Researcher Profile and Settings

Master

Affiliation (Master)

• Faculty of Advanced Life Science　Advanced Transdisciplinary Science　Soft & Wet Matter Science

Affiliation (Master)

• Faculty of Advanced Life Science　Advanced Transdisciplinary Science　Soft & Wet Matter Science

researchmap

Profile and Settings

Profile and Settings

• Name (Japanese)

  Nakajima

• Name (Kana)

  Tasuku

• Name

  201301091105747825

Achievement

Research Interests

• Polymer Gel   Polymer Chemistry   メカノケミストリー   Functional Polymers   犠牲結合   液晶ゲル   

Research Areas

• Nanotechnology/Materials / Polymer materials / Polymer Gel

Research Experience

• 2020/11 - Today JST, PRESTO Researcher
• 2019/04 - Today Faculty of Advanced Life Science, Hokkaido University Associate Professor
• 2011/10 - 2019/03 Faculty of Advanced Life Science, Hokkaido University Assistant Professor
• 2011/04 - 2011/09 The University of Tokyo The Graduate School of Engineering

Education

• 2006/04 - 2011/03  北海道大学大学院
• 2002/04 - 2006/03  Hokkaido University  School of Science

Awards

• 2022/05 日本レオロジー学会 2021年度日本レオロジー学会奨励賞
  
• 2021/08 北海道大学 全学教育科目に係る授業アンケートにおけるエクセレント・ティーチャーズ
  
• 2021/04 文部科学省 令和3年度科学技術分野の文部科学大臣表彰 若手科学者賞
  
• 2021/02 北海道大学 令和２年度教育研究総長表彰
  
• 2020/09 Hokkaido University Excellent teacher award
   

  受賞者: 中島祐
• 2019/05 高分子学会 広報委員会パブリシティ賞
   

  受賞者: 中島 祐
• 2019/01 RSC Soft Matter Presentation Award
   

  受賞者: Tasuku Nakajima
• 2017/01 Hokkaido University Hokkaido University President's Award of Research
   

  受賞者: Tasuku Nakajima
• 2016/05 Society of Polymer Science, Japan Award for Encouragement of Research in Polymer Science
   

  受賞者: Tasuku Nakajima
• 2015/03 Hokkaido University Hokkaido University President's Award of Research
   

  受賞者: Tasuku Nakajima
• 2015/03 Hokkaido University Hokkaido University President's Award of Education
   

  受賞者: Tasuku Nakajima
• 2014/08 Hokkaido University Excellent teacher award
   

  受賞者: Tasuku Nakajima
• 2013/10 日本ゴム協会 第25回エラストマー討論会 優秀発表賞
   

  受賞者: 中島 祐
• 2012/10 Soft Matter Poster Prize at the 9th International Gel Symposium
   

  受賞者: 中島 祐
• 2012/05 日本化学会 優秀講演賞（産業）
   

  受賞者: 中島 祐

Published Papers

• 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) 0027-8424 2024/07/17 

  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).
• 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) 0027-8424 2024/06/26 

  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.
• 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 2024/05/15
• Effect of Predamage on the Fracture Energy of Double-Network Hydrogels

  Yong Zheng, Yiru Wang, Tasuku Nakajima, Jian Ping Gong

  ACS Macro Letters 2024/01/11
• 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 2023/12/22
• 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 1755-4330 2023/12/05
• Thermoresponsive Lamellar Hydrogels with Tunable Turbidity, Structural Color, and Anisotropic Swelling

  Yang Han, Yunzhou Guo, Tasuku Nakajima, Jian Ping Gong

  ACS Applied Materials & Interfaces 2023/11/29 [Refereed][Not invited]
  
• 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 0024-9297 2023/05/17 [Refereed][Not invited]
  
• 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) 2023/05/10 [Refereed][Not invited]
   

  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.
• Mechanical Model for Super-Anisotropic Swelling of the Multi-Cylindrical PDGI/PAAm Gels

  Tasuku Nakajima, Kei Mito, Jian Ping Gong

  Polymers MDPI AG 15 (7) 1624 - 1624 2023/03/24 [Refereed][Not invited]
   

  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.
• 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 0002-7863 2023/03/23 [Refereed]
  
• 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 (1) 2023/01/20 [Refereed][Not invited]
   

  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.
• 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 2051-6347 2023 [Refereed][Not invited]
   

  Double-network (DN) gels are unique mechanochemical materials owing to their structures that can be dynamically remodelled during use.
• 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 56 (2) 535 - 544 0024-9297 2022/12/16 [Refereed][Not invited]
  
• 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

  2022/11/23 

  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 0935-9648 2022/11/18 [Refereed][Not invited]
  
• Force-triggered rapid microstructure growth on hydrogel surface for on-demand functions

