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

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Profile and Settings

Affiliation

• Hokkaido University, Faculty of Advanced Life Science Division of Advanced Transdisciplinary Sciences, Professor

Profile and Settings

• Name (Japanese)

  Kurokawa

• Name (Kana)

  Takayuki

• Name

  200901041426432834

Alternate Names

https://altair.sci.hokudai.ac.jp/tsl/

Affiliation

• Hokkaido University, Faculty of Advanced Life Science Division of Advanced Transdisciplinary Sciences, Professor

Achievement

Research Interests

• 高強度   生体材料   犠牲結合   自然再生   ダブルネットワークゲル   DNゲル   硝子軟骨   軟骨再生   質量分析   軟骨分子   組織再生誘導基材   人工軟骨   アクチュエーター   関節軟骨欠損   バイオトライボロジー   関節軟骨   軟骨分化   軟・硬複合界面   低摩擦   再生医療   細胞外マトリックス   ソフト&ウェット   ソフトマター   細胞内情報伝達   分子機序   細胞メカニクス   ソフト&ウェットマテリアル   高分子ゲル   機能性   高強度ゲル   機能性ゲル   摩擦   ゲル   gel Highstrength-gel   

Research Areas

• Life sciences / Biomaterials
• Life sciences / Biomedical engineering
• Nanotechnology/Materials / Polymer materials
• Nanotechnology/Materials / Polymer chemistry

Research Experience

• 2017/07 - Today Hokkaido University Faculty of Advanced Life Science Professor
• 2013/04 - 2017/06 Hokkaido University Faculty of Advanced Life Science Associate Professor
• 2009/04 - 2013/03 Hokkaido University
• 2007/04 - 2009/03 Hokkaido University Faculty of Science
• 2006/01 - 2007/03 理化学研究所 協力研究員

Education

•        - 2005/12  Hokkaido University  Graduate School of Science
•        - 2000/03  Hokkaido University  School of Science

Awards

• 2022/11 株式会社リバネス フォーカスシステムズ賞
   生物に近い材料「ハイドロゲル」の活用
• 2017/02 平成28年度北海道大学研究総長賞・奨励賞
  
• 2016/02 平成27年度北海道大学研究総長賞・優秀賞
  
• 2015/03 平成2６年度北海道大学研究総長賞・優秀賞
  
• 2010/05 高分子学会 平成21年度高分子研究奨励賞
   犠牲的結合の導入により高力学物性を示す新規ハイドロゲルの創製

Published Papers

• Pre-yielding and necking process of double network hydrogels revealed by sample geometry effects

  Masahiro Yoshida, Ryuji Kiyama, Ye Zhang, Daniel R. King, Takayuki Kurokawa, Jian Ping Gong

  Extreme Mechanics Letters 69 102163 - 102163 2352-4316 2024/06 [Refereed][Not invited]
  
• Spatial Analysis of the Damage Zone in Double Network Hydrogel Using the Microelectrode Technique

  Takuya Nishimura, Honglei Guo, Yoshinori Katsuyama, Masahiro Yoshida, Jian Ping Gong, Takayuki Kurokawa

  Macromolecules 57 (4) 1502 - 1508 0024-9297 2024/02/09 [Refereed][Not invited]
  
• Tunable structure of chimeric isomaltomegalosaccharides with double α-(1 → 4)-glucosyl chains enhances the solubility of water-insoluble bioactive compounds

  Weeranuch Lang, Takayoshi Tagami, Yuya Kumagai, Seiya Tanaka, Hye-Jin Kang, Masayuki Okuyama, Wataru Saburi, Haruhide Mori, Tohru Hira, Chaehun Lee, Takuya Isono, Toshifumi Satoh, Hiroshi Hara, Takayuki Kurokawa, Nobuo Sakairi, Yoshiaki Yuguchi, Atsuo Kimura

  Carbohydrate Polymers 319 121185 - 121185 0144-8617 2023/11 [Refereed][Not invited]
  
• Novel endoscopic management of gastroenterological anastomosis leakage by injecting gel-forming solutions: an experimental animal study.

  Yusuke Watanabe, Keiko Yamamoto, Zijian Yang, Haruna Tsuchibora, Masakazu Fujii, Masayoshi Ono, Shoko Ono, Takayuki Kurokawa, Naoya Sakamoto

  Surgical endoscopy 2023/07/19 [Refereed]
   

  BACKGROUND: Anastomotic leakage (AL) after gastrointestinal surgery remains a challenging complication that requires surgical or non-surgical treatment. Although various therapeutic endoscopic techniques are available, no definitive interventions exist. We developed a therapeutic endoscopic submucosal injection method using novel gel-forming mixed solutions to close AL and evaluated the elasticity of the developed hydrogel. The safety and efficacy of the injection method were explored in porcine AL models. METHODS: We developed a novel gel-forming solution, and the formed gel lasted approximately one week within the gastrointestinal wall. An indentation test evaluated the elasticity of the novel hydrogel. After the confirmation of AL on porcine anterior gastric walls, sodium alginate was endoscopically injected into the submucosal layer around the leakage site circularly, followed by a calcium lactate/chitosan-based solution. After that, the outcomes data were collected, and histopathological effectiveness was evaluated. RESULTS: The increased sodium alginate elasticity with the addition of calcium lactate/chitosan-based solution facilitated long-lasting gel formation. Four pigs with AL underwent this intervention consecutively. Each endoscopic injection was completed in less than 5 min. No significant complications were observed for 3 weeks after the intervention. All AL sites were macroscopically healed. Histopathologic findings at 3 weeks showed that the wall defect was filled with collagen fibers that had grown around the site of the muscle layer tear. No tissue necrosis was observed. CONCLUSION: This preclinical study demonstrated that the therapeutic injection method for gastroenterological AL using gel-forming solutions could be an alternative endoscopic treatment, especially in patients with severe conditions or comorbidities. The optimal target of this treatment is small size and early AL without poor blood flow or intense hypertrophic scar lesions.
• Origin of Surface Charge of Double Network Hydrogels Prepared by Sequential Polymerization

  Martin Frauenlob, Honglei Guo, Takayuki Kurokawa, Jian Ping Gong

  ACS Macro Letters 12 (7) 860 - 865 2161-1653 2023/06/20
• Engineering of an electrically charged hydrogel implanted into a traumatic brain injury model for stepwise neuronal tissue reconstruction

  Satoshi Tanikawa, Yuki Ebisu, Tomáš Sedlačík, Shingo Semba, Takayuki Nonoyama, Takayuki Kurokawa, Akira Hirota, Taiga Takahashi, Kazushi Yamaguchi, Masamichi Imajo, Hinako Kato, Takuya Nishimura, Zen-ichi Tanei, Masumi Tsuda, Tomomi Nemoto, Jian Ping Gong, Shinya Tanaka

  Scientific Reports 13 (2233) 2023/02/14 [Refereed]
   

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

  Ryuji Kiyama, Masahiro Yoshida, Takayuki Nonoyama, Tomas Sedlacik, Hiroshi Jinnai, Takayuki Kurokawa, Tasuku Nakajima, Jian Ping Gong

  Advanced Materials 35 (1) 2208902 - 2208902 0935-9648 2022/11/18 [Refereed][Not invited]
  
• Gluing blood into gel by electrostatic interaction using a water-soluble polymer as an embolic agent.

  Zhiping Jin, Hailong Fan, Toshiya Osanai, Takayuki Nonoyama, Takayuki Kurokawa, Hideki Hyodoh, Kotaro Matoba, Akiko Takeuchi, Jian Ping Gong, Miki Fujimura

  Proceedings of the National Academy of Sciences of the United States of America 119 (42) e2206685119  2022/10/18 [Refereed][Not invited]
   

  Liquid embolic agents are widely used for the endovascular embolization of vascular conditions. However, embolization based on phase transition is limited by the adhesion of the microcatheter to the embolic agent, use of an organic solvent, unintentional catheter retention, and other complications. By mimicking thrombus formation, a water-soluble polymer that rapidly glues blood into a gel without triggering coagulation was developed. The polymer, which consists of cationic and aromatic residues with adjacent sequences, shows electrostatic adhesion with negatively charged blood substances in a physiological environment, while common polycations cannot. Aqueous polymer solutions are injectable through clinical microcatheters and needles. The formed blood gel neither adhered to the catheter nor blocked the port. Postoperative computed tomography imaging showed that the polymer can block the rat femoral artery in vivo and remain at the injection site without nontarget embolization. This study provides an alternative for the development of waterborne embolic agents.
• Surfactant induced bilayer-micelle transition for emergence of functions in anisotropic hydrogel

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

  Journal of Materials Chemistry B 10 (41) 8386 - 8397 2050-750X 2022/06/23 [Refereed]
   

  Tuning the self-assembled structures in amorphous hydrogels will enrich the functionality of hydrogels. In this study, we tuned the structure of a photonic hydrogel, which consists of polymeric lamellar bilayers...
• 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 2022/06/02 [Refereed]
   

  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.
• Evaluation of biological responses to micro-particles derived from a double network hydrogel

  Gen Matsumae, Mohamad Alaa Terkawi, Takayuki Nonoyama, Takayuki Kurokawa, Daisuke Takahashi, Tomohiro Shimizu, Ken Kadoya, Jian Ping Gong, Kazunori Yasuda, Norimasa Iwasaki

  Biomaterials Science 2047-4830 2022/03/16 [Refereed]
   

  Double network hydrogels have been proven to be a substitute biomaterial for cartilage. For further applications as articular cartilages, it is essential to understand the biological reactions that might be initiated by their micro-particles.
• High strength hydrogels enable dendrite-free Zn metal anodes and high-capacity Zn-MnO2 batteries via a modified mechanical suppression effect

  Ruijie Zhu, Huijun Yang, Wei Cui, Laras Fadillah, Tianhong Huang, Zetao Xiong, Chunmei Tang, Damian Kowalski, Sho Kitano, Chunyu Zhu, Daniel R. King, Takayuki Kurokawa, Yoshitaka Aoki, Hiroki Habazaki

  JOURNAL OF MATERIALS CHEMISTRY A 10 (6) 3122 - 3133 2050-7488 2022/02/14 [Refereed]
   

  Rechargeable aqueous zinc-ion batteries (RAZIBs) have some inherent advantages such as intrinsic safety, low-cost and theoretically high energy density, making them a current topic of interest. However, the phenomenon of zinc (Zn) dendrite growth at the anode results in the instability of RAZIBs and limits their real-world application. Herein, by employing a high strength hydrogel polymer electrolyte, the growth of dendritic Zn crystals is effectively eliminated through the mechanical suppression effect, resulting in a stable Zn anode that demonstrates dendrite-free plating/stripping with a long lifespan. Even under a high current density of 5 mA cm(-2), the Zn||Zn symmetric cell is shown to have a cyclic lifetime of longer than 1000 hours. Moreover, the stable cyclic performance of the Zn anode spawns a Zn||MnO2 battery with high capacity (4.8-1.9 mA h cm(-2)) and long lifetime (500 cycles at 9.2 mA cm(-2), 1C), which can meet the practical demands for portable devices. This work shows that high strength polymer gel electrolytes with internal energy dissipation mechanisms can overcome previous challenges that prevented practical utilization of RAZIBs. Together with the outstanding cyclic properties of the high capacity Zn||MnO2 batteries, this work provides a new pathway toward designing high energy density RAZIBs.
• Quantitative determination of cation–π interactions between metal ions and aromatic groups in aqueous media by a hydrogel Donnan potential method

  Hailong Fan, Honglei Guo, Takayuki Kurokawa, Jian Ping Gong

  Physical Chemistry Chemical Physics 24 (10) 6126 - 6132 1463-9076 2022/02 [Refereed]
   

  The binding ratios of various metal ions to aromatic groups by cation–π interactions in aqueous media have been quantitatively calculated by using Donnan potential measurements.
• 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]
  
• 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 2021/12/18 [Refereed]
  
• In Situ Evaluation of the Polymer Concentration Distribution of Microphase-Separated Polyelectrolyte Hydrogels by the Microelectrode Technique

  Takuya Nishimura, Honglei Guo, Ryuji Kiyama, Yoshinori Katsuyama, Jian Ping Gong, Takayuki Kurokawa

  Macromolecules 54 (23) 10776 - 10785 0024-9297 2021/12/14 [Refereed]
  
• 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]
   

  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.
• Hydroxyapatite-hybridized double-network hydrogel surface enhances differentiation of bone marrow-derived mesenchymal stem cells to osteogenic cells.

  Takuma Kaibara, Lei Wang, Masumi Tsuda, Takayuki Nonoyama, Takayuki Kurokawa, Norimasa Iwasaki, Jian Ping Gong, Shinya Tanaka, Kazunori Yasuda

  Journal of biomedical materials research. Part A 110 (4) 747 - 760 2021/10/28 [Refereed][Not invited]
   

  Recently, we have developed a hydroxyapatite (HAp)-hybridized double-network (DN) hydrogel (HAp/DN gel), which can robustly bond to the bone tissue in the living body. The purpose of this study is to clarify whether the HAp/DN gel surface can differentiate the bone marrow-derived mesenchymal stem cells (MSCs) to osteogenic cells. We used the MSCs which were harvested from the rabbit bone marrow and cultured on the polystyrene (PS) dish using the autogenous serum-supplemented medium. First, we confirmed the properties of MSCs by evaluating colony forming unit capacity, expression of MSC markers using flow cytometry, and multidifferential capacity. Secondly, polymerase chain reaction analysis demonstrated that the HAp/DN gel surface significantly enhanced mRNA expression of the eight osteogenic markers (TGF-β1, BMP-2, Runx2, Col-1, ALP, OPN, BSP, and OCN) in the cultured MSCs at 7 days than the PS surfaces (p < 0.0001), while the DN gel and HAp surfaces provided no or only a slight effect on the expression of these markers except for Runx2. Additionally, the alkaline phosphatase activity was significantly higher in the cells cultured on the HAp/DN gel surface than in the other three material surfaces (p < 0.0001). Thirdly, when the HAp/DN gel plug was implanted into the rabbit bone marrow, MSC marker-positive cells were recruited in the tissue generated around the plug at 3 days, and Runx2 and OCN were highly expressed in these cells. In conclusion, this study demonstrated that the HAp/DN gel surface can differentiate the MSCs into osteogenic cells.
• Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism

  Wei Cui, Yiwan Huang, Liang Chen, Yong Zheng, Yoshiyuki Saruwatari, Chung-Yuen Hui, Takayuki Kurokawa, Daniel R. King, Jian Ping Gong

  Matter 2590-2385 2021/09 [Refereed]
  
• Fast in vivo fixation of double network hydrogel to bone by monetite surface hybridization

  Takayuki NONOYAMA, Lei WANG, Ryuji KIYAMA, Naohiro KASHIMURA, Kazunori YASUDA, Shinya TANAKA, Takayuki KUROKAWA, Jian Ping GONG

  Journal of the Ceramic Society of Japan 129 (9) 584 - 589 1882-0743 2021/09/01 [Refereed]
  
• Rapid reprogramming of tumour cells into cancer stem cells on double-network hydrogels.

