observed that the uniaxial stress-strain curve of the hydrogel can be well predicted by the worm-like chain model using the structure parameters determined from the fitting of the Q-E experimental curve.

刺激応答性発色ゲル
堀端修人, 中島 祐, 龔 剣萍
応用物理学会・有機分子・バイオエレクトロニクス分科会 会誌, 29, 4, 232, 235, Nov. 2018, [Invited]
Japanese, Scientific journal

Multiscale Energy Dissipation Mechanism in Tough and Self-Healing Hydrogels
Kunpeng Cui, Tao Lin Sun, Xiaobin Liang, Ken Nakajima, Ya Nan Ye, Liang Chen, Takayuki Kurokawa, Jian Ping Gong
Physical Review Letters, 121, 18, 185501, AMER PHYSICAL SOC, Oct. 2018, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］
English, Scientific journal, Understanding the energy dissipation mechanism during deformation is essential for the design and application of tough soft materials. We show that, in a class of tough and self-healing polyampholyte hydrogels, a bicontinuous network structure, consisting of a hard network and a soft network, is formed, independently of the chemical details of the hydrogels. Multiscale internal rupture processes, in which the double-network effect plays an important role, are found to be responsible for the large energy dissipation of these hydrogels.

Micro Patterning of Hydroxyapatite by Soft Lithography on Hydrogels for Selective Osteoconduction
Ryuji Kiyama, Takayuki Nonoyama, Susumu Wada, Shingo Semba, Nobuto Kitamura, Tasuku Nakajima, Takayuki Kurokawa, Kazunori Yasuda, Shinya Tanaka, Jian Ping Gong
Acta Biomaterialia, 81, 60, 69, Oct. 2018, [Peer-reviewed], [Corresponding author], [International Magazine]
English, Scientific journal, Mechanically robust hydrogels are promising biomaterials as artificial supportive tissue. These applications require selective and robust bonding of the hydrogels to living tissue. Recently, we achieved strong in vivo bone bonding of a tough double network (DN) hydrogel, a potential material for use as artificial cartilage and tendon, by hybridizing osteoconductive hydroxyapatite (HAp) in the gel surface layer. In this work, we report micro patterning of HAp at the surface of the DN hydrogel for selective osteoconduction. Utilizing the dissolution of HAp in an acidic environment, the soft lithography technique using an acid gel stamp was adopted to form a high-resolution HAp pattern on the gel. The HAp-patterned gel showed well-regulated migration and adhesion of cells in vitro. Moreover, the HAp-patterned gel showed selective and robust bonding to the rabbit bone tissue in vivo. This HAp soft lithography technique allows for simple and quick preparation of tailor-made osteoconductive hydrogels and can be applied to other hydrogels for selective bone bonding. STATEMENT OF SIGNIFICANCE: Hydrogels, preserving large amount of water, have been studied for next-generation artificial soft tissues. However, fixation of hydrogels to living tissue was unsolved issue for clinical application. Recently, we achieved robust bonding of a tough double network gel to bone in vivo by coating of osteoconductive hydroxyapatite in the gel surface layer. For further progress for practical use, we report the micro patterning of HAp at the surface of the DN hydrogel by using soft lithography technique, to perform selective bonding to only objective area without unnecessary coalescence. The HAp lithography technique is simple, quick and non-toxic method to prepare tailor-made osteoconductive hydrogels and has universality of species of hydrogels.

Tough Particle-Based Double Network Hydrogels for Functional Solid Surface Coatings
Riku Takahashi, Kouichi Shimano, Haruka Okazaki, Takayuki Kurokawa, Tasuku Nakajima, Takayuki Nonoyama, Daniel R. King, Jian Ping Gong
Advanced Materials Interface, 5, 23, 1801018, Oct. 2018, [Peer-reviewed]
English, Scientific journal

Elastic-Plastic Transformation of Polyelectrolyte Complex Hydrogels from Chitosan and Sodium Hyaluronate
Ran Shi, Tao Lin Sun, Feng Luo, Tasuku Nakajima, Takayuki Kurokawa, Yue Zhen Bin, Michael Rubinstein, Jian Ping Gong
Macromolecules, 51, 21, 8887, 8898, Oct. 2018, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, Hydrogels formed by polyelectrolyte complexation (PEC) of oppositely charged biopolymers, free of any chemical additives, are promising biomaterials. In this work, the mechanical behavior of hydrogels consisting of positively charged chitosan and negatively charged sodium hyaluronate (HA) at balanced charge composition is investigated. These hydrogels exhibit strong tensile strain and strain rate dependence. They are elastic-like, independent of the strain rate at small strain, but exhibit plastic-like behavior above the yield point by showing a monotonous decrease of the stress. The cyclic tensile test demonstrates that these hydrogels exhibit small and quickly recoverable hysteresis in the elastic-like region, but large and partially recoverable hysteresis above the yield point. The stress relaxation experiment shows a plateau in the reduced stress followed by an abrupt fracture, and the time-to-failure decreases exponentially with increasing applied step-strain. Such elastic-to-plastic-like transformation of the biopolymer PEC gels is quite different from the behaviors of PEC hydrogels formed by oppositely charged vinyl-type synthetic polyelectrolytes due to the difference in flexibility, charge density, and ionic bond strength of these polymers.

How Supertough Gels Break
Itamar Kolvin, John M. Kolinski, Jian Ping Gong, Jay Fineberg
Physical Review Letters, 121, 13, 135501, Sep. 2018, [Peer-reviewed], ［Internationally co-authored］, [International Magazine]
English, Scientific journal

Distinctive Characteristics of Internal Fracture in Tough Double Network Hydrogels Revealed by Various Modes of Stretching
Thanh-Tam Mai, Takahiro Matsuda, Tasuku Nakajima, Jian Ping Gong, Kenji Urayama
Macromolecules, 51, 14, 5245, 5257, Jul. 2018, [Peer-reviewed]
English, Scientific journal

Tough Hydrogels with Fast, Strong, and Reversible Underwater Adhesion Based on a Multi-Scale Design
Ping Rao, Tao Lin Sun, Liang Chen, Riku Takahashi, Gento Shinohara, Hui Guo, Daniel R. King, Takayuki Kurokawa, Jian Ping Gong
Advanced Materials, 30, 32, 1801884, Jun. 2018, [Peer-reviewed], [Corresponding author], [International Magazine]
English, Scientific journal, Hydrogels have promising applications in diverse areas, especially wet environments including tissue engineering, wound dressing, biomedical devices, and underwater soft robotics. Despite strong demands in such applications and great progress in irreversible bonding of robust hydrogels to diverse synthetic and biological surfaces, tough hydrogels with fast, strong, and reversible underwater adhesion are still not available. Herein, a strategy to develop hydrogels demonstrating such characteristics by combining macroscale surface engineering and nanoscale dynamic bonds is proposed. Based on this strategy, excellent underwater adhesion performance of tough hydrogels with dynamic ionic and hydrogen bonds, on diverse substrates, including hard glasses, soft hydrogels, and biological tissues is obtained. The proposed strategy can be generalized to develop other soft materials with underwater adhesion.

Tough and Self-Recoverable Thin Hydrogel Membranes for Biological Applications
Ya Nan Ye, Martin Frauenlob, Lei Wang, Masumi Tsuda, Tao Lin Sun, Kunpeng Cui, Riku Takahashi, Huijie Zhang, Tasuku Nakajima, Takayuki Nonoyama, Takayuki Kurokawa, Shinya Tanaka, Jian Ping Gong
Advanced Functional Materials, 28, 31, 1801489, WILEY-V C H VERLAG GMBH, Jun. 2018, [Peer-reviewed], [Corresponding author]
English, Scientific journal, Tough and self-recoverable hydrogel membranes with micrometer-scale thickness are promising for biomedical applications, which, however, rarely be realized due to the intrinsic brittleness of hydrogels. In this work, for the first time, by combing noncovalent DN strategy and spin-coating method, we successfully fabricated thin (thickness: 5-100 mu m), yet tough (work of extension at fracture: 10(5)-10(7) J m(-3)) and 100% self-recoverable hydrogel membranes with high water content (62-97 wt%) in large size (approximate to 100 cm(2)). Amphiphilic triblock copolymers, which form physical gels by self-assembly, were used for the first network. Linear polymers that physically associate with the hydrophilic midblocks of the first network, were chosen for the second network. The inter-network associations serve as reversible sacrificial bonds that impart toughness and self-recovery properties on the hydrogel membranes. The excellent mechanical properties of these obtained tough and thin gel membranes are comparable, or even superior to many biological membranes. The in vitro and in vivo tests show that these hydrogel membranes are biocompatible, and postoperative nonadhesive to neighboring organs. The excellent mechanical and biocompatible properties make these thin hydrogel membranes potentially suitable for use as biological or postoperative antiadhesive membranes.

高強度・高靭性ダブルネットワークゲルの開発とソフト人工軟骨への応用　　　　　　　　　　　　　　　
野々山貴行, 龔 剣萍, 安田和則
機能材料, 38, 5, 51, 59, May 2018, [Invited]
Japanese, Scientific journal

Creating Stiff, Tough, and Functional Hydrogel Composites with Low-Melting-Point Alloys
Riku Takahashi, Tao Lin Sun, Yoshiyuki Saruwatari, Takayuki Kurokawa, Daniel R. King, Jian Ping Gong
Advanced Materials, 30, 16, 1706885, Wiley-VCH Verlag, 19 Apr. 2018, [Peer-reviewed], [Corresponding author]
English, Scientific journal, Reinforcing hydrogels with a rigid scaffold is a promising method to greatly expand the mechanical and physical properties of hydrogels. One of the challenges of creating hydrogel composites is the significant stress that occurs due to swelling mismatch between the water-swollen hydrogel matrix and the rigid skeleton in aqueous media. This stress can cause physical deformation (wrinkling, buckling, or fracture), preventing the fabrication of robust composites. Here, a simple yet versatile method is introduced to create “macroscale” hydrogel composites, by utilizing a rigid reinforcing phase that can relieve stress-induced deformation. A low-melting-point alloy that can transform from a load-bearing solid state to a free-deformable liquid state at relatively low temperature is used as a reinforcing skeleton, which enables the release of any swelling mismatch, regardless of the matrix swelling degree in liquid media. This design can generally provide hydrogels with hybridized functions, including excellent mechanical properties, shape memory, and thermal healing, which are often difficult or impossible to achieve with single-component hydrogel systems. Furthermore, this technique enables controlled electrochemical reactions and channel-structure templating in hydrogel matrices. This work may play an important role in the future design of soft robots, wearable electronics, and biocompatible functional materials.

新規技術を用いた新しい研究アプローチ 高分子ハイドロゲルによる癌幹細胞へのリプログラミング誘導技術　　　　　　　　　　　　　　　
津田 真寿美, 鈴鹿 淳, 王 磊, 仙葉 慎吾, 油谷 幸代, 黒川 孝幸, 近江谷 克裕, 安田 和則, グン 剣萍, 田中 伸哉
日本病理学会会誌, 107, 1, 217, 217, (一社)日本病理学会, Apr. 2018
Japanese

Fracture Process of Double-Network Gels by Coarse-Grained Molecular Dynamics Simulation
Yuji Higuchi, Keisuke Saito, Takamasa Sakai, Jian Ping Gong, Momoji Kubo
MACROMOLECULES, 51, 8, 3075, 3087, AMER CHEMICAL SOC, Apr. 2018, [Peer-reviewed]
English, Scientific journal, Double-network (DN) gels consisting of highly and slightly cross linked networks exhibit good mechanical properties, complicated deformation behavior, and fracture processes owing to the existence of a large number of influential parameters. To determine the effects of these factors at the molecular level to improve the mechanical properties further, we studied the fracture processes of DN gels using a coarse-grained molecular dynamics simulation. First, we propose a modeling method for DN gels consisting of highly (first) and slightly (second) cross-linked networks. Then, we stretch the DN gels and investigate the effects of the network ratio, chain length, and first- and second-network structures on the mechanical properties. During the stretching, the stress increases with the bond breaking in the first network. Then, the stress further increases with the simultaneous bond breaking in the first and second networks when they are entangled with one another. Finally, the bond breaking in the first network stops, and only the bond breaking in the second network occurs. The second network remains at a high strain, which prevents rupture of the gel. We find that (i) a low concentration of the first network is necessary for the gel to exhibit the properties of both the first and second networks, (ii) a tense first network increases the Young's modulus, and (iii) the second network with a long chain length and separated cross linking points increases the peak stress and ductility. We have therefore successfully elucidated the effects of the network structures on the mechanical properties of DN gels.

A Facile Method to Fabricate Anisotropic Hydrogels with Perfectly Aligned Hierarchical Fibrous Structures
Md. Tariful Islam Mredha, Yun Zhou Guo, Takayuki Nonoyama, Tasuku Nakajima, Takayuki Kurokawa, Jian Ping Gong
Advanced Materials, 30, 9, 1704937, 1704937, Wiley, Mar. 2018, [Peer-reviewed], [Corresponding author], [International Magazine]
English, Scientific journal, Natural structural materials (such as tendons and ligaments) are comprised of multiscale hierarchical architectures, with dimensions ranging from nano- to macroscale, which are difficult to mimic synthetically. Here a bioinspired, facile method to fabricate anisotropic hydrogels with perfectly aligned multiscale hierarchical fibrous structures similar to those of tendons and ligaments is reported. The method includes drying a diluted physical hydrogel in air by confining its length direction. During this process, sufficiently high tensile stress is built along the length direction to align the polymer chains and multiscale fibrous structures (from nano- to submicro- to microscale) are spontaneously formed in the bulk material, which are well-retained in the reswollen gel. The method is useful for relatively rigid polymers (such as alginate and cellulose), which are susceptible to mechanical signal. By controlling the drying with or without prestretching, the degree of alignment, size of superstructures, and the strength of supramolecular interactions can be tuned, which sensitively influence the strength and toughness of the hydrogels. The mechanical properties are comparable with those of natural ligaments. This study provides a general strategy for designing hydrogels with highly ordered hierarchical structures, which opens routes for the development of many functional biomimetic materials for biomedical applications.

Tough and variable-band-gap photonic hydrogel displaying programmable angle-dependent colors
Md. Anamul Haque, Kei Mito, Takayuki Kurokawa, Tasuku Nakajima, Takayuki Nonoyama, Muhammad Ilyas, Jian Ping Gong
ACS Omega, 3, 1, 55, 62, American Chemical Society, 2018, [Peer-reviewed], [Corresponding author], ［Internationally co-authored］, [International Magazine]
English, Scientific journal, One-dimensional photonic crystals or multilayer films produce colors that change depending on viewing and light illumination angles because of the periodic refractive index variation in alternating layers that satisfy Bragg’s law. Recently, we have developed multilayered photonic hydrogels of two distinct bulk geometries that possess an alternating structure of a rigid polymeric lamellar bilayer and a ductile polyacrylamide (PAAm) matrix. In this paper, we focus on fabrication of composite gels with variable photonic band gaps by controlling the PAAm layer thickness. We report programmable angle-dependent and angle-independent structural colors produced by composite hydrogels, which is achieved by varying bulk and internal geometries. In the sheet geometry, where the lamellae are aligned parallel to the sheet surface, the photonic gel sheet exhibits strong angle-dependent colors. On the other hand, when lamellae are coaxially aligned in a cylindrical geometry, the gel rod exhibits an angle-independent color, in sharp contrast with the gel sheet. Rocking curves have been constructed to justify the diverse angle-dependent behavior of various geometries. Despite varying the bulk geometry, the tunable photonic gels exhibit strong mechanical performances and toughness. The distinct angle dependence of these tough photonic materials with variable band gaps could benefit light modulation in displays and sensor technologies.

Anisotropic Growth of Hydroxyapatite in Stretched Double Network Hydrogel
Kazuki Fukao, Takayuki Nonoyama, Ryuji Kiyama, Kazuya Furusawa, Takayuki Kurokawa, Tasuku Nakajima, Jian Ping Gong
ACS Nano, 11, 12, 12103, 12110, American Chemical Society, 26 Dec. 2017, [Peer-reviewed]
English, Scientific journal, Bone tissues possess excellent mechanical properties such as compatibility between strength and flexibility and load bearing owing to the hybridization of organic/inorganic matters with anisotropic structure. To synthetically mimic such an anisotropic structure of natural organic/inorganic hybrid materials, we carried out hydroxyapatite (HAp) mineralization in stretched tough double network (DN) hydrogels. Anisotropic mineralization of HAp took place in stretched hydrogels, as revealed by high brightness synchrotron X-ray scattering and transmission electron microscopic observation. The c-axis of mineralized HAp aligned along the stretching direction, and the orientation degree S calculated from scattering profiles increased with increasing in the elongation ratio λ of the DN gel, and S at λ = 4 became comparable to that of rabbit tibial bones. The morphology of HAp polycrystal gradually changed from spherical to unidirectional rod-like shape with increased elongation ratio. A possible mechanism for the anisotropic mineralization is proposed, which would be one of the keys to develop mechanically anisotropic organic/inorganic hybrid materials.

Inorganic/Organic Double-Network Gels Containing Ionic Liquids
Eiji Kamio, Tomoki Yasui, Yu Iida, Jian Ping Gong, Hideto Matsuyama
ADVANCED MATERIALS, 29, 47, 1704118, WILEY-V C H VERLAG GMBH, Dec. 2017, [Peer-reviewed]
English, Scientific journal, Highly robust ion gels, termed double-network (DN) ion gels, composed of inorganic/organic interpenetrating networks and a large amount of ionic liquids (ILs), are fabricated. The DN ion gels with an 80 wt% IL content show extraordinarily high mechanical strength: more than 28 MPa of compressive fracture stress. In the DN ion gel preparation, a brittle inorganic network of physically bonded silica nanoparticles and a ductile organic network of polydimethylacrylamide (PDMAAm) are formed in the IL. Because of the different reaction mechanisms of the inorganic/organic networks, the DN ion gels can be formed by an easy and free-shapeable one-pot synthesis. They can be prepared in a controllable manner by manipulating the formation order of the inorganic and organic networks via not only multistep but also single-step processes. When silica particles form a network prior to the PDMAAm network formation, DN ion gels can be prepared. The brittle silica particle network in the DN ion gel, serving as sacrificial bonds, easily ruptures under loading to dissipate energy, while the ductile PDMAAm network maintains the shape of the material by the rubber elasticity. Given the reversible physical bonding between the silica particles, the DN ion gels exhibit a significant degree of self-recovery by annealing.

ダブルネットワークゲル（ DN ゲル）の軟骨応用に向けた検討
野々山貴行, 中島祐, 黒川孝幸, 北村信人, 安田和則, 龔剣萍
FC Report, 35, 4, 148, 152, Oct. 2017
Japanese, Scientific journal

Water-Triggered Ductile-Brittle Transition of Anisotropic Lamellar Hydrogels and Effect of Confinement on Polymer Dynamics
Muhammad Ilyas, Md. Anamul Haque, Youfeng Yue, Takayuki Kurokawa, Tasuku Nakajima, Takayuki Nonoyama, Jian Ping Gong
MACROMOLECULES, 50, 20, 8169, 8177, AMER CHEMICAL SOC, Oct. 2017, [Peer-reviewed]
English, Scientific journal, We study the effect of dehydration On the structure and mechanical properties of anisotropic lamellar hydrogels, consisting of alternative stacking of several thousands of nanoscale rigid bilayers from amphiphilic poly(dodecyl glyceryl itaconate) (PDGI) and submicroscale soft hydrogel layers from hydrophilic polyacrylamide (PAAm) networks. We found that the layered microstructure is well preserved with dehydration, and a ductile-brittle transition occurs at the critical water-content. This, transition is related to the rubbery-glassy transition of the PAAm layers, which occurs at 58 wt % water content and is much higher than 26 wt% of bulk PAAm hydrogels. Such specific behavior of the lamellar hydrogels indicates that the dynamics of the submicroscale PAAm hydrated layer intercalated between the rigid bilayers are very different from its bulk state.

Supramolecular hydrogels with multi-cylindrical lamellar bilayers: Swelling-induced contraction and anisotropic molecular diffusion
Kei Mito, Md. Anamul Haque, Tasuku Nakajima, Maki Uchiumi, Takayuki Kurokawa, Takayuki Nonoyama, Jian Ping Gong
POLYMER, 128, 373, 378, ELSEVIER SCI LTD, Oct. 2017, [Peer-reviewed], [Invited]
English, Scientific journal, Novel, supramolecular, anisotropic hydrogels (called MC-PDGI gels) are presented in this study. These MC-PDGI gels consist of multi-cylindrical lipid bilayers aligned in a uniaxial manner and embedded in a soft hydrogel matrix. The bilayers and the hydrogel interact weakly due to hydrogen bonding. These MC-PDGI gels swell after exposure to water, which causes their volume and diameter to increase while simultaneously causing their length to decrease. This anisotropic swelling-induced contraction behavior is the result of competition between the isotropic elasticity of the hydrogel matrix and the interfacial tension of the lipid bilayers. Moreover, the MC-PDGI gels exhibit unique quasi one-dimensional diffusion behavior owing to the difficulty of molecular penetration through the multi-layered lipid bilayers. These materials would be useful for prolonged drug release or as an actuator. (C) 2017 Elsevier Ltd. All rights reserved.

Tough, self-recovery and self-healing polyampholyte hydrogels
Tao Lin Sun, Kunpeng Cui, Jian Ping Gong
POLYMER SCIENCE SERIES C, 59, 1, 11, 17, MAIK NAUKA/INTERPERIODICA/SPRINGER, Sep. 2017, [Peer-reviewed], [Invited]
English, Scientific journal, This article reviews the recently developed tough, self-recovery, and self-healing polyampholyte hydrogels. Polyampholyte hydrogels are synthesized using one-step radical copolymerization of cationic and anionic monomers with equal charges at high monomer concentration. The random copolymerization process makes the ionic monomers randomly distributing along the backbones, resulting in the formation of ionic bonds with a wide strength distribution via inter and intra chain complexation in the polymer network, weak bond and strong bonds. The strong bonds serve as permanent cross-linking, integrating the hydrogels to impart the elastic behavior, while the weak bonds can break upon the loading, dissipating energy to give the toughness, and re-form again after unloading to enable the self-recovery behavior. Accordingly, polyampholyte hydrogels have condensed polymers in water (ca 40-50 wt %). They are strongly viscoelastic and have a high toughness (fracture energy of 4000 J/m(2)), a wide range of tuning modulus (0.01 to 8 MPa), 100% self-recovery, and a high self-healing efficiency after cutting.

Anisotropic tough double network hydrogel from fish collagen and its spontaneous in vivo bonding to bone
Md. Tariful Islam Mredha, Nobuto Kitamura, Takayuki Nonoyama, Susumu Wada, Keiko Goto, Xi Zhang, Tasuku Nakajima, Takayuki Kurokawa, Yasuaki Takagi, Kazunori Yasuda, Jian Ping Gong
BIOMATERIALS, 132, 85, 95, ELSEVIER SCI LTD, Jul. 2017, [Peer-reviewed]
English, Scientific journal, Soft supporting tissues in the human body, such as cartilages and ligaments, are tough materials and firmly fixed to bones. These soft tissues, once injured, cannot regenerate spontaneously in vivo. Developing tough and biocompatible hydrogels as artificial soft supporting tissues would substantially improve outcomes after soft tissue injury. Collagen is the main rigid component in soft connective tissues which is organized in various hierarchical arrays. We have successfully developed a novel class of collagen fibril-based tough hydrogels based on the double network (DN) concept using swim bladder collagen (SBC) extracted from Bester sturgeon fish. The DN hydrogels, SBC/PDMAAm, are composed of physically/chemically crosslinked anisotropic SBC fibril as the first network and neutral, biocompatible poly(N,N'-dimethylacrylamide) (PDMAAm) as the second network. The anisotropic structure of SBC fibril network, which is well retained in the DN hydrogels, is formed by free injection method, taking advantage of the excellent fibrillogenesis capacity of SBC. The denaturation temperature of collagen is improved in the DN hydrogels. These DN gels possess anisotropic swelling behavior, exhibit excellent mechanical properties comparable to natural cartilage. The 4 weeks implantation of the gels in the osteochondral defect of rabbit knee also shows excellent biomechanical performance in vivo. Furthermore, the hydroxyapatite (HAp) coated DN gels, HAp/SBC/PDMAAm gels, strongly bond to bone after 4 weeks. This new class of collagen-based hybrid DN gels, as soft and elastic ceramics, having good biomechanical performance and strong bonding ability with bone would expand the choice for designing next generation orthopedic implants such as artificial cartilage, bone defect repair material in the load bearing region of the body. (C) 2017 Elsevier Ltd. All rights reserved.

Effects of osteochondral defect size on cartilage regeneration using a double-network hydrogel
Kotaro Higa, Nobuto Kitamura, Keiko Goto, Takayuki Kurokawa, Jian Ping Gong, Fuminori Kanaya, Kazunori Yasuda
BMC MUSCULOSKELETAL DISORDERS, 18, 210, BIOMED CENTRAL LTD, May 2017, [Peer-reviewed]
English, Scientific journal, Background: There has been increased interest in one-step cell-free procedures to avoid the problems related to cell manipulation and its inherent disadvantages. We have studied the chondrogenic induction ability of a PAMPS/PDMAAm double-network (DN) gel and found it to induce chondrogenesis in animal osteochondral defect models. The purpose of this study was to investigate whether the healing process and the degree of cartilage regeneration induced by the cell-free method using DN gel are influenced by the size of osteochondral defects.
Methods: A total of 63 mature female Japanese white rabbits were used in this study, randomly divided into 3 groups of 21 rabbits each. A 2.5-mm diameter osteochondral defect was created in the femoral trochlea of the patellofemoral joint of bilateral knees in Group I, a 4.3-mm osteochondral defect in Group II, and a 5.8-mm osteochondral defect in Group III. In the right knee of each animal, a DN gel plug was implanted so that a vacant space of 2-mm depth was left above the plug. In the left knee, we did not conduct any treatment to obtain control data. Animals were sacrificed at 2, 4, and 12 weeks after surgery, and gross and histological evaluations were made.
Results: The present study demonstrated that all sizes of the DN gel implanted defects as well as the 2.5mm untreated defects showed cartilage regeneration at 4 and 12 weeks. The 4.3-mm and 5.8-mm untreated defects did not show cartilage regeneration during the 12-week period. The quantitative score reported by O'Driscoll et al. was significantly higher in the 4.3-mm and 5.8-mm DN gel-implanted defects than the untreated defects at 4 and 12 weeks (p < 0.05). The 2.5-mm and 4.3-mm DN gel implanted defects maintained relatively high macroscopic and histological scores for the 12-week implantation period, while the histological score of the 5.8-mm DN gel implanted defect had decreased somewhat but statistically significantly at 12 weeks (p = 0.0057).
Conclusions: The DN gel induced cartilage regeneration in defects between 2.5 and 5.8 mm, offering a promising device to establish a cell-free cartilage regeneration therapy and applicable to various sizes of osteochondral defects.

Tough polyion-complex hydrogels from soft to stiff controlled by monomer structure
Feng Luo, Tao Lin Sun, Tasuku Nakajima, Takayuki Kurokawa, Xufeng Li, Honglei Guo, Yiwan Huang, Huijie Zhang, Jian Ping Gong
POLYMER, 116, 487, 497, ELSEVIER SCI LTD, May 2017, [Peer-reviewed], [Invited]
English, Scientific journal, Tough hydrogels with adjustable stiffness are expected for adapting application as various biomaterials. Oppositely charged polyelectrolytes form tough and self-healing physical polyion-complex (PIC) hydrogels via formation of inter-chain ionic bonds with a wide distribution in bond strength. The strong bonds serve as permanent crosslinking to impart elasticity and the weak bonds as reversible sacrificial bonds to dissipate energy and to self-heal. In this work, we fabricate four PIC hydrogels using four positively charged trimethyl-ammonium monomers with slightly different chemical moieties and a same negatively charged polymer. The obtained PIC hydrogels all show high toughness but large difference in stiffness, extensibility, and self-recovery kinetics. With slight difference in the monomer structure of the polycations, the modulus of the hydrogels varies over two orders in magnitude, from 0.36 to 56 MPa, and the difference in elongation at break is up to five times. The presence of acryloyl moiety and methyl moiety increase the stiffness of the hydrogels. In the temperature range studied, all the four PIC hydrogels exhibit the rheological simple behaviours, following the time-temperature superposition principle. The four samples show quite different dynamic relaxation spectra over wide frequency range, revealing large difference in the strength distribution of dynamic ionic bonds. SEM observation reveals quite different phase separation structure for the four samples, in which the polymer chain stiffness should play an important role. This understanding of structure-properties of the PIC hydrogels will merit the designing of various supramolecular tough hydrogels and therefore broaden the scope of hydrogels for the applications as biomaterials. (C) 2017 Elsevier Ltd. All rights reserved.

Bulk Energy Dissipation Mechanism for the Fracture of Tough and Self-Healing Hydrogels
Tao Lin Sun, Feng Luo, Wei Hong, Kunpeng Cui, Yiwan Huang, Hui Jie Zhang, Daniel R. King, Takayuki Kurokawa, Tasuku Nakajima, Jian Ping Gong
MACROMOLECULES, 50, 7, 2923, 2931, AMER CHEMICAL SOC, Apr. 2017, [Peer-reviewed]
English, Scientific journal, Recently, many tough and self-healing hydro gels have been developed based on physical bonds as reversible sacrificial bonds. As breaking and re-forming of physical bonds are time-dependent, these hydrogels are viscoelastic and the deformation rate and temperature pronouncedly influence their fracture behavior. Using a polyampholyte hydrogel as a model system, we observed that the time temperature superposition principle is obeyed not only for the small strain rheology but also for the large strain hysteresis energy dissipation and the fracture energy below a certain temperature. The three processes possess the same shift factors that obey the equation of Williams, Landel, and Ferry (WLF) time temperature equivalence. The fracture energy F scales with the crack velocity V-c over a wide velocity range as Gamma similar to V-c(alpha) (alpha = 0.21). The exponent alpha of the power law is well-related to the exponent kappa of the relaxation modulus G(t) similar to t(-kappa) (kappa = 0.26), obeying the prediction alpha = kappa/(1 + kappa) from classic viscoelasticity theory. These results show that the fracture energy of the polyampholyte gel is dominated by the bulk viscoelastic energy dissipated around the crack tip. This investigation gives an insight into designing tough and self-healing hydrogels and predicting their fracture behaviors from their dynamic mechanical spectrum.

Energy-Dissipative Matrices Enable Synergistic Toughening in Fiber Reinforced Soft Composites
Yiwan Huang, Daniel R. King, Tao Lin Sun, Takayuki Nonoyama, Takayuki Kurokawa, Tasuku Nakajima, Jian Ping Gong
ADVANCED FUNCTIONAL MATERIALS, 27, 9, 1605350, WILEY-V C H VERLAG GMBH, Mar. 2017, [Peer-reviewed]
English, Scientific journal, Tough hydrogels have shown strong potential as structural biomaterials. These hydrogels alone, however, possess limited mechanical properties (such as low modulus) when compared to some load-bearing tissues, e.g., ligaments and tendons. Developing both strong and tough soft materials is still a challenge. To overcome this obstacle, a new material design strategy has been recently introduced by combining tough hydrogels with woven fiber fabric to create fiber reinforced soft composites (FRSCs). The new FRSCs exhibit extremely high toughness and tensile properties, far superior to those of the neat components, indicating a synergistic effect. Here, focus is on understanding the role of energy dissipation of the soft matrix in the synergistic toughening of FRSCs. By selecting a range of soft matrix materials, from tough hydrogels to weak hydrogels and even a commercially available elastomer, the toughness of the matrix is determined to play a critical role in achieving extremely tough FRSCs. This work provides a good guide toward the universal design of soft composites with extraordinary fracture resistance capacity.

Stimuli-Responsive Transformation of a Gradient Gel
Tasuku Nakajima, Kenta Hiwatashi, Jian Hu, Takayuki Kurokawa, Jian Ping Gong
KOBUNSHI RONBUNSHU, 74, 4, 311, 318, SOC POLYMER SCIENCE JAPAN, 2017, [Peer-reviewed], [Invited]
Japanese, Scientific journal, A gradient particle double network gel (P-DN gel) which exhibits unique conformation changes has been fabricated. A gradient P-DN gel consists of polyanion microgel particles with a concentration gradient and a poly(acrylamide) (PAAm) network as a matrix. In order to make the gradient structure, the gel precursor solution containing acrylamide, the microgel particles and some other additives was electrophoresed before its polymerization. When the gradient P-DN gel was soaked in pure water, it macroscopically formed a helical conformation due to a swelling mismatch induced by the gradient structure of the microgels. Moreover, when the gradient P-DN gel was immersed in an ethanol/water mixed solution and in a NaCl aqueous solution, the conformation of the gel dynamically changed to flat- and cylinder-shapes, respectively. These unique conformation changes can be qualitatively explained by considering not only the swelling mismatch but also an edge effect.

刺激応答性構造色と異方的物性を示すリオトロピック液晶ゲル
中島祐, 龔剣萍
液晶, 20, 4, 212, 217, Oct. 2016, [Peer-reviewed], [Invited]
Japanese, Scientific journal

Hydroxyapatite-coated double network hydrogel directly bondable to the bone: Biological and biomechanical evaluations of the bonding property in an osteochondral defect
Susumu Wada, Nobuto Kitamura, Takayuki Nonoyama, Ryuji Kiyama, Takayuki Kurokawa, Jian Ping Gong, Kazunori Yasuda
ACTA BIOMATERIALIA, 44, 125, 134, ELSEVIER SCI LTD, Oct. 2016, [Peer-reviewed]
English, Scientific journal, We have developed a novel hydroxyapatite (HAp)-coated double-network (DN) hydrogel (HAp/DN gel). The purpose of this study was to determine details of the cell and tissue responses around the implanted HAp/DN gel and to determine how quickly and strongly the HAp/DN gel bonds to the bone in a rabbit osteochondral defect model. Immature osteoid tissue was formed in the space between the HAp/DN gel and the bone at 2 weeks, and the osteoid tissue was mineralized at 4 weeks. The push-out load of the HAp/DN gel averaged 37.54 N and 42.15 N at 4 and 12 weeks, respectively, while the push-out load of the DN gel averaged less than 5 N. The bonding area of the HAp/DN gel to the bone was above 80% by 4 weeks, and above 90% at 12 weeks. This study demonstrated that the HAp/DN gel enhanced osseointegration at an early stage after implantation. The presence of nanoscale structures in addition to osseointegration of HAp promoted osteoblast adhesion onto the surface of the HAp/DN gel. The HAp/DN gel has the potential to improve the implant-tissue interface in next-generation orthopaedic implants such as artificial cartilage.
Statement of Significance
Recent studies have reported the development of various hydrogels that are sufficiently tough for application as soft supporting tissues. However, fixation of hydrogels on bone surfaces with appropriate strength is a great challenge. We have developed a novel, tough hydrogel hybridizing hydroxyapatite (HAp/DN gel), which is directly bondable to the bone. The present study demonstrated that the HAp/DN gel enhanced osseointegration in the early stage after implantation. The presence of nanoscale structures in addition to the osseointegration ability of hydroxyapatite promoted osteoblast adhesion onto the surface of the HAp/DN gel. The HAp/DN gel has the potential to improve the implant-tissue interface in next-generation orthopaedic implants such as artificial cartilage. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Sensing surface mechanical deformation using active probes driven by motor proteins
Daisuke Inoue, Takahiro Nitta, Arif Md. Rashedul Kabir, Kazuki Sada, Jian Ping Gong, Akihiko Konagaya, Akira Kakugo
NATURE COMMUNICATIONS, 7, 12557, NATURE PUBLISHING GROUP, Oct. 2016, [Peer-reviewed]
English, Scientific journal, Studying mechanical deformation at the surface of soft materials has been challenging due to the difficulty in separating surface deformation from the bulk elasticity of the materials. Here, we introduce a new approach for studying the surface mechanical deformation of a soft material by utilizing a large number of self-propelled microprobes driven by motor proteins on the surface of the material. Information about the surface mechanical deformation of the soft material is obtained through changes in mobility of the microprobes wandering across the surface of the soft material. The active microprobes respond to mechanical deformation of the surface and readily change their velocity and direction depending on the extent and mode of surface deformation. This highly parallel and reliable method of sensing mechanical deformation at the surface of soft materials is expected to find applications that explore surface mechanics of soft materials and consequently would greatly benefit the surface science.

Fundamental biomaterial properties of tough glycosaminoglycan-containing double network hydrogels newly developed using the molecular stent method
Kotaro Higa, Nobuto Kitamura, Takayuki Kurokawa, Keiko Goto, Susumu Wada, Takayuki Nonoyama, Fuminori Kanaya, Kazuyuki Sugahara, Jian Ping Gong, Kazunori Yasuda
ACTA BIOMATERIALIA, 43, 38, 49, ELSEVIER SCI LTD, Oct. 2016, [Peer-reviewed]
English, Scientific journal, The purpose of this study was to clarify fundamental mechanical properties and biological responses of the sodium hyaluronate-containing double network (HA-DN) gel and chondroitin sulfate-containing double network (CS-DN) gel, which were newly developed using the molecular stent method. This study discovered the following facts. First, these hydrogels had high mechanical performance comparable to the native cartilage tissue, and the mechanical properties were not affected by immersion in the saline solution for 12 weeks. Secondly, the mechanical properties of the CS-DN gel were not significantly reduced at 12 weeks in vivo, while the mechanical properties of the HA-DN gel were significantly deteriorated at 6 weeks. Thirdly, the degree of inflammation around the HA-DN gel was the same as that around the negative control. The CS-DN gel showed a mild but significant foreign body reaction, which was significantly greater than the negative control and less than the positive control at 1 week, while the inflammation was reduced to the same level as the negative control at 4 and 6 weeks. Fourthly, these gels induced differentiation of the ATDC5 cells into chondrocytes in the culture with the insulin free maintenance medium. These findings suggest that these tough hydrogels are potential biomaterials for future application to therapeutic implants such as artificial cartilage.
Statement of Significance
The present study reported fundamental biomaterial properties of the sodium hyaluronate-containing double network (HA-DN) gel and chondroitin sulfate-containing double network (CS-DN) gel, which were newly developed using the molecular stent method. Both the HA- and CS-DN gels had high mechanical properties comparable to the cartilage tissue and showed the ability to induce chondrogenic differentiation of ATDC5 cells in vitro. They are potential biomaterials that may meet the requirements of artificial cartilage concerning the material properties. Further, these DN gels can be also applied to the implantable inducer for cell-free cartilage regeneration therapy. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In vivo cartilage regeneration induced by a double-network hydrogel: Evaluation of a novel therapeutic strategy for femoral articular cartilage defects in a sheep model
Nobuto Kitamura, Masashi Yokota, Takayuki Kurokawa, Jian Ping Gong, Kazunori Yasuda
JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 104, 9, 2159, 2165, WILEY-BLACKWELL, Sep. 2016, [Peer-reviewed]
English, Scientific journal, The purpose of this study was to establish the efficacy of a therapeutic strategy for an articular cartilage defect using a poly-(2-acrylamido-2-methylpropanesulfonic acid)/poly-(N,N'-dimethyl acrylamide) DN gel in a sheep model. Seventeen mature sheep were used in this study. We created a 6.0-mm osteochondral defect in the femoral trochlea of the patellofemoral (PF) joint and the medial condyle of the tibiofemoral (TF) joint. A cylindrical DN gel plug was implanted into the defect of the right knee so that a vacant space of the planned depths of 2.0 mm in group I, 3.0 mm in group II, and 4.0 mm in group III were left. In the left knee, we created a defect with the same depth as the right knee. The regenerated tissues were evaluated with the O'Driscoll score and real-time PCR analysis of the cartilage marker genes at 12 weeks. The DN gel implanted defect of group II in the PF and TF joints was completely filled with a sufficient volume of the proteoglycan-rich tissue stained with Safranin-O. The score showed that group II was significantly greater than groups I and III when treated with DN gel in the PF joint (p=0.0441, p=0.0174, respectively) and in the TF joint (p=0.0019, p=0.0006, respectively). This study has clarified the short-term efficacy of the cartilage regeneration strategy using the DN gel in a sheep model. (c) 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2159-2165, 2016.

ハイドロキシアパタイト複合化PAMPS/PDMAAmダブルネットワークゲル人工軟骨の関節内におけるin vivo骨接着性評価
和田 進, 北村 信人, 野々山 貴行, 木山 竜二, 仙葉 愼吾, 小野寺 純, 横田 正司, 後藤 佳子, 比嘉 浩太郎, 黒川 孝幸, Gong Jian Ping, 安田 和則
日本整形外科学会雑誌, 90, 8, S1598, S1598, (公社)日本整形外科学会, Aug. 2016
Japanese

Creep Behavior and Delayed Fracture of Tough Polyampholyte Hydrogels by Tensile Test
Sadia Nazneen Karobi, Tao Lin Sun, Takayuki Kurokawa, Feng Luo, Tasuku Nakajima, Takayuki Nonoyama, Jian Ping Gong
MACROMOLECULES, 49, 15, 5630, 5636, AMER CHEMICAL SOC, Aug. 2016, [Peer-reviewed]
English, Scientific journal, Polyampholyte (PA) hydrogels are a new class of tough and selfhealing supramolecular hydrogels that have a potential as load-bearing soft materials. Studying on the creep behavior of these hydrogels and understanding the molecular mechanism are important for prediction of lifetime of the materials. In the present work, we study the creep rupture dynamics of the PA hydrogels with and without chemical cross-linking, in a certain observation time window. We have found that above some critical loading stress both physical and lightly chemically cross-linked hydrogels undergo creep rupture while moderately chemically cross-linked hydrogel resists creep flow. To elucidate the molecular mechanism, we have further compared the creep behaviors of the physical and lightly chemically cross-linked samples. The creep rate of the samples decreases with the creep time, following a power law relation, regardless of the loading stress variation. The fracture time of both of these hydrogels exponentially decreases with the increase of the loading stress, following the same master curve at high loading stress region, while the behavior of the two samples becomes different in the low loading stress region. We have explained the delayed fracture dynamics at high loading stress region in terms of a relatively weak strong bond rupture mechanism.

Double-Network Hydrogels Strongly Bondable to Bones by Spontaneous Osteogenesis Penetration
Takayuki Nonoyama, Susumu Wada, Ryuji Kiyama, Nobuto Kitamura, Md. Tariful Islam Mredha, Xi Zhang, Takayuki Kurokawa, Tasuku Nakajima, Yasuaki Takagi, Kazunori Yasuda, Jian Ping Gong
ADVANCED MATERIALS, 28, 31, 6740, +, WILEY-V C H VERLAG GMBH, Aug. 2016, [Peer-reviewed]
English, Scientific journal, On implanting hydroxyapatite-mineralized tough hydrogel into osteochondral defects of rabbits, osteogenesis spontaneously penetrates into the gel matrix owing to the semi-permeablility of the hydrogel. The gradient layer (around 40 mu m thick) contributes quite strong bonding of the gel to bone. This is the first success in realizing the robust osteointegration of tough hydrogels, and the method is simple and feasible for practical use.

Molecular Structure and Properties of Click Hydrogels with Controlled Dangling End Defect
Ao-kai Zhang, Jun Ling, Kewen Li, Guo-dong Fu, Tasuku Nakajima, Takayuki Nonoyama, Takayuki Kurokawa, Jian Ping Gong
JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, 54, 13, 1227, 1236, WILEY-BLACKWELL, Jul. 2016, [Peer-reviewed]
English, Scientific journal, In this study, controlled amount of dangling ends is introduced to the two series of poly(ethylene glycol)-based hydrogel networks with three and four crosslinking functionality by using click chemistry. The structure of the gels with regulated defect percentage is confirmed by comparing the results of low-field NMR characterization and Monte Carlo simulation. The mechanical properties of these gels were characterized by tensile stress-strain behaviors of the gels, and the results are analyzed by Gent model and Mooney-Rivlin model. The shear modulus of the swollen gels is found to be dependent on the functionality of the network, and decreases with the defect percentage. Furthermore, the value of shear modulus well obeys the Phantom model for all the gels with varied percentage of the defects. The maximum extension ratio, obtained from the fitting of Gent model, is also found to be dependent on the functionality of the network, and does not change with the defect percentage, except at very high defect percentage. The value of the maximum extension ratio is between that predicted from Phantom model and the Affine model. This indicates that at the large deformation, the fluctuation of the crosslinking points is suppressed for some extend but still exists. Polymer volume fractions at various defect percentages obtained from prediction of Flory-Rehner model are found to be in well agreement with the swelling experiment. All these results indicate that click chemistry is a powerful method to regulate the network structure and mechanical properties of the gels. (C) 2016 Wiley Periodicals, Inc.

Self-Healing Behaviors of Tough Polyampholyte Hydrogels
Abu Bin Ihsan, Tao Lin Sun, Takayuki Kurokawa, Sadia Nazneen Karobi, Tasuku Nakajima, Takayuki Nonoyama, Chanchal Kumar Roy, Feng Luo, Jian Ping Gong
MACROMOLECULES, 49, 11, 4245, 4252, AMER CHEMICAL SOC, Jun. 2016, [Peer-reviewed]
English, Scientific journal, Recently, polyampolytes have been discovered to form hydrogels that possess high toughness, full resilience, and self-healing between two cut surfaces. The self-healing of this class of hydrogels is based on the re-forming of the multiple Tonic bonds at the fractured surfaces, in which the mobility of the polymer segments and strength of the ionic bonds play an important role. In this work, we study the effects of healing temperature and chemistry of the polyampholyte hydrogels (chemical cross -linker density and chemical structure of the monomers) on the healing kinetics and healing efficiency. The high healing temperature substantially accelerates the self-healing kinetics. Chemical cross-linking reduces the self-healing efficiency. Monomers with more hydrophobic feature give a low self-healing efficiency. For polyampholyte physical hydrogels with a softening temperature below the room temperature, excellent-healing efficiency (similar to 84% on average and maximum 99%) was observed without any external stimuli.- We found a correlation between the self-healing efficiency and the fraction of dynamic bonds in the total bonds for relatively soft samples, which is an evidence that the self healing is due to the re-forming of dynamic bonds.

Tough Physical Double-Network Hydrogels Based on Amphiphilic Triblock Copolymers
Hui Jie Zhang, Tao Lin Sun, Ao Kai Zhang, Yumihiko Ikura, Tasuku Nakajima, Takayuki Nonoyama, Takayuki Kurokawa, Osamu Ito, Hiroyuki Ishitobi, Jian Ping Gong
ADVANCED MATERIALS, 28, 24, 4884, 4890, WILEY-V C H VERLAG GMBH, Jun. 2016, [Peer-reviewed]
English, Scientific journal, A series of physical double-network hydrogels is synthesized based on an amphiphilic triblock copolymer. The gel, which contains strong hydrophobic domains and sacrificial dynamic bonds of hydrogen bonds, is stiff and tough, and even stiffens in concentrated saline solution. Furthermore, due to its supramolecular structure, the gel features improved self-healing and self-recovery abilities.

Tough bacterial nanocellulose hydrogels based on the double-network technique　　　　　　　　　　　　　　　
Anamul Haque, Takayuki Kurokawa, Jian Ping Gong
Bacterial NanoCellulose: A Sophisticated Multifunctional Material, 73, 89, CRC Press, 19 Apr. 2016
English, In book

Quantitative Observation of Electric Potential Distribution of Brittle Polyelectrolyte Hydrogels Using Microelectrode Technique
Honglei Guo, Takayuki Kurokawa, Masakazu Takahata, Wei Hong, Yoshinori Katsuyama, Feng Luo, Jamil Ahmed, Tasuku Nakajima, Takayuki Nonoyama, Jian Ping Gong
MACROMOLECULES, 49, 8, 3100, 3108, AMER CHEMICAL SOC, Apr. 2016, [Peer-reviewed]
English, Scientific journal, We report, for the first time, the quantitative measurement of the local electric potential of brittle polyelectrolyte hydrogels using the microelectrode technique (MET). Given the solid-like nature of the hydrogels, the difficulty of applying MET is how to make a good contact of the microelectrode to the hydrogel. Poor local contact substantial underestimates the potential. We observed that, the potential measured decays exponentially with the increase of capillary diameter of the microelectrode. This behavior is related to the capillary wall thickness that determines the contact distance of the electrode probe to the hydrogel. The characteristic decay length in respective to the wall thickness is very close to the local Debye length around the capillary. The latter is much larger than that of the bath solution due to the reverse osmosis effect. By using microelectrodes with a tip wall thickness less than the local Debye length, the Donnan potential of polyelectrolyte gel could be accurately measured. Using a micromanipulator, the inserting process of the microelectrode is precisely controlled, and the depth profile of electric potential in the hydrogels can be measured with a spatial resolution down to similar to 5 nm. From the spatial distribution of potential, the microstructure of hydrogels both in bulk and near the surface, the thickness of ultrathin hydrogels, and the heterogeneous layered structure of composite gels, can be determined accurately. The MET established in this work provides a powerful tool for direct characterization of the spatial distribution of electric potential of hydrogels.

Strong and Tough Polyion-Complex Hydrogels from Oppositely Charged Polyelectrolytes: A Comparative Study with Polyampholyte Hydrogels
Feng Luo, Tao Lin Sun, Tasuku Nakajima, Daniel R. King, Takayuki Kurokawa, Yu Zhao, Abu Bin Ihsan, Xufeng Li, Honglei Guo, Jian Ping Gong
MACROMOLECULES, 49, 7, 2750, 2760, AMER CHEMICAL SOC, Apr. 2016
English, Scientific journal, Oppositely charged homopolyelectrolytes were found to form strong, tough, and self-healing polyion-complex (PIC) hydrogels, similar to polyampholytes (PA) which have opposite charges randomly distributed on the same polymer chains. The excellent mechanical performances of these two novel hydrogels are the results of dynamic ionic bonds formation between entangled polymer chains. For the PIC system, only interchain bonding occurs, while for the PA system both inter- and intrachain bonding exist. In addition, the ion pairs are expected to form stronger bonding in the PIC system than those in the PA system. In this work, we performed a comparative study of PIC hydrogels with the PA hydrogels. The PIC hydrogels are synthesized by sequential homopolymerization of cationic and anionic monomers at varied formulation, and their swelling and mechanical properties are systematically studied in comparison to the PA hydrogels that were synthesized from random copolymerization of anionic monomers and cationic monomers of the similar formulation. Different from the PA system which only forms tough hydrogels around zero net charge composition without chemical cross-linking, the PIC system forms tough physical hydrogels even at weakly off balanced charge composition. At the charge-balanced composition, the low entanglement concentration of homocharged polyelectrolyte chains leads to tough PIC hydrogels formation at much lower concentrations than that of PA hydrogels. As a result, the PIC hydrogels are much tougher than the PA hydrogels prepared at the same monomer composition. In similar to PA hydrogels, the PIC hydrogels also exhibit broad dynamic mechanical spectra, indicating the formation of ion complexes with widely ranged bond strength. The PIC hydrogels have strong viscoelasticity in comparison with PA hydrogels. However, the two systems show the similar activation energies of the dynamic mechanical spectra. The SEM microstructural observation shows that the PIC hydrogels have segregated structure while PA hydrogels are more homogeneous.

Yielding Criteria of Double Network Hydrogels
Takahiro Matsuda, Tasuku Nakajima, Yuki Fukuda, Wei Hong, Takamasa Sakai, Takayuki Kurokawa, Ung-il Chung, Jian Ping Gong
MACROMOLECULES, 49, 5, 1865, 1872, AMER CHEMICAL SOC, Mar. 2016, [Peer-reviewed]
English, Scientific journal, Double network (DN) gels, consisting of a brittle first and flexible second network, have been known to be extremely tough and functional hydrogels. In a DN gel subjected to force, the brittle first network breaks prior to the fracture of the flexible network. This process, referred to as internal fracture, dissipates energy and increases the energy required to completely fracture DN gels. Such internal fracture macroscopically appears as a yielding-like phenomenon. The aim of this paper is to investigate the relationship between the yield point and the first network molecular structure of DN gels to more deeply understand the internal fracture mechanism of DN gels. To achieve this goal, we synthesized DN gels having a tetra-PEG first network, which is known to be a nearly ideal and well-controlled network gel. We have found that yielding of the DN gels occurs when the first network strands reach their extension limit (finite extensibility), regardless of their deformation mode. This conclusion not only helps by further understanding the toughening mechanism of DN gels but also allows for the design of DN gels with precisely controlled mechanical properties.

Synthetic PAMPS gel activates BMP/Smad signaling pathway in ATDC5 cells, which plays a significant role in the gel-induced chondrogenic differentiation
Keiko Goto, Taichi Kimura, Nobuto Kitamura, Shingo Semba, Yoshihiro Ohmiya, Sachiyo Aburatani, Satoko Matsukura, Masumi Tsuda, Takayuki Kurokawa, Jian Ping Gong, Shinya Tanaka, Kazunori Yasuda
JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 104, 3, 734, 746, WILEY-BLACKWELL, Mar. 2016, [Peer-reviewed]
English, Scientific journal, The purposes of this study were to identify signaling pathways that were specifically activated in ATDC5 cells cultured on poly (2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) gel in insulin-free maintenance medium and to evaluate the significance of the determined signaling pathways in the chondrogenic differentiation induced by this gel. In this study, ATDC5 cells cultured on PAMPS gel using the maintenance medium without insulin (PAMPS Culture) were compared with cells cultured on polystyrene using the differentiation medium containing insulin (PS-I Culture). The microarray analysis, Western blot analysis, and real-time PCR analysis demonstrated that the TGF-/BMP signaling pathway was significantly enhanced at Days 1, 2, and 3 in the PAMPS Culture when compared with the PS-I Culture. Inhibition of the BMP type-I receptor reduced the phosphorylation level of Smad1/5 and expression of type-2 collagen and aggrecan mRNA in the cells accompanied by a reduction in cell aggregation at Day 13 in the PAMPS Culture. The inhibition of the TGF-/BMP signaling pathway significantly inhibited the chondrogenic differentiation induced by the PAMPS gel. The present study demonstrated that synthetic PAMPS gel activates the TGF-/BMP/Smad signaling pathway in the ATDC5 cells in the absence of insulin, and that this activation plays a significant role in the chondrogenic differentiation induced by PAMPS gel. (c) 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 734-746, 2016.

Stretching-induced ion complexation in physical polyampholyte hydrogels
Kunpeng Cui, Tao Lin Sun, Takayuki Kurokawa, Tasuku Nakajima, Takayuki Nonoyama, Liang Chen, Jian Ping Gong
SOFT MATTER, 12, 43, 8833, 8840, ROYAL SOC CHEMISTRY, 2016, [Peer-reviewed]
English, Scientific journal, Recently, we have developed a series of charge balanced polyampholyte (PA) physical hydrogels by random copolymerization in water, which show extraordinarily high toughness, self-healing ability and viscoelasticity. The excellent performance of PA hydrogels is ascribed to dynamic ionic bond formation through inter-and intra-chain interactions. The randomness results in ionic bonds of wide strength distribution, the strong bonds, which serve as permanent crosslinking, imparting the elasticity, while the weak bonds reversibly break and re-form, dissipating energy. In this work, we developed a simple physical method, called a pre-stretching method, to promote the performance of PA hydrogels. By imposing a pre-stretching on the sample in the as-prepared state, ion complexation during dialysis is prominently accelerated and the final performance is largely promoted. Further analysis suggests that the strong bond formation induced by pre-stretching is responsible for the change in final performance. Pre-stretching decreases the entropy of the system and increases the chain alignment, resulting in an increased possibility for strong bond formation.

Decoupling dual-stimuli responses in patterned lamellar hydrogels as photonic sensors
Youfeng Yue, Xufeng Li, Takayuki Kurokawa, Md. Anamul Haque, Jian Ping Gong
JOURNAL OF MATERIALS CHEMISTRY B, 4, 23, 4104, 4109, ROYAL SOC CHEMISTRY, 2016, [Peer-reviewed]
English, Scientific journal, This work developed a photonic hydrogel that is responsive to, and can distinguish between two stimuli of stress and pH. Patterning is used to locally change the chemistry of a one-dimensional (1D) photonic gel, such that the native region is responsive to mechanical stress while the chemically modified region is responsive to both mechanical stress and pH. By combining the optical signals in the native region and the modified region, one can distinguish the stimuli between pH and stress. Specifically, the native 1D photonic gel is composed of periodically aligned polymeric bilayers in a soft polyacrylamide (PAAm) network. The chemical modification is done by partially hydrolyzing PAAm into sodium polyacrylic acid in some patterned regions, which imparts pH sensitivity, in addition to the stress sensitivity, to these regions.

Coupled instabilities of surface crease and bulk bending during fast free swelling of hydrogels
Riku Takahashi, Yumihiko Ikura, Daniel R. King, Takayuki Nonoyama, Tasuku Nakajima, Takayuki Kurokawa, Hirotoshi Kuroda, Yoshihiro Tonegawa, Jian Ping Gong
SOFT MATTER, 12, 23, 5081, 5088, ROYAL SOC CHEMISTRY, 2016, [Peer-reviewed]
English, Scientific journal, Most studies on hydrogel swelling instability have been focused on a constrained boundary condition. In this paper, we studied the mechanical instability of a piece of disc-shaped hydrogel during free swelling. The fast swelling of the gel induces two swelling mismatches; a surface-inner layer mismatch and an annulus-disc mismatch, which lead to the formation of a surface crease pattern and a saddle-like bulk bending, respectively. For the first time, a stripe-like surface crease that is at a right angle on the two surfaces of the gel was observed. This stripe pattern is related to the mechanical coupling of surface instability and bulk bending, which is justified by investigating the swelling-induced surface pattern on thin hydrogel sheets fixed onto a saddle-shaped substrate prior to swelling. A theoretical mechanism based on an energy model was developed to show an anisotropic stripe-like surface crease pattern on a saddle-shaped surface. These results might be helpful to develop novel strategies for controlling crease patterns on soft and wet materials by changing their three-dimensional shape.

Structure Transition and Function Modification of a Hydrogel Based on Lamellar Bilayers
Kei Mito, Tasuku Nakajima, Takayuki Nonoyama, Jian Ping Gong
KOBUNSHI RONBUNSHU, 73, 2, 157, 165, SOC POLYMER SCIENCE JAPAN, 2016, [Peer-reviewed], [Invited]
Japanese, Scientific journal, Lipid molecules form anisotropic self-assembled structures such as worm-like micelles or lipid bilayers. Recently the authors have successfully introduced and immobilized uniaxially-oriented lipid bilayers of poly(dodecyl glyceryl itaconate) (PDGI) into the polyacrylamide (PAAm) gel matrix to obtain stable gel-bilayer composites (called PDGI/PAAm gels) with anisotropic structure and functions, such as unidirectional swelling or anisotropic diffusion. One question about this complek is why such a dynamic lipid bilayer structure can be well-stabilized in PAAm gels. In this paper, we focus on the bilayer structure of the PDGI/PAAm gels. In the fast part, the stabilization mechanism of lipid bilayers in the gels, due to hydrogen bonding between PDGI and PAAm, is discussed. In the second part, structure transition and function modification of the PDGI/PAAm gels by insertion of more lipid molecules into bilayers is investigated.