  Qifeng Mu, Kunpeng Cui, Wang Zhi jian, 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) 2041-1723 2022/10/20 [Refereed][Not invited]
   

  AbstractLiving 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.
• 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 0024-9297 2022/10/18 [Refereed][Not invited]
  
• 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 0002-7863 2022/02/11 [Refereed][Not invited]
  
• 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 2352-4316 2022/02 [Refereed][Not invited]
  
• Surfactant induced bilayer-micelle transition for emergence of functions in anisotropic hydrogel

  Md Anamul Haque, Takayuki Kurokawa, Tasuku Nakajima, Gen Kamita, Zannatul Fatema, Jian Ping Gong

  Journal of Materials Chemistry B 10 (41) 8386 - 8397 2050-750X 2022 [Refereed][Not invited]
   

  The polymer-surfactant-assembled lamellar bilayer structure in the hydrogel matrix is tuned by simple molecular triggering to achieve variable macroscopic functionalities of soft photonic hydrogel.
• 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 1759-9954 2022 [Refereed][Not invited]
   

  Biodegradable double network (DN) gels with remarkably high mechanical strength and toughness were synthesised. The biodegradable DN gels can be potentially applied in biomedical applications such as cartilage regeneration.
• 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 1385-8947 2022/01 [Refereed][Not invited]
  
• 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) 0027-8424 2021/12/07 [Refereed][Not invited]
   

  Fracture in soft materials often couples a wide range of time and length scales. To date, research is mostly focused at the meso- and macroscale in which the continuum mechanics approach is expected to work, and the deformation surrounding the crack tip can be directly observed. Yet understanding at the network scale is very limited. A relevant question is how does chain dynamics at the network scale control fracture in rate-independent materials? Here, we study the role of polymer dynamics on the fracture and nonlinear crack tip behaviors of rate-independent double-network gels. We believe this work is crucially important for understanding the dynamic molecular process of fracture and for further facilitating theoretical approaches to predict failure in soft materials.
• 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 0024-9297 2021/11/23 [Refereed][Not invited]
  
• 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 0897-4756 2021/05/11 [Refereed][Not invited]
  
• 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 0027-8424 2021/04/06 [Refereed][Not invited]
   

  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.
• 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 2021/04/01 [Refereed]
   

  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.
• Correction to 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 (24) 10737 - 10737 2020/12/22
• 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 1944-8244 2020/11/04 [Refereed]
  
• 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 0024-9297 2020/10/27 [Refereed]
  
• 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 0897-4756 2020/10/13 [Refereed]
   

  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.
• 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 1525-7797 2020/10/12 [Refereed]
  
• 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 1744-683X 2020/10 [Refereed][Not invited]
   

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

• 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 0024-9297 2020/06/12 [Refereed][Not invited]
  
• 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 2020/02/25 [Refereed][Not invited]
  
• 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 0887-6266 2020
• Double-network gels as polyelectrolyte gels with salt-insensitive swelling properties

  Tasuku Nakajima, Takaharu Chida, Kei Mito, Takayuki Kurokawa, Jian Ping Gong

  Soft Matter 16 (23) 5487 - 5496 2020 [Refereed][Not invited]
   

  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.
• 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 2019/11/26 [Refereed][Not invited]
  
• 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 2019/11/19 [Refereed][Not invited]
  
• 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 American Chemical Society ({ACS}) 52 (19) 7369 - 7378 0024-9297 2019/10 [Refereed][Not invited]
   

  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.
• 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 2019/09 [Refereed][Not invited]
  
• 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 - 121686 2019/09 [Refereed][Not invited]
  
• 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 2019/08 [Not refereed][Invited]
  
• Tough Triblock Copolymer Hydrogels with Different Micromorphologies for Medical and Sensory Materials

  Hui Jie Zhang, Feng Luo, Yanan Ye, Tao Lin Sun, Takayuki Nonoyama, Takayuki Kurokawa, Tasuku Nakajima

  ACS Applied Polymer Materials American Chemical Society ({ACS}) 1 (8) 1948 - 1953 2637-6105 2019/08 [Refereed][Not invited]
   

  Tough triblock copolymer hydrogels with microstructures of sphere, cylinder, and laminae were constructed using a newly developed "drying and swelling" method without changing the chemical structures of their monomeric units. These tough triblock copolymer hydrogels commonly showed high fracture stress of similar to 10 MPa but exhibited varied elastic moduli depending on their microstructures. Furthermore, the constructed laminar gel formed pH-sensitive photonic gel at the base conditions, providing the gel application with potential as a sensor. Given their high toughness, biocompatibility, and tunable modulus, this study helps expand the potential application of amphiphilic block copolymer hydrogels for medical and industrial use.
• 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 2019/05/28 [Refereed][Not invited]
  