  Jun Suzuka, Masumi Tsuda, Lei Wang, Shinji Kohsaka, Karin Kishida, Shingo Semba, Hirokazu Sugino, Sachiyo Aburatani, Martin Frauenlob, Takayuki Kurokawa, Shinya Kojima, Toshihide Ueno, Yoshihiro Ohmiya, Hiroyuki Mano, Kazunori Yasuda, Jian Ping Gong, Shinya Tanaka

  Nature biomedical engineering 5 (8) 914 - 925 2021/08 [Refereed]
   

  Cancer recurrence can arise owing to rare circulating cancer stem cells (CSCs) that are resistant to chemotherapies and radiotherapies. Here, we show that a double-network hydrogel can rapidly reprogramme differentiated cancer cells into CSCs. Spheroids expressing elevated levels of the stemness genes Sox2, Oct3/4 and Nanog formed within 24 h of seeding the gel with cells from any of six human cancer cell lines or with brain cancer cells resected from patients with glioblastoma. Human brain cancer cells cultured on the double-network hydrogel and intracranially injected in immunodeficient mice led to higher tumorigenicity than brain cancer cells cultured on single-network gels. We also show that the double-network gel induced the phosphorylation of tyrosine kinases, that gel-induced CSCs from primary brain cancer cells were eradicated by an inhibitor of the platelet-derived growth factor receptor, and that calcium channel receptors and the protein osteopontin were essential for the regulation of gel-mediated induction of stemness in brain cancer cells.
• Flower-like Photonic Hydrogel with Superstructure Induced via Modulated Shear Field

  Ya Nan Ye, Md Anamul Haque, Akane Inoue, Yoshinori Katsuyama, Takayuki Kurokawa, Jian Ping Gong

  ACS MACRO LETTERS 10 (6) 708 - 713 2021/06 [Refereed]
   

  Biological tissues usually have complex superstructures and elaborated functionalities. However, creating superstructures in soft and wet hydrogels is challenging because of the absence of effective approaches to control the molecular orientation. Here we introduce a method to create superstructures in photonic hydrogels comprising lamellar bilayers intercalated in the cross-linked polymer network. The orientation of lamellar bilayers in the photonic gel, which are sensitive to shear, is modulated by applying a gradient shear field on the precursor solution using a customized rheometer. The difference in orientation of lamellar bilayers leads to swelling mismatch in the radial direction, endowing the disk-shape hydrogel with a macroscopic flower-like shape with a central dome and an edge petal, along with a bright photonic color. By characterization of the swelling anisotropy of the radial profile, the shear rate required for the unidirectional orientation of lamellar bilayers was extracted. Moreover, a delayed polymerization experiment was designed to measure the lifetime of aligned lamellar bilayers, which reveals the domain size of lamellar bilayers in the precursor solution. Furthermore, we also demonstrated that the hydrogel flowers could fade and rebloom reversibly in response to external stimuli. This work presents a strategy to develop superstructures in hydrogels and sheds light on designing biomimetic materials with intricately architectural superstructure.
• 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 [Refereed]
   

  High modulus, toughness, and fatigue resistance are usually difficult to be obtained simultaneously in rubbery materials. Here, we report that by superimposing the nanophase separation structure in double network (DN) elastomers using immiscible polymers, the modulus, fracture energy, and energy release rate of fatigue threshold are enhanced all together by 13, 5, and 5 times, respectively. We reveal that the interplay between the DN structure and the nanophase separation structure brings two effects synergistically: (1) formation of nanoclusters overstresses and homogenizes the sacrificial network, thereby remarkably increasing the modulus and yielding stress and (2) the nanoclusters act as viscoelastic nanofillers dissipating energy and pinning the crack propagation, thereby significantly enhancing toughness and fatigue resistance. This work provides a facile approach to superimpose high-order structures in DN materials for excellent mechanical performance. The clarified synergetic effects should be universal for DN materials made of immiscible polymers. We believe that this work will facilitate more studies on elastomers and gels along this line.
• 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 of the United States of America 118 (14) 2021/04/06 [Refereed]
   

  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.
• Effect of mesoscale phase contrast on fatigue-delaying behavior of self-healing hydrogels.

  Xueyu Li, Kunpeng Cui, Takayuki Kurokawa, Ya Nan Ye, Tao Lin Sun, Chengtao Yu, Costantino Creton, Jian Ping Gong

  Science advances 7 (16) 2021/04 [Refereed]
   

  We investigate the fatigue resistance of chemically cross-linked polyampholyte hydrogels with a hierarchical structure due to phase separation and find that the details of the structure, as characterized by SAXS, control the mechanisms of crack propagation. When gels exhibit a strong phase contrast and a low cross-linking level, the stress singularity around the crack tip is gradually eliminated with increasing fatigue cycles and this suppresses crack growth, beneficial for high fatigue resistance. On the contrary, the stress concentration persists in weakly phase-separated gels, resulting in low fatigue resistance. A material parameter, λtran, is identified, correlated to the onset of non-affine deformation of the mesophase structure in a hydrogel without crack, which governs the slow-to-fast transition in fatigue crack growth. The detailed role played by the mesoscale structure on fatigue resistance provides design principles for developing self-healing, tough, and fatigue-resistant soft materials.
• Experimental Verification of the Balance between Elastic Pressure and Ionic Osmotic Pressure of Highly Swollen Charged Gels.

  Tasuku Nakajima, Ken-Ichi Hoshino, Honglei Guo, Takayuki Kurokawa, Jian Ping Gong

  Gels (Basel, Switzerland) 7 (2) 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 1520-5002 2020/12/22
• Stress Relaxation and Underlying Structure Evolution in Tough and Self-Healing Hydrogels

  Kunpeng Cui, Ya Nan Ye, Chengtao Yu, Xueyu Li, Takayuki Kurokawa, Jian Ping Gong

  ACS Macro Letters 9 (11) 1582 - 1589 2161-1653 2020/11/17 [Refereed]
  
• Polyzwitterions as a Versatile Building Block of Tough Hydrogels: From Polyelectrolyte Complex Gels to Double-Network Gels.

  Haiyan Yin, Daniel R King, Tao Lin Sun, Yoshiyuki Saruwatari, Tasuku Nakajima, Takayuki Kurokawa, Jian Ping Gong

  ACS applied materials & interfaces 12 (44) 50068 - 50076 2020/11/04 [Refereed]
   

  The high water content of hydrogels makes them important as synthetic biomaterials, and tuning the mechanical properties of hydrogels to match those of natural tissues without changing chemistry is usually difficult. In this study, we have developed a series of hydrogels with varied stiffness, strength, and toughness based on a combination of poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS), a strong acidic polyelectrolyte, and poly-N-(carboxymethyl)-N,N-dimethyl-2-(methacryloyloxy) ethanaminium) (PCDME), a polyzwitterion with a weak acidic moiety. We demonstrate that modifying the true molar ratio, R, of PCDME to PAMPS results in four unique categories of hydrogels with different swelling ratios and Young's moduli. When R < 1, a negatively charged polyelectrolyte gel (PE) is formed; when 1 < R < 3, a tough and viscoelastic polyelectrolyte complex gel (PEC) is formed; when 3 < R < 6.5, a conventional, elastic interpenetrating network gel (IPN) is formed; and when R > 6.5, a tough and stiff double-network gel (DN) is formed. Both the PEC and DN gels exhibit high toughness and fracture stress, up to 1.8 and 1.5 MPa, respectively. Importantly, the PEC gels exhibit strong recovery properties along with high toughness, distinguishing them from DN gels. Without requiring a change in chemistry, we can tune the mechanical response of hydrogels over a wide spectrum, making this a useful system of soft and hydrated biomaterials.
• 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 21 (10) 4220 - 4230 2020/10/12 [Refereed]
   

  Chitin is a biopolymer, which has been proven to be a biomedical material candidate, yet the weak mechanical properties seriously limit their potentials. In this work, a chitin-based double-network (DN) hydrogel has been designed as a potential superficial repairing material. The hydrogel was synthesized through a double-network (DN) strategy composing hybrid regenerated chitin nanofiber (RCN)-poly (ethylene glycol diglycidyl ether) (PEGDE) as the first network and polyacrylamide (PAAm) as the second network. The hybrid RCN-PEGDE/PAAm DN hydrogel was strong and tough, possessing Young's modulus (elasticity) E 0.097 ± 0.020 MPa, fracture stress σf 0.449 ± 0.025 MPa, and work of fracture Wf 5.75 ± 0.35 MJ·m-3. The obtained DN hydrogel was strong enough for surgical requirements in the usage of soft tissue scaffolds. In addition, chitin endowed the DN hydrogel with good bacterial resistance and accelerated fibroblast proliferation, which increased the NIH3T3 cell number by nearly five times within 3 days. Subcutaneous implantation studies showed that the DN hydrogel did not induce inflammation after 4 weeks, suggesting a good biosafety in vivo. These results indicated that the hybrid RCN-PEGDE/PAAm DN hydrogel had great prospect as a rapid soft-tissue-repairing material.
• 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 2020/09/30 [Refereed]
   

  Double-network (DN) gels, consisting of brittle first and ductile second networks, possess extraordinary strength, extensibility, and fracture toughness while maintaining a high solvent content. Herein, we prepare DN gels consisting of various concentrations of the first and second networks to investigate the effect of each network structure on the tensile and fracture properties of DN gels. The results showed that the tensile properties of DN gels before yielding are mainly dominated by the first network, serving as a skeleton, whereas the properties after necking are determined by both networks. Moreover, we found that the DN gels with significant energy dissipation capacities exhibit high fracture resistance. Thus, this study not only confirms the factors determining the mechanical characteristics of DN gels but also explains how the two networks concertedly improve the toughness of DN gels.
• Hydrogels as dynamic memory with forgetting ability

  Chengtao Yu, Honglei Guo, Kunpeng Cui, Xueyu Li, Ya Nan Ye, Takayuki Kurokawa, Jian Ping Gong

  Proceedings of the National Academy of Sciences 117 (32) 202006842 - 202006842 0027-8424 2020/07/27 [Refereed][Not invited]
   

  The memory of our brain, stored in soft matter, is dynamic, and it forgets spontaneously to filter unimportant information. By contrast, the existing manmade memory, made from hard materials, is static, and it does not forget without external stimuli. Here we propose a principle for developing dynamic memory from soft hydrogels with temperature-sensitive dynamic bonds. The memorizing–forgetting behavior is achieved based on fast water uptake and slow water release upon thermal stimulus, as well as thermal-history-dependent transparency change of these gels. The forgetting time is proportional to the thermal learning time, in analogy to the behavior of brain. The memory is stable against temperature fluctuation and large stretching; moreover, the forgetting process is programmable. This principle may inspire future research on dynamic memory based on the nonequilibrium process of soft matter.
• Bactericidal effect of cationic hydrogels prepared from hydrophilic polymers

  Yuki Shibata, Takayuki Kurokawa, Tomoyasu Aizawa, Jian Ping Gong

  Journal of Applied Polymer Science 49583 - 49583 0021-8995 2020/07/24 [Refereed][Not invited]
  
• Phase Separation Behavior in Tough and Self-Healing Polyampholyte Hydrogels

  Kunpeng Cui, Ya Nan Ye, Tao Lin Sun, Chengtao Yu, Xueyu Li, Takayuki Kurokawa, Jian Ping Gong

  Macromolecules 0024-9297 2020/06/26 [Refereed][Not invited]
  
• Fiber‐Reinforced Viscoelastomers Show Extraordinary Crack Resistance That Exceeds Metals

  Wei Cui, Daniel R. King, Yiwan Huang, Liang Chen, Tao Lin Sun, Yunzhou Guo, Yoshiyuki Saruwatari, Chung‐Yuen Hui, Takayuki Kurokawa, Jian Ping Gong

  Advanced Materials 32 (31) 1907180 - 1907180 0935-9648 2020/06/25 [Refereed][Not invited]
   

  Soft fiber-reinforced polymers (FRPs), consisting of rubbery matrices and rigid fabrics, are widely utilized in industry because they possess high specific strength in tension while allowing flexural deformation under bending or twisting. Nevertheless, existing soft FRPs are relatively weak against crack propagation due to interfacial delamination, which substantially increases their risk of failure during use. In this work, a class of soft FRPs that possess high specific strength while simultaneously showing extraordinary crack resistance are developed. The strategy is to synthesize tough viscoelastic matrices from acrylate monomers in the presence of woven fabrics, which generates soft composites with a strong interface and interlocking structure. Such composites exhibit fracture energy, Γ, of up to 2500 kJ m-2 , exceeding the toughest existing materials. Experimental elucidation shows that the fracture energy obeys a simple relation, Γ = W · lT , where W is the volume-weighted average of work of extension at fracture of the two components and lT is the force transfer length that scales with the square root of fiber/matrix modulus ratio. Superior Γ is achieved through a combination of extraordinarily large lT (10-100 mm), resulting from the extremely high fiber/matrix modulus ratios (104 -105 ), and the maximized energy dissipation density, W. The elucidated quantitative relationship provides guidance toward the design of extremely tough soft composites.
• 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 2020/06/23 [Refereed][Not invited]
  
• Anisotropic Double-Network Hydrogels via Controlled Orientation of a Physical Sacrificial Network

  Daniel R. King, Riku Takahashi, Takuma Ikai, Kazuki Fukao, Takayuki Kurokawa, Jian Ping Gong

  ACS Applied Polymer Materials 2020/06/12 [Refereed][Not invited]
  
• Synthetic PAMPS Gel Induces Chondrogenic Differentiation of ATDC5 Cells via a Novel Protein Reservoir Function

  Shingo Semba, Nobuto Kitamura, Masumi Tsuda, Keiko Goto, Sadamu Kurono, Yoshihiro Ohmiya, Takayuki Kurokawa, Jian Ping Gong, Kazunori Yasuda, Shinya Tanaka

  Journal of Biomedical Materials Research Part A 109 (3) 354 - 364 2020/06 [Refereed][Not invited]
   

  We previously demonstrated that a synthetic negatively charged poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) gel induced chondrogenic differentiation of ATDC5 cells. In this study, we clarified the underlying molecular mechanism, in particular, focusing on the events that occurred at the interface between the gel and the cells. Gene expression profiling revealed that the expression of extracellular components was enhanced in the ATDC5 cells that were cultured on the PAMPS gel, suggesting that extracellular proteins secreted from the ATDC5 cells might be adsorbed in the PAMPS gel, thereby contributing to the induction of chondrogenic differentiation. Therefore, we created "Treated-PAMPS gel," which adsorbed various proteins secreted from the cultured ATDC5 cells during 7 days. Proteomic analysis identified 27 proteins, including extracellular matrix proteins such as Types I, III, and V collagens and thrombospondin (THBS) in the Treated-PAMPS gel. The Treated-PAMPS gel preferentially induced expression of chondrogenic markers, namely, aggrecan and Type II collagen, in the ATDC5 cells compared with the untreated PAMPS gel. Addition of recombinant THBS1 to the ATDC5 cells significantly enhanced the PAMPS-induced chondrogenic differentiation, whereas knockdown of THBS1 completely abolished this response. In conclusion, we demonstrated that the PAMPS gel has the potential to induce chondrogenic differentiation through novel reservoir functions, and the adsorbed THBS plays a significant role in the induction.
• Integrin α4 Mediates ATDC5 Cell Adhesion to Negatively Charged Synthetic Polymer Hydrogel Leading to Chondrogenic Differentiatio

  Daiki Hashimoto, Shingo Semba, Masumi Tsuda, Takayuki Kurokawa, Nobuto Kitamura, Kazunori Yasuda, Jian Ping Gong, Shinya Tanaka