Double-network hydrogel and its potential biomedical application: A review
Takayuki Nonoyama, Jian Ping Gong
PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE, 229, 12, 853, 863, SAGE PUBLICATIONS LTD, Dec. 2015, [Peer-reviewed], [Invited]
English, Scientific journal, Double-network hydrogels are one of the most promising candidates as artificial soft supporting tissues owing to their excellent mechanical performance, water storage capability, and biocompatibility. A double-network hydrogel consists of two contrasting polymer networks: rigid and brittle first network and soft and ductile second network. To satisfy this double-network requirement, polyelectrolyte and neutral polymer are suitable as the first and the second networks, respectively. Combination of these two networks gives rise to extraordinarily tough double-network hydrogel as a result of substantial internal fracture of the brittle first network at large deformation, which contributes to the energy dissipation. Therefore, the first network serves as the sacrificial bonds to toughen the material. The double-network principle is universal and many kinds of double-network hydrogels composed of various chemical species have been developed. Moreover, a molecular stent technology has been developed to synthesize the double-network hydrogels using neutral polymer network as the brittle first network. The sulfonic double-network hydrogel was found to induce spontaneous hyaline cartilage regeneration in vivo.

Self-Adjustable Adhesion of Polyampholyte Hydrogels
Chanchal Kumar Roy, Hong Lei Guo, Tao Lin Sun, Abu Bin Ihsan, Takayuki Kurokawa, Masakazu Takahata, Takayuki Nonoyama, Tasuku Nakajima, Jian Ping Gong
ADVANCED MATERIALS, 27, 45, 7344, +, WILEY-V C H VERLAG GMBH, Dec. 2015, [Peer-reviewed]
English, Scientific journal, Developing nonspecific, fast, and strong adhesives that can glue hydrogels and biotissues substantially promotes the application of hydrogels as biomaterials. Inspired by the ubiquitous adhesiveness of bacteria, it is reported that neutral polyampholyte hydrogels, through their self-adjustable surface, can show rapid, strong, and reversible adhesion to charged hydrogels and biological tissues through the Coulombic interaction.

Phase-Separation-Induced Anomalous Stiffening, Toughening, and Self-Healing of Polyacrylamide Gels
Koshiro Sato, Tasuku Nakajima, Toshiyuki Hisamatsu, Takayuki Nonoyama, Takayuki Kurokawa, Jian Ping Gong
ADVANCED MATERIALS, 27, 43, 6990, +, WILEY-V C H VERLAG GMBH, Nov. 2015, [Peer-reviewed]
English, Scientific journal, Novel, tough, strong, and self-healable polyacrylamide (PAAm) gels are fabricated by inducing an appropriate phase-separation structure using a poor solvent. The phase separation induces a gel-glass-like transition of the PAAm gels, providing the gels an anomalously high modulus (211 MPa), fracture stress (7.13 MPa), and fracture energy (4.16 x 10(4) J m(-2)), while keeping a high solvent content (approximate to 60 vol%).

Extremely tough composites from fabric reinforced polyampholyte hydrogels
Daniel R. King, Tao Lin Sun, Yiwan Huang, Takayuki Kurokawa, Takayuki Nonoyama, Alfred J. Crosby, Jian Ping Gong
MATERIALS HORIZONS, 2, 6, 584, 591, ROYAL SOC CHEMISTRY, Nov. 2015, [Peer-reviewed]
English, Scientific journal, Ligaments are unique wet biological tissues with high tensile modulus and fracture stress, combined with high bending flexibility. Developing synthetic materials with these properties is a significant challenge. Hydrogel composites made from high stiffness fabrics is a strategy to develop such unique materials; however, the ability to produce these materials has proven difficult, since common hydrogels swell in water and interact poorly with solid components, limiting the transfer of force from the fabric to the hydrogel matrix. In this work, for the first time, we successfully produce extraordinarily tough hydrogel composites by strategically selecting a recently developed tough hydrogel that de-swells in water. The new composites, consisting of polyampholyte hydrogels and glass fiber woven fabrics, exhibit extremely high effective toughness (250 000 J m(-2)), high tear strength (similar to 65 N mm(-1)), high tensile modulus (606 MPa), and low bending modulus (4.7 MPa). Even though these composites are composed of water-containing, biocompatible materials, their mechanical properties are comparable to high toughness Kevlar/polyurethane blends and fiber-reinforced polymers. Importantly, the mechanical properties of these composites greatly outperform the properties of either individual component. A mechanism is proposed based on established fabric tearing theory, which will enable the development of a new generation of mechanically robust composites based on fabrics. These results will be important towards developing soft biological prosthetics, and more generally for commercial applications such as tear-resistant gloves and bulletproof vests.

Anisotropic Gelation Induced by Very Little Amount of Filamentous Actin
Kazuhiro Shikinaka, Manami Misu, Hidemitsu Furukawa, Akira Kakugo, Jian Ping Gong
MACROMOLECULAR CHEMISTRY AND PHYSICS, 216, 20, 2007, 2011, WILEY-V C H VERLAG GMBH, Oct. 2015, [Peer-reviewed]
English, Scientific journal, In this paper, the hydrogel is created with oriented structure by addition of very little amount of dopant, filamentous actin (F-actin), which is 1/50 000 of lower critical concentration for nematic phase in F-actin aqueous solution. The orientation mechanism of polymer network differs depending on the concentration of F-actin. Furthermore, it is first exhibited that the role of polyelectrolyte for the emergence of anisotropy of gel is differed depending on its concentration by using digestion method to F-actins, experimentally.

バイオミネラリゼーションにより複合化したハイドロキシアパタイトコーティングPAMPS/PDMAAmダブルネットワークゲルの骨接着性の評価
和田 進, 北村 信人, 野々山 貴行, 木山 竜二, 仙葉 愼吾, 比嘉 浩太郎, 黒川 孝幸, Gong Jian Ping, 安田 和則
日本整形外科学会雑誌, 89, 8, S1585, S1585, (公社)日本整形外科学会, Sep. 2015
Japanese

PAMPSゲルはATDC5細胞の軟骨分化においてBMP/Smadシグナル経路を活性化する
後藤 佳子, 北村 信人, 木村 太一, 仙葉 愼吾, 黒川 孝幸, Gong Jian Ping, 田中 伸哉, 安田 和則
日本整形外科学会雑誌, 89, 8, S1708, S1708, (公社)日本整形外科学会, Sep. 2015
Japanese

Free Reprocessability of Tough and Self-Healing Hydrogels Based on Polyion Complex
Feng Luo, Tao Lin Sun, Tasuku Nakajima, Takayuki Kurokawa, Abu Bin Ihsan, Xufeng Li, Honglei Guo, Jian Ping Gong
ACS MACRO LETTERS, 4, 9, 961, 964, AMER CHEMICAL SOC, Sep. 2015, [Peer-reviewed]
English, Scientific journal, Tough hydrogels with facile processability to reform into various shapes are required in many practical applications. In this work, we reported that a novel, tough, and self-healing physical hydrogel based on polyion complex (PIC) can be dissolved in 4 M NaCl solution to form a PIC solution. The PIC solution can be easily reprocessed into various shapes, such as thin films, sheets, fibers, and capsules, by using simple methods, such as casting and injection, while maintaining excellent mechanical properties comparable to, or even better than, the original hydrogel. The reprocessability and robust mechanical properties of PIC hydrogels are promising for practical applications in soft materials, especially in 3D/4D printing technology.

皮膚を規範とした革新的機能材料・ラメラ構造を有するハイドロゲルの構造色と強靭性
黒川 孝幸, ムハンマド アナムル ハック, 龔 剣萍
工業材料, 63, 8, 64, 68, 日刊工業出版プロダクション ; 1955-, Aug. 2015, [Invited]
Japanese, Scientific journal

Friction of Zwitterionic Hydrogel by Dynamic Polymer Adsorption
Jamil Ahmed, Tetsurou Yamamoto, Honglei Guo, Takayuki Kurokawa, Takayuki Nonoyama, Tasuku Nakajima, Jian Ping Gong
MACROMOLECULES, 48, 15, 5394, 5401, AMER CHEMICAL SOC, Aug. 2015, [Peer-reviewed]
English, Scientific journal, A simplified model describing the sliding friction of hydrogel on solid surface by dynamic adsorption of the polymer chains is proposed on the basis of polymer adsorption-repulsion theory. This dynamic adsorption model is used to analyze the friction results of zwitterionic hydrogels sliding over glass substrates with different substrate wettability, hydrogel swelling degree, ionic strength, and pH of bath solution. The adsorption time tau(b) of polymer strands is found to decrease with the increase in sliding velocity or the Weissenberg number as a result of stretching. The adsorption time tau(0)(b), and the adsorption energy U-ads at stress-free condition, which are characteristic for each friction system, are also estimated. Roughly, a master curve is observed for the normalized adsorption lifetime tau(b)/tau(0)(b) and the Weissenberg number, with less dependence on the adsorption energy and the bulk properties of the gels in the observed experimental conditions. Thus, the dynamic adsorption model successfully correlates the frictional behavior of hydrogels with the adsorption dynamics of polymer strands, which gives insight into the molecular design of hydrogels with predefined frictional properties for biomedical applications.

Drag force on micron-sized objects with different surface morphologies in a flow with a small Reynolds number
Arif Md Rashedul Kabir, Daisuke Inoue, Yuri Kishimoto, Jun-ichi Hotta, Keiji Sasaki, Noboru Kitamura, Jian Ping Gong, Hiroyuki Mayama, Akira Kakugo
POLYMER JOURNAL, 47, 8, 564, 570, NATURE PUBLISHING GROUP, Aug. 2015, [Peer-reviewed]
English, Scientific journal, The lack of a suitable experimental setup and a limited number of in vitro investigations have impeded understanding of the factors that have important roles in altering the drag force acting on tiny microobjects in a fluidic medium. Here we investigated how the surface morphology affects the drag force acting on microparticles. The drag coefficient for micron-sized polymer-grafted polystyrene (PS) and negatively charged hard (silica) and soft (hydrogel) spheres were evaluated and compared with that of a PS particle. The drag coefficient of the PS particle was found to be comparable to that predicted according to the Stokes' formula for a hard sphere. By contrast, polymer-grafted PS and negatively charged hard and soft spheres showed a considerable deviation from the Stokes' formula. The drag coefficient decreased by similar to 60 and similar to 86% for the negatively charged hard and soft spheres, respectively, whereas it increased by similar to 20% for the polymer-grafted PS particles with respect to that of the PS particle. This work reveals the role of the surface morphology of small objects in altering the drag force acting on them; such knowledge may help elucidate the mechanism by which the surface morphology of aquatic microorganisms helps them to control the drag force, which consequently might facilitate the invention of new technologies for micromachines or microdevices.

Tunable one-dimensional photonic crystals from soft materials
Youfeng Yue, Jian Ping Gong
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY C-PHOTOCHEMISTRY REVIEWS, 23, 45, 67, ELSEVIER SCIENCE BV, Jun. 2015, [Peer-reviewed], [Invited]
English, Scientific journal, Photonic crystals are periodic dielectric nanostructures that can affect the propagation of light. Polymer-based photonic crystals have attracted great attentions for their potential application as sensors or optical switches due to their stimuli-responsive properties. This review summarizes the recent developments in one-dimensional (1-D) polymer-based photonic crystals, including the inspiration of the material from nature, principles for design and fabrication, mechanism of color tuning, and their tunable structural color in responsive to various stimuli. A number of fabrication methods, either by bottom-up or top-down approaches for 1-D polymeric photonic crystals have been overviewed. (C) 2015 Elsevier B.V. All rights reserved.

高強度ゲルをつくる
中島祐, 龔剣萍
高分子, 64, 6, 367, 369, May 2015, [Invited]
Japanese, Scientific journal

Oppositely Charged Polyelectrolytes Form Tough, Self-Healing, and Rebuildable Hydrogels
Feng Luo, Tao Lin Sun, Tasuku Nakajima, Takayuki Kurokawa, Yu Zhao, Koshiro Sato, Abu Bin Ihsan, Xufeng Li, Honglei Guo, Jian Ping Gong
ADVANCED MATERIALS, 27, 17, 2722, +, WILEY-V C H VERLAG GMBH, May 2015, [Peer-reviewed]
English, Scientific journal, A series of tough polyion complex hydrogels is synthesized by sequential homopolymerization of cationic and anionic monomers. Owing to the reversible interpolymer ionic bonding, the materials are self-healable under ambient conditions with the aid of saline solution. Furthermore, self-glued bulk hydrogels can be built from their microgels, which is promising for 3D/4D printing and the additive manufacturing of hydrogels.

Hydrogels as feeder-free scaffolds for long-term self-renewal of mouse induced pluripotent stem cells
Jing Jing Yang, Jian Fang Liu, Takayuki Kurokawa, Kazuhiro Kitada, Jian Ping Gong
JOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE, 9, 4, 375, 388, WILEY-BLACKWELL, Apr. 2015, [Peer-reviewed]
English, Scientific journal, Expanding undifferentiated induced pluripotent stem (iPS) cells in vitro is a basic requirement for application of iPS cells in both fundamental research and clinical regeneration. In this study, we intended to establish a simple, low cost and efficient method for the long-term self-renewal of mouse induced pluripotent stem (miPS) cells without using feeder-cells and adhesive proteins. Three scaffolds were selected for the long-term subculture of miPS cells over two months starting from passages 14 to 29: 1) a gelatin coated polystyrene (Gelatin-PS) that is a widely used scaffold for self-renewal of mouse embryonic stem (mES) cells; 2) a neutral hydrogel poly(N,N-dimethylacrylamide) (PDMAAm); and 3) a negatively charged hydrogel poly(2-acrylamido-2-methyl-propane sulfonic acid sodium salt) (PNaAMPS). Each passaged miPS cells on these scaffolds were cryopreserved successfully and the revived cells showed high viability and proliferation. The passaged miPS cells maintained a high undifferentiated state on all three scaffolds and a high level of pluripotency by expressing differentiation markers in vitro and forming teratomas in SCID mice with derivatives of all three germ layers. Compared to Gelatin-PS, the two hydrogels exhibited much better self-renewal performance in terms of high proliferation rate and level of expression of undifferentiated gene markers as well as efficiency in pluripotent teratoma formation. Furthermore, the PNaAMPS hydrogel demonstrated a slightly higher efficiency and simpler operation of cell expansion than the PDMAAm hydrogel. To conclude, PNaAMPS hydrogel is an excellent feeder-free scaffold because of its simplicity, low cost and high efficiency in expanding a large number of miPS cells in vitro. Copyright (c) 2012 John Wiley & Sons, Ltd.

Polymer Adsorbed Bilayer Membranes Form Self-Healing Hydrogels with Tunable Superstructure
Xufeng Li, Takayuki Kurokawa, Riku Takahashi, Md. Anamul Haque, Youfeng Yue, Tasuku Nakajima, Jan Ping Gong
MACROMOLECULES, 48, 7, 2277, 2282, AMER CHEMICAL SOC, Apr. 2015, [Peer-reviewed]
English, Scientific journal, We report that polymers can support bilayer membranes to form physical hydrogels of self-healing and tunable isotropic/anisotropic structure. The system consists of poly(dodecyl glyceryl itaconate) (PDGI) which forms lamellar bilayers and polyacrylamide (PAAm) which adsorbs on the bilayer surfaces via hydrogen bond formation. Adsorption of PAAm brings two effects: disturbs the bilayer packing and causes bending of the bilayers; increases the effective thickness of the bilayers and enhances the repulsion between the bilayers due to excluded volume effect. Competition of these two effects brings about sharp superstructure transition from isotropic multilayer foam phase to unidirectionally aligned lamellar phase. Accompanied by this structure transition, the bulk hydrogel exhibits isotropic/anisotropic swelling. The physical gels exhibit high tensile strength and self-healing properties that can be understood by the sacrificial bonds mechanism.

小さな力で多彩な色をだす構造色ゲル―新しいメカノクロミック材料の合成法とその応用
Tasuku Nakajima, Jian Ping Gong
化学, 70, 4, 32, 36, Mar. 2015, [Invited]
Japanese, Scientific journal

In Vitro Platelet Adhesion of PNaAMPS/PAAm and PNaAMPS/PDMAAm Double-Network Hydrogels
Wen Jiang Zheng, Zhen Qi Liu, Feng Xu, Jie Gao, Yong Mei Chen, Jian Ping Gong, Yoshihito Osada
MACROMOLECULAR CHEMISTRY AND PHYSICS, 216, 6, 641, 649, WILEY-V C H VERLAG GMBH, Mar. 2015, [Peer-reviewed]
English, Scientific journal, Nowadays, tough double-network (DN) hydrogels have attracted great attention owing to their excellent mechanical properties and good biocompatibility, which give them the potential to be used as blood-contacting soft tissue prostheses and medical devices. However, the study of platelet adhesion behavior on the surface of DN hydrogels has not been reported yet. In this work, the human platelet adhesion on the surface of poly (sodium 2-acrylamido-2-methyl-propanesulfonate) PNaAMPS/poly acrylamide (PAAm) and PNaAMPS/poly (N,N-dimethylacrylamide) (PDMAAm) DN hydrogels is investigated under static conditions in vitro. The numbers of adherent platelets on PNaAMPS/PAAm and PNaAMPS/PDMAAm hydrogels are 16 +/- 7 and 9 +/- 8 cells per 10(4) m(2), respectively, which are far less than 297 +/- 41 cells per 10(4) m(2) on polyethylene terephthalate (PET) and 187 +/- 26 cells per 10(4) m(2) on negatively charged PNaAMPS (4 mol%) hydrogel. The results indicate the excellent antiplatelet performance of DN hydrogels. Moreover, the platelet adhesion mechanism is also discussed. The platelet adhesion is affected by the chemical component, zeta potential, and serum proteins adsorption of the hydrogel.

Molecular structure of self-healing polyampholyte hydrogels analyzed from tensile behaviors
Tao Lin Sun, Feng Luo, Takayuki Kurokawa, Sadia Nazneen Karobi, Tasuku Nakajima, Jian Ping Gong
SOFT MATTER, 11, 48, 9355, 9366, ROYAL SOC CHEMISTRY, 2015, [Peer-reviewed]
English, Scientific journal, Recently, charge balanced polyampholytes (PA) have been found to form tough and self-healing hydrogels. This class of physical hydrogels have a very high equilibrated polymer concentration in water (ca. 40-50 wt%), and are strongly viscoelastic. They are synthesized by random copolymerization of equal amounts of oppositely charged monomers at a high concentration, followed by a dialysis process of the small counter-ions and co-ions in water. The randomly distributed, opposite charges of the polymer form multiple ionic bonds of intra-and inter-chains with strength distribution. The strong interchain bonds, stabilized by topological entanglement, serve as quasi-permanent crosslinks, imparting the elasticity, while the weak bonds, both inter-and intra-chains, reversibly break and re-form to dissipate energy to toughen the materials. In this work, we intend to clarify the structure of the physical PA hydrogels from the tensile behaviors of the PA hydrogels. To clarify the structure and its formation mechanism, we analysed the tensile behaviors of the samples before and after the dialysis. We separated the quasi-permanent crosslinking of strong inter-chain bonds and the dynamic crosslinking of weak inter-chain bonds by using a combined model that consists of the Upper Convected Maxwell model and the Gent strain hardening model. The model fitting of the tensile behaviors extracts quantitative structural parameters, including the densities of weak and strong inter-chain bonds and the theoretical finite extensibility of polymer chains. Based on the fitting results of the combined model, the structural parameters of partial chains at a fixed observation time, including the Kuhn number, Kuhn length, and chain conformation, are determined using the scaling theory. The effects of monomer concentration at preparation, the effect of dialysis and the initial strain rate on the dynamic structure of PA gels, are discussed based on these analyses.

Swim bladder collagen forms hydrogel with macroscopic superstructure by diffusion induced fast gelation
Md. Tariful Islam Mredha, Xi Zhang, Takayuki Nonoyama, Tasuku Nakajima, Takayuki Kurokawa, Yasuaki Takagid, Jian Ping Gong
JOURNAL OF MATERIALS CHEMISTRY B, 3, 39, 7658, 7666, ROYAL SOC CHEMISTRY, 2015, [Peer-reviewed]
English, Scientific journal, Marine collagen has been attracting attention as a medical material in recent times due to the low risk of pathogen infection compared to animal collagen. Type I collagen extracted from the swim bladder of Bester sturgeon fish has excellent characteristics such as high denaturation temperature, high solubility, low viscosity and an extremely fast rate to form large bundle of fibers under certain conditions. These specific characteristics of swim bladder collagen (SBC) permit us to create stable, disk shaped hydrogels with concentric orientation of collagen fibers by the controlled diffusion of neutral buffer through collagen solution at room temperature. However, traditionally used animal collagens, e.g. calf skin collagen (CSC) and porcine skin collagen (PSC), could not form any stable and oriented structure by this method. The mechanism of the superstructure formation of SBC by a diffusion induced gelation process has been explored. The fast fibrillogenesis rate of SBC causes a quick squeezing out of the solvent from the gel phase to the sol phase during gelation, which builds an internal stress at the gel-sol interface. The tensile stress induces the collagen molecules of the gel phase to align along the gel-sol interface direction to give this concentric ring-shaped orientation pattern. On the other hand, the slow fibrillogenesis rate of animal collagens due to the high viscosity of the solution does not favor the ordered structure formation. The denaturation temperature of SBC increases significantly from 31 degrees C to 43 degrees C after gelation, whereas that of CSC and PSC were found to increase a little. Rheology experiment shows that the SBC gel has storage modulus larger than 15 kPa. The SBC hydrogels with thermal and mechanical stability have potential as bio-materials for tissue engineering applications.

Quasi-unidirectional shrinkage of gels with well-oriented lipid bilayers upon uniaxial stretching
Tasuku Nakajima, Corentin Durand, Xu Feng Li, Md. Anamul Haque, Takayuki Kurokawa, Jian Ping Gong
SOFT MATTER, 11, 2, 237, 240, ROYAL SOC CHEMISTRY, 2015, [Peer-reviewed]
English, Scientific journal, PDGI-PAAm gels with well oriented lipid bilayers show a quasi-unidirectional shrinkage upon uniaxial stretching along the bilayers. They shrink largely parallel to the bilayer but slightly perpendicular to it in order not to increase the bilayer area and its interfacial energy. Such an anisotropic deformation can be well-modelled based on classical theories for gel networks and lipid layers.

Solvent and Ca2+ triggered robust and fast stress generation by ultrathin triple-network hydrogels
Songmiao Liang, Jian Hu, Zi Liang Wu, Takayuki Kurokawa, Jian Ping Gong
Extreme Mechanics Letters, 1, 17, 22, Elsevier Ltd, 01 Dec. 2014, [Peer-reviewed]
English, Scientific journal, Solvent-triggered isometric stress generation of an ultrathin and tough triple-network (TN) hydrogel was systematically studied as functions of the pre-strain and ethanol/water mixture solvent. The obtained results along with the solvent-induced changes in the volume and modulus of the hydrogel were further analyzed with emphasis on clarifying the stress generation mechanism of the TN gel. Ca2+-triggered stress generation of the gel was also preliminarily explored. High stress generation of 0.4 MPa was obtained within tens of seconds at the low pre-strain of 25% by alternating water and ethanol. Both negative and positive stress generation of the gel were achieved just by changing the composition of the ethanol/water mixture solvent. Mechanism analysis indicates that, modulus change of the gel is the dominant reason for their solvent-triggered high and fast stress generation. In the case of the Ca2+-triggered stress generation of the gel, it is also attributed to the modulus change induced by the physical cross-linking of Ca2+ between the negatively charged first network chains of the TN hydrogel.

In Situ Observation of Ca2+ Diffusion-Induced Superstructure Formation of a Rigid Polyanion
Zi Liang Wu, Riku Takahashi, Daisuke Sawada, Md. Arifuzzaman, Tasuku Nakajima, Takayuki Kurokawa, Jian Hu, Jian Ping Gong
MACROMOLECULES, 47, 20, 7208, 7214, AMER CHEMICAL SOC, Oct. 2014, [Peer-reviewed]
English, Scientific journal, Diffusion of multivalent metallic ions into aqueous solution of rigid, negatively charged macromolecules of high concentration is an effective approach to prepare macroscopically anisotropic hydrogels. However, the mechanism for superstructure formation is still not clear. By observing the mixing process of a small drop of CaCl2 solution with solution of a rigid polyanion, poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT), under the polarizing optical microscope, the diffusion profile of Ca2+ and detailed anisotropic gelation process of PBDT are revealed. Diffusion of Ca2+ into the surrounding PBDT solution immediately induces the formation of physical liquid crystalline (LC) gel with concentric alignment of PBDT. The thickness d of this region increases with diffusion time t, obeying the diffusion law d similar to t1/2. A thin ring of constant width (similar to 100 mu m) with radial alignment of PBDT appears at the diffusion/reaction front, ahead of the concentric alignment region. When two drops of CaCl2 fluxes meet, their outside thin rings interact with each other and the PBDT in this contacting region orients +/- 45 degrees to the midline of the two drops. From these observations, we rationally contend that the internal stress induced by the contraction of gel phase is responsible for the ion diffusion-induced PBDT orientations. This structure formation mechanism gives insight into other diffusion-directed anisotropic gelation systems.

Significant increase in Young's modulus of ATDC5 cells during chondrogenic differentiation induced by PAMPS/PDMAAm double-network gel: Comparison with induction by insulin
Eijiro Maeda, Takehiro Tsutsumi, Nobuto Kitamura, Takayuki Kurokawa, Jian Ping Gong, Kazunori Yasuda, Toshiro Ohashi
JOURNAL OF BIOMECHANICS, 47, 13, 3408, 3414, ELSEVIER SCI LTD, Oct. 2014, [Peer-reviewed]
English, Scientific journal, A double-network (DN) gel, which was composed of poly(2-acrylamido-2-methylpropanesulfonic acid) and poly(N,N'-dimethyl acrylamide) (PAMPS/PDMAAm), has the potential to induce chondrogenesis both in vitro and in vivo. The present study investigated the biomechanical and biological responses of chondrogenic progenitor ATDC5 cells cultured on the DN gel. ATDC5 cells were cultured on a polystyrene surface without insulin (Culture 1) and with insulin (Culture 2), and on the DN gel without insulin (Culture 3). The cultured cells were evaluated using micropipette aspiration for cell Young's modulus and qPCR for gene expression of chondrogenic and actin organization markers on days 3, 7 and 14. On day 3, the cells in Culture 3 formed nodules, in which the cells exhibited an actin cortical layer inside them, and gene expression of type-II collagen, aggrecan, and SOX9 was significantly higher in Culture 3 than Cultures 1 and 2 (p < 0.05). Young's modulus in Culture 3 was significantly higher than that in Culture 1 throughout the testing period (p < 0.05) and that in Culture 2 on day 14 (p < 0.01). There was continuous expression of actin organization markers in Culture 3. This study highlights that the cells on the DN gel increased the modulus and mRNA expression of chondrogenic markers at an earlier time point with a greater magnitude compared to those on the polystyrene surface with insulin. This study also demonstrates a possible strong interrelation among alteration of cell mechanical properties, changes in actin organization and the induction of chondrogenic differentiation. (C) 2014 Elsevier Ltd. All rights reserved.

Effects of culture on PAMPS/PDMAAm double-network gel on chondrogenic differentiation of mouse C3H10T1/2 cells: in vitro experimental study
Yusuke Inagaki, Nobuto Kitamura, Takayuki Kurokawa, Yasuhito Tanaka, Jian P. Gong, Kazunori Yasuda, Harukazu Tohyama
BMC MUSCULOSKELETAL DISORDERS, 15, 320, BIOMED CENTRAL LTD, Sep. 2014, [Peer-reviewed]
English, Scientific journal, Background: Recently, several animal studies have found that spontaneous hyaline cartilage regeneration can be induced in vivo within a large osteochondral defect by implanting a synthetic double-network (DN) hydrogel, which is composed of poly-(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) and poly-(N,N'-dimethyl acrylamide) (PDMAAm), at the bottom of the defect. However, the effect of hydrogel on hyaline cartilage regeneration remains unexplained. The purpose of this study was to investigate the chondrogenic differentiation of C3H10T1/2 cells on PAMPS/PDMAAm DN gel.
Methods: C3H10T1/2 cells of 1.0 x 10(5) were cultured on PAMPS/PDMAAm DN gel in polystyrene tissue culture dishes or directly on polystyrene tissue culture dishes. We compared cultured cells on PAMPS/PDMAAm DN gel with those on polystyrene dishes by morphology using phase-contrast microscopy, mRNA expression of aggrecan, type I collagen, type II collagen, Sox 9 and osteocalcin using real-time RT-PCR, and local expression of type II collagen using immunocytochemistry.
Results: C3H10T1/2 cells cultured on the PAMPS/PDMAAm DN gels formed focal adhesions, aggregated rapidly and developed into large nodules within 7 days, while the cells cultured on the polystyrene surface did not. The mRNA levels of aggrecan, type I collagen, type II collagen, Sox 9 and osteocalcin were significantly greater in cells cultured on the PAMPS/PDMAAm DN gel than in those cultured on polystyrene dishes. In addition, C3H10T1/2 cells cultured on PAMPS/PDMAAm DN gel expressed more type II collagen at the protein level when compared with cells cultured on polystyrene dishes.
Conclusions: The present study showed that PAMPS/PDMAAm DN gel enhanced chondrogenesis of C3H10T1/2 cells, which are functionally similar to mesenchymal stem cells. This suggests that mesenchymal stem cells from the bone marrow contribute to spontaneous hyaline cartilage regeneration in vivo in large osteochondral defects after implantation of PAMPS/PDMAAm DN gels.

Crack Blunting and Advancing Behaviors of Tough and Self-healing Polyampholyte Hydrogel
Feng Luo, Tao Lin Sun, Tasuku Nakajima, Takayuki Kurokawa, Yu Zhao, Abu Bin Ihsan, Hong Lei Guo, Xu Feng Li, Jian Ping Gong
MACROMOLECULES, 47, 17, 6037, 6046, AMER CHEMICAL SOC, Sep. 2014, [Peer-reviewed]
English, Scientific journal, Recently, we have reported that polyampholytes, synthesized from free radical copolymerization of anionic monomer and cationic monomer, form physical hydrogels of high toughness and self-healing. The random distribution of the opposite charges forms ionic bonds of a wide distribution of strength. The strong bonds serve as permanent cross-links, imparting elasticity, whereas the weak bonds serves as reversible sacrificial bonds by breaking and reforming to dissipate energy. In this work, we focus on the rupture behaviors of the polyampholyte physical hydrogel, P(NaSS-co-MPTC), copolymerized from sodium p-styrenesulfonate (NaSS) and 3-(methacryloylamino)propyltrimethylammonium chloride (MPTC). Tensile test and pure shear test were performed at various stretch rates in the viscoelastic responses region of the material. Tensile test showed yielding, strain softening, and strain hardening, revealing the dually cross-linked feature of the gel. Pure shear test showed crack blunting at the notched tip and a large yielding zone with butterfly shaped birefringence pattern ahead of the crack tip. After blunting, crack advanced at steady-state velocity with a constant angle. The conditions for the occurrence of crack blunting and variables governing the crack advancing angle are discussed. We found that even for these highly stretchable samples, significant blunting only occurs when the tensile fracture stress sigma(f) is larger than modulus E by a factor of about 2, in consistent with Huis theoretical prediction for elastic materials. The crack advancing angle theta was found to be proportional to sigma(y)/E over a wide stretch rate range, where sigma(y) is the yielding stress. In addition, the fracture energy was correlated to small strain modulus by a power law in the viscoelastic response region. This systematic study will merit revealing the fracture mechanism of tough viscoelastic materials including biological tissues and recently developed tough and highly stretchable hydrogels.

Mechano-actuated ultrafast full-colour switching in layered photonic hydrogels
Youfeng Yue, Takayuki Kurokawa, Md Anamul Haque, Tasuku Nakajima, Takayuki Nonoyama, Xufeng Li, Itsuro Kajiwara, Jian Ping Gong
NATURE COMMUNICATIONS, 5, 4659, NATURE PUBLISHING GROUP, Aug. 2014, [Peer-reviewed]
English, Scientific journal, Photonic crystals with tunability in the visible region are of great interest for controlling light diffraction. Mechanochromic photonic materials are periodically structured soft materials designed with a photonic stop-band that can be tuned by mechanical forces to reflect specific colours. Soft photonic materials with broad colour tunability and fast colour switching are invaluable for application. Here we report a novel mechano-actuated, soft photonic hydrogel that has an ultrafast-response time, full-colour tunable range, high spatial resolution and can be actuated by a very small compressive stress. In addition, the material has excellent mechanical stability and the colour can be reversibly switched at high frequency more than 10,000 times without degradation. This material can be used in optical devices, such as full-colour display and sensors to visualize the time evolution of complicated stress/strain fields, for example, generated during the motion of biological cells.

Control superstructure of rigid polyelectrolytes in oppositely charged hydrogels via programmed internal stress
Riku Takahashi, Zi Liang Wu, Md Arifuzzaman, Takayuki Nonoyama, Tasuku Nakajima, Takayuki Kurokawa, Jian Ping Gong
NATURE COMMUNICATIONS, 5, 4490, NATURE PUBLISHING GROUP, Aug. 2014, [Peer-reviewed]
English, Scientific journal, Biomacromolecules usually form complex superstructures in natural biotissues, such as different alignments of collagen fibres in articular cartilages, for multifunctionalities. Inspired by nature, there are efforts towards developing multiscale ordered structures in hydrogels (recognized as one of the best candidates of soft biotissues). However, creating complex superstructures in gels are hardly realized because of the absence of effective approaches to control the localized molecular orientation. Here we introduce a method to create various superstructures of rigid polyanions in polycationic hydrogels. The control of localized orientation of rigid molecules, which are sensitive to the internal stress field of the gel, is achieved by tuning the swelling mismatch between masked and unmasked regions of the photolithographic patterned gel. Furthermore, we develop a double network structure to toughen the hydrogels with programmed superstructures, which deform reversibly under large strain. This work presents a promising pathway to develop superstructures in hydrogels and should shed light on designing biomimetic materials with intricate molecular alignments.

Hyaluronic acid enhances the effect of the PAMPS/PDMAAm double-network hydrogel on chondrogenic differentiation of ATDC5 cells
Nobuto Kitamura, Takayuki Kurokawa, Takaaki Fukui, Jian P. Gong, Kazunori Yasuda
BMC MUSCULOSKELETAL DISORDERS, 15, 222, BIOMED CENTRAL LTD, Jul. 2014, [Peer-reviewed]
English, Scientific journal, Background: A double-network (DN) gel, which was composed of poly-(2-Acrylamido-2-methylpropanesulfonic acid) and poly-(N,N'-dimethyl acrylamide) (PAMPS/PDMAAm), has the potential to induce chondrogenesis both in vitro and in vivo. The present study investigated whether DN gel induced chondrogenic differentiation of ATDC5 cells in a maintenance medium without insulin, and whether supplementation of hyaluronic acid enhanced the chondrogenic differentiation effect of DN gel.
Methods: ATDC5 cells were cultured on the DN gel and the polystyrene (PS) dish in maintenance media without insulin for 21 days. Hyaluronic acid having a molecular weight of approximately 800 kDa was supplemented into the medium so that the concentration became 0.01, 0.1, or 1.0 mg/mL. The cultured cells were evaluated using immunocytochemistry for type-2 collagen and real time PCR for gene expression of type-2 collagen, aggrecan, and Sox9 at 7 and 21 days of culture.
Results: The cells cultured on the DN gel formed nodules and were stained with an anti-type-2 collagen antibody, and expression of type-2 collagen and aggrecan mRNA was significantly greater on the DN gel than on the PS dish surface (p < 0.05) in the hyaluronic acid-free maintenance medium. Hyaluronic acid supplementation of a high concentration (1.0 mg/mL) significantly enhanced expression of type-2 collagen and aggrecan mRNA in comparison with culture without hyaluronic acid at 21 days (p < 0.05).
Conclusions: The DN gel induced chondrogenic differentiation of ATDC5 cells without insulin. This effect was significantly affected by hyaluronic acid, depending on the level of concentration. There is a high possibility that hyaluronic acid plays an important role in the in vivo hyaline cartilage regeneration phenomenon induced by the DN gel.

Fracture Process of Microgel-Reinforced Hydrogels under Uniaxial Tension
Jian Hu, Takayuki Kurokawa, Tasuku Nakajima, Zi Liang Wu, Song Miao Liang, Jian Ping Gong
MACROMOLECULES, 47, 11, 3587, 3594, AMER CHEMICAL SOC, Jun. 2014, [Peer-reviewed]
English, Scientific journal, We have found that lightly cross-linked neutral hydrogels containing microgels of densely cross-linked polyelectrolyte show high strength and toughness. These kinds of hydrogels, named as microgel-reinforced (MR) hydrogels, are a two-phase composite, where the disperse phase is the microgel with the double network (DN) structure and the continuous phase is the soft neutral gel matrix. The brittle polyelectrolyte network of the DN microgels, though in disperse phase, also serves as sacrificial bonds to toughen the material, similar to conventional DN gels. In this paper, we study the internal fracture process of the MR gel under uniaxial tension. The tensile stress-strain curve of the MR gel is charaterized by four regions according to its differential curve: elastic region (0 < epsilon < 1), preyielding region (1 < epsilon < 3), yielding region (3 < epsilon < 7), and strain hardening region (epsilon > 7). The morphology change of microgels in the reswollen MR gels after prestretching tells that the internal fracture of microgels, which occurs beyond the elastic region (epsilon > 1), is anisotropic. That is, the short chains in the tensile direction fracture first (1 < epsilon < 3); at large stretching, both the long chains in the tensile direction and the short chains in the transverse direction fracture (3 < epsilon < 7), followed by the fracture of the long chains in the transverse direction (epsilon > 7). These anisotropic fracture behaviors are in similar to bulk DN gels. Moreover, at each stage of the tensile process, large microgels always fracture prior to small ones and own higher fracture efficiency in the chain rupture than the smaller ones. This size effect is attributed to the stress concentration effect around the two poles of large microgels induced by the close distance from their neighboring microgels.

Sliding Friction of Zwitterionic Hydrogel and Its Electrostatic Origin
Jamil Ahmed, Honglei Guo, Tetsurou Yamamoto, Takayuki Kurokawa, Masakazu Takahata, Tasuku Nakajima, Jian Ping Gong
MACROMOLECULES, 47, 9, 3101, 3107, AMER CHEMICAL SOC, May 2014, [Peer-reviewed]
English, Scientific journal, Polyzwitterionic materials, which have both cationic and anionic groups in each repeating unit of polymer, show excellent antibiofouling properties. In this study, the surface friction of carboxybetaine type zwitterionic hydrogels, poly(N-(carboxymethyl)-N,N-dimethy1-2-(methacryloyloxy)-ethanaminium, inner salt) (PCDME), against glass substrates were investigated in aqueous solutions. The friction measurement was performed using a rheometer with parallel plate geometry and the sliding interface was monitored during the measurement. The frictional stress on glass was high in water and it showed weak dependence on pressure as long as the two sliding surfaces were in complete contact. The results performed in solutions with varied ionic strength revealed that the high friction on glass substrates has an electrostatic origin. The electrostatic potential measurement revealed that the PCDME gels have an isoelectric point at pH 8.5. Since the glass substrates carrying negative charges in pure water, the gel and the glass have electrostatic attraction in water. Study on the effect of pH has shown that below pH 8.5, attraction between the positively charged gels and negatively charged glass gives high friction, while above pH 8.5, the electrical double layer repulsion between two negatively charged surfaces gives low friction. From these results, it is concluded that although the PCDME gels behave like neutral gels in the bulk properties, their surface properties sensitively change with pH and ionic strength of the medium.

Materials both Tough and Soft
Jian Ping Gong
SCIENCE, 344, 6180, 161, 162, AMER ASSOC ADVANCEMENT SCIENCE, Apr. 2014, [Invited]
English, Scientific journal

Intra-articular administration of hyaluronic acid increases the volume of the hyaline cartilage regenerated in a large osteochondral defect by implantation of a double-network gel
Takaaki Fukui, Nobuto Kitamura, Takayuki Kurokawa, Masashi Yokota, Eiji Kondo, Jian Ping Gong, Kazunori Yasuda
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 25, 4, 1173, 1182, SPRINGER, Apr. 2014, [Peer-reviewed]
English, Scientific journal, Implantation of PAMPS/PDMAAm double-network (DN) gel can induce hyaline cartilage regeneration in the osteochondral defect. However, it is a problem that the volume of the regenerated cartilage tissue is gradually reduced at 12 weeks. This study investigated whether intra-articular administration of hyaluronic acid (HA) increases the volume of the cartilage regenerated with the DN gel at 12 weeks. A total of 48 rabbits were used in this study. A cylindrical osteochondral defect created in the bilateral femoral trochlea was treated with DN gel (Group DN) or left without any implantation (Group C). In both Groups, we injected 1.0 mL of HA in the left knee, and 1.0 mL of saline solution in the right knee. Quantitative histological evaluations were performed at 2, 4, and 12 weeks, and PCR analysis was performed at 2 and 4 weeks after surgery. In Group DN, the proteoglycan-rich area was significantly greater in the HA-injected knees than in the saline-injected knees at 12 weeks (P = 0.0247), and expression of type 2 collagen, aggrecan, and Sox9 mRNAs was significantly greater in the HA-injected knees than in the saline-injected knees at 2 weeks (P = 0.0475, P = 0.0257, P = 0.0222, respectively). The intra-articular administration of HA significantly enhanced these gene expression at 2 weeks and significantly increased the volume of the hyaline cartilage regenerated by implantation of a DN gel at 12 weeks. This information is important to develop an additional method to increase the volume of the hyaline cartilage tissue in a potential cartilage regeneration strategy using the DN gel.

一軸配向二分子膜によるハイドロゲルの高靱性化　　　　　　　　　　　　　　　
中島 祐, グン剣萍
超分子研究会アニュアルレビュー, 34, 14, 15, Mar. 2014, [Invited]
Japanese, Scientific journal

Polyelectrolyte hydrogels for replacement and regeneration of biological tissues
Hyuck Joon Kwon, Kazunori Yasuda, Jian Ping Gong, Yoshihiro Ohmiya
MACROMOLECULAR RESEARCH, 22, 3, 227, 235, POLYMER SOC KOREA, Mar. 2014, [Peer-reviewed], [Invited]
English, Scientific journal, Polyelectrolyte gels are charged polymer networks with macro-ions fixed on the polymer chains. These gels have considerable potential for biological applications such as cellular scaffolds and the replacement of various biological tissues. Moreover, high strength up to several tens of megapascals can be obtained with polyelectrolyte gels by incorporating double network structure in the gel. This article gives a concise review to introduce the fundamental properties of polyelectrolyte gels and biological applications for tissue engineering using their characteristic properties. Applications of polyelectrolyte gels have been highlighted in the fields of artificial muscle, artificial corneas, artificial cartilage, scaffolds for in vitro stem cell culture, and scaffolds for in vivo cartilage regeneration. This review suggests that polyelectrolyte gels would be a useful material for the successful replacement and regeneration of damaged or diseased tissues.

Prolonged morphometric study of barnacles grown on soft substrata of hydrogels and elastomers
Nafees Ahmed, Takayuki Murosaki, Takayuki Kurokawa, Akira Kakugo, Shintaro Yashima, Yasuyuki Nogata, Jian Ping Gong
BIOFOULING, 30, 3, 271, 279, TAYLOR & FRANCIS LTD, Mar. 2014, [Peer-reviewed]
English, Scientific journal, A long-term investigation of the shell shape and the basal morphology of barnacles grown on tough, double-network (DN) hydrogels and polydimethylsiloxane (PDMS) elastomer was conducted in a laboratory environment. The elastic modulus of these soft substrata varied between 0.01 and 0.47MPa. Polystyrene (PS) (elastic modulus, 3 GPa) was used as a hard substratum control. It was found that the shell shape and the basal plate morphology of barnacles were different on the rigid PS substratum compared to the soft substrata of PDMS and DN hydrogels. Barnacles on the PS substratum had a truncated cone shape with a flat basal plate while on soft PDMS and DN gels, barnacles had a pseudo-cylindrical shape and their basal plates showed curvature. In addition, a large adhesive layer was observed under barnacles on PDMS, but not on DN gels. The effect of substratum stiffness is discussed in terms of barnacle muscle contraction, whereby the relative stiffness of the substratum compared to that of the muscle is considered as the key parameter.

Brittle-ductile transition of double network hydrogels: Mechanical balance of two networks as the key factor
Saika Ahmed, Tasuku Nakajima, Takayuki Kurokawa, Md Anamul Haque, Jian Ping Gong
POLYMER, 55, 3, 914, 923, ELSEVIER SCI LTD, Feb. 2014, [Peer-reviewed]
English, Scientific journal, Tough double network (DN) hydrogels are a kind of interpenetrating network (IPN) gels with a contrasting structure; they consist of a rigid and brittle 1st network with dilute, densely cross-linked short chains and a soft and ductile 2nd network with concentrated, loosely cross-linked long chains. In this work, we focus on how the brittle gel changes into a tough one by increasing the amount of ductile component. By comparing the molecular structures of the individual first network and second network gels, we found that the true key mechanical factor that governs the brittle ductile transition is the fracture stress ratio of the two networks, sigma(f,2)/sigma(f,1). This ratio is related to the density ratio of elastically effective polymer strands of the two networks, nu(e,2)/nu(e,1), where the inter-network topological entanglement makes dominant contribution to nu(e,2). When nu(e,2)/nu(e,1) < k = 3.8-9.5, the second network fractures right after the fracture of the first network, and the gels are brittle. When nu(e,2)/nu(e,1) > k, only the first network fractures. As a result, the brittle first network serves as sacrificial bonds, imparting toughness of DN gels. The study also confirms that the load transfer between the two networks is via inter-network topological entanglement. This result provides essential information to design tough materials based on the double network concept. (C) 2014 Elsevier Ltd. All rights reserved.

In situ observation of a hydrogel-glass interface during sliding friction
Tetsurou Yamamoto, Takayuki Kurokawa, Jamil Ahmed, Gen Kamita, Shintaro Yashima, Yuichiro Furukawa, Yuko Ota, Hidemitsu Furukawa, Jian Ping Gong
SOFT MATTER, 10, 30, 5589, 5596, ROYAL SOC CHEMISTRY, 2014, [Peer-reviewed]
English, Scientific journal, Direct observation of hydrogel contact with a solid surface in water is indispensable for understanding the friction, lubrication, and adhesion of hydrogels under water. However, this is a difficult task since the refractive index of hydrogels is very close to that of water. In this paper, we present a novel method to in situ observe the macroscopic contact of hydrogels with a solid surface based on the principle of critical refraction. This method was applied to investigate the sliding friction of a polyacrylamide (PAAm) hydrogel with glass by using a strain-controlled parallel-plate rheometer. The study revealed that when the compressive pressure is not very high, the hydrogel forms a heterogeneous contact with the glass, and a macro-scale water drop is trapped at the soft interface. The pre-trapped water spreads over the interface to decrease the contact area with the increase in sliding velocity, which dramatically reduces the friction of the hydrogel. The study also revealed that this heterogeneous contact is the reason for the poor reproducibility of hydrogel friction that has been often observed in previous studies. Under the condition of homogeneous full contact, the molecular origin of hydrogel friction in water is discussed. This study highlights the importance of direct interfacial observation to reveal the friction mechanism of hydrogels.

Friction of hydrogels with controlled surface roughness on solid flat substrates
Shintaro Yashima, Natsuko Takase, Takayuki Kurokawa, Jian Ping Gong
SOFT MATTER, 10, 18, 3192, 3199, ROYAL SOC CHEMISTRY, 2014, [Peer-reviewed]
English, Scientific journal, This study investigated the effect of hydrogel surface roughness on its sliding friction against a solid substrate having modestly adhesive interaction with hydrogels under small normal pressure in water. The friction test was performed between bulk polyacrylamide hydrogels of varied surface roughness and a smooth glass substrate by using a strain-controlled rheometer with parallel-plates geometry. At small pressure (normal strain 1.4-3.6%), the flat surface gel showed a poor reproducibility in friction. In contrast, the gels with a surface roughness of 1-10 mm order showed well reproducible friction behaviors and their frictional stress was larger than that of the flat surface hydrogel. Furthermore, the flat gel showed an elasto-hydrodynamic transition while the rough gels showed a monotonous decrease of friction with velocity. The difference between the flat surface and the rough surface diminished with the increase of the normal pressure. These phenomena are associated with the different contact behaviors of these soft hydrogels in liquid, as revealed by the observation of the interface using a confocal laser microscope.

Proteoglycans and Glycosaminoglycans Improve Toughness of Biocompatible Double Network Hydrogels
Yu Zhao, Tasuku Nakajima, Jing Jing Yang, Takayuki Kurokawa, Jian Liu, Jishun Lu, Shuji Mizumoto, Kazuyuki Sugahara, Nobuto Kitamura, Kazunori Yasuda, A. U. D. Daniels, Jian Ping Gong
ADVANCED MATERIALS, 26, 3, 436, 442, WILEY-V C H VERLAG GMBH, Jan. 2014, [Peer-reviewed]
English, Scientific journal

Hydrogel friction and lubrication
Jian Liu, Jian Ping Gong
Aqueous Lubrication: Natural and Biomimetic Approaches, 145, 181, World Scientific Publishing Co., 01 Jan. 2014
English, In book, Sliding friction is one of the oldest problems in physics and certainly one of the most important subjects from a practical point of view. Many different terms and approaches have been used to describe friction. For friction in the presence of lubricating oil, the behavior is usually divided into three regimes. In the boundary lubrication (BL) regime, which occurs at low sliding velocity when there is negligible fluid entrainment into the contact zone, the load is carried by the contacting asperities and friction is dependent on the surface and interfacial film properties at the molecular scale. In the hydrodynamic lubrication regime, a film of lubricant, whose thickness depends on the viscosity and entrainment velocity, is entrained to fully separate the solid surfaces. The friction now depends on the rheological properties of the lubricant film in the contact zone, under the high-shearrate condition that prevails there. Sophisticated solutions of the Reynolds equation have evolved to explain friction on the basis of the continuum flow of liquids. The fundamental view here is that liquids resist deformation against force that increases with velocity. The dependence of force on velocity is linear for the simplest case (said to be “Newtonian”). Even modern treatments consider that when velocity is increased, the force required to accomplish deformation increases with a positive slope. The mixed regime is termed as a friction transition regime here, which lies between boundary lubrication and hydrodynamic lubrication. In this regime both the boundary film and bulk lubricant play crucial roles in determining friction.

Geometric and edge effects on swelling-induced ordered structure formation in polyelectrolyte hydrogels
Md. Arifuzzaman, Zi Liang Wu, Riku Takahashi, Takayuki Kurokawa, Tasuku Nakajima, Jian Ping Gong
Macromolecules, 46, 22, 9083, 9090, 26 Nov. 2013, [Peer-reviewed]
English, Scientific journal, In this paper, we developed several kinds of ordered structures in hydrogels with different geometries and sizes by harnessing heterogeneous swelling induced mechanical instability, i.e., surface creasing, which leads to molecular orientations along the tensile direction. These hydrogels were synthesized by polymerization of a cationic monomer, N-[3-(N,N-dimethylamino) propyl] acrylamide methyl chloride quaternary (DMAPAA-Q) and a chemical cross-linker, in the presence of a small amount of the semirigid polyanion, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT), as dopant. During the swelling process of as-prepared gels, surface creasing occurs and induces formation of a lattice-like periodic ordered structure, which is maintained in the swollen gels due to the formation of strong polyion complex. Besides this structure formed at the central part of gel sheets, PBDTs align parallel to the gel boundary at the edge of gels with a cuboid, disk, or ring shape. The size of the two regions with different structures and the size of each unit of lattice-like pattern are related to the geometry and size of the gels. The formation of different ordered structures was found due to the different mechanical instabilities at different parts of the gel during the heterogeneous swelling. This work presenting the creation of ordered structures in hydrogels by tuning the mechanical instability will pave the way to develop other functional structured materials and merit revealing the formation mechanism of ordered structures in soft biotissues during the nonequilibrium growth. © 2013 American Chemical Society.

Fracture energy of polymer gels with controlled network structures
Yuki Akagi, Hayato Sakurai, Jian Ping Gong, Ung-il Chung, Takamasa Sakai
JOURNAL OF CHEMICAL PHYSICS, 139, 14, 144905-1, 144905-6, AMER INST PHYSICS, Oct. 2013, [Peer-reviewed]
English, Scientific journal, We have investigated the fracture behaviors of tetra-arm polyethylene glycol (Tetra-PEG) gels with controlled network structures. Tetra-PEG gels were prepared by AB-type crosslink-coupling of mutually reactive tetra-arm prepolymers with different concentrations and molecular weights. This series of controlled network structures, for the first time, enabled us to quantitatively examine the Lake-Thomas model, which is the most popular model predicting fracture energies of elastomers. The experimental data showed good agreement with the Lake-Thomas model, and indicated a new molecular interpretation for the displacement length (L), the area around a crack tip within which the network strands are fully stretched. L corresponded to the three times of end-to-end distance of network strands, regardless of all parameters examined. We conclude that the Lake-Thomas model can quantitatively predict the fracture energy of polymer network without trapped entanglements, with the enhancement factor being near 3. (C) 2013 AIP Publishing LLC.

Physical hydrogels composed of polyampholytes demonstrate high toughness and viscoelasticity
Tao Lin Sun, Takayuki Kurokawa, Shinya Kuroda, Abu Bin Ihsan, Taigo Akasaki, Koshiro Sato, Md Anamul Haque, Tasuku Nakajima, Jian Ping Gong
NATURE MATERIALS, 12, 10, 932, 937, NATURE PUBLISHING GROUP, Oct. 2013, [Peer-reviewed]
English, Scientific journal, Hydrogels attract great attention as biomaterials as a result of their soft and wet nature, similar to that of biological tissues. Recent inventions of several tough hydrogels show their potential as structural biomaterials, such as cartilage. Any given application, however, requires a combination of mechanical properties including stiffness, strength, toughness, damping, fatigue resistance and self-healing, along with biocompatibility. This combination is rarely realized. Here, we report that polyampholytes, polymers bearing randomly dispersed cationic and anionic repeat groups, form tough and viscoelastic hydrogels with multiple mechanical properties. The randomness makes ionic bonds of a wide distribution of strength. The strong bonds serve as permanent crosslinks, imparting elasticity, whereas the weak bonds reversibly break and re-form, dissipating energy. These physical hydrogels of supramolecular structure can be tuned to change multiple mechanical properties over wide ranges by using diverse ionic combinations. This polyampholyte approach is synthetically simple and dramatically increases the choice of tough hydrogels for applications.

Hydrogel with Unidirectional Alignment of Lamellar Bilayers: Its Structural Color and Mechanical Response
Koshiro Sato, Md. Anamul Haque, Gen Kamita, You Feng Yue, Takayuki Kurokawa, Jian Ping Gong
Journal of the Japan Society of Colour Material, 86, 8, 290, 294, Japan Society of Colour Material, Aug. 2013, [Peer-reviewed], [Invited]
Japanese, Scientific journal, A lot of animals and plants have structural color consisted of ordered structure. Recently attempts to introduce this ordered structure into polymer are attracting extensive attention in the field of sensor. We pay attention to dodecylglyceryl itaconate (DGI) that can form periodically ordered bilayer structure in water. This review describes synthesis, anisotropic structure and mechanical properties, and stress/straininduced change in structural color of a photonic hydrogel with ordered structure consisting of DGI and acrylamide.

DNゲルによるATDC5細胞の軟骨分化誘導に関する力学的機序の解明 1細胞の力学的特性の変化とアクチン修飾タンパク質発現との関連
前田 英次郎, 堤 健博, 黒川 孝幸, 北村 信人, Gong Jian Ping, 安田 和則, 大橋 俊朗
日本整形外科学会雑誌, 87, 8, S1408, S1408, (公社)日本整形外科学会, Aug. 2013
Japanese

Tuning Mechanical Properties of Chondroitin Sulfate-Based Double-Network Hydrogels
Tiffany C. Suekama, Jian Hu, Takayuki Kurokawa, Jian Ping Gong, Stevin H. Gehrke
MACROMOLECULAR SYMPOSIA, 329, 1, 9, 18, WILEY-V C H VERLAG GMBH, Jul. 2013, [Peer-reviewed], [Invited]
English, International conference proceedings, High strength double-network (DN) biopolymer-based hydrogels were created using copolymers of methacrylated chondroitin sulfate (MCS) and poly (ethylene glycol) diacrylate (PEGDA) as the first network and polyacrylamide (PAAm) as the second network. The concentration and cross-linking of the networks were adjusted to control the mechanical properties including the failure stress, failure strain, Young's modulus, and yielding behavior. First, we increased the cross-linking of the first network both by increasing the MCS concentration from 13 to 20 wt% and by copolymerizing MCS with 2 to 6 wt% PEGDA. The additional cross-linking increased the Young's modulus as much as five times, reaching 3.3 MPa, and the failure stress up as much as four times, reaching 2.9 MPa. However, this also reduced failure strain from a high of 2.9 mm/mm to a low of 0.12 mm/mm and diminished the yielding region. Changes in the concentrations of acrylamide or its cross-linking with N,N'-methylenebisacrylamide (BIS) in the second network had a lesser effect on the DN properties. We hypothesized that to obtain a yielding region which results in high toughness, we need to alter the cross-linking of the first network such that the yield stress of the MCS-PEGDA/PAAm DN does not exceed the failure stress of PAAm network. Because of the wide range of mechanical properties achieved in these DNs with limited changes in the swelling degrees, unlike conventional single-network gels, the DN approach allows attainment of a much greater range of mechanical behavior than is possible with single networks.

Optical and mechanical properties of a hydrogel based on lamellar bilayers
Takayuki Kurokawa, Md. Anamul Haque, Jian Ping Gong
Kobunshi Ronbunshu, 70, 7, 309, 316, Jul. 2013, [Peer-reviewed], [Invited]
Japanese, Scientific journal, In this highlight, we introduce a novel anisotropic hydrogel with a perfect ID photonic crystal structure based on the uni-axial alignment of lamellar bilayers. The polymerized lamellar bilayers were stacked periodically and entrapped in a Polyacrylamide matrix. This hydrogel shows perfect one-dimensional swelling and magnificent structural color by multilayer interference according to Bragg's law of diffraction. Owing to the softness and large deformability, the color of the gel can reversibly be tuned by compressive mechanical stimulation over the entire visible wavelength range. The single-domain lamellar bilayers not only diffract light, but also serve as reversible sacrificial 'bonds' that dissociate upon deformation, exhibiting large hysteresis as an energy dissipation mechanism. This gives the gel high tensile strength and fatigue resistance. Both the molecular dissociation and lipid-like mobile nature of DGI molecules in the bilayers dramatically enhance the resistance against crack propagation by showing an extra-ordinary blunting effect, which gives the gel very high toughness. ©2013, The Society of Polymer Science,.