• Hydrophobic Hydrogels with Fruit‐Like Structure and Functions

  Guo Hui, Nakajima Tasuku, Hourdet Dominique, Marcellan Alba, Creton Costantino, Hong Wei, Kurokawa Takayuki, Gong Jian Ping

  Advanced Materials 31 (25) e1900702  1521-4095 2019/05 [Refereed][Not invited]
   

  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.
• Mechanoresponsive self-growing hydrogels inspired by muscle training

  Takahiro Matsuda, Runa Kawakami, Ryo Namba, Tasuku Nakajima, Jian Ping Gong

  Science 363 (6426) 504 - 508 2019/02/01 [Refereed][Not invited]
  
• 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 2019 [Refereed][Not invited]
  
• 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 1744-683X 2018/12 [Refereed][Not invited]
   

  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 2423-8805 2018/11 [Not refereed][Invited]
  
• 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 American Chemical Society ({ACS}) 51 (21) 8887 - 8898 2018/11 [Refereed][Not invited]
   

  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.
• 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 Interfaces 1801018 - 1801018 2196-7350 2018/10/04 [Refereed][Not invited]
  
• 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 Elsevier {BV} 81 60 - 69 1742-7061 2018/10 [Refereed][Not invited]
   

  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.
• 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 2018/07/24 [Refereed][Not invited]
  
• 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, Hui Jie Zhang, Tasuku Nakajima, Takayuki Nonoyama, Takayuki Kurokawa, Shinya Tanaka, Jian Ping Gong

  Advanced Functional Materials Wiley 28 (31) 1801489  1616-301X 2018/06 [Refereed][Not invited]
   

  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.
• 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  1521-4095 2018/03/01 [Refereed][Not invited]
   

  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 2470-1343 2018 [Refereed][Not invited]
   

  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 1936-086X 2017/12/26 [Refereed][Not invited]
   

  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.
• 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 0911-5269 2017/10 [Not refereed][Not invited]
  
• 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 0024-9297 2017/10 [Refereed][Not invited]
   

  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 0032-3861 2017/10 [Refereed][Not invited]
   

  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.
• 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 0142-9612 2017/07 [Refereed][Not invited]
   

  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.
• 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 0032-3861 2017/05 [Refereed][Not invited]
   

  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 0024-9297 2017/04 [Refereed][Not invited]
   

  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) 1616-301X 2017/03 [Refereed][Not invited]
   

  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.
• Generalization of the sacrificial bond principle for gel and elastomer toughening

  Nakajima, Tasuku

  Polymer Journal 49 (6) 2017
• Stimuli-Responsive Transformation of a Gradient Gel

  Tasuku Nakajima, Kenta Hiwatashi, Jian Hu, Takayuki Kurokawa, Jian Ping Gong

  KOBUNSHI RONBUNSHU 74 (4) 311 - 318 0386-2186 2017 [Refereed][Not invited]
   

  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.
• Double Networkゲルをマトリックスとした骨組織類似構造の創製

  深尾 一城, 野々山 貴行, 黒川 孝幸, 中島 祐, きょう 剣萍

  日本バイオマテリアル学会大会予稿集 日本バイオマテリアル学会 シンポジウム2016 237 - 237 2016/11
• 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 1880-6449 2016/10 [Refereed][Invited]
  
• 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 - + 0935-9648 2016/08 [Refereed][Not invited]
   

  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.
• 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 0024-9297 2016/08 [Refereed][Not invited]
   

  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.
• 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 0887-6266 2016/07 [Refereed][Not invited]
   

  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.
• 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 0935-9648 2016/06 [Refereed][Not invited]
   

  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.
• 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 0024-9297 2016/06 [Refereed][Not invited]
   

  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.
• 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 0024-9297 2016/04 [Refereed][Not invited]
   

  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.
• 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 0024-9297 2016/04 [Refereed][Not invited]
   

  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.
• 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 0024-9297 2016/03 [Refereed][Not invited]
   

  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.
• 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 0386-2186 2016 [Refereed][Invited]
   

  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.
• 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 1744-683X 2016 [Refereed][Not invited]
   

  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.
• 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 1744-683X 2016 [Refereed][Not invited]
   

  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.
• 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 - + 0935-9648 2015/12 [Refereed][Not invited]
   

  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 - + 0935-9648 2015/11 [Refereed][Not invited]
   

  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%).
• 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 2161-1653 2015/09 [Refereed][Not invited]
   

  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.
• 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 0024-9297 2015/08 [Refereed][Not invited]
   

  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.
• 高強度ゲルをつくる

  中島祐, 龔剣萍

  高分子 64 (6) 367 - 369 0454-1138 2015/05 [Not refereed][Invited]
  
• 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 - + 0935-9648 2015/05 [Refereed][Not invited]
   

  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.
• 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 0024-9297 2015/04 [Refereed][Not invited]
   

  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.
• 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 0024-9297 2015/04 [Refereed][Not invited]
   