  Biochemical and Biophysical Research Communications 528 (1) 120 - 126 2020/05 [Refereed][Not invited]
   

  Negatively charged synthetic hydrogels have been known to facilitate various cellular responses including cell adhesion, proliferation, and differentiation; however, the molecular mechanism of hydrogel-dependent control of cell behavior remains unclear. Recently, we reported that negatively charged poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) gel induces chondrogenic differentiation of ATDC5 cells via novel protein reservoir function. In this study, we identified the cell adhesion molecules binding to PAMPS gels that act as mechanoreceptors. First, we performed a pull-down assay by particle gels using cell membrane proteins of ATDC5, and found that multiple membrane proteins bound to the PAMPS gel, whereas the uncharged poly(N,N'-dimethylacrylamide) gel as control did not bind to any membrane proteins. Western blot analysis indicated differential binding of integrin (ITG) isoforms to the PAMPS gel, in which the α4 isoform, but not α5 and αv, efficiently bound to the PAMPS gel. ITG α4 knockdown decreased cell spreading of ATDC5 on PAMPS gels, whereas the enhanced expression increased the behavior. Furthermore, ITG α4 depletion suppressed PAMPS gel-induced expression of bone morphogenic protein (BMP) 4 contributing to chondrogenic differentiation, in concordance with the reduction of ERK activation. These results demonstrated that membrane protein binding to PAMPS gels occurred in a charge-dependent manner, and that ITG α4 plays a crucial role in cell spreading on PAMPS gels and acts as a mechanoreceptor triggering cellular signaling leads to chondrogenic differentiation.
• 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 2020/05 [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.
• Mesoscale Bicontinuous Networks in Self-healing Hydrogels Delay Fatigue Fracture

  Xueyu Li, Kunpeng Cui, Tao Lin Sun, Lingpu Meng, Chengtao Yu, Liangbin Li, Costantino Creton, Takayuki Kurokawa, Jian Ping Gong

  Proceedings of the National Academy of Sciences 117 (14) 7606 - 7612 2020/03 [Refereed][Not invited]
   

  Load-bearing biological tissues, such as muscles, are highly fatigue-resistant, but how the exquisite hierarchical structures of biological tissues contribute to their excellent fatigue resistance is not well understood. In this work, we study antifatigue properties of soft materials with hierarchical structures using polyampholyte hydrogels (PA gels) as a simple model system. PA gels are tough and self-healing, consisting of reversible ionic bonds at the 1-nm scale, a cross-linked polymer network at the 10-nm scale, and bicontinuous hard/soft phase networks at the 100-nm scale. We find that the polymer network at the 10-nm scale determines the threshold of energy release rate G 0 above which the crack grows, while the bicontinuous phase networks at the 100-nm scale significantly decelerate the crack advance until a transition G tran far above G 0 In situ small-angle X-ray scattering analysis reveals that the hard phase network suppresses the crack advance to show decelerated fatigue fracture, and G tran corresponds to the rupture of the hard phase network.
• Tough gel - Calcium Phosphate Composite for Artificial Cartilage and Bonding to Bone

  野々山貴行, 木山竜二, 深尾一城, 安田和則, 黒川孝幸, 龔剣萍

  Bulletin of the Ceramics Society of Japan 日本セラミックス協会 55 (3) 166 - 170 0009-031X 2020/03 [Not refereed][Not invited]
  
• Non-Linear Rheological Study of Hydrogel Sliding Friction in Water and Concentrated Hyaluronan Solution

  Satoshi Hirayama, Takayuki Kurokawa, Jian Ping Gong

  Tribology International 147 106270  2020/02 [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 53 (4) 1154 - 1163 2020/01/31 [Refereed][Not invited]
  
• Surface charge dominated protein absorption on hydrogels.

  Honglei Guo, Yuto Uehara, Takahiro Matsuda, Ryuji Kiyama, Long Li, Jamil Ahmed, Yoshinori Katsuyama, Takayuki Nonoyama, Takayuki Kurokawa

  Soft matter 16 (7) 1897 - 1907 2020/01/29 [Refereed][Not invited]
   

  Soft tissue engineering requires antifouling materials that are biocompatible and mechanically flexible. Conventional hydrogels containing more than 70 wt% water are thus promising antifouling material candidates. However, some hydrogels are difficult to apply in internal body organs because of undesirable protein absorption on their surfaces. Due to the lack of an effective method for observing the true charge densities of hydrogels, the reason why electrostatic interactions dominate protein absorption behavior remains unclear. In this work, we adopt the microelectrode technique (MET) to study the electrical potentials of hydrogels with negative, positive, and neutral potentials and demonstrate the protein absorption behaviors on those hydrogels. The results show that MET is an effective method to obtain the surface charge densities of various hydrogels. Furthermore, the amounts of absorbed proteins on the gels were quantified with respect to the charge densities of the hydrogels. The results indicate that electrostatic absorption is quantitatively dominated by a combination of hydrogel charge density and overall protein charge. Based on the knowledge obtained in this work, the effects of hydrogel surface charges on protein absorption can be better understood. Thus, the results are expected to promote the application of hydrogels in tissue engineering.
• 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
• Relaxation Dynamics and Underlying Mechanism of a Thermally Reversible Gel from Symmetric Triblock Copolymer

  Ya Nan Ye, Kunpeng Cui, Tsutomu Indei, Tasuku Nakajima, Dominique Hourdet, Takayuki Kurokawa, Jian Ping Gong

  Macromolecules 52 (22) 8651 - 8661 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]
  
• Adjacent Cationic-Aromatic Sequences Yield Strong Electrostatic Adhesion of Hydrogels in Seawater

  Hailong Fan, Jiahui Wang, Zhen Tao, Junchao Huang, Ping Rao, Takayuki Kurokawa, Jian Ping Gong

  Nature Communications 10 (1) 5127 - 5127 2019/11 [Refereed][Not invited]
   

  Electrostatic interaction is strong but usually diminishes in high ionic-strength environments. Biosystems can use this interaction through adjacent cationic-aromatic amino acids sequence of proteins even in a saline medium. Application of such specific sequence to the development of cationic polymer materials adhesive to negatively charged surfaces in saline environments is challenging due to the difficulty in controlling the copolymer sequences. Here, we discover that copolymers with adjacent cation-aromatic sequences can be synthesized through cation-π complex-aided free-radical polymerization. Sequence controlled hydrogels from diverse cation/aromatic monomers exhibit fast, strong but reversible adhesion to negatively charged surfaces in seawater. Aromatics on copolymers are found to enhance the electrostatic interactions of their adjacent cationic residues to the counter surfaces, even in a high ionic-strength medium that screens the electrostatic interaction for common polyelectrolytes. This work opens a pathway to develop adhesives using saline water.
• Effect of Structure Heterogeneity on Mechanical Performance of Physical Polyampholytes Hydrogels

  Cui Kunpeng, Ye Ya Nan, Sun Tao Lin, Chen Liang, Li Xueyu, Kurokawa Takayuki, Nakajima Tasuku, Nonoyama Takayuki, Gong Jian Ping

  MACROMOLECULES 52 (19) 7369 - 7378 0024-9297 2019/10/08 [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.
• Tough double network elastomers reinforced by the amorphous cellulose network

  Murai Joji, Nakajima Tasuku, Matsuda Takahiro, Tsunoda Katsuhiko, Nonoyama Takayuki, Kurokawa Takayuki, Gong Jian Ping

  POLYMER 178 0032-3861 2019/09/12 [Refereed][Not invited]
  
• Fabrication of Tough Hydrogels Composites from Photo-responsive Polymers to Show Double Network Effecte polymers to show double network effect

  Zhen Tao, Hailong Fan, Junchao Huang, Tao Lin Sun, Takayuki Kurokawa, Jian Ping Gong

  ACS Applied Materials & Interfaces 11 (40) 37139 - 37146 2019/09 [Refereed][Not invited]
   

  Inspired by the toughening mechanism of double-network (DN) gels, tough hydrogel composites with a sandwich structure were fabricated from photoresponsive polymers. By copolymerization of hydrophilic monomers, 2-ureidoethyl methacrylate (UM), and photoresponsive hydrophobic monomers, (2-nitrobenzyloxycarbonylaminoethyl methacrylate (NBOC)) at high concentrations, physical hydrogels that are soft and highly stretchable are formed due to the hydrophobic associations of NBOC, serving as dynamic crosslinkers. By UV irradiation, the physical crosslinking switches into chemical crosslinking, and the soft physical hydrogels transform into rigid and less stretchable chemical hydrogels. By UV curing the surface layers of the physical hydrogels, we prepared hydrogel composites having a sandwiched structure with two rigid outer layers and a soft inner layer. The molecular-level continuous interfaces and matched swelling ratios between the layers ensure the macroscale hydrogel composites' high strength and toughness with a DN gel effect. The outer layers fracture preferentially at deformation, playing a role like the first network of a DN gel, while the inner layer maintains the integrity, playing a role resembling the second network. The evolution of the fracture morphology of the rigid layers gives useful insight into the internal fracture process of DN gels.
• 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]
  
• Macroscale Double Networks: Design Criteria for Optimizing Strength and Toughness

  Daniel R. King, Tsuyoshi Okumura, Riku Takahashi, Takayuki Kurokawa, Jian Ping Gong

  ACS Applied Materials and Interfaces 11 (38) 35343 - 35353 2019/09 [Refereed][Not invited]
   

  The double network concept, based on the fracture of sacrificial bonds, has been revolutionary toward the creation of robust soft materials. Based on the essence of double network hydrogels, macroscale, three-dimensional printed rigid sacrificial networks are embedded within silicone rubber stretchable matrices. Preferential fracture of the sacrificial network results in a ∼60 time increase in stiffness and a ∼50% increase in the work of extension compared with the neat matrix. Maximizing yield strength while maintaining multistep internal fracture occurs when the strength of the sacrificial network approaches the strength of the matrix. Upon determining the optimal sacrificial network strength, the sacrificial bond section density can be increased to maximize energy dissipation and toughening efficiencies up to ∼70% of the maximum theoretical toughness are achieved. High toughness and dissipation are achieved because topological interlocking enables significant force transmission to the sacrificial network at smaller length scales than interfacial adhesion, allowing much higher sacrificial bond density. This method is general and can be used with a variety of materials systems, without requiring strong interfacial adhesion, contrasting traditional composite systems. Demonstrating that the double network concept can be used at length scales far beyond the molecular scale will have important implications toward the development of future structural materials.
• Modulation and Characterization of the Double Network Hydrogel Surface-Bulk Transition

  Martin Frauenlob, Daniel R. King, Honglei Guo, Seiichiro Ishihara, Masumi Tsuda, Takayuki Kurokawa, Hisashi Haga, Shinya Tanaka, Jian Ping Gong

  Macromolecules 2019/08 [Refereed][Not invited]
  
• Tough Triblock Copolymer Hydrogels with Different Micromorphologies for Medical and Sensory Materials

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

  ACS APPLIED POLYMER MATERIALS 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.
• Double Network Hydrogels Based on Semi-rigid Polyelectrolyte Physical Networks

  Riku Takahashi, Takuma Ikai, Takayuki Kurokawa, Daniel R. King, Jian Ping Gong

  Journal of Materials Chemistry B 7 (41) 6347 - 6354 2019/07 [Refereed][Invited]
   

  Applying the double network principle to develop tough hydrogels with different polymer chemistries is important for the potential application of hydrogel materials. Synthesis of the two interpenetrated networks with contrasting structure and properties required for double networks usually involves a two-step polymerization process. In this work, we present a new method to synthesize tough double network hydrogels by post-physical crosslinking of linear semi-rigid polyelectrolytes entrapped in a chemically crosslinked neutral network. Owing to their semi-rigid structure, the linear polyelectrolytes form a brittle physical network above their overlap concentration in multi-valent ZrCl2O ion solutions without macroscopic phase separation within the flexible neutral network. The double network hydrogels thus prepared exhibit high modulus (∼1.7 MPa), strength (∼1.3 MPa), fracture strain (∼7.3), and strain energy density (∼5.9 MJ m-3), while containing over 80% water. These materials also exhibit modest self-healing ability (∼51% after 30 minutes), demonstrating an additional benefit of a physical sacrificial network. This method is simpler than the conventional two-step polymerization and could be applied to develop tough hydrogels from rigid polyelectrolytes, including biopolymers such as DNA, HA, and chondroitin sulfate.
• Facile Synthesis of Novel Elastomers with Tunable Dynamics for Toughness, Self-Healing and Adhesion

  Liang Chen, Tao Lin Sun, Kunpeng Cui, Daniel R. King, Takayuki Kurokawa, Yoshiyuki Saruwatari, Jian Ping Gong

  Journal of Materials Chemistry A 7 (29) 17334 - 17344 2019/06 [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.
• Superior Fracture Resistance of Fiber Reinforced Polyampholyte Hydrogels Achieved by Extraordinarily Large Energy-dissipative Process Zones

  Yiwan Huang, Daniel R. King, Wei Cui, Tao Lin Sun, Honglei Guo, Takayuki Kurokawa, Hugh R. Brown, Chung-Yuen Hui, Jian Ping Gong

  Journal of Materials Chemistry A 7 (22) 13431 - 13440 2019/04 [Refereed][Not invited]
  
• Designing Responsive Photonic Crystal Patterns by Using Laser Engraving

  Yue Youfeng, Kurokawa Takayuki

  ACS APPLIED MATERIALS & INTERFACES 11 (11) 10841 - 10847 1944-8244 2019/03/20 [Refereed][Not invited]
   

  Soft photonic crystals are periodic nanostructures that have attracted much attention for their applications in sensors, owing to their tunable structural colors in response to external stimuli. Patterned photonic crystals provide a novel strategy for constructing high-performance photonic materials with unique structures and functions. In this work, laser engraving is used for the first time to design patterns on a layered photonic hydrogel. This approach is based on the integration of laser power and chemical modifications to embed different polymer composites (polyelectrolyte and neutral polymers) along a prescribed laser-printed path. The polyelectrolyte and neutral composites show differential swelling or shrinking, causing a mechanical instability in the layered hydrogel. The resultant soft polymeric materials appear as synchronous tuning in the photonic band gaps in response to external stimuli. This approach is favorable for designing responsive photonic crystals with controllable optical properties and 3D shape transformation. Moreover, it is of great use in developing advanced photonic crystals for applications in sensors, soft actuators, and drug release.
• Osteochondral Autograft Transplantation Technique Augmented by an Ultrapurified Alginate Gel Enhances Osteochondral Repair in a Rabbit Model.