Multi-functions of hydrogel with bilayer-based lamellar structure
Md. Anamul Haque, Jian Ping Gong
REACTIVE & FUNCTIONAL POLYMERS, 73, 7, 929, 935, ELSEVIER SCIENCE BV, Jul. 2013, [Peer-reviewed], [Invited]
English, Scientific journal, A novel hybrid hydrogel has been developed by combining bilayer-based lamellar structure of a self-assembled polymer surfactant and polymer network of conventional hydrogel system. A wide range of lamellar structure from micro-domain up to macro-domain (cm-scale) has been successfully generated in the hydrogel. Flat, infinitely large, and perfectly aligned lamellar macro-domain was formed by applying mechanical shear to the gel forming precursor solution containing monomer, cross-linker, and initiator. The obtained hydrogel system contains macroscopic, single-domain, periodical stacking of integrated microscopic lamellar bilayers inside the polymer matrix of the hydrogel. Periodical stacking of the bilayers in the hydrogel selectively diffract visible light to exhibit magnificent structural color. Due to the uniaxial orientation of the bilayer, the hydrogel possesses superb functions that have never been realized before, such as the one-dimensional swelling, anisotropic Young's modulus, anisotropic molecular permeation, and diffusion. Furthermore, the hydrogel exhibits excellent color tuning ability over a wide spectrum range by mechanical stimuli. (c) 2013 Elsevier Ltd. All rights reserved.

Lamellar hydrogels with high toughness and ternary tunable photonic stop-band
You Feng Yue, M. Anamul Haque, Takayuki Kurokawa, Tasuku Nakajima, Jian Ping Gong
Advanced Materials, 25, 22, 3106, 3110, 11 Jun. 2013, [Peer-reviewed]
English, Scientific journal, A lamellar hydrogel with high toughness, exhibiting ternary stimuli-responsive structural color changes has been synthesized. The gel consists of alternating hard layers of a polymeric surfactant (PDGI) and soft layers of interpenetrating networks of poly(acrylamide)-poly(acrylic acid). Reversible, wide range switching of the stop-band position was achieved using different external stimuli of temperature, pH, and stress/strain. Copyright © 2013 WILEY-VCH Verlag GmbH &
Co. KGaA, Weinheim.

Synthesis and Fracture Process Analysis of Double Network Hydrogels with a Well-Defined First Network
Tasuku Nakajima, Yuki Fukuda, Takayuld Kurokawa, Takamasa Sakai, Ung-il Chung, Jian Ping Gong
ACS MACRO LETTERS, 2, 6, 518, 521, AMER CHEMICAL SOC, Jun. 2013, [Peer-reviewed]
English, Scientific journal, To investigate the effect of inhomogeneity in the first network on the enormously high toughness of double network (DN) gels, we fabricated DN gels with a nearly homogeneous first network structure (named St-TPEG/PAAm DN gels) based on tetra-PEG (TPEG) gels via a molecular stent method. The St-TPEG/PAAm DN gels also show excellent mechanical properties and yielding-like phenomena comparable to conventional DN gels. This result demonstrates that the inhomogeneity within the first network is not essential for the specific toughening mechanism of DN gels. On the other hand, the St-TPEG/PAAm DN gels and conventional DN gels undergo substantially different fracture processes before the yielding point. This suggests the importance of a "homogenization process" for the yielding of DN gels. Since the St-TPEG/PAAm DN gels consist of a well-defined first network, they may serve as model DN gels in the future for further studies on fracture processes of DN gels.

Supramolecular Assemblies of a Semirigid Polyanion in Aqueous Solutions
Zi Liang Wu, Md. Arifuzzaman, Takayuki Kurokawa, Khoa Le, Jian Hu, Tao Lin Sun, Hidemitsu Furukawa, Hiroyasu Masunaga, Jian Ping Gong
MACROMOLECULES, 46, 9, 3581, 3586, AMER CHEMICAL SOC, May 2013, [Peer-reviewed]
English, Scientific journal, In this article, we report the supramolecular assemblies of a semirigid polyelectrolyte, poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT) in water. Cryo-TEM observation and SAXS measurement reveal that PBDT forms bundle-like structure even in very dilute concentration, C-p, of 0.02 wt %. These bundle-like assemblies serve as new primary building blocks and self-assemble further as C-p increases, to form large associations with or without long-range orientation. When 2 wt % < C-p < 6 wt %, liquid liquid phase separation occurs. Some of the supramolecular associations form bipolar liquid crystalline (LC) droplets via a typical nucleation and growth process. The droplets grow up by the coalescence of small ones and sediment under the gravity and coalesce to form a bottom nematic phase. When C-p 6 wt %, the solutions are in a uniform nematic phase. The existence of these preliminary supramolecular assemblies of PBDT in aqueous solutions should be crucial for the formation of nematic LC phase at a significantly low C-p, as well as the formation of macroscopic ordered structures in hydrogels via electrostatic interaction between PBDT and oppositely charge multivalent metallic ion or polycation.

Double-network acrylamide hydrogel compositions adapted to achieve cartilage-like dynamic stiffness
S. Ronken, D. Wirz, A. U. Daniels, T. Kurokawa, J. P. Gong, M. P. Arnold
BIOMECHANICS AND MODELING IN MECHANOBIOLOGY, 12, 2, 243, 248, SPRINGER HEIDELBERG, Apr. 2013, [Peer-reviewed]
English, Scientific journal, Since articular cartilage has a limited potential for spontaneous healing, various techniques are employed to repair cartilage lesions. Acrylate-based double-network (DN) hydrogels containing similar to 90% water have shown promising properties as repair materials for skeletal system soft tissues. Although their mechanical properties approach those of native cartilage, the critical factor-stiffness-of DN-gels does not equal the stiffness of articular cartilage. This study investigated whether revised PAMPS/PAAm compositions with lower water content result in stiffness parameters closer to cartilage. DN-gels containing 61, 86 and 90% water were evaluated using two non-destructive, mm-scale indentation test modes: fast-impact (FI) and slow-sinusoidal (SS) deformation. Deformation resistance (dynamic modulus) and energy handling (loss angle) were determined. The dynamic modulus increased with decreasing water content in both testing modes. In the 61% water DN-gel, the modulus resembled that of cartilage (FI-mode: DN-gel = 12, cartilage = 17; SS-mode: DN-gel = 4, cartilage = 1.7 MPa). Loss angle increased with decreasing water content in fast-impact, but not in slow-sinusoidal deformation. However, loss angle was still much lower than cartilage (FI: DN-gel = 5, cartilage = 11; SS: DN-gel = 10, cartilage = 32A degrees), indicating somewhat less ability to dissipate energy. Overall, results show that it is possible to adapt DN-gel composition to produce dynamic stiffness properties close to normal articular cartilage.

Relaxation modes in chemically cross-linked poly(2-methacryloyloxyethyl phosphorylcholine) hydrogels
Tatsuro Goda, Hidemitsu Furukawa, Jian Ping Gong, Kazuhiko Ishihara
Soft Matter, 9, 7, 2166, 2171, Royal Society of Chemistry, 21 Feb. 2013, [Peer-reviewed]
English, Scientific journal, We investigated the relaxation modes of autocorrelation functions obtained by dynamic light scattering (DLS) of chemically cross-linked zwitterionic hydrogels comprising poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) as the main chain of the network. A time- and space-averaged (i.e., an ensemble-averaged) autocorrelation function was obtained using a home-built DLS apparatus enabling automated positioning of a sample. The equilibrated hydrogels exhibited fast and slow relaxations
the former was derived from thermodynamic fluctuations of the polymer network whose cross-link distances were modeled by the Stokes-Einstein equation, whereas the latter depended on cross-linking densities, cross-linker type, and external electrolytes in the hydrogels, suggesting a mesoscopic weak segment-segment interaction driven by electrostatic forces or by the salting-out effect. These observations may aid in the regulation of network integrity and hydration state of the polymer in PMPC hydrogels. © 2013 The Royal Society of Chemistry.

海の生き物に学ぶ低環境負荷型抗付着材料の創製 : フジツボに対するハイドロゲルの抗付着効果
黒川 孝幸, 龔 剣萍, 室﨑 喬之, 野方 靖行
PEN, 3, 11, 3, 8, 産業技術総合研究所, Feb. 2013, [Invited]
Japanese, Scientific journal, 海辺を散歩するとフジツボ類や貝類、藻類等の岩場にへばりついて生きている生物をよく見ることができる。これら海洋付着生物は海洋資源として有用な反面、汚損生物として負の側面も持ち合わせている。例を挙げると、船底に付着する事で水の抵抗が増し船の燃費を増大させる、養殖漁網の網の目を詰まらせる事で養殖魚を窒息死させる、取水口を詰まらせる事で臨海発電所の冷却機能を低下させる等があり、海洋付着生物は世界中のあらゆる海に関わる産業に大きな経済的損失を与えている

Hyaluronic acid affects the in vitro induction effects of Synthetic PAMPS and PDMAAm hydrogels on chondrogenic differentiation of ATDC5 cells, depending on the level of concentration
Katsuhisa Yoshikawa, Nobuto Kitamura, Takayuki Kurokawa, Jian Ping Gong, Yutaka Nohara, Kazunori Yasuda
BMC MUSCULOSKELETAL DISORDERS, 14, 56, BIOMED CENTRAL LTD, Feb. 2013, [Peer-reviewed]
English, Scientific journal, Background: It has been a common belief that articular cartilage tissue cannot regenerate in vivo. Recently, however, we have found that spontaneous hyaline cartilage regeneration can be induced in vivo by implanting a synthetic double-network (DN) hydrogel, which is composed of poly-(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) and poly-(N,N'-dimethyl acrylamide) (PDMAAm). However, the mechanism of this phenomenon has not been clarified. Recently, we have found that single-network PAMPS and PDMAAm gels can induce chondrogenic differentiation of ATDC5 cells in vitro even in a maintenance medium. In the in vivo condition, there is a strong possibility that the induction effect of the gel itself is enhanced by some molecules which exist in the joint. We have noticed that the joint fluid naturally contains hyaluronic acid (HA). The purpose of this study is to clarify in vitro effects of supplementation of HA on the differentiation effect of the PAMPS and PDMAAm gels.
Methods: We cultured the ATDC5 cells on the PAMPS gel, the PDMAAm gel, and the polystyrene (PS) dish surface with the maintenance medium without insulin for 7 days. HA having a molecular weight of approximately 800 kDa was supplemented into the medium so that the concentration became 0.00, 0.01, 0.10, or 1.00 mg/mL. We evaluated the cultured cells with phase-contrast microscopy and PCR analyses.
Results: On the PAMPS gel, supplementation with HA of 0.01 and 0.10 mg/mL significantly increased expression of type-2 collagen mRNA (p = 0.0008 and p = 0.0413) and aggrecan mRNA (p = 0.0073 and p = 0.0196) than that without HA. On the PDMAAm gel, supplementation with HA of 1.00 mg/mL significantly reduced expression of these genes in comparison with the culture without HA (p = 0.0426 and p = 0.0218).
Conclusions: The in vitro induction effects of the PAMPS and PDMAAm gels on chondrogenic differentiation of ATDC5 cells are significantly affected by HA, depending on the level of concentration. These results suggested that there is a high possibility that HA plays an important role in the in vivo spontaneous hyaline cartilage regeneration phenomenon induced by the PAMPS/PDMAAm DN gel.

Double-Network Strategy Improves Fracture Properties of Chondroitin Sulfate Networks
Tiffany C. Suekama, Jian Hu, Takayuki Kurokawa, Jian Ping Gong, Stevin H. Gehrke
ACS MACRO LETTERS, 2, 2, 137, 140, AMER CHEMICAL SOC, Feb. 2013, [Peer-reviewed]
English, Scientific journal, A tough and ductile, ultrathin film, double-network (DN), biopolymer-based hydrogel displaying the yielding phenomenon was synthesized from methacrylated chondroitin sulfate (MCS) and polyacrylamide (PAAm). The DN of MCS/PAAm exhibited a failure stress more than 20 times greater than the single network (SN) of either MCS or PAAm and exhibited yielding stresses over 1500 kPa. In addition, the stress-strain behavior with a yielding region was also seen in a hydrogel of MCS and poly(N,N-dimethyl acrylamide) (PDMAAm). By replacing PAAm with PDMAAm, interactions known to toughen networks are removed. This demonstration supports the idea that the brittle/ductile combination is key to the DN effect over specific interactions between the networks. The MCS/PAAm and MCS/PDMAAm DN hydrogels had comparable mechanical properties to the archtypal DN hydrogels of poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS)/PAAm. In addition, these tough and ductile, biopolymer-based, double-network hydrogels demonstrated a substantial yielding region.

Transition between Phantom and Affine Network Model Observed in Polymer Gels with Controlled Network Structure
Yuki Akagi, Jian Ping Gong, Ung-il Chung, Takamasa Sakai
MACROMOLECULES, 46, 3, 1035, 1040, AMER CHEMICAL SOC, Feb. 2013, [Peer-reviewed]
English, Scientific journal, The elastic moduli of elastomeric materials are predicted by the affine or phantom or junction affine network models. Although these models are often used, we do not know the requirement conditions for each model or even the validity of each model. The validation of these models is difficult because of the network heterogeneity. In this study, we tried to evaluate these models using Tetra-PEG gel, which has extremely homogeneous network structure. We performed the stretching and tearing tests, and for the first time, observed the transition between the phantom and affine network models around the overlapping concentration of prepolymers.

A phase diagram of neutral polyampholyte - from solution to tough hydrogel
Abu Bin Ihsan, Tao Lin Sun, Shinya Kuroda, Md. Anamul Haque, Takayuki Kurokawa, Tasuku Nakajima, Jian Ping Gong
JOURNAL OF MATERIALS CHEMISTRY B, 1, 36, 4555, 4562, ROYAL SOC CHEMISTRY, 2013, [Peer-reviewed]
English, Scientific journal, Our recent study has revealed that neutral polyampholytes form tough physical hydrogels above a critical concentration C-m,C-c by forming ionic bonds of wide strength distribution. In this work, we systematically investigate the behavior of a polyampholyte system, poly(NaSS-co-DMAEA-Q), randomly copolymerized from oppositely charged monomers, sodium p-styrenesulfonate (NaSS) and acryloyloxethyltrimethylammonium chloride (DMAEA-Q) without and with a slight chemical cross-linking. A phase diagram of formulation has been constructed in the space of monomer concentration C-m and cross-linker density C-MBAA. Three phases are observed for the as-synthesized samples: homogeneous solution at dilute C-m, phase separation at semi-dilute C-m, and homogenous gel at concentrated C-m. Above a critical C-m,C-c, the polyampholyte forms a supramolecular hydrogel with high toughness by dialysis of the mobile counter-ions, which substantially stabilizes both the intra-and inter chain ionic bonds. The presence of the chemical cross-linker (C-MBAA > 0) brings about a shift of the tough gel phase to lower C-m,C-c. The tough polyampholyte gel, containing similar to 50 wt % water, is highly stretchable and tough, exhibits fracture stress of sigma(b) similar to 0.4 MPa, fracture strain of epsilon(b) similar to 30, and the work of extension at fracture W-ext similar to 4 MJ m(-3). These values are at the level of most tough soft materials. Owing to the reversible ion bonds, the poly(NaSS-co-DMAEA-Q) gels also exhibit complete self-recovery (100%) and high fatigue resistance upon repeated large deformation.

Barnacle Settlement Behavior on Natural Polymer Gels
Takayuki Murosaki, Takaya Noguchi, Yasuyuki Nogata, Jian Ping Gong
KOBUNSHI RONBUNSHU, 70, 7, 326, 330, SOC POLYMER SCIENCE JAPAN, 2013, [Peer-reviewed], [Invited]
Japanese, Scientific journal, In this study, we investigate the settlement behavior of barnacle cyprid larvae on several kinds of natural polymer gels. 24 well plates were used for all of the settlement tests. The results show that several natural polymer gels have antifouling activities against barnacle settlement In particular, agarose gels show high antifouling performance. The antifouling activities of a K-carrageenan gel is relatively low compared with other natural polymer gels, however it shows high release activity against settled barnacles. Furthermore, the results from the settlement test of agarose coated wells indicate that antifouling properties of hydrogels consist of inhibition, anti-adhesion, and easy release effects.

Double network hydrogels from polyzwitterions: high mechanical strength and excellent anti-biofouling properties
Haiyan Yin, Taigo Akasaki, Tao Lin Sun, Tasuku Nakajima, Takayuki Kurokawa, Takayuki Nonoyama, Toshio Taira, Yoshiyuki Saruwatari, Jian Ping Gong
JOURNAL OF MATERIALS CHEMISTRY B, 1, 30, 3685, 3693, ROYAL SOC CHEMISTRY, 2013, [Peer-reviewed]
English, Scientific journal, Polyzwitterionic materials, which have both cationic and anionic groups in the polymeric repeat unit, show excellent anti-biofouling properties and are drawing more attention in the biomedical field. In this study, we have successfully synthesized novel single network hydrogels and double network (DN) hydrogels from the zwitterionic monomer, N-(carboxymethyl)-N,N-dimethyl-2-(methacryloyloxy) ethanaminium, inner salt (CDME). The polyCDME (PCDME) single network hydrogel behaves like a hydrophilic neutral hydrogel and its properties are not sensitive to temperature, pH, or ionic strength over a wide range. DN hydrogels using the poly(2-acrylamido-2-methylpropanesulfonic) (PAMPS) as the first network and PCDME as the second network, having a Young's modulus of 0.2-0.9 MPa, possess excellent mechanical strength (fracture stress: 1.2-1.4 MPa, fracture strain: 2.2-6.0 mm/mm) and toughness (work of extension at fracture: 0.9-2.4 MJ m(-3)) depending on the composition ratio of PCDME to PAMPS. The strength and toughness of the optimized PAMPS/PCDME DN is comparable to the normal PAMPS/PAAm DN hydrogels that use poly(acrylamide) (PAAm) as the second network. By macrophage adhesion test, both the PCDME hydrogels and the PAMPS/PCDME DN hydrogels have shown excellent anti-biofouling properties. These results demonstrate that the PCDME-based DN hydrogels have high potential as a novel soft and wet biomaterial.

Growth of ring-shaped microtubule assemblies through stepwise active self-organisation
Daisuke Inoue, Arif Md Rashedul Kabir, Hiroyuki Mayama, Jian Ping Gong, Kazuki Sada, Akira Kakugo
SOFT MATTER, 9, 29, 7061, 7068, ROYAL SOC CHEMISTRY, 2013, [Peer-reviewed]
English, Scientific journal, The microtubule (MT)-kinesin system is a promising candidate for constructing artificial biomachines. The active self-organisation (AcSO) method has been developed to integrate MT filaments into highly organised assembled structures. The creation of ring-shaped MT assemblies is one of the outcomes of the organisation process and holds prospects for use in future nano-technological applications. However, making use of ring-shaped MT assemblies in practical applications requires further control of the size of these assemblies, which has not yet been addressed. In this work, we demonstrated AcSO of MTs in a stepwise manner inside an inert atmosphere. We show that in an inert atmosphere, AcSO could be performed several times (at least nine times), and as a result, this method successfully increased the thickness of ring-shaped MT assemblies.

Lamellar-micelle transition in a hydrogel induced by polyethylene glycol grafting
Md Anamul Haque, Takayuki Kurokawa, Jian Ping Gong
SOFT MATTER, 9, 21, 5223, 5230, ROYAL SOC CHEMISTRY, 2013, [Peer-reviewed]
English, Scientific journal, We demonstrate, for the first time, a distinct change of the bulk properties of a hydrogel based on the lamellar-micelle transition. The hydrogel consists of thousands of periodical stacks of bilayer membranes, poly(dodecyl glyceryl itaconate) (PDGI), inside a dilute polyacrylamide network. Along with a bright structure color, the hydrogel exhibits a strong anisotropy in its bulk properties. By grafting a short chain polymer lipid, poly(ethylene glycol) dodecyl ether (C12EO23), to the bilayer membrane, sharp changes in the structure color, swelling and modulus of the hydrogel are observed in a narrow C12EO23 concentration range. These changes are ascribed to the structure transition of the single domain lamellar phase to the multi-domain micelle phase of PDGI, induced by the excluded volume effect of two dimensionally grafted poly(ethylene glycols) (PEG). By controlling the water permeable nano-channels formed during the structure transition, a specific molecular diffusion and recognition are demonstrated. This lamellar bilayer hydrogel could be a new insight into the lipid bilayer system to investigate the nature of biological membranes by the bulk behaviors of hydrogels.

Influence of the gel thickness on in vivo hyaline cartilage regeneration induced by double-network gel implanted at the bottom of a large osteochondral defect: Short-term results
Hidetoshi Matsuda, Nobuto Kitamura, Takayuki Kurokawa, Kazunobu Arakaki, Jian Ping Gong, Fuminori Kanaya, Kazunori Yasuda
BMC MUSCULOSKELETAL DISORDERS, 14, 50, BIOMED CENTRAL LTD, Jan. 2013, [Peer-reviewed]
English, Scientific journal, Background: A double-network (DN) gel, which is composed of poly(2-acrylamido-2-methylpropanesulfonic acid) and poly(N,N'-dimethyl acrylamide), can induce hyaline cartilage regeneration in vivo in a large osteochondral defect. The purpose of this study was to clarify the influence of the thickness of the implanted DN gel on the induction ability of hyaline cartilage regeneration.
Methods: Thirty-eight mature rabbits were used in this study. We created an osteochondral defect having a diameter of 4.3-mm in the patellofemoral joint. The knees were randomly divided into 4 groups (Group I: 0.5-mm thick gel, Group II: 1.0-mm thick gel, Group III: 5.0-mm thick gel, and Group IV: untreated control). Animals in each group were further divided into 3 sub-groups depending on the gel implant position (2.0-, 3.0-, or 4.0-mm depth from the articular surface) in the defect. The regenerated tissues were evaluated with the Wayne's gross and histological grading scales and real time PCR analysis of the cartilage marker genes at 4 weeks.
Results: According to the total Wayne's score, when the depth of the final vacant space was set at 2.0 mm, the scores in Groups I, II, and III were significantly greater than that Group IV (p < 0.05), although there were no significant differences between Groups I and IV at a 3.0-mm deep vacant space. The expression levels of type-2 collagen in Groups II and III were significantly higher (p < 0.05) than that in Group IV.
Conclusions: The 1.0-mm thick DN gel sheet had the same ability to induce hyaline cartilage regeneration as the 5.0-mm thick DN gel plug. However, the induction ability of the 0.5-mm thick sheet was significantly lower when compared with the 1.0-mm thick gel sheet. The 1.0-mm DN gel sheet is a promising device to establish a cell-free cartilage regeneration strategy that minimizes bone loss from the gel implantation.

Relaxation Modes in Chemically Cross-linked Poly(2-methacryloyloxyethyl phosphorylcholine) Hydrogel
Tatsuro Goda, Hidemitsu Furukawa, Jian Ping Gong, Kazuhiko Ishihara
Soft Matter, 9, 7, 2166, 2171, Jan. 2013, [Peer-reviewed]
English, Scientific journal

Characterization of internal fracture process of double network hydrogels under uniaxial elongation
Tasuku Nakajima, Takayuki Kurokawa, Saika Ahmed, Wen-li Wu, Jian Ping Gong
SOFT MATTER, 9, 6, 1955, 1966, ROYAL SOC CHEMISTRY, 2013, [Peer-reviewed]
English, Scientific journal, Previously we revealed that the high toughness of double network hydrogels (DN gels) derives from the internal fracture of the brittle network during deformation, which dissipates energy as sacrificial bonds. In this study, we intend to elucidate the detailed internal fracture process of DN gels. We quantitatively analysed the tensile hysteresis and re-swelling behaviour of a DN gel that shows a well-defined necking and strain hardening, and obtained the following new findings: (1) fracture of the 1st network PAMPS starts far below the yielding strain, and 90% of the initially load-bearing PAMPS chains already break at the necking point. (2) The dominant internal fracture process occurs in the necking and hardening region, although the softening mainly occurs before necking. (3) The internal fracture efficiency is very high, 85% of the work is used for the internal fracture and 9% of all PAMPS chains break at sample failure. (4) The internal fracture is anisotropic, fracture occurs perpendicular to the tensile direction, in preference to the other two directions, but the fracture anisotropy decreases in the hardening region. Results (1) and (2) are in agreement with a hierarchical structural model of the PAMPS network. Based on these findings, we present a revised description of the fracture process of DN gels.

High fracture efficiency and stress concentration phenomenon for microgel-reinforced hydrogels based on double-network principle
Jian Hu, Takayuki Kurokawa, Tasuku Nakajima, Tao Lin Sun, Tiffany Suekama, Zi Liang Wu, Song Miao Liang, Jian Ping Gong
Macromolecules, 45, 23, 9445, 9451, 11 Dec. 2012, [Peer-reviewed]
English, Scientific journal, Double-network hydrogels (DN gels) have aroused considerable interest because of their excellent mechanical strength and toughness, low sliding friction, good biocompatibility, as well as wide tunability in components. By revisiting DN gels, we provide an ingenious way to fabricate a kind of strong and tough microgel-reinforced hydrogels (MR gels), that densely cross-linked polyelectrolyte microgels of poly(2-acrylamido-2-methylpropanesulfonic sodium) (PNaAMPS) (replacing the densely cross-linked PNaAMPS macro-network for conventional DN gels) are incorporated into sparsely cross-linked neutral polyacrylamide (PAAm) matrix. The structure of MR gels can be considered as a two-phase composite, where the disperse phase is the rigid DN microgels, and the continuous phase is the soft PAAm matrix. Similar to DN gels, MR gels show the irreversible energy dissipation in the hysteresis measurement, demonstrating the permanent fracture of the brittle PNaAMPS phase. Thus, the discontinuous brittle phase also serves as sacrificial bonds. Through quantitative comparison of the hysteresis curves with DN gels and monitoring the morphology change of the embedded microgels in MR gels during the real-time stretching process, we conclude that the DN microgels in MR gels show four times higher in fracture efficiency of the sacrificial bonds than bulk DN gels at the same strain, as a result of the stress concentration around the microgels. © 2012 American Chemical Society.

A Universal Molecular Stent Method to Toughen any Hydrogels Based on Double Network Concept
Tasuku Nakajima, Hitomi Sato, Yu Zhao, Shinya Kawahara, Takayuki Kurokawa, Kazuyuki Sugahara, Jian Ping Gong
ADVANCED FUNCTIONAL MATERIALS, 22, 21, 4426, 4432, WILEY-V C H VERLAG GMBH, Nov. 2012, [Peer-reviewed]
English, Scientific journal, Double-network hydrogels (DN gels), despite their high water content, are the strongest and toughest soft and wet materials available. However, in conventional DN gels, which show extraordinarily high mechanical performance comparable to that of industrial rubbers, the first network must be a strong polyelectrolyte and this requirement greatly hinders the widespread application of these gels. A general method involving the use of a molecular stent for the synthesis of tough DN gels using any hydrophilic polymer as the first network is reported. This is the first reported method for the synthesis of tough DN gels using various neutral or weak polyelectrolyte hydrogels as the first network. This method helps extend the DN gel concept to various functional polymers and may increase the number of applications of hydrogels in various fields.

Poly(2-acrylamido-2-methylpropanesulfonic acid) gel induces articular cartilage regeneration in vivo: Comparisons of the induction ability between single- and double-network gels
Munehiro Ogawa, Nobuto Kitamura, Takayuki Kurokawa, Kazunobu Arakaki, Yasuhito Tanaka, Jian Ping Gong, Kazunori Yasuda
JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 100A, 9, 2244, 2251, WILEY-BLACKWELL, Sep. 2012, [Invited]
English, Scientific journal, The purpose of this study was to determine the in vivo cartilage induction effect of the poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) single-network (SN) gel and poly(N,N'-dimethyl acrylamide) (PDMAAm) SN gel in comparison with that of the PAMPS/PDMAAm double-network (DN) gel. An osteochondral defect created in rabbit trochlea was treated with PAMPS/PDMAAm DN, PAMPS SN, or PDMAAm SN gel implantation or left untreated. The gel was implanted into the defect so that a 2-mm depth remained. The defects were examined by histologic and immunohistochemical evaluations, surface assessment using confocal laser scanning microscopy, and real-time polymerase chain reaction analysis at 4 weeks. Samples were quantitatively evaluated with a scoring system reported by Wayne et al. The PAMPS/PDMAAm DN gel-implanted defect was filled with the hyaline-like cartilage tissue. The PAMPS SN gel-implanted defect was filled inhomogenously with hyaline/fibrocartilage tissue. The histology score of the defect treated with PAMPS/PDMAAm DN gel was significantly higher than those treated with PAMPS and PDMAAm SN gels, and the untreated defect (p = 0.0408, p < 0.0001, and p < 0.0001, respectively) and the scores of the defect treated with PAMPS SN gel were significantly higher than those treated with PDMAAm SN gel and the untreated defect (p = 0.0026 and p = 0.0026, respectively). These results suggested that the PAMPS SN gel has an ability that can induce hyaline cartilage regeneration in vivo, but that the PDMAAm SN gel does not. The current study indicates that the chondrogenic potential of a negatively charged PAMPS gel component plays an important role in the cartilage regeneration ability of the PAMPS/PDMAAm DN gel in vivo. (c) 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 100A: 22442251, 2012.

埋植されるPAMPS/PDMAAmダブルネットワークゲルシートの厚さがそのin vivo硝子軟骨再生誘導能に与える効果
松田 英敏, 北村 信人, 黒川 孝幸, 新垣 和伸, Gong Jian Ping, 金谷 文則, 安田 和則
日本整形外科学会雑誌, 86, 8, S1139, S1139, (公社)日本整形外科学会, Aug. 2012
Japanese

Hydrogels with a macroscopic-scale liquid crystal structure by self-assembly of a semi-rigid polyion complex
Zii Liang Wu, Takayuki Kurokawa, Jian Ping Gong
POLYMER JOURNAL, 44, 6, 503, 511, NATURE PUBLISHING GROUP, Jun. 2012, [Peer-reviewed]
English, Scientific journal, Designing hydrogels with self-assembled or self-organized structures has become an attractive field of research because these hydrogels usually have robust functions and promising applications, such as in artificial tissues and optical sensors. However, the self-organized structures developed in synthetic hydrogels via molecular self-assembly are generally limited to the sub-micrometer or micrometer level, which is far from the related scale achieved in biological tissues. Therefore, it is desirable to create macroscopically ordered structures in hydrogels; these structures should greatly improve the material's functionalities, such as their optical properties. In this review, we generally introduce our recent studies on the synthesis of hydrogels with macroscopic-scale liquid crystal structures based on the self-assembly of a semi-rigid polyanion, poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT). Upon electrostatic interaction with multivalent cations or polycations, PBDT molecules form semi-rigid complexes or mesoscopic bundles that further self-assemble into macroscopic organized structures and are frozen by the subsequent gelation process. We have developed physical hydrogels with centimeter-scale anisotropic structures, polycationic hydrogels with millimeter-scale cylindrically symmetric structures and plate gels with cubic-packed concentric domains. This work should contribute to the development of macroscopic self-organized structures in hydrogel materials with specific functions. Polymer Journal (2012) 44, 503-511; doi: 10.1038/pj.2012.74; published online 25 April 2012

Structure Optimization and Mechanical Model for Microgel-Reinforced Hydrogels with High Strength and Toughness
Jian Hu, Takayuki Kurokawa, Kenta Hiwatashi, Tasuku Nakajima, Zi Liang Wu, Song Miao Liang, Jian Ping Gong
MACROMOLECULES, 45, 12, 5218, 5228, AMER CHEMICAL SOC, Jun. 2012, [Peer-reviewed]
English, Scientific journal, In this work, the mechanical behavior of sparsely cross-linked, neutral polyacrylamide (PAAm) hydrogels containing densely cross-linked polyelectrolyte microgels of poly(2-acrylamido-2-methylpropanesulfonic sodium) (PNaAMPS) were studied systematically by varying the formulations. The microgel-reinforced (MR) hydrogels have a two-phase composite structure, where the disperse phase is the rigid double-network (DN) microgels, and the continuous phase is the soft PAAm matrix. At the optimal formulation, the MR gels showed high mechanical strength and toughness, comparable to conventional DN hydrogels. The two critical parameters for the substantial enhancement of mechanical strength and toughness of MR gels are the concentration of PNaAMPS microgel and the molar ratio of the PAAm to the PNaAMPS in the microgel phase. Selective dyeing of the embedded microgels in MR gels allowed for visualization of the deformation of microgels, and we found that the local strain of microgels was much smaller than the global strain applied on MR gels; this indicates that isostress model (Reuss's model) is more suitable than isostrain model (Voigt's model) for this composite system.

Toughness Enhancement and Stick-Slip Tearing of Double-Network Hydrogels in Poly(ethylene glycol) Solution
Songmiao Liang, Jian Flu, Zi Liang Wu, Takayuki Kurokawa, Jian Ping Gong
MACROMOLECULES, 45, 11, 4758, 4763, AMER CHEMICAL SOC, Jun. 2012, [Peer-reviewed]
English, Scientific journal, Using a thin film double-network (DN) hydrogels of 100 mu m thickness, the behaviors of DN gels, from poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) as the first network and polyacrylamide (PAAm) as the second network, swelled in poly(ethylene glycol) (PEG) aqueous solution of short molecular weight (M-w: 400 g/mol) are investigated. Comparing with the conventional DN gels that are swelled in water, the toughness of the DN gels swelled in PEG solution is largely enhanced, as revealed by the tensile test and tearing test. Furthermore, a transition in the crack propagation dynamics, from the steady-state mode in water to the stick-slip instability mode in PEG solution, is observed in the tearing test. The morphology around the crack front of the DN gels also changes with the presence of PEG, and characteristic triangular-like damage patterns are observed. Besides, spicule-like structures are observed on the fractured surface, either in water or in PEG solution. The PEG-induced behaviors are associated with the molecular interaction of PEG to polyacrylamide, the second ductile network of the DN gels.

Active self-organization of microtubules in an inert chamber system
Arif Md Rashedul Kabir, Daisuke Inoue, Akira Kakugo, Kazuki Sada, Jian Ping Gong
POLYMER JOURNAL, 44, 6, 607, 611, NATURE PUBLISHING GROUP, Jun. 2012, [Peer-reviewed]
English, Scientific journal, Microtubule-kinesin system is considered as a building block for the construction of artificial biomachines, and active self-organization of microtubules has been used to integrate their structural organization and achieve amplified functions similar to those observed in natural systems. However, the short lifetime of assembled structures has limited their use in organized systems. In the present study, we demonstrated that the use of an inert atmosphere in the self-organization of microtubules allows the assembled structures to remain active for a prolonged period of time (10 times longer). The longer lifetime achieved in the present study will facilitate the development of assembled microtubules for designing biomolecular motor-based efficient artificial biomachines with prolonged lifetimes. Polymer Journal (2012) 44, 607-611; doi:10.1038/pj.2012.26; published online 4 April 2012

Self-assembled structures of a semi-rigid polyanion in aqueous solutions and hydrogels
Sun TaoLin, Wu ZiLiang, Gong JianPing
SCIENCE CHINA-CHEMISTRY, 55, 5, 735, 742, SCIENCE PRESS, May 2012, [Peer-reviewed]
English, Scientific journal, Poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT), a kind of liquid-crystalline (LC) molecule, has high molecular weight, negative charge and a semi-rigid structure. The aqueous solution of PBDT shows nematic liquid crystalline state above a critical PBDT concentration, C (LC)*, of 2 wt%-3wt%. Different from the flexible polyelectrolyte, PBDT shows a variety of self-assembling structures in aqueous solution with and without salt due to the semi-rigid nature and highly charged property. In addition, the hydrogels with ordered structure are developed by polymerizing a cationic monomer N-[3-(N,N-dimethylamino) propyl] acrylamide methyl chloride quarternary (DMAPAA-Q) in the presence of a small amount of PBDT below the C (LC)*. During the polymerization of cationic monomer, the polycations form a complex with semi-rigid PBDT through electrostatic interaction; these complexes self-assemble into ordered structures that are frozen in the hydrogel. Several different structures, including the anisotropic, dual network-like structure, and cylindrically symmetric structure, with various length scales from micrometer to millimeter, are observed. The hydrogels with ordered liquid crystalline assemblies and particular optical properties should promise applications in many fields, such as in bionics, tissue engineering, and mechano-optical sensors.

Super tough double network hydrogels and their application as biomaterials
Md. Anamul Haque, Takayuki Kurokawa, Jian Ping Gong
POLYMER, 53, 9, 1805, 1822, ELSEVIER SCI LTD, Apr. 2012, [Peer-reviewed]
English, Scientific journal, The double network (ON) technique, developed by authors' group, provides an innovative and universal pass way to fabricate hydrogels with super high toughness comparable to rubbers. The excellent mechanical performances of ON hydrogels originate from the specific combination of two networks with contrasting structures. The first brittle network serves as sacrificial bonds, which breaks into small clusters to efficiently disperse the stress around the crack tip into the surrounding damage zone, while the second ductile polymer chains act as hidden length, which extends extensively to sustain large deformation. Based on the principle of ON hydrogel, the author's group recently has developed several novel systems and techniques, which has greatly expanded the practical accessibility of ON technique for practical use. The ON principle and the ON gel have already attracted much attention in the soft matter community. Inspired by the ON principle, many research groups have also designed and developed some innovative hydrogels with large enhancement in their mechanical strength and toughness. Some tough hydrogels fabricated by the ON technique also exhibit good biocompatibility and low friction resistance with promising prospective in industrial and medicine fields, especially for load-bearing artificial soft tissues such as artificial cartilage. In this feature article, we address the major concept and toughening mechanism of ON gel, then we describe some recent novel hydrogel systems based on the ON concept, and finally the applicability of ON gel as soft biomaterials is discussed. (C) 2012 Elsevier Ltd. All rights reserved.

生体分子モーターの自発的高次構造形成　　　　　　　　　　　　　　　
敷中一洋, 角五 彰, 龔 剣萍
液晶, 16, 1, 45, 51, Jan. 2012, [Invited]
Japanese, Scientific journal

Anisotropic hydrogel based on bilayers: color, strength, toughness, and fatigue resistance
Md Anamul Haque, Takayuki Kurokawa, Jian Ping Gong
SOFT MATTER, 8, 31, 8008, 8016, ROYAL SOC CHEMISTRY, 2012, [Peer-reviewed], [Invited]
English, Scientific journal, In this highlight, we introduce a novel anisotropic hydrogel with a perfect 1D photonic crystal structure based on the uniaxial alignment of lamellar bilayers. The gel was synthesized in a one-pot polymerization from a precursor solution containing a polymerizable surfactant (dodecyl glyceryl itaconate: DGI), acrylamide, and a cross-linker. By applying shear flow to the precursor solution, lamellar bilayers of self-assembled DGI were aligned in one direction parallel to the substrate surface. The polymerized lamellar bilayers were stacked periodically and entrapped in the polyacrylamide matrix to give a hydrogel with a 1D photonic crystal structure. This hydrogel, containing 94-95 wt% water and 1.0-1.5 wt% bilayer molecules, shows perfect one-dimensional swelling, strong anisotropy in the elastic modulus, and magnificent structural color by multilayer interference according to Bragg's law of diffraction. Owing to the softness and large deformability, the color of the gel can be reversibly tuned by both compressive and tensile mechanical stimuli over the entire wavelength range of visible color. The single-domain lamellar bilayer not only diffracts light but also serves as a reversible sacrificial bond that dissociates upon deformation, exhibiting large hysteresis as an energy dissipation mechanism, which gives the gel high tensile strength and fatigue resistance. Both the molecular dissociation and lipid-like mobile nature of DGI molecules in the bilayers dramatically enhance the resistance against crack propagation by the formation of extraordinary blunting, which gives the gel an extraordinarily high toughness.

Nematic growth of microtubules that changed into giant spiral structure through partial depolymerization and subsequent dynamic ordering
Kiyotaka Shigehara, Hiroki Kudoh, Saori Mori, Yoshiki Tamura, Akira Kakugo, Ryuzo Kawamura, Hidemitsu Furukawa, Jian Ping Gong, Hiroyasu Masunaga, Tomomi Masui, Satoshi Koizumi, Kazuhiro Shikinaka
SOFT MATTER, 8, 45, 11544, 11551, ROYAL SOC CHEMISTRY, 2012, [Peer-reviewed]
English, Scientific journal, In a long capillary cell with temperature gradient, tubulin dimers with alpha and beta subunits polymerized according to the preferential polarity, i.e., the anisotropic spiral addition of the dimers to the beta-terminated "plus end" dominated the formation of microtubules. As the result, the helical hollow cylinders generated the oriented nematic liquid crystalline structure with centimeter-length. In the next stage, where microtubules were under the partial polymerization/depolymerization equilibrium due to the concentration fluctuation, the dynamic rearrangement of microtubules such as their shortening (depolymerization) and subsequent tilting of orientation axis caused the structural change from the oriented nematic liquid crystalline structure to some giant spiral structure which was subjected by the ordered dipole and the helical chirality of microtubules.

Formation of ring-shaped assembly of microtubules with a narrow size distribution at an air-buffer interface
Arif Md Rashedul Kabir, Shoki Wada, Daisuke Inoue, Yoshiki Tamura, Tamaki Kajihara, Hiroyuki Mayama, Kazuki Sada, Akira Kakugo, Jian Ping Gong
SOFT MATTER, 8, 42, 10863, 10867, ROYAL SOC CHEMISTRY, 2012, [Peer-reviewed]
English, Scientific journal, Biopolymers such as actin, microtubules and DNA are well known for their fascinating in vivo self-organization phenomena. Considerable efforts have been devoted to mimicking their organization process in vitro that produced ring-shaped or toroid structures in an irreversible manner. However, understanding the factors that lead to formation of such assembled structures deserves more investigation to achieve a unified insight into the assembly process, particularly of the microtubules. Here, we report an active assembly process of microtubules (MTs) at an air-buffer interface that resulted in ring-shaped microtubule structures with a narrow size distribution and a high yield. Using an "air-buffer interface control system" combined with the newly developed "inert chamber system (ICS)" we have also successfully observed the reversible conformational transition between ring-and linear-shaped microtubules at the air-buffer interface. This is the first ever direct in situ observation of a reversible assembly process of MTs and probably provides us with valuable discernment to understand the in vivo organizational behavior of biopolymers.

Swelling-induced long-range ordered structure formation in polyelectrolyte hydrogel
Md Arifuzzaman, Zi Liang Wu, Takayuki Kurokawa, Akira Kakugo, Jian Ping Gong
SOFT MATTER, 8, 31, 8060, 8066, ROYAL SOC CHEMISTRY, 2012, [Peer-reviewed]
English, Scientific journal, A millimeter-scale periodic structure is created in a polyelectrolyte hydrogel by the rapid-heterogeneous swelling process, and is frozen by the polyion complexation of the polyelectrolyte network with the oppositely charged, semi-rigid polyelectrolyte. The hydrogel is synthesized from a cationic monomer, N-[3-(N,N-dimethylamino)propyl] acrylamide methyl chloride quaternary (DMAPAA-Q), in the presence of a small amount of the oppositely charged poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT) that has a semi-rigid nature. During the swelling process, surface creasing due to the large mismatching of swelling degree between the surface layer and the inner one of the poly DMAPAA-Q (PDMAPAA-Q) gel occurs, which induces highly oriented semi-rigid PBDT molecules along the tensile direction of the crease pattern. To accompany the evolution of surface creasing, a lattice-like periodic birefringence pattern is formed, which is frozen permanently by the strong polyion complex formation, even after the surface instability pattern of the gel disappears completely throughout the dynamic coalescence. In this work we rationally clarified that formation of such a long-range ordered non-equilibrium structure in the polyelectrolyte hydrogel by the rapid-heterogeneous swelling process requires the following three indispensable conditions: (i) swelling-induced surface creasing; (ii) polyion complex formation; and (iii) a semi-rigid or rigid dopant. This sort of non-equilibrium structure formation mechanism may help understand how biomacromolecules that are rigid polyelectrolytes, such as deoxyribonucleic acid, microtubules and actin filaments, form rich architectures during the growth of biological organs.

Antifouling properties of hydrogels
Takayuki Murosaki, Nafees Ahmed, Jian Ping Gong
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 12, 6, 064706, NATL INST MATERIALS SCIENCE, Dec. 2011, [Peer-reviewed], [Invited]
English, Scientific journal, Marine sessile organisms easily adhere to submerged solids such as rocks, metals and plastics, but not to seaweeds and fishes, which are covered with soft and wet 'hydrogel'. Inspired by this fact, we have studied long-term antifouling properties of hydrogels against marine sessile organisms. Hydrogels, especially those containing hydroxy group and sulfonic group, show excellent antifouling activity against barnacles both in laboratory assays and in the marine environment. The extreme low settlement on hydrogels in vitro and in vivo is mainly caused by antifouling properties against the barnacle cypris.

Formation of motile assembly of microtubules driven by kinesins
Ryuzo Kawamura, Akira Kakugo, Kazuhiro Shikinaka, Yoshihito Osada, Jian Ping Gong
SMART MATERIALS AND STRUCTURES, 20, 12, 124007, IOP PUBLISHING LTD, Dec. 2011, [Peer-reviewed]
English, Scientific journal, Microtubule (MT) and kinesin are rail and motor proteins that are involved in various moving events of eukaryotic cells in natural systems. In vitro, the sliding motion of microtubules (rail) can be reproduced on a kinesin (motor protein)-coated surface coupled with adenosine triphosphate (ATP) hydrolysis, which is called a `motility assay'. Based on this technique, a method was recently established to form MT assemblies by an active self-assembly (AcSA) process, in which MTs are crosslinked during a sliding motion on a kinesin-coated surface. Streptavidin (ST) was employed as glue to crosslink biotin-labeled MTs. Various shapes, sizes, and motilities were formed with the AcSA MT assemblies, depending on the initial conditions. In this paper, we briefly review our recent work on the formation of MT assemblies on a kinesin-coated surface.

Novel Developed Systems and Techniques Based on Double-Network Principle
Zi Liang Wu, Takayuki Kurokawa, Jian Ping Gong
BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, 84, 12, 1295, 1311, CHEMICAL SOC JAPAN, Dec. 2011, [Peer-reviewed]
English, Scientific journal, The double-network hydrogels (DN gels), developed by our group in 2003, have attracted increasing attention clue to their excellent mechanical performance and unique fracture mechanism. The anomalously large fracture energy of DN gels up to 2200J m(-2) originates from the specific combination of two networks with contrasting properties. The first brittle network serves as sacrificial bonds, which breaks into small clusters to efficiently disperse the stress around the crack tip into the surrounding damage zone, while the second ductile polymer chains act as hidden length, which extends extensively to sustain large deformation. The DN gels also exhibit good biocompatibility and low friction resistance. Owing to these superior properties. DN gels possess promising prospective in industrial and medicine fields, especially for load-bearing artificial soft tissues such as artificial cartilage. However, there are several critical problems limiting the practical applications of DN gels, such as how to produce tough artificial tissue with complex shapes or bond a gel to a solid substrate. To address these specific issues, we have developed new systems and techniques based on the DN principle. These achievements, including synthesis of ultrathin DN gels, bonding of one gel to another gel or solid substrate, free-shaping of DN gels, enhancing typical single network gels by creating a DN structure, will be briefly introduced in this account paper. We believe that these new techniques will substantially promote the practical applications of ON hydrogels and extent the DN principle to other systems.

Rapid and Reversible Tuning of Structural Color of a Hydrogel over the Entire Visible Spectrum by Mechanical Stimulation
Md. Anamul Haque, Takayuki Kurokawa, Gen Kamita, Youfeng Yue, Jian Ping Gong
CHEMISTRY OF MATERIALS, 23, 23, 5200, 5207, AMER CHEMICAL SOC, Dec. 2011, [Peer-reviewed]
English, Scientific journal, In this work, we report a rubberlike elastic hydrogel containing microdomains of bilayers periodically stacked into the polymer network that satisfy the Bragg's law of diffraction. The rubberlike elastic hydrogel has been synthesized by applying double network principle into a viscoelastic hydrogel containing single-domain macroscopic lamellar bilayer. The hydrogel is able to tune the magnificent structural color reversibly over the entire wavelength range of visible spectrum as fast as the uniaxial tensile stretching and compressive deformation are applied and released. Owing to the strength, softness, and rubberlike elastic deformability, the tunable hydrogel can be used extensively to design a new class of soft tactile sensor as an advanced stress sensor that is able to detect a local deformation of a complicated force field.

Lamellar Bilayers as Reversible Sacrificial Bonds To Toughen Hydrogel: Hysteresis, Self-Recovery, Fatigue Resistance, and Crack Blunting
M. Anamul Haque, Takayuki Kurokawa, Gen Kamita, J. Ping Gong
MACROMOLECULES, 44, 22, 8916, 8924, AMER CHEMICAL SOC, Nov. 2011, [Peer-reviewed]
English, Scientific journal, We report the extraordinary toughness, hysteresis, self-recovery, and persistent fatigue resistance of an anisotropic hydrogel with single-domain lamellar structure, consisting of periodical stacking of several thousands of rigid, hydrophobic bilayers in the ductile, hydrophilic polymer matrix. The stratified lamellar bilayers not only diffract light to exhibit magnificent structural color but also serve as reversible sacrificial bonds that dissociate upon deformation, exhibiting large hysteresis as an energy dissipation mechanism. Both the molecular dissociation and lipid-like mobile nature of bilayers dramatically enhance the resistance to crack propagation by suppressing the stress concentration at the crack tip with the formation of extraordinary crack blunting. This unique toughening phenomenon could allow deep insight into the toughening mechanism of the hydrogel-like soft materials such as biological soft tissues.

Effect of Hyaluronan Solution on Dynamic Friction of PVA Gel Sliding on Weakly Adhesive Glass Substrate
Yukihiro Nakano, Takayuki Kurokawa, Miao Du, Jian Liu, Taiki Tominaga, Yoshihito Osada, Jian Ping Gong
MACROMOLECULES, 44, 22, 8908, 8915, AMER CHEMICAL SOC, Nov. 2011, [Peer-reviewed]
English, Scientific journal, We study the sliding friction of poly(vinyl alcohol) (PVA) gel against glass substrate in hyaluronan (HA) aqueous solution with various concentrations and two molecular weights. The frictional stress decreases with increase of concentration of HA at low sliding velocity, and the lowest friction appears in HA 10c* (c* is the overlap concentration) solution; after that, it increases slightly with the concentration. By assuming that a continuous HA lubricant layer is formed at the interface, which screens PVA adsorption to substrate, we estimate the thickness of the lubrication film in concentrated HA solution. In addition, we perform frictional measurement in poly(ethylene oxide) (PEO) aqueous solutions and proteoglycan solutions. By comparing the frictional behavior with that in HA solutions, we observe a universal relationship between the zero-shear rate viscosity of polymer solution and the friction at low sliding velocity region, regardless the change in the lubricating polymer species.

Prolongation of the Active Lifetime of a Biomolecular Motor for in Vitro Motility Assay by Using an Inert Atmosphere
Arif Md. Rashedul Kabir, Daisuke Inoue, Akira Kakugo, Akiko Kamei, Jian Ping Gong
LANGMUIR, 27, 22, 13659, 13668, AMER CHEMICAL SOC, Nov. 2011, [Peer-reviewed]
English, Scientific journal, Over the last few decades, the in vitro motility assay has been performed to probe the biophysical and chemo-mechanical properties as well as the self-organization process of biomolecular motor systems such as actin - myosin and microtubule - kinesin. However, aggression of the reactive oxygen species (ROS) and concomitant termination of the activity of biomolecular motors during investigation remains a drawback of this assay. Despite enzymatic protection that makes use of a combination of glucose, glucose oxidase, and catalase, the active lifetime of biomolecular motors is found to be only a few hours and this short lifetime restricts further study on those systems. We have solved this problem by using a newly developed system of the in vitro motility assay that is conducted in an inert nitrogen gas atmosphere free of ROS. Using microtubule kinesin as a model system we have shown that our system has prolonged the active lifetime of the biomolecular motor until several days and even a week by protecting it from oxidative damage.

How to Integrate Biological Motors towards Bio-Actuators Fueled by ATP
Arif Md. Rashedul Kabir, Akira Kakugo, Jian Ping Gong, Yoshihito Osada
MACROMOLECULAR BIOSCIENCE, 11, 10, 1314, 1324, WILEY-V C H VERLAG GMBH, Oct. 2011, [Invited]
English, Scientific journal, Biological motors, driven by the conversion of chemical energy into mechanical energy, are much more efficient than man-made machines. The development of such efficient biomimetic motor systems in vitro is currently a vital need. However, great difficulty lies in how to integrate the sophisticated functions of the constituent components to obtain a performance as in the case of natural living systems. Based on 'active' and 'passive' self-organization principles, it has been demonstrated that the functions of motor protein systems can be integrated to obtain complex hierarchical structures that can work as actuators. Most of the works discussed here concern two-dimensional behavior, and recent works aim to explore the three-dimensional features of such artificial bio-mechanical systems.

Controlled Clockwise-Counterclockwise Motion of the Ring-Shaped Microtubules Assembly
Akira Kakugo, Arif Md. Rashedul Kabir, Natsuki Hosoda, Kazuhiro Shikinaka, Jian Ping Gong
BIOMACROMOLECULES, 12, 10, 3394, 3399, AMER CHEMICAL SOC, Oct. 2011, [Peer-reviewed]
English, Scientific journal, The microtubule (MT)-kinesin system has been propose as the building block of biomolecular motor based artificial biomachines. Considerable efforts have been devoted to integrate this system that produced a variety of ordered structures including the ring-shaped MT assembly which is being considered as a promising candidate for the further development of the biomachines. However, lack of proper knowledge that might help tune the direction of Motion of ring-shaped microtubule assembly from counterclockwise to clockwise direction, and vice versa, significantly restricted their potential applications. We report our success in controlling the direction of rotational motion of ring-shaped MT assembly by altering the preparation conditions of microtubules. The change in the direction of rotation of MT rings could be interpreted in terms of the accompanied structural rearrangement of the MT lattice. For achieving handedness-regulated efficient biomachines having tunable asymmetric property, our study will be significantly directive.

Microgel-Reinforced Hydrogel Films with High Mechanical Strength and Their Visible Mesoscale Fracture Structure
Jian Hu, Kenta Hiwatashi, Takayuki Kurokawa, Song Miao Liang, Zi Liang Wu, Jian Ping Gong
MACROMOLECULES, 44, 19, 7775, 7781, AMER CHEMICAL SOC, Oct. 2011, [Peer-reviewed]
English, Scientific journal, The poor mechanical properties remain the largest barrier to traditional synthetic hydrogels for extensive practical applications, such as tissue scaffolds. In this work, we have synthesized the hydrogel films in the presence of microgel precursors of various chemical species with different charges. The hydrogels fabricated have a novel two-phase composite structure, where the continuous phase is a loosely cross-linked polyacrylamide (PAAm) matrix and the disperse phase is virtually double-network (DN) microgels. Named as microgel-reinforced (MR) hydrogels, they exhibited dramatic enhancement in mechanical strength and toughness, in comparison to the hydrogels with no microgels. MR hydrogels showed the comparable mechanical properties with the conventional bicontinuous DN hydrogels. By visualizing the embedded microgels before, during, and after the elongation, mesoscale fractures of the microgels phase were confirmed, which should effectively blunt the crack and enhance the fracture propagation resistance. Therefore, we conclude that the essential reinforcement principle of MR gels roots in the sacrificial bonds effect contributed by the microgels. This work provides a novel universal pathway to synthesize hydrogel thin films with high strength and toughness from various microgels and may open a new avenue for the application of hydrogels in various fields, such as fast responsive actuators, fuel cell films, wound dressings, etc.

Acrylamide Polymer Double-Network Hydrogels: Candidate Cartilage Repair Materials with Cartilage-Like Dynamic Stiffness and Attractive Surgery-Related Attachment Mechanics
Markus P. Arnold, Alma U. Daniels, Sarah Ronken, Helena Ardura Garcia, Niklaus F. Friederich, Takayuki Kurokawa, Jian P. Gong, Dieter Wirz
CARTILAGE, 2, 4, 374, 383, SAGE PUBLICATIONS INC, Oct. 2011, [Peer-reviewed]
English, Scientific journal, Background: In focal repair of joint cartilage and meniscus, initial stiffness and strength of repairs are generally much less than surrounding tissue. This increases early failure potential. Secure primary fixation of the repair material is also a problem. Acrylamide polymer double-network (DN) hydrogels are candidate-improved repair materials. DN gels have exceptional strength and toughness compared to ordinary gels. This stems from the double-network structure in which there is a high molar ratio of the second network to the first network, with the first network highly crosslinked and the second loosely crosslinked. Previous studies of acrylic PAMPS/PDMAAm and PAMPS/PAAm DN gels demonstrated physicochemical stability and tissue compatibility as well as the ability to foster cartilage formation. Methods: Mechanical properties related to surgical use were tested in 2 types of DN gels. Results: Remarkably, these >90%-water DN gels exhibited dynamic impact stiffness (E*) values (similar to 1.1 and similar to 1.5 MPa) approaching swine meniscus (similar to 2.9 MPa). Dynamic impact energy-absorbing capability was much lower (median loss angles of similar to 2 degrees) than swine meniscus (>10 degrees), but it is intriguing that >90%-water materials can efficiently store energy. Also, fine 4/0 suture tear-out strength approached cartilage (similar to 2.1 and similar to 7.1 N v. similar to 13.5 N). Initial strength of attachment of DN gels to cartilage with acrylic tissue adhesive was also high (similar to 0.20 and similar to 0.15 N/mm(2)). Conclusions: DN gel strength and toughness properties stem from optimized entanglement of the 2 network components. DN gels thus have obvious structural parallels with cartilaginous tissues, and their surgical handling properties make them ideal candidates for clinical use.

Gel: A Potential Material as Artificial Soft Tissue
Yong Mei Chen, Jian Ping Gong, Yoshihito Osada
Macromolecular Engineering: Precise Synthesis, Materials Properties, Applications, 4, 2689, 2717, Wiley-VCH, 23 Sep. 2011, [Peer-reviewed]
English, In book

Gene expression profile of the cartilage tissue spontaneously regenerated in vivo by using a novel double-network gel: Comparisons with the normal articular cartilage
Ryusei Imabuchi, Yoshihiro Ohmiya, Hyuck Joon Kwon, Shin Onodera, Nobuto Kitamura, Takayuki Kurokawa, Jian Ping Gong, Kazunori Yasuda
BMC MUSCULOSKELETAL DISORDERS, 12, 213, BIOMED CENTRAL LTD, Sep. 2011, [Peer-reviewed]
English, Scientific journal, Background: We have recently found a phenomenon that spontaneous regeneration of a hyaline cartilage-like tissue can be induced in a large osteochondral defect by implanting a double-network (DN) hydrogel plug, which was composed of poly-(2-Acrylamido-2-methylpropanesulfonic acid) and poly-(N, N'-Dimetyl acrylamide), at the bottom of the defect. The purpose of this study was to clarify gene expression profile of the regenerated tissue in comparison with that of the normal articular cartilage.
Methods: We created a cylindrical osteochondral defect in the rabbit femoral grooves. Then, we implanted the DN gel plug at the bottom of the defect. At 2 and 4 weeks after surgery, the regenerated tissue was analyzed using DNA microarray and immunohistochemical examinations.
Results: The gene expression profiles of the regenerated tissues were macroscopically similar to the normal cartilage, but showed some minor differences. The expression degree of COL2A1, COL1A2, COL10A1, DCN, FMOD, SPARC, FLOD2, CHAD, CTGF, and COMP genes was greater in the regenerated tissue than in the normal cartilage. The top 30 genes that expressed 5 times or more in the regenerated tissue as compared with the normal cartilage included type-2 collagen, type-10 collagen, FN, vimentin, COMP, EF1alpha, TFCP2, and GAPDH genes.
Conclusions: The tissue regenerated by using the DN gel was genetically similar but not completely identical to articular cartilage. The genetic data shown in this study are useful for future studies to identify specific genes involved in spontaneous cartilage regeneration.