  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 0451-1964 2015/03 [Not refereed][Invited]
  
• 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 2050-750X 2015 [Refereed][Not invited]
   

  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 1744-683X 2015 [Refereed][Not invited]
   

  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.
• 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 1744-683X 2015 [Refereed][Not invited]
   

  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.
• 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 0024-9297 2014/10 [Refereed][Not invited]
   

  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.
• 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 0024-9297 2014/09 [Refereed][Not invited]
   

  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 2041-1723 2014/08 [Refereed][Not invited]
   

  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 2041-1723 2014/08 [Refereed][Not invited]
   

  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.
• 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 0024-9297 2014/06 [Refereed][Not invited]
   

  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 0024-9297 2014/05 [Refereed][Not invited]
   

  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.
• 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 2014/03 [Not refereed][Invited]
  
• 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 0032-3861 2014/02 [Refereed][Not invited]
   

  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.
• 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 0935-9648 2014/01 [Refereed][Not invited]
  
• 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 0024-9297 2013/11/26 [Refereed][Not invited]
   

  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.
• 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 1476-1122 2013/10 [Refereed][Not invited]
   

  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.
• 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 1476-1122 2013/10 [Refereed][Not invited]
   

  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.
• 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 0935-9648 2013/06/11 [Refereed][Not invited]
   

  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 2161-1653 2013/06 [Refereed][Not invited]
   

  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.
• 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 2161-1653 2013/06 [Refereed][Not invited]
   

  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.
• 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 2050-750X 2013 [Refereed][Not invited]
   

  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.
• 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 1744-683X 2013 [Refereed][Not invited]
   

  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.
• 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 Royal Society of Chemistry ({RSC}) 1 (36) 4555 - 4562 2050-750X 2013 [Refereed][Not invited]
   

  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.
• 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 0024-9297 2012/12 [Refereed][Not invited]
   

  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 crosslinked 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.
• 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 1616-301X 2012/11 [Refereed][Not invited]
   

  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.
• 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 0024-9297 2012/06 [Refereed][Not invited]
   

  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.
• 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 0887-6266 2011/09 [Refereed][Not invited]
   

  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
• 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 0024-9297 2010/11 [Refereed][Not invited]
   

  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
• 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 1759-9954 2010/07 [Refereed][Not invited]
   

  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.
• 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 (1) 122 - + 1022-1360 2010 [Refereed][Not invited]
   

  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.
• 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 0024-9297 2009/03 [Refereed][Not invited]
   

  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.
• 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 012016  1742-6596 2009 [Refereed][Not invited]
   

  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.
• 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 0256-7679 2009/01 [Refereed][Invited]
   

  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.
• 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 0024-9297 2007/09 [Refereed][Not invited]
   

  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.
• 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 

  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.

MISC

• 新陳代謝して成長するゲル

  中島祐, GONG Jian Ping  化学と教育  69-  (3)  2021
• Self-Growing Gels Inspired by Biological Metabolism

  中島祐, 中島祐  繊維学会予稿集(CD-ROM)  76-  (1)  2021
• いきものみたいなもの「栄養」を取り込んで成長するゲル

  中島祐  高分子  69-  (4)  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
• 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
• 固体内部からのGraft‐gelationによる高靱性ゲルの固体表面へのコーティング

  塩本健悟, 中島祐, 黒川孝幸, GONG Jang Ping  高分子学会予稿集(CD-ROM)  63-  (1)  ROMBUNNO.1PC061  2014/05/09  [Not refereed][Not invited]
  
• DNゲルの強靱性に対する数理的考察

  井倉弓彦, 中島祐, 野々山貴行, 黒川孝幸, GONG Jian Ping, 長山雅晴  高分子学会予稿集(CD-ROM)  63-  (1)  ROMBUNNO.2PD046  2014/05/09  [Not refereed][Not invited]
  
• 軟骨再生ハイドロゲルと骨組織の接着を目指した高靱性DNゲル表面におけるHApのバイオミネラリゼーション

  木山竜二, 野々山貴行, 黒川孝幸, 中島祐, GONG Jian Ping  日本セラミックス協会年会講演予稿集(CD-ROM)  2014-  ROMBUNNO.1P141  2014/03/07  [Not refereed][Not invited]
  
• 高強度ハイドロゲルとバイオセラミックスの融合:ソフトセラミックスの創製

  野々山貴行, 木山竜二, 黒川孝幸, 中島祐, GONG Jian Ping  日本セラミックス協会年会講演予稿集(CD-ROM)  2014-  ROMBUNNO.1J24  2014/03/07  [Not refereed][Not invited]
  
• ゲルの異方的膨潤が誘起する液晶性高分子の超構造形成

  高橋陸, 中島祐, 黒川孝幸, 野々山貴行, グン剣萍  化学系学協会北海道支部冬季研究発表会講演要旨集(CD-ROM)  2014-  ROMBUNNO.P38  2014/01/28  [Not refereed][Not invited]
  