  Ryosuke Hishimura, Tomohiro Onodera, Kazutoshi Hontani, Rikiya Baba, Kentaro Homan, Shinji Matsubara, Zenta Joutoku, WooYoung Kim, Takayuki Nonoyama, Takayuki Kurokawa, Jian Ping Gong, Norimasa Iwasaki

  The American journal of sports medicine 47 (2) 468 - 478 0363-5465 2019/02 [Refereed][Not invited]
   

  BACKGROUND: One of the most important limitations of osteochondral autograft transplantation (OAT) is the adverse effect on donor sites in the knee. To decrease the number and/or size of osteochondral defects, we devised a method with biomaterial implantation after OAT. HYPOTHESIS: OAT augmented by ultrapurified alginate (UPAL) gel enhances cartilage repair capacity. STUDY DESIGN: Controlled laboratory study. METHODS: Seventy-five osteochondral defects in rabbits were divided into 3 groups: osteochondral defects with OAT alone, defects with OAT augmented by UPAL gel (combined group), and defects without intervention as controls. Macroscopic and histological evaluations of the reparative tissues were performed at 4 and 12 weeks postoperatively. Histological evaluation of graft cartilage degradation was also performed. To evaluate the effects of UPAL gel on graft healing, repaired bone volumes and osseointegration of the graft were evaluated. Collagen orientation and the mechanical properties of the reparative tissue and graft cartilage were also evaluated qualitatively. RESULTS: The macroscopic and histological evaluations of the combined group were significantly superior to the other groups at 12 weeks postoperatively. Regarding degenerative change of the graft, the histological scores of the combined group were significantly higher than those of the OAT-alone group. The values of repaired subchondral bone volumes and osseointegration of the graft were almost identical in both groups. Collagen orientation and the mechanical properties of the reparative tissue and graft cartilage were significantly better in the combined group than in the other groups. CONCLUSION: Administration of UPAL gel in OAT enhanced cartilage repair and protected graft cartilage without inhibiting subchondral bone repair and graft survival. CLINICAL RELEVANCE: OAT augmented by UPAL gel decreases the number and/or size of osteochondral grafts, minimizing the risk of donor site morbidity. This combination technique has the potential to improve clinical outcomes and expand the surgical indications for OAT.
• Shearing-induced Contact Pattern Formation in Hydrogels Sliding in Polymer Solution

  Shintaro Yashima, Satoshi Hirayama, Takayuki Kurokawa, Thomas Salez, Haruna Takefuji, Wei Hong, Jian Ping Gong

  Soft Matter 15 (9) 1953 - 1959 2019/01 [Refereed][Not invited]
   

  The contact of a hydrogel during the rotational shearing on a glass surface in concentrated polymer solution was observed in situ. Dynamic contact patterns that rotate in-phase with the rotational shearing of the gel were observed for the first time. The contact patterns with a periodicity in the circumferential direction appeared and became fine with the shearing time. The patterns appeared more quickly at an elevated sliding velocity, polymer concentration, and normal pressure. Furthermore, the softness of the gel also substantially influenced the characteristics of the patterns. The pattern formation was discussed in terms of the non-linear rheology of the polymer solution at the rotational soft interface.
• Polyelectrolyte Complexation via Viscoelastic Phase Separation Results in Tough and Self-Recovering Porous Hydrogels

  Kohei Murakawa, Daniel R. King, Tao Lin Sun, Honglei Guo, Takayuki Kurokawa, Jian Ping Gong

  Journal of Materials Chemistry B 7 (35) 5296 - 5305 2019 [Refereed][Not invited]
   

  Polyelectrolyte complexation between oppositely charged polyelectrolytes forms coacervates in dilute solutions and thin films in concentrated solutions. It is difficult to obtain macroscopically uniform bulk polyelectrolyte complex (PEC) materials, since the two polymers form insoluble complexes quickly at the contact interface during mixing, resulting in heterogeneous aggregates. Here, we succeeded in preparing bulk PEC materials based on desalting-induced polyelectrolyte complexation via viscoelastic phase separation. With a high ionic strength aqueous medium, a homogeneous and concentrated solution containing oppositely charged polyelectrolytes is prepared. Desalting of the counter-ions and co-ions of the solution through semi-permeable membranes induces viscoelastic phase separation of the solution to form a physical hydrogel with open pore structure. Regulating the charge ratio of the two oppositely charged polymers results in significant changes in the porous morphology and mechanical properties. The charge-balanced PEC hydrogels show unique properties including high toughness and self-recovery due to the reversible ionic associations. The porous yet tough properties of bulk PEC hydrogels makes them potential candidates for applications such as cell scaffolds.
• Tough Particle-Based Double Network Hydrogels for Functional Solid Surface Coatings

  Takayuki Kurokawa

  Advanced Materials Interfaces 5 (23) 2196-7350 2018/12/07 [Refereed][Not invited]
  
• Multiscale Energy Dissipation Mechanism in Tough and Self-Healing Hydrogels

  Cui Kunpeng, Sun Tao Lin, Liang Xiaobin, Nakajima Ken, Ye Ya Nan, Chen Liang, Kurokawa Takayuki, Gong Jian Ping

  PHYSICAL REVIEW LETTERS 121 (18) 185501 - 185501 0031-9007 2018/10/31 [Refereed][Not invited]
   

  Understanding the energy dissipation mechanism during deformation is essential for the design and application of tough soft materials. We show that, in a class of tough and self-healing polyampholyte hydrogels, a bicontinuous network structure, consisting of a hard network and a soft network, is formed, independently of the chemical details of the hydrogels. Multiscale internal rupture processes, in which the double-network effect plays an important role, are found to be responsible for the large energy dissipation of these hydrogels.
• Elastic-Plastic Transformation of Polyelectrolyte Complex Hydrogels from Chitosan and Sodium Hyaluronate

  Ran Shi, Tao Lin Sun, Feng Luo, Tasuku Nakajima, Takayuki Kurokawa, Yue Zhen Bin, Michael Rubinstein, Jian Ping Gong

  Macromolecules 51 (21) 8887 - 8898 2018/10 [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.
• Micro patterning of hydroxyapatite by soft lithography on hydrogels for selective osteoconduction.

  Ryuji Kiyama, Takayuki Nonoyama, Susumu Wada, Shingo Semba, Nobuto Kitamura, Tasuku Nakajima, Takayuki Kurokawa, Kazunori Yasuda, Shinya Tanaka, Jian Ping Gong

  Acta biomaterialia 81 60 - 69 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.
• Tough and Self-Recoverable Thin Hydrogel Membranes for Biological Applications

  Ye Ya Nan, Frauenlob Martin, Wang Lei, Tsuda Masumi, Sun Tao Lin, Cui Kunpeng, Takahashi Riku, Zhang Hui Jie, Nakajima Tasuku, Nonoyama Takayuki, Kurokawa Takayuki, Tanaka Shinya, Gong Jian Ping

  ADVANCED FUNCTIONAL MATERIALS 28 (31) 1616-301X 2018/08/01 [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.
• Tough Hydrogels with Fast, Strong, and Reversible Underwater Adhesion Based on a Multiscale Design

  Rao Ping, Sun Tao Lin, Chen Liang, Takahashi RIku, Shinohara, G, Guo Hui, King Daniel Rudolf, Kurokawa Takayuki, Gong Jian Ping

  Advanced Materials 30 (32) 1801884  2018/06 [Refereed][Not invited]
   

  Hydrogels have promising applications in diverse areas, especially wet environments including tissue engineering, wound dressing, biomedical devices, and underwater soft robotics. Despite strong demands in such applications and great progress in irreversible bonding of robust hydrogels to diverse synthetic and biological surfaces, tough hydrogels with fast, strong, and reversible underwater adhesion are still not available. Herein, a strategy to develop hydrogels demonstrating such characteristics by combining macroscale surface engineering and nanoscale dynamic bonds is proposed. Based on this strategy, excellent underwater adhesion performance of tough hydrogels with dynamic ionic and hydrogen bonds, on diverse substrates, including hard glasses, soft hydrogels, and biological tissues is obtained. The proposed strategy can be generalized to develop other soft materials with underwater adhesion.
• 高分子ゲルの新たな機能と医療への応用 (特集 ソフトマター研究開発の最先端)

  黒川 孝幸

  Soft matter = ソフトマター : "やわらかい物質"と計測・評価の技術情報誌 メカニカル・テック社 (1) 16 - 18 2018/04/05 [Not refereed]
  
• A Facile Method to Fabricate Anisotropic Hydrogels with Perfectly Aligned Hierarchical Fibrous Structures

  Mredha Md. Tariful Islam, Guo Yun Zhou, Nonoyama Takayuki, Nakajima Tasuku, Kurokawa Takayuki, Gong Jian Ping

  ADVANCED MATERIALS 30 (9) 0935-9648 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.
• Creating Stiff, Tough, and Functional Hydrogel Composites with Low-Melting-Point Alloys

  Takahashi Riku, Sun Tao Lin, Saruwatari Y, Kurokawa Takayuki, King Daniel Rudolf, Gong Jian Ping

  Advanced Materials 30 (16) 1706885  2018/02 [Refereed][Not invited]
   

  Reinforcing hydrogels with a rigid scaffold is a promising method to greatly expand the mechanical and physical properties of hydrogels. One of the challenges of creating hydrogel composites is the significant stress that occurs due to swelling mismatch between the water-swollen hydrogel matrix and the rigid skeleton in aqueous media. This stress can cause physical deformation (wrinkling, buckling, or fracture), preventing the fabrication of robust composites. Here, a simple yet versatile method is introduced to create "macroscale" hydrogel composites, by utilizing a rigid reinforcing phase that can relieve stress-induced deformation. A low-melting-point alloy that can transform from a load-bearing solid state to a free-deformable liquid state at relatively low temperature is used as a reinforcing skeleton, which enables the release of any swelling mismatch, regardless of the matrix swelling degree in liquid media. This design can generally provide hydrogels with hybridized functions, including excellent mechanical properties, shape memory, and thermal healing, which are often difficult or impossible to achieve with single-component hydrogel systems. Furthermore, this technique enables controlled electrochemical reactions and channel-structure templating in hydrogel matrices. This work may play an important role in the future design of soft robots, wearable electronics, and biocompatible functional materials.
• Tough and Variable-Band-Gap Photonic Hydrogel Displaying Programmable Angle-Dependent Colors

  Haque Md. Anamul, Mito Kei, Kurokawa Takayuki, Nakajima Tasuku, Nonoyama Takayuki, Ilyas Muhammad, Gong Jian Ping

  ACS OMEGA 3 (1) 55 - 62 2470-1343 2018/01 [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 1936-0851 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.
• Effects of osteochondral defect size on cartilage regeneration using a double-network hydrogel

  Kotaro Higa, Nobuto Kitamura, Keiko Goto, Takayuki Kurokawa, Jian Ping Gong, Fuminori Kanaya, Kazunori Yasuda

  BMC MUSCULOSKELETAL DISORDERS 18 (1) 210 - 210 1471-2474 2017/05 [Refereed][Not invited]
   

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

  Huang Yiwan, King Daniel R, Sun Tao Lin, Nonoyama Takayuki, Kurokawa Takayuki, Nakajima Tasuku, Gong Jian Ping

  Advanced Functional Materials Wiley 27 (9) 1605350 - 1605350 1616-301X 2017 [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.
• 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.
• Hydroxyapatite-coated double network hydrogel directly bondable to the bone: Biological and biomechanical evaluations of the bonding property in an osteochondral defect

  Susumu Wada, Nobuto Kitamura, Takayuki Nonoyama, Ryuji Kiyama, Takayuki Kurokawa, Jian Ping Gong, Kazunori Yasuda

  ACTA BIOMATERIALIA 44 125 - 134 1742-7061 2016/10 [Refereed][Not invited]
   

  We have developed a novel hydroxyapatite (HAp)-coated double-network (DN) hydrogel (HAp/DN gel). The purpose of this study was to determine details of the cell and tissue responses around the implanted HAp/DN gel and to determine how quickly and strongly the HAp/DN gel bonds to the bone in a rabbit osteochondral defect model. Immature osteoid tissue was formed in the space between the HAp/DN gel and the bone at 2 weeks, and the osteoid tissue was mineralized at 4 weeks. The push-out load of the HAp/DN gel averaged 37.54 N and 42.15 N at 4 and 12 weeks, respectively, while the push-out load of the DN gel averaged less than 5 N. The bonding area of the HAp/DN gel to the bone was above 80% by 4 weeks, and above 90% at 12 weeks. This study demonstrated that the HAp/DN gel enhanced osseointegration at an early stage after implantation. The presence of nanoscale structures in addition to osseointegration of HAp promoted osteoblast adhesion onto the surface of the HAp/DN gel. The HAp/DN gel has the potential to improve the implant-tissue interface in next-generation orthopaedic implants such as artificial cartilage. Statement of Significance Recent studies have reported the development of various hydrogels that are sufficiently tough for application as soft supporting tissues. However, fixation of hydrogels on bone surfaces with appropriate strength is a great challenge. We have developed a novel, tough hydrogel hybridizing hydroxyapatite (HAp/DN gel), which is directly bondable to the bone. The present study demonstrated that the HAp/DN gel enhanced osseointegration in the early stage after implantation. The presence of nanoscale structures in addition to the osseointegration ability of hydroxyapatite promoted osteoblast adhesion onto the surface of the HAp/DN gel. The HAp/DN gel has the potential to improve the implant-tissue interface in next-generation orthopaedic implants such as artificial cartilage. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
• Fundamental biomaterial properties of tough glycosaminoglycan-containing double network hydrogels newly developed using the molecular stent method

  Kotaro Higa, Nobuto Kitamura, Takayuki Kurokawa, Keiko Goto, Susumu Wada, Takayuki Nonoyama, Fuminori Kanaya, Kazuyuki Sugahara, Jian Ping Gong, Kazunori Yasuda

  ACTA BIOMATERIALIA 43 38 - 49 1742-7061 2016/10 [Refereed][Not invited]
   

  The purpose of this study was to clarify fundamental mechanical properties and biological responses of the sodium hyaluronate-containing double network (HA-DN) gel and chondroitin sulfate-containing double network (CS-DN) gel, which were newly developed using the molecular stent method. This study discovered the following facts. First, these hydrogels had high mechanical performance comparable to the native cartilage tissue, and the mechanical properties were not affected by immersion in the saline solution for 12 weeks. Secondly, the mechanical properties of the CS-DN gel were not significantly reduced at 12 weeks in vivo, while the mechanical properties of the HA-DN gel were significantly deteriorated at 6 weeks. Thirdly, the degree of inflammation around the HA-DN gel was the same as that around the negative control. The CS-DN gel showed a mild but significant foreign body reaction, which was significantly greater than the negative control and less than the positive control at 1 week, while the inflammation was reduced to the same level as the negative control at 4 and 6 weeks. Fourthly, these gels induced differentiation of the ATDC5 cells into chondrocytes in the culture with the insulin free maintenance medium. These findings suggest that these tough hydrogels are potential biomaterials for future application to therapeutic implants such as artificial cartilage. Statement of Significance The present study reported fundamental biomaterial properties of the sodium hyaluronate-containing double network (HA-DN) gel and chondroitin sulfate-containing double network (CS-DN) gel, which were newly developed using the molecular stent method. Both the HA- and CS-DN gels had high mechanical properties comparable to the cartilage tissue and showed the ability to induce chondrogenic differentiation of ATDC5 cells in vitro. They are potential biomaterials that may meet the requirements of artificial cartilage concerning the material properties. Further, these DN gels can be also applied to the implantable inducer for cell-free cartilage regeneration therapy. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
• In vivo cartilage regeneration induced by a double-network hydrogel: Evaluation of a novel therapeutic strategy for femoral articular cartilage defects in a sheep model

  Nobuto Kitamura, Masashi Yokota, Takayuki Kurokawa, Jian Ping Gong, Kazunori Yasuda

  JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A 104 (9) 2159 - 2165 1549-3296 2016/09 [Refereed][Not invited]
   