Dynamic Behavior and Spontaneous Differentiation of Mouse Embryoid Bodies on Hydrogel Substrates of Different Surface Charge and Chemical Structures
Jian Fang Liu, Yong Mei Chen, Jing Jing Yang, Takayuki Kurokawa, Akira Kakugo, Kimiko Yamamoto, Jian Ping Gong
TISSUE ENGINEERING PART A, 17, 17-18, 2343, 2357, MARY ANN LIEBERT, INC, Sep. 2011, [Peer-reviewed]
English, Scientific journal, Differentiation of embryoid bodies (EBs) into particular cell lineages has been extensively studied. There is an increasing interest in the effect of soft hydrogel scaffolds on the behavior of EBs, such as the initial adhesion, dynamic morphology change, and differentiation. In this study, without adding any other bioactive factors in the serum-containing medium, dynamic behaviors of mouse EBs loaded on the surface of hydrogels with different surface charge and chemical structures are investigated. EBs adhered quickly to negatively charged poly(sodium p-styrene sulfonate) (PNaSS) hydrogels, which facilitates EBs spreading, migration, and differentiation into three germ layers with high efficiency of cardiomyocytes differentiation, similar to that on gelatin coated polystyrene (PS) culture plate. While on neutral poly(acrylamide) (PAAm) hydrogels, EBs maintained the initial spherical morphology with high expression of pluripotency-related markers in the short culture periods, and then showed the significantly greater levels of selected endoderm markers after long-time culture. EBs cultured on negatively charged poly(2-acrylamido-2-methyl-propane sulfonic acid sodium salt) (PNaAMPS) gels demonstrated the analogous behaviors with that of neutral PAAm gels at early differentiation phase (day 4 + 1). Then, their adhesion, spreading and differentiation were quite similar to that on negatively charged PNaSS gels. The correlation between surface properties of hydrogels and EBs differentiation was discussed.

Effect of Void Structure on the Toughness of Double Network Hydrogels
Tasuku Nakajima, Hidemitsu Furukawa, Yoshimi Tanaka, Takayuki Kurokawa, Jian Ping Gong
JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, 49, 17, 1246, 1254, WILEY-BLACKWELL, Sep. 2011, [Peer-reviewed]
English, Scientific journal, Introduction of soft filler in a hard body, which is one of the common toughening methods of hard polymeric materials, was applied for further toughening of robust double network (DN) hydrogels composed of poly(2-acrylamido-2-methylpropanesulfonic acid) gels (PAMPS gels) as the first component and polyacrylamide (PAAm) as the second component. The fracture energy of the DN gels with the void structure (called void-DN gels) became twice when the volume fraction of void was 1-3 vol % and the void diameter was much larger than the Flory radius of the PAAm chains. Such toughening was induced by wider range of internal fracture of the PAMPS network derived from partial stress concentration near void structure. Considering the mechanical tests and the dynamic light scattering results, it is implied that the absence of the load-bearing PAAm structure inside the void is important for the toughening. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1246-1254, 2011

PAMPS/PDMAAmダブルネットワークゲルが培養ATDC5細胞の軟骨分化に与える効果 PAMPSおよびPDMAAmゲルの効果との比較
北村 信人, 権 赫準, 近江谷 克裕, 黒川 孝幸, グン 剣萍, 安田 和則
日本整形外科学会雑誌, 85, 8, S1264, S1264, (公社)日本整形外科学会, Aug. 2011
Japanese

ゲル-物性の研究と再生医療への応用
黒川孝幸, 龔剣萍
未来材料, 11, 8, 2, 4, エヌ・ティー・エス, Aug. 2011, [Invited]
Japanese, Scientific journal

Surfactant-induced friction reduction for hydrogels in the boundary lubrication regime
Kosuke Kamada, Hidemitsu Furukawa, Takayuki Kurokawa, Tomohiro Tada, Taiki Tominaga, Yukihiro Nakano, Jian Ping Gong
JOURNAL OF PHYSICS-CONDENSED MATTER, 23, 28, 284107, IOP PUBLISHING LTD, Jul. 2011, [Peer-reviewed]
English, Scientific journal, We studied the ability of surfactants to reduce friction by boundary lubrication for a bulk hydrogel sliding on a solid surface in an aqueous solution. A piece of negatively charged polyelectrolyte hydrogel was slid across solid surfaces with various levels of hydrophobicity, using a strain-controlled parallel-plate rheometer in water. A dramatic reduction in the sliding friction, especially in the low velocity region, was detected by the addition of a surfactant to the water medium. This friction reduction was only observed in gel-solid friction but not in solid-solid friction, indicating that the soft and wet nature of the gel surface was crucial for this surfactant-induced friction reduction. This phenomenon reveals that surfactants can remain at the gel-mated interface, thus preventing direct interfacial interaction between the sliding surfaces, and significantly decreasing the frictional stress. The reported dramatic reduction in friction highlights the frictional characteristics of soft and wet hydrogel materials.

Hydrogels with self-assembling ordered structures and their functions
Zi Liang Wu, Jian Ping Gong
NPG ASIA MATERIALS, 3, 4, 57, 64, NATURE PUBLISHING GROUP, Jun. 2011, [Peer-reviewed], [Invited]
English, Scientific journal, Biological soft tissue and synthesized hydrogel both belong to the same 'soft and wet' class of substances, that is, they are both soft and contain water. However, whereas biological tissue such as muscles displays various forms of functionality, hydrogels generally have poor functionality, primarily due to the difference in structure biological tissue has a sophisticated structure whereas most hydrogels are amorphous. In recent years, biomacromolecules, block copolymers and liquid-crystalline molecules have been used to develop self-assembled architectures in synthetic physical or chemical hydrogels via intermolecular noncovalent interactions such as ionic bonding, hydrophobic interactions and hydrogen bonding. Ordered structures on various length scales endow the hydrogels with additional functions with promising applications in materials science, such as in tissue engineering and mechano-optical sensors. In this review, we briefly describe the recent developments in designing hydrogels with ordered structures of molecular assemblies and the resultant functionalities.

Induction of Spontaneous Hyaline Cartilage Regeneration Using a Double-Network Gel Efficacy of a Novel Therapeutic Strategy for an Articular Cartilage Defect
Nobuto Kitamura, Kazunori Yasuda, Munehiro Ogawa, Kazunobu Arakaki, Shuken Kai, Shin Onodera, Takayuki Kurokawa, Jian Ping Gong
AMERICAN JOURNAL OF SPORTS MEDICINE, 39, 6, 1160, 1169, SAGE PUBLICATIONS INC, Jun. 2011, [Invited]
English, Scientific journal, Background: A double-network (DN) gel, which was composed of poly-(2-acrylamido-2-methylpropanesulfonic acid) and poly(N, N'-dimetyl acrylamide) (PAMPS/PDMAAm), has the potential to induce chondrogenesis both in vitro and in vivo.
Purpose: To establish the efficacy of a therapeutic strategy for an articular cartilage defect using a DN gel.
Study Design: Controlled laboratory study.
Methods: A 4.3-mm-diameter osteochondral defect was created in rabbit trochlea. A DN gel plug was implanted into the defect of the right knee so that a defect 2 mm in depth remained after surgery. An untreated defect of the left knee provided control data. The osteochondral defects created were examined by histological and immunohistochemical evaluations, surface assessment using confocal laser scanning microscopy, and real-time polymerase chain reaction (PCR) analysis at 4 and 12 weeks. Samples were quantitatively evaluated with 2 scoring systems reported by Wayne et al and O'Driscoll et al.
Results: The DN gel-implanted defect was filled with a sufficient volume of the hyaline cartilage tissue rich in proteoglycan and type 2 collagen. Quantitative evaluation using the grading scales revealed a significantly higher score in the DN gel-implanted defects compared with the untreated control at each period (P<.0001). The mean relative values of type 2 collagen mRNAs in the regenerated tissue were obviously higher in the DN gel-implanted defect than in the untreated control at each period. The mean surface roughness of the untreated control was significantly higher than the normal cartilage at 12 weeks (P=.0106), while there was no statistical difference between the DN gel-implanted and normal knees.
Conclusion: This study using the mature rabbit femoral trochlea osteochondral defect model demonstrated that DN gel implantation is an effective treatment to induce cartilage regeneration in vivo without any cultured cells or mammalian-derived scaffolds.

Strain-Induced Molecular Reorientation and Birefringence Reversion of a Robust, Anisotropic Double-Network Hydrogel
Zi Liang Wu, Daisuke Sawada, Takayuki Kurokawa, Akira Kakugo, Wei Yang, Hidemitsu Furukawa, Jian Ping Gong
MACROMOLECULES, 44, 9, 3542, 3547, AMER CHEMICAL SOC, May 2011, [Peer-reviewed]
English, Scientific journal, A robust, macroscopically anisotropic double-network (A-DN) hydrogel has been developed by combining the first anisotropic, physically cross-linked network of semirigid poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT) and the second chemically cross-linked network of flexible polyacrylamide (PAAm) through double-network technology. Owing to the cooperative orientation of the self-assembled bundle structure of semirigid PBDTs, the A-DN gel shows a very sensitive and strong birefringence change upon deformation, which is always dominated by PBDT for the wide strain range investigated (epsilon = 0-18), regardless the fact that PAAm is in large excess. When the initial alignment of PBDT is vertical to the elongation direction, a birefringence reversion occurs at epsilon similar to 0.5, indicating that the initial vertical alignment of PBDT is overwhelmed by the strain-induced parallel alignment, even at such a small strain due to the cooperative reorientation of PBDT.

Anisotropic Hydrogel from Complexation-Driven Reorientation of Semirigid Polyanion at Ca2+ Diffusion Flux Front
Zi Liang Wu, Takayuki Kurokawa, Daisuke Sawada, Jian Hu, Hidemitsu Furukawa, Jian Ping Gong
MACROMOLECULES, 44, 9, 3535, 3541, AMER CHEMICAL SOC, May 2011, [Peer-reviewed]
English, Scientific journal, We report a macroscopically anisotropic hydrogel developed by the facile dialysis of a synthetic semirigid polyanion in aqueous solution of multivalent cations. By the uniaxial diffusion of Ca2+ into two ends of a thin rectangular reaction cell containing semirigid polyanion poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT) aqueous solution, centimeter-scale anisotropic hydrogels with the PBDT molecules and their self-assembled fibrous bundles align in perpendicular to the Ca2+ diffusion direction are obtained. The anisotropic gel shows a higher elastic modulus and tensile fracture stress/strain in the direction parallel to the PBDT orientation than that of perpendicular direction. By observing in situ the gelation process, an extraordinary molecular reorientation of PBDT at the Ca2+ diffusion flux front is observed for the first time. The mechanism for the molecular reorientation is discussed in terms of complexation and gelation.

Direct Observation on the Surface Fracture of Ultrathin Film Double-Network Hydrogels
Songmiao Liang, Zi Liang Wu, Jian Hu, Takayuki Kurokawa, Qiu Ming Yu, Jian Ping Gong
MACROMOLECULES, 44, 8, 3016, 3020, AMER CHEMICAL SOC, Apr. 2011, [Peer-reviewed]
English, Scientific journal, Double-network (DN) hydrogels have attracted much attention in the soft matter community due to their excellent mechanical performance and unique fracture mechanism. On the basis of ultrathin film technique and optical microscope, we here report a method which is quite effective for accessing the fractured microstructure of DN hydrogels formed during the tensile and tearing process. During tensile deformation, fracture of the first network occurs even before yielding occurs. Concomitant with the yielding, wrinkle-like structure, which is due to the fracture of the first network, is clearly observed for the first time. This wrinkle-like structure disappears upon further deformation to strain-hardening region because of the further fracture of the first network. Similar microstructures are observed at the crack tip for samples experienced the tearing test. This work provides direct proofs for the assumption concerning the occurrence of local yielding and the formation of a huge damage zone at the crack tip during the crack propagation process of DN hydrogels.

Robust bonding and one-step facile synthesis of tough hydrogels with desirable shape by virtue of the double network structure
Junji Saito, Hidemitsu Furukawa, Takayuki Kurokawa, Rikimaru Kuwabara, Shinya Kuroda, Jian Hu, Yoshimi Tanaka, Jian Ping Gong, Nobuto Kitamura, Kazunori Yasuda
POLYMER CHEMISTRY, 2, 3, 575, 580, ROYAL SOC CHEMISTRY, Mar. 2011, [Peer-reviewed]
English, Scientific journal, Robust bonding of a hydrogel in aqueous environment, either to another hydrogel or to a solid, is one of the major unsolved issues for the practical applications of hydrogels in various fields. Here we report robust bonding between a pair of hydrogel sheets, containing over 90 wt% of water, by applying the double-network (DN) structure. In the optimal condition, the peeling energy of the united gel sheets reaches 1200 J m(-2), which is comparable to the bulk fracture energy of a normal type of tough DN gels. This hydrogel bonding technique is also applied to form tough bonding between hydrogel and plastic plates. Furthermore, based on this technique, we have developed a facile method to synthesize robust double network hydrogels with any desirable free-shape from micro-gel precursors. These novel techniques will substantially merit the applications of the tough hydrogels in various fields, such as an artificial meniscus.

Joint immobilization inhibits spontaneous hyaline cartilage regeneration induced by a novel double-network gel implantation
Kazunobu Arakaki, Nobuto Kitamura, Takayuki Kurokawa, Shin Onodera, Fuminori Kanaya, Jian-Ping Gong, Kazunori Yasuda
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 22, 2, 417, 425, SPRINGER, Feb. 2011, [Peer-reviewed]
English, Scientific journal, We have recently discovered that spontaneous hyaline cartilage regeneration can be induced in an osteochondral defect in the rabbit, when we implant a novel double-network (DN) gel plug at the bottom of the defect. To clarify whether joint immobilization inhibits the spontaneous hyaline cartilage regeneration, we conducted this study with 20 rabbits. At 4 or 12 weeks after surgery, the defect in the mobile knees was filled with a sufficient volume of the hyaline cartilage tissue rich in proteoglycan and type-2 collagen, while no cartilage tissues were observed in the defect in the immobilized knees. Type-2 collagen, Aggrecan, and SOX9 mRNAs were expressed only in the mobile knees at each period. This study demonstrated that joint immobilization significantly inhibits the spontaneous hyaline cartilage regeneration induced by the DN gel implantation. This fact suggested that the mechanical environment is one of the significant factors to induce this phenomenon.

Spontaneous hyaline cartilage regeneration can be induced in an osteochondral defect created in the femoral condyle using a novel double-network hydrogel
Masashi Yokota, Kazunori Yasuda, Nobuto Kitamura, Kazunobu Arakaki, Shin Onodera, Takayuki Kurokawa, Jian-Ping Gong
BMC MUSCULOSKELETAL DISORDERS, 12, -, 49, -, BIOMED CENTRAL LTD, Feb. 2011, [Peer-reviewed]
English, Scientific journal, Background: Functional repair of articular osteochondral defects remains a major challenge not only in the field of knee surgery but also in tissue regeneration medicine. The purpose is to clarify whether the spontaneous hyaline cartilage regeneration can be induced in a large osteochondral defect created in the femoral condyle by means of implanting a novel double-network (DN) gel at the bottom of the defect.
Methods: Twenty-five mature rabbits were used in this study. In the bilateral knees of each animal, we created an osteochondral defect having a diameter of 2.4-mm in the medial condyle. Then, in 21 rabbits, we implanted a DN gel plug into a right knee defect so that a vacant space of 1.5-mm depth (in Group I), 2.5-mm depth (in Group II), or 3.5-mm depth (in Group III) was left. In the left knee, we did not apply any treatment to the defect to obtain the control data. All the rabbits were sacrificed at 4 weeks, and the gross and histological evaluations were performed. The remaining 4 rabbits underwent the same treatment as used in Group II, and real-time PCR analysis was performed at 4 weeks.
Results: The defect in Group II was filled with a sufficient volume of the hyaline cartilage tissue rich in proteoglycan and type-2 collagen. The Wayne's gross appearance and histology scores showed that Group II was significantly greater than Group I, III, and Control (p < 0.012). The relative expression level of type-2 collagen, aggrecan, and SOX9 mRNAs was significantly greater in Group II than in the control group (p < 0.023).
Conclusions: This study demonstrated that spontaneous hyaline cartilage regeneration can be induced in vivo in an osteochondral defect created in the femoral condyle by means of implanting the DN gel plug at the bottom of the defect so that an approximately 2-mm deep vacant space was intentionally left in the defect. This fact has prompted us to propose an innovative strategy without cell culture to repair osteochondral lesions in the femoral condyle.

Synthetic hydrogels as scaffolds for manipulating endothelium cell behaviors
Yong-mei Chen, Jing-jing Yang, Yoshihito Osada, Jian Ping Gong
CHINESE JOURNAL OF POLYMER SCIENCE, 29, 1, 23, 41, SPRINGER, Jan. 2011, [Peer-reviewed], [Invited]
English, Scientific journal, Synthetic hydrogels can be used as scaffolds that not only favor endothelial cells (ECs) proliferation but also manipulate the behaviors and functions of the ECs. In this review paper, the effect of chemical structure, Young's modulus (E) and zeta potential (zeta) of synthetic hydrogel scaffolds on static cell behaviors, including cell morphology, proliferation, cytoskeleton structure and focal adhesion, and on dynamic cell behaviors, including migration velocity and morphology oscillation, as well as on EC function such as anti-platelet adhesion, are reported. It was found that negatively charged hydrogels, poly(2-acrylamido-2-methylpropanesulfonic sodium) (PNaAMPS) and poly(sodium p-styrene sulphonate) (PNaSS), can directly promote cell proliferation, with no need of surface modification by any cell-adhesive proteins or peptides at the environment of serum-containing medium. In addition, the Young's modulus (E) and zeta potential (zeta) of hydrogel scaffolds are quantitatively tuned by copolymer hydrogels, poly(NaAMPS-co-DMAAm) and poly(NaSS-co-DMAAm), in which the two kinds of negatively charged monomers NaAMPS and NaSS are copolymerized with neutral monomer, N,N-dimethylacrylamide (DMAAm). It was found that the critical zeta potential of hydrogels manipulating EC morphology, proliferation, and motility is zeta (critical) = -20.83 mV and zeta (critical) = -14.0 mV for poly(NaAMPS-co-DMAAm) and poly(NaSS-co-DMAAm), respectively. The above mentioned EC behaviors well correlate with the adsorption of fibronectin, a kind of cell-adhesive protein, on the hydrogel surfaces. Furthermore, adhered platelets on the EC monolayers cultured on the hydrogel scaffolds obviously decreases with an increase of the Young's modulus (E) of the hydrogels, especially when E > 60 kPa. Glycocalyx assay and gene expression of ECs demonstrate that the anti-platelet adhesion well correlates with the EC-specific glycocalyx. The above investigation suggests that understanding the relationship between physic-chemical properties of synthetic hydrogels and cell responses is essential to design optimal soft and wet scaffolds for tissue engineering.

Long-term in situ observation of barnacle growth on soft substrates with different elasticity and wettability
Nafees Ahmed, Takayuki Murosaki, Akira Kakugo, Takayuki Kurokawa, Jian Ping Gong, Yasuyuki Nogata
SOFT MATTER, 7, 16, 7281, 7290, ROYAL SOC CHEMISTRY, 2011, [Peer-reviewed]
English, Scientific journal, In this paper, settlement, metamorphosis, and long term growth of barnacles on soft substrates with a wide elasticity range (modulus 0.01-0.47 MPa) as well as with the variation in wettability were investigated for the first time in vitro, in the laboratory environment. Tough double-network (DN) hydrogels and polydimethylsiloxane (PDMS) were used as the soft hydrophilic substrates and hydrophobic substrates, respectively, and polystyrene (PS), a hard and hydrophobic substrate, was used as a control. It was observed that (1) the initial settlement and metamorphosis of cyprid larvae dramatically increase with the substrate elastic modulus while not showing an explicit dependence on the substrate wettability; (2) the growth rate of barnacles on both DN gels and PDMSs does not show an explicit dependence on the elasticity of the soft substrates, while it shows a slightly higher value on the hydrophobic PDMSs than on the hydrophilic DN gels; (3) the growth rate on these soft substrates is explicitly lower than that on the rigid PS substrate at the late stage of the growth; (4) the "self-release'' phenomenon of barnacles was observed for the PDMS substrate with a modulus higher than 0.01 MPa. Based on these observations, the antifouling effects of the soft substrates on barnacles were discussed.

Dynamic self-organization and polymorphism of microtubule assembly through active interactions with kinesin
Yoshiki Tamura, Ryuzo Kawamura, Kazuhiro Shikinaka, Akira Kakugo, Yoshihito Osada, Jian Ping Gong, Hiroyuki Mayama
SOFT MATTER, 7, 12, 5654, 5659, ROYAL SOC CHEMISTRY, 2011, [Peer-reviewed]
English, Scientific journal, In this study, we show that the energy-dissipative active self-assembly of microtubules (MTs) via a kinesin-based motility system produces various MT assemblies such as bundle-, network-, and ring-shaped structures depending on the initial conditions. Structural polymorphism of the MT assembly is depicted through phase diagrams, and morphogenesis of the MT assembly is discussed based on the following factors: binding force between MTs and motility-driving force from kinesins. This study provides new insights into the energy-dissipative dynamic self-organization of biological systems.

Hydrogel with cubic-packed giant concentric domains of semi-rigid polyion complex
Zi Liang Wu, Md Arifuzzaman, Takayuki Kurokawa, Hidemitsu Furukawa, Jian Ping Gong
SOFT MATTER, 7, 5, 1884, 1889, ROYAL SOC CHEMISTRY, 2011, [Peer-reviewed]
English, Scientific journal, We report a novel giant oriented structure observed in plate hydrogels synthesized by photo-polymerization of cationic monomers with a cross-linker in the presence of a semi-rigid polyanion as the dopant. The giant structure, formed via self-assembly of the semi-rigid polyion complex, consists of millimetre-scale cubic packed concentric cylindrical domains that are sandwiched by two homeotropically aligned outer layers. A universal relationship between the diameter of the cylinders D and the thickness of the swollen gel T is observed, as D = 0.5T, regardless the change in the concentrations of the polyanion and precursor cationic monomer. This result permits us to induce the giant concentric structure into hydrogels with tunable cylindrical sizes.

Unidirectional Alignment of Lamellar Bilayer in Hydrogel: One-Dimensional Swelling, Anisotropic Modulus, and Stress/Strain Tunable Structural Color
Md. Anamul Haque, Gen Kamita, Takayuki Kurokawa, Kaoru Tsujii, Jian Ping Gong
ADVANCED MATERIALS, 22, 45, 5110, +, WILEY-V C H VERLAG GMBH, Dec. 2010, [Peer-reviewed]
English, Scientific journal, A novel anisotropic hydrogel, consisting of lamellar bilayers and a polymer network, with unidirectional alignment of the bilayer structure has been synthesized. The unidirectional orientation of bilayer in the gels leads to one-dimensional swelling, strong anisotropy in elastic modulus, and exhibits excellent visible color. The gel shows reversibly tunable structural color under mechanical stimulation and could be the basis for a deformation-based color display.

海藻にフジツボが付着しないのはなぜか−海藻に学ぶ抗生物付着ゲルの開発−　　　　　　　　　　　　　　　
室﨑喬之, 龔剣萍
BIOINDUSTRY, 27, 12, 63, 71, Nov. 2010, [Invited]
Japanese, Scientific journal

Study on the Sliding Friction of Endothelial Cells Cultured on Hydrogel and the Role of Glycocalyx on Friction Reduction
Yong Mei Chen, Takayuki Kurokawa, Taiki Tominaga, Kazunori Yasuda, Yoshihito Osada, Jian Ping Gong, Kimiko Yamamoto, Joji Ando
ADVANCED ENGINEERING MATERIALS, 12, 11, B628, B636, WILEY-V C H VERLAG GMBH, Nov. 2010, [Peer-reviewed]
English, Scientific journal, We investigate the sliding friction of HUVEC monolayers cultured on PNaSS gel, intending to elucidate the role of glycocalyx on the surface of ECs in friction reduction. Three sets of HUVEC monolayers are investigated: an as-cultured HUVEC monolayer; a HUVEC monolayer treated with TGF-beta(1), which increases the glycocalyx by 148%; and a HUVEC monolayer treated with heparinase I, which reduces the glycocalyx by 57%. When being slid on a flat, glass surface, the frictional stress of the HUVEC monolayer decreases in the order: heparinase-I-treated> as-cultured> TGF-beta(1)-treated samples. The results suggest that glycocalyx may play a role in reducing the friction of endothelial cell monolayer.

Water-Induced Brittle-Ductile Transition of Double Network Hydrogels
Hiroko Itagaki, Takayuki Kurokawa, Hidemitsu Furukawa, Tasuku Nakajima, Yukiteru Katsumoto, Jian Ping Gong
MACROMOLECULES, 43, 22, 9495, 9500, AMER CHEMICAL SOC, Nov. 2010, [Peer-reviewed]
English, Scientific journal, In the previous studies, we have developed double network hydrogels (DN gels) with extra ordinarily high mechanical strength and toughness although the gels contain 90 wt % of water In this study we investigated the effect of water content on the mechanical behavior of the DN gel consists of poly(2 acrylamido 2 methylpropanesulfonic acid) gels (PAMPS gels) as the first network and polyacrylamide gels (PAAm gels) as the second network When the DN gel was dried gradually from its equilibrium swelling state (90 wt % water content) it exhibited a ductile behavior with a very high fracture stress and strain at an intermediate water content c (65 wt % < c < 75%) and then became brittle upon further decreasing in water content (c < 60 wt %) The behavior of the DN gel was compared with the corresponding single network gels, PAMPS and PAAm It is found that at the intermediate water content the fracture stress and strain of PAAm gel reached maximum, and the brittle ductile change of DN gel upon with the change in water content was the results of the change in the mechanical properties of PAAm network

Gene expression, glycocalyx assay, and surface properties of human endothelial cells cultured on hydrogel matrix with sulfonic moiety: Effect of elasticity of hydrogel
Jing Jing Yang, Yong Mei Chen, Takayuki Kurokawa, Jian Ping Gong, Shin Onodera, Kazunori Yasuda
JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 95A, 2, 531, 542, WILEY-LISS, Nov. 2010, [Peer-reviewed]
English, Scientific journal, We measured the gene expression, glycocalyx content, and surface properties of human coronary artery endothelial cells (HCAECs) cultured on poly(sodium p-styrene sulfonate) (PNaSS) hydrogels with various levels of elasticity ranged in 3-300 kPa. We found that all HCAECs reached confluence on these hydrogels while retaining the similar expression of EC-specific markers to that on polystyrene (PS), a widely used scaffold in cell culture in vitro. Real-time polymerase chain reaction (PCR) and glycosaminoglycan (GAG) assay showed that the amount of EC-specific glycocalyx secreted by HCAECs cultured on PNaSS gels was higher than that cultured on PS, and it increased with an increase of gel elasticity. Furthermore, the HCAECs cultured on PNaSS gels showed excellent property against platelet adhesion and lower surface friction than that on PS. The platelet adhesion and surface friction of HCAECs cultured on PNaSS gels also depend on the elasticity of gels. The largest amount of EC-specific glycocalyx, excellent blood compatibility, and the lowest friction were observed when the elastic modulus of the gel was larger than 60 kPa. Overall, HCAECs cultured on these hydrogels have better properties than those cultured on PS scaffold, demonstrating the PNaSS gels can be used as potential tissue engineering material for blood vessels. (C) 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 95A: 531542, 2010.

Dual Network Formation in Polyelectrolyte Hydrogel via Viscoelastic Phase Separation: Role of Ionic Strength and Polymerization Kinetics
Zi Liang Wu, Takayuki Kurokawa, Songmiao Liang, Jian Ping Gong
MACROMOLECULES, 43, 19, 8202, 8208, AMER CHEMICAL SOC, Oct. 2010, [Peer-reviewed]
English, Scientific journal, In this Article, we report a systematic research on a hydrogel with dual networks or 10(4) times difference in mesh sizes. The structure was developed by polymerizing a cationic monomer N-[3-(N.N-dimethylamino)propyl] acrylamide methyl chloride quarternary (DMAPAA-Q) in the presence of a small amount of semirigid polyanion, poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT). During the polymerization, polyion complexes were formed, which caused viscoelastic phase separation (VPS) due to the self-assembly of the semirigid polyion complexes, whereupon the dynamic coupling or phase separation and gelation is crucial for the structure formation. When PBDT was above its overlap concentration (C(PBDT) > C*), a critical concentration of cationic monomer, C(Q) approximate to 1.5 M, was observed, below which VPS occurred and turbid hydrogels with the dual network structure were formed, whereas above which, a transparent, anisotropic hydrogel was formed. It has been elucidated that the critical effect of C(Q) on the VPS process is through the ionic strength mechanism. That is, the abundant unreacted cationic monomer at high C(Q) behaves as a simple salt that screens the electrostatic interaction between the polycation and PBDT and therefore suppresses the occurrence of the phase separation. Furthermore, we investigated the effects of reaction kinetics on the VPS and the microstructure of gels by changing the concentrations of photoinitiator and chemical cross-linker. The dual network gels possess controllable turbidity degrees and mesh sizes corresponding to different quench depths of the phase separation. On the basis of these results, as well as in situ observation of the structure formation during the polymerization, we proposed a detailed mechanism for the formation or dual networks and the anisotropic hydrogels.

An Approach towards Artificial Biotissues
KAKUGO Akira, GONG JianPing
Seibutsu Butsuri, 50, 5, 244, 247, The Biophysical Society of Japan General Incorporated Association, 25 Sep. 2010
Japanese

PAMPSおよびPDMAAmゲルはPAMPS/PDMAAmダブルネットワークゲルと同じ関節軟骨自然再生誘導能を有するか
小川 宗宏, 北村 信人, 新垣 和伸, 黒川 孝幸, Gong Jian Ping, 田中 康仁, 高倉 義典, 安田 和則
日本整形外科学会雑誌, 84, 8, S1061, S1061, (公社)日本整形外科学会, Aug. 2010
Japanese

Spontaneous Redifferentiation of Dedifferentiated Human Articular Chondrocytes on Hydrogel Surfaces
Jing Jing Yang, Yong Mei Chen, Jian Fang Liu, Takayuki Kurokawa, Jian Ping Gong
TISSUE ENGINEERING PART A, 16, 8, 2529, 2540, MARY ANN LIEBERT, INC, Aug. 2010, [Peer-reviewed]
English, Scientific journal, Chondrocytes rapidly dedifferentiate into a more fibroblastic phenotype on a two-dimensional polystyrene substratum. This impedes fundamental research on these cells as well as their clinical application. This study investigated the redifferentiation behavior of dedifferentiated chondrocytes on a hydrogel substratum. Dedifferentiated normal human articular chondrocyte-knee (NHAC-kn) cells were released from the sixth-passage monolayer cultured on a polystyrene surface. These cells were then subcultured on a chemically crosslinked copolymer hydrogel, that is, poly(NaAMPS-co-DMAAm), and the cells thus obtained were used as the seventh-passage cultivation. Copolymer gels were synthesized from a negatively charged monomer, the sodium salt of 2-acrylamido-2-methyl-1-propanesulfonic acid (NaAMPS), and a neutral monomer, N,N-dimethylacrylamide (DMAAm). These gels were of different compositions because the molar fraction (F) of NaAMPS was varied (F = 0, 0.2, 0.4, 0.6, 0.8, and 1.0). The dedifferentiated NHAC-kn cells spontaneously redifferentiated to normal NHAC-kn cells on neutral (F = 0) and poly(NaAMPS-co-DMAAm) hydrogels of low charge density (F = 0.2). This was deduced from the cell morphology and expression of cartilage-specific genes and proteins. These results should enable us to establish a simple and efficient method for preparing large amounts of chondrocytes by cultivation on the surfaces of neutral and low-charge-density hydrogels.

高強度ダブルネットワークゲル　　　　　　　　　　　　　　　
黒川孝幸, 龔剣萍
化学工学会誌, 74, 7, 338, 340, Jul. 2010, [Invited]
Japanese, Scientific journal

Hydrogels with Cylindrically Symmetric Structure at Macroscopic Scale by Self-Assembly of Semi-rigid Polyion Complex
Zi Liang Wu, Takayuki Kurokawa, Songmiao Liang, Hidemitsu Furukawa, Jian Ping Gong
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132, 29, 10064, 10069, AMER CHEMICAL SOC, Jul. 2010, [Peer-reviewed]
English, Scientific journal, A hydrogel with cylindrically symmetric structure at macroscopic scale has been developed by polymerization of a cationic monomer in the presence of a small amount of semi-rigid polyanion poly(2,2'-disulfony1-4,4'-benzidine terephthalamide) (PBDT) in a cylinder glass tube. The polyion complex radially aligns in the outer region of the synthesized cylinder gel. On the other hand, it orients in concentric and axial directions in the inner region. To the authors' knowledge, this is the first report of such millimeter-scale ordered structure developed in a polymeric hydrogel. We elucidate that homeotropic alignment on the glass wall is energetically favorable for the semi-rigid polyion complex, resulting in the radial orientation in the outer region. In the inner region, the oriented structures result from the monomer diffusion (due to the heterogeneous polymerization) that induces PBDT orientation perpendicular to the diffusion direction. The structured gels showing sensitive response of birefringence to external force are expected to find applications in optical sensors.

A facile method for synthesizing free-shaped and tough double network hydrogels using physically crosslinked poly(vinyl alcohol) as an internal mold
Tasuku Nakajima, Naoyuki Takedomi, Takayuki Kurokawa, Hidemitsu Furukawa, Jian Ping Gong
POLYMER CHEMISTRY, 1, 5, 693, 697, ROYAL SOC CHEMISTRY, Jul. 2010, [Peer-reviewed], [Invited]
English, Scientific journal, The creation of double network hydrogels (DN gels), which show extremely high mechanical strength, enable hydrogels to be applied both in medical and industrial fields. However, one obstacle for various applications is the lack of formability of DN gels, owing to the brittleness of the first network PAMPS gels. In order to overcome this problem, we synthesized free-shaped DN gels (called PVA-DN gels) by using a physically cross-linked PVA gel as an "internal mold". PVA-DN gels can form any complex shapes and their mechanical properties were comparable to those of conventional DN gels. This study may expand the application of tough hydrogels.

Artificial cartilage made from a novel double-network hydrogel: In vivo effects on the normal cartilage and ex vivo evaluation of the friction property
Kazunobu Arakaki, Nobuto Kitamura, Hiroyuki Fujiki, Takayuki Kurokawa, Mikio Iwamoto, Masaru Ueno, Fuminori Kanaya, Yoshihito Osada, Jian Ping Gong, Kazunori Yasuda
JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 93A, 3, 1160, 1168, WILEY-LISS, Jun. 2010, [Peer-reviewed]
English, Scientific journal, This study evaluated the in vivo influence of a poly-(2-Acrylamido-2-methylpropane sulfonic acid)/poly(N,N'-dimetyl acrylamide) (PAMPS/PDMAAm) double-network (DN) hydrogel on counterface cartilage in rabbit knee joints and its ex vivo friction properties on normal cartilage. In the first experiment, the DN gel was implanted in a surgically created defect in the femoral trochlea of rabbit knee joints and the left knee was used as the control. Evaluations using a confocal laser scanning microscopy demonstrated that the DN gel did not affect the surface microstructure (surface roughness, the number of small pits) of the counterface cartilage in viva at 4 and 12 weeks. The histology also showed that the DN gel had no pathological damage on the cartilage matrices and cells at 4 weeks. However, two of the five DN gel-implanted knees showed mild irregularity on the counterface cartilage surface at 12 weeks. In the second experiment, the friction property between the normal and the artificial cartilage was determined using a joint simulator apparatus. The ex vivo mean friction coefficient of the DN gel to normal cartilage was 0.029, while that of the normal-to-normal cartilage articulation was 0.188. The coefficient of the DN gel-to-normal cartilage articulation was significantly lower than that of the normal-to-normal cartilage articulation (p < 0.0001). This study suggested that the PAMPS/PDMAAm DN gel has very low friction coefficient on normal cartilage and has no significant detrimental effects on counterface cartilage in vivo, and can be a promising material to develop the artificial cartilage. (C) 2009 Wiley Periodicals, Inc. J Biomed Mater Res 93A: 1160-1168, 2010

Microtubule bundle formation driven by ATP: the effect of concentrations of kinesin, streptavidin and microtubules
Ryuzo Kawamura, Akira Kakugo, Yoshihito Osada, Jian Ping Gong
NANOTECHNOLOGY, 21, 14, 145603, IOP PUBLISHING LTD, Apr. 2010, [Peer-reviewed]
English, Scientific journal, Recently, a method was established for the formation of microtubule (MT) assemblies by an active self-organization (AcSO) process, in which MTs were crosslinked during sliding motion on a kinesin-coated surface, and this was coupled with adenosine triphosphate (ATP) hydrolysis. Streptavidin (ST) was the glue used to crosslink biotin-labeled MTs. Although most of the MT assemblies were in the bundle form, they varied in size, shape and motility, depending on the initial conditions used. In this paper, we systematically examined the effects of the concentrations of kinesin, ST and MT on the formation of MT bundles under the initial conditions of the process.

Formation of a strong hydrogel-porous solid interface via the double-network principle
Takayuki Kurokawa, Hidemitsu Furukawa, Wei Wang, Yoshimi Tanaka, Jian Ping Gong
ACTA BIOMATERIALIA, 6, 4, 1353, 1359, ELSEVIER SCI LTD, Apr. 2010, [Peer-reviewed]
English, Scientific journal, A method for binding a tough double-network (ON) hydrogel and a porous solid utilizing the double-network principle is proposed. The effects of the pore size of the solid and the structure of the DN gel in the pores on bonding strength were investigated by a peeling test. Porous solids with pore sizes of the order of several microns afforded strong gel-substrate interfaces. Under optimal conditions a bonding strength as high as similar to 1000 N m(-1) was reached. The results obtained were compared with the strength of the bulk DN gel, and discussed in terms of the double-network principle at the bonding interface. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

超高強度ダブルネットワークゲルの創製とその高強度化メカニズム
中島 祐, 龔 剣萍
物性研究, 93, 5, 551, 557, 物性研究刊行会, Feb. 2010, [Invited]
Japanese, Scientific journal

Ligament-like tough double-network hydrogel based on bacterial cellulose
Yui Hagiwara, Ananda Putra, Akira Kakugo, Hidemitsu Furukawa, Jian Ping Gong
CELLULOSE, 17, 1, 93, 101, SPRINGER, Feb. 2010, [Peer-reviewed], [Invited]
English, Scientific journal, Using the double-network (DN) method, bacterial cellulose/polyacrylamide (BC/PAAm) DN gels able to sustain not only high elongation but also high compression have been synthesized by combining BC gel as the first network with PAAm as the second network in the presence of N,N'-methylene bisacrylamide (MBAA) as a cross-linker. This DN gel was obtained by modifying the monomer concentration of the second network, acrylamide monomer (AAm) and MBAA, and by controlling the water content of the first network, BC gel. The mechanical properties are discussed in term of the swelling degree (q), which is independent of the concentration of AAm and MBAA. It was found that, for BC/PAAm DN gels with the first network formed from BC gel with high q (BC(q=120)), the tensile and compressive modulus (E) scales with q as E proportional to q(-2). The tensile fracture stress, sigma(F), of this DN gel was almost independent of q, that is sigma(F) proportional to q(0); but the compressive fracture stress, sigma(F), scaled with q as E proportional to q(-2). Meanwhile, the tensile and compressive fracture strain (epsilon(F)) of the gel is almost independent of q, which is caused by AAm concentration change, but linearly increased with q, which is caused by MBAA concentration change. Furthermore, by decreasing the water content of the BC gel prior to polymerization of the second (PAAm) network, a ligament-like tough BC/PAAm DN gel could be obtained with tensile strength of 40 MPa.

In vitro differentiation of chondrogenic ATDC5 cells is enhanced by culturing on synthetic hydrogels with various charge densities
Hyuck Joon Kwon, Kazunori Yasuda, Yoshihiro Ohmiya, Ken-ichi Honma, Yong Mei Chen, Jian Ping Gong
ACTA BIOMATERIALIA, 6, 2, 494, 501, ELSEVIER SCI LTD, Feb. 2010, [Peer-reviewed]
English, Scientific journal, We investigated the behavior of chondrogenic ATDC5 cells on synthetic polymer gels with various charge densities: negatively charged poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) gel, neutral poly(dimethylacrylamide) (PDMAAm) gel, and copolymer gels of 2-acrylamido-2-methyl-1-propanesulfonic acid and dimethylacrylamide P(AMPS-co-DMAAm) with different compositions (molar fractions of AMPS, F = 0.25, 0.5, 0.75). In insulin-free maintenance medium, the ATDC5 cells cultured on the highly negatively charged gels - PAMPS gel and the P(AMPS-co-DMAAm) copolymer gels (F = 0.75) - spread and became confluent at day 7, and interestingly formed nodules at day 14, expressing type 11 collagen and proteoglycan. This result demonstrates that the highly negatively charged gels can induce chondrogenic differentiation of ATDC5 cells even in insulin-free maintenance medium, in which the ATDC5 cells cultured on the standard polystyrene dish cannot differentiate into chondrocytes. In insulin-supplemented differentiation medium, ATDC5 cells cultured on the PDMAAm gel made focal adhesions, rapidly aggregated and formed large nodules within 7 days, expressing significantly greater levels of type 11 collagen and proteoglycan than cells cultured on the polystyrene dish and the negatively charged gels. These results showed that the neutral gel accelerated chondrogenic differentiation of ATDC5 cells cultured in the differentiation medium. We suggest that the highly negatively charged PAMPS gel and the neutral PDMAAm gel are interesting biomaterials for cartilage tissue engineering as a scaffold with the potential to induce chondrogenic differentiation. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Why are double network hydrogels so tough?
Jian Ping Gong
SOFT MATTER, 6, 12, 2583, 2590, ROYAL SOC CHEMISTRY, 2010, [Peer-reviewed], [Invited]
English, Scientific journal, Double-network (DN) gels have drawn much attention as an innovative material having both high water content (ca. 90 wt%) and high mechanical strength and toughness. DN gels are characterized by a special network structure consisting of two types of polymer components with opposite physical natures: the minor component is abundantly cross-linked polyelectrolytes (rigid skeleton) and the major component comprises of poorly cross-linked neutral polymers (ductile substance). The former and the latter components are referred to as the first network and the second network, respectively, since the synthesis should be done in this order to realize high mechanical strength. For DN gels synthesized under suitable conditions (choice of polymers, feed compositions, atmosphere for reaction, etc.), they possess hardness (elastic modulus of 0.1-1.0 MPa), strength (failure tensile nominal stress 1-10 MPa, strain 1000-2000%; failure compressive nominal stress 20-60 MPa, strain 90-95%), and toughness (tearing fracture energy of 100 similar to 1000 J m(-2)). These excellent mechanical performances are comparable to that of rubbers and soft load-bearing bio-tissues. The mechanical behaviors of DN gels are inconsistent with general mechanisms that enhance the toughness of soft polymeric materials. Thus, DN gels present an interesting and challenging problem in polymer mechanics. Extensive experimental and theoretical studies have shown that the toughening of DN gel is based on a local yielding mechanism, which has some common features with other brittle and ductile nano-composite materials, such as bones and dentins.

A Deformation Mechanism for Double-Network Hydrogels with Enhanced Toughness
Tasuku Nakajima, Hidemitsu Furukawa, Jian Ping Gong, Eric K. Lin, Wen-li Wu
POLYMER NETWORKS: SYNTHESIS, PROPERTIES, THEORY AND APPLICATIONS, 291-292, 122, +, WILEY-V C H VERLAG GMBH, 2010, [Peer-reviewed], [Invited]
English, International conference proceedings, The long-standing pursuit of a synthetic equivalent to tissue cartilage has sprouted significant new activities in strategies for new material synthesis, among them a noticeable one being the double-network hydrogels (DN-gels) scheme. DN-gels were prepared from the combination of an anionic polyelectrolyte network and a lightly crosslinked neutral polymer. These hydrogels exhibit an intriguing combination of properties intrinsic to natural cartilage: a low surface friction coefficient and a fracture toughness much higher than either of the constituent materials. The reinforcement of a hard, brittle polymer gel with a soft, viscoelastic neutral polymer is counter-intuitive. Based on our recent results from neutron scattering measurements, we proposed a deformation mechanism where the molecular association between these two polymers plays a pivotal role. In this work, we further evaluate the proposed mechanism by performing mechanical measurements on DN-gel samples with different polyelectrolyte network structure. The experimental results provide qualitative support for the proposed deformation mechanism.

Hierarchical structures of the actin/polycation complexes, investigated by ultra-small-angle neutron scattering and fluorescence microscopy
Tomomi Masui, Satoshi Koizumi, Takeji Hashimoto, Kazuhiro Shikinaka, Akira Kakugo, Jian Ping Gong
SOFT MATTER, 6, 9, 2021, 2030, ROYAL SOC CHEMISTRY, 2010, [Peer-reviewed]
English, Scientific journal, By employing a combined method of ultra-small-angle & small-angle neutron scattering (USANS&SANS) and fluorescence microscopy (FM), we investigated the solution mixtures of filamentous actin (F-actin) and the synthesized cationic polymer poly-N-[3-(dimethylamino) propyl] acrylamide methylchloride quaternary (PDMAPAA-Q). The combined USANS&SANS method, covering a wide range of length scales from 10 micrometres to nanometres, plays a crucial role in elucidating the hierarchical structure of the complex structure, as it is in an aqueous solution. FM determined that the complex of F-actin and PDMAPAA-Q appears with a finite size (> 10 mu m), referred to as a superbundle, and its morphology changes from a globular one to a stretched one by increasing the salt (KCl) concentration C(s) from 0.01 to 0.3 M. USANS& SANS revealed that the superbundle is composed of a structural unit of a protobundle, in which PDMAPAA-Q binds F-actins in order to form a hexagonal lattice. The diameter of the protobundle (D(II)), determined by USANS& SANS, increases from 40 to 290 nm as C(s) increases from 0.01 to 0.3 M. In order to explain the finite-size & hierarchical condensation observed in the actin/PDMAPAA-Q solution, we employ a scenario of imperfect charge neutralization between F-actins and PDMAPAA-Q. Due to the chain connectivity of PDMAPAA-Q, a spatial distribution of positive charges around the F-actins becomes inhomogeneous, so that the repulsive electrostatic interaction appearing in the protobundle limits bundle formation with an infinite-size. The morphology of the superbundles is controlled by the bending rigidity due to individual protobundles, which significantly increases as D(II) increases.

A Polysaccharide-Based Container Transportation System Powered by Molecular Motors
Youichi Tsuchiya, Tomotaka Komori, Minako Hirano, Tomohiro Shiraki, Akira Kakugo, Toru Ide, Jian-Ping Gong, Sunao Yamada, Toshio Yanagida, Seiji Shinkai
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 49, 4, 724, 727, WILEY-V C H VERLAG GMBH, 2010, [Peer-reviewed]
English, Scientific journal

Selective Formation of a Linear-Shaped Bundle of Microtubules
Ryuzo Kawamura, Akira Kakugo, Yoshihito Osada, Jian Ping Gong
LANGMUIR, 26, 1, 533, 537, AMER CHEMICAL SOC, Jan. 2010, [Peer-reviewed]
English, Scientific journal, By using rigid microtubules (MTs) prepared by polymerization with guanylyl-(alpha, beta)-methylene-diphosphonate GMPCPP, giant straight-shaped MT bundles were selectively obtained through a dynamic self-assembly process. We demonstrate the effect of the rigidity oil the shape and motility of MT bundle composed of GMPCPP-polymerized MTs (GMPCPP-MTs) compared with control MTs that were polymerized with GTP and stabilized with paclitaxel.

Formation of Well-Oriented Microtubules with Preferential Polarity in a Confined Space under a Temperature Gradient
Akira Kakugo, Yoshiki Tamura, Kazuhiro Shikinaka, Momoko Yoshida, Ryuzo Kawamura, Hidemitsu Furukawa, Yoshihito Osada, Jian Ping Gong
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 131, 50, 18089, 18095, AMER CHEMICAL SOC, Dec. 2009, [Peer-reviewed]
English, Scientific journal, Tubulin polymerization in a confined space under a temperature gradient produced well-oriented microtubule assemblies with preferential polarity. We analyzed the structure and polarity of these assemblies at various levels of resolution by performing polarized light microscopy (millimeter order), fluorescence microscopy (micrometer order), and transmission electron microscopy (nanometer order).

Mesoscopic Network Structure of a Semi-Rigid Polyion Complex Nested in a Polycationic Hydrogel
Zi Liang Wu, Hidemitsu Furukawa, Wei Yang, Jian Ping Gong
ADVANCED MATERIALS, 21, 46, 4696, +, WILEY-V C H VERLAG GMBH, Dec. 2009, [Peer-reviewed]
English, Scientific journal, A dual network gel, consisting of a micrometer-scaled network-like structure of a semirigid polyion complex nested in a nanometer-scaled polycationic network, has been developed by polymerization of a cationic monomer in the presence of a small amount of semi-rigid polyanion as dopant. Self-assembly and viscoelastic phase separation (see figure) compete with each other during the polymerization and render the micrometer-scaled network structure, which is permanently frozen by the subsequent gelation.

ATP-Fueled Soft Gel Machine with Well-Oriented Structure Constructed Using Actin-Myosin System
Kazuhiro Shikinaka, Shintaro Takaoka, Akira Kakugo, Yoshihito Osada, Jian Ping Gong
JOURNAL OF APPLIED POLYMER SCIENCE, 114, 4, 2087, 2092, JOHN WILEY & SONS INC, Nov. 2009, [Peer-reviewed]
English, Scientific journal, Fibrous actomyosin gel was obtained by applying an external shear stress to actomyosin solution injected from a syringe and then performing chemical cross-linking. The actomyosin gel shrunk when ATP was added, and the shrinkage ratio was proportional to its ATPase activity. The shrinkage of the gel was repeatable at least for four times. Furthermore, the shrinkage of the gel enhanced the regular orientation of the actin and myosin filaments in the gel, which in turn enhanced the shrinking velocity of the gel. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 2087-2092, 2009

Development of a reciprocating-wear testing machine under an ex vivo condition to evaluate the effect of artificial cartilage on articulating cartilage
FUJIKI Hiroyuki, DAIMARUYA Masashi, KITAMURA Nobuto, KONDO Eiji, YASUDA Kazunori, CHEN Yong Mei, GONG Jian Ping, OSADA Yoshihito
Japanese journal of clinical biomechanics, 30, 0, 63, 70, 日本臨床バイオメカニクス学会, 20 Sep. 2009
Japanese

家兎膝関節骨軟骨欠損における高機能ダブルネットワークゲルを用いたin vivo軟骨自然再生誘導
北村 信人, 新垣 和伸, 黒川 孝幸, Gong Jian Ping, 長田 義仁, 安田 和則
日本整形外科学会雑誌, 83, 8, S1195, S1195, (公社)日本整形外科学会, Aug. 2009
Japanese

Electric field effect on the Sliding friction of a charged gel
Masakazu Takata, Tetsuo Yamaguchi, Jian Ping Gong, Masao Doi
Journal of the Physical Society of Japan, 78, 8, 084602-1, 081602-5, Aug. 2009, [Peer-reviewed]
English, Scientific journal, Sliding friction of a charged gel on a substrate was investigated by applying electric voltage between gel and the substrate. It is found that the sliding friction increases markedly with the increase of the applied voltage; the friction coefficient increased by a factor of about 10 when 70 V voltage is applied. This voltage dependence of frictional force is explained by using the adhesion friction model proposed by Schallamach. © 2009 The Physical Society of Japan.

First Observation of Stick-Slip Instability in Tearing of Poly(vinyl alcohol) Gel Sheets
Yoshimi Tanaka, Hiroyuki Abe, Takayuki Kurokawa, Hidemitsu Furukawa, Jian Ping Gong
MACROMOLECULES, 42, 15, 5425, 5426, AMER CHEMICAL SOC, Aug. 2009, [Peer-reviewed]
English, Scientific journal

Nano-biomachine from actin and myosin gels
Yoshihito Osada, Jian Ping Gong
POLYMER SCIENCE SERIES A, 51, 6, 689, 700, MAIK NAUKA/INTERPERIODICA/SPRINGER, Jun. 2009, [Invited]
English, Scientific journal, We introduce here an ATP (adenosine triphosphate)-fueled nano-biomachine constructed from actin and myosin gels. Various types of chemically cross-linked actin gel, which are tens of times larger in size than native actin filaments (F-actin), were formed by complexing with cation-polymers and placed on a chemically cross-linked myosin gel. By adding dilute solution of ATP, they moved along the myosin gel with a velocity as high as that of native F-actin by coupling to ATP hydrolysis. Formation mechanism and structure of actin complexes as well as those of myosin gels were studied in detail and elucidated with the specific characteristics of the motility. These results demonstrate that one can construct nano-biomachines fueled by chemical energy of ATP with controlled motility.

Direct Observation of Damage Zone around Crack Tips in Double-Network Gels
Qiu Ming Yu, Yoshimi Tanaka, Hidemitsu Furukawa, Takayuki Kurokawa, Jian Ping Gong
MACROMOLECULES, 42, 12, 3852, 3855, AMER CHEMICAL SOC, Jun. 2009, [Peer-reviewed]
English, Scientific journal

高強度ＤＮゲルの開発と関節軟骨再生誘導への応用　　　　　　　　　　　　　　　
中島 祐, 龔 剣萍, 安田和則
工業材料, 57, 6, 38, 41, May 2009, [Invited]
Japanese, Scientific journal

Double Network Hydrogel with High Modulus and Toughness : A Novel Material for Load-Bearing Soft Tissues
GONG Jian Ping
高分子, 58, 5, 327, 331, 高分子学会, May 2009, [Invited]
Japanese, Scientific journal

Photoinduced in situ formation of various F-actin assemblies with a photoresponsive polycation
Manami Misu, Hidemitsu Furukawa, Hyuck-Joon Kwon, Kazuhiro Shikinaka, Akira Kakugo, Toshifumi Satoh, Yoshihito Osada, Jian Ping Gong
JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 89A, 2, 424, 431, WILEY-LISS, May 2009, [Peer-reviewed]
English, Scientific journal, We developed a novel in situ method for the control of F-actin assembly by using a synthetic photoresponsive polycation. The photoresponsive polycation mainly comprises a water-soluble cationic monomer and also contains a small amount of the monomer of a triphenylmethane leucohydroxide derivative (20 mol %), which is a well-known photochromic molecule that can be cationized in aqueous solution by ultra violet (UV) irradiation, thereby causing an increase in the total charge on the photoresponsive polycation. Thus, by exposure to UV radiation in aqueous solution, F-actin and the photoresponsive polycation start assembling into F-actin/photoresponsive polycation complexes of various morphologies Such as bundles, coils, and networks, depending upon the concentrations of both the F-actin and salt. Further, localized UV irradiation can be applied in order to control the local formation of F-actin/photoresponsive polycation complexes. Thus, this technique provides a novel method for the spatiotemporal control of F-actin assembly and can be applied to investigate the unknown characteristics of F-actin. (C) 2008 Wiley Periodicals, Inc. J Biomed Mater Res 89A: 424-431, 2009

A Novel Double-Network Hydrogel Induces Spontaneous Articular Cartilage Regeneration in vivo in a Large Osteochondral Defect
Kazunori Yasuda, Nobuto Kitamura, Jian Ping Gong, Kazunobu Arakaki, Hyuck Joon Kwon, Shin Onodera, Yong Mei Chen, Takayuki Kurokawa, Fuminori Kanaya, Yoshihiro Ohmiya, Yoshihito Osada
MACROMOLECULAR BIOSCIENCE, 9, 4, 307, 316, WILEY-V C H VERLAG GMBH, Apr. 2009, [Peer-reviewed]
English, Scientific journal, We have developed a novel method to induce spontaneous hyaline cartilage regeneration in vivo for a large osteochondral defect by implanting a plug made from a double-network hydrogel composed of poly(2-acrylamido-2-methylpropanesulfonic acid) and poly(N,N'-dimethylacrylamide) at the bottom of the defect, leaving the cavity vacant. In cells regenerated in the treated defect, type-2 collagen, Aggrican, and SOX9 mRNAs were highly expressed and the regenerated matrix was rich in proteoglycan and type-2 collagen at 4 weeks. This fact gave a significant modification to the commonly established concept that hyaline cartilage tissue cannot regenerate in vivo. This study prompted an innovative strategy in the field of joint ON gel surgery to repair an osteochondral defect using an advanced, high-function hydrogel.

True Chemical Structure of Double Network Hydrogels
Tasuku Nakajima, Hidemitsu Furukawa, Yoshimi Tanaka, Takayuki Kurokawa, Yoshihito Osada, Jian Ping Gong
MACROMOLECULES, 42, 6, 2184, 2189, AMER CHEMICAL SOC, Mar. 2009, [Peer-reviewed]
English, Scientific journal, We elucidate why the anomalous high strength of double network gels is obtained when the second network is polymerized without any cross-linkers. We have synthesized truly independent-DN gels (named "t-DN" gels), which do not have any covalent bonds between the first and the second networks, and showed that the t-DN gels cannot be toughened by the un-cross-linked second network. It means that the high strength of Usual DIN gels without the cross-linker of the second network is actually achieved by the interconnection between the two networks through covalent bonds (so usual DN gels were named "c-DN" gels). Further, we found that the t-DN gels become stronger than the c-DN gels when the second network is loosely cross-linked. As the t-DN gels have a more simple structure than the c-DN gels, we expect that the toughening mechanism of DN gels will be clarified by studying the t-DN gels in the future.

Mechanism on Polarity Sorting of Actin Bundles Formed with Polycations
Kazuhiro Shikinaka, Akira Kakugo, Yoshihito Osada, Han Ping Gong
LANGMUIR, 25, 3, 1554, 1557, AMER CHEMICAL SOC, Feb. 2009, [Peer-reviewed]
English, Scientific journal, In this paper we explored factors that determine the polarity of an Actin bundle formed with polycation through electrostatic interaction. We found that the polarity decreases with an increase in the polycation concentration while it hardly depends on the KCl salt concentration. Additionally, the polarity of the Actin bundle increases with an increase in the degree of polymerization of the polycation at a constant polymer concentration. From these results we proposed that the kinetics of nuclei formation determines the polarity of the Actin bundle.

Dynamics in Multicomponent Polyelectrolyte Solutions
Sanghun Lee, Vijay R. Tirumala, Michihiro Nagao, Taiki Tominaga, Eric K. Lin, Jian Ping Gong, Wen-li Wu
MACROMOLECULES, 42, 4, 1293, 1299, AMER CHEMICAL SOC, Feb. 2009, [Peer-reviewed]
English, Scientific journal, Double-network hydrogels (DN-gels) prepared from the combination of a moderately cross-linked anionic polyelectrolyte (poly(2-acrylamido-2-methyl-1-propanesulfonic acid), PAMPS) and an un-cross-linked linear polymer (polyacrylamide, PAAm) Solution show strong mechanical properties far superior to that of their individual Constituents. To determine the origin of the superior properties of DN-gels, we investigated the structure and the chain dynamics of model PAMPS/PAAm solution blends using small-angle neutron scattering and neutron spin-echo measurements. Akcasu's dynamic scattering theory fora multicomponent System is modified to include polyelectrolytes, and the resulting equation describes well the neutron spin-echo results over the entire wavevector ran,ye covered in our experiments, Parameters such as effective solvent viscosity were deduced from the measured data using the modified Akcasu equation. Both the relaxation time at large length scales (10-100 nm) and the segmental diffusion coefficient at short length scales (1-10 A) or the effective solvent viscosity show good accordance with the macroscopic rheological behavior of the solution blends.