• Double network構造を有する強靭エラストマーの創製

  米田有希, 中島祐, 黒川孝幸, 佐田和己, 小門憲太, ぐん剣萍  化学系学協会北海道支部冬季研究発表会講演要旨集(CD-ROM)  2014-  ROMBUNNO.P39  2014/01/28  [Not refereed][Not invited]
  
• ゲル‐固体間の強靭な接着を目指した,重合開始点を含有する基板からのゲル重合

  塩本健悟, 岡崎春香, 中島祐, 黒川孝幸, ぐん剣萍  化学系学協会北海道支部冬季研究発表会講演要旨集(CD-ROM)  2014-  ROMBUNNO.2A09  2014/01/28  [Not refereed][Not invited]
  
• 配向したラメラ構造を有するゲルの異常変形挙動

  中島祐, HAQUE Md. Anamul, 黒川孝幸, GONG Jian Ping  高分子ゲル研究討論会講演要旨集  25th-  31  -32  2014/01/15  [Not refereed][Not invited]
  
• 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
• 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
• 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~高分子水溶液とゲルの構造変化観察~

  古橋由梨, 中島祐, 黒川孝幸, 黒川孝幸, 古川英光, 山田幸司, ぐん剣萍  高分子学会北海道支部研究発表会講演要旨集  45th-  2011
• 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(<特集>ゲル研究の新展開)

  中島 祐, 〓 剣萍  物性研究  93-  (5)  551  -557  2010/02/05  [Not refereed][Not invited]
  
• 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
• 蛍光プローブによるハイドロゲルのラジカル重合過程の観察

  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  高分子学会予稿集(CD-ROM)  59-  (1 Disk1)  2010
• 超高強度ゲルの創製XXV]:一軸伸長下におけるDNゲルの内部破壊挙動の考察

  中島祐, YU Qiu Ming, 黒川孝幸, 黒川孝幸, 古川英光, GONG Jian Ping  高分子学会予稿集(CD-ROM)  59-  (2 Disk1)  2010
• 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~高分子水溶液の構造変化の観察~

  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  高分子学会予稿集(CD-ROM)  59-  (2 Disk1)  2010
• 高強度DNゲルの開発と関節軟骨再生誘導への応用 (特集 生体材料の最新開発動向)

  中島 祐, ぐん ちぇんぴん, 安田 和則  工業材料  57-  (6)  38  -41  2009/06  [Not refereed][Not invited]
  
• 高強度ハイドロゲルのコーティングと固体基板との高強度接着

  桜井翔太, 古川英光, 中島祐, 黒川孝幸, 田中良巳, GONG Jian Ping  高分子ゲル研究討論会講演要旨集  20th-  2009
• DNゲルの高強度化メカニズム

  大井彰, 中島祐, 黒川孝幸, 古川英光, 田中良巳, きょう剣萍  高分子学会北海道支部研究発表会講演要旨集  43rd-  2009
• 超高強度ゲルの創製(XXI)静・動的光散乱によるDNゲルのダメージゾーンの研究

  YU Qiu Ming, 古川英光, 古川英光, 田中良巳, 田中良巳, 中島祐, 黒川孝幸, 黒川孝幸, GONG Jian Ping  高分子学会予稿集(CD-ROM)  58-  (2 Disk1)  2009
• DNゲルの強度に対する水の効果~FT-IRによるゲル-溶媒間相互作用解析~

  板垣裕子, 中島祐, 勝本之晶, 黒川孝幸, 黒川孝幸, 古川英光, 古川英光, GONG Jian Ping  高分子学会予稿集(CD-ROM)  58-  (2 Disk1)  2009
• 超高強度ゲルの創製[XVII]:両網目の協同性

  中島祐, 古川英光, 田中良巳, 黒川孝幸, GONG Jian Ping, 長田義仁  高分子ゲル研究討論会講演要旨集  19th-  2008
• 超高強度DNゲルの高強度化条件探索

  中島祐, 古川英光, 田中良巳, 黒川孝幸, GONG Jian Ping, 長田義仁  高分子学会北海道支部研究発表会講演要旨集  42nd-  2008
• Creation of Double Network Hydrogels with Extremely High Strength and Its Anomalous Fracture Mechanism

  Tasuku Nakajima, Yoshimi Tanaka, Hidemitsu Furukawa, Takayuki Kurokawa, Jian Ping Gong  KOBUNSHI RONBUNSHU  65-  (12)  707  -715  2008  [Not refereed][Not invited]
   