  The purpose of this study was to establish the efficacy of a therapeutic strategy for an articular cartilage defect using a poly-(2-acrylamido-2-methylpropanesulfonic acid)/poly-(N,N'-dimethyl acrylamide) DN gel in a sheep model. Seventeen mature sheep were used in this study. We created a 6.0-mm osteochondral defect in the femoral trochlea of the patellofemoral (PF) joint and the medial condyle of the tibiofemoral (TF) joint. A cylindrical DN gel plug was implanted into the defect of the right knee so that a vacant space of the planned depths of 2.0 mm in group I, 3.0 mm in group II, and 4.0 mm in group III were left. In the left knee, we created a defect with the same depth as the right knee. The regenerated tissues were evaluated with the O'Driscoll score and real-time PCR analysis of the cartilage marker genes at 12 weeks. The DN gel implanted defect of group II in the PF and TF joints was completely filled with a sufficient volume of the proteoglycan-rich tissue stained with Safranin-O. The score showed that group II was significantly greater than groups I and III when treated with DN gel in the PF joint (p=0.0441, p=0.0174, respectively) and in the TF joint (p=0.0019, p=0.0006, respectively). This study has clarified the short-term efficacy of the cartilage regeneration strategy using the DN gel in a sheep model. (c) 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2159-2165, 2016.
• 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.
• 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.
• 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.
• Tough bacterial nanocellulose hydrogels based on the double-network technique

  Anamul Haque, Takayuki Kurokawa, Jian Ping Gong

  Bacterial NanoCellulose: A Sophisticated Multifunctional Material 73 - 89 2016/04/19
• 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.
• Synthetic PAMPS gel activates BMP/Smad signaling pathway in ATDC5 cells, which plays a significant role in the gel-induced chondrogenic differentiation

  Keiko Goto, Taichi Kimura, Nobuto Kitamura, Shingo Semba, Yoshihiro Ohmiya, Sachiyo Aburatani, Satoko Matsukura, Masumi Tsuda, Takayuki Kurokawa, Jian Ping Gong, Shinya Tanaka, Kazunori Yasuda

  JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A 104 (3) 734 - 746 1549-3296 2016/03 [Refereed][Not invited]
   

  The purposes of this study were to identify signaling pathways that were specifically activated in ATDC5 cells cultured on poly (2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) gel in insulin-free maintenance medium and to evaluate the significance of the determined signaling pathways in the chondrogenic differentiation induced by this gel. In this study, ATDC5 cells cultured on PAMPS gel using the maintenance medium without insulin (PAMPS Culture) were compared with cells cultured on polystyrene using the differentiation medium containing insulin (PS-I Culture). The microarray analysis, Western blot analysis, and real-time PCR analysis demonstrated that the TGF-/BMP signaling pathway was significantly enhanced at Days 1, 2, and 3 in the PAMPS Culture when compared with the PS-I Culture. Inhibition of the BMP type-I receptor reduced the phosphorylation level of Smad1/5 and expression of type-2 collagen and aggrecan mRNA in the cells accompanied by a reduction in cell aggregation at Day 13 in the PAMPS Culture. The inhibition of the TGF-/BMP signaling pathway significantly inhibited the chondrogenic differentiation induced by the PAMPS gel. The present study demonstrated that synthetic PAMPS gel activates the TGF-/BMP/Smad signaling pathway in the ATDC5 cells in the absence of insulin, and that this activation plays a significant role in the chondrogenic differentiation induced by PAMPS gel. (c) 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 734-746, 2016.
• 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.
• Competition between plasticity-controlled and crack-growth controlled failure in static and cyclic fatigue of thermoplastic polymer systems

  Takayuki Kurokawa

  Polymer Testing 2016
• Strong and Tough Polyion-Complex Hydrogels from Oppositely Charged Polyelectrolytes: A Comparative Study with Polyampholyte Hydrogels

  Luo Feng, Sun Tao Lin, Nakajima Tasuku, King Daniel R, Kurokawa Takayuki, Zhao Yu, Bin Ihsan Abu, Li Xufeng, Guo Honglei, Gong Jian Ping

  Macromolecules American Chemical Society 49 (7) 2750 - 2760 0024-9297 2016 [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 resultsof dynamic ionic bonds formation between entangled polymer chains. For the PICsystem, only interchain bonding occurs, while for the PA system both inter- andintrachain bonding exist. In addition, the ion pairs are expected to form strongerbonding in the PIC system than those in the PA system. In this work, we performeda comparative study of PIC hydrogels with the PA hydrogels. The PIC hydrogels aresynthesized by sequential homopolymerization of cationic and anionic monomers atvaried formulation, and their swelling and mechanical properties are systematicallystudied in comparison to the PA hydrogels that were synthesized from randomcopolymerization of anionic monomers and cationic monomers of the similarformulation. Different from the PA system which only forms tough hydrogels aroundzero net charge composition without chemical cross-linking, the PIC system forms tough physical hydrogels even at weakly offbalancedcharge composition. At the charge-balanced composition, the low entanglement concentration of homochargedpolyelectrolyte chains leads to tough PIC hydrogels formation at much lower concentrations than that of PA hydrogels. As aresult, the PIC hydrogels are much tougher than the PA hydrogels prepared at the same monomer composition. In similar to PAhydrogels, the PIC hydrogels also exhibit broad dynamic mechanical spectra, indicating the formation of ion complexes withwidely ranged bond strength. The PIC hydrogels have strong viscoelasticity in comparison with PA hydrogels. However, the twosystems show the similar activation energies of the dynamic mechanical spectra. The SEM microstructural observation shows thatthe PIC hydrogels have segregated structure while PA hydrogels are more homogeneous.
• 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.
• 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.
• Decoupling dual-stimuli responses in patterned lamellar hydrogels as photonic sensors

  Youfeng Yue, Xufeng Li, Takayuki Kurokawa, Md. Anamul Haque, Jian Ping Gong

  JOURNAL OF MATERIALS CHEMISTRY B 4 (23) 4104 - 4109 2050-750X 2016 [Refereed][Not invited]
   

  This work developed a photonic hydrogel that is responsive to, and can distinguish between two stimuli of stress and pH. Patterning is used to locally change the chemistry of a one-dimensional (1D) photonic gel, such that the native region is responsive to mechanical stress while the chemically modified region is responsive to both mechanical stress and pH. By combining the optical signals in the native region and the modified region, one can distinguish the stimuli between pH and stress. Specifically, the native 1D photonic gel is composed of periodically aligned polymeric bilayers in a soft polyacrylamide (PAAm) network. The chemical modification is done by partially hydrolyzing PAAm into sodium polyacrylic acid in some patterned regions, which imparts pH sensitivity, in addition to the stress sensitivity, to these regions.
• 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 2015/08 [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.
• 皮膚を規範とした革新的機能材料・ラメラ構造を有するハイドロゲルの構造色と強靭性

  黒川 孝幸, ムハンマド アナムル ハック, 龔 剣萍

  工業材料 日刊工業出版プロダクション ; 1955- 63 (8) 64 - 68 0452-2834 2015/08 [Not refereed][Invited]
  
• 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.
• 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.
• Hydrogels as feeder-free scaffolds for long-term self-renewal of mouse induced pluripotent stem cells

  Jing Jing Yang, Jian Fang Liu, Takayuki Kurokawa, Kazuhiro Kitada, Jian Ping Gong

  JOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE 9 (4) 375 - 388 1932-6254 2015/04 [Refereed][Not invited]
   

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

  King Daniel R, Sun Tao Lin, Huang Yiwan, Kurokawa Takayuki, Nonoyama Takayuki, Crosby Alfred J, Gong Jian Ping

  Mater. Horiz. Royal Society of Chemistry 2 (6) 584 - 591 2051-6347 2015 [Refereed][Not invited]
   

  Ligaments are unique wet biological tissues with high tensile modulus and fracture stress, combined with high bending flexibility. Developing synthetic materials with these properties is a significant challenge. Hydrogel composites made from high stiffness fabrics is a strategy to develop such unique materials; however, the ability to produce these materials has proven difficult, since common hydrogels swell in water and interact poorly with solid components, limiting the transfer of force from the fabric to the hydrogel matrix. In this work, for the first time, we successfully produce extraordinarily tough hydrogel composites by strategically selecting a recently developed tough hydrogel that de-swells in water. The new composites, consisting of polyampholyte hydrogels and glass fiber woven fabrics, exhibit extremely high effective toughness (250 000 J m(-2)), high tear strength (similar to 65 N mm(-1)), high tensile modulus (606 MPa), and low bending modulus (4.7 MPa). Even though these composites are composed of water-containing, biocompatible materials, their mechanical properties are comparable to high toughness Kevlar/polyurethane blends and fiber-reinforced polymers. Importantly, the mechanical properties of these composites greatly outperform the properties of either individual component. A mechanism is proposed based on established fabric tearing theory, which will enable the development of a new generation of mechanically robust composites based on fabrics. These results will be important towards developing soft biological prosthetics, and more generally for commercial applications such as tear-resistant gloves and bulletproof vests.
• 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.
• 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.
• 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.
• Solvent and Ca2+ triggered robust and fast stress generation by ultrathin triple-network hydrogels

  Takayuki Kurokawa

  Extreme Mechanics Letters 1 17 - 22 2014/12 [Refereed][Not invited]
  
• 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.
• Significant increase in Young's modulus of ATDC5 cells during chondrogenic differentiation induced by PAMPS/PDMAAm double-network gel: Comparison with induction by insulin

  Eijiro Maeda, Takehiro Tsutsumi, Nobuto Kitamura, Takayuki Kurokawa, Jian Ping Gong, Kazunori Yasuda, Toshiro Ohashi

  JOURNAL OF BIOMECHANICS 13 47 (13) 3408 - 3414 0021-9290 2014/10 [Refereed][Not invited]
   

  A double-network (DN) gel, which was composed of poly(2-acrylamido-2-methylpropanesulfonic acid) and poly(N,N'-dimethyl acrylamide) (PAMPS/PDMAAm), has the potential to induce chondrogenesis both in vitro and in vivo. The present study investigated the biomechanical and biological responses of chondrogenic progenitor ATDC5 cells cultured on the DN gel. ATDC5 cells were cultured on a polystyrene surface without insulin (Culture 1) and with insulin (Culture 2), and on the DN gel without insulin (Culture 3). The cultured cells were evaluated using micropipette aspiration for cell Young's modulus and qPCR for gene expression of chondrogenic and actin organization markers on days 3, 7 and 14. On day 3, the cells in Culture 3 formed nodules, in which the cells exhibited an actin cortical layer inside them, and gene expression of type-II collagen, aggrecan, and SOX9 was significantly higher in Culture 3 than Cultures 1 and 2 (p < 0.05). Young's modulus in Culture 3 was significantly higher than that in Culture 1 throughout the testing period (p < 0.05) and that in Culture 2 on day 14 (p < 0.01). There was continuous expression of actin organization markers in Culture 3. This study highlights that the cells on the DN gel increased the modulus and mRNA expression of chondrogenic markers at an earlier time point with a greater magnitude compared to those on the polystyrene surface with insulin. This study also demonstrates a possible strong interrelation among alteration of cell mechanical properties, changes in actin organization and the induction of chondrogenic differentiation. (C) 2014 Elsevier Ltd. All rights reserved.
• 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.
• Effects of culture on PAMPS/PDMAAm double-network gel on chondrogenic differentiation of mouse C3H10T1/2 cells: in vitro experimental study

  Yusuke Inagaki, Nobuto Kitamura, Takayuki Kurokawa, Yasuhito Tanaka, Jian P. Gong, Kazunori Yasuda, Harukazu Tohyama

  BMC MUSCULOSKELETAL DISORDERS 15 320  1471-2474 2014/09 [Refereed][Not invited]
   

  Background: Recently, several animal studies have found that spontaneous hyaline cartilage regeneration can be induced in vivo within a large osteochondral defect by implanting a synthetic double-network (DN) hydrogel, which is composed of poly-(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) and poly-(N,N'-dimethyl acrylamide) (PDMAAm), at the bottom of the defect. However, the effect of hydrogel on hyaline cartilage regeneration remains unexplained. The purpose of this study was to investigate the chondrogenic differentiation of C3H10T1/2 cells on PAMPS/PDMAAm DN gel. Methods: C3H10T1/2 cells of 1.0 x 10(5) were cultured on PAMPS/PDMAAm DN gel in polystyrene tissue culture dishes or directly on polystyrene tissue culture dishes. We compared cultured cells on PAMPS/PDMAAm DN gel with those on polystyrene dishes by morphology using phase-contrast microscopy, mRNA expression of aggrecan, type I collagen, type II collagen, Sox 9 and osteocalcin using real-time RT-PCR, and local expression of type II collagen using immunocytochemistry. Results: C3H10T1/2 cells cultured on the PAMPS/PDMAAm DN gels formed focal adhesions, aggregated rapidly and developed into large nodules within 7 days, while the cells cultured on the polystyrene surface did not. The mRNA levels of aggrecan, type I collagen, type II collagen, Sox 9 and osteocalcin were significantly greater in cells cultured on the PAMPS/PDMAAm DN gel than in those cultured on polystyrene dishes. In addition, C3H10T1/2 cells cultured on PAMPS/PDMAAm DN gel expressed more type II collagen at the protein level when compared with cells cultured on polystyrene dishes. Conclusions: The present study showed that PAMPS/PDMAAm DN gel enhanced chondrogenesis of C3H10T1/2 cells, which are functionally similar to mesenchymal stem cells. This suggests that mesenchymal stem cells from the bone marrow contribute to spontaneous hyaline cartilage regeneration in vivo in large osteochondral defects after implantation of PAMPS/PDMAAm DN gels.
• Control superstructure of rigid polyelectrolytes in oppositely charged hydrogels via programmed internal stress

  Riku Takahashi, Zi Liang Wu, Md Arifuzzaman, Takayuki Nonoyama, Tasuku Nakajima, Takayuki Kurokawa, Jian Ping Gong

  NATURE COMMUNICATIONS 5 4490  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.
• Mechano-actuated ultrafast full-colour switching in layered photonic hydrogels

  Youfeng Yue, Takayuki Kurokawa, Md Anamul Haque, Tasuku Nakajima, Takayuki Nonoyama, Xufeng Li, Itsuro Kajiwara, Jian Ping Gong

  NATURE COMMUNICATIONS 5 4659  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.
• Hyaluronic acid enhances the effect of the PAMPS/PDMAAm double-network hydrogel on chondrogenic differentiation of ATDC5 cells

  Nobuto Kitamura, Takayuki Kurokawa, Takaaki Fukui, Jian P. Gong, Kazunori Yasuda

  BMC MUSCULOSKELETAL DISORDERS 15 222  1471-2474 2014/07 [Refereed][Not invited]
   