Adhesion, Spreading, and Proliferation of Endothelial Cells on Charged Hydrogels
Yong Mei Chen, Jing Jing Yang, Jian Ping Gong
JOURNAL OF ADHESION, 85, 11, 839, 868, TAYLOR & FRANCIS LTD, 2009, [Peer-reviewed], [Invited]
English, Scientific journal, As soft and wet scaffolds, hydrogels are attractive materials for tissue engineering due to their similarity in structure and properties to living tissue. For designing hydrogels as potential artificial tissues, some basic requirements, such as a high level of cellular viability, suitable viscoelasticity, and high mechanical strength, are required. However, it is difficult to develop a hydrogel that satisfies even two of these requirements at the same time. In this review, our recent advances in developing synthetic hydrogels as cell culture scaffold are summarized. We found that endothelial cells (ECs) can proliferate directly on some synthetic hydrogels with negative charge, so long as the hydrogels have a Zeta potential lower than ca. -20mV, and the cell behavior can be controlled by adjusting the hydrogel's charge density. Furthermore, confluent EC monolayers cultured on the hydrogels show excellent platelet compatibility, compared with an EC monolayer cultured on a polystyrene plate. On the basis of the above study, we have further developed micro-patterned hydrogels for selective cell spreading, proliferation, and orientation. We have also developed tough hydrogels on which cells show viability. These results will promote the potential applications of synthetic hydrogels in tissue engineering.

SUPER TOUGH GELS WITH A DOUBLE NETWORK STRUCTURE
Tasuku Nakajima, Takayuki Kurokawa, Hidemitsu Furukawa, Qiu Ming Yu, Yoshimi Tanaka, Yoshihito Osada, Jian Ping Gong
CHINESE JOURNAL OF POLYMER SCIENCE, 27, 1, 1, 9, WORLD SCIENTIFIC PUBL CO PTE LTD, Jan. 2009, [Peer-reviewed], [Invited]
English, Scientific journal, Living tissues work with fantastic functions in soft and wet gel-like state. Thus, hydrogels have attracted much attention as excellent soft and wet materials, suitable for making artificial organs for medical treatments. However, conventional hydrogels are mechanically too weak for practical uses. We have created double network (DN) hydrogels with extremely high mechanical strength in order to overcome this problem. DN gels are interpenetrating network (IPN) hydrogels consisting of rigid polyelectrolyte and soft neutral polymer. Their excellent mechanical properties cannot be explained by the standard fracture theories. In this paper, we discuss about the toughening mechanism of DN gels in accordance with their characteristic behavior, such as large hysteresis and necking phenomenon. We also describe the results on tissue engineering application of DN gels.

Ultrathin tough double network hydrogels showing adjustable muscle-like isometric force generation triggered by solvent
Songmiao Liang, Qiu Ming Yu, Haiyan Yin, Zi Liang Wu, Takayuki Kurokawa, Jian Ping Gong
CHEMICAL COMMUNICATIONS, 48, 7518, 7520, ROYAL SOC CHEMISTRY, 2009, [Peer-reviewed]
English, Scientific journal, Ultrathin double-network hydrogels, which have super-high toughness under micro-scale thickness (elastic elongation epsilon(b) > 1000%, tensile strength sigma(b) > 2 MPa and tearing energy G similar to B 600 J m(-2)), and solvent-triggered fast and high isometric stress generation, were synthesized by coupling the salt-controlled swelling process and polymer chain pre-reinforced technique.

Brittle, ductile, paste-like behaviors and distinct necking of double network gels with enhanced heterogeneity
Yasunori Kawauchi, Yoshimi Tanaka, Hidemitsu Furukawa, Takayuki Kurokawa, Tasuku Nakajima, Yoshihito Osada, Jian Ping Gong
Journal of Physics: Conference Series, 184, 12016, (8pp), Institute of Physics Publishing, 2009, [Peer-reviewed], [Invited]
English, International conference proceedings, We propose a simple method to obtain double network (DN) hydrogels containing 85-90wt% water with various kinds of mechanical performance by taking advantage of the heterogeneity of the first network: By synthesizing the first network in a poor solvent that enhancing the heterogeneity of the network, the DN gel exhibits rich mechanical behavior: from brittle, ductile (necking), to paste-like. For a proper heterogeneity, a distinct necking deformation with extensibility of about 20 times is observed for post-necking gels. The necking gels have a high initial modulus (0.1-0.5 MPa) and high mechanical toughness (nominal fracture stress: 1 MPa), both values are similar to that of living tissues. © 2009 IOP Publishing Ltd.

Orientated Bacterial Cellulose Culture Controlled by Liquid Substrate of Silicone Oil with Different Viscosity and Thickness
Ananda Putra, Akira Kakugo, Hidemitsu Furukawa, Jian Ping Gong
POLYMER JOURNAL, 41, 9, 764, 770, SOC POLYMER SCIENCE JAPAN, 2009, [Peer-reviewed]
English, Scientific journal, We report the effect of oxygen and viscoelasticity of culture interface on the orientation of bacterial cellulose (BC) fibril synthesized by Acetobacter xylimum (ATCC 53582) at a silicone oil/culture medium (liquid/liquid system) interface. In this work, we used the silicone oil with various kinematic viscosities, v ranging from 10 to 3000 centistokes (CS). We found that the birefringence, Delta n as a measure of degree of orientation, fibril width, w, swelling degree, q, and tensile modulus, E, increased as increase the thickness and viscosity of silicone oil. However, fracture stress, sigma(F) and fracture strain, lambda(F) decreased with increase the silicone oil thickness and viscosity. Further, we also found that viscoelasticity of culture interface plays an important role to determine the orientation alignment of BC fibrils. Meanwhile, oxygen did not show significant influence on orientation of BC fibrils.

Antifouling properties of tough gels against barnacles in a long-term marine environment experiment
T. Murosaki, T. Noguchi, K. Hashimoto, A. Kakugo, T. Kurokawa, J. Saito, Y. M. Chen, H. Furukawa, J. P. Gong
BIOFOULING, 25, 7, 657, 666, TAYLOR & FRANCIS LTD, 2009, [Peer-reviewed]
English, Scientific journal, In the marine environment, the antifouling (AF) properties of various kinds of hydrogels against sessile marine organisms (algae, sea squirts, barnacles) were tested in a long-term experiment. The results demonstrate that most hydrogels can endure at least 2 months in the marine environment. In particular, mechanically tough PAMPS/PAAm DN and PVA gels exhibited AF activity against marine sessile organisms, especially barnacles, for as long as 330 days. The AF ability of hydrogels toward barnacles is explained in terms of an `easy-release' mechanism in which the high water content and the elastic modulus of the gel are two important parameters.

Synthesis of Novel Double Network Hydrogels via Atom Transfer Radical Polymerization
Xufeng Ni, Ananda Putra, Hidemitsu Furukawa, Jian Ping Gong
COMPOSITE INTERFACES, 16, 4-6, 433, 446, VSP BV, 2009, [Peer-reviewed], [Invited]
English, Scientific journal, Novel double network (DN) hydrogels were prepared via atom transfer radical polymerization (ATRP) of the first network using two different initiators, and followed by ultraviolet (UV) photo-initiated polymerization for the second network. The first networks DN hydrogels were prepared by using two different initiators; one is a one-side initiator, and the other is a double-side initiator. The mechanical properties of various DN gels, such as water content and compressive strength, were studied. The network structure of the DN hydrogels was also characterized by dynamic light scattering. Thus, we demonstrated that the ATRP method is useful to control the network structure of the first network for DN gels. Extensive inhomogeneous structure of the first network wits obtained by ATRP method and increased both the swelling degree and softness of DN gels. (C) Koninklijke Brill NV, Leiden, 2009

Nonvolatile and Shape-Memorized Bacterial Cellulose Gels Swollen by Poly(ethylene glycol)
Yukari Numata, Kazumi Muromoto, Hidemitsu Furukawa, Jian Ping Gong, Kenji Tajima, Masanobu Munekata
POLYMER JOURNAL, 41, 7, 524, 525, SOC POLYMER SCIENCE JAPAN, 2009, [Peer-reviewed]
English, Scientific journal

Friction between like-charged hydrogels-combined mechanisms of boundary, hydrated and elastohydrodynamic lubrication
Shinsuke Oogaki, Go Kagata, Takayuki Kurokawa, Shinya Kuroda, Yoshihito Osada, Jian Ping Gong
SOFT MATTER, 5, 9, 1879, 1887, ROYAL SOC CHEMISTRY, 2009, [Peer-reviewed]
English, Scientific journal, The friction between two like-charged polyelectrolyte gels in pure water is measured by using a normal strain-controlled rheometer with a parallel-plates geometry. The effects of normal stress, gel elasticity and sample thickness on the velocity dependence of friction between the gels are investigated. The frictional stress demonstrates strong velocity dependence (liquid-like) when the gel is soft and thick, while it demonstrates a weak or even no velocity dependence (solid-like) when the gel is rigid and thin. The former is interpreted by a combined mechanism of boundary lubrication and hydrated lubrication, wherein the thickness of the lubricating layer is velocity-independent, due to the formation of an electric double layer at the soft and repulsive interfaces. On the other hand, the latter is interpreted by a combined mechanism of boundary lubrication and elastohydrodynamic lubrication, wherein the thickness of the lubricating layer is velocity-enhanced by the water entrainment during sliding. The friction of the soft, thick sample is related to micro-contact while that of the rigid, thin sample is related to macroscopic geometric effect. This work may contribute to the science of friction between two soft and repulsive interfaces in water.

Dynamic cell behavior on synthetic hydrogels with different charge densities
Yong Mei Chen, Rie Ogawa, Akira Kakugo, Yoshihito Osada, Jian Ping Gong
SOFT MATTER, 5, 9, 1804, 1811, ROYAL SOC CHEMISTRY, 2009, [Peer-reviewed]
English, Scientific journal, A series of polyNaSS-co-DMAAm) hydrogels with zeta potentials (zeta) in the range -8.8--20.5 mV and a constant Young's modulus E) of ca. 200 kPa were designed for studying the effect of the charge density of hydrogels on dynamic cell behavior. The zeta was adjusted by tuning the molar friction of negatively charged sodium p-styrene sulfonate NaSS) contained in the monomer mixture [ NaSS and N, N-dimethyl acrylamide DMAAm)] for gelation. A critical zeta potential, which controls cell behavior, zeta(crit) = -14.0 mV, was observed. When zeta > zeta(crit), the cells exhibited a small spreading area, fast migration velocity, and a large migration distance, with concurrent deficiency in actin fibers and less prominent focal adhesions. Conversely, when zeta <= zeta(crit), the cells exhibited a large spreading area, slow migration velocity, and a short migration distance, with concurrent well-developed actin fibers and prominent focal adhesions. Furthermore, cells repeatedly oscillated in a stick-slip mode from a spreading shape to a round shape on the hydrogels with zeta > zeta(crit), although were unable to proliferate. The cell behavior is well correlated with the adsorbed fibronectin on the hydrogel surfaces.

Antifouling activity of synthetic polymer gels against cyprids of the barnacle (Balanus amphitrite) in vitro
T. Murosaki, T. Noguchi, A. Kakugo, A. Putra, T. Kurokawa, H. Furukawa, Y. Osada, J. P. Gong, Y. Nogata, K. Matsumura, E. Yoshimura, N. Fusetani
BIOFOULING, 25, 4, 313, 320, TAYLOR & FRANCIS LTD, 2009, [Peer-reviewed]
English, Scientific journal, Barnacle (Balanus amphitrite) settlement on synthetic hydrogels with various chemical structures was tested in laboratory assays. The results demonstrated that cyprids settle less or not at all on hydrogels and PDMS elastomer compared with the polystyrene control. The low settlement on gels is most likely due to the 'easy release' of initially attached cyprids from the gel surfaces. This low adhesion of cyprids is independent of surface hydrophilicity or hydrophobicity, and of surface charge. The results also revealed that hydrogels can be categorized into two groups. One group showed an extremely strong antifouling (AF) performance that was independent of the elasticity (E) or swelling degree (q) of the gels. The second group showed relatively less strong AF performance that was E- or q-dependent. In the latter case, E, rather than the q, may be the more important factor for cyprid settlement.

Tuning of cell proliferation on tough gels by critical charge effect
Yong Mei Chen, Jian Ping Gong, Masaru Tanaka, Kazunori Yasuda, Sadaaki Yamamoto, Masatsugu Shimomura, Yoshihito Osada
JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 88A, 1, 74, 83, WILEY-LISS, Jan. 2009, [Peer-reviewed]
English, Scientific journal, Tough triple network (TN) hydrogels that facilitate cell spreading and proliferation and, at the same time, preserve high mechanical strength are synthesized by the introduction of a proper component of negatively charged moiety, poly(2-acrylamido-2-methyl-propane sulfonic acid sodium salt) (PNaAMPS), on which cells proliferate, with neutral moiety, poly(N,N-dimethylacrylamide) (DMAAm), on which cells do not proliferate, as the third network component, to PNaAMPS/PDMAAm double network (DN) gels. For synthesizing the tough TN gels to support cell viability, the effect of charge density on the behaviors of three kinds of cells, bovine fetal aorta endothelial cells (BFAECs), human umbilical endothelial cells (HUVECs), and rabbit synovial tissue-derived fibroblast cells (RSTFCs) were systematically investigated on poly(NaAMPS-co-DMAAm) gels with different charge density of the gels was tuned by changing the molar fraction (F) of negatively charged monomer in the copolymer hydrogels. Critical F, which corresponds to a critical value of the zeta potential (zeta), is observed for cell spreading and proliferation. The critical F for observed for cell spreading and proliferation. The critical F for BFAECs and HUVECs proliferate to confluent is F = 0.14 (zeta = -20 mV), whereas the critical F for RSTFCs shifts to F = 0.7 (zeta = -28.5 mV). The effect of gel charge density on cell behavior is correlated well with the total adsorbed proteins and fibronectin. By applying these results, cell proliferation is successfully realized on the tough TN hydrogels without surface modification with any cell adhesive proteins or peptides. The results will substantially promote the application of tough hydrogels as soft and west tissues. (C) 2008 Wiley Periodicals, Inc. J Biomed Mater Res 88A: 53-64, 2009

Structural approaches on the toughness in double network hydrogels
Taiki Tominaga, Yoshihito Osada, Jian Ping Gong
NATO Science for Peace and Security Series A: Chemistry and Biology, 117, 138, 2009
Scientific journal, Most hydrogels are mechanically too weak to be used as any load bearing devices. We have overcome this problem by synthesizing hydrogels with a double network (DN) structure. Despite the presence of 90% water in their composition, these tough gels exhibit a fracture stress of 170 kg/cm , similar to that of cartilage. The relation between their mechanical strength and structure for a wide range of conditions should be analyzed to apprehend the origin of the toughness of the DN-gels. We recently reported some experi- mental results obtained by dynamic light scattering and small angle neutron scattering. Some new experimental results obtained by neutron scattering in both deformed and undeformed conditions provided for a new under- standing of the origin of toughness. We review the studies on the structure of DN-gels towards understanding of the toughness origin. Studies on DN-gels for biomedical applications are also described. © 2009 Springer Science + Business Media B.V. 2

４種類のダブルネットワークハイドロゲルの圧縮ひずみ速度依存特性−関節軟骨との比較−　　　　　　　　　　　　　　　
藤木裕行, 臺丸谷政志, 陳 咏梅, 龔 剣萍, 長田義仁, 安田和則
日本臨床バイオメカニクス学会誌, 29, 261, 266, Dec. 2008
Japanese, Scientific journal

Highly Extensible Double-Network Gels with Self-Assembling Anisotropic Structure
Wei Yang, Hidemitsu Furukawa, Jian Ping Gong
ADVANCED MATERIALS, 20, 23, 4499, 4503, WILEY-V C H VERLAG GMBH, Dec. 2008, [Peer-reviewed]
English, Scientific journal, Novel hydrogels that possess highly ordered anisotropic structures have been synthesized by controlling the diffusion direction of multivalent ions that act as cross-linkers into a semi-rigid polyelectrolyte solution. A double network (DN) technique is then used to form highly ordered DN gels with excellent mechanical properties, e.g., an extensibility of over 2200% the original length under uniaxial elongation.

モータータンパク質でソフトアクチュエーター ―ナノからマクロへ―　　　　　　　　　　　　　　　
川村隆三, 龔剣萍
未来材料, 8, 11, 58, 59, Nov. 2008, [Invited]
Japanese, Scientific journal

Friction properties of polymer gel with high mechanical strength
島津英一郎, 江上正樹, 黒川孝幸, 龔剣萍
NTN technical review, 76, 76, 45, 50, NTN, Oct. 2008
Japanese, Scientific journal

Tear Velocity Dependence of High-Strength Double Network Gels in Comparison with Fast and Slow Relaxation Modes Observed by Scanning Microscopic Light Scattering
Hidemitsu Furukawa, Rikimaru Kuwabara, Yoshimi Tanaka, Takayuki Kurokawa, Yang-Ho Na, Yoshihito Osada, Jian Ping Gong
MACROMOLECULES, 41, 19, 7173, 7178, AMER CHEMICAL SOC, Oct. 2008, [Peer-reviewed]
English, Scientific journal, To investigate the mechanical strength of double network (DN) gels in a wide dynamical range, the gel solvent was replaced with viscous solvents-ethylene glycol and glycerol-and with their mixtures with water. The viscosity dependence of fracture energy in a tearing test was weak but demonstrated the existence of characteristic tear velocity for maximum fracture energy as a function of solvent viscosity. Fast and slow relaxation modes in the gels' dynamics were simultaneously observed by scanning microscopic light scattering, which reveals that the DN-gel structure stays unperturbed by the solvent change. These results implied that the solvent viscosity weakly affect the toughness and structure of the DN gels. Further, we demonstrated that the effect of solvent viscosity on the fracture energy can be incorporated into a scaled tear velocity that distributes over 6 orders of magnitude. We concluded that the viscous friction between polymer and solvent is not particularly significant for the energy dissipation of DN-gel fracture.

Morphogenesis of Liposomes Caused by Polycation-Induced Actin Assembly Formation
Haruka Maemichi, Kazuhiro Shikinaka, Akira Kakugo, Hidemitsu Furukawa, Yoshihito Osada, Han Ping Gong
LANGMUIR, 24, 20, 11975, 11981, AMER CHEMICAL SOC, Oct. 2008, [Peer-reviewed]
English, Scientific journal, We investigated the effects of polycation-mediated actin assembly on the morphological transformation of the lipid vesicle membrane by spatiotemporally controlling actin assembly. By triggering the radical polymerization of the cationic monomer using UV irradiation, we achieved a varied photoinduced assembly of actin in bulk solution. Furthermore, we designed liposomes containing actin and cationic monomers. In these actin-encapsulated liposomes, various actin assemblies were formed by UV irradiation similar to that observed in bulk solution. Moreover, morphogenesis of actin-encapsulated liposomes was observed in liposomes encapsulated with G-actin but not with F-actin. This result indicates that a dynamic polymerization of G-actin is important for vesicle protrusion.

Integration of motor proteins - Towards an ATP fueled soft actuator
Akira Kakugo, Kazuhiro Shikinaka, Jian Ping Gong
INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 9, 9, 1685, 1703, MDPI AG, Sep. 2008, [Peer-reviewed], [Invited]
English, Scientific journal, We present a soft bio-machine constructed from biological motors (actin/myosin). We have found that chemically cross-linked polymer-actin complex gel filaments can move on myosin coated surfaces with a velocity as high as that of native F-actin, by coupling to ATP hydrolysis. Additionally, it is shown that the velocity of polymer-actin complex gel depends on the species of polycations binding to the F-actins. Since the design of functional actuators of well-defined size and morphology is important, the structural behavior of polymer-actin complexes has been investigated. Our results show that the morphology and growth size of polymer-actin complex can be controlled by changes in the electrostatic interactions between F-actins and polycations. Our results indicate that bio actuators with desired shapes can be created by using a polymer-actin complex.

Tough Hydrogel - Learn from Nature
Hidemitsu Furukawa, Jian Ping Gong
Advances in Science and Technology, 61, 40, 45, Sep. 2008, [Peer-reviewed], [Invited]
English, Scientific journal

Ring-shaped assembly of microtubules shows preferential counterclockwise motion
Ryuzo Kawamura, Akira Kakugo, Kazuhiro Shikinaka, Yoshihito Osada, Jian Ping Gong
BIOMACROMOLECULES, 9, 9, 2277, 2282, AMER CHEMICAL SOC, Sep. 2008, [Peer-reviewed]
English, Scientific journal, In this paper, we reveal that microtubules (MTs), reconstructed from tubulin in vitro in the presence of guanosine-5'-triphosphate (GTP), have a ring or spiral shape on a motor protein-fixed surface, and these MTs show biased motion in the counterclockwise direction. By cross-linking these MTs during the sliding motion, we obtained large ring-shaped MT assemblies, 1 similar to 12.6 mu m in diameter. The ratio of the rings rotating in the counterclockwise direction to those rotating in the clockwise direction was approximately 3/1. Under optimized conditions, the ratio was as high as 14/1. Thus, We Successfully obtained aggregated MTs with a large hierarchic structure that shows a preferential motion, through a dynamic process in vitro.

Localized yielding around crack tips of double-network gels(a)
Yoshimi Tanaka, Yasunori Kawauchi, Takayuki Kurokawa, Hidemitsu Furukawa, Takaharu Okajima, Jian Ping Gong
MACROMOLECULAR RAPID COMMUNICATIONS, 29, 18, 1514, 1520, WILEY-V C H VERLAG GMBH, Sep. 2008, [Peer-reviewed]
English, Scientific journal, Double-network (DN) gels, a type of interpenetrating polymer network (IPN) consisting of rigid and flexible polymer components, exhibit two outstanding mechanical behaviors: yielding deformation of the entire specimen in tensile tests and quite high fracture energy in tearing tests. In this study, atomic force microscope (AFM) measurements were conducted on DN gels to determine the local Young's moduli immediately below the fracture surfaces E-f and below the usual molded surfaces E-m, and compare the local modulus with bulk Young's moduli measured before and after the yielding deformation, denoted as E-h and E-s, respectively. E-m and E-h are around 0.1 MPa; E-f and E-s, around 0.01 MPa, one order lower than the former two moduli. The order relation indicates that yielding deformation occurred locally around the crack tip of the DN gel during fracture. This supports the basic assumption of phenomenological models recently proposed to explain high fracture energy of DN gels.

Molecular model for toughening in double-network hydrogels
Vijay R. Tirumala, Taiki Tominaga, Sanghun Lee, Paul D. Butler, Eric K. Lin, Jian Ping Gong, Wen-li Wu
JOURNAL OF PHYSICAL CHEMISTRY B, 112, 27, 8024, 8031, AMER CHEMICAL SOC, Jul. 2008, [Peer-reviewed]
English, Scientific journal, A molecular mechanism is proposed for the toughness enhancement observed in double-network (DN) hydrogels prepared from poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) polyelectrolyte network and poly(acrylamide) (PAAm) linear polymer. It is an extension of, the phenomenological model set forth recently by Gong et al. (Macromolecules 2007, 40, 6658-6664). This mechanism rationalizes the changes in molecular structure of the DN gel constituents observed via in situ neutron scattering measurements, the composition dependence of the solution viscosity, and the thermodynamic interaction parameters of PAMPS and PAAm molecules obtained previously from neutron scattering studies. More specifically, this proposed mechanism provides an explanation for the observed periodic compositional fluctuations in the micrometer range induced by large strain deformation.

Friction and Lubrication of Gels : Toward the Low Friction of Bio-tissue
YASHIMA Shintaro, NAKANO Yukihiro, GONG Jian Ping
Journal of Japanese Society of Biorheology, 22, 2, 10, 24, JAPANESE SOCIETY OF BIORHEOLOGY, Jun. 2008, [Invited]
Japanese, Scientific journal, We have systematically studied the surface sliding friction of hydrogels, and various unique features in gel friction have been discovered. The frictional force and its dependencies on the load are quite different depending on the chemical structures of the gels, surface properties of the opposing substrates, and the measurement condition, which are completely different from those of solids. Most importantly, the friction coefficient of gels exhibits a value as low as 0.001, which cannot be obtained from the friction between two solid materials.
Recently, we developed a general method to synthesize hydrogels with extremely low friction by introducing linear polymer brush on the surface of gels. Then, the frictional coefficient became μ=10^-4.
However, conventional gels are mechanically too weak to be used as loading bearing materials. We recently developed anomalously strong gels by introducing a double network structure of the gel. These high strength hydrogels, containing 90 % water, sustain a compressive pressure as high as decades of MPa and show a high wear resistance due to their low friction. These gels might open new era of soft and wet materials for substituting articular cartilage and other tissues.

Novel Oriented Bacterial Cellulose Gels on Oxygen-Permeable Substrates
Ananda Putra, Hidemitsu Furukawa, Akira Kakugo, Jian Ping Gong
Cellulose Communications, 15, 2, 73, 78, セルロ-ス学会, Jun. 2008, [Invited]
English, Scientific journal

高強度・高機能ゲルの開発とその生体材料への応用　　　　　　　　　　　　　　　
陳咏梅, 龔剣萍
ファインケミカル, 37, 6, 5, 14, May 2008, [Invited]
Japanese, Scientific journal

ＡＴＰ駆動型ソフトバイオマシンの創製
角五 彰, グン剣萍, 長田義仁
化学と工業, 61, 5, 510, 513, 日本化学会, 01 May 2008, [Invited]
Japanese, Scientific journal

Thermodynamic interactions in double-network hydrogels
Taiki Tominaga, Vijay R. Tirumala, Sanghun Lee, Eric K. Lin, Jian Ping Gong, Wen-Li Wu
JOURNAL OF PHYSICAL CHEMISTRY B, 112, 13, 3903, 3909, AMER CHEMICAL SOC, Apr. 2008, [Peer-reviewed]
English, Scientific journal, Double-network hydrogels (DN-gels) prepared from the combination of a moderately cross-linked anionic polyelectrolyte (PE) and an uncross-linked linear polymer solution (NP) exhibit mechanical properties such as fracture toughness that are intriguingly superior to that of their individual constituents. The scheme of double-network preparation, however, is. not equally successful for all polyelectrolyte/neutral polymer pairs. A successful example is the combination of poly(2-acrylamido-2-methyl-1-propane sulfortic acid) (PAMPS) cross-linked network and linear polyacrylamide (PAAm), which results in DN-gels with fracture strength under compression approaching that of articular cartilage (, 20 MPa). Small-angle neutron scattering was used to determine the thermodynamic interaction parameters for PAMPS and PAAm in water as a first step to elucidate the molecular origin responsible for this superior property. Measurements on PAMPS/PAAm DN-gels and their solution blend counterparts indicate that the two polymers interact favorably with each other while in water. This favorable PAMPS/PAAm interaction given by the condition chi(PE-NP) << chi(PE-water) <chi(NP-water), where chi is the Flory-Huggins interaction parameter, is consistent with some of the salient features of the DN structure revealed by SANS, and it may also contribute to the ultimate mechanical properties of DN-gels.

Tubular bacterial cellulose gel with oriented fibrils on the curved surface
Ananda Putra, Akira Kakugo, Hidemitsu Furukawa, Jian P. Gong, Yoshihito Osada
POLYMER, 49, 7, 1885, 1891, ELSEVIER SCI LTD, Apr. 2008, [Peer-reviewed]
English, Scientific journal, On static cultivation, Acetobacter xylinum synthesizes bacterial cellulose (BC) that has a gel-like fibril network with inappropriate orientation at the air/liquid interface. This can be easily molded into desired shapes and sizes during synthesis. Here, we report a simple technique to synthesize tubular BC (BC-TS) gel with proper fibril orientation. We found that culturing BC in oxygen-permeable silicone tubes with inner diameter < 8 mm yields a BC-TS gel of the desired length, inner diameter, and thickness with uniaxially oriented fibrils. The fibrils are oriented along the longitudinal axis of the silicone tube, independent of gravity, oxygen availability, and the morphology of the inner surface of the silicone tube but dependent on the curvature of the silicone tube. The degree of orientation (Delta n) of the BC-TS fibrils, as revealed by their birefringence, increases with decrease in the inner diameter of the silicone tube. BC-TS with a uniaxially oriented fibril structure has excellent mechanical properties and holds promise for use as a microvessel or soft tissue material in medical and pharmaceutical applications. (c) 2008 Elsevier Ltd. All rights reserved.

Self-assembling structure in solution of a semirigid polyelectrolyte
Wei Yang, Hidemitsu Furukawa, Yukari Shigekura, Kazuhiro Shikinaka, Yoshihito Osada, Jian Ping Gong
MACROMOLECULES, 41, 5, 1791, 1799, AMER CHEMICAL SOC, Mar. 2008, [Peer-reviewed]
English, Scientific journal, We investigated the self-assembling structure in aqueous solution of polyelectrolyte poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT), which has a rigid chemical structure of polyaramide in the main chain. It is found that PBDT exhibits a stretched semirigid conformation in solution, regardless of PBDT concentration, C-P, or salt addition. PBDT in water exhibits both a very low overlap concentration, C*, and a lower critical concentration of nernatic liquid crystal, C-LC*. In the intermediate region of C* < C-P < C-LC*, PBDT forms cluster-like isotropic self-assembly. Moreover, in the intermediate region of C* < C-P < C-LC*, the addition of NaCl induces the alternation of structure from a cluster-like isotropic self-assembly to a fiber-like anisotropic one. Further addition of NaCl induces a network-like huge self-assembling structure, as the stoichiometric molar ratio of [NaCl] to [NaSO3-] increases beyond 1. The semirigid polyelectrolyte probably has hidden potential for structural polymorphism in aqueous solutions in the presence of salt.

Biological responses of novel high-toughness double network hydrogels in muscle and the subcutaneous tissues
Yoshie Tanabe, Kazunori Yasuda, Chinatsu Azuma, Hiroko Taniguro, Shin Onodera, Akira Suzuki, Yong Mei Chen, Jian Ping Gong, Yoshihito Osada
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 19, 3, 1379, 1387, SPRINGER, Mar. 2008, [Peer-reviewed]
English, Scientific journal, The study evaluated biological reaction of four types of novel double network gels in muscle and subcutaneous tissues, using implantation tests according to the international guideline. The implantation tests demonstrated that, although poly (2-acrylamide-2-metyl-propane sulfonic acid)/poly (N,N'-dimetyl acrylamide) (PAMPS/PDMAAm) gel induced a mild inflammation at 1 week, the degree of the inflammation significantly decreased into the same degree as that of the negative control at 4 and 6 weeks. This gel has a potential to be applied as artificial cartilage. In addition, Cellulose/Gelatin gel showed the same degree of inflammation as that of the negative control at 1 week, and then, showed a gradually absorbable property at 4 and 6 weeks. This gel has a potential to be applied as an absorbable implant. The PAMPS/polyacrylamide and Cellulose/PDMAAm gels induced a significant inflammation at each week. These DN gels are difficult to be applied as clinical implants in the current situation.

Observation of the three-dimensional structure of actin bundles formed with polycations
Kazuhiro Shikinaka, Hyuckjoon Kwon, Akira Kakugo, Hidemitsu Furukawa, Yoshihito Sada, Jian Ping Gong, Yoshitaka Aoyama, Hideo Nishioka, Hiroshi Jinnai, Takaharu Okajima
BIOMACROMOLECULES, 9, 2, 537, 542, AMER CHEMICAL SOC, Feb. 2008, [Peer-reviewed]
English, Scientific journal, Three-dimensional structures of actin bundles formed with polycations were observed by using transmission electron microtomography and atomic force microscopy. We found, for the first time, that the cross-sectional morphology of actin bundles depends on the polycation species and ionic strength, while it is insensitive to the degree of polymerization and concentration of polycation. Actin bundles formed with poly-N-[3-(dimethylamino)propyl] acrylamide methyl chloride quaternary show a ribbon-like cross-sectional morphology in low salt concentrations that changes to cylindrical cross-sectional morphology with hexagonal packing of the actin filaments in high salt concentrations. Contrastingly, actin bundles formed with poly-L-lysine show triangular cross-sectional morphology with hexagonal packing of the actin filaments. These variations in cross-sectional morphology are discussed in terms of anisotropy in the electrostatic energy barrier.

Flower Petal-like Pattern on Soft Hydrogels during Vodka Spreading
Daisaku Kaneko, Hidemitsu Furukawa, Yoshirni Tanaka, Yoshihito Osada, Jian Ping Gong
COLLOIDS FOR NANO- AND BIOTECHNOLOGY, 135, 225, +, SPRINGER-VERLAG BERLIN, 2008, [Peer-reviewed]
English, International conference proceedings, Flower petal-like pattern has been observed during Vodka spreading on gel surfaces. Since the spreading kinetics vanishes within a few seconds, the flower petal-like pattern is extremely impressive like shooting-up of fireworks. This pattern can be formed when ethanol/water mixtures having more than 25 vol. % of ethanol are used as spreading liquid and soft gels with storage modulus less than 10(4) Pa are used as underlying substrates. The origin of this phenomenon is discussed in terms of instability of leading edge of spreading liquid on soft hydrogels.

Interfacial water structure at polymer gel/quartz interfaces investigated by sum frequency generation spectroscopy
Hidenori Noguchi, Minowa Hiroshi, Taiki Tominaga, Jian Ping Gong, Yoshihito Osada, Kohei Uosaki
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 10, 32, 4987, 4993, ROYAL SOC CHEMISTRY, 2008, [Peer-reviewed]
English, Scientific journal, Interfacial structures of water at polyvinyl alcohol (PVA) and poly(2-acrylamido-2-methypropane) sulfonic acid sodium salt (PNaAMPS)/quartz interfaces were investigated by sum frequency generation (SFG) spectroscopy. Two broad peaks were observed in OH stretching region at 3200 and 3400 cm(-1), corresponding to the symmetric OH stretching of tetrahedrally coordinated, i.e., strongly hydrogen bonded "ice-like" water, and the asymmetric OH stretching of water in a more random arrangement, i.e., weakly hydrogen bonded "liquid-like" water, respectively, in both cases. The "liquid-like" water became dominant when the PVA gel was pressed against the quartz surface. The relative intensity of the SFG signal due to the "liquid-like" water to that due to the "ice-like water" at the quartz surface modified with a self-assembled monolayer of aminopropyltrimethoxysilane (APS) became higher when the negatively charged PNaMPS gel was contacted to the APS modified quartz surface in a solution of pH = 12, where the surface was negatively charged and electrostatic repulsive interaction and low friction were present between the PNaMPS gel and the APS modified surface. It, however, did not change in a solution of pH = 2, where the surface was positively charged and electrostatic attractive interaction and very high friction were present between the PNaMPS gel and the APS modified surface. These results suggest the important role of water structure for small friction at the polymer gel/solid interface.

Friction of a soft hydrogel on rough solid substrates
Taiki Tominaga, Takayuki Kurokawa, Hidemitsu Furukawa, Yoshihito Osada, Jian Ping Gong
SOFT MATTER, 4, 8, 1645, 1652, ROYAL SOC CHEMISTRY, 2008, [Peer-reviewed]
English, Scientific journal, We investigated the sliding friction between a soft hydrogel and rough and weakly adhesive solid substrates in a water environment. Polyvinyl alcohol (PVA) hydrogels of different elastic moduli and two sets of glass substrates with different contact angles to water, all of which varied in their surface roughness, were used. The friction measurement was performed by using a strain-controlled parallel-plate rheometer. With an increase in substrate roughness, the friction in the low velocity region increased slightly, while it decreased significantly above a critical velocity on a surface with a roughness larger than 1 mm. Below this critical velocity, the frictional stress changed with the glass substrate surface energy, while above this critical velocity, it was not sensitive to the glass substrate surface energy. The velocity-dependence of friction on rough surfaces is explained in terms of surface contact dynamics and is characterized by two velocities, i.e., nu(f) and nu(drainage). The former is determined by the cooperative diffusion constant of the gels, and the latter is by the surface roughness of the substrate and the normal pressure applied on the gel.

Effect of substrate adhesion and hydrophobicity on hydrogel friction
Taiki Tominaga, Naoyuki Takedomi, Hynek Biederman, Hidemitsu Furukawa, Yoshihito Osada, Jian Ping Gong
SOFT MATTER, 4, 5, 1033, 1040, ROYAL SOC CHEMISTRY, 2008, [Peer-reviewed]
English, Scientific journal, In this paper, the frictional behavior of a neutral hydrogel, polyvinyl alcohol (PVA), on smooth solid substrates with various levels of hydrophobicity have been investigated in water using a strain-controlled parallel-plate rheometer. For the sliding velocity dependence of friction, we detected a distinct friction transition on hydrophobic substrates that are strongly adhesive to the gel, while no clear transition was observed on hydrophilic substrates that are weakly adhesive to the gel. Even on the most hydrophobic substrate, the maximum frictional stress is approximately 1/10-1/5 of the gel's elastic modulus under a large normal strain of 26%. Furthermore, the frictional stress on hydrophobic substrates in the high velocity region, larger than the transition, is much lower than that on hydrophilic ones. We attempted to explain these phenomena with the help of two models: a molecular model based on the thermal fluctuations occurring during adsorption-desorption of polymers and a continuum mechanics model based on elastic dewetting and forced wetting.

Production of bacterial cellulose with well oriented fibril on PDMS substrate
Ananda Putra, Akira Kakugo, Hidentitsu Furukawa, Jian P. Gong, Yoshihito Osada, Tetsuya Uemura, Masafumi Yamamoto
POLYMER JOURNAL, 40, 2, 137, 142, SOC POLYMER SCIENCE JAPAN, 2008, [Peer-reviewed]
English, Scientific journal, Acetobacterxylinum, which is an aerobic bacterium, synthesizes bacterial cellulose (BC) with unoriented microfibril network in form of gel at the air and liquid interface (BC-air). In this work, we discovered that BC gel produced on an oxygen permeable substrate of polydimethylsiloxane (PDMS) shows strong birefringence with colorful images, indicating a liquid crystal-like structure. Furthermore, we found that uni-axially oriented BC gels can be obtained by culturing the BC on the PDMS with ridged morphology. The degree of orientation of BC gels, as revealed by the birefringence, increases with the decrease in the ridge size of the PDMS substrate. An optimum ridge size of 4.5 mu m was observed where the BC gels show the highest birefringence (Delta n), the highest fracture stress (sigma), highest swelling degree (q), the lowest elastic modulus (E), and the thickest BC fibril. The optimum ridge size is related to the contour length of the bacteria cells. When the ridge size was smaller than 4.5 mu m, the Delta n steeply decreased to a value comparable to that on smooth flat PDMS mold surface. The fracture stress, sigma of the uni-axially oriented BC gel under elongation was 4.6 MPa, which was 2.3 times higher than that of BC-air (sigma = 2 MPa).

Integration of Biomolecular Motors: Toward an ATP Fueled Soft Moving System　　　　　　　　　　　　　　　
Kazuhiro Shikinaka, Ryuzo Kawamura, Akira Kakugo, Hidemitsu Furukawa, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 57, 106, 2008
English, Scientific journal

The molecular origin of enhanced toughness in double-network hydrogels: A neutron scattering study
Taiki Tominaga, Vijay R. Tirumala, Eric K. Lin, Jian Ping Gong, Hidemitsu Furukawa, Yoshihito Osada, Wen-li Wu
POLYMER, 48, 26, 7449, 7454, ELSEVIER SCI LTD, Dec. 2007, [Peer-reviewed]
English, Scientific journal, Double-network hydrogels (DN-gels) are a new class of crosslinked polymer networks with extraordinary mechanical properties while containing 80-90 vol.% water. Small-angle neutron scattering (SANS) was applied to investigate the molecular origin of the mechanical properties observed in DN-gels. We present SANS results in both deformed and undeformed conditions for a tough DN-gel made of poly-(2-acrylamido-2-methyl-1-propane sulfonic acid) (PAMPS) and polyacrylamide (PAAm). The SANS measurements indicate that deformation of DN-gels results in periodic and mesoscale (similar to 1.5 mu m) compositional fluctuations in both PAMPS and PAAm. In addition, SANS measurements also indicate that the DN-gel constituents interact favorably with each other while in water. This favorable interaction between PAMPS and PAAm is consistent with the rheological results on solution mixtures of these two polymers. The implications of the above observations to toughening mechanisms are discussed. Published by Elsevier Ltd.

Importance of entanglement between first and second components in high-strength double network gels
Mei Huang, Hidemitsu Furukawa, Yoshimi Tanaka, Tasuku Nakajima, Yoshihito Osada, Jian Ping Gong
MACROMOLECULES, 40, 18, 6658, 6664, AMER CHEMICAL SOC, Sep. 2007, [Peer-reviewed]
English, Scientific journal, The double network (DN) gels, composed of a minor component, chemically cross-linked polyelectrolyte (first network), and the major one, linear neutral polymer (second network), exhibit anomalously high mechanical strengths. In this study, adopting the concentration of the second polymer as the experimental parameter, we investigate the relation between the mechanical strength and the dynamics of polymer concentration fluctuation. The former is measured by compression and tearing tests; the latter is measured by a special dynamic light scattering technique (called SMILS) suitable for polymer gels. The mechanical strength is enhanced when the concentration is so high that the second polymer chains strongly entangle each other. The main finding of SMILS is that the diffusion constant of the concentration fluctuation of the second polymer is increased by the existence of the first network despite the minority of the first component (<(1)/(10) in monomer ratio to the second component). This indicates that there is entanglement also between the first and the second polymers. The inter-species entanglement and inhomogeneities of the first network suggested in our previous study [Macromolecules 2004, 37, 5370] give support to the crack model concerned with yielding around the crack tip, which explains the high mechanical strength.

Friction and Lubrication of Hydrogel
KAKUGO Akira, GONG JianPing, OSADA Yoshihito
Seibutsu Butsuri, 47, 4, 253, 258, The Biophysical Society of Japan General Incorporated Association, 26 Jul. 2007, [Invited]
Japanese, Scientific journal

Influence of cyclohexane vapor on stick-slip friction between mica surfaces
Satomi Ohnishi, Daisaku Kaneko, Jian Ping Gong, Yoshihito Osada, A. M. Stewart, Vassili V. Yaminsky
LANGMUIR, 23, 13, 7032, 7038, AMER CHEMICAL SOC, Jun. 2007, [Peer-reviewed]
English, Scientific journal, Stick-slip friction between mica surfaces under cyclohexane vapor has been investigated with the Surface Force Apparatus. The dynamic shear stress decreased from 60 to 10 MPa with increasing relative vapor pressure (rvp) from 5% to 50%. Between a rvp of 50% and 80%, the shear stress remained at similar to 10 MPa, with a slight decrease on increasing the rvp. At a rvp greater than 80%, the values of shear stress were below 5 MPa. The stick-slip behavior was observed in the rvp range of 20% to saturation. When the rvp reached 20%, stick-slip appeared but faded out with sliding time. At a rvp greater than 50%, the stick-slip pattern was stable without fading. By taking into account the size of the meniscus formed by capillary condensation of the liquid around the contact area and the Laplace pressure, the dependence of shear stress and the stick-slip modulation on rvp suggests that the origin of the stick-slip observed in cyclohexane vapor is as follows: At a rvp greater than 50%, where stable sick-slip is observed, the stick-slip caused by the cyclohexane layering in the contact area is of essentially the same origin as that observed with mica surfaces sliding in bulk cyclohexane liquid. As with the bulk liquid experiment, decreasing the layer thickness (or the number of the layers) between the surfaces increases the shear stress at the onset of slip. In the vapor phase experiments, the stick-slip is enhanced by the increase of the negative Laplace pressure in the capillary condensed liquid, thereby forcing the surfaces toward each other more strongly with decreasing rvp. In the rvp range between 20% and 50%, where the fading stick-slip is observed, the condensate liquid seeps into the contact area under the influence of the applied tangential force and thus triggers the slip motion. Due to the small condensation volume, the liquid condensed around the contact area is exhausted in the process of repeating stick-slip. As the slip length is limited to the meniscus size, the stick-slip amplitude becomes smaller, and eventually the surfaces start sliding without stick-slip.

Friction of soft gel in dilute polymer solution
Miao Du, Yasuyuki Maki, Taiki Tominaga, Hidemitsu Furukawa, Jian Ping Gong, Yoshihito Osada, Qiang Zheng
MACROMOLECULES, 40, 12, 4313, 4321, AMER CHEMICAL SOC, Jun. 2007, [Peer-reviewed]
English, Scientific journal, We study the friction behaviors of poly(vinyl alcohol) (PVA) gel sliding against glass surface in dilute poly(ethylene oxide) (PEO) aqueous solution with various molecular weights, M-w, and concentrations. At low sliding velocity (10(-5), 10(-1) m/s), distinct PEO polymer effects are observed: The frictional stress in PEO 2E4 (M-w = 2 x 10(4) g/mol) solutions is lower than that in pure water, decreasing with the increase in PEO concentration and reaching a minimum at the crossover concentration, c*. However, in higher molecular weight solution, PEO 4E6 (M-w = 4 x 10(6) g/mol), this friction reduction effect is only observed for very dilute concentration (0.01 c* solution), and the friction stress in higher concentration (0.1 c*, 0.30, and c* solution) is higher than that in pure water, accompanied by the appearance of "plateau". At fast sliding velocity (10(-2), 10(-1) m/s), all the friction curves in dilute PEO solution superpose with the curve in pure water, independent of M, and concentration of PEO. These results indicate that in the low sliding velocity region, where adsorption of PVA gel on glass plays the dominant role in friction, PEO chain screens the adsorption of PVA chains to glass surface. In the fast sliding velocity region, PEO chain is either extensively stretched or forms a deplete layer on the glass surface by the high shear rate, so the liquid lubrication with a viscosity of eta approximate to eta(water) prevails. The results also support the theoretical prediction that the effective concentration of PEO in the confined 2-dimentional space between get and glass interface is enhanced for high molecular weight PEO.

Actin network formation by unidirectional polycation diffusion
Hyuck Joon Kwon, Akira Kakugo, Takehiro Ura, Takaharu Okajima, Yoshimi Tanaka, Hidemitsu Furukawa, Yoshihito Osada, Jian Ping Gong
LANGMUIR, 23, 11, 6257, 6262, AMER CHEMICAL SOC, May 2007, [Peer-reviewed]
English, Scientific journal, We show that F-actins form three-dimensional giant network under uni-directional diffusion of polycations, at a dilute actin concentration (0.01 mg/mL) that only bundles are formed by homogeneous mixing with polycations. The mesh size of the actin network depends on polycation concentration and ionic strength, while bundle thickness of network depends only on ionic strength, which indicates that actin network is formed through nucleation-growth mechanism. The mesh size and the bundle thickness are determined by nucleus concentration and nucleus size, respectively. The atomic force microscopy measurement correlates the elasticity of the actin network, E, with the mesh size, xi, as E similar to xi(-1), while the bundle thickness, D dependence of E cannot be described by a simple scaling relation. E similar to D-6.5 when D is small and E similar to D-0.1 when D is large. Our study on the self-assembly of actin network under asymmetric polycation condition would provide the crucial insight into the organization of biopolymers in polarized condition of cell.

Biodegradation of high-toughness double network hydrogels as potential materials for artificial cartilage
Chinatsu Azuma, Kazunori Yasuda, Yoshie Tanabe, Hiroko Taniguro, Fuminori Kanaya, Atsushi Nakayama, Yong Mei Chen, Jian Ping Gong, Yoshihito Osada
JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 81A, 2, 373, 380, WILEY-LISS, May 2007, [Peer-reviewed]
English, Scientific journal, This study evaluated biodegradation properties of four novel high-toughness double network (DN) hydrogels as potential materials for artificial cartilage. Concerning each DN gel material, a total of 12 specimens were prepared, and 6 of the 12 specimens were examined to determine the mechanical properties without any treatments. The remaining 6 specimens were implanted into the subcutaneous tissue, using 6 mature female rabbits. At 6 weeks after implantation, the mechanical properties and the water content of the implanted specimens were measured. In the poly(2-acrylamide-2-methyl-propane sulfonic acid)/poly (N,N'-dimethyl acrylamide) DN gel, the ultimate stress and the tangent modulus were significantly increased from 3.10 and 0.20 MPa, respectively, to 5.40 and 0.37 MPa, respectively, with a significant reduction of the water content after implantation (94 to 91%). In the poly(2-acrylamide-2-methyl-propane sulfonic acid) /polyacrylamide DN gel and the cellulose /poly(dimethyl acrylamide) DN gel, the stress (11.4 and 1.90 MPa, respectively) and the modulus (0.30 and 1.70 MPa, respectively) or the water content rarely changed after implantation (90 and 85%, respectively). In the bacterial cellulose/gelatin DN gel, the ultimate stress was dramatically reduced from 4.30 to 1.98 MPa with a significant increase of the water content after implantation (78 to 86%). This study implied that these DN gels except for the cellulose/gelatin DN gel are potential materials that may meet the requirements of artificial cartilage. (c) 2006 Wiley Periodicals, Inc.

Bacterial cellulose based hydrogel for articular soft tissues
Akira Kakugo, Jian Ping Gong, Yoshihito Osada
Cellulose Communications, 14, 2, 50, 54, セルロ-ス学会, Apr. 2007, [Invited]
English, Scientific journal

Friction coefficient between rubber and solid substrate - Effect of rubber thickness
Daisaku Kaneko, Masaki Oshikawa, Tetsuo Yamaguchi, Jian Ping Gong, Masao Doi
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 76, 4, 43601-1, 43601-3, PHYSICAL SOC JAPAN, Apr. 2007, [Peer-reviewed]
English, Scientific journal, The frictional coefficient mu between poly(dimethylsiloxane) (PDMS) rubber and glass plate with PDMS lubricant is measured for various thickness of rubber sample. The friction coefficient of thick sample is shown to be an order of magnitude larger than that of thin sample. The phenomenon is interpreted as the transition from the hydrodynamic lubrication to the boundary lubrication.

Large strain hysteresis and mullins effect of tough double-network hydrogels
Rebecca E. Webber, Costantino Creton, Hugh R. Brown, Jian Ping Gong
MACROMOLECULES, 40, 8, 2919, 2927, AMER CHEMICAL SOC, Apr. 2007, [Peer-reviewed]
English, Scientific journal, Systematic loading and unloading experiments, in uniaxial tension and uniaxial compression, have been performed on a double-network hydrogel exhibiting a very high toughness. We observed a significant hysteresis during the first loading cycle that increased strongly with the applied maximum deformation. A large hysteresis was not observed during a second loading cycle, implying that the initial hysteresis can be attributed to the fracture of covalent bonds in the primary network. We report this type of dissipative mechanism for polymer gels for the first time. Assuming that the entire energy dissipated during the hysteresis cycle can be attributed to the fracture of network strands by a Lake-Thomas mechanism, our results suggest that the fracture and unloading of only 1% of the bonds within the network leads to a decrease of up to 80% of the number of strands. These results also demonstrate the very large degree of heterogeneity within the hydrogel network. If such a dissipative mechanism is active at the crack tip, it will most likely greatly increase the energy necessary to propagate a macroscopic crack, elucidating the origin of the toughness in these interesting materials.

Anisotropic gelation seeded by a rod-like polyelectrolyte
Yukari Shigekura, Hidemitsu Furukawa, Wei Yang, Yong Mei Chen, Tatsuo Kaneko, Yoshihito Osada, Jian Ping Gong
MACROMOLECULES, 40, 7, 2477, 2485, AMER CHEMICAL SOC, Apr. 2007, [Peer-reviewed]
English, Scientific journal, We previously discovered that isotropic monomer solution shows birefringence due to its anisotropic structure after gelation in the presence of a small amount of rod-like polyelectrolyte. Here, we focus on what mechanism is responsible for the formation of anisotropic structure during gelation. Various optical measurements are performed to elucidate the structure change during gelation. The structure before and during gelation is in situ observed by scanning microscopic light scattering, confocal laser scanning microscope, polarizing optical microscope and depolarizing small angle light scattering. It is found that the existence of a large-size structure in monomer solution with the rod-like polyelectrolyte is essentially important to induce birefringence during gelation. The possible mechanism of the anisotropic structure formation during gelation seeded by a rod-like polyelectrolyte is proposed based on the results of these observations.

Platelet adhesion to human umbilical vein endothelial cells cultured on anionic hydrogel scaffolds
Yong Mei Chen, Masaru Tanaka, Jian Ping Gong, Kazunori Yasuda, Sadaaki Yamamoto, Masatsugu Shimomura, Yoshihito Osada
BIOMATERIALS, 28, 10, 1752, 1760, ELSEVIER SCI LTD, Apr. 2007, [Peer-reviewed]
English, Scientific journal, In this work we describe experiments designed to understand the human platelet adhesion to human umbilical vein endothelial cells (HUVECs) cultured on various kinds of chemically cross-linked anionic hydrogels, which were synthesized by radical polymerization. HUVECs could proliferate to sub-confluent or confluent on poly(acrylic acid) (PAA), poly(2-acrylamido-2-methyl-propane sulfonic acid sodium salt) (PNaAMPS), and poly(sodium p-styrene sulfonate) (PNaSS) gels. The proliferation behavior was not sensitive to the crosslinker concentration of the gels. However, the platelet adhesion on the HUVECs cultured on these gels showed different behavior, as revealed by human platelet adhesion test in static conditions. Only a few platelets adhered on the HUVEC sheets cultured on PNaAMPS gels with 4 and 10 mol% cross-linker concentrations, and completely no platelet adhered on the HUVEC sheets cultured on PNaSS gels with 4 and 10 mol% cross-linker concentrations. On the other hand, a large number of platelets adhered on the HUVECs cultured on PAA gels with 1, 2mol% cross-linker concentrations and PNaAMPS gel with 2mol% cross-linker concentration. Furthermore, the study showed that promote of the glycocalyx of HUVECs with transforming growth factor-beta(1) (TGF-beta(1)) decreased platelet adhesion, and degrade the glycocalyx with heparinase I increased platelet adhesion. The results suggested that the glycocalyx of cultured HUVECs modulates platelet compatibility, and the amount of glycocalyx secreted by HUVECs dependents on the chemical structure and crosslinker concentration of gel scaffolds. This result should be applied to make the hybrid artificial blood vessel composes of gels and endothelial cells with high platelet compatibility. (c) 2006 Elsevier Ltd. All rights reserved.

Surface sliding friction of negatively charged polyelectrolyte gels
Go Kagata, Jian Ping Gong
COLLOIDS AND SURFACES B-BIOINTERFACES, 56, 1-2, 296, 302, ELSEVIER SCIENCE BV, Apr. 2007, [Peer-reviewed]
English, Scientific journal, The friction between two polyelectrolyte gels carrying the same or opposite sign of charges has been investigated using a rheometer. It is found that the friction was strongly dependent on the interfacial interaction between two gel surfaces. In the repulsive interaction case, especially, the friction was extremely low. The friction behavior is attempted to be described in terms of the hydrodynamic lubrication of the solvent layer between two like-charged gel surfaces, which is formed due to the electrostatic repulsion of the two gel surfaces. From the theoretical analysis (hydrodynamic mechanism), the friction behaviors were explained qualitatively, all of the experimental results, nevertheless, could not be understood well. The viscoelastic feature of the gel and the non-Newtonian behavior of water at the friction interface are considered to be important to elucidate the gel friction. (c) 2006 Elsevier B.V. All rights reserved.

Motility and structural polymorphism of polymer-actin complex gel
Hyuck Joon Kwon, Kazuhiro Shikinaka, Akira Kakugo, Hidemitsu Furukawa, Yoshihito Osada, Jian Ping Gong
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 7, 3, 844, 847, AMER SCIENTIFIC PUBLISHERS, Mar. 2007, [Peer-reviewed]
English, Scientific journal, We report a soft gel machine reconstructed from muscle proteins. We have found that chemically cross-linked polymer-actin complex gel can move on myosin coated surface with a velocity as high as that of native F-actin, by coupling to ATP hydrolysis. Additionally, it is shown that the velocity and motional pattern of polymer-actin complex gel depends on the morphology of polymer-complex gels. Since the designing of functional actuator into well-defined size and morphology is important, the structural behavior of polymer-actin complexes has been investigated. This result shows that the morphology and growth size of polymer-actin complex can be controlled by change of electrostatic interaction between F-actins and polycations. Our results indicate that bio actuator with desired shape can be created by using polymer-actin complex.

Selective cell spreading, proliferation, and orientation on micropatterned gel surfaces
Yong Mei Chen, Kui Chuan Shen, Jian Ping Gong, Yoshihito Osada
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 7, 3, 773, 779, AMER SCIENTIFIC PUBLISHERS, Mar. 2007, [Peer-reviewed]
English, Scientific journal, Hydrogel micropatterns of 10 similar to 200 mu m in width were introduced during the polymerization of 2-acrylamido-2-methyl-propane sulfonic acid sodium salt (NaAMPS) on the surface of polyacrylamide (PAAm) gel. Behaviors of endothelial cells on the micropatterned PNaAMPS/PAAm gel surfaces were studied. Cells selectively proliferate on micropatterned PNaAMPS surface but not on PAAm surface, which requires no modification with any cell adhesive proteins or peptides. We found that decrease of the width of the micropatterns could increase the degree of anisotropic spreading of cells and the degree of cell orientation. These results demonstrated that the topographical micropatterns of hydrogel could control cell behaviors.

Anisotropic structure in gels induced by a little amount of rod-like polyelectrolyte
古川英光, 重倉ゆかり, 長田義仁, 龔剣萍
Journal of the Japanese Liquid Crystal Society, 11, 2, 153, 159, 日本液晶学会事務局, 2007, [Invited]
Japanese, Scientific journal

Growth and morphology of polymer-actin complexes
Hyuck Joon Kwon, Kazuhiro Shikinaka, Akira Kakugo, Hidemitsu Furukawa, Yoshihito Osada, Jian Ping Gong
CHINESE JOURNAL OF POLYMER SCIENCE, 25, 1, 47, 55, SPRINGER, Jan. 2007, [Invited]
English, Scientific journal, F-actins are semi-flexible polyelectrolytes and can be assembled into large polymer-actin complex with polymorphism through electrostatic interaction with polycations. This study investigates the structural phase behavior and the growth of polymer-actin complexes in terms of its longitudinal and lateral sizes. Our results show that formation of polymer-actin complexes is cooperative, and morphology and growth of polymer-actin complexes depend on polycation species and concentrations of polycation and salt in a constant actin concentration. We found that the longitudinal growth and lateral growth of polymer-actin complexes are dominated by different factors. This induces the structural polymorphism of polymer-actin complexes. Major factors to influence the polymorphism of polymer-actin complexes in polyelectrolyte system have been discussed. Our results indicate that the semi-flexible polyelectrolyte nature of F-actins is important for controlling the morphology and growth of actin architectures in cell.