  Hydrogels have attracted much attention as potential soft and wet materials because of their unique properties, such as low surface friction and volume phase transition. However, conventional hydrogels are mechanically too weak and unsuitable for practical uses. Inspired by the structure of articular cartilage, a natural tough hydrogels, we have created novel hydrogels with extremely high mechanical strength. The gels are a kind of interpenetrating networks (IPN) consisting of rigid polyelectrolyte and soft neutral polymers, and show a compressive fracture stress of 60 MPa, 3000% of tensile strain and 2500 J/m(2) of fracture energy. Such mechanical properties cannot be explained by the standard theories about fracture of soft polymer systems. In this paper, we discuss, based on our recent papers, the synthesis conditions to obtain the tough hydrogels and physical mechanism under the high toughness. The essential point is that partial breakage of the rigid component causes formation of yielding zone around crack tip, which leads to a large dissipation for the crack propagation. We also describe several results on tissue engineering application of the hydrogels.
• 20aRE-7 High-Strength Soft & Wet Matter (3) : Entanglement Effect in Double-Network Gels

  Furukawa Hidemitsu, Huang Mei, Nakajima Tasuku, Tanaka Yoshimi, Kurokawa Takayuki, Gong Jian Ping, Osada Yoshihito  Meeting abstracts of the Physical Society of Japan  62-  (1)  346  -346  2007/02/28  [Not refereed][Not invited]
  
• 超高強度ゲルの創製[XVI]:Truly Independent Double Network gelと不均一構造との関係性

  中島祐, 川内保範, 古川英光, 田中良巳, 黒川孝幸, GONG Jian Ping, 長田義仁  高分子学会予稿集(CD-ROM)  56-  (2 Disk1)  2007
• 疎密構造の制御によるDouble Networkゲルの高強度化

  中島祐, 川内保範, 古川英光, 田中良巳, 黒川孝幸, きょう剣萍, きょう剣萍, 長田義仁  高分子学会北海道支部研究発表会講演要旨集  41st-  2007
• 超高強度ゲルの創製[XIV]:疎密構造が誘起するDNゲルのNecking現象

  中島祐, 古川英光, 川内保範, 田中良巳, 黒川孝幸, GONG Jian Ping, GONG Jian Ping, 長田義仁  高分子学会予稿集(CD-ROM)  56-  (1 Disk1)  2007
• 超高強度ゲルの創製[XII]制御されたvoid構造の効果

  中島祐, 古川英光, 田中良巳, 黒川孝幸, GONG Jian Ping, GONG Jian Ping, 長田義仁  高分子学会予稿集(CD-ROM)  55-  (2 Disk1)  2006

Association Memberships

• THE CHEMICAL SOCIETY OF JAPAN   THE SOCIETY OF POLYMER SCIENCE, JAPAN   日本機械学会   日本レオロジー学会   

Research Projects

• Design of Low Entropy Polymer Network Materials for Unique Functions

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2022/12 -2029/03 

  Author : グン 剣萍, Li Xiang, 野々山 貴行, 中島 祐
• Design engineering for outstanding materials with controlled soft-stiff heterogeneity

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2024/04 -2027/03 

  Author : 篠崎 健二, 加藤 和明, 中島 祐, 菊池 将一
• Metabolic Material System: Material Growth by Metabolic-like Destruction and Remodeling

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2022/04 -2027/03 

  Author : グン 剣萍, 中島 祐, 印出井 努, 野々山 貴行
• Establishment of a framework for self-evolving materials through mechanical training

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2022/04 -2025/03 

  Author : グン 剣萍, 印出井 努, 野々山 貴行, キング ダニエル, 中島 祐
• 未踏高分子材料群「極限伸長網目」の学理構築

  科学技術振興機構：戦略的な研究開発の推進 戦略的創造研究推進事業 さきがけ

  Date (from‐to) : 2020 -2023 

  Author : 中島 祐

   

  ゲル・ゴムなどのソフト高分子網目材料は、そのナノスケール網目鎖のコイル状構造に由来した柔軟性、伸張性を示します。本研究では、これら材料の網目鎖を極度に伸長させ、新奇力学機能を有する未踏材料「極限伸長網目」を創製します。自由エネルギー的に不利な極限伸長網目の合成法を確立し、そのナノ伸長構造に由来する特異な力学特性を見出します。得られた材料は、易分解材料、力で機能化する材料などへの応用展開を図ります。
• Utilizing the Sacrificial Bonding Principle to Create Soft-Hard Composites with Toughness that Surpasses Metals and Novel Functions

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S)

  Date (from‐to) : 2017/05 -2022/03 

  Author : グン 剣萍, 黒川 孝幸, 野々山 貴行, キング ダニエル, 中島 祐

   