  Background: A double-network (DN) gel, which was composed of poly-(2-Acrylamido-2-methylpropanesulfonic acid) and poly-(N,N'-dimethyl acrylamide) (PAMPS/PDMAAm), has the potential to induce chondrogenesis both in vitro and in vivo. The present study investigated whether DN gel induced chondrogenic differentiation of ATDC5 cells in a maintenance medium without insulin, and whether supplementation of hyaluronic acid enhanced the chondrogenic differentiation effect of DN gel. Methods: ATDC5 cells were cultured on the DN gel and the polystyrene (PS) dish in maintenance media without insulin for 21 days. Hyaluronic acid having a molecular weight of approximately 800 kDa was supplemented into the medium so that the concentration became 0.01, 0.1, or 1.0 mg/mL. The cultured cells were evaluated using immunocytochemistry for type-2 collagen and real time PCR for gene expression of type-2 collagen, aggrecan, and Sox9 at 7 and 21 days of culture. Results: The cells cultured on the DN gel formed nodules and were stained with an anti-type-2 collagen antibody, and expression of type-2 collagen and aggrecan mRNA was significantly greater on the DN gel than on the PS dish surface (p < 0.05) in the hyaluronic acid-free maintenance medium. Hyaluronic acid supplementation of a high concentration (1.0 mg/mL) significantly enhanced expression of type-2 collagen and aggrecan mRNA in comparison with culture without hyaluronic acid at 21 days (p < 0.05). Conclusions: The DN gel induced chondrogenic differentiation of ATDC5 cells without insulin. This effect was significantly affected by hyaluronic acid, depending on the level of concentration. There is a high possibility that hyaluronic acid plays an important role in the in vivo hyaline cartilage regeneration phenomenon induced by the DN gel.
• Fracture Process of Microgel-Reinforced Hydrogels under Uniaxial Tension

  Jian Hu, Takayuki Kurokawa, Tasuku Nakajima, Zi Liang Wu, Song Miao Liang, Jian Ping Gong

  MACROMOLECULES 47 (11) 3587 - 3594 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.
• Intra-articular administration of hyaluronic acid increases the volume of the hyaline cartilage regenerated in a large osteochondral defect by implantation of a double-network gel

  Takaaki Fukui, Nobuto Kitamura, Takayuki Kurokawa, Masashi Yokota, Eiji Kondo, Jian Ping Gong, Kazunori Yasuda

  JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE 25 (4) 1173 - 1182 0957-4530 2014/04 [Refereed][Not invited]
   

  Implantation of PAMPS/PDMAAm double-network (DN) gel can induce hyaline cartilage regeneration in the osteochondral defect. However, it is a problem that the volume of the regenerated cartilage tissue is gradually reduced at 12 weeks. This study investigated whether intra-articular administration of hyaluronic acid (HA) increases the volume of the cartilage regenerated with the DN gel at 12 weeks. A total of 48 rabbits were used in this study. A cylindrical osteochondral defect created in the bilateral femoral trochlea was treated with DN gel (Group DN) or left without any implantation (Group C). In both Groups, we injected 1.0 mL of HA in the left knee, and 1.0 mL of saline solution in the right knee. Quantitative histological evaluations were performed at 2, 4, and 12 weeks, and PCR analysis was performed at 2 and 4 weeks after surgery. In Group DN, the proteoglycan-rich area was significantly greater in the HA-injected knees than in the saline-injected knees at 12 weeks (P = 0.0247), and expression of type 2 collagen, aggrecan, and Sox9 mRNAs was significantly greater in the HA-injected knees than in the saline-injected knees at 2 weeks (P = 0.0475, P = 0.0257, P = 0.0222, respectively). The intra-articular administration of HA significantly enhanced these gene expression at 2 weeks and significantly increased the volume of the hyaline cartilage regenerated by implantation of a DN gel at 12 weeks. This information is important to develop an additional method to increase the volume of the hyaline cartilage tissue in a potential cartilage regeneration strategy using the DN gel.
• Prolonged morphometric study of barnacles grown on soft substrata of hydrogels and elastomers

  Nafees Ahmed, Takayuki Murosaki, Takayuki Kurokawa, Akira Kakugo, Shintaro Yashima, Yasuyuki Nogata, Jian Ping Gong

  BIOFOULING 30 (3) 271 - 279 0892-7014 2014/03 [Refereed][Not invited]
   

  A long-term investigation of the shell shape and the basal morphology of barnacles grown on tough, double-network (DN) hydrogels and polydimethylsiloxane (PDMS) elastomer was conducted in a laboratory environment. The elastic modulus of these soft substrata varied between 0.01 and 0.47MPa. Polystyrene (PS) (elastic modulus, 3 GPa) was used as a hard substratum control. It was found that the shell shape and the basal plate morphology of barnacles were different on the rigid PS substratum compared to the soft substrata of PDMS and DN hydrogels. Barnacles on the PS substratum had a truncated cone shape with a flat basal plate while on soft PDMS and DN gels, barnacles had a pseudo-cylindrical shape and their basal plates showed curvature. In addition, a large adhesive layer was observed under barnacles on PDMS, but not on DN gels. The effect of substratum stiffness is discussed in terms of barnacle muscle contraction, whereby the relative stiffness of the substratum compared to that of the muscle is considered as the key parameter.
• Brittle-ductile transition of double network hydrogels: Mechanical balance of two networks as the key factor

  Saika Ahmed, Tasuku Nakajima, Takayuki Kurokawa, Md Anamul Haque, Jian Ping Gong

  POLYMER 55 (3) 914 - 923 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]
  
• Friction of hydrogels with controlled surface roughness on solid flat substrates

  Shintaro Yashima, Natsuko Takase, Takayuki Kurokawa, Jian Ping Gong

  SOFT MATTER 10 (18) 3192 - 3199 1744-683X 2014 [Refereed][Not invited]
   

  This study investigated the effect of hydrogel surface roughness on its sliding friction against a solid substrate having modestly adhesive interaction with hydrogels under small normal pressure in water. The friction test was performed between bulk polyacrylamide hydrogels of varied surface roughness and a smooth glass substrate by using a strain-controlled rheometer with parallel-plates geometry. At small pressure (normal strain 1.4-3.6%), the flat surface gel showed a poor reproducibility in friction. In contrast, the gels with a surface roughness of 1-10 mm order showed well reproducible friction behaviors and their frictional stress was larger than that of the flat surface hydrogel. Furthermore, the flat gel showed an elasto-hydrodynamic transition while the rough gels showed a monotonous decrease of friction with velocity. The difference between the flat surface and the rough surface diminished with the increase of the normal pressure. These phenomena are associated with the different contact behaviors of these soft hydrogels in liquid, as revealed by the observation of the interface using a confocal laser microscope.
• In situ observation of a hydrogel-glass interface during sliding friction

  Tetsurou Yamamoto, Takayuki Kurokawa, Jamil Ahmed, Gen Kamita, Shintaro Yashima, Yuichiro Furukawa, Yuko Ota, Hidemitsu Furukawa, Jian Ping Gong

  SOFT MATTER 10 (30) 5589 - 5596 1744-683X 2014 [Refereed][Not invited]
   

  Direct observation of hydrogel contact with a solid surface in water is indispensable for understanding the friction, lubrication, and adhesion of hydrogels under water. However, this is a difficult task since the refractive index of hydrogels is very close to that of water. In this paper, we present a novel method to in situ observe the macroscopic contact of hydrogels with a solid surface based on the principle of critical refraction. This method was applied to investigate the sliding friction of a polyacrylamide (PAAm) hydrogel with glass by using a strain-controlled parallel-plate rheometer. The study revealed that when the compressive pressure is not very high, the hydrogel forms a heterogeneous contact with the glass, and a macro-scale water drop is trapped at the soft interface. The pre-trapped water spreads over the interface to decrease the contact area with the increase in sliding velocity, which dramatically reduces the friction of the hydrogel. The study also revealed that this heterogeneous contact is the reason for the poor reproducibility of hydrogel friction that has been often observed in previous studies. Under the condition of homogeneous full contact, the molecular origin of hydrogel friction in water is discussed. This study highlights the importance of direct interfacial observation to reveal the friction mechanism of hydrogels.
• 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.
• Double network hydrogels from polyzwitterions: high mechanical strength and excellent anti-biofouling properties

  YIN HAIYAN, AKASAKI TAIGO, SUN TAO LIN, NAKAJIMA TASUKU, KUROKAWA TAKAYUKI, NONOYAMA TAKAYUKI, TAIRA TOSHIO, SARUWATARI YOSHIYUKI, GONG JIAN PING

  J Mater Chem B Mater Biol Med Royal Society of Chemistry 1 (30) 3685 - 3693 2050-750X 2013/08/14 [Not 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.
• Tuning Mechanical Properties of Chondroitin Sulfate-Based Double-Network Hydrogels

  Tiffany C. Suekama, Jian Hu, Takayuki Kurokawa, Jian Ping Gong, Stevin H. Gehrke

  MACROMOLECULAR SYMPOSIA 329 (1) 9 - 18 1022-1360 2013/07 [Refereed][Not invited]
   

  High strength double-network (DN) biopolymer-based hydrogels were created using copolymers of methacrylated chondroitin sulfate (MCS) and poly (ethylene glycol) diacrylate (PEGDA) as the first network and polyacrylamide (PAAm) as the second network. The concentration and cross-linking of the networks were adjusted to control the mechanical properties including the failure stress, failure strain, Young's modulus, and yielding behavior. First, we increased the cross-linking of the first network both by increasing the MCS concentration from 13 to 20 wt% and by copolymerizing MCS with 2 to 6 wt% PEGDA. The additional cross-linking increased the Young's modulus as much as five times, reaching 3.3 MPa, and the failure stress up as much as four times, reaching 2.9 MPa. However, this also reduced failure strain from a high of 2.9 mm/mm to a low of 0.12 mm/mm and diminished the yielding region. Changes in the concentrations of acrylamide or its cross-linking with N,N'-methylenebisacrylamide (BIS) in the second network had a lesser effect on the DN properties. We hypothesized that to obtain a yielding region which results in high toughness, we need to alter the cross-linking of the first network such that the yield stress of the MCS-PEGDA/PAAm DN does not exceed the failure stress of PAAm network. Because of the wide range of mechanical properties achieved in these DNs with limited changes in the swelling degrees, unlike conventional single-network gels, the DN approach allows attainment of a much greater range of mechanical behavior than is possible with single networks.
• 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

  Nakajima, Tasuku, Fukuda, Yuki, Kurokawa, Takayuki, Sakai, Takamasa, Chung, Ung-il, Gong, Jian Ping

  ACS MACRO LETTERS American Chemical Society 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.
• Lamellar-Micelle Transition in a Hydrogel Induced by Polyethylene Glycol Grafting

  Md. Anamul Haque, Takayuki Kurokawa, Jian Ping Gong

  Soft Matter Royal Society of Chemistry 9 (21) 5223 - 5230 1744-683X 2013/04 [Refereed][Not invited]
  
• Suprarmolecular Assemblies of a Semirigid Polyanion in Aqueous Solutions

  Zi Liang Wu, Md. Arifuzzaman, Takayuki Kurokawa, Khoa Le, Jian Hu, Tao Lin Sun, Hidemitsu Furukawa, Hiroyasu Masunaga, Jian Ping Gong

  Macromolecules 46 (9) 3581 - 3586 0024-9297 2013/04 [Refereed][Not invited]
   

  In this article, we report the supramolecular assemblies of a semirigid polyelectrolyte, poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT) in water. Cryo-TEM observation and SAXS measurement reveal that PBDT forms bundle-like structure even in very dilute concentration, C-p, of 0.02 wt %. These bundle-like assemblies serve as new primary building blocks and self-assemble further as C-p increases, to form large associations with or without long-range orientation. When 2 wt % < C-p < 6 wt %, liquid liquid phase separation occurs. Some of the supramolecular associations form bipolar liquid crystalline (LC) droplets via a typical nucleation and growth process. The droplets grow up by the coalescence of small ones and sediment under the gravity and coalesce to form a bottom nematic phase. When C-p 6 wt %, the solutions are in a uniform nematic phase. The existence of these preliminary supramolecular assemblies of PBDT in aqueous solutions should be crucial for the formation of nematic LC phase at a significantly low C-p, as well as the formation of macroscopic ordered structures in hydrogels via electrostatic interaction between PBDT and oppositely charge multivalent metallic ion or polycation.
• Double-Network Strategy Improves Fracture Properties of Chondroitin Sulfate Networks

  Tiffany C. Suekama, Jian Hu, Takayuki Kurokawa, Jian Ping Gong, Stevin H. Gehrke

  ACS MACRO LETTERS 2 (2) 137 - 140 2161-1653 2013/02 [Refereed][Not invited]
   

  A tough and ductile, ultrathin film, double-network (DN), biopolymer-based hydrogel displaying the yielding phenomenon was synthesized from methacrylated chondroitin sulfate (MCS) and polyacrylamide (PAAm). The DN of MCS/PAAm exhibited a failure stress more than 20 times greater than the single network (SN) of either MCS or PAAm and exhibited yielding stresses over 1500 kPa. In addition, the stress-strain behavior with a yielding region was also seen in a hydrogel of MCS and poly(N,N-dimethyl acrylamide) (PDMAAm). By replacing PAAm with PDMAAm, interactions known to toughen networks are removed. This demonstration supports the idea that the brittle/ductile combination is key to the DN effect over specific interactions between the networks. The MCS/PAAm and MCS/PDMAAm DN hydrogels had comparable mechanical properties to the archtypal DN hydrogels of poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS)/PAAm. In addition, these tough and ductile, biopolymer-based, double-network hydrogels demonstrated a substantial yielding region.
• Hyaluronic acid affects the in vitro induction effects of Synthetic PAMPS and PDMAAm hydrogels on chondrogenic differentiation of ATDC5 cells, depending on the level of concentration

  Katsuhisa Yoshikawa, Nobuto Kitamura, Takayuki Kurokawa, Jian Ping Gong, Yutaka Nohara, Kazunori Yasuda

  BMC MUSCULOSKELETAL DISORDERS 14 56  1471-2474 2013/02 [Refereed][Not invited]
   

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

  Takayuki Kurokawa

  Bacterial Nanocellulose: a Sophisticated Multifunctional Material 2013
• Double-network acrylamide hydrogel compositions adapted to achieve cartilage-like dynamic stiffness

  Takayuki Kurokawa

  Biomechanics and Modeling in Mechanobiology 12 (2) 243 - 248 2013 [Refereed][Not invited]
  
• A phase diagram of neutral polyampholyte - from solution to tough hydrogel

  Abu Bin Ihsan, Tao Lin Sun, Shinya Kuroda, Md. Anamul Haque, Takayuki Kurokawa, Tasuku Nakajima, Jian Ping Gong

  JOURNAL OF MATERIALS CHEMISTRY B 1 (36) 4555 - 4562 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.
• 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.
• Influence of the gel thickness on in vivo hyaline cartilage regeneration induced by double-network gel implanted at the bottom of a large osteochondral defect: Short-term results

  Hidetoshi Matsuda, Nobuto Kitamura, Takayuki Kurokawa, Kazunobu Arakaki, Jian Ping Gong, Fuminori Kanaya, Kazunori Yasuda

  BMC MUSCULOSKELETAL DISORDERS 14 50  1471-2474 2013/01 [Refereed][Not invited]
   