Gel biomachine based on muscle proteins
Hyuck Joon Kwon, Kazuhiro Shikinaka, Akira Kakugo, Jian Ping Gong, Yoshihito Osada
POLYMER BULLETIN, 58, 1, 43, 52, SPRINGER, Jan. 2007, [Peer-reviewed]
English, Scientific journal, We have created an ATP-fueled soft gel machine constructed from muscle proteins. Chemically cross-linked gels of the polymer-actin complex of the length several decades times the length of native actin filament (F-actin) move on myosin-coated surface with a velocity as high as that of native F-actin, by coupling to ATP hydrolysis. The motility observed in muscle protein-gels suggests that one might construct a soft machine fueled by chemical energy using actin and myosin molecules as elements. We have investigated the growth process of polymer-actin complexes and the correlation between the polarity and the motility of polymer-actin complex gels.

2P161 Dynamic self-assembly of microtubule complex by kinesin : toward ATP-fueled actuator(Molecular motors,Poster Presentations)
Kawamura Ryuzo, Kakugo Akira, Furukawa Hidemitsu, Gong Jian Ping, Osada Yoshihito
Seibutsu Butsuri, 47, S153, The Biophysical Society of Japan General Incorporated Association, 2007
English

Negatively charged polyelectrolyte gels as bio-tissue model system and for biomedical application
Hyuck Joon Kwon, Jian Ping Gong
CURRENT OPINION IN COLLOID & INTERFACE SCIENCE, 11, 6, 345, 350, ELSEVIER SCIENCE LONDON, Dec. 2006, [Invited]
English, Scientific journal, Polyelectrolyte gels are charged polymer networks with macro-ions fixed on the polymer chains. In the present paper, the fundamental aspects, properties and application of negatively charged polyelectrolyte gels are reviewed, focusing on the interaction between polyelectrolyte gels and proteins, the surface friction and mechanical strength of polyelectrolyte gels. These characteristic properties of polyelectrolyte gels have considerable potential for practical application, such as soft scaffold of cells, construction of biomimetic actuator and replacement of biological tissues. (C) 2006 Elsevier Ltd. All rights reserved.

Anisotropic polyion-complex gels via template polymerization
Yukari Shigekura, Hidemitsu Furukawa, Yongmei Chen, Yongmei Chen, Tatsuo Kaneko, Wei Yang, Jian Ping Gong, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 55, 1754, 19 Oct. 2006
We focus on highly-charged rigid-rod poly(2,2′-disulfonyl-4,4′- benzidine terephthalamide)(PBDT), which behaves as mesogen in water to induce lyotropic self-organization from a very low concentrations of 2.8wt.%. By template (matrix) polymerization of N-[3-(N,N-dimethylamino)propyl]acrylamide methyl chloride quarternary (DMAPAA-Q) with a very little amount of PBDT, the polyioncomplex gels that contains ordered network structure can be synthesized. In this study, scanning microscopic light scattering shows that PBDT and DMAPAA-Q aqueous solution forms some large structure before gelation, which may be related to the gelation induced orientation.

Anisotropic nucleation growth of actin bundle: A model for determining the well-defined thickness of bundles
Hyuck Joon Kwon, Yoshimi Tanaka, Akira Kakugo, Kazuhiro Shikinaka, Hidemitsu Furukawa, Yoshihito Osada, Jian Ping Gong
BIOCHEMISTRY, 45, 34, 10313, 10318, AMER CHEMICAL SOC, Aug. 2006, [Peer-reviewed]
English, Scientific journal, Biopolymers such as DNA, F-actins, and microtubules, which are highly charged, rodlike polyelectrolytes, are assembled into architectures with defined morphology and size by electrostatic interaction with multivalent cations (or polycations) in vivo and in vitro. The physical origin to determine their morphology and size is not clearly understood yet. Our results show that the actin bundle formation consists of two stages: the thickness of actin bundles is determined nearly at the initial stage, while the length of actin bundles is determined later on. It is also found that the thickness of actin bundles decreases with the increase of polycation-mediated attraction between F-actins. From these results, we propose the anisotropic nucleation-growth mechanism, in which the thickness of actin bundles is determined by critical nucleus size, whereas the length of actin bundles is determined by the concentration of free actins relative to nucleus concentration. Observing that polycations are concentrated in some sites of actin bundles, which are thought to be nucleation sites to initiate the formation of actin bundles, supports this model. This anisotropic nucleation-growth mechanism of actin bundles can be broadly applied to the self-assembly of rodlike polyelectrolytes.

Catch and release of DNA in coacervate-dispersed gels
Asami Ohsugi, Hidemitsu Furukawa, Akira Kakugo, Yoshihito Osada, Jian Ping Gong
MACROMOLECULAR RAPID COMMUNICATIONS, 27, 15, 1242, 1246, WILEY-V C H VERLAG GMBH, Aug. 2006, [Peer-reviewed]
English, Scientific journal, We have synthesized novel coacervate-droplet gels, which were applied to controlling the transportation of DNA in electrophoresis. Coacervate droplets are colloidal particles and they are usually composed of positive and negative polyelectrolytes. However, the polyzwitterion (polyampholyte) PDMAPS can form coacervate droplets in water by itself, since PDMAPS has both positive and negative charges in each side group of main chain. Coacervate droplets have a unique nature and can catch charged macromolecules such as DNA. In order to utilize the nature of the PDMAPS coacervate droplets for the catch and release of DNA, we stabilized PDMAPS droplets in gels. The droplets catch the DNA in electrophoresis and the release of DNA can be controlled by temperature and salt addition.

Surface friction of gellan gels
Zhouting Jiang, Taiki Tominaga, Kosuke Kamata, Yoshihito Osada, Jian Ping Gong
COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 284, 56, 60, ELSEVIER SCIENCE BV, Aug. 2006, [Peer-reviewed]
English, Scientific journal, The surface friction of three kinds of gellan gets, non-purified gellan gel, Ca2+ form gellan gel, and Na+ form gellan gel, has been investigated against a glass substrate in water and NaCl aqueous solution. The non-purified gellan gels exhibit the lowest friction in pure water, especially at a low sliding velocity, showing a frictional coefficient of 0.001. The frictional stresses of gellan gels increase with the increase of storage time in water or NaCl aqueous solution. Comparing with Ca2+-gellan gel and Na+-gellan gel, the non-purified gellan gel is more instable. Relatively low friction is observed in Ne-gellan gels in a salt concentration as high as 0.05 M. The low friction in a high ionic strength is attributed to the rigid double helical structure of the gel. (c) 2005 Elsevier B.V. All rights reserved.

Necking phenomenon of double-network gels
YH Na, Y Tanaka, Y Kawauchi, H Furukawa, T Sumiyoshi, JP Gong, Y Osada
MACROMOLECULES, 39, 14, 4641, 4645, AMER CHEMICAL SOC, Jul. 2006, [Peer-reviewed]
English, Scientific journal

Self-assembly of rod-like polyelectrolytes in aqueous solution　　　　　　　　　　　　　　　
Wei Yang, Hidemitsu Furukawa, Yukari Shigekura, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 55, 2, 3161, 3162, 2006
Japanese, International conference proceedings, Poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT) which is a water-soluble, rigid-rod, synthetic polyelectrolyte,can be used as biological polyelectrolyte model. The solution properties of PBDT was studied with dynamic light scattering and transmission electron microscopy, especially to investigate the structure and the effect of salt on the properties. We found interestingly that PBDT forms network-like structure by only addition of NaCl. There is a critical concentration of NaCl, above which PBDT can form it.

Creation of hydrogels with ultra high mechanical strength [XII]: The effect of controlled void structure　　　　　　　　　　　　　　　
Tasuku Nakajima, Hidemitsu Furukawa, Yoshimi Tanaka, Takayuki Kurokawa, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 55, 2, 3212, 3213, 2006
Japanese, International conference proceedings, We have recently synthesized Double Network hydrogels (DN gels) with anomalously high mechanical strength. We consider that the toughness of DN gels is caused by the inhomogeneous structure of 1st network gel. To clarify the effect of the inhomogeneous structure, we introduce the controlled void structure into DN gels by using silica particle. Both the size and density of the void structure are varied systematically to prepare void-DN gels. The fracture energy of void-DN gels were measured by tearing test and the network structure in void-DN gels were observed by scanning microscopic light scattering. We discuss the relation between the mechanical properties and void structure in DN gels.

Creation of hydrogels with ultra high mechanical strength [XIII]: The necking phenomenon in double network gels　　　　　　　　　　　　　　　
Yasunori Kawauchi, Rikimaru Kuwabara, Hidemitsu Furukawa, Yang-Ho Na, Yoshimi Tanaka, Takayuki Kurokawa, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 55, 2, 3214, 3215, 2006
Japanese, International conference proceedings, We have recently synthesized DN gels with ultra high mechanical strength. The DN gels consist of polyelectrolyte gels as the 1st network and neutral gels (or linear polymer) as the 2nd network. The previous research with dynamic light scattering proposed that the 1st network has inhomogeneous structure with large voids, where such voids structure is important for the strength enhancement of DN gels. When poor solvent is used to introduce much inhomogeneous structure inside DN gels, the necking phenomenon was observed in the DN gels. We think the research of this new phenomenon leads to clarify the mechanism of strength enhancement of DN gels.

Ultra-small-angle neutron scattering study of actin-polymer complexes formation　　　　　　　　　　　　　　　
Tomomi Masui, Kazuhiro Shikinaka, Hyuck Joon Kwon, Satoshi Koizumi, Takeji Hashimoto, Hiroki Iwash, Akira Kakugo, Jian Ping Gong
Polymer Preprints, Japan, 55, 2, 3923, 3924, 2006
Japanese, International conference proceedings, We have investigated the structure formation of actin-polymer complexes using ultra-small-angle neutron scattering technique. SANS profile from the actin solution shows q-1 dependence at 0.005<
q<
0.04 A -1 which indicates that the actin has the cylindrical structure, however more low q region shows q-4 dependence which indicates that there are some aggregation of actin filaments. The addition of PDMAPAA-Q increases the SANS profiles at low q region, which indicates the formation of actin-polymer complexes. We extract the structure information from the SANS profiles and discuss the actin-polymer interactions.

Three dimensional structure observation of giant actin complexes by transmission electron microtomography　　　　　　　　　　　　　　　
Kazuhiro Shikinaka, Hyuckjoon Kwon, Akira Kakugo, Hidemitsu Furukawa, Jian Ping Gong, Yoshihito Osada, Hideo Nishioka, Hiroshi Jinnai
Polymer Preprints, Japan, 55, 2, 3921, 3922, 2006
Japanese, International conference proceedings, We have reported that polymer-actin complexes are obtained by mixing F-actin with synthetic polymers carrying positive charges. We found that the polymer-actin complex shows various morphology depending on polycation and salt concentration. In this study, we report that the three dimensional structure analysis of polymer-actin complexes by using transmission electron microtomography (TEMT). We found that the polymer-actin complex is flattened bundle in the low salt concentration, while that is cylindrical bundle in high salt concentration. It means that three dimensional structure of polymer-actin complex is determined by the magnitude of electrostatic repulsion force in F-actins.

Hydrated lubrication and friction of gels - Its richness and complexity　　　　　　　　　　　　　　　
Jian Ping Gong, Go Kagata, Takayuki Kurokawa, Yoshihito Osada
Polymer Preprints, Japan, 55, 2, 4257, 4259, 2006
Japanese, International conference proceedings, Biological connective tissues, such as cartilage, corneal stroma, are essentially hydrogels consisting of fibrous collagen and proteoglycans. Few are known of the surface properties of the hydrogel, although we observe fascinating tribological behavior of biological soft tissues, such as the extremely low friction between animal cartilages. We consider that the role of solvated polymer network existing in extracellular matrix as a gel state is critically important in the specific frictional behavior of cartilages. In order to elucidate the general tribological features of solvated polymer matrix, friction of various kinds of hydrogels have been investigated, and very rich and complex frictional behaviors are observed. The friction force and its dependencies on the load are quite different depending on the chemical structures of the gels, surface properties of the opposing substrates, and the measurement condition, which are totally different from those of solids. Most importantly, the coefficient of friction of gels, μ, changes in a wide range and exhibits very low values (μ ≈ 10-3 -10-5), which can not be obtained from the friction between two solid materials.

Catch and release of DNA in coacervate-dispersed gels　　　　　　　　　　　　　　　
Asami Ohsugi, Hidemitsu Furukawa, Akira Kakugo, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 55, 1, 1753, 2006
Japanese, International conference proceedings, Coacervate droplets are colloidal particles, which are usually composed of positive and negative polyelectrolytes. However, a polyzwitterion PDMAPS, which has both positive and negative charge in a polymer side chain, forms coacervate droplets in water by itself. PDMAPS coacervate can catch DNA and keep it in. In order to utilize PDMAPS coacervate, we synthesized "coacervate-dispersed gels" to stabilize PDMAPS droplets in the gels. Thus we succeeded to show that the coacervate-dispersed gels can be applied to control the transport of DNA in electrophoresis gels.

Oriented bacterial cellulose gel produced in confined space　　　　　　　　　　　　　　　
Ananda Putra, Akira Kakugo, Hidemistu Furukawa, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 55, 1, 1846, 2006
English, International conference proceedings

Spatio-temporal control of actin self-organization by photo responsive polymer　　　　　　　　　　　　　　　
Manami Misu, Hyuck-Joon Kwon, Kazuhiro Shikinaka, Akira Kakugo, Hidemitsu Furukawa, Jian Ping Gong, Yoshihito Osada, Toshifumi Satoh
Polymer Preprints, Japan, 55, 1, 1848, 2006
Japanese, International conference proceedings, In this study, we created biomimetic system of stimulus-induced actin organization by using photo responsive polymer. Photo responsive polymer was prepared by radical-copolymerization of DMAPAA-Q and Leucohydroxide, which can generate cation on UV irradiation at 250-420nm. We observed that UV illumination induces F-actins to be assembled into large complex cooperatively in the presence of poly(Leucohydroxide-co DMAPAA-Q). This self assembly system based on photo responsive polymer will lead to the creation of new biomimetic actuator.

Gel-gel adhesion by double network structure　　　　　　　　　　　　　　　
Junji Saito, Rikimaru Kuwabara, Yoshimi Tanaka, Hidemitsu Furukawa, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 55, 1, 1052, 2006
Japanese, International conference proceedings, We found that a pair of 1st network PAMPS gel sheets strongly adhere to each other by introducing the 2nd network PAAm into the system. The strength of fracture energy under peeling test becomes comparable to that of double network gels under tearing test. We showed that the strong adhesion can be achieved if the cross-linking density of 2nd network is more than a certain value. It means that double network structure can realize strong gel-gel adhesion.

The surface friction of hydrogel (26) - Effect of gel stiffness on the elastic-hydrodynamic transition　　　　　　　　　　　　　　　
Miao Du, Naoyuki Takedomi, Taki Tominaga, Hidemitsu Furukawa, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 55, 1, 1120, 2006
English, International conference proceedings

高分子ゲルの超低摩擦　　　　　　　　　　　　　　　
龔剣萍
トライボロジスト, 51, 12, 867, 872, 2006, [Invited]
Japanese, Scientific journal

うなぎに学んだ超低摩擦ゲル　　　　　　　　　　　　　　　
武富直之, 龔剣萍
接着の技術, 26, 3, 43, 48, 2006, [Invited]
Japanese, Scientific journal

Hydrogels with Extremely High Mechanical Strength
SAITO Junji, GONG Jian Ping, OSADA Yoshihito
MEMBRANE, 31, 6, 302, 306, THE MEMBRANE SOCIETY OF JAPAN, 2006, [Invited]
Japanese, Scientific journal

ナノテクノロジーによる人工軟骨の創成　　　　　　　　　　　　　　　
室崎喬之, 龔剣萍, 長田義仁
日本臨牀, 64, 2, 206, 214, 2006, [Invited]
Japanese, Scientific journal

Polyelectrolyte gels-fundamentals and applications
Hyuck Joon Kwon, Yoshihito Osada, Jian Ping Gong
POLYMER JOURNAL, 38, 12, 1211, 1219, SOC POLYMER SCIENCE JAPAN, 2006, [Invited]
English, Scientific journal, Polyelectrolyte gels are charged polymer networks with macro-ions fixed on polymer chains. This present paper introduces fundamental aspects, properties and application of negatively charged polyelectrolyte gels, focusing on the electrical properties of polyelectrolyte gels, diffusion of proteins in polyelectrolyte gels, interactions between polyelectrolyte gels and oppositely charged molecules, and mechanical strength of polyelectrolyte based gels. These characteristic properties of polyelectrolyte gels have considerable potential for applications, such as soft and wet scaffolds of cells, soft actuators and replacement of biological tissues.

Friction and lubrication of hydrogels - its richness and complexity
Jian Ping Gong
SOFT MATTER, 2, 7, 544, 552, ROYAL SOC CHEMISTRY, 2006, [Peer-reviewed], [Invited]
English, Scientific journal, Biological connective tissues, such as cartilage and corneal stroma, are essentially hydrogels consisting of fibrous collagen and proteoglycans. Little is known of the surface properties of the hydrogel, although we observe fascinating tribological behavior in biological soft tissues, such as extremely low friction between animal cartilages. We consider that the role of the solvated polymer network existing in the extracellular matrix as a gel state is critically important in the specific frictional behavior of cartilages. In order to elucidate the general tribological features of a solvated polymer matrix, the friction of various kinds of hydrogels has been investigated, and very rich and complex frictional behaviors are observed. The friction force and its dependence on the load differ with the chemical structure of the gels, surface properties of the opposing substrates, and the measurement conditions, which are totally different from those of solids. Most importantly, the coefficient of friction of gels, m, varies over a wide range and exhibits very low values (mu approximate to 10(-3)-10(-4)), which cannot be obtained from the friction between two solid materials. A repulsion-adsorption model has been proposed to explain the gel friction, which says that the friction is due to lubrication of a hydrated layer of polymer chains when the polymer chain of the gel is non-adhesive (repulsive) to the substrate, and the friction is due to elastic deformation of the adsorbed polymer chain when it is adhesive to the substrate.

Surface properties of endothelial cells cultured on hydrogels
Chen Y.M, Tanaka M, Gong J.P, Kazunori Y, Yamamoto S, Shimomura M, Osada Y
Polymer Preprints, Japan, 55, 2, 4860, 2006, [Peer-reviewed]

Superlow friction of polymer gel
Jian Ping Gong
JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS, 51, 12, 867, 872, JAPAN SOC TRIBOLOGISTS, 2006, [Peer-reviewed]
Japanese, Scientific journal

Polyioncomplex gels with liquid crystal structure
Yukari Shigekura, Yongmei Chen, Yongmei Chen, Daisaku Kaneko, Hidemitsu Furukawa, Jian Ping Gong, Jian Ping Gong, Yoshihito Osada, Yoshihito Osada, Tatsuo Kaneko
Polymer Preprints, Japan, 54, 1525, 01 Dec. 2005
We study a novel kind of polyioncomplex gels with liquid crystalline structure. We focus on highly-charged rigid-rod poly(2,2′-disulfonyl-4, 4′-benzidine terephthalamide)(PBDT), which behaves as mesogen in water to induce lyotropic self-organization from a very low concentrations of 2.8wt.%. By template (matrix) polymerization with N-[3-(N,N-dimethylamino)propyl] acrylamide, methyl chloride quarternary (DMAPAA-Q) under the condition where the charge ratio of PBDT as a liquid crystal molecule to DMAPAA-Q as a monomer is 1:26, the gels exhibit strong birefringence. Here, the PBDT concentration in the gels is 1/20 of lower critical PBDT concentration in aqueous solution. It means that by adding a very little amount of ionic mesogen template the birefringence polyioncomplex gels that contains ordered network structure can be synthesized.

Morphology of actin assemblies in response to polycation and salts
HJ Kwon, A Kakugo, K Shikinaka, Y Osada, JP Gong
BIOMACROMOLECULES, 6, 6, 3005, 3009, AMER CHEMICAL SOC, Nov. 2005, [Peer-reviewed]
English, Scientific journal, F-actins are semi-flexible polyelectrolytes and can be assembled into a large polymer-actin complex with polymorphism through electrostatic interaction with polycations. This study investigates the structural phase behavior and the growth of polymer-actin complexes in terms of its longitudinal and lateral sizes in various polycation and KCl concentrations for a constant actin concentration. Our results show that the longitudinal growth and lateral growth of polymer-actin complexes, initiated by a common nucleation process, are dominated by different factors in subsequent growth process. This induces the structural polymorphism of polymer-actin complexes. Major factors to influence the polymorphism of polymer-actin complexes in polyelectrolyte systems have been discussed. Our results indicate that the semiflexible polyelectrolyte nature of F-actins is important for controlling the morphology and growth of actin architectures in cells.

Anisotropic polyion-complex gels via template polymerization
Y Shigekura, YM Chen, H Furukawa, T Kaneko, D Kaneko, Y Osada, JP Gong
ADVANCED MATERIALS, 17, 22, 2695, +, WILEY-V C H VERLAG GMBH, Nov. 2005, [Peer-reviewed]
English, Scientific journal, Anisotropic gels containing a very small amount of liquid crystals have been prepared. The gels exhibit strong birefringence, even after swelling, under crossed polarizers, although the monomer solutions do not (see Figure). The swollen gels have a liquid-crystal concentration (C-LC) of only 0.14 wt.-%.

Effect of polymer entanglement on the toughening of double network hydrogels
H Tsukeshiba, M Huang, YH Na, T Kurokawa, R Kuwabara, Y Tanaka, H Furukawa, Y Osada, JP Gong
JOURNAL OF PHYSICAL CHEMISTRY B, 109, 34, 16304, 16309, AMER CHEMICAL SOC, Sep. 2005, [Peer-reviewed]
English, Scientific journal, The mechanical strength of double network (DN) gels consisting of highly cross-linked poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) as the first component and linear polyacrylamide (PAAm) as the second component has been investigated by varying the molecular weight of the second polymer PAAm, M-w. The experimental results reveal that, for toughening of the DN gels, (1) M-w is one of the dominant parameters, (2) there is a critical value of M-w = 10(6) for a remarkable enhancement: (3) the fracture energy of DN gels with a M-w, larger than 101 reaches a value as high as 10(3) J/m(2). By plotting the strength of DN gels (fracture stress sigma and fracture energy G) against a characteristic parameter of c[eta]. where c is the average concentration of PAAm in the DN gels and [eta] is the intrinsic viscosity of PAAm. it is found that the dramatic increase in the mechanical strength of the DN gels occurs above the region where linear PAAm chains are entangled with each other. Thus, we conclude that the entanglement between the second component PAAm plays an important role of the toughening mechanism of DN gels. This result supports the heterogeneous model, which predicts the presence of "voids" of the first network PAMPS with a size much larger than the radius of the second polymer PAAm.

Elastic-hydrodynamic transition of gel friction
T Kurokawa, T Tominaga, Y Katsuyama, R Kuwabara, H Furukawa, Y Osada, JP Gong
LANGMUIR, 21, 19, 8643, 8648, AMER CHEMICAL SOC, Sep. 2005, [Peer-reviewed]
English, Scientific journal, We report the surface sliding friction of a high strength gel against a glass substrate under a normal pressure range of 0.01-2.5 MPa. The friction of the gel swollen with different viscous solvents is investigated over a wide velocity range. A velocity-viscosity conversion relationship is established. From the velocity-viscosity conversion relationship, a master curve that is characteristic to the elastic-hydrodynamic transition is observed. The results indicate that the adsorption model proposed by our previous work is valid even under a pressure up to MPa orders, which is the order of pressure that a cartilage sustains in the articular joints.

Gel machines constructed from chemically cross-linked actins and myosins
A Kakugo, K Shikinaka, JP Gong, Y Osada
POLYMER, 46, 18, 7759, 7770, ELSEVIER SCI LTD, Aug. 2005, [Peer-reviewed]
English, Scientific journal, We report an ATP fueled soft gel machine reconstructed from muscle proteins of actin and myosin. Chemically cross-linked actin gel filaments, several decade times the length of native actin filaments (F-actin) move along a chemically cross-linked myosin fibrous gel (1 cm long and 50 mu m in diameter) with a velocity as high as that of native F-actin, by coupling to ATP hydrolysis. The motility observed in muscle protein-gels suggests that one might reconstruct a soft machine fueled by chemical energy by using actin and myosin molecules as elementary elements. (c) 2005 Elsevier Ltd. All rights reserved.

Cultivation of endothelial cells on adhesive protein-free synthetic polymer gels
YM Chen, N Shiraishi, H Satokawa, A Kakugo, T Narita, JP Gong, Y Osada, K Yamamoto, J Ando
BIOMATERIALS, 26, 22, 4588, 4596, ELSEVIER SCI LTD, Aug. 2005, [Peer-reviewed]
English, Scientific journal, Various hydrogels without modification by any cell adhesive proteins have been investigated as cell scaffolds. The present study shows that bovine fetal aorta endothelial cells can adhere, spread, proliferate, and reach confluence on poly(acrylic acid), poly(sodium p-styrene sulfonate), and poly(2-acrylamido-2- methyl-l-propanesulfonic sodium) gels, whereas cells reach subconfluence on poly(vinyl alcohol) and poly(meth acrylic acid) gels. The proliferation behavior was sensitive to both hydrogel charge density and crosslinker concentration. The relationship between cell proliferation and zeta potential of gels was discussed. It was found that hydrogels with a negative zeta potential higher than about 20mV facilitates cell proliferation. (c) 2004 Elsevier Ltd. All rights reserved.

Biomechanical properties of high-toughness double network hydrogels
K Yasuda, JP Gong, Y Katsuyama, A Nakayama, Y Tanabe, E Kondo, M Ueno, Y Osada
BIOMATERIALS, 26, 21, 4468, 4475, ELSEVIER SCI LTD, Jul. 2005, [Peer-reviewed]
English, Scientific journal, This study evaluated the wear property of four novel double-network (DN) hydrogels, which was composed of two kinds of hydrophilic polymers, using pin-on-flat wear testing. The gels involve PAMPS-PAAm get which consists of poly(2-acrylamide-2metyl-propane sulfonic acid) and polyacrylamide, PAMPS-PDAAAm gel which consists of poly(2-acrylamide-2-metyl-propane sulfonic acid) and poly(N,N'-dimetyl acrylamide), Cellulose/PDMAAm gel which consists of bacterial Cellulose and poly dimetylacrylamide, and Cellulose-Gelatin gel which consists of bacterial Cellulose and Gelatin. Ultra-high molecular weight polyethylene (UHMWPE) was used as a control of a clinically available material. Using a reciprocating apparatus, 10(6) Cycles of friction between a flat specimen and ceramic pin were repeated in water under a contact pressure of 0.1 MPa. To determine the depth and the roughness of the concave lesion created by wear, a confocal laser microscope was used. As a result, the maximum wear depth of the PAMPS-PDMAAm gel (3.20 mu m) was minimal in the five materials, while there was no significant difference compared to UHMWPE. There were significant differences between UHMWPE and one of the other three gels. The PAMPS-PAAm gel (9.50 mu m), the Cellulose PDMAAm gel (7.80 mu m), and the Cellulose-Gelatin gel (1302.40 mu m). This study demonstrated that the PAMPS-PDMAAm DN gel has an amazing wear property as a hydrogel that is comparable to the UHMWPE. In addition, the PAMPS-PAAm and Cellulose-PDMAAm DN gels are also resistant to wear to greater degrees than conventionally reported hydrogels. On the other hand, this study showed that the Cellulose-Gelatin DN gel was not resistant to wear. (c) 2004 Elsevier Ltd. All rights reserved.

Determination of fracture energy of high strength double network hydrogels
Y Tanaka, R Kuwabara, YH Na, T Kurokawa, JP Gong, Y Osada
JOURNAL OF PHYSICAL CHEMISTRY B, 109, 23, 11559, 11562, AMER CHEMICAL SOC, Jun. 2005, [Peer-reviewed]
English, Scientific journal, The fracture energy G of double network (DN) gels, consisting of poly(2-acrylamido-2-tnethylpropanesulfonic acid) (PAMPS) as the first network and poly(acrylamide) (PAAm) as the second network, was measured by the tearing test as a function of the crack velocity V. The following results were obtained: (i) The fracture energy G ranges from 10(2) to similar to 10(3) J/m(2), which is 100-1000 times larger than that of normal PAAm gels (10 J/m(2)) or PAMPS gels (10(-1) J/m(2)) with similar polymer concentrations to the DN gels. (ii) G shows weak dependence on the crack velocity V. (iii) G at a given value of V increases with decreasing of cross-linking density of the 2nd network. The measured values of G were compared with three theories that describe different mechanisms enhancing the fracture energy of soft polymeric systems. A mechanism relating to a heterogeneous structure of the DN gel is convincing for the remarkable large values of G.

Polarity and motility of large polymer-actin complexes
A Kakugo, K Shikinaka, N Takekawa, S Sugimoto, Y Osada, JP Gong
BIOMACROMOLECULES, 6, 2, 845, 849, AMER CHEMICAL SOC, Mar. 2005, [Peer-reviewed]
English, Scientific journal, The polarity of polymer-actin complexes obtained by mixing F-actin with synthetic polymers carrying positive charges such as poly(L-lysine), x,y-ionene bromide polymers, and poly{N-[3-(dimethylamino)propyl]-acrylamide} (PDMAPAA-Q) have been investigated. Actin complexes formed with poly(L-lysine) and PDMAPAA-Q, which carry charges on their side chains, show a higher polarity than those formed with x,y-ionene bromide polymers, which have charges on their chain backbones. All these polymer-actin complex gels show motility on the surfaces coated with myosin by coupling to adenosine 5'-triphosphate hydrolysis. A linear correlation between the polarity of polymer-actin complex gels and the motility is observed.

Kinetics of fluid spreading on viscoelastic substrates
D Kaneko, JP Gong, M Zrinyl, Y Osada
JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, 43, 5, 562, 572, JOHN WILEY & SONS INC, Mar. 2005, [Peer-reviewed]
English, Scientific journal, The spontaneous spreading of non-film-forming fluids on the surfaces of aqueous solutions of poly(2-acrylamido-2-methyl-propanesulfonic acid) and its chemically crosslinked gels was studied. The experiments were performed in the same concentration range for the solutions and gels, far above the overlap concentration of the polymer solutions. The leading edge (R) of the spreading liquid showed a power-law behavior with time t: R = K(t + c)(alpha), where alpha is the spreading exponent and K is the spreading prefactor. alpha and K were significantly different for the polymer solutions and gels. Here c was a constant that depended on the initial conditions of the spreading liquids. Depending on the polymer concentration, alpha of the polymer solutions varied between the upper (3/4) and lower (1/10) theoretical limits for viscose liquids and solids, respectively. This indicates that no universal scaling law exists for the spreading process on viscoelastic surfaces. On the polymer gels, which were elastic substrates, universal values of alpha could be observed and could be expressed as R proportional to (t + c)(0.45) and R proportional to (t + c)(0.3) for miscible and nonmiscible spreading liquids, respectively; they showed no dependence on the polymer concentration or network mesh size. This shows that on an elastic gel surface, spreading is more or less similar to that on a solid surface. (C) 2005 Wiley Periodicals, Inc.

Mechanically strong hydrogels with ultra-low frictional coefficients
D Kaneko, T Tada, T Kurokawa, JP Gong, Y Osada
ADVANCED MATERIALS, 17, 5, 535, +, WILEY-V C H VERLAG GMBH, Mar. 2005, [Peer-reviewed]
English, Scientific journal, High-strength, low-frictional-coefficient gels are produced by adding a third component to a double-network gel (DN gel), of either a weakly crosslinked network or non-crosslinked linear chains (to produce, respectively, a triple-network gel (TN gel) and a DN-L gel, see Figure). All the gels are highly transparent. The DN-L gel shows a fracture strength as high as 9 MPa and its frictional coefficient is as low as 10(-5) under an extremely high pressure of the order of sub-MPa.

Nano-gel machine reconstructed from muscle proteins
Kazuhiro Shikinaka, Akira Kakugo, Jian Ping Gong, Yoshihito Osada
e-Journal of Surface Science and Nanotechnology, 3, 51, 54, 14 Feb. 2005
English, Scientific journal, There are two basic differences in the motion between a human-made machine and a biological motor. One is in their principles. The motion of a human-made machine, which is constructed from hard and dry materials such as metals, ceramics or plastics, is realized by the relative displacement of the macroscopic constitute parts of the machine. In contrast to this, the motion of a living organism, which consists of soft and wet protein and tissues, is caused by the molecular deformation that is integrated to a macroscopic level through its hierarchical structure. The other is in their energy sources. The human-made machine is fueled by electrical or thermal energy with efficiency around 30%, but a biological motor is driven by direct conversion from the chemical energy with efficiency as high as 80-90%. In order to create biomimetic motility systems, polymer gels have been employed using their reversible size and shape change, thereby realizing the motion by integrating the deformation on a molecular level. Along this line, several kinds of artificial soft machines have been constructed using synthetic polymer gels in the past years. Gelooper (gel-looper), gelf (gel golf), gel valves, chemical motor, etc., are examples. However, the lack of hierarchical structures and energy sources inside the gel lead to a decreased response and restricts the further application of such actuators for practical use in human bodies. Here we report an ATP fueled soft gel machine reconstructed from muscle proteins of actin and myosin. Chemically cross-linked actin gel filaments, several decade times the length of native actin filaments (F-actin) move along a chemically cross-linked myosin fibrous gel (1 cm long and 50μm in diameter) with a velocity as high as that of native F-actin, by coupling to ATP hydrolysis. The motility observed in muscle protein-gels suggests that one might reconstruct a soft machine fueled by chemical energy by using actin and myosin molecules as elementary elements. © 2005 The Surface Science Society of Japan.

Toughening of hydrogels with double network structure
Yang-Ho Na, Yoshinori Katsuyama, Rikimaru Kuwabara, Takayuki Kurokawa, Yoshihito Osada, Mitsuhiro Shibayama, Jian Ping Gong
e-Journal of Surface Science and Nanotechnology, 3, 8, 11, 08 Jan. 2005
English, International conference proceedings, Hydrogels are made of swollen polymer networks containing more than 90% water. If modified with free chains on their surface, gels exhibit low surface friction and thus have been attractive candidates as artificial cartilage and low frictional materials. However, most hydrogels are mechanically too weak to be used as any load bearing devices. We have overcome this problem by synthesizing hydrogels with a double network (DN) structure. Despite of 90% water, these tough gels exhibit a fracture stress of 170 kg/cm 2, similar to that of cartilage. Extremely high mechanical property is due to peculiarly inhomogeneous structure of DN gels. The inhomogeneous structure is thought that large 'voids' of the first network may exist, and the second polymers exist in 'voids' of first network act as 'molecular crack-stopper' in DN gels, keeping the crack from growing to a macroscopic level. © 2005 The Surface Science Society of Japan.

Creation of nano-biomachine with muscle proteins [12] motility assay of myosin coated beads on actin gel sheet built by polymer interaction　　　　　　　　　　　　　　　
Kazuhiro Shikinaka, Akira Kakugo, Hidemitsu Furukawa, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 54, 1, 1532, 2005
Japanese, International conference proceedings, We had reported motility of polymer-actin complex (actin gel) on myosin gel. Actin gel was obtained by mixing F-actin with synthetic polymers carrying positive charges. We found that all actin gels exhibit motility with a translational motion on the surface coated with myosin, regardless the chemical structure of the polymers, but the velocity of complex gels depends on polycation species. Here, we report that the motility assay of myosin coated beads on actin gel sheet obtained by mixing actin with polycation at high concentration. Myosin coated beads on actin gel sheet exhibits motility with a velocity as high as 7. 06μm/ sec, which is seven times faster than that of actin gel on the surface coated with myosin.

Three dimensional actin network formed by synthetic polycation(3) Major factors to determine longitudinal and lateral growth of actin complex　　　　　　　　　　　　　　　
Hyuckjoon Kwon, Akira Kakugo, Hidemitsu Furukawa, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 54, 1, 1531, 2005
Japanese, International conference proceedings, The growth pattern of actin complex was investigated in various condition. It was observed that the length of actin complex increases at first, and then decreases with the increase of PDMAPAA-Q. However, TEM observation showed that the thickness of acitin bundles to constitute network remains constant from 10-5 to 10-3M but begins to increase significantly from 10-2M. This results indicate that longitudinal growth is independent of lateral growth of actin complex. Next, we investigated the effect of KCl concentration on growth of actin complex. It was shown that both length and thickness of actin complex increase with increasing KCl concentration. Consequently, it was thought that the length of actin complex is determined by the ratio of F-actins available for growth to nuclei, while the thickness of actin bundles is determined by the balance between attraction and electrostatic repulsion in F-actins.

Actin polymerization in confined spatial　　　　　　　　　　　　　　　
Takehiro Ura, Akira Kakugo, Hidemitsu Furukawa, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 54, 1, 1530, 2005
Japanese, International conference proceedings, Intracellular actin plays an important role in numerous vital activities such as cell motility and structural support. But a lot of studies have been carried out in bulk solution. In the case of living cell, interaction between many other proteins is not negligible. From these reasons, we studied behavior of actins encapsulated in liposome as a model of plasma membrane and examine the effect of confined spatial space for actin polymerization. As a result, we found that F-actin encapsulated liposome shows faster Brownian motion than that of G-actin encapsulated liposome.

The toughening mechanism of double-network gels and structural inhomogeneity of 1st network　　　　　　　　　　　　　　　
Rikimaru Kuwabara, Hidemitsu Furukawa, Yang-Ho Na, Yasunori Kawauchi, Yoshimi Tanaka, Takayuki Kurokawa, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 54, 1, 1307, 2005
Japanese, International conference proceedings, We have developed double network hydrogels with extremely high mechanical strength, which are consist of polyelectrolyte 1st network and neutral 2nd network interpenetrated with each other. From the result of DLS, we have found that the 1st network has an inhomogeneous structure with large voids in the 1st network. In this study, we investigated the structural inhomogeneity of 1st network and its effect on the mechanical strength of DN gels. The experimental results showed that the remarkable high mechanical strength of DN gels only exhibits in case of inhomogeneous structure of 1st network. The toughening mechanism of DN gels was discussed in terms of composite materials and the structural imhomogeneity.

Creation of hydrogels with ultra high mechanical strength [XI]: Strength enhancement in double network gels by controlling inhomogeneous structure of 1st network gel　　　　　　　　　　　　　　　
Yasunori Kawauchi, Rikimaru Kuwabara, Hidemitsu Furukawa, Yang-Ho Na, Yoshimi Tanaka, Takayuki Kurokawa, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 54, 2, 4688, 4689, 2005
Japanese, International conference proceedings, We have recently synthesized DN gels with ultra high mechanical strength. The DN gels consist of polyelectrolyte gels as the 1st network and neutral gels (or linear polymer) as the 2nd network. The previous research with dynamic light scattering proposed that the 1st network has inhomogeneous structure with large voids, where such voids structure is important for the strength enhancement of DN gels. In the present study, the inhomogeneous structure was altered by using poor solvent to introduce the phase-separated structure inside DN gels. It is found that there is a maximum peak of the fracture energy, depending on the degree of the inhomogeneous structure. This result suggested that the inhomogeneous structure related to the strength enhancement of DN gels has an appropriate size.

Creation of hydrogels with ultra high mechanical strength (X) -role of the 2nd network entanglement on the toughening of double network gels (X)　　　　　　　　　　　　　　　
Mei Huang, Rikimaru Kuwabara, Yang-Ho Na, Hiroyuki Tsukeshiba, Yoshimi Tanaka, Takayuki Kurokawa, Hidemitsu Furukawa, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 54, 1, 868, 2005
English, International conference proceedings

Development of drag force measurement system in micro channel and effect of surface structure on hydrodynamics of microparticle　　　　　　　　　　　　　　　
Yuri Kishimoto, Akira Kakugo, Hidemitsu Furukawa, Jian Ping Gong, Yoshihito Osada, Junichi Hotta, Keiji Sasaki, Noboru Kitamura
Polymer Preprints, Japan, 54, 2, 4668, 4669, 2005
Japanese, International conference proceedings, Smoothly swimming motion of underwater microorganisms has not been understood yet. However, it is supposed that many polymer chains grafted on their surfaces play an important role in the motion. The object of this study is to clarify the influence of the surface structure on the drag force of microparticles. The various kinds of the surface structure are introduced to the microparticles with iniferter polymerization. The system having the position sensor, which is equipped with a laser tweezer and a quadrant photodiode, makes it possible to precisely observe the drag force. By using this system, the drag force of different microparticles, which have grafted polymer chains or surfactant on the surface, was measured and compared with unmodified polystyrene microparticles.

Cultivation of endothelial cells on polymer hydrogels (4) dynamic behavior of the cells on hydrogels　　　　　　　　　　　　　　　
Rie Ogawa, Yong Mei Chen, Akira Kakugo, Hidemitsu Furukawa, Jian Ping Gong, Yoshihito Osada
Polymer Preprints, Japan, 54, 2, 4723, 4724, 2005
Japanese, International conference proceedings, We found that endothelial cells can proliferate on synthetic hydrogels, PNaSS, without any surface modification by cell adhesive protein. The objective of this study is to analyze the effect of the physical properties of hydrogels on the dynamic behavior and morphology of the cells. The elasticity and charge density of hydrogels were controlled by altering the crosslinker concentration and the molar fraction of PNaSS in poly (NaSS-co-DMAAm) respectively. In order to analyze the dynamic behavior of the cells, time-lapse images were captured every 10 min from 6 to 12 hours. It was found that the moving speed of the cells increases with the charge density of hydrogels and the upper surface area of the cells increases with both the elasticity and the charge density of hydrogels.

ゲルの極低摩擦　　　　　　　　　　　　　　　
龔 剣萍, 長田義仁
日本機械学会誌, 108, 1042, 28, 29, 2005, [Invited]
Japanese, Scientific journal

Tough Gel with Low Surface Friction
GONG Jian Ping
GOMU, 78, 4, 130, 134, THE SOCIRETY OF RUBBER SCIENCE AND TECHNOLOGYY, JAPAN, 2005, [Invited]
Japanese, Scientific journal, The author's research group have systematically studied the surface sliding friction of hydrogels, and various unique features in gel friction have been discovered. The frictional force and its dependencies on the load are quite different depending on the chemical structures of the gels, surface properties of the opposing substrates, and the measurement condition, which are completely different from those of solids. Most importantly, the friction coefficient of gels exhibits a value as low as 0.001, which cannot be obtained from the friction between two solid materials.
Therefore, gels have a high potential as a low friction material, such as an artificial cartilage. However, conventional gels are mechanically too weak to be used as load bearing materials. The author's research group recently developed a general method to obtain very strong gels by introducing a double network structure of the gel. These high strength hydrogels, containing 90% water, sustain a compressive pressure as high as decades of MPa and show a high wear resistance due to their extremely low friction. These gels might open new era of soft and wet materials for substituting articular cartilage and other tissues.

Novel hydrogels with excellent mechanical performance
Y Tanaka, JP Gong, Y Osada
PROGRESS IN POLYMER SCIENCE, 30, 1, 1, 9, PERGAMON-ELSEVIER SCIENCE LTD, Jan. 2005, [Invited]
English, Scientific journal, Three kinds of novel hydrogels with excellent mechanical performance have been developed, based on different concepts. Two of them exhibit high resistance to extension, up to 10-20 times the original length, by introducing special cross-linking structures. The third has a high modulus (sub-megapascal), with a failure compressive stress as high as 20 MPa, through a double network structure. In this article, we describe the structural and mechanical features of these gels, and the status of current studies (C) 2005 Elsevier Ltd. All rights reserved.

3P136 Structural polymorphism and growth of actin complex in polyelectrolyte system
Kwon H.J., Shikinaka M., Kakugo A., Hurukawa H., Gong Jianping, Osada Y.
Seibutsu Butsuri, 45, S237, The Biophysical Society of Japan General Incorporated Association, 2005
Japanese

Characteristics of chemically cross-linked myosin gels
A Kakugo, S Sugimoto, K Shikinaka, JP Gong, Y Osada
JOURNAL OF BIOMATERIALS SCIENCE-POLYMER EDITION, 16, 2, 203, 218, VSP BV, 2005, [Peer-reviewed]
English, Scientific journal, Myosin gels, 10 mm x 10 mm x 1 mm in size, were obtained by chemical cross-linking of scallop myosin using 1-ethyl-3-(3-dimethylaminoprolyl) carbodiimide hydrochloride (EDC), glutaraldehyde (GA), or transglutaminase (TG). All myosin gels showed high Mg-ATPase activity, although it sensitively depended on the species of cross-linker used. Among cross-linkers used, myosin gel cross-linked by TG showed the highest sensitivity, almost as high as that of native myosin. The motility assay of native actin filament on the myosin gel showed that all these myosin gels can give motion to actin filament. Among them the one cross-linked by TG had the highest average velocity and the lowest threshold concentration of ATP for movement of the actin filament and the values are nearly the same as that of native myosin. In order to give the actin filament motion with preferential direction, we attempted to make myosin gel with oriented structure by applying a shear stress. Myosin gel with oriented filament array 1 cm long and 50 pm in diameter was obtained. We found that actin filaments prefer to move along the axis of the oriented myosin gel with an increased velocity.

High mechanical strength double-network hydrogel with bacterial cellulose
A Nakayama, A Kakugo, JP Gong, Y Osada, M Takai, T Erata, S Kawano
ADVANCED FUNCTIONAL MATERIALS, 14, 11, 1124, 1128, WILEY-V C H VERLAG GMBH, Nov. 2004, [Peer-reviewed]
English, Scientific journal, Double-network (DN) hydrogels with high mechanical strength have been synthesized using the natural polymers bacterial cellulose (BC) and gelatin. As-prepared BC contains 90% water that can easily be squeezed out, with no more recovery in its swelling property. Gelatin gel is brittle and is easily broken into fragments under a modest compression. In contrast, the fracture strength and elastic modulus of a BC-gelatin DN gel under compressive stress are on the order of megapascals, which are several orders of magnitude higher than those of gelatin gel, and almost equivalent to those of articular cartilage. A similar enhancement in the mechanical strength was also observed for the combination of BC with polysaccharides, such as sodium alginate, gellan gum, and i-carrageenan.

Surface friction of poly(dimethyl siloxane) gel and its transition phenomenon
Tomohiro Tada, Daisaku Kaneko, Jian Ping Gong, Tatsuo Kaneko, Yoshihito Osada
Tribology Letters, 17, 3, 505, 511, Oct. 2004, [Peer-reviewed]
English, Scientific journal, The surface sliding friction of chemically cross-linked poly(dimethyl siloxane) (PDMS) swollen with linear PDMS as an oligomer is investigated. The friction force f increases with the normal pressure P in a power-law relation f∝ Pα, where the exponent α changes in a range of 0-1, depending on the degree of polymerization, Npoly, of the linear PDMS oligomer. When Npoly is in a range of 240-320, a dramatic decrease in friction force is observed at a critical normal pressure, Pc, leading to a very low friction coefficient on the order of 10-3 at high-pressure ranges. The Pc increases with decreasing network size Nnet of the gel and also with increasing polymer length related to Npoly. One possible explanation for this transition phenomenon in friction is that linear PDMS molecules are exuded from the gel network beyond a certain pressure and behave as polymer brushes, which are able to reduce the friction. © 2004 Springer Science+Business Media, Inc.

Surface friction of hydrogels with well-defined polyelectrolyte brushes
Y Ohsedo, R Takashina, JP Gong, Y Osada
LANGMUIR, 20, 16, 6549, 6555, AMER CHEMICAL SOC, Aug. 2004, [Peer-reviewed]
English, Scientific journal, Hydrogels of poly(2-hydroxyethyl methacrylate) (PHEMA) with well-defined polyelectrolyte brushes of poly(sodium 4-styrenesulfonate) (PNaSS) of various molecular weights were synthesized, keeping the distance between the polymer brushes constant at ca. 20 nm. The effect of polyelectrolyte brush length on the sliding friction against a glass plate, an electrorepulsive solid substrate, was investigated in water in a velocity range of 7.5 x 10(-5) to 7.5 x 10(-2) m/s. It is found that the presence of polymer brush can dramatically reduce the friction when the polymer brushes are short. With an increase in the length of the polymer brush, this drag reduction effect only works at a low sliding velocity, and the gel with long polymer brushes even shows a higher friction than that of a normal network gel at a high sliding velocity. The strong polymer length and sliding velocity dependence indicate a dynamic mechanism of the polymer brush effect.

Structural characteristics of double network gels with extremely high mechanical strength
YH Na, T Kurokawa, Y Katsuyama, H Tsukeshiba, JP Gong, Y Osada, S Okabe, T Karino, M Shibayama
MACROMOLECULES, 37, 14, 5370, 5374, AMER CHEMICAL SOC, Jul. 2004, [Peer-reviewed]
English, Scientific journal, The dynamic aspect of double network (DN) gels showing an extremely high mechanical strength has been investigated by dynamic light scattering (DLS) measurements. The DN gels are formed from highly cross-linked poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) as the first network and loosely cross-linked (or non-cross-linked) polyacrylamide (PAAm) as the second network. The results of DLS show that the presence of slow mode besides the gel mode (fast mode) enhances the strength of DN gels at the low cross-linking density of the second network. The dynamics of the slow mode cannot be explained in terms of reptational motion of the second component in the first network, but it is similar to the translational motion of PAAm polymers in a semidilute solution. A strong velocity dependence of the mechanical strength is observed at a shear rate close to the inverse of the relaxation time of the slow mode. These results suggest that large "voids" of the first network may exist, and PAAm polymers that exist in "voids" act as a "molecular crack stopper" in DN gels, keeping the crack from growing to a macroscopic level.

Shear-induced mesophase organization of polyanionic rigid rods in aqueous solution
T Funaki, T Kaneko, K Yamaoka, Y Ohsedo, JP Gong, Y Osada, Y Shibasaki, M Ueda
LANGMUIR, 20, 15, 6518, 6520, AMER CHEMICAL SOC, Jul. 2004, [Peer-reviewed]
English, Scientific journal

Thermoresponsive Shrinkage Triggered by Mesophase Transition in Liquid Crystalline Physical Hydrogels
Tatsuo Kaneko, Kanji Yamaoka, Yoshihito Osada, Jian Ping Gong
Macromolecules, 37, 14, 5385, 5388, Jun. 2004, [Peer-reviewed]
English, Scientific journal

Polymer gels (Reprinted from Functional Monomers and Polymers, pg 497-528, 1997)
Y Osada, JP Gong, Y Tanaka
JOURNAL OF MACROMOLECULAR SCIENCE-POLYMER REVIEWS, C44, 1, 87, 112, MARCEL DEKKER INC, Feb. 2004, [Invited]
English, Scientific journal, An overview was given on polymer gel with respect to its structure, gelation process, properties, and applications. In a structural analysis it is necessary to have a different scale depending on the gel structure observed. Properties and responses of polymer gels were widely described with the explanation for solvent properties and phase transition, thermoresponse, chemical response, and electric properties. The potential application of gels has also been shown concerning biomedical use, drug. delivery system, and selective separation.

Cooperative binding in surfactant–polymer association: A brief overview　　　　　　　　　　　　　　　
Rupali Gangopadhyay, Jian Ping Gong, Yoshihito Osada
Reflexive Polymers and Hydrogels: Understanding and Designing Fast Responsive Polymeric Systems, 165, 188, CRC Press, 01 Jan. 2004
English, In book, Surfactants are defined as molecules having long hydrophobic tails and strongly hydrophilic head groups. These molecules have a number of interesting and important properties like aggregating into micelles and binding with different organic systems.1-20 Among these combinations, much attention has been paid to the surfactant-polymer association and different aspects of such combinations have been widely studied. The excellent application potentials of such systems in mimicking biological systems and fabricating fast responsive devices and artificial muscles have been explored. In fact, the surfactant-polymer assembly is considered one of the most popular responsive systems. Obviously the thermodynamic and kinetic behaviors of surfactant binding to linear and crosslinked polymers have raised a great deal of scientific interest.

高強度低摩擦ソフトマテリアルの創製とその人工半月板への応用　　　　　　　　　　　　　　　
桑原力丸, 安田和則, 龔剣萍, 長田義仁
医学のあゆみ, 221, 7, 771, 772, 2004, [Invited]
Japanese, Scientific journal

1P168 Three-dimensional network formation by self-organization of actin on gel surface
Ura T., Kakugo A., Gong Jian Ping, Osada Y.
Seibutsu Butsuri, 44, S71, The Biophysical Society of Japan General Incorporated Association, 2004
Japanese

Liquid crystalline hydrogels: Mesomorphic behavior of amphiphilic polyacrylates bearing cholesterol mesogen
T Kaneko, H Nagasawa, JP Gong, Y Osada
MACROMOLECULES, 37, 1, 187, 191, AMER CHEMICAL SOC, Jan. 2004, [Peer-reviewed]
English, Scientific journal, Copolymers composed of 5-acryloyloxypentyl cholesterate (Ch5A) and acrylic acid (AA), poly(Ch5A-co-AA)s, were prepared changing their molar ratio, and their mesomorphic behaviors were investigated. Wide- and small-angle X-ray diffraction studies showed that poly(Ch5A-co-AA)s with a Ch5A mole fraction, F, of 0.20 and larger showed the smectic A phase in which side chains are arranged perpendicularly to the main-chain axis forming bilayers. The structural ordering and the clearing temperature, T-c, increased with decreasing F. The copolymers with F of around 0.10 exhibited a mesophase showing extremely high T-c and longer periodic spacing than the SmA phase. The copolymers of F = 0.05 and higher were not dissolved in water but swelled to form hydrogels with mesomorphic properties, presumably due to the physical cross-linking of hydrophobic aggregates of Ch5A side chains. The relationship between the uncommon thermotropic behavior and the mesomorphic structure formed by the specific interaction of chiral Ch5A components was discussed.

Influence of shear stress on cationic surfactant uptake by anionic gels
YM Chen, Y Katsuyama, JP Gong, Y Osada
JOURNAL OF PHYSICAL CHEMISTRY B, 107, 49, 13601, 13607, AMER CHEMICAL SOC, Dec. 2003, [Peer-reviewed]
English, Scientific journal, Kinetic studies of cationic surfactant uptake by anionic polymer gel membrane under various shear flow have been performed, varying the alkyl chain length of surfactant, the ionic strength of surfactant solution, and the charge density of gel. By exposing the gel surface to a shear flow of ca. 1 Pa, the rate of surfactant uptake is distinctly enhanced, while the maximum binding ratio to the gel is not influenced. A linear relationship between the surfactant initial flux and shear stress has been established. At a high ionic strength, the effect of shear stress is suppressed, suggesting that the enhancement of surfactant uptake under shear flow is caused by a decrease in the surface electrostatic potential of the negatively charged polyelectrolyte get, which favors the uptake of the positively charged surfactant. From the Nernst and Planck equation, a relationship between the surfactant uptake kinetics and the electrostatic field is derived that allows us to estimate the shear stress dependence of the change in the electrostatic field on the gel surface. The origin of the shear-induced surface electrostatic field change is discussed.

Growth of large polymer-actin complexes
A Kakugo, K Shikinaka, K Matsumoto, JP Gong, Y Osada
BIOCONJUGATE CHEMISTRY, 14, 6, 1185, 1190, AMER CHEMICAL SOC, Nov. 2003, [Peer-reviewed]
English, Scientific journal, Polymer-actin complexes as large as 10-50 mum with filamentous, branched, stranded, and ring shapes are obtained when fluorescent phalloidin-labeled F-actin is mixed with some synthetic polymers carrying positive charges such as poly-L-lysine, x,y-ionene bromide polymers. All growth of these complexes occurs cooperatively at some certain critical polymer concentrations, regardless of the chemical structure of the polymer, while the morphology of the complexes is substantially influenced by the chemical structure of the polymer. Poly-Lys-actin complex grows preferentially along the filament axis even above the critical concentration. 3,3-ionene-actin complexes show completely homogeneous filaments below the critical concentration but forms bundles at a higher concentration. Occasionally, ring shape complexes can be observed in the 6,6-ionene-actin complex.

Effect of hydrophobic side chain on poly(carboxyl acid) dissociation and surfactant binding
YM Chen, S Matsumoto, JP Gong, Y Osada
MACROMOLECULES, 36, 23, 8830, 8835, AMER CHEMICAL SOC, Nov. 2003, [Peer-reviewed]
English, Scientific journal, Copolymers consisting of acrylic acid (AA) and 12-acryloyldodecanoic acid (ADA) [poly(ADA-co-AA)] were synthesized, and their dissociation behaviors and binding characteristics with ionic surfactant, dodecylpyridinium. chloride, were investigated. The dissociation is strongly suppressed in the presence of ADA, and when the ADA molar fraction (F-ADA) is 0.5, the copolymer exhibits a distinct two-stage dissociation associated with AA and ADA. The binding process is also changed by the presence of ADA. When the ADA content is low, the surfactants bind cooperatively to form a stoichiometric complex. An increase in ADA content brings about noncooperative and nonstoichiometric complexion. The initiation constant (K-0) for an isolated surfactant binding to poly(ADA(F-ADA = 1.0)) is more than 3 orders of magnitude larger than that of poly(AA(FADA = 0)), indicating that the initiation of the binding is associated not only with the electrostatic interaction but also with the hydrophobic interaction between the alkyl chains of surfactant and ADA. The structure of surfactant-poly(ADA-co-AA) complexes changes from micelle-like to lamellar-like with the increase in F-ADA.

Thickness decrease of a grafted polyelectrolyte membrane exposed to shear flow
D Kaneko, T Narita, JP Gong, Y Osada, J Ando, K Yamamoto, S Ohnishi, VV Yaminsky
JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, 41, 22, 2808, 2815, JOHN WILEY & SONS INC, Nov. 2003, [Peer-reviewed]
English, Scientific journal, The effect of the shear flow on the thickness change of a polyelectrolyte membrane grafted onto a glass substrate was directly investigated with a flow cell combined with a confocal laser scanning microscope. The membrane thickness decreased proportionally to an increase in the shear stress of the flow when the shear rate exceeded a critical value of 1 s(-1). The higher the ionic strength was of the fluid, the greater the thinning effect was. The correlation between the critical shear rate and the relaxation of the polymer in the gel membrane was examined. (C) 2003 Wiley Periodicals, Inc.

Study on doping behaviors of vinyl hydrogels with pendant terthiophenes
L Chen, JP Gong, Y Ohsedo, Y Osada
MACROMOLECULAR CHEMISTRY AND PHYSICS, 204, 17, 2142, 2146, WILEY-V C H VERLAG GMBH, Nov. 2003, [Peer-reviewed]
English, Scientific journal, The water-swollen poly(AA3T-co-NaSS) and poly(AA3T-co-PEG) gels were synthesized by radical copolymerization of the monomer, [ (2,2:5',2"-terthiophen-5-yl)methyl acrylate] (AA3T), containing pendant terthiophenes as an electron-conducting material with a soluble monomer, sodium p-styrenesulfonate (NaSS), or oligo(ethylene glycol) (PEG); their swelling, spectral, and doping behaviors were investigated. The degree of swelling of the poly(AA3T-co-PEG) gel was independent of the pH, whereas that of poly(AA3T-co-NaSS) gel increases abruptly below pH 3, which suggests self-doping between the AA3T and NaSS groups. The self-doping is not suppressed by cross-linking. Both poly(AA3T-co-NaSS) and poly(AA3T-co-PEG) gels can be chemically doped with concentrated HCl or HClO4 solution.