  本年度は主に、ハードマター相の犠牲結合が複合材料の強靭化に及ぼす効果を解明した。最初に、mmスケールの多様な二次元長方格子（犠牲結合）を設計し、高性能3Dプリンターによって作製した。次いで、高靱性の柔らかい材料をマトリックス相として格子と複合させ、巨視的なスケールでのダブルネットワーク複合体を創製した。二次元格子の骨格の太さを制御した実験より、引張試験における多段階の格子の破断（すなわち犠牲結合原理の発現）は、二次元格子の強度がマトリックスの強度を上回った場合に生じることが分かった。また格子の節の数を制御した実験より、節の数を増やすほど引張試験時における格子の破断イベント数が増えるために材料が強靭となるが、強靭性はある一定の値で頭打ちになることが分かった。さらに多様な材質による二次元格子を検討した結果、どのような材質を用いても複合材料は強靭になったことから、格子の化学的性質（例えば表面の接着性）は強靭化に大きな影響を及ぼさず、格子とマトリックスの力学物性の関係性が強靭化度合の決定の主要因であることが明らかとなった。 次いで、多様な二次元・三次元格子を設計し、格子のポアソン比を変化させた複合材料を創製した。骨格として、具体的には負のポアソン比を持つオーセチック構造や、正のポアソン比を持つハニカム構造などを用いた。引張試験結果より、複合材料の強度は格子とマトリックスのポアソン比のミスマッチが大きいほど高くなることが示唆された。偏光顕微鏡観察の結果、本現象は、複合材料の変形時、ポアソン比のミスマッチによりマトリックスが局所的に（巨視的な変形よりも）極めて大きく変形することによって引き起こされていることが示唆された。また、ポアソン比のミスマッチによりマトリックスが（通常では起こりえない）体積変形を強いられることも原因の１つではないかと考えられ、現在検証を進めている。
• Experimental investigation of single polymer chain mechanics via analysis of mechanical analysis of gels

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (A)

  Date (from‐to) : 2017/04 -2021/03 

  Author : NAKAJIMA TASUKU

   

  Mechanical properties of polymeric materials are mainly determined by mechanical properties of polymer chains inside. Thus, experimental determination of mechanical properties of single polymer chain is important for widespread applications of polymeric materials. However, experimental techniques to measure the properties of single polymer chain have been still in development. In this study, we succeeded in extracting the mechanical properties of single polymer chain, especially its extremely stretched state, by analyzing the stretching and swelling tests of the macroscale polymer gels.
• Creation of soft/hard complex materials tougher than metal based on the

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2017/04 -2018/03 

  Author : グン 剣萍, 黒川 孝幸, 中島 祐, 野々山 貴行, キング ダニエル

   

  本研究では、高靭性ゲルの力学挙動（引張試験で見られる降伏現象、弾性率の低下を伴うヒステリシス現象、および引裂試験で見られる亀裂周辺の降伏領域(内部破壊領域)の形成）の三つの特徴を評価することによって、ゲルの靭性及びその高靭性化機構を解明することを目的とした。研究機関内には、ポリアンフォライトゲル/グラスファイバー織物の複合体について、様々な幅のサンプルを作製して引裂試験を行い、破壊エネルギーと降伏領域の関係を見積もった。サンプルの幅が降伏領域のサイズ（~cm）より小さい場合、複合体の破壊エネルギーはサンプルの幅と正の相関があった。一方、サンプルの幅が降伏領域より大きい場合、複合体の破壊エネルギーはサンプルの幅に依存しなかった。これは、本複合体の異常に高い破壊エネルギーが、亀裂近傍の降伏領域形成によるエネルギー散逸によることを強く示唆する結果である。また、破壊されたサンプルを走査型電子顕微鏡で観察した結果、繊維近傍におけるゲル層の破壊が確認された。ここから、本複合体の変形時には、ゲル-繊維間の応力伝達により、ゲル層の変形と破壊によるエネルギー散逸が高効率で発生し、それが本複合体を高効率にタフ化していることが示唆された。
• Creation of Tough Elastomer Based on DN Principle for Toughening of Hydrogels

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)

  Date (from‐to) : 2014/04 -2017/03 

  Author : NAKAJIMA Tasuku

   

  Elastomer is unique and exclusive solid due to its anomalous softness and extensibility. For toughening of rubbers, dispersion of filler has been exclusively applied for a long time. However, recently significant improvement of elastomer toughness by this method has no longer been reported because this traditional method had been already studied for a long period. On the other hand, our group has created double network (DN) hydrogels with extremely high toughness comparable to industrial rubbers, despite 90wt% of water content. Tough DN gels are comprised of the two independent networks, which are brittle 1st and ductile 2nd networks. Note that gels and elastomers are essentially same in the mechanical viewpoint; mechanical behavior of both of them follows rubber elasticity theory. Inspired by the DN gel studies, in this research project I have created a series of tough elastomer by introduction of contrasting double network structure.
• Proof of the Universality of Sacrificial Bond Principle and Creation of Tough Functional Hydrogels with Variety of Sacrificial Bonds