  Background: A double-network (DN) gel, which is composed of poly(2-acrylamido-2-methylpropanesulfonic acid) and poly(N,N'-dimethyl acrylamide), can induce hyaline cartilage regeneration in vivo in a large osteochondral defect. The purpose of this study was to clarify the influence of the thickness of the implanted DN gel on the induction ability of hyaline cartilage regeneration. Methods: Thirty-eight mature rabbits were used in this study. We created an osteochondral defect having a diameter of 4.3-mm in the patellofemoral joint. The knees were randomly divided into 4 groups (Group I: 0.5-mm thick gel, Group II: 1.0-mm thick gel, Group III: 5.0-mm thick gel, and Group IV: untreated control). Animals in each group were further divided into 3 sub-groups depending on the gel implant position (2.0-, 3.0-, or 4.0-mm depth from the articular surface) in the defect. The regenerated tissues were evaluated with the Wayne's gross and histological grading scales and real time PCR analysis of the cartilage marker genes at 4 weeks. Results: According to the total Wayne's score, when the depth of the final vacant space was set at 2.0 mm, the scores in Groups I, II, and III were significantly greater than that Group IV (p < 0.05), although there were no significant differences between Groups I and IV at a 3.0-mm deep vacant space. The expression levels of type-2 collagen in Groups II and III were significantly higher (p < 0.05) than that in Group IV. Conclusions: The 1.0-mm thick DN gel sheet had the same ability to induce hyaline cartilage regeneration as the 5.0-mm thick DN gel plug. However, the induction ability of the 0.5-mm thick sheet was significantly lower when compared with the 1.0-mm thick gel sheet. The 1.0-mm DN gel sheet is a promising device to establish a cell-free cartilage regeneration strategy that minimizes bone loss from the gel implantation.
• 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.
• Poly(2-acrylamido-2-methylpropanesulfonic acid) gel induces articular cartilage regeneration in vivo: Comparisons of the induction ability between single- and double-network gels

  Munehiro Ogawa, Nobuto Kitamura, Takayuki Kurokawa, Kazunobu Arakaki, Yasuhito Tanaka, Jian Ping Gong, Kazunori Yasuda

  JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A 100A (9) 2244 - 2251 1549-3296 2012/09 [Refereed][Not invited]
   

  The purpose of this study was to determine the in vivo cartilage induction effect of the poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) single-network (SN) gel and poly(N,N'-dimethyl acrylamide) (PDMAAm) SN gel in comparison with that of the PAMPS/PDMAAm double-network (DN) gel. An osteochondral defect created in rabbit trochlea was treated with PAMPS/PDMAAm DN, PAMPS SN, or PDMAAm SN gel implantation or left untreated. The gel was implanted into the defect so that a 2-mm depth remained. The defects were examined by histologic and immunohistochemical evaluations, surface assessment using confocal laser scanning microscopy, and real-time polymerase chain reaction analysis at 4 weeks. Samples were quantitatively evaluated with a scoring system reported by Wayne et al. The PAMPS/PDMAAm DN gel-implanted defect was filled with the hyaline-like cartilage tissue. The PAMPS SN gel-implanted defect was filled inhomogenously with hyaline/fibrocartilage tissue. The histology score of the defect treated with PAMPS/PDMAAm DN gel was significantly higher than those treated with PAMPS and PDMAAm SN gels, and the untreated defect (p = 0.0408, p < 0.0001, and p < 0.0001, respectively) and the scores of the defect treated with PAMPS SN gel were significantly higher than those treated with PDMAAm SN gel and the untreated defect (p = 0.0026 and p = 0.0026, respectively). These results suggested that the PAMPS SN gel has an ability that can induce hyaline cartilage regeneration in vivo, but that the PDMAAm SN gel does not. The current study indicates that the chondrogenic potential of a negatively charged PAMPS gel component plays an important role in the cartilage regeneration ability of the PAMPS/PDMAAm DN gel in vivo. (c) 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 100A: 22442251, 2012.
• Hydrogels with a macroscopic-scale liquid crystal structure by self-assembly of a semi-rigid polyion complex

  Zii Liang Wu, Takayuki Kurokawa, Jian Ping Gong

  POLYMER JOURNAL 44 (6) 503 - 511 0032-3896 2012/06 [Refereed][Not invited]
   

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

  Jian Hu, Takayuki Kurokawa, Kenta Hiwatashi, Tasuku Nakajima, Zi Liang Wu, Song Miao Liang, Jian Ping Gong

  MACROMOLECULES 45 (12) 5218 - 5228 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.
• Toughness Enhancement and Stick-Slip Tearing of Double-Network Hydrogels in Poly(ethylene glycol) Solution

  Songmiao Liang, Jian Flu, Zi Liang Wu, Takayuki Kurokawa, Jian Ping Gong

  MACROMOLECULES 45 (11) 4758 - 4763 0024-9297 2012/06 [Refereed][Not invited]
   

  Using a thin film double-network (DN) hydrogels of 100 mu m thickness, the behaviors of DN gels, from poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) as the first network and polyacrylamide (PAAm) as the second network, swelled in poly(ethylene glycol) (PEG) aqueous solution of short molecular weight (M-w: 400 g/mol) are investigated. Comparing with the conventional DN gels that are swelled in water, the toughness of the DN gels swelled in PEG solution is largely enhanced, as revealed by the tensile test and tearing test. Furthermore, a transition in the crack propagation dynamics, from the steady-state mode in water to the stick-slip instability mode in PEG solution, is observed in the tearing test. The morphology around the crack front of the DN gels also changes with the presence of PEG, and characteristic triangular-like damage patterns are observed. Besides, spicule-like structures are observed on the fractured surface, either in water or in PEG solution. The PEG-induced behaviors are associated with the molecular interaction of PEG to polyacrylamide, the second ductile network of the DN gels.
• Super tough double network hydrogels and their application as biomaterials

  Md. Anamul Haque, Takayuki Kurokawa, Jian Ping Gong

  POLYMER 53 (9) 1805 - 1822 0032-3861 2012/04 [Refereed][Not invited]
   

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

  Md Arifuzzaman, Zi Liang Wu, Takayuki Kurokawa, Akira Kakugo, Jian Ping Gong

  SOFT MATTER 8 (31) 8060 - 8066 1744-683X 2012 [Refereed][Not invited]
   

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

  Md Anamul Haque, Takayuki Kurokawa, Jian Ping Gong

  SOFT MATTER 8 (31) 8008 - 8016 1744-683X 2012 [Refereed][Not invited]
   

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

  Md. Anamul Haque, Takayuki Kurokawa, Gen Kamita, Youfeng Yue, Jian Ping Gong

  CHEMISTRY OF MATERIALS 23 (23) 5200 - 5207 0897-4756 2011/12 [Refereed][Not invited]
   

  In this work, we report a rubberlike elastic hydrogel containing microdomains of bilayers periodically stacked into the polymer network that satisfy the Bragg's law of diffraction. The rubberlike elastic hydrogel has been synthesized by applying double network principle into a viscoelastic hydrogel containing single-domain macroscopic lamellar bilayer. The hydrogel is able to tune the magnificent structural color reversibly over the entire wavelength range of visible spectrum as fast as the uniaxial tensile stretching and compressive deformation are applied and released. Owing to the strength, softness, and rubberlike elastic deformability, the tunable hydrogel can be used extensively to design a new class of soft tactile sensor as an advanced stress sensor that is able to detect a local deformation of a complicated force field.
• Novel Developed Systems and Techniques Based on Double-Network Principle

  Zi Liang Wu, Takayuki Kurokawa, Jian Ping Gong

  BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 84 (12) 1295 - 1311 0009-2673 2011/12 [Refereed][Not invited]
   

  The double-network hydrogels (DN gels), developed by our group in 2003, have attracted increasing attention clue to their excellent mechanical performance and unique fracture mechanism. The anomalously large fracture energy of DN gels up to 2200J m(-2) originates from the specific combination of two networks with contrasting properties. The first brittle network serves as sacrificial bonds, which breaks into small clusters to efficiently disperse the stress around the crack tip into the surrounding damage zone, while the second ductile polymer chains act as hidden length, which extends extensively to sustain large deformation. The DN gels also exhibit good biocompatibility and low friction resistance. Owing to these superior properties. DN gels possess promising prospective in industrial and medicine fields, especially for load-bearing artificial soft tissues such as artificial cartilage. However, there are several critical problems limiting the practical applications of DN gels, such as how to produce tough artificial tissue with complex shapes or bond a gel to a solid substrate. To address these specific issues, we have developed new systems and techniques based on the DN principle. These achievements, including synthesis of ultrathin DN gels, bonding of one gel to another gel or solid substrate, free-shaping of DN gels, enhancing typical single network gels by creating a DN structure, will be briefly introduced in this account paper. We believe that these new techniques will substantially promote the practical applications of ON hydrogels and extent the DN principle to other systems.
• Lamellar Bilayers as Reversible Sacrificial Bonds To Toughen Hydrogel: Hysteresis, Self-Recovery, Fatigue Resistance, and Crack Blunting

  M. Anamul Haque, Takayuki Kurokawa, Gen Kamita, J. Ping Gong

  MACROMOLECULES 44 (22) 8916 - 8924 0024-9297 2011/11 [Refereed][Not invited]
   

  We report the extraordinary toughness, hysteresis, self-recovery, and persistent fatigue resistance of an anisotropic hydrogel with single-domain lamellar structure, consisting of periodical stacking of several thousands of rigid, hydrophobic bilayers in the ductile, hydrophilic polymer matrix. The stratified lamellar bilayers not only diffract light to exhibit magnificent structural color but also serve as reversible sacrificial bonds that dissociate upon deformation, exhibiting large hysteresis as an energy dissipation mechanism. Both the molecular dissociation and lipid-like mobile nature of bilayers dramatically enhance the resistance to crack propagation by suppressing the stress concentration at the crack tip with the formation of extraordinary crack blunting. This unique toughening phenomenon could allow deep insight into the toughening mechanism of the hydrogel-like soft materials such as biological soft tissues.
• Effect of Hyaluronan Solution on Dynamic Friction of PVA Gel Sliding on Weakly Adhesive Glass Substrate

  Yukihiro Nakano, Takayuki Kurokawa, Miao Du, Jian Liu, Taiki Tominaga, Yoshihito Osada, Jian Ping Gong

  MACROMOLECULES 44 (22) 8908 - 8915 0024-9297 2011/11 [Refereed][Not invited]
   

  We study the sliding friction of poly(vinyl alcohol) (PVA) gel against glass substrate in hyaluronan (HA) aqueous solution with various concentrations and two molecular weights. The frictional stress decreases with increase of concentration of HA at low sliding velocity, and the lowest friction appears in HA 10c* (c* is the overlap concentration) solution; after that, it increases slightly with the concentration. By assuming that a continuous HA lubricant layer is formed at the interface, which screens PVA adsorption to substrate, we estimate the thickness of the lubrication film in concentrated HA solution. In addition, we perform frictional measurement in poly(ethylene oxide) (PEO) aqueous solutions and proteoglycan solutions. By comparing the frictional behavior with that in HA solutions, we observe a universal relationship between the zero-shear rate viscosity of polymer solution and the friction at low sliding velocity region, regardless the change in the lubricating polymer species.
• Microgel-Reinforced Hydrogel Films with High Mechanical Strength and Their Visible Mesoscale Fracture Structure

  Jian Hu, Kenta Hiwatashi, Takayuki Kurokawa, Song Miao Liang, Zi Liang Wu, Jian Ping Gong

  MACROMOLECULES 44 (19) 7775 - 7781 0024-9297 2011/10 [Refereed][Not invited]
   

  The poor mechanical properties remain the largest barrier to traditional synthetic hydrogels for extensive practical applications, such as tissue scaffolds. In this work, we have synthesized the hydrogel films in the presence of microgel precursors of various chemical species with different charges. The hydrogels fabricated have a novel two-phase composite structure, where the continuous phase is a loosely cross-linked polyacrylamide (PAAm) matrix and the disperse phase is virtually double-network (DN) microgels. Named as microgel-reinforced (MR) hydrogels, they exhibited dramatic enhancement in mechanical strength and toughness, in comparison to the hydrogels with no microgels. MR hydrogels showed the comparable mechanical properties with the conventional bicontinuous DN hydrogels. By visualizing the embedded microgels before, during, and after the elongation, mesoscale fractures of the microgels phase were confirmed, which should effectively blunt the crack and enhance the fracture propagation resistance. Therefore, we conclude that the essential reinforcement principle of MR gels roots in the sacrificial bonds effect contributed by the microgels. This work provides a novel universal pathway to synthesize hydrogel thin films with high strength and toughness from various microgels and may open a new avenue for the application of hydrogels in various fields, such as fast responsive actuators, fuel cell films, wound dressings, etc.
• Acrylamide Polymer Double-Network Hydrogels: Candidate Cartilage Repair Materials with Cartilage-Like Dynamic Stiffness and Attractive Surgery-Related Attachment Mechanics

  Markus P. Arnold, Alma U. Daniels, Sarah Ronken, Helena Ardura Garcia, Niklaus F. Friederich, Takayuki Kurokawa, Jian P. Gong, Dieter Wirz

  CARTILAGE 2 (4) 374 - 383 1947-6035 2011/10 [Refereed][Not invited]
   

  Background: In focal repair of joint cartilage and meniscus, initial stiffness and strength of repairs are generally much less than surrounding tissue. This increases early failure potential. Secure primary fixation of the repair material is also a problem. Acrylamide polymer double-network (DN) hydrogels are candidate-improved repair materials. DN gels have exceptional strength and toughness compared to ordinary gels. This stems from the double-network structure in which there is a high molar ratio of the second network to the first network, with the first network highly crosslinked and the second loosely crosslinked. Previous studies of acrylic PAMPS/PDMAAm and PAMPS/PAAm DN gels demonstrated physicochemical stability and tissue compatibility as well as the ability to foster cartilage formation. Methods: Mechanical properties related to surgical use were tested in 2 types of DN gels. Results: Remarkably, these >90%-water DN gels exhibited dynamic impact stiffness (E*) values (similar to 1.1 and similar to 1.5 MPa) approaching swine meniscus (similar to 2.9 MPa). Dynamic impact energy-absorbing capability was much lower (median loss angles of similar to 2 degrees) than swine meniscus (>10 degrees), but it is intriguing that >90%-water materials can efficiently store energy. Also, fine 4/0 suture tear-out strength approached cartilage (similar to 2.1 and similar to 7.1 N v. similar to 13.5 N). Initial strength of attachment of DN gels to cartilage with acrylic tissue adhesive was also high (similar to 0.20 and similar to 0.15 N/mm(2)). Conclusions: DN gel strength and toughness properties stem from optimized entanglement of the 2 network components. DN gels thus have obvious structural parallels with cartilaginous tissues, and their surgical handling properties make them ideal candidates for clinical use.
• Dynamic Behavior and Spontaneous Differentiation of Mouse Embryoid Bodies on Hydrogel Substrates of Different Surface Charge and Chemical Structures

  Jian Fang Liu, Yong Mei Chen, Jing Jing Yang, Takayuki Kurokawa, Akira Kakugo, Kimiko Yamamoto, Jian Ping Gong

  TISSUE ENGINEERING PART A 17 (17-18) 2343 - 2357 1937-3341 2011/09 [Refereed][Not invited]
   