Formation of giant needle-like polycation-bile acid complexes
T Kaneko, A Ichikawa, JP Gong, Y Osada
MACROMOLECULAR RAPID COMMUNICATIONS, 24, 13, 789, 792, WILEY-V C H VERLAG GMBH, Sep. 2003, [Peer-reviewed]
English, Scientific journal, The complexation of bile acids with various solvated polycations was studied. A one-to-one complex was precipitated when an aqueous solution of cholic acid sodium salt (CA) was mixed with aqueous solutions of 3,3-ionene and grew to form crystals with needle-like morphology, 3 millimeters in length. Hydrogen bonding of hydroxyls at the steroid face and the spacing between cationic sites of polycations were crucial for the formation of the giant needle.

Liquid crystalline gels. 4. Water- and stress-induced mesophase transition
K Yamaoka, T Kaneko, JP Gong, Y Osada
LANGMUIR, 19, 20, 8134, 8136, AMER CHEMICAL SOC, Sep. 2003, [Peer-reviewed]
English, Scientific journal, A stretching test of the hydrogel with a smectic A (SmA) type of liquid crystalline structure, poly(11-cyanobiphenyloxyundecyl acrylate-co-acrylic acid), poly(11CBA-co-AA), was carried out in terms of various water contents. It was found that Young's modulus of the hydrogel substantially decreased with increasing the swelling degree, q, but suddenly jumped up at q = 1.13. Wide- and small-angle X-ray diffraction studies revealed that the hydrogel underwent a mesophase transition from the SmA to smectic I (SmI) phase between these q values. When the samples were further stretched, the backward transition from the SmI to SmA phase occurred accompanied by "necking". The possible mechanism of the tension-induced mesophase transition is proposed.

Friction of gels. 7. Observation of static friction between like-charged gels
G Kagata, JP Gong, Y Osada
JOURNAL OF PHYSICAL CHEMISTRY B, 107, 37, 10221, 10225, AMER CHEMICAL SOC, Sep. 2003, [Peer-reviewed]
English, Scientific journal, An extensive static friction has been observed when two like-charged polyelectrolyte gels are slid over each other in water. The two like-charged gel surfaces could not slip with each other at the initial shearing until the shear stress acting on the interface exceeded a certain critical value. The critical yield shear stress (static friction) and strain did not show a distinct dependence on the shearing rate but decreased with increasing temperature. The value of the static friction also increased with the increase in the normal pressure and effect of pressure becomes more substantial at a higher temperature. Furthermore, the static friction decreased 3-4 times when the counterions of the polyelectrolyte gels were changed from Na+ to Cs+. The observation of the static friction indicates that our previously proposed repulsion-adsorption model, which predicts a hydrodynamic mechanism with no static friction for two like-charged hydrogels in pure water, requires modification. Possible origins of the static friction are discussed.

Friction of Gels. 7. Observation of Static Friction Between Like-Charged Gels
Go Kagata, Jian Ping Gong, Yoshihito Osada
J. Phys. Chem. B, 107, 37, 10221, 10225, Aug. 2003, [Peer-reviewed]
English, Scientific journal

Double-network hydrogels with extremely high mechanical strength
JP Gong, Y Katsuyama, T Kurokawa, Y Osada
ADVANCED MATERIALS, 15, 14, 1155, +, WILEY-V C H VERLAG GMBH, Jul. 2003, [Peer-reviewed]
English, Scientific journal, Very strong hydrogels (with a fracture strength of some tens of MPa), as required for both industrial and biomedical applications, have been generated by inducing a double-network (DN) structure for various combinations of hydrophilic polymers. The Figure shows a hydrogel before, during, and after application of a fracture stress of 17.2 MPa.

Surface friction of polyelectrolyte gels
Jian Ping Gong, Go Kagata, Yoshihito Osada
Macromolecular Symposia, 195, 209, 216, Jun. 2003, [Invited]
English, International conference proceedings, The friction between two chemically cross-linked polyelectrolyte gels carrying the same sign of charges has been investigated in pure water as well as in salt solutions using a rheometer. It is found that the friction was largely dependent on the charge densities of the gel surface and the ionic strength of the aqueous solution. The chemical structures of the polyelectrolyte gels also play an important role. The friction is described in terms of the hydrodynamic lubrication of the solvent layer between the two gel surfaces, which is formed due to the electrostatic repulsion of the two gel surfaces. The thickness of the solvent layer has been estimated using the Poisson-Boltzmann equation supposing that the ionic osmotic pressure is balanced by the normal pressure applied on the gel. The friction values have been calculated by considering the shear flow of solvent in gel region using the Debye-Binkman equation. For strongly charged polyelectrolyte gels swollen in pure water, the theoretical analysis shows that the friction coefficient almost has no dependence on the water content of the gel, which well agrees with the experimental observations.

Water-swollen hydrogels with pendant terthiophenes
L Chen, JP Gong, Y Ohsedo, Y Osada
MACROMOLECULAR CHEMISTRY AND PHYSICS, 204, 4, 661, 665, WILEY-V C H VERLAG GMBH, Mar. 2003, [Peer-reviewed]
English, Scientific journal, A chemically cross-linked and water-swollen poly(AA3T-co-AA) gel having pendant terthiophenes was synthesized by radical copolymerization of [ (2.2':5',2"-terthiophen-5-yl-)methyl acrylate] (AA3T) and acrylic acid (AA), and its swelling, dissociation, and doping behaviors were studied. The gel swells in high pH solution, which is associated with the dissociation and, hence, electrostatic repulsion of the AA units and the pH value at which the swelling starts increases with increasing AA3T composition. The dissociation of the gels is suppressed, presumably due to the incorporation of the hydrophobic AA3T unit, and, once started, the dissociation could be promoted by AA3T in the low pH region. Poly(AA3T-co-AA) copolymers and gels can be easily electrochemically and chemically doped. The volume change of the gels is observed during doping/undoping and the maximum volume change reached was about 50%.

ソフトアンドウェットマター−ゲル−の摩擦　　　　　　　　　　　　　　　
富永大輝, 龔剣萍, 長田義仁
表面, 40, 9, 317, 323, 2003, [Invited]
Japanese, Scientific journal

筋肉タンパクによるゲルマシーンの創製　　　　　　　　　　　　　　　
角五彰, 龔剣萍, 長田義仁
化学工業, 55, 4, 34, 42, 2003, [Invited]
Japanese, Scientific journal

筋肉タンパクによるナノバイオマシーンの創製　　　　　　　　　　　　　　　
敷中一洋, 角五彰, 龔剣萍, 長田義仁
Bio Medical Quick Review Net., 2003, [Invited]
Japanese, Scientific journal

Surface Friction of Polymer Gel
GONG Jian Ping, OSADA Yoshihito
Kobunshi, 52, 9, 711, 716, The Society of Polymer Science, Japan, 2003, [Invited]
Japanese, Scientific journal

Substrate effect on the formation of hydrogels with heterogeneous network structure
P Mao, PG Jian, Y Osada
CHEMICAL RECORD, 3, 1, 40, 50, JOHN WILEY & SONS INC, 2003, [Invited]
English, Scientific journal, It was found that when an aqueous solution of vinyl monomers is polymerized on a hydrophobic substrate, obvious heterogeneity occurs in the region of the interface. This substrate effect was observed on polytetrafluroethylene (Teflon), polypropylene (PP), polyethylene (PE), polystyrene (PS), and polyvinylchloride (PVC), but not on hydrophilic substrates. Compared with synthesis on hydrophilic surfaces, the surfaces of hydrogels synthesized on a hydrophobic substrate exhibit a larger degree of swelling, a lower surface coefficient of friction and elastic modulus, weaker interfacial adhesion, and reduced interaction with biological cells. This substrate effect has been observed for many types of aqueous monomer solutions. It was found that the above properties are related to the loosely cross-linked architecture, containing some graft-like polymer chains, that is formed on the gel surface when the gel is prepared on a hydrophobic substrate. To understand the mechanism of the substrate effect, two novel optical methods, electric speckle pattern interferometry (ESPI) and real-time laser sheet refraction (RT-LSR), were developed. It was found that oxygen trapped in the composite interface between the monomer solution and rough hydrophobic substrates played an important role in the substrate effect. (C) 2003 The Japan Chemical Journal Forum and Wiley Periodicals, Inc.

Substrate effect on topographical, elastic, and frictional properties of hydrogels
T Kurokawa, JP Gong, Y Osada
MACROMOLECULES, 35, 21, 8161, 8166, AMER CHEMICAL SOC, Oct. 2002, [Peer-reviewed]
English, Scientific journal, Cross-linked poly(N,N'-dimethyl acrylamide) hydrogels were prepared on hydrophilic silicon substrates or hydrophobic polystyrene substrates and their topographical elastic properties were investigated by atomic force microscopy (AFM). The gels prepared on the hydrophobic substrate have a much rougher surface morphology with a lower surface elastic modulus than those prepared on the hydrophilic substrate. The topographical and mechanical properties of the gel have little influence on the surface friction, and the lower surface friction observed for the gel prepared on the hydrophobic substrate was attributed to the presence of dangling free polymer chains formed in the course of the polymerization.

Polymer gels as soft and wet chemomechanical systems - an approach to artificial muscles
D Kaneko, JP Gong, Y Osada
JOURNAL OF MATERIALS CHEMISTRY, 12, 8, 2169, +, ROYAL SOC CHEMISTRY, Aug. 2002, [Invited]
English, Scientific journal

Gel machines constructed from chemically cross-linked actins and myosins
A Kakugo, S Sugimoto, JP Gong, Y Osada
ADVANCED MATERIALS, 14, 16, 1124, 1126, WILEY-BLACKWELL, Aug. 2002, [Peer-reviewed]
English, Scientific journal

Gel machines constructed from chemically cross-linked actins and myosins
Akira Kakugo, Shin Sugimoto, Jian Ping Gong, Yoshihito Osada
Advanced Materials, 14, 16, 1124, 1126, Aug. 2002, [Peer-reviewed]

Inhibitory effects of hydrogels on the adhesion, germination, and development of zoospores originating from Laminaria angustata
Yoshinori Katsuyama, Takayuki Kurokawa, Tatsuo Kaneko, Jian Ping Gong, Yoshihito Osada, Norishige Yotsukura, Taizo Motomura
Macromolecular Chemistry and Physics, 203, 163, 169, 10 Jun. 2002
The inhibition of germination and development of zoospores originating from Laminaria angustata originated on various kinds of hydrogels is studied. The effects of the water content of the gel (the degree of swelling), the electrical nature (neutral, positive charge, negative charge), the charge density, the counterions of hydrogels on the inhibition of zoospore germination and development of gametophytes are phenomenologically investigated. Among the gels investigated, poly(acrylic acid) (PAA) gel showed a dramatic inhibition to germination, and might serve as a novel, environmentally safe inhibitor of zoospore adhesion.

Hydrogels with crystalline or liquid crystalline structure
T Miyazaki, K Yamaoka, JP Gong, Y Osada
MACROMOLECULAR RAPID COMMUNICATIONS, 23, 8, 447, 455, WILEY-V C H VERLAG GMBH, Jun. 2002, [Invited]
English, Scientific journal, The formation of ordered structure in hydrogels derived from copolymers of hydrophilic and hydrophobic monomers with crystalline or liquid-crystal-line moieties is reviewed. The role of water in the formation of ordered structure and its influence on the thermal and mechanical properties of hydrogels are clarified. For example, by inducing a certain amount of water, an amorphous to crystalline transition occurs in gels of acrylic acid/alkyl acrylate copolymers. On the other hand, water induces a liquid-crystalline (SmA) to liquid-crystalline (SmI) transition in copolymers consisting of acrylic acid and -11-(4'-cyanobiphenyloxy)undecyl acrylate. These specific features regarding the formation of ordered structures in hydrogels might shed some light on the formation of ordered structure in biological tissues.

Preparation of Molecularly Oriented Hydrogels and their Structures and Functions
KANEKO Tatsuo, YAMAOKA Kanji, GONG Jian Ping, OSADA Yoshihito
高分子学会予稿集, 51, 1, 53, 55, 10 May 2002
Japanese

Friction of gels. 6. Effects of sliding velocity and viscoelastic responses of the network
Go Kagata, Jian Ping Gong, Yoshihito Osada
Journal of Physical Chemistry B, 106, 18, 4596, 4601, 09 May 2002, [Peer-reviewed]
English, Scientific journal, The velocity dependence of gel friction was investigated in pure water and in salt solutions to elucidate the effect of interracial interaction with substrates. When the gel and the substrate were repulsive, the frictional force depended strongly on the sliding velocity, whereupon the higher the normal compressive strain, the stronger the velocity dependence of the friction. The frictional force per unit area, f, was found to follow a power law as f ∝ vβ, where the exponent, β, depends on the normal compressive strain. This result shows that the gel friction in the repulsive case cannot be explained in terms of the simple hydrodynamic mechanism, from which f ∝ v1.0 is predicted. On the contrary, in the attractive case, the frictional force showed a maximum value with increase in the sliding velocity, which qualitatively coincides with our repulsion-adsorption model proposed previously.

Self-propagating association of zwitterionic polymers initiated by ionene polymers
K Okawa, PP Gong, Y Osada
MACROMOLECULAR RAPID COMMUNICATIONS, 23, 7, 423, 425, WILEY-V C H VERLAG GMBH, May 2002, [Peer-reviewed]
English, Scientific journal, A self-propagating association of zwitterionic polymers is observed when a small amount of x,y-ionene bromide (x=3 or 6; y=3, 4, 6, 10 or 12) polymer is added to aqueous solution of zwitterionic polymer, poly[3-dimethyl(methacryloyloxyethyl)ammoniumpropanesulfonate] (PDMAPS), to give large amount of PDMAPS precipitate. The self-propagating association initiated by ionene polymers is explained in terms of the electrostatic interaction between the ionene polymers and the zwitterionic polymers whereupon the geometry of the charges on the polymer chains plays an important role.

Friction of gels. 6. Effects of sliding velocity and viscoelastic responses of the network
G Kagata, JP Gong, Y Osada
JOURNAL OF PHYSICAL CHEMISTRY B, 106, 18, 4596, 4601, AMER CHEMICAL SOC, May 2002, [Peer-reviewed]
English, Scientific journal, The velocity dependence of gel friction was investigated in pure water and in salt solutions to elucidate the effect of interfacial interaction with substrates. When the gel and the substrate were repulsive, the frictional force depended strongly on the sliding velocity, whereupon the higher the normal compressive strain, the stronger the velocity dependence of the friction. The frictional force per unit area,f, was found to follow a power law as f proportional to upsilon(beta), where the exponent, beta, depends on the normal compressive strain, This result shows that the gel friction in the repulsive case cannot be explained in terms of the simple hydrodynamic mechanism, from which f proportional to upsilon(1.0) is predicted. On the contrary, in the attractive case, the frictional force showed a maximum value with increase in the sliding velocity, which qualitatively coincides with our repulsion-adsorption model proposed previously.

Effect of surface roughness of hydrophobic substrate on heterogeneous polymerization of hydrogels
Mao Peng, Takayuki Kurokawa, Jian Ping Gong, Yoshihito Osada, Qiang Zheng
Journal of Physical Chemistry B, 106, 12, 3073, 3081, 28 Mar. 2002, [Peer-reviewed]
English, Scientific journal, Theoretical analysis predicted that a gas layer is trapped between an aqueous solution and a rough hydrophobic substrate, and that the volume of the gas increases with the hydrophobicity and the surface roughness of the substrate. The heterogeneous structure formation of hydrogel on hydrophobic substrate is explained in terms of the retardation of the radical polymerization by residual oxygen trapped at the hydrophobic surface. The polymerization of 2-acrylamide-2-methyl' 1-propanesulfonic acid (AMPS) aqueous solution on Teflon substrate is experimentally studied by using a novel real time laser sheet refraction (RT-LSR) technique, and it is elucidated that residual oxygen in the trapped gas phase obviously retarded the polymerization of AMPS on the Teflon surface and lead to the formation of heterogeneous structure of the gel. The higher the oxygen concentration, the rougher the Teflon surface, the more significant of the substrate effect, which is in agreement with the theoretical prediction.

Gels stimulables (Intelligent gels)　　　　　　　　　　　　　　　
Hiroki Nagasawa, Jian Ping Gong, Yoshihito Osada
Materiaux Adaptatifs, 251, 175, 181, Mar. 2002, [Peer-reviewed], [Invited]
English, Scientific journal

Surface friction of polymer gels
JP Gong, Y Osada
PROGRESS IN POLYMER SCIENCE, 27, 1, 3, 38, PERGAMON-ELSEVIER SCIENCE LTD, Feb. 2002, [Invited]
English, Scientific journal, The sliding friction of various kinds of hydrogels on solid surfaces or on gels has been studied and it was found that the frictional behaviors of the hydrogels do not conform to Amonton's law F = muW, which well describes the friction of solids. The frictional force and its dependences on the load are quite different depending on the chemical structures of the gels, surface properties of the opposing surfaces, and the measurement condition. Additionally, the frictional coefficient la of the gel reaches a value as low as similar to 10(-3) which is much lower than those observed in solid materials. Theoretical analysis on the mechanism of the gel friction shows that the gel friction can be explained in terms of interfacial interaction, either attractive or repulsive, between the polymer chain and the solid surface. In the repulsive case, the friction is described in terms of the hydrodynamic lubrication of the solvent layer at the interface, which is formed due to the electrostatic repulsion of the two surfaces. For the attractive case, in addition to the hydrodynamic friction, the force to detach the adsorbing chain from the substrate appears as friction. The theoretical results coincide well with experimental observations that confirm the essential feature of the model. (C) 2001 Elsevier Science Ltd. All rights reserved.

Novel thermosensitive IPN hydrogel having a phase transition without volume change
L Chen, JP Gong, Y Osada
MACROMOLECULAR RAPID COMMUNICATIONS, 23, 3, 171, 174, WILEY-V C H VERLAG GMBH, Feb. 2002, [Peer-reviewed]
English, Scientific journal, A novel thermosensitive interpenetrating network (IPN) hydrogel was prepared from an aqueous solution of poly[3,3-dimethyl(methacryloyloxyethyl)-propylammonium sulfonate] infiltrating a crosslinked sulfobetaine polymer, poly(2-acrylamido-2-methylpropylsulfonic acid). The IPN gel shows an upper critical solution temperature (UCST) depending on the molar ratio of the components and the presence of salt. In contrast to conventional gels, the IPN gel exhibits no volume phase transition after traversing the UCST.

Water-induced crystallization of hydrogels
T Miyazaki, T Kaneko, JP Gong, Y Osada, M Demura, M Suzuki
LANGMUIR, 18, 4, 965, 967, AMER CHEMICAL SOC, Feb. 2002, [Peer-reviewed]
English, Scientific journal, We discovered that an amorphous-crystalline transition occurs when a small amount of water is introduced into an amphiphilic copolymer network consisting of n-alkyl acrylate (n = 14, 16, 18, 20, 22) and acrylic acid. Differential scanning calorimetry and X-ray diffraction studies show that the dry polymer network is in an amorphous state regardless of the presence of the crystalline moiety. By introduction of water to the polymer network, a crystalline structure attributed to the side-by-side packing of the alkyl chain is formed and the melting temperature of the crystalline increases with the amount of water and saturated to that of homo-n-alkyl acrylate polymers at a water content of 5 wt %. The mechanism of the water-induced amorphous-crystalline transition is explained in terms of enhanced mobility of the main chain due to hydration of the carboxyl groups of the polymer network.

ゲルの機能からみた生体組織の役割
附柴裕之, 龔剣萍, 長田義仁
日本バイオレオロジー学会誌(B&R), 16, 2, 51, 60, 特定非営利活動法人 日本バイオレオロジー学会, 2002, [Invited]
Japanese, Scientific journal

Inhibitory effects of hydrogels on the adhesion, germination, and development of zoospores originating from Laminaria angustata
Yoshinori Katsuyama, Takayuki Kurokawa, Tatsuo Kaneko, Jian Ping Gong, Yoshihito Osada, Norishige Yotsukura, Taizo Motomura
Macromolecular Bioscience, 2, 4, 163, 169, 2002, [Peer-reviewed]
English, Scientific journal, The inhibition of germination and development of zoospores originating from Laminaria angustata originated on various kinds of hydrogels is studied. The effects of the water content of the gel (the degree of swelling), the electrical nature (neutral, positive charge, negative charge), the charge density, the counterions of hydrogels on the inhibition of zoospore germination and development of gametophytes are phenomenologically investigated. Among the gels investigated, poly(acrylic acid) (PAA) gel showed a dramatic inhibition to germination, and might serve as a novel, environmentally safe inhibitor of zoospore adhesion. © Wiley-VCH Verlag GmbH, 69469 Weinheim 2002.

Crystalline structure and thermal behavior of water-soluble copolymers with pendant terthiophenes
L Chen, T Kaneko, JP Gong, Y Osada, Y Ohsedo, Y Shirota
MACROMOLECULAR CHEMISTRY AND PHYSICS, 203, 1, 176, 181, WILEY-V C H VERLAG GMBH, Jan. 2002, [Peer-reviewed]
English, Scientific journal, The water-soluble copolymers having pendant terthiophene, poly(AA3T-co-AA), were synthesized by radical copolymerization of [ (2,2': 5', 2"-terthiophen-5-yl)methyl acrylate] (AA3T) and acrylic acid (AA), and their molecular structures and thermal behaviors were studied, X-ray diffraction study showed that the copolymers containing a certain amount of AA3T can form the crystals with monolayer structure, while incorporation of too many AA units into the copolymers disrupted this structure. Possible mechanism of self-doping on heating was discussed in terms of interaction between AA3T unit with AA unit in the copolymers.

Real-time laser sheet refraction to monitor in situ the heterogeneity of polymerization process on Teflon surface
M. Peng, Jian Ping Gong, Y. Osada, X. Zhang, Q. Zheng
Macromolecules, 34, 22, 7829, 7835, 23 Nov. 2001, [Peer-reviewed]
English, Scientific journal, Real-time laser sheet refraction (RT-LSR) was used to study the polymerization kinetics of the hydrophilic monomer 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) in aqueous solution and the heterogeneity of the polymerization process on the surface of a Teflon substrate. The spatial distribution of refractive index along the vertical direction in the polymer solution was obtained in real time from the deflection of refracted light during polymerization. It was found that the polymerization of AMPS in the aqueous solution follows the first-order reaction mechanism. Inhomogeneous distribution of refractive index in the interface region near the Teflon surface, which results from the suppression of polymerization in the interface region, is also observed directly.

Surface friction of polymer gels 2. Effect of charge
G Kagata, JP Gong, Y Osada
WEAR, 251, 1-12, 1188, 1192, ELSEVIER SCIENCE SA, Oct. 2001, [Peer-reviewed]
English, Scientific journal, The friction between two chemically cross-linked polyelectrolyte gels carrying the same sign of charges has been investigated in pure water as well as in salt solutions. The friction was largely dependent on the charge densities of the gel surface and the ionic strength of the aqueous solution. The friction is described in terms of the hydrodynamic lubrication of the solvent layer between the two gel surfaces, which is formed due to the electrostatic repulsion of the two gel surfaces. The thickness of the solvent layer is estimated using the Poisson-Boltzmann equation supposing that the ionic osmotic pressure is balanced by the normal pressure applied on the gel. The friction values are calculated by considering the shear flow of solvent in the gel region using the Debye-Binkman equation. For strongly charged polyelectrolyte gels swollen in pure water, the theoretical analysis shows that the friction coefficient has almost no dependence on the water content of the gel, which agrees well with the experimental observations. (C) 2001 Elsevier Science B.V. All rights reserved.

Surface friction of polymer gels 1. Effect of interfacial interaction
JP Gong, G Kagata, Y Iwasaki, Y Osada
WEAR, 251, 1-12, 1183, 1187, ELSEVIER SCIENCE SA, Oct. 2001, [Peer-reviewed]
English, Scientific journal, The sliding friction of various kinds of hydrogels has been studied and it was found that the frictional behaviors of the hydrogels do not conform to Amontons' law, F = muW, that well describes the friction of many solids. The frictional force and its dependencies of on load are quite different depending on the chemical structures of the gels, surface properties of the opposing substrates, and the measurement condition. The gel friction is explained in terms of interfacial interaction, either attractive or repulsive, between the polymer chain and the solid surface. According to this model, friction is ascribed to the viscous flow of solvent at the interface in the repulsive case. In the attractive case, the force to detach the adsorbing chain from the substrate appears as friction. Surface adhesion between glass particles and gels measured by AFM showed a good correlation with the friction, which support the repulsion-adsorption model proposed by the authors. (C) 2001 Elsevier Science B.V. All rights reserved.

Effects of carboxyls attached at alkyl side chain ends on the lamellar structure of hydrogels
Takashi Miyazaki, Tatsuo Kaneko, Jian Ping Gong, Yoshihito Osada
Macromolecules, 34, 17, 6024, 6028, 14 Aug. 2001, [Peer-reviewed]
English, Scientific journal, Two kinds of water-swollen hydrogels composed of three monomers-poly(stearyl acrylate (C18A)-co-n-alkyl acrylates (CnA)-co-acrylic acid (AA)) and poly(16-acryloyloxyhexadecanoic acid (AHA)-co-CnA-co-AA) (n is the number of carbon atoms of side chains: n = 14, 16, 18, 20, 22)-were synthesized, and their structures were investigated by wide-angle X-ray diffraction (WAXD) and small-angle X-ray diffraction (SAXD). Both gels formed the crystalline structure with the lamellae. In the case of poly(C18A-co-CnA-co-AA) gels, both the lamellar thickness, d2, and the melting temperature, Tm, increased with the increase in n, suggesting that C18A and CnA form molecularly mixed crystalline domains. On the other hand, d2 of poly(AHA-co-CnA-co-AA) gels was much smaller than that of poly(CnA-co-AA) gels, and Tm was constant regardless of n. An abrupt decrease in Tm was observed for poly(AHA-co-C18A-co-AA) gels at an AHA composition of 0.8. These results indicate that carboxyls attached at alkyl side chain end of AHA significantly shorten and stabilize the lamellae of the hydrogel due to the cooperative hydrogen bonding and rearrangement of the lamellar structure occurred.

Microrheological investigation of substrate-induced gradient structure in hydrogels
Tetsuharu Narita, Alexandra Knaebel, Jean-Pierre Munch, Sanveur Jean Candau, Jian Ping Gong, Yoshihito Osada
Macromolecules, 34, 16, 5725, 5726, 31 Jul. 2001, [Peer-reviewed]
English, Scientific journal, The microrheological investigation of substrate-induced gradient structure in hydrogels was made. It was observed that hydrophobicity of the substrate perturbed the gelation process over a large spatial range. The crosslinking density of the gels decreased upon increasing the interface between the gel and the substrate. It was also accompanied by an increase in the structural inhomogeneties in the gel.

Synthesis of hydrogels with extremely low surface friction
JP Gong, T Kurokawa, T Narita, G Kagata, Y Osada, G Nishimura, M Kinjo
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 123, 23, 5582, 5583, AMER CHEMICAL SOC, Jun. 2001, [Peer-reviewed]
English, Scientific journal

Heterogeneous polymerization of hydrogels on hydrophobic substrate
Akishige Kii, Jian Xu, Jian Ping Gong, Yoshihito Osada, Xianmin Zhang
Journal of Physical Chemistry B, 105, 20, 4565, 4571, 24 May 2001, [Peer-reviewed]
English, Scientific journal, The substrate effect on the inhomogeneous gelation is in situ studied using various monomers: 2-acrylamide-2-methyl-1-propanesulfonic acid (AMPS), acrylic acid, and N,N′-dimethylacrylamide on various hydrophobic substrates with different surface tensions: poly(tetrafluoroethylene), polypropylene, polyethylene, polystyrene, and poly(vinyl chloride) in aqueous solution as well as in organic solvent by means of electronic speckle pattern interferometry. When the polymerization is carried out in water, a clear interface appears in the vicinity of the hydrophobic substrates at a critical time when the auto-acceleration of the polymerization starts. The polymerization on the hydrophobic substrate is suppressed after the appearance of the interface which gives rise to a heterogeneous gel structure. The thickness of the substrate-induced inhomogeneous layer increases with the square root of the polymerization time, showing the feature of monomer diffusion. An enhanced heterogeneous polymerization occurs on the hydrophobic substrate with a lower surface tension. These effects are greatly suppressed when the polymerization is carried out in ethanol and in the presence of hydrophobic monomer, giving rise to a homogeneous gelation. The correlation between the surface tension of the substrates and the interface strength in water suggests that the substrate-induced interface formation might be associated with the high interfacial tension between the substrate and the polymerizing solution.

A possible mechanism for the substrate effect on hydrogel formation
JP Gong, A Kii, J Xu, Y Hattori, Y Osada
JOURNAL OF PHYSICAL CHEMISTRY B, 105, 20, 4572, 4576, AMER CHEMICAL SOC, May 2001, [Peer-reviewed]
English, Scientific journal, A possible mechanism for the formation of the substrate-induced interface during the gelation, which leads to heterogeneous polymerization, is proposed. According to this mechanism, a surface polymer deplete layer would be formed during the polymerization due to the high interfacial energy between the hydrophobic substrate and the aqueous polymerizing solution. When the polymer concentration attains the critical value at which an extensive entanglement occurs, and/or a chemical network forms, the thickness of the deplete layer increases dramatically to a macroscopic level to give an interface, due to the weak elasticity of the network. Theoretical model describing relations between the substrate surface tension, the increment in the surf ace tension of the solution upon polymerization, and the predicted position of the interface show a resonable agreement with the experimental data.

Liquid crystalline gels. 3. Role of hydrogen bonding in the formation and stabilization of mesophase structures
Kanji Yamaoka, Tatsuo Kaneko, Jian Ping Gong, Yoshihito Osada
Macromolecules, 34, 5, 1470, 1476, ACS, 27 Feb. 2001, [Peer-reviewed]
English, Scientific journal, Copolymers composed of various amounts of 4′-(11-acryloyloxyundecyloxy)biphenyl-4-carboxylic acid (11ABA) and acrylic acid (AA), poly(11ABA-co-AA)s, were synthesized, and their liquid crystalline structures were investigated both in dry and in water-swollen states. Wide- and small-angle X-ray studies revealed that both dry and swollen poly(11ABA-co-AA)s show a liquid crystalline structure, which transforms from smectic C with the bilayer (SmC2) to smectic C with the monolayer (SmC1), when the 11ABA composition, F([11ABA]/([11ABA]+[AA])), decreases from 0.72 to 0.44. The phase diagram of these copolymers was established by changing F and the temperature. It shows that the samples can build up a liquid crystalline structure for F as low as 0.07 at the elevated temperature of 155 °C. The enhanced ordering of the liquid crystalline structure and the thermostability of the copolymers were explained in terms of hydrogen bonding formed between carboxyls of mesogenic side chains and AA.

Kinetic study of cell disruption by ionic polymers with varied charge density
T Narita, R Ohtakeyama, M Matsukata, JP Gong, Y Osada
COLLOID AND POLYMER SCIENCE, 279, 2, 178, 183, SPRINGER-VERLAG, Feb. 2001, [Peer-reviewed]
English, Scientific journal, The effect of charge density and hydrophobicity of the polymeric cations on cell disruption is studied thermodynamically and kinetically by using the budding yeast protoplast. It is found that cationic polymers drastically disrupt the cells above a certain concentration while nonionic and anionic ones do not. Reduced charge density of copolymers of cationic and nonionic monomers resulted in decreased cell disruption. However, it is further experimentally proved that the disruption of the cells occurs only when the polycation has a certain hydrophobicity. The stronger the hydrophobicity of the cationic polymer, the more cooperatively the cells are disrupted.

Surface of Gel as the Extremely Low Friction Material
KUROKAWA Takayuki, GONG Jian Ping, OSADA Yoshihito
Oleoscience : Journal of Japan Oil Chemists' Society, 1, 9, 929, 934,926, 日本油化学会, 2001, [Invited]
Japanese, Scientific journal

高分子ゲルの表面摩擦特性 ─超低摩擦特性の開発─　　　　　　　　　　　　　　　
大垣伸介, 龔剣萍, 長田義仁
バイオサイエンスとインダストリー, 59, 12, 819, 824, 2001, [Invited]
Japanese, Scientific journal

ソフトアクチュエーター
角五彰, 杉本信, 龔剣萍, 長田義仁
表面技術, 52, 4, 317, 323, The Surface Finishing Society of Japan, 2001, [Invited]
Japanese, Scientific journal

ゲルの摩擦
加々田剛, 龔剣萍, 長田義仁
固体物理, 36, 2, 103, 111, アグネ技術センタ-, 2001, [Invited]
Japanese, Scientific journal

Shape memory functions and motility of amphiphilic polymer gels
T Mitsumata, JP Gong, Y Osada
POLYMERS FOR ADVANCED TECHNOLOGIES, 12, 1-2, 136, 150, WILEY-BLACKWELL, Jan. 2001, [Invited]
English, Scientific journal, Amphiphilic polymer gels which can swell in both organic fluid and water have been widely investigated. We have discovered that this class of gels shows two special characteristics, i.e. the shape memory function and the spontaneous motion. The principle of the shape memory is based on a reversible order-disorder transition associated with interactions between the alkyl side chains of the stearyl acrylate units. This effect is completely different from the one of shape memory alloys. When the swollen gel is heated, its Young's modulus decreases by about three orders of magnitude, from 10(7) dyn/cm(2) at 25 degreesC to 10(4) dyn/cm(2) at 50 degreesC. These drastic changes in the mechanical properties enable the gel to show the shape memory function. Another feature of these gels is the spontaneous motion. The mechanism of the motion originates from the difference of surface tension between water and organic solvent that is pumped out by osmotic and hydrostatic pressures from the gel. Recently, we have succeeded to change the random motion to a translational one with a velocity of 77 mm/sec or rotational one with a maximum speed of 400 rpm. Motivated by this, electric power generator called "solvent-driven chemical motor" has been constructed. The generator produced an electric power with a maximum electromotive force of 15 mV and electric power of 0.2 muW. Copyright (C) 2001 John Wiley & Sons, Ltd.

Spreading of liquids on gel surfaces
D Szabo, S Akiyoshi, T Matsunaga, JP Gong, Y Osada, M Zrinyi
JOURNAL OF CHEMICAL PHYSICS, 113, 18, 8253, 8259, AMER INST PHYSICS, Nov. 2000, [Peer-reviewed]
English, Scientific journal, In this work we present a simple model for the kinetics of spreading of film-forming liquids on polymer gels. The model is compared with experiments and fair agreement is obtained. The spreading process can be theorized by considering the gel as a thick liquid layer containing a fibrous material (i.e., the polymer network). The spreading theory of Joos and Pintens is extended in such a way that the penetration of the flow into the bulk of the gel-which plays the major role in the kinetics of the spreading-is described by the Debye-Brinkman equation. It is also shown that spreading experiments can provide information on the surface structure of the underlying gel. (C) 2000 American Institute of Physics. [S0021-9606(00)70540-X].

Intelligent gel - Surface properties and functions of gels
JP Gong, G Kagata, Y Osada
MACROMOLECULAR SYMPOSIA, 159, 215, 220, WILEY-V C H VERLAG GMBH, Oct. 2000, [Invited]
English, Scientific journal, The sliding friction of various kinds of hydrogels has been studied and it was found that the frictional behaviors of the hydrogels do not conform to Amonton's law F = muW, which well describes the friction of solids. The frictional force and its dependencies of on the load are quite different depending on the chemical structures of the gels, surface properties of the opposing substrates, and the measurement condition. The gel friction is explained in terms of interfacial interaction, either attractive or repulsive, between the polymer chain and the solid surface. According to this model, the frictional is ascribed to the viscous flow of solvent at the interface in the repulsive case. In the attractive case, the force to detach the adsorbing chain from the substrate appears as friction. Surface adhesion between glass particles and gels measured by AFM showed a good correlation with the friction, which support the repulsion-adsorption model proposed by authors.

Ionization and order-disorder transition of hydrogels with ionizable hydrophobic side chain
A Matsuda, Y Katayama, T Kaneko, JP Gong, Y Osada
JOURNAL OF MOLECULAR STRUCTURE, 554, 1, 91, 97, ELSEVIER SCIENCE BV, Oct. 2000, [Peer-reviewed]
English, Scientific journal, pH dependence of the structural change of the amphiphilic copolymer gels containing the crystallizable side chain with carboxylic end group, poly(16-acryloylhexadecanoic acid (AHA)-co-acrylic acid (AA)), has been investigated. The poly(AHA-co-AA) gels could maintain the crystalline domain of AHA units up to pH = 11 at ambient temperature, which abruptly transferred into disordered state beyond this pH due to the dissociation of the carboxylic group of AHA. However, the addition of salt or divalent ion enabled to crystallize the gel even at pH = 11.5 due to the effective shielding of the electrostatic repulsion. The mechanism of order-disorder transition through changes of pH and salt concentration was discussed in terms of association-dissociation of AHA groups. (C) 2000 Elsevier Science B.V. All rights reserved.

Effect of charge on protein diffusion in hydrogels
N Hirota, Y Kumaki, T Narita, JP Gong, Y Osada
JOURNAL OF PHYSICAL CHEMISTRY B, 104, 42, 9898, 9903, AMER CHEMICAL SOC, Oct. 2000, [Peer-reviewed]
English, Scientific journal, To study the effect of charge on protein diffusion in hydrogels, mutual diffusion of a globular protein, myoglobin, has been investigated at various pH and ionic strength levels in two kinds of polysaccharide gels, neutral agarose gel and anionic carrageenan gel, by the recently developed electronic speckle pattern interferometry method. In the uncharged agarose gel, diffusions of myoglobin art: not effected by the change in pH and the ionic strength, indicating no electrostatic interaction between the gel and myoglobin. The experimental data in agarose gel agree with the combined model proposed by Clague and Philips for the diffusion of spheres in hydrogels. While in the negatively charged lambda -carrageenan gel, the diffusion of myoglobin is accelerated by electrostatic attraction when the pH is lower than the isoelectric point (pI) of the protein, but it is extensively hindered by the electrostatic repulsion when pH > pi. The diffusion of myoglobin in lambda -carrageenan gel agrees with the Tsai and Strieder model to give an apparent radius of the protein at various pH values.

Effects of charge density and hydrophobicity of ionene polymer on cell binding and viability
T Narita, R Ohtakeyama, M Nishino, JP Gong, Y Osada
COLLOID AND POLYMER SCIENCE, 278, 9, 884, 887, SPRINGER-VERLAG, Sep. 2000, [Peer-reviewed]
English, Scientific journal, The binding of cationic ionenes onto budding protoplast was investigated and the results were associated with the cell viability. There are critical numbers of carbon atoms to induce effective cell disruption and cell binding. The longer the alkyl chain of the ionene, the lower the concentration at which cell disruption occurs. The ionenes with increased charge density undergo effective binding, while almost 2 orders of magnitude higher concentration are required for effective cell disruption. These results were associated with the cooperativity of the binding process, which induces local stress and solubilization of the lipid membrane.

Effect of Aspect Ratio on Protein Diffusion in Hydrogels
Jian Ping Gong, Naoki Hirota, Akira Kakugo, Tetsuharu Narita, Yoshihito Osada
J. Phys. Chem. B, 104, 42, 9904, 9908, Sep. 2000, [Peer-reviewed]
English, Scientific journal

Liquid crystalline hydrogels. 2. Effects of water on the structural ordering
Tatsuo Kaneko, Kanji Yamaoka, Jian Ping Gong, Yoshihito Osada
Macromolecules, 33, 12, 4422, 4426, ACS, 13 Jun. 2000, [Peer-reviewed]
English, Scientific journal, The effects of water on the liquid crystalline structure of the copolymer poly(11-(4′-cyanobiphenyloxy)undecyl acrylate-co-acrylic acid)s (poly(11CBA-co-AA)s) were investigated. When the molar fraction of 11CBA, F, was higher than 0.26, the copolymers did not dissolve but swelled in water to give the hydrogels, keeping the smectic A ordering. This smectic A phase of the copolymers of F = 0.37 and 0.29 transferred to more organized smectic I ordering by further incorporation of water, while the SmA ordering of the copolymer of F = 0.26 disappeared to give the amorphous state. The role of water and the mechanism for forming a liquid crystalline structure in the hydrogel have been discussed.

Doping effects of water-soluble poly(3-thiopheneacetic acid) (P3TAA) and its gel
BS Kim, L Chen, JP Gong, Y Osada
KOREA POLYMER JOURNAL, 8, 3, 116, 119, POLYMER SOC KOREA, Jun. 2000, [Peer-reviewed]
English, Scientific journal, The doping behaviors of water-soluble poly(3-thiopheneacetic acid) (P3TAA) and its gel using I-2 and concentrated HClO4 aqueous solutions were investigated by UV-Visible absorption spectrometer. Electrical conductivity of the doped polythiophene gel was also studied. I-doping of water-soluble P3TAA gave rise to a new broad polaron peak at around 749 nm, which corresponds to localization of electron. It was found that doping ability of P3TAA gel was strikingly dependent on the concentration of HClO solution.

Surface dynamic friction of polymer gels
JP Gong, G Kagata, Y Iwasaki, Y Osada
CHINESE JOURNAL OF POLYMER SCIENCE, 18, 3, 271, 275, SPRINGER-VERLAG BERLIN, May 2000, [Invited]
English, Scientific journal, The sliding friction of various kinds of hydrogels has been studied and it was Found that the frictional behaviors of the hydrogels do not conform to Amonton's law F = mu W which well describes the friction of solids. The frictional force and its dependence on the load are quite different depending on the chemical structures of the gels, surface properties of the opposing substrates, and the measurement condition. The gel friction is explained in terms of interfacial interaction, either attractive or repulsive, between the polymer chain and the solid surface. According to this model, the friction is ascribed to the viscous flow of solvent at the interface in the repulsive case. In the attractive case, the force to detach the adsorbing chain from the substrate appears as friction. The surface adhesion between glass particles and gels measured by AFM showed a good correlation with the friction, which supported the repulsion-adsorption model proposed by the authors.

Fluorinated water-swollen hydrogels with molecular and supramolecular organization
Atsushi Matsuda, Tatsuo Kaneko, Jianping Gong, Yoshihito Osada
Macromolecules, 33, 7, 2535, 2538, ACS, 04 Apr. 2000, [Peer-reviewed]
English, Scientific journal, Moderately water-swollen hydrogels were prepared by copolymerizing n-stearyl acrylate (SA), 2,2,2-trifluoroethyl acrylate (TFEA), and acrylic acid (AA), and the effects of water and TFEA on the molecular and supramolecular structure were investigated. An incorporation of TFEA brought about a decreased d2 spacing (long-range ordering) presumably due to a local render amorphous while d1 (short-range ordering) was kept constant. Enhanced effects of water and stretching on the supramolecular organization were demonstrated. The transition temperature at which Young's modulus abruptly changes could be controlled by changing the TFEA content of the gel.

Friction of Gels. 5. Negative Load Dependence of Polysaccharide Gels
J. P. Gong, Y. Iwasaki, Y. Osada
J. Phys. Chem. B, 104, 15, 3423, 3428, Mar. 2000, [Peer-reviewed]
English, Scientific journal

ゲル運動素子によるケミカルモーター　　　　　　　　　　　　　　　
龔剣萍, 長田義仁
化学と工業, 53, 2, 184, 187, 2000, [Invited]
Japanese, Scientific journal

Surface Dynamic Friction of Polymer Gels　　　　　　　　　　　　　　　
P. Gong, Go Kagata, Y. Osada
Reports on Progress in Polymer Physics in Japan, 43, 141, 162, 2000, [Invited]
English, Scientific journal

Hydrogels with the ordered structures
T. Miyazaki, K. Yamaoka, T. Kaneko, J. P. Gong, Y. Osada
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 1, 4, 201, 210, TAYLOR & FRANCIS LTD, 2000, [Invited]
English, Scientific journal, A water-swollen hydrogel with a molecularly-ordered structure was prepared by copolymerizing acrylic acid and acrylic monomer containing hydrophobic long alkyl or mesogenic moiety. The gels with a long alkyl side chain formed the crystalline structure and undergo the reversible order disorder transition with change in temperature or solvent composition which accompanied a dramatic change in Young's modulus. These gels exhibited such chemomechanical behaviors as the shape memory and the rotational motility on the water surface. On the other hand, the gels with the mesogenic side chain formed the liquid crystalline structure with polymorphism in water, and mesophase diagram was established by changing copolymer composition and water content. Mechanism of these structural and chemomechanical behaviors has been explained in terms of order disorder transition. (C) 2001 Published by Elsevier Science Ltd.

Substrate effects of gel surfaces on cell adhesion and disruption
Tetsuharu Narita, Aki Hirai, Jian Xu, Jian Ping Gong, Yoshihito Osada
Biomacromolecules, 1, 2, 162, 167, American Chemical Society, 2000, [Peer-reviewed]
English, Scientific journal, Substrate effects of hydrogel surfaces prepared on hydrophilic and hydrophobic substrates on the cell adhesion and disruption were studied. The adhesion of tobacco protoplasts onto anionic hydrogels was strongly influenced by the substrates on which the gels were synthesized. In the case of anionic poly(2-acrylamido-2-methylpropanesulfonic acid) gel, more cells adhered on the gel surface prepared on hydrophobic substrates than that prepared on hydrophilic substrates. On the other hand, in the case of cationic quaternized poly(dimethylaminopropylacrylamide) gel, cell disruption occurred in a few seconds accompanied with an intensive release of cellular contents on the gel surface prepared on the hydrophilic substrates, while the cationic gel synthesized on hydrophobic substrates induced no cell disruption. These different behaviors of the cell have been made in terms of different structures of gel surfaces associated with the presence of flexible dangling chains.

Effects of polyelectrolyte complexation on the UCST of zwitterionic polymer
L. Chen, Y. Honma, T. Mizutani, D. J. Liaw, J. P. Gong, Y. Osada
Polymer, 41, 1, 141, 147, Elsevier Science Ltd, Jan. 2000, [Peer-reviewed]
English, Scientific journal, A zwitterionic polymer - poly-3-dimethyl(methacryloyloxyethyl)ammonium propane sulfonate (PDMAPS) - was synthesized and its complexation behaviors with polyanion: poly-2-acrylamido-2-methyl propane sulfonic acid (PAMPS)
and polycation: poly-3-acryloylamino propyl trimethyl ammonium chloride (PDMAPAA-Q)
or: x,y-ionene bromides (x = 3,6
y = 3,4) have been studied. One of the characteristic features of these complexes is that they are soluble, in spite of the abolishment of positive or negative charge of PDMAPS after the complexation and is able to exhibit UCST depending on the concentration and the mixing molar ratio. It was found that PDMAPS-PAMPS complex dramatically increases the viscosity to give a network structure through electrostatic interaction extensively decreasing the UCST, while the PDMAPS-polycation complex first decreases, but then increases the UCST without forming the network. The mechanism of different behaviors of these complexes has been discussed.

Liquid-crystalline hydrogels. 1. Enhanced effects of incorporation of acrylic acid units on the liquid-crystalline ordering
T Kaneko, K Yamaoka, JP Gong, Y Osada
MACROMOLECULES, 33, 2, 412, 418, AMER CHEMICAL SOC, Jan. 2000, [Peer-reviewed]
English, Scientific journal, Copolymers composed of 11-(4'-cyanobiphenyloxy)undecyl acrylate (11CBA) and acrylic acid (AA), poly(11CBA-co-AA)s, were prepared by changing their molar ratio, and their structures were investigated under various temperatures. From wide- and small-angle X-ray studies, it was found that poly(11CBA) and poly(11CBA-co-AA)s with a mole fraction of 11CBA more than 0.26 showed the smectic A (SmA) phase with a layer spacing (d(2)) of 46-58 Angstrom, to which the mesogenic moiety of 11CBA attached perpendicularly with a side-by-side spacing of 4.3 Angstrom (d(1)). The ordering as well as the d(2) spacing of the smectic layer increased by incorporating an appropriate amount of AA. At the same time, the isotropic temperature of the copolymer increased with AA content. The enhanced ordering and the thermostability by introducing AA were explained in terms of the cooperative hydrogen interaction between the carboxylic groups of AA.

Environmental responses of polythiophene hydrogels
Li Chen, ByoungSuhk Kim, Masahiko Nishino, Jian Ping Gong, Yoshihito Osada
Macromolecules, 33, 4, 1232, 1236, ACS, 2000, [Peer-reviewed]
English, Scientific journal, A chemically cross-linked and water-swollen poly(3-thiopheneacetic acid) (P3TAA) gel was synthesized, and its swelling and spectral changes associated with its ionization were studied. The gel undergoes an abrupt red shift in the electronic spectra at a certain pH, suggesting that a conformational transition due to ionization occurred despite the chemical cross-linkage. By changing the solvent composition, during cross-linking, gels with an enhanced π conjugated structure were prepared. By doping of P3TAA gel with a HClO4 solution, a satisfactorily high electrical conductivity was obtained.

Solution and electrical properties of the water-soluble poly(3-thiopheneacetic acid) and its hydrogel
BS Kim, L Chen, JP Gong, Y Osada
MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 349, 335, 338, GORDON BREACH SCI PUBL LTD, 2000, [Peer-reviewed]
English, Scientific journal, The water-swollen poly(3-thiopheneacetic acid) (P3TAA) gels with various degree of cross-linkage (DCL) were synthesized. Doping behaviors of watersoluble polythiophene and its gel using I-2 and concentrated HClO4 solution as dopants were studied. Electrical conductivity of doped polythiophene gel was investigated. Tn addition, we have investigated chemomechanical behavior by electric field, and the possibility of polythiophene gel as an electrode is introduced.

Chemomechanical bending behaviors of ionizable thin films with gradient network-size
GB Park, Y Kagami, JP Gong, DC Lee, Y Osada
THIN SOLID FILMS, 350, 1-2, 289, 294, ELSEVIER SCIENCE SA, Aug. 1999, [Peer-reviewed]
English, Scientific journal, An ionizable thin film with gradient network size in direction of thickness was prepared using 10-undecenoic acid(UA) by plasma polymerization. Gradient structure in the network size was estimated by values of relative diffusion coefficient of ferocian ions through the film. The obtained film was found to show chemomechanical behavior. The film bent in alkaline solution due to anisotropic swelling in direction of thickness and recovered to the original shape in acid solution. (C) 1999 Elsevier Science S.A. All rights reserved.

Complexation and crystallization of anionic phthalocyanine with soluble and cross-linked polycations
T Kaneko, S Orita, JP Gong, Y Osada
LANGMUIR, 15, 17, 5670, 5675, AMER CHEMICAL SOC, Aug. 1999, [Peer-reviewed]
English, Scientific journal, The complexation and crystallization of the tetrasodium salt of copper tetrasulfophthalocyanine (CuTSPc) with the solvated polycations poly((acryloyloxy)ethylpyridinium bromide) (PC2py) and poly((acryloyloxy)dodecylpyridinium bromide) (PC12py) and their gels were studied. CuTSPc binds to PC2py cooperatively and stoichiometrically, while it binds to PC12py in a cooperative but nonstoichiometric way. The wide-angle X-ray diffraction (WAXD) pattern of the CuTSPc-PC12py complex showed high crystallinity, in which the CuTSPc molecules formed hexagonal columns. On the other hand, diffraction peaks were weaker in the WAXD pattern of the CuTSPc-PC2py complex. The longer side chain of the polycations gives the bound CuTSPc molecules sufficient mobility and space to form better organized crystals. The complex of the CuTSPc-PC12py gel also crystallized despite the low mobility of the side chain since the main chain is restrained by cross-linkages.

Effects of counterions and co-ions on the surfactant binding process in the charged polymer network
T Narita, N Hirota, JP Gong, Y Osada
JOURNAL OF PHYSICAL CHEMISTRY B, 103, 30, 6262, 6266, AMER CHEMICAL SOC, Jul. 1999, [Peer-reviewed]
English, Scientific journal, Kinetic studies of cationic surfactant uptake in an anionic polymer network have been performed, varying the species of co-ions of the surfactant and counterions of the charged network. It was found that the rate of surfactant uptake is distinctly dependent on both the counterions and co-ions which could be explained in terms of the ion pair diffusion mechanism associated with their mobilities in the network. A simple linear relation between the surfactant flux and the harmonic mean of the molar mobilities of the surfactant ion, its co-ion, and the network counterion has been established experimentally.

Investigation of molecular diffusion in hydrogel by electronic speckle pattern interferometry
XM Zhang, N Hirota, T Narita, JP Gong, Y Osada, KS Chen
JOURNAL OF PHYSICAL CHEMISTRY B, 103, 29, 6069, 6074, AMER CHEMICAL SOC, Jul. 1999, [Peer-reviewed]
English, Scientific journal, The technique of real-time electronic speckle pattern interferometry (ESPI) is proposed to study the diffusion process of surfactants and proteins in gels. The diffusion coefficient is simply and directly determined from the interferograms. The experiments were carried out on a series of surfactants as well as on a myoglobin diffusion in agarose gels. The agreement of the diffusion coefficient values obtained from ESPI with those obtained by electrical conductance: measurement or the reported data demonstrates the usefulness of the method. Moreover, spatial distribution of refractive index change in the gel can be determined by phase evaluation. Fick's law for diffusion is utilized to analyze the spatial distribution of the diffuser concentration curves in gel, which are compared with experimental data. We find that the agarose gel in surfactant solution shrinks slightly, which increases the density of the gel and leads to the additional refractive index change. The effect of gel shrinking to surfactant diffusion is discussed, and the distribution of density variation of the gel with time is evaluated.

Friction of gels. 4. Friction on charged gels
JP Gong, G Kagata, Y Osada
JOURNAL OF PHYSICAL CHEMISTRY B, 103, 29, 6007, 6014, AMER CHEMICAL SOC, Jul. 1999, [Peer-reviewed]
English, Scientific journal, The friction between two chemically cross-linked polyelectrolyte gels carrying the same sign of charges has been investigated in pure water as well as in salt solutions using a rheometer. It is found that the friction was largely dependent on the charge densities of the gel surface and the ionic strength of the aqueous solution. The chemical structures of the polyelectrolyte gels also play an important role. The friction is described in terms of the hydrodynamic lubrication of the solvent layer between the two gel surfaces, which is formed due to the electrostatic repulsion of the two gel surfaces. The thickness of the solvent layer has been estimated using the Poisson-Boltzmann equation supposing that the ionic osmotic pressure is balanced by the normal pressure applied on the gel. The friction values have been calculated by considering the shear flow of solvent in gel region using the Debye-Binkman equation. For strongly charged polyelectrolyte gels swollen in pure water, the theoretical analysis shows that the friction coefficient almost has no dependence on the water content of the gel, which well agrees with the experimental observations.

Titration behavior and spectral transitions of water-soluble polythiophene carboxylic acids
Byoungsuhk Kim, Li Chen, Jianping Gong, Yoshihito Osada
Macromolecules, 32, 12, 3964, 3969, ACS, 15 Jun. 1999, [Peer-reviewed]
English, Scientific journal, Water-soluble poly(3-thiophene acetic acid) (P3TAA) and its copolymers with 3-n-methylthiophene or with 3-n-octadecylthiophene were synthesized. The solution properties of these water-soluble polythiophene carboxylic acids were studied by potentiometric titration, viscosity measurements, and UV-visible spectroscopy. We have found that the Henderson-Hasselbach plot of the titration curve showed an inflection of the slope around pH = 5-6. The reduced viscosity and electronic spectra of the P3TAA aqueous solution also showed an abrupt change at this pH region. These results are quite different from that of a common flexible polyelectrolyte, such as poly(acrylic acid) (PAA) and strongly suggest that the pH-induced abrupt conformational changes occurred from the aggregated state to the extended state of the polymer main chain. The observed results are explained in terms of the rigid hydrophobic main chain and the nature of the conjugated polymer.

Surface friction of hydrogels
JP Gong, Y Iwasaki, G Kagata, Y Osada
PROCEEDINGS OF THE JAPAN ACADEMY SERIES B-PHYSICAL AND BIOLOGICAL SCIENCES, 75, 6, 122, 126, JAPAN ACAD, Jun. 1999, [Invited]
English, Scientific journal, The sliding fiction of various kinds of hydrogels has been studied and it was found that the frictional behaviors of the hydrogels do not conform to Amonton's law F = mu W, which well describes the friction of solids. The frictional force and its dependencies on the load are quite different depending on the chemical structures of the gels, surface properties of the opposing substrates, and the measurement condition. The gel friction is explained in terms of interfacial interaction, either attractive or repulsive, between the polymer chain and the solid surface. According to this model, the frictional force is ascribed to the viscous flow of solvent at the interface in the repulsive case. In the attractive case, the force to detach the adsorbing chain from the substrate appears as friction. Surface adhesion between glass particles and gels measured by AFM showed a good correlation with the friction, which support the repulsion-adsorption model proposed by authors.

Magnetism and compressive modulus of magnetic fluid containing gels
T Mitsumata, K Ikeda, JP Gong, Y Osada, D Szabo, M Zrinyi
JOURNAL OF APPLIED PHYSICS, 85, 12, 8451, 8455, AMER INST PHYSICS, Jun. 1999, [Peer-reviewed]
English, Scientific journal, We have investigated the magnetism and have measured the compressive modulus of magnetic fluid containing gels, called ferrogels, in the presence of magnetic field. No hysteresis was shown in the magnetization curve of the ferrogel suggesting a super paramagnetic response. The equilibrium compressive modulus of the ferrogel was measured up to 4 kOe and the modulus with field was much higher than that without field. The mean change in modulus increased with increasing magnetic field, and it saturates above 2 kOe. The mean and maximum change in modulus at 4 kOe was 31 and 71 Pa which corresponds to 19% and 46% increases of that without field, respectively. The change in modulus has been analyzed theoretically and is well explained in terms of the magnetism of ferrogels. (C) 1999 American Institute of Physics. [S0021-8979(99)03612-9].

Friction of Gels. 3. Friction on Solid Surfaces
J. P. Gong, Y. Iwasaki, Y. Osada, K. Kurihara, Y. Hamai
J. Phys. Chem. B, 103, 29, 6001, 6006, May 1999, [Peer-reviewed]
English, Scientific journal

Adsorption of bovine serum albumin to yeast protoplast
M Matsukata, M Nishino, JP Gong, Y Osada, Y Sakurai, T Okano
COLLOIDS AND SURFACES B-BIOINTERFACES, 13, 4, 203, 211, ELSEVIER SCIENCE BV, May 1999, [Peer-reviewed]
English, Scientific journal, Interaction between protein and cell was discussed using bovine serum albumin (BSA) and yeast protoplast. Glutaraldehyde was used for crosslinking intracellular and intrinsic membrane proteins, which enabled experiments to be carried under various conditions such as pH, salt, and temperature. BSA bound to the surface of yeast protoplast mainly due to the electrostatic interaction, which was determined by investigating the surface potential of the protoplast and the binding isotherms at various pHs. The BSA binding demonstrated the modified Langmuir type and the binding constants and cooperativity parameters were calculated. At the isoelectric point of both BSA and protoplast, the amount of binding obtained the maximum, while at lower and higher pH the binding was significantly decreased. The binding was further discussed in terms of lipid fluidity of the protoplast. (C) 1999 Elsevier Science B.V. All rights reserved.