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S)

  Date (from‐to) : 2012/05 -2017/03 

  Author : Gong Jian Ping, NONOYAMA Takayuki, SUN Taolin

   

  Gels have been anticipated as tissue-like functional materials, but generally they are mechanically too weak to be applied widely. On the other hand, recently our group has proposed "sacrificial bond principle", where toughness of gels can be effectively improved by introducing weak and brittle bonds into soft and stretchable networks. In this project, we have created a series of extremely tough gels using this principle, e.g., variants of double network gels featuring covalent sacrificial bonds, polyampholyte gels containing ionic sacrificial bonds, and phase-separated polyacrylamide gels exhibiting super toughness based on solvophobic sacrificial bonds. We have also succeeded in adding functions corresponding to chemical species of sacrificial bonds to the tough gels, e.g., self-healing properties to polyampholyte gels and bioactivity to double network gels containing biopolymers. Through these studies, we have confirmed generality and diversity of sacrificial bond principle.
• 「犠牲結合原理」の普遍性の証明と多様な犠牲結合による高靭性ゲルの創製

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2012 -2012 

  Author : グン 剣萍, 黒川 孝幸, 中島 祐

   

  本研究では、高靭性ゲルの力学挙動(引張試験で見られる降伏現象、弾性率の低下を伴うヒステリシス現象、および引裂試験で見られる亀裂周辺の降伏領域(内部破壊領域)の形成)の三つの特徴を評価することによって、ゲルの靭性及びその高靭性化機構を解明することを目的とする。具体的には、多様な犠牲結合構造を導入したゲルに対して、引張試験で降伏応力、ヒステリシス面積および変形前後の弾性率の変化、引裂試験で破壊エネルギーを測定し、ゲルに導入した犠牲結合の密度との関係を定量化した。さらに、引裂試験時における亀裂周辺の降伏領域の厚さをレーザー顕微鏡で測定し、破壊された犠牲結合と破壊エネルギーとの相関を調べた。
• 高分子ステント法による、超高強度ダブルネットワークゲルの高強度化手法の一般化

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for JSPS Fellows

  Date (from‐to) : 2010 -2011 

  Author : 中島 祐

   

  昨年度は本分子ステント法の基礎技術を確立し、あらゆる親水性ポリマーから高強度St-DNゲルが創成可能であることを示した。そこで本年度は、本方法を様々な系へと拡張し、新規機能性高強度ゲルの開発を目指した。最初に、疎水性高分子を1st networkとした高強度ハイドロゲルの創製を行った。本ゲルは、一般的なDNゲルと同様に高い強度を示した他、ハイドロゲルでありながら水に対する高い接触角(80°)を示した。次に、配向高分子フィルムを作製し、これを1st networkに用いることで、物性に異方性のあるSt-DNゲルを合成した。本ゲルは、配向フィルムの構造を反映し、一軸に膨潤する、一方向のみに引き裂き可能などの興味深い新規物性を示した。以上より、疎水性高分子を基にした新規機能性DNゲルの開発に成功した。本結果は、DNゲルの高強度化手法を更に拡張し、従来は実現できなかった機能を発現させたという点で画期的である。また、ステントによるゲル膨潤挙動の理論的な考察を行った。中性ゲルに強電解質高分子(ステント)を導入すると、ステントの持つ高い浸透圧のためにゲルは膨潤する。ステント濃度が0.5Mに達するまでは、ゲルの膨潤挙動は一般的なゲル膨潤理論で説明可能であった。一方、ステント濃度が0.5M以上になると、ゲルの実際の膨潤度は理論値を下回った。本現象は、ステント濃度が大きい時、1st networkゲルの分子鎖の伸び切りが起こっていることを示している。また、本ゲルを基にSt-DNゲルを合成したところ、ステント濃度が0.5M以下の場合、ゲルの力学強度はステント濃度の増加に伴って大きくなるが、0.5M以上ではほぼ同じであった。ここから、St-DNゲルは1st networkが伸び切っているときに高強度化されることが示唆された。以上の成果を基に、現在4編の論文を投稿、あるいは執筆中である。

Industrial Property Rights

• 特開2012-036262:高分子ゲル及びその製造方法  2012/02/23

  グン 剣萍, 黒川 孝幸, 中島 祐, 佐藤 仁美  国立大学法人北海道大学  201203074986301962
• 特開2009-298971:高分子ゲルおよびその製造方法  2009/12/24

  グン 剣萍, 古川 英光, 黒川 孝幸, 武富 直之, 中島 祐  国立大学法人 北海道大学  200903019311227740
• 特開2009-185156:高分子ゲルおよびその製造方法  2009/08/20

  ▲ぐん▼ 剣萍, 古川 英光, 黒川 孝幸, 黒田 慎也, 中島 祐  国立大学法人 北海道大学  200903066520680760