  Differentiation of embryoid bodies (EBs) into particular cell lineages has been extensively studied. There is an increasing interest in the effect of soft hydrogel scaffolds on the behavior of EBs, such as the initial adhesion, dynamic morphology change, and differentiation. In this study, without adding any other bioactive factors in the serum-containing medium, dynamic behaviors of mouse EBs loaded on the surface of hydrogels with different surface charge and chemical structures are investigated. EBs adhered quickly to negatively charged poly(sodium p-styrene sulfonate) (PNaSS) hydrogels, which facilitates EBs spreading, migration, and differentiation into three germ layers with high efficiency of cardiomyocytes differentiation, similar to that on gelatin coated polystyrene (PS) culture plate. While on neutral poly(acrylamide) (PAAm) hydrogels, EBs maintained the initial spherical morphology with high expression of pluripotency-related markers in the short culture periods, and then showed the significantly greater levels of selected endoderm markers after long-time culture. EBs cultured on negatively charged poly(2-acrylamido-2-methyl-propane sulfonic acid sodium salt) (PNaAMPS) gels demonstrated the analogous behaviors with that of neutral PAAm gels at early differentiation phase (day 4 + 1). Then, their adhesion, spreading and differentiation were quite similar to that on negatively charged PNaSS gels. The correlation between surface properties of hydrogels and EBs differentiation was discussed.
• Effect of Void Structure on the Toughness of Double Network Hydrogels

  Tasuku Nakajima, Hidemitsu Furukawa, Yoshimi Tanaka, Takayuki Kurokawa, Jian Ping Gong

  JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS 49 (17) 1246 - 1254 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
• Dynamic Behavior and Spontaneous Differentiation of Mouse Embryoid Bodies on Hydrogel Substrates of Different Surface Charge and Chemical Structures

  Jian Fang Liu, Yong Mei Chen, Jing Jing Yang, Takayuki Kurokawa, Akira Kakugo, Kimiko Yamamoto, Jian Ping Gong

  TISSUE ENGINEERING PART A 17 (17-18) 2343 - 2357 1937-3341 2011/09 [Refereed][Not invited]
   

  Differentiation of embryoid bodies (EBs) into particular cell lineages has been extensively studied. There is an increasing interest in the effect of soft hydrogel scaffolds on the behavior of EBs, such as the initial adhesion, dynamic morphology change, and differentiation. In this study, without adding any other bioactive factors in the serum-containing medium, dynamic behaviors of mouse EBs loaded on the surface of hydrogels with different surface charge and chemical structures are investigated. EBs adhered quickly to negatively charged poly(sodium p-styrene sulfonate) (PNaSS) hydrogels, which facilitates EBs spreading, migration, and differentiation into three germ layers with high efficiency of cardiomyocytes differentiation, similar to that on gelatin coated polystyrene (PS) culture plate. While on neutral poly(acrylamide) (PAAm) hydrogels, EBs maintained the initial spherical morphology with high expression of pluripotency-related markers in the short culture periods, and then showed the significantly greater levels of selected endoderm markers after long-time culture. EBs cultured on negatively charged poly(2-acrylamido-2-methyl-propane sulfonic acid sodium salt) (PNaAMPS) gels demonstrated the analogous behaviors with that of neutral PAAm gels at early differentiation phase (day 4 + 1). Then, their adhesion, spreading and differentiation were quite similar to that on negatively charged PNaSS gels. The correlation between surface properties of hydrogels and EBs differentiation was discussed.
• Gene expression profile of the cartilage tissue spontaneously regenerated in vivo by using a novel double-network gel: Comparisons with the normal articular cartilage

  Ryusei Imabuchi, Yoshihiro Ohmiya, Hyuck Joon Kwon, Shin Onodera, Nobuto Kitamura, Takayuki Kurokawa, Jian Ping Gong, Kazunori Yasuda

  BMC MUSCULOSKELETAL DISORDERS 12 213  1471-2474 2011/09 [Refereed][Not invited]
   

  Background: We have recently found a phenomenon that spontaneous regeneration of a hyaline cartilage-like tissue can be induced in a large osteochondral defect by implanting a double-network (DN) hydrogel plug, which was composed of poly-(2-Acrylamido-2-methylpropanesulfonic acid) and poly-(N, N'-Dimetyl acrylamide), at the bottom of the defect. The purpose of this study was to clarify gene expression profile of the regenerated tissue in comparison with that of the normal articular cartilage. Methods: We created a cylindrical osteochondral defect in the rabbit femoral grooves. Then, we implanted the DN gel plug at the bottom of the defect. At 2 and 4 weeks after surgery, the regenerated tissue was analyzed using DNA microarray and immunohistochemical examinations. Results: The gene expression profiles of the regenerated tissues were macroscopically similar to the normal cartilage, but showed some minor differences. The expression degree of COL2A1, COL1A2, COL10A1, DCN, FMOD, SPARC, FLOD2, CHAD, CTGF, and COMP genes was greater in the regenerated tissue than in the normal cartilage. The top 30 genes that expressed 5 times or more in the regenerated tissue as compared with the normal cartilage included type-2 collagen, type-10 collagen, FN, vimentin, COMP, EF1alpha, TFCP2, and GAPDH genes. Conclusions: The tissue regenerated by using the DN gel was genetically similar but not completely identical to articular cartilage. The genetic data shown in this study are useful for future studies to identify specific genes involved in spontaneous cartilage regeneration.
• Surfactant-induced friction reduction for hydrogels in the boundary lubrication regime

  Kosuke Kamada, Hidemitsu Furukawa, Takayuki Kurokawa, Tomohiro Tada, Taiki Tominaga, Yukihiro Nakano, Jian Ping Gong

  JOURNAL OF PHYSICS-CONDENSED MATTER 23 (28) 284107  0953-8984 2011/07 [Refereed][Not invited]
   

  We studied the ability of surfactants to reduce friction by boundary lubrication for a bulk hydrogel sliding on a solid surface in an aqueous solution. A piece of negatively charged polyelectrolyte hydrogel was slid across solid surfaces with various levels of hydrophobicity, using a strain-controlled parallel-plate rheometer in water. A dramatic reduction in the sliding friction, especially in the low velocity region, was detected by the addition of a surfactant to the water medium. This friction reduction was only observed in gel-solid friction but not in solid-solid friction, indicating that the soft and wet nature of the gel surface was crucial for this surfactant-induced friction reduction. This phenomenon reveals that surfactants can remain at the gel-mated interface, thus preventing direct interfacial interaction between the sliding surfaces, and significantly decreasing the frictional stress. The reported dramatic reduction in friction highlights the frictional characteristics of soft and wet hydrogel materials.
• Induction of Spontaneous Hyaline Cartilage Regeneration Using a Double-Network Gel Efficacy of a Novel Therapeutic Strategy for an Articular Cartilage Defect

  Nobuto Kitamura, Kazunori Yasuda, Munehiro Ogawa, Kazunobu Arakaki, Shuken Kai, Shin Onodera, Takayuki Kurokawa, Jian Ping Gong

  AMERICAN JOURNAL OF SPORTS MEDICINE 39 (6) 1160 - 1169 0363-5465 2011/06 [Refereed][Not invited]
   

  Background: A double-network (DN) gel, which was composed of poly-(2-acrylamido-2-methylpropanesulfonic acid) and poly(N, N'-dimetyl acrylamide) (PAMPS/PDMAAm), has the potential to induce chondrogenesis both in vitro and in vivo. Purpose: To establish the efficacy of a therapeutic strategy for an articular cartilage defect using a DN gel. Study Design: Controlled laboratory study. Methods: A 4.3-mm-diameter osteochondral defect was created in rabbit trochlea. A DN gel plug was implanted into the defect of the right knee so that a defect 2 mm in depth remained after surgery. An untreated defect of the left knee provided control data. The osteochondral defects created were examined by histological and immunohistochemical evaluations, surface assessment using confocal laser scanning microscopy, and real-time polymerase chain reaction (PCR) analysis at 4 and 12 weeks. Samples were quantitatively evaluated with 2 scoring systems reported by Wayne et al and O'Driscoll et al. Results: The DN gel-implanted defect was filled with a sufficient volume of the hyaline cartilage tissue rich in proteoglycan and type 2 collagen. Quantitative evaluation using the grading scales revealed a significantly higher score in the DN gel-implanted defects compared with the untreated control at each period (P<.0001). The mean relative values of type 2 collagen mRNAs in the regenerated tissue were obviously higher in the DN gel-implanted defect than in the untreated control at each period. The mean surface roughness of the untreated control was significantly higher than the normal cartilage at 12 weeks (P=.0106), while there was no statistical difference between the DN gel-implanted and normal knees. Conclusion: This study using the mature rabbit femoral trochlea osteochondral defect model demonstrated that DN gel implantation is an effective treatment to induce cartilage regeneration in vivo without any cultured cells or mammalian-derived scaffolds.
• Anisotropic Hydrogel from Complexation-Driven Reorientation of Semirigid Polyanion at Ca2+ Diffusion Flux Front

  Zi Liang Wu, Takayuki Kurokawa, Daisuke Sawada, Jian Hu, Hidemitsu Furukawa, Jian Ping Gong

  MACROMOLECULES 44 (9) 3535 - 3541 0024-9297 2011/05 [Refereed][Not invited]
   

  We report a macroscopically anisotropic hydrogel developed by the facile dialysis of a synthetic semirigid polyanion in aqueous solution of multivalent cations. By the uniaxial diffusion of Ca2+ into two ends of a thin rectangular reaction cell containing semirigid polyanion poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT) aqueous solution, centimeter-scale anisotropic hydrogels with the PBDT molecules and their self-assembled fibrous bundles align in perpendicular to the Ca2+ diffusion direction are obtained. The anisotropic gel shows a higher elastic modulus and tensile fracture stress/strain in the direction parallel to the PBDT orientation than that of perpendicular direction. By observing in situ the gelation process, an extraordinary molecular reorientation of PBDT at the Ca2+ diffusion flux front is observed for the first time. The mechanism for the molecular reorientation is discussed in terms of complexation and gelation.
• Strain-Induced Molecular Reorientation and Birefringence Reversion of a Robust, Anisotropic Double-Network Hydrogel

  Zi Liang Wu, Daisuke Sawada, Takayuki Kurokawa, Akira Kakugo, Wei Yang, Hidemitsu Furukawa, Jian Ping Gong

  MACROMOLECULES 44 (9) 3542 - 3547 0024-9297 2011/05 [Refereed][Not invited]
   

  A robust, macroscopically anisotropic double-network (A-DN) hydrogel has been developed by combining the first anisotropic, physically cross-linked network of semirigid poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT) and the second chemically cross-linked network of flexible polyacrylamide (PAAm) through double-network technology. Owing to the cooperative orientation of the self-assembled bundle structure of semirigid PBDTs, the A-DN gel shows a very sensitive and strong birefringence change upon deformation, which is always dominated by PBDT for the wide strain range investigated (epsilon = 0-18), regardless the fact that PAAm is in large excess. When the initial alignment of PBDT is vertical to the elongation direction, a birefringence reversion occurs at epsilon similar to 0.5, indicating that the initial vertical alignment of PBDT is overwhelmed by the strain-induced parallel alignment, even at such a small strain due to the cooperative reorientation of PBDT.
• Direct Observation on the Surface Fracture of Ultrathin Film Double-Network Hydrogels

  Songmiao Liang, Zi Liang Wu, Jian Hu, Takayuki Kurokawa, Qiu Ming Yu, Jian Ping Gong

  MACROMOLECULES 44 (8) 3016 - 3020 0024-9297 2011/04 [Refereed][Not invited]
   

  Double-network (DN) hydrogels have attracted much attention in the soft matter community due to their excellent mechanical performance and unique fracture mechanism. On the basis of ultrathin film technique and optical microscope, we here report a method which is quite effective for accessing the fractured microstructure of DN hydrogels formed during the tensile and tearing process. During tensile deformation, fracture of the first network occurs even before yielding occurs. Concomitant with the yielding, wrinkle-like structure, which is due to the fracture of the first network, is clearly observed for the first time. This wrinkle-like structure disappears upon further deformation to strain-hardening region because of the further fracture of the first network. Similar microstructures are observed at the crack tip for samples experienced the tearing test. This work provides direct proofs for the assumption concerning the occurrence of local yielding and the formation of a huge damage zone at the crack tip during the crack propagation process of DN hydrogels.
• Contribution of Sarcoplasmic Reticulum Ca(2+) Release and Ca(2+) Transporters on Sarcolemmal Channels to Ca(2+) Transient in Fetal Mouse Heart

  Mari Takizawa, Takahiro Ishiwata, Yoichi Kawamura, Takashi Kanai, Takayuki Kurokawa, Mitsunori Nishiyama, Hideyuki Ishida, Yuh Asano, Shigeaki Nonoyama

  PEDIATRIC RESEARCH 4 69 (4) 306 - 311 0031-3998 2011/04 [Refereed][Not invited]
   

  Sarcoplasmic reticulum (SR) Ca(2+) release has been shown not to be the predominant mechanism responsible for excitation-contraction (E-C) coupling in fetal myocytes. However, most of the studies have been conducted either on primary cultures or acutely isolated cells, in which an apparent reduction of ryanodine receptor density have been reported. We aimed to elucidate the contribution of SR Ca(2+) release and Ca(2+) transporters on sarcolemmal channels to Ca(2+) transients in fetal mouse whole hearts. On embryonic day 13.5, ryanodine significantly reduced the amplitude of the Ca(2+) transient to 27.2 +/- 4.4% of the control, and both nickel and SEA0400 significantly prolonged the time to peak from 84 +/- 2 ms to 140 +/- 5 ms and 129 +/- 6 ms, respectively, whereas nifedipine did not alter it. Therefore, at early fetal stages, SR Ca(2+) release should be an important component of E-C coupling, and T-type Ca(2+) channel and reverse mode sodium-calcium exchanger (NCX)-mediated SR Ca(2+) release could be the predominant contributors. Using embryonic mouse cultured cardiomyocytes, we showed that both nifedipine and nickel inhibited the ability of NCX to extrude Ca(2+) from the cytosol. From these results, we propose a novel idea concerning E-C coupling in immature heart. (Pediatr Res 69: 306-311, 2011)
• Robust bonding and one-step facile synthesis of tough hydrogels with desirable shape by virtue of the double network structure

  Junji Saito, Hidemitsu Furukawa, Takayuki Kurokawa, Rikimaru Kuwabara, Shinya Kuroda, Jian Hu, Yoshimi Tanaka, Jian Ping Gong, Nobuto Kitamura, Kazunori Yasuda

  POLYMER CHEMISTRY 2 (3) 575 - 580 1759-9954 2011/03 [Refereed][Not invited]
   

  Robust bonding of a hydrogel in aqueous environment, either to another hydrogel or to a solid, is one of the major unsolved issues for the practical applications of hydrogels in various fields. Here we report robust bonding between a pair of hydrogel sheets, containing over 90 wt% of water, by applying the double-network (DN) structure. In the optimal condition, the peeling energy of the united gel sheets reaches 1200 J m(-2), which is comparable to the bulk fracture energy of a normal type of tough DN gels. This hydrogel bonding technique is also applied to form tough bonding between hydrogel and plastic plates. Furthermore, based on this technique, we have developed a facile method to synthesize robust double network hydrogels with any desirable free-shape from micro-gel precursors. These novel techniques will substantially merit the applications of the tough hydrogels in various fields, such as an artificial meniscus.
• Joint immobilization inhibits spontaneous hyaline cartilage regeneration induced by a novel double-network gel implantation

  Kazunobu Arakaki, Nobuto Kitamura, Takayuki Kurokawa, Shin Onodera, Fuminori Kanaya, Jian-Ping Gong, Kazunori Yasuda

  JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE 22 (2) 417 - 425 0957-4530 2011/02 [Refereed][Not invited]
   

  We have recently discovered that spontaneous hyaline cartilage regeneration can be induced in an osteochondral defect in the rabbit, when we implant a novel double-network (DN) gel plug at