In situ Monitoring of Hydrogel Polymerization Using Speckle Interferometry
X. M. Zhang, J. Xu, K. Okawa, Y. Katsuyama, J. P. Gong, Y. Osada, K. S. Chen
J. Phys. Chem. B, 103, 15, 2888, 2891, Mar. 1999, [Peer-reviewed]
English, Scientific journal

Molecular and supramolecular structures of complexes formed by polyelectrolyte-surfactant interactions: Effects of charge density and compositions
BS Kim, M Ishizawa, JP Gong, Y Osada
JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY, 37, 5, 635, 644, WILEY-BLACKWELL, Mar. 1999, [Peer-reviewed]
English, Scientific journal, The process of complex formation and the structure of the complexes were studied for the surfactant binding of the N-alkylpyridinium chlorides (CnPyCl, n = 12, 16) to the sodium salt of poly(styrenesulfonate) (NaPS) and its copolymer with styrene. Both the NaPS and the amphiphilic copolymer form non-stoichiometric complexes with an excess of the cationic surfactants. The NaPS-complex with pronounced short-range (d(1)) and long-range (d(2)) orderings is insoluble, and the amphiphilic copolymer-complex is water-soluble when bound with extra charges. The mechanism of the complex formation was discussed in terms of the charge density and chemical composition of the polymers. (C) 1999 John Wiley & Sons, Inc.

双性イオン高分子と高分子電解質との相互作用によるUCST制御
陳莉, 龔剣萍, 長田義仁
高分子加工別冊, 48, 11, 500, 505, 高分子刊行会, 1999, [Invited]
Japanese, Scientific journal

Specific Surface Friction of Polymer Gels:Experimental Results and Theoretical Analysis
KAGATA Go, GONG Jianping, OSADA Yoshihito
Journal of Network Polymer,Japan, 20, 3, 130, 137, Japan Thermosetting Plastics Industry Association, 1999, [Invited]
Japanese, Scientific journal, The sliding friction of various kinds of hydrogels has been studied. It was found that the frictional behaviors of the hydrogels did not conform to Amonton's law F=mW. The gel friction is explained in terms of interfacial interaction, either attractive or repulsive, between polymer chains and solid surfaces. According to this repulsion-adsorption model proposed by authors, the friction is ascribed, in the repulsive case, to the viscous flow of solvent at the interface; and in the attractive case, the force to detach the absorbing chain from the substrate.

生物はなぜ滑らかに動けるのか
龔剣萍, 長田義仁
科学, 69, 8, 672, 680, 岩波書店, 1999, [Invited]
Japanese, Scientific journal

高分子ゲル-界面活性剤相互作用のダイナミックス
成田哲治, 龔剣萍, 長田義仁
高分子加工, 48, 6, 268, 274, 高分子刊行会, 1999, [Invited]
Japanese, Scientific journal

秩序-無秩序転移するハイドロゲル─その形状記憶特性と運動特性─
龔剣萍, 長田義仁
機能材料, 19, 3, 5, 12, シ-エムシ-, 1999, [Invited]
Japanese, Scientific journal

Surfactant binding by polyelectrolyte gels and its application to electro-driven chemomechanics
ByoungSuhk Kim, Jianping Gong, Yoshihito Osada
Polymer International, 48, 8, 691, 698, John Wiley and Sons Ltd, 1999, [Invited]
English, Scientific journal, Surfactant binding and molecular assembly reactions of solvated and weakly cross-linked polyelectrolytes having charges on the side chain and on the backbone have been studied using various kinds of oppositely charged surfactants. We have found that there are three categories of surfactant binding: they are cooperative and stoichiometric, non-cooperative and stoichiometric, and cooperative and non-stoichiometric. The modes of these categories are predominantly determined by the steric chemical structure of the surfactant, hydrophobicity and charge densities of the polyelectrolytes. The mechanism of complex formation and the structure formation are discussed. A water-swollen polymer gel which swings and undulates water backwards was made by applying an electric field and making a reversible assembly-reaction of surfactant on the gel. Using this principle, a fish-like soft-machine was made which slowly moves forwards by undulating its tail. The motion is analysed and the mechanism is discussed. © 1999 Society of Chemical Industry.

Soft and Wet Materials: Polymer Gels
Y. Osada, J. P. Gong
Advanced Materials, 10, 11, 827, 837, Jan. 1999, [Invited]
English, Scientific journal

Polymer-surfactant interactions: their cooperativity and stoichiometry
N Isogai, T Narita, L Chen, M Hirata, JP Gong, Y Osada
COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 147, 1-2, 189, 201, ELSEVIER SCIENCE BV, Jan. 1999, [Peer-reviewed]
English, Scientific journal, Surfactant bindings with solvated and crosslinked polyelectrolytes having charges on the side chain as well as chain backbone have been studied using various kinds of oppositely charged surfactants. We have found that there are three categories of the surfactant binding: they are cooperative and stoichiometric, non-cooperative and stoichiometric and cooperative and non-stoichiometric. The modes of these categories are predominantly determined by the steric chemical structure of the surfactant, hydrophobicity and the charge densities of the polyelectrolytes. Process and mechanism of the surfactant binding have been discussed. (C) 1999 Elsevier Science B.V. All rights reserved.

Synthesis and properties of poly(3-thiopheneacetic acid) and its networks via electropolymerization
DJ Liaw, BY Liaw, JP Gong, Y Osada
SYNTHETIC METALS, 99, 1, 53, 59, ELSEVIER SCIENCE SA, Jan. 1999, [Peer-reviewed]
English, Scientific journal, The brittle property of poly(3-thiopheneacetic acid) film has been rectified via network formation, as derived from electropolymerization of 3-thiopheneacetic acid with 3,3'-bithiophene or hexamethylene diisocyanate-bithiophene, without losing its conductivity and self-doping property. Solvent swelling behaviors of poly(3-thiophene acetic acid) and its network films rely on the film composition and solvent. The network film crosslinked by 3,3'-bithiophene exhibits a drastic volume change when the temperature exceeds 100 degrees C. The passivation mechanism proposed here explains the electrical conductivity's decrease and the LR spectra's changes after iodine doping. (C) 1999 Elsevier Science S.A. All rights reserved.

Shape memory gels with multi-stimuli-responses
Tatsuo Kaneko, Takashi Miyazaki, Kanji Yamaoka, Yuichi Katayama, Atsushi Matsuda, Jian Ping Gong, Yoshihito Osada
Proceedings of SPIE - The International Society for Optical Engineering, 3669, 199, 208, 01 Jan. 1999
The shape memory effect with multi stimuli responses of the hydrogels having the various type of long alkyl chains: poly (stearyl acrylate -co- acrylic acid) p(HA-co-AA), poly(16-acryloylhexadecanoic acid -co- acrylic acid) p(AHA-co-AA), poly(12-acryloyldodecanoic acid -co- acrylic acid) p(ADA-co-AA), and poly (stearyl acrylate -co- methyl acrylate) p(SA-co-MA) were investigated. P(SA-co-AA) gel exhibited the reversible order-disorder transition on heating at 49 °C and on cooling at 42 °C. The transition was derived from the melting of the hydrophobic domain formed by the long alkyl side chain. The Young's modulus decreased dramatically during the transition. Besides this gel showed the shape memory effect based on the order-disorder transition. The shape of deformed p(SA-co-AA) gel recovered very quickly (5s). In the p(SA-co-MA)gel system, the transition temperature could be varied. Moreover, p(AHA-co-AA) gel responded to not only temperature change but also change of pH and solvent composition.

Gel friction: A model based on surface repulsion and adsorption
J Gong, Y Osada
JOURNAL OF CHEMICAL PHYSICS, 109, 18, 8062, 8068, AMER INST PHYSICS, Nov. 1998, [Peer-reviewed]
English, Scientific journal, A model describing the frictional force produced when a polymer gel is sliding on a solid surface has been proposed from the viewpoint of solvated polymer repulsion and adsorption theory at a solid surface. General relations for the frictional force f expressed as functions of the normal loading P, sliding velocity nu, the polymer volume fraction phi, or the elastic modulus E of the gel, etc., have been derived by applying scaling relations to the model. For the repulsive case, fis ascribed to the viscous flow of solvent at the interface and f is theoretically demonstrated to be proportional to the sliding velocity nu and the normal pressure P when the pressure is smaller than the elastic modulus of the gel. For the attractive case, in addition to the hydrodynamic friction, the force to detach the adsorbing chain from the substrate appears as friction. When nu is not very large, f proportional to nu. At an intermediate velocity, f has a velocity dependence less than Linear, depending on the strength of adsorption. At a higher sliding velocity, f proportional to nu again since the hydrodynamic friction becomes predominant at this stage. The theoretical results coincide well with some experimental observations that confirm the essential feature of the model. (C) 1998 American Institute of Physics. [S0021-9606(98)70342-3]

Solvent-driven chemical motor
T Mitsumata, K Ikeda, JP Gong, Y Osada
APPLIED PHYSICS LETTERS, 73, 16, 2366, 2368, AMER INST PHYSICS, Oct. 1998, [Peer-reviewed]
English, Scientific journal, A solvent-driven chemical motor using amphiphilic polymer gel has been fabricated. The driving force of the gel originates from the surface tension of spreading organic fluid which is pumped out by osmotic and hydrostatic pressures in the gel. A tetrahydrofurane-swollen gel equipped with a spouting hole made a controlled translational motion with a velocity of 77 mm/s or rotational motion with a maximum speed of 400 rpm and a torque of 10(-9)-10(-7) Nm on the water surface. A generator to produce an electric power with a maximum electromotive force of 15 mV and electric power of 0.2 mu W has also been constructed. The successful fabrication of gel motor may produce a new era of soft machine systems which work without pollution and unnecessary intermediates. (C) 1998 American Institute of Physics. [S0003-6951(98)02642-4].

Low-Frequency Dielectric Relaxation of Polyelectrolyte Gels
Tetsu Mitsumata, Jian Ping Gong, Kazuo Ikeda, Yoshihito Osada
J. Phys. Chem. B, 102, 27, 5246, 5251, Jun. 1998, [Peer-reviewed]
English, Scientific journal

Kinetic Study of Surfactant Binding into Polymer Gel- Experimental and Theoretical Analyses
Tetsu Mitsumata, Jian Ping Gong, Kazuo Ikeda, Yoshihito Osada
J. Phys. Chem. B, 102, 23, 4566, 4572, May 1998, [Peer-reviewed]
English, Scientific journal

Effect of Water and Cross-linkage on the formation of Organized Structure in the Hydrogel
Atsushi Matsuda, Jian Ping Gong, Yoshihito Osada
Polymer Gels and Networks, 6, 5, 307, 317, Apr. 1998, [Peer-reviewed]
English, Scientific journal

Surfactant binding of polycations carrying charges on the chain backbone: Cooperativity, stoichiometry and crystallinity
Li Chen, Shuyan Yu, Yoshiharu Kagami, Jianping Gong, Yoshihito Osada
Macromolecules, 31, 3, 787, 794, American Chemical Society, 10 Feb. 1998, [Peer-reviewed]
English, Scientific journal, Studies on the interaction between polycations carrying charges on the chain backbone [x,y-ionene bromides (x = 3, 6, 12
y = 3, 4, 6, 12)] and anionic surfactants (sodium alkyl sulfates and sodium alkanesulfonates) have been made in water. It was found that there are two categories of surfactant binding: one is the formation of insoluble complex with one-to-one composition and the other is that of soluble complex with nonstoichiometric composition. Some of these complexes have ordered structure on a molecular and a supramolecular level, wherein the charge density and the alkyl size separating the charges on the chain backbone play an important role. The mechanism and process of the complex formation have been discussed.

Polymer gels as a chemical valve
M Nishino, JP Gong, Y Osada
BIOSEPARATION, 7, 4-5, 269, 280, KLUWER ACADEMIC PUBL, 1998, [Invited]
English, Scientific journal

Cooperative binding of surfactants with solubilized polymers and networks
T Narita, JP Gong, Y Osada
WILEY POLYMER NETWORKS GROUP REVIEW SERIES, VOL 1 - CHEMICAL AND PHYSICAL NETWORKS, 1, 477, 488, JOHN WILEY & SONS LTD, 1998, [Invited]
English, International conference proceedings, The cooperative binding of a Linear as well as a crosslinked polyelectrolyte with an oppositely charged surfactant has been analyzed experimentally and theoretically. The experimental results showed that the presence of crosslinkage significantly enhances the initiation process but strongly suppresses the cooperativity of the binding. In the theoretical analysis, the hydrophobic interaction has been treated using the nearest neighbour interaction model, while the electrostatic interaction has been calculated using the rod-like model. The general formulas derived on the basis of the free energy minimum principle demonstrated that the crosslinkage enhances the initiation process but strongly suppresses the cooperativity due to the osmotic pressure in the network domain. The theoretical results showed fairly good agreement with the experimental data, confirming the essential features of the theory.

Two step surfactant binding of solvated and cross-linked poly(N-isopropylacrylamide-co-(2-acrylamido-2-methyl propane sulfonic acid))
M Matsukata, M Hirata, JP Gong, Y Osada, Y Sakurai, T Okano
COLLOID AND POLYMER SCIENCE, 276, 1, 11, 18, SPRINGER VERLAG, Jan. 1998, [Peer-reviewed]
English, Scientific journal, A solvated and cross-linked copolymer of N-isopropylacrylamide (IPAAm) and 2-(acrylamido)-2-methyl propane sulfonic acid (AMPS) was synthesized and its interaction with cationic surfactant lauryl-pyridinium chloride (C12PyCl) was investigated. The solvated copolymer exhibited a lower critical solution temperature (LCST) in water, which was extensively shifted to a higher temperature due to the increase of hydrophilicity introduced by AMPS. In C12PyCl solution, LCST of the copolymer was dramatically decreased due to the binding of C12PyCl to AMPS unit, forming a stoichiometric complex. However, in the concentrated C12PyCl solution, its LCST increased due to the non-stoichiometric complex formation. This phenomenon was further examined in the cross-linked copolymer, analyzed by binding isotherms. Two-step binding of surfactant was demonstrated followed by gel shrinking and re-swelling. This binding mechanism was further discussed regarding the effect of charge density and the hydrophobicity of the main-chain backbone in terms of electrostatic and hydrophobic interactions.

Enhanced velocity of surfactant binding after the volume collapse of an oppositely charged gel
T Narita, JP Gong, Y Osada
MACROMOLECULAR RAPID COMMUNICATIONS, 18, 9, 853, 857, HUTHIG & WEPF VERLAG, Sep. 1997, [Peer-reviewed]
English, Scientific journal, This paper is a kinetic study of the interaction between an ionic surfactant and an oppositely charged polymer gel. The volume collapse of the gel enhances substantially the velocity of surfactant uptake, despite the decreased free volume for diffusion. This indicates that the increased charge density of the polymer network accelerates the surfactant binding.

Friction of gels
JP Gong, M Higa, Y Iwasaki, Y Katsuyama, Y Osada
JOURNAL OF PHYSICAL CHEMISTRY B, 101, 28, 5487, 5489, AMER CHEMICAL SOC, Jul. 1997, [Peer-reviewed]
English, Scientific journal, The sliding friction of various kinds of hydrogels has been investigated, and it has been found that the frictional behaviors of these hydrogels do not conform to Amonton's law F = mu W, which well describes the friction of a solid. Instead, the friction force F of the gel shows slight dependence on the load W in the investigated load range, while it strongly depends on the sliding velocity. Additionally, the frictional coefficient mu of the gel reaches a value as low as similar to 10(-3), which is smaller than those observed in solid materials.

Chemomechanical polymer gel with fish-like motion
Y Ueoka, J Gong, Y Osada
JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES, 8, 5, 465, 471, TECHNOMIC PUBL CO INC, May 1997, [Peer-reviewed]
English, Scientific journal, A water-swollen polymer gel which swings and undulates water backward was made by applying an electric field and making a reversible assembly-reaction of surfactant on the gel. Using this principle a fish-like soft-machine slowly moving forward by undulating the tail was made. The motion was analyzed and the mechanism was discussed.

Electrical conductance of polyelectrolyte gels
JP Gong, N Komatsu, T Nitta, Y Osada
JOURNAL OF PHYSICAL CHEMISTRY B, 101, 5, 740, 745, AMER CHEMICAL SOC, Jan. 1997, [Peer-reviewed]
English, Scientific journal, An attempt to establish a systematic method to precisely evaluate the electrical conductivity of highly water-swollen polyelectrolyte gels was made. It was found that the electrical conductivity and the activation energy of fully ionized polyelectrolyte gel such as cross-linked poly(3-acrylamido-2-methylpropanesulfonic acid) gels with various counterions are almost identical with those of linear polymer in a wide range of swelling, indicating that the conduction of an ionic gel is essentially performed by the ''free'' counterions of Manning's condensation theory.

Formation of soluble complexes by two-step surfactant bindings
SY Yu, M Hirata, L Chen, S Matsumoto, M Matsukata, JP Gong, Y Osada
MACROMOLECULES, 29, 24, 8021, 8023, AMER CHEMICAL SOC, Nov. 1996, [Peer-reviewed]
English, Scientific journal

A comparative study on the cooperative binding of surfactants with solubilized polymers and networks
JP Gong, T Mizutani, Y Osada
POLYMERS FOR ADVANCED TECHNOLOGIES, 7, 10, 797, 804, JOHN WILEY & SONS LTD, Oct. 1996, [Peer-reviewed]
English, Scientific journal, The cooperative binding of a linear as well as a crosslinked polyelectrolyte with an oppositely charged surfactant has been analyzed theoretically and experimentally. The experimental results showed that the presence of crosslinkage significantly enhances the initiation process but strongly suppresses the cooperation of the binding. In the theoretical analysis, the hydrophobic interaction has been treated using the nearest-neighbor interaction model, while the electrostatic interaction has been calculated using a rodlike model. The general formulas derived on the basis of the free energy minimum principle demonstrated that the crosslinkage enhances the initiation process but strongly suppresses the cooperation owing to the osmotic pressure in the network domain. The theoretical results showed fairly good agreement with the experimental data, confirming the essential features of the theory.

Thermosensitive polymer gel by reversible surfactant binding
N Isogai, JP Gong, Y Osada
MACROMOLECULES, 29, 21, 6803, 6806, AMER CHEMICAL SOC, Oct. 1996, [Peer-reviewed]
English, Scientific journal, A discontinuous volume collapse occurs on binding of tetraphenylphosphonium chloride (TPPC) to the anionic polyelectrolyte network poly[2-(acrylamido)-2-methylpropanesulfonic acid] (PAMPS) gel. The amount of TPPC inducing volume collapse decreases with increasing temperature. The TPPC binding to the gel is noncooperative and insensitive to temperature change in spite of the strong hydrophobic interaction of TPPC. The mechanism of the TPPC binding is discussed.

Shape memory behaviors of crosslinked copolymers containing stearyl acrylate
Y Kagami, JP Gong, Y Osada
MACROMOLECULAR RAPID COMMUNICATIONS, 17, 8, 539, 543, HUTHIG & WEPF VERLAG, Aug. 1996, [Peer-reviewed]
English, Scientific journal, Shape memory polymers were prepared by copolymerizing stearyl acrylate and methyl acrylate. The principle of this shape memory effect is based on reversible order-disorder transition of crystalline aggregates of stearyl moieties. A specific feature of this type of shape memory copolymer is that the transition temperature at which the polymer abruptly becomes soft and deforms can be controlled by changing the monomer composition, which enables one to adjust the shape memory effect at a desired temperature. Mechanism and process of the shape memory behaviors were discussed.

Motion of polymer gels by spreading organic fluid on water
JP Gong, S Matsumoto, M Uchida, N Isogai, Y Osada
JOURNAL OF PHYSICAL CHEMISTRY, 100, 26, 11092, 11097, AMER CHEMICAL SOC, Jun. 1996, [Peer-reviewed]
English, Scientific journal, We have constructed a new class of polymer gel that undergoes translational and rotational motions in water. These polymer gels consist of cross-linked hydrophobic-hydrophilic copolymers, which swell in water-miscible organic fluid but collapse in water. When these gels swollen in organic solvent are placed on supporting water, they start to do motion. The mode of motion depends on the shape of the gel: a disk- or spherical shaped gel exhibits translational motion while a triangular or a cubic one exhibits rotation. The velocity and duration of gel motion are strongly associated with its size and chemical structure. The driving force of the motion is originated from the surface spreading of organic solvent, which is pumped out of the gel because of the high osmotic pressure and hydrostatic pressure in the gel.

Polymer gel: soft and wet intelligent material
Yoshihito Osada, Y. Ueoka, J. P. Gong
Proceedings of SPIE - The International Society for Optical Engineering, 2779, 344, 348, Society of Photo-Optical Instrumentation Engineers, 1996
English, International conference proceedings, We have developed an electrically-driven chemomechanical system which shows quick responses with fish-like motility. Behaviors and principle of electrically-driven motion of the polymer gel have been studied. The principle of motility of this system is based upon an electrokinetic molecular assembly reaction of surfactant molecules on the hydrogel caused by both electrostatic and hydrophobic interactions. The cooperative binding of a linear as well as a cross-linked polyelectrolyte with surfactants has been theoretically analyzed. The general formulas derived on the basis of the free energy minimum principle predicted that the cross- linking enhances the initiation process but strongly suppresses the cooperativity due to the osmotic pressure in the network domain. The theoretical results showed fairly good agreement with the experimental data, confirming the essential features of the theory.

MODELING AND SIMULATION OF ELECTROSTATIC POTENTIAL DISTRIBUTION IN POLYELECTROLYTE GELS
JP GONG, Y OSADA
ELECTROCHIMICA ACTA, 40, 13-14, 2445, 2447, PERGAMON-ELSEVIER SCIENCE LTD, Oct. 1995, [Peer-reviewed]
English, Scientific journal, The electrostatic potential energy distribution of polyelectrolyte gels has been modelled and simulated on the basis of Poisson-Boltzmann equation. The simulation was carried out with a three dimensional network model. The simulation reveals that there exist deep electrostatic potential wells at every crosslinking point and potential valleys around the polymer chains. The simulation results also indicated that a strong electrostatic field exists near the polymer chains especially around the crosslinking points. Various abnormal phenomena observed in the polymer gel, such as the presence of non-frozen water, higher electroconductivity at low temperature, electrocontractile behavior, etc., are considered to be associated with the presence of this strong electric field.

SOFT AND WET TOUCH-SENSING SYSTEM MADE OF HYDROGEL
K SAWAHATA, JP GONG, Y OSADA
MACROMOLECULAR RAPID COMMUNICATIONS, 16, 10, 713, 716, HUTHIG & WEPF VERLAG, Oct. 1995, [Peer-reviewed]
English, Scientific journal, Mechanical deformation of water-swollen polyelectrolyte gels with carboxylic groups induces a spontaneous ionization, which in turn produces an electrical potential as large as a few millivolts. On the base of this phenomenon, a tactile sensor capable of lighting a photo diode array according to the amplitude of deformation has been made. This system may offer a soft and wet touch-sensor due to its soft tissue-like theological characteristics.

THEORETICAL-ANALYSIS OF THE CROSS-LINKING EFFECT ON THE POLYELECTROLYTE-SURFACTANT INTERACTION
JP GONG, Y OSADA
JOURNAL OF PHYSICAL CHEMISTRY, 99, 27, 10971, 10975, AMER CHEMICAL SOC, Jul. 1995, [Peer-reviewed]
English, Scientific journal, The cooperative binding of a linear as well as a cross-linked polyelectrolyte with an oppositely charged surfactant has been theoretically analyzed. The hydrophobic interaction has been treated using the nearest-neighbor interaction model, while the electrostatic interaction has been calculated using the rodlike model. The general formulas derived on the basis of the free energy minimum principle predicted that the crosslinkage enhances the initiation process but strongly suppresses the cooperativity due to the osmotic pressure in the network domain. The theoretical results showed fairly good agreement with the experimental data, confirming the essential features of the theory.

PRESENCE OF ELECTROSTATIC POTENTIAL WELLS IN THE IONIC POLYMER NETWORK
JP GONG, Y OSADA
CHEMISTRY LETTERS, 6, 449, 450, CHEMICAL SOC JAPAN, Jun. 1995, [Peer-reviewed]
English, Scientific journal, The electrostatic potential distribution of cross-linked polyelectrolyte gels has been numerically calculated on the base of Poisson-Boltzmann equation using a three dimensional network geometry. The simulational result revealed that besides potential energy valleys around the polymer chains, there should exist deep electrostatic potential energy wells at every crosslinking point.

SPONTANEOUS MOTION OF AMPHOTERIC POLYMER GELS ON WATER
Y OSADA, JP GONG, M UCHIDA, N ISOGAI
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 34, 4B, L511, L512, JAPAN J APPLIED PHYSICS, Apr. 1995, [Peer-reviewed]
English, Scientific journal, We have discovered that cross-linked hydrophobic-hydrophilic copolymer gels swollen in organic solvent undergo spontaneous motion when immersed in water. The mode of motion largely depends on the shape of the gel: a disc-shaped gel exhibits translational motion while a triangular or a square shaped one exhibits rotation. The velocity and duration of gel motion are strongly associated with its size and chemical structure. We consider that the gel, immersed in water, rapidly forms a partially organized structure on its outer surface and gradually shrinks, simultaneously producing high osmotic pressure and hydrostatic pressure. By virtue of these two pressures, the organic solvent is released from the gel and the gel obtains a net reaction force to induce motion, presumably due to its heterogeneous structure.

ELECTROCONDUCTIVE ORGANOGEL .6. THERMAL AND ELECTROCONDUCTIVE CHARACTERISTICS OF A CHARGED POLYPEPTIDE GEL IN ORGANIC MEDIUM
T NISHIDE, JP GONG, H YASUNAGA, N NISHI, Y OSADA
MACROMOLECULES, 27, 26, 7877, 7879, AMER CHEMICAL SOC, Dec. 1994, [Peer-reviewed]
English, Scientific journal, A novel electroconductive polypeptide gel based on a formation of a charge-transfer (CT) complex between poly(L-lysine) (PLL) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) was prepared. The PLL gel extensively swelled in dimethyl sulfoxide (DMSO) containing TCNQ and showed a dark green color to give PLL(+)TCNQ(-). Differential scanning calorimetric (DSC) measurement showed a significant depression of the melting temperature. The electrical conductivity of the PLL(+)TCNQ(-) gel below melting temperature of DMSO was nearly 3 orders of magnitude higher than the corresponding solution. These phenomena were explained in terms of the extensive association of DMSO molecules with the charged network through strong electrostatic interaction.

ELECTROKINETIC MODELING OF THE CONTRACTILE PHENOMENA OF POLYELECTROLYTE GELS - ONE-DIMENSIONAL CAPILLARY MODEL
JP GONG, T NITTA, Y OSADA
JOURNAL OF PHYSICAL CHEMISTRY, 98, 38, 9583, 9587, AMER CHEMICAL SOC, Sep. 1994, [Peer-reviewed]
English, Scientific journal, When a water-swollen polyelectrolyte gel is interposed between a pair of electrodes and DC current is applied, the gel undergoes electrically-induced chemomechanical contraction and concomitant water exudation in the air. Tn order to clarify the mechanism, a one-dimensional electrokinetic model of the contractile phenomenon of polymer gels under an electric field was postulated based on Poisson-Boltzmann and Navier-Stokes equations. This model well characterized the nature of the contraction profiles and theoretically predicted that the rate of contraction linearly depends on the electric field, and the contraction efficiency inversely depends on the cross-linking density. The model also showed a good agreement with experimental data and qualitatively demonstrated that the electrically-induced contraction of the gel is dominated by electrokinetic processes of hydrated ions and water in the polymer gels.

INVESTIGATION OF PRECIPITATE FORMATION ON LASER-ABLATED YBA2CU3O7-DELTA THIN-FILMS
JP GONG, M KAWASAKI, K FUJITO, R TSUCHIYA, M YOSHIMOTO, H KOINUMA
PHYSICAL REVIEW B, 50, 5, 3280, 3287, AMERICAN PHYSICAL SOC, Aug. 1994, [Peer-reviewed]
English, Scientific journal, We have investigated systematically the particle formation on the surface of high-quality YBa2Cu3O7-delta (YBCO) epitaxial films grown by pulsed laser deposition. Scanning-Auger-electron spectroscopy identified two types of precipitates, i.e., BaCuO2 and CuO, on the films deposited from a stoichiometric YBCO target. The coexistence of these two phases with a YBCO matrix film is well explained by the pseudoternary phase diagram of YO1.5-BaO-CuO, assuming a slight Y deficiency in the film. The precipitate formation was reduced when the films were grown under conditions slightly deviated from the optimum for the formation of well-equilibrated, highly crystalline, and high-T(c) and high-J(c) films. Under such thermodynamically off-equilibrated conditions, the phase separation into YBCO and secondary phases is presumed to be kinetically prevented to give solid-soluted films and off-stoichiometric compositions and inferior crystallinity and superconductivity. The film-thickness dependences of the precipitate density and size were quantitatively analyzed by scanning electron microscopy to indicate that the nucleation of precipitates occurred by the initial 50 nm growth of the film to, be followed by the increase of the precipitate's size. The use of off-axis polished substrates could successfully suppress the nucleation of the precipitates. A possible mechanism of precipitate formation is proposed.

CRYOGENIC SCANNING-TUNNELING-MICROSCOPY SPECTROSCOPY ON THE (001) SURFACES OF YBA2CU3OY EPITAXIAL THIN-FILMS
M NANTOH, T HASEGAWA, W YAMAGUCHI, A TAKAGI, M OGINO, K KITAZAWA, M KAWASAKI, JP GONG, H KOINUMA
JOURNAL OF APPLIED PHYSICS, 75, 10, 5227, 5232, AMER INST PHYSICS, May 1994, [Peer-reviewed]
English, Scientific journal, As-grown surfaces of c-axis-oriented laser-ablated YBa2Cu3Oy (YBCO) films have been investigated by scanning tunneling microscopy and spectroscopy (STM/STS) at 4.2 K. The square atomic arrangement with an average spacing of 0.4 nm was observed on the specimens even after exposure to ambient atmosphere, indicating that the (001) surface of the YBCO thin film was stable and free from severe contamination or chemical reaction. The STS observations revealed the semiconductive nature of the surface with a band gap of 0.1 eV However, the tunneling spectrum varied its shape depending on the tip-to-sample distance and a clear superconducting gap structure with 2DELTA approximately 40 meV appeared when the STM tip was closer to the surface than the usual position of the scanning mode, suggesting that the semiconductive layer is confined in the surface region of atomic size thickness.

CRYOGENIC STM STS OBSERVATION ON OXIDE SUPERCONDUCTORS
M NANTOH, T HASEGAWA, M KAWASAKI, JP GONG, K FUJITO, A TAKAGI, W YAMAGUCHI, M OGINO, H KOINUMA, K KITAZAWA
JOURNAL OF SUPERCONDUCTIVITY, 7, 2, 349, 353, PLENUM PUBL CORP, Apr. 1994, [Peer-reviewed]
English, Scientific journal, The topographic and electronic properties of the surfaces of (001) and (110) oriented YBa2Cu3Oy epitaxial films have been probed by atomic resolution STM/STS at 4.2 K. The STM image on the (001) surface clearly revealed the atomic corrugation of the tetragonal lattice with an average spacing of 0.4 nm, while on the (110) surface the orthorhombic atomic lattice, corresponding to the Cu atoms of both CuO2 and CuO chain planes, was observed. The STS result on the (001) surface indicated the semiconducting nature of the terminating layer. As the tunneling tip came closer to the surface, however, the shape of the tunneling spectrum became more metallic and showed a superconducting energy gap, which seems to arise from the underlying superconducting layer. On the other hand, the tunneling spectra on the (110) surface indicated superconducting gap structures, independent of the tip-sample distance.

ソフト＆ウェットマテリアル―ゲル　　　　　　　　　　　　　　　
グン剣萍, 長田義仁
固体物理, 30, 11, 982, 989, 1994, [Invited]
Japanese, Scientific journal

Electro-Driven Gel Actuator　　　　　　　　　　　　　　　
Y. Osada, H. Okuzaki, J. P. Gong
Trends in Polym. Sci, 2, 61, 66, 1994, [Invited]
English, Scientific journal

Electro-Driven Gel Motility on the Base of Cooperative Molecular Assembly Reaction　　　　　　　　　　　　　　　
Y. Osada, H. Okuzaki, J. P. Gong, T. Nitta
Polym. Sci, 36, 340, 351, 1994, [Invited]
English, Scientific journal

ELECTRICAL CONTROL OF POLYMER ASSOCIATION AND ITS CHEMOMECHANICAL BEHAVIOR
S MAEKAWA, JP GONG, Y OSADA
MACROMOLECULAR RAPID COMMUNICATIONS, 15, 1, 73, 79, HUTHIG & WEPF VERLAG, Jan. 1994, [Peer-reviewed]
English, Scientific journal

Photo-Current Characteristics of Two-Layered Organic Thin Films Prepared by Plasma Polymerization
Jianping Gong, Satomi Ohnishi, Yoshihito Osada
Polymer Journal, 26, 6, 754, 757, 1994, [Peer-reviewed]
English, Scientific journal

Electrical Control of Polymer Association and Its Chemomechanical Behaviors
S. Maekawa, J. P. Gong, Y. Osada
Macromol. Rapid Commun., 15, 1, 73, 79, Jan. 1994, [Peer-reviewed]
English, Scientific journal

Iridescent coloration of a copolymer gel in an organic solvent
Jianping Gong, Hidenori Okuzaki, Yoshihito Osada
Macromolecular Chemistry and Physics, 195, 5, 1871, 1876, 1994, [Peer-reviewed]
English, Scientific journal, A polymer gel formed from acrylic acid and methyl acrylate, moderately swollen in toluene or benzene, exhibits iridescent coloration. The color changes with temperature and composition of the gel. This phenomenon has been associated with specific scattering of light. © 1994 Hüthig &
Wepf Verlag, Basel

SUPPRESSION OF PRECIPITATE FORMATION IN HETEROEPITAXIAL GROWTH OF YBA2CU3O7-DELTA FILM ON MISORIENTED SRTIO3 SUBSTRATES
JP GONG, M KAWASAKI, K FUJITO, R TSUCHIYA, M YOSHIMOTO, H KOINUMA
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 33, 1A, L20, L23, JAPAN J APPLIED PHYSICS, Jan. 1994, [Peer-reviewed]
English, Scientific journal, We have investigated the effect of misoriented substrates on precipitate formation in c-axis-oriented YBa2Cu3O7-delta films grown by the pulsed laser deposition technique. The films grown on exact SrTiO3(100) substrates had precipitate densities as high as 10(7)-10(8)/cm2, whereas the films on substrates with surfaces misoriented from (100) by 0.5-degrees-1-degrees had fewer precipitates by two to three orders of magnitude. A film surface of 10(5)/CM2 precipitates can give 90% probability of a precipitate-free practical device size area (10 mum x 10 mum), providing a high possibility of successful fabrication of a Josephson tunnel junction.

SURFACE AND INTERFACE CHARACTERIZATION OF HIGH-T(C) RELATED EPITAXIAL-FILMS BY STM/STS AND XPS
H KOINUMA, S GONDA, JP GONG, M KAWASAKI, M YOSHIMOTO, M NANTOH, T HASEGAWA, K KITAZAWA
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 54, 10, 1215, 1218, PERGAMON-ELSEVIER SCIENCE LTD, Oct. 1993, [Peer-reviewed]
English, Scientific journal, We have fabricated high quality and chemically stable epitaxial films of YBa2Cu3O7-delta (YBCO) and SrTiO3 by pulsed laser deposition (PLD) technique and investigated their surface morphology, electronic state, and growth mode. The cryoganic STM/STS measurements on small area (4x4nm) c-oriented YBCO films resulted in the simultaneous observations of lattice images and tunneling spectra with 20meV energy gap. A gap spectrum exhibited almost zero conductance, favoring s-wave superconductivity. Wider scans of the film surfaces by AFM and SEM, however, revealed granular structure of the surfaces with a root mean square (rms) roughness of 5nm, which is far larger than the coherence length of YBCO. Much smoother surfaces were obtained for a- and (110) oriented films. Atomic images and conductive layers could be identified by STM for these films. The surface morphology of epitaxial SrTiO3 films prepared under high vacuum (<10(-5)Torr:MBE) conditions was found to be improved to such an extent as to show atomically flat images in AFM and STM analyses. By in situ XPS analyses, valence states and film growth mode of SrTiO3 epitaxial films were elucidated on an atomic layer level. Discussions are extended to the processes for controlling the growth mode and carrieres of high Tc related oxide films as well s for fabricating SIS tunnel junctions.

HETEROEPITAXIAL GROWTH OF C-AXIS-ORIENTED BATIO3 THIN-FILMS WITH AN ATOMICALLY SMOOTH SURFACE
JP GONG, M KAWASAKI, K FUJITO, U TANAKA, N ISHIZAWA, M YOSHIMOTO, H KOINUMA, M KUMAGAI, K HIRAI, K HORIGUCHI
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 32, 5A, L687, L689, JAPAN J APPLIED PHYSICS, May 1993, [Peer-reviewed]
English, Scientific journal, C-axis-oriented barium titanate (BaTiO3) epitaxial films with an atomically smooth surface have been fabricated on SrTiO3 {100} substrates using the pulsed laser deposition technique. The crystal structure and epitaxial orientation of the films have been analyzed by means of 2theta/theta X-ray diffractometry and 4-circle X-ray diffractometry, The highly oriented and epitaxial crystallinity is also shown by means of Rutherford backscattering spectrometry which gave a chi(min) of 1.7%. The atomically smooth surface comparable to that of the SrTiO3 substrate is revealed by means of atomic force microscopy. The breakdown electric field of the BaTiO3 film is as high as 10(6) V/cm.

PREPARATION AND NANOSCALE CHARACTERIZATION OF HIGHLY STABLE YBA2CU3O7-DELTA THIN-FILMS
M KAWASAKI, JP GONG, M NANTOH, T HASEGAWA, K KITAZAWA, M KUMAGAI, K HIRAI, K HORIGUCHI, M YOSHIMOTO, H KOINUMA
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 32, 4, 1612, 1616, JAPAN J APPLIED PHYSICS, Apr. 1993, [Peer-reviewed]
English, Scientific journal, High-quality c-axis-oriented YBa2Cu3O7-delta (YBCO) films were prepared using the laser ablation method. Films with a full width at half-maximum of the (005) X-ray diffraction peak as narrow as 0.1-degrees and an chi(min) of Rutherford backscattering spectrometry as low as 3.5% were obtained by optimizing the experimental conditions. The atomic image and superconducting gap at 4.2 K were simultaneously observed for the first time on these high-quality YBCO films by scanning tunneling microscopy and scanning tunneling spectroscopy. Such observations, even after the film was stored in air for three weeks, indicates that YBCO film is sufficiently chemically and physically stable to prevent significant deterioration in superconductivity at the film surface.

STIMULI-RESPONSIVE POLYMER GELS AND THEIR APPLICATION TO CHEMOMECHANICAL SYSTEMS
Y OSADA, JP GONG
PROGRESS IN POLYMER SCIENCE, 18, 2, 187, 226, PERGAMON-ELSEVIER SCIENCE LTD, 1993, [Peer-reviewed], [Invited]
English, Scientific journal

PREPARATION OF POLYMERIC METAL-TETRACYANOQUINODIMETHANE FILM AND ITS BISTABLE SWITCHING
JP GONG, Y OSADA
APPLIED PHYSICS LETTERS, 61, 23, 2787, 2789, AMER INST PHYSICS, Dec. 1992, [Peer-reviewed]
English, Scientific journal, Metal salts of charge transfer complex such as CuTCNQ, LiTCNQ and others have been found to dissolve in water when mixed with polyethyleneimine (PEI). From electronic spectra it was supposed that metal salts of organic complex form trilateral complex with PEI in water. Homogeneous and continuous polymeric thin film was prepared by casting this solution. The film with a thickness of 150-200 nm showed field-induced bistable switching from low to high impedance regime at a field strength of 4 x 10(4) V/mm. A possible switching mechanism was briefly discussed.

ELECTROCONDUCTIVE ORGANOGEL .4. ELECTRODRIVEN CHEMOMECHANICAL BEHAVIORS OF CHARGE-TRANSFER COMPLEX GEL IN ORGANIC-SOLVENT
JP GONG, KAWAKAMI, I, Y OSADA
MACROMOLECULES, 24, 25, 6582, 6587, AMER CHEMICAL SOC, Dec. 1991, [Peer-reviewed]
English, Scientific journal, The effect of 7,7,8,8-tetracyanoquinodimethane (TCNQ) doping on the electroconductivity of cross-linked poly[N-[3-(dimethylamino)propyl]acrylamide] (PDMAPAA) gel, swollen in N,N-dimethylformamide (DMF), was investigated. The gel showed ionic conductivity as high as 10(-4) S cm-1 by TCNQ doping due to the formation of an ionic species of the charge-transfer (CT) complex between PDMAPAA gel and TCNQ. It was found that this type of CT gel undergoes rapid contraction by applying dc voltage, and the rate as well as the efficiency of the organogel much exceeded those of hydrogel. The mechanism of such an electrodriven chemomechanical contraction was explained in terms of an electrokinetic process, and the simple mathematical model of the contraction was postulated.

FABRICATION OF CERAMICS HETEROJUNCTIONS AND LAYERED CUPRATES BY EPITAXIAL LAYER-BY-LAYER GROWTH
M YOSHIMOTO, H NAGATA, S GONDA, JP GONG, H OHKUBO, H KOINUMA
PHYSICA C, 190, 1-2, 43, 45, ELSEVIER SCIENCE BV, Dec. 1991, [Peer-reviewed]
English, Scientific journal, Atomically regulated layers of perovskite oxides and alkaline earth cuprates were fabricated by laser MBE with the aid of RHEED intensity oscillations clearly observed during film growth. A ceramic superlattice composed of lattice-matched SrVO3-x and SrTiO3-y perovskites was prepared on an atomic scale by counting the number of RHEED oscillation. In situ RHEED and XPS analyses indicate that the interface between the laterally grown SrCuO2-z epitaxial film and the SrTiO3(001) substrate has a transition layer of about 1 nm thick, which apparently reflects an inhomogeneous growth manner at the initial stage.

LASER MBE OF LAYERED [ (AE)2+/(CUO2)2-]N (AE = SR OR BA) LATTICES
M YOSHIMOTO, H NAGATA, JP GONG, H OHKUBO, H KOINUMA
PHYSICA C, 185, Pt 3, 2085, 2086, ELSEVIER SCIENCE BV, Dec. 1991, [Peer-reviewed]
English, Scientific journal, Pulsed laser deposition in ultrahigh vacuum was verified to be a promising method to deposit epitaxial films composed of bi-layered [ (AE)2+/(CuO2)2-]n (AE = Sr or Ba) lattices. As-grown films deposited on SrTiO3(001) substrates under NO2 flushing exhibited a metallic conduction.

ELECTROCONDUCTIVE ORGANOGEL .3. PREPARATION AND PROPERTIES OF A CHARGE-TRANSFER COMPLEX GEL IN AN ORGANIC-SOLVENT
JP GONG, KAWAKAMI, I, VG SERGEYEV, Y OSADA
MACROMOLECULES, 24, 19, 5246, 5250, AMER CHEMICAL SOC, Sep. 1991, [Peer-reviewed]
English, Scientific journal, A novel ionic organogel based on a polymeric charge-transfer (CT) complex was prepared. Cross-linked poly[N-[3-(dimethylamino)propyl]acrylamide] (PDMAPAA) gel was synthesized in DMF, followed by subsequent doping of 7,7,8,8-tetracyanoquinodimethane (TCNQ). The PDMAPAA gel showed extensive swelling and exhibited a green color when doped. Spectrophotometric and kinetic studies revealed that swelling and coloration are due to formation of various kinds of ionic species formed by the CT complex between the polymeric network and TCNQ, and the process of complex formation was analyzed. From Flory's theory an equation of swelling of the organogel was derived as a function of charge density of ionic species and compared with experimental results.

SYNTHESIS, MECHANISM, AND APPLICATION OF AN ELECTRO-DRIVEN CHEMOMECHANICAL SYSTEM USING POLYMER GELS
Y OSADA, JP GONG, K SAWAHATA
JOURNAL OF MACROMOLECULAR SCIENCE-CHEMISTRY, A28, 11-12, 1189, 1205, MARCEL DEKKER INC, 1991, [Invited]
English, Scientific journal, When a water-swollen polyelectrolyte gel is interposed between a pair of electrodes and dc is applied, the gel undergoes electrochemomechanical contraction and concomitant water exudation. Microparticles of crosslinked poly(acrylic acid) also undergoes reversible shrinkage by the electric field. The contraction was associated with the electrohydrodynamic transport of hydrated ions, and an equation expressing the rate of size change was derived as a function of voltage, charge density, and degree of swelling. Applications of this phenomenon to drug delivery systems, artificial muscles lifting and lowering a load, and some gel actuators walking in water are introduced.

FRACTAL PATTERN-FORMATION OF METAL-CONTAINING POLYMERIC THIN-FILMS PREPARED BY PLASMA REACTION
J GONG, Y KAGAMI, K YAMADA, Y OSADA
BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, 63, 6, 1578, 1583, CHEMICAL SOC JAPAN, Jun. 1990, [Peer-reviewed]
English, Scientific journal

PREPARATION, STRUCTURE AND ELECTRIC PROPERTIES OF PLASMA-POLYMERIZED METAL-CONTAINING ORGANIC THIN-FILMS
Y KAGAMI, K YAMADA, T YAMAUCHI, J GONG, Y OSADA
PLASMA POLYMERIZATION AND PLASMA INTERACTIONS WITH POLYMERIC MATERIALS, 46, 289, 314, JOHN WILEY & SONS INC, 1990, [Invited]
English, International conference proceedings

Structure and Unique Functions of Anisotropic Hydrogels Comprising Uniaxially Aligned Lamellar Bilayers
Yue Youfeng, Yue Youfeng, Gong Jian Ping, Gong Jian Ping, Bulletin of the Chemical Society of Japan (Web), 94, 9, 2021

Therapeutic Effect of Ultra-Purified Alginate gel Containing Bone Marrow Aspirate Concentrate on Osteochondral Defects
XU Liang, 瓜田淳, 小野寺智洋, 菱村亮介, 野々山貴行, 濱崎雅成, 宮崎拓自, LIANG Dawei, 宝満健太郎, GONG Jian Ping, 岩崎倫政, 日本軟骨代謝学会プログラム・抄録集, 33rd, 2020

Anisotropic Bilayer-hybrid Gels: Fabrication and Water Induced Rubbery-Glassy Transition
ILYAS Muhammad, HAQUE Md Anamul, YUE Youfeng, KUROKAWA Takayuki, NAKAJIMA Tasuku, NONOYAMA Takayuki, GONG Jian Ping, 高分子学会予稿集(CD-ROM), 67, 2, 2018

骨形成に再利用される合成HAp系インプラントの同位体顕微鏡観察
野々山貴行, 鈴木裕貴, 木山竜二, WANG Lei, 津田真寿美, 安田和則, 田中伸哉, 永田康祐, 藤田龍介, 坂本直哉, 圦本尚義, GONG Jian Ping, 日本セラミックス協会秋季シンポジウム講演予稿集(CD-ROM), 31st, 2018

Tough double-network hydrogel as an artificial cartilage
北村 信人, 黒川 孝幸, 安田 和則, グン 剣萍, 整形・災害外科, 60, 11, 1409, 1415, Oct. 2017
金原出版, Japanese

Water Triggered Ductile-Brittle Transition of Anisotropic Lamellar Hydrogels
ILYAS Muhammad, HAQUE Md Anamul, YUE Youfeng, KUROKAWA Takayuki, NAKAJIMA Tasuku, NONOYAMA Takayuki, GONG Jian Ping, 高分子学会予稿集(CD-ROM), 66, 2, 2017

軟骨基質高分子を複合化したダブルネットワークゲルの生体材料特性評価 軟骨再生誘導材料としての可能性
比嘉 浩太郎, 北村 信人, 後藤 佳子, 黒川 孝幸, 和田 進, 野々山 貴行, Gong Jian Ping, 金谷 文則, 安田 和則, 日本整形外科学会雑誌, 90, 8, S1726, S1726, Aug. 2016
(公社)日本整形外科学会, Japanese

ハイドロゲルの細胞基盤への応用,その優位性 (特集 再生医療の発展に待たれる三次元細胞培養用の培地,足場材料開発)
柴田 優輝, 黒川 孝幸, 龔 剣萍, Material stage, 15, 11, 5, 10, Feb. 2016
技術情報協会, Japanese

Hyaluronic Acid Enhances Induction Effects of Synthetic Hydrogels on Chondrogenic Differentiation of ATDC5 Cells In Vitro
YOSHIKAWA Katsuhisa, Japanese Journal of Joint Diseases, 32, 1, 9, 15, 2013
Introduction: Recently, we reported that PAMPS and PDMAAm gels induce the chondrogenic differentiation of ATDC5 cells in vitro in maintenance medium without insulin. We hypothesized that hyaluronic acid (HA) affects the in vitro induction effects of PAMPS and PDMAAm gels on the chondrogenic differentiation of ATDC5 cells, depending on the concentration. The purpose of this study was to test this hypothesis.Methods: This study consisted of three sub-studies: the first was performed to assess the fundamental effects (without HA) of the PAMPS gel, PDMAAm gel, and polystyrene dish surfaces on the chondrogenic differentiation of ATDC5 cells cultured in maintenance medium and in differentiation medium (containing insulin). The second and third sub-studies were performed to analyze the effects of HA supplementation (three concentrations) of the two media on the chondrogenic differentiation of ATDC5 cells cultured on PAMPS and PDMAAm gels, respectively. At 7 days of culture, the gene expression of cartilage markers was examined using real-time polymerase chain reaction analysis.Results: On the PAMPS gel with the maintenance medium, HA at concentrations of 0.01 and 0.10 mg/mL significantly increased the expression of Col-2 mRNA and aggrecan mRNA in comparison to those without HA. In the cells cultured in the differentiation medium, HA at a concentration of 0.01 mg/mL significantly increased mRNA expression of Col-2 and aggrecan genes in comparison to those without HA. On the PDMAAm gel with the maintenance medium, HA at a concentration of 1.00 mg/mL significantly reduced the expression of these genes in comparison to those without HA.Conclusion: Mechanical signals from each hydrogel surface significantly affect the chondrogenic differentiation of ATDC5 cells, and HA affects the mechanical signals from each hydrogel surface, depending on the concentration., Japanese Society for Joint Diseases, Japanese

Hydrogels as feeder-free scaffolds for long-term self-renewal of mouse induced pluripotent stem (mips) cells.
Yang Jing Jing, Liu Jian Fang, Kurokawa Takayuki, Kitada Kazuhiro, Gong Jian Ping, Journal of Tissue Engineering and Regenerative Medicine, 20 Nov. 2012
Expanding undifferentiated induced pluripotent stem (iPS) cells in vitro is a basic requirement for application of iPS cells in both fundamental research and clinical regeneration. In this study, we intended to establish a simple, low cost and efficient method for the long-term self-renewal of mouse induced pluripotent stem (miPS) cells without using feeder-cells and adhesive proteins. Three scaffolds were selected for the long-term subculture of miPS cells over two months starting from passages 14 to 29: 1) a gelatin coated polystyrene (Gelatin-PS) that is a widely used scaffold for self-renewal of mouse embryonic stem (mES) cells; 2) a neutral hydrogel poly(N,N-dimethylacrylamide) (PDMAAm); and 3) a negatively charged hydrogel poly(2-acrylamido-2-methyl-propane sulfonic acid sodium salt) (PNaAMPS). Each passaged miPS cells on these scaffolds were cryopreserved successfully and the revived cells showed high viability and proliferation. The passaged miPS cells maintained a high undifferentiated state on all three scaffolds and a high level of pluripotency by expressing differentiation markers in vitro and forming teratomas in SCID mice with derivatives of all three germ layers. Compared to Gelatin-PS, the two hydrogels exhibited much better self-renewal performance in terms of high proliferation rate and level of expression of undifferentiated gene markers as well as efficiency in pluripotent teratoma formation. Furthermore, the PNaAMPS hydrogel demonstrated a slightly higher efficiency and simpler operation of cell expansion than the PDMAAm hydrogel. To conclude, PNaAMPS hydrogel is an excellent feeder-free scaffold because of its simplicity, low cost and high efficiency in expanding a large number of miPS cells in vitro. Copyright © 2012 John Wiley & Sons, Ltd., John Wiley & Sons, English

羊膝関節の広範囲骨軟骨欠損における高機能ゲルプラグを用いたin vivo軟骨自然再生誘導
横田 正司, 北村 信人, 新垣 和伸, 小野寺 伸, 近藤 英司, 安田 和則, 黒川 孝幸, Gong Jian Ping, きょう 剣萍, 北海道整形災害外科学会雑誌, 54, 1, 81, 82, Aug. 2012
北海道整形災害外科学会, Japanese

Controlled and Selective Swelling of an Anisotropic Hydrogel by Restricted Diffusion of Water
HAQUE Md. Anamul, UCHIUMI Maki, YOUFENG Yue, KUROKAWA Takayuki, NAKAJIMA Tasuku, GONG Jian Ping, 高分子学会予稿集(CD-ROM), 61, 1, 2012

Fracture Behavior of an Anisotropic Hydrogel Containing Nano-Scale Bilayer with Macro-scale Ordering
HAQUE Md. Anamul, KUROKAWA Takayuki, NAKAJIMA Tasuku, YUE Youfeng, GONG Jian Ping, 高分子学会予稿集(CD-ROM), 61, 1, 2012

Effect of Water Content on the Mechanical Properties of an Anisotropic Hydrogel Containing Macro-sacle Bilayer
HAQUE Md. Anamul, KUROKAWA Takayuki, NAKAJIMA Tasuku, YUE Youfeng, AHMED Saika, GONG Jian Ping, 高分子学会予稿集(CD-ROM), 61, 2, 2012

Fracture Behavior of an Anisotropic Hydrogel Containing Nano-Scale Bilayer with Macro-scale Ordering
HAQUE Md. Anamul, KUROKAWA Takayuki, NAKAJIMA Tasuku, YUE Youfeng, GONG Jian Ping, 高分子学会予稿集(CD-ROM), 61, 2, 2012

Mechanics and physics of hydrogels
Jian Ping Gong, Wei Hong, SOFT MATTER, 8, 31, 8006, 8007, 2012
ROYAL SOC CHEMISTRY, English, Others

大腿脛骨関節の骨軟骨欠損に対する高機能ゲルプラグを用いた硝子軟骨自然再生誘導
横田 正司, 北村 信人, 新垣 和伸, 小野寺 伸, 近藤 英司, 黒川 孝幸, Gong Jian Ping, 安田 和則, 日本整形外科学会雑誌, 85, 8, S1263, S1263, Aug. 2011
(公社)日本整形外科学会, Japanese

Exotic function found in assembly of bio molecular motor obtained through active self-organization
井上 大介, 角五 彰, Gong Jian Ping, 化学工業, 62, 7, 489, 493, Jul. 2011
化学工業社, Japanese

Robust bonding and one-step facile synthesis of tough hydrogels with desirable shape by virtue of the double network structure
Junji Saito, Hidemitsu Furukawa, Takayuki Kurokawa, Rikimaru Kuwabara, Shinya Kuroda, Jian Hu, Yoshimi Tanaka, Jian Ping Gong, Nobuto Kitamura, Kazunori Yasuda, Polymer Chemistry, 2, 3, 575, 580, Mar. 2011
Robust bonding of a hydrogel in aqueous environment, either to another hydrogel or to a solid, is one of the major unsolved issues for the practical applications of hydrogels in various fields. Here we report robust bonding between a pair of hydrogel sheets, containing over 90 wt% of water, by applying the double-network (DN) structure. In the optimal condition, the peeling energy of the united gel sheets reaches 1200 J m-2, which is comparable to the bulk fracture energy of a normal type of tough DN gels. This hydrogel bonding technique is also applied to form tough bonding between hydrogel and plastic plates. Furthermore, based on this technique, we have developed a facile method to synthesize robust double network hydrogels with any desirable free-shape from micro-gel precursors. These novel techniques will substantially merit the applications of the tough hydrogels in various fields, such as an artificial meniscus. © The Royal Society of Chemistry 2011., English

新規両親媒性ソルバトクロミック蛍光色素の合成とその応用~形状記憶ゲルの観察~
古橋由梨, 中島祐, 黒川孝幸, 黒川孝幸, 古川英光, 山田幸司, GONG Jian Ping, 高分子ゲル研究討論会講演要旨集, 22nd, 2011

One-dimensional Swelling of an Anisotropic Hydrogel by Controlled Two-dimensional Diffusion of Water
HAQUE Md. Anamul, MAKI Uchiumi, YOUFENG Yue, KUROKAWA Takayuki, GONG Jian Ping, 高分子学会予稿集(CD-ROM), 60, 2 Disk1, 2011

Spontaneous Redifferentiation of Dedifferentiated Human Articular Chondrocytes on Hydrogel Surfaces
Yang Jing Jing, Chen Yong Mei, Liu Jian Fang, Kurokawa Takayuki, Gong Jian Ping, Tissue Engineering Part A, 16, 8, 2529, 2540, 05 Aug. 2010
Chondrocytes rapidly dedifferentiate into a more fibroblastic phenotype on a two-dimensional polystyrene substratum. This impedes fundamental research on these cells as well as their clinical application. This study investigated the redifferentiation behavior of dedifferentiated chondrocytes on a hydrogel substratum. Dedifferentiated normal human articular chondrocyte–knee (NHAC-kn) cells were released from the sixth-passage monolayer cultured on a polystyrene surface. These cells were then subcultured on a chemically crosslinked copolymer hydrogel, that is, poly(NaAMPS-co-DMAAm), and the cells thus obtained were used as the seventhpassage cultivation. Copolymer gels were synthesized from a negatively charged monomer, the sodium salt of 2-acrylamido-2-methyl-1-propanesulfonic acid (NaAMPS), and a neutral monomer, N,N-dimethylacrylamide (DMAAm). These gels were of different compositions because the molar fraction (F) of NaAMPS was varied (F¼0, 0.2, 0.4, 0.6, 0.8, and 1.0). The dedifferentiated NHAC-kn cells spontaneously redifferentiated to normal NHAC-kn cells on neutral (F¼0) and poly(NaAMPS-co-DMAAm) hydrogels of low charge density (F¼0.2). This was deduced from the cell morphology and expression of cartilage-specific genes and proteins. These results should enable us to establish a simple and efficient method for preparing large amounts of chondrocytes by cultivation on the surfaces of neutral and low-charge-density hydrogels., Mary Ann Liebert

Women be Ambitious to Make Social Contribution
GONG Jian Ping, 高分子, 59, 4, 225, 225, 01 Apr. 2010
Japanese

Part I: 第1章 フロントランナーに聞く　　　　　　　　　　　　　　　
グン 剣萍, CSJカレントレビュー 驚異のソフトマテリアル―最新の機能性ゲル研究, 2, 9, Apr. 2010, [Invited]
Japanese, Others

仕事と私事　　　　　　　　　　　　　　　
グン 剣萍, 高分子, 59, 4, 225, 225, Mar. 2010, [Invited]
Japanese, Others

力学的ヒステリシスと膨潤度から見る,DNゲルの破壊挙動
中島祐, 中島祐, YU Qiu Ming, 田中良巳, 田中良巳, 黒川孝幸, 黒川孝幸, 古川英光, 古川英光, GONG Jian Ping, LIN Eric, WU Wen-li, 高分子ゲル研究討論会講演要旨集, 21st, 2010

超高強度Double-Networkゲルの創製(XXII):延伸性が高破壊エネルギーに与える影響
YU Qiu Ming, 黒川孝幸, 黒川孝幸, 中島祐, 古川英光, 田中良巳, GONG Jian Ping, 高分子学会予稿集(CD-ROM), 59, 1 Disk1, 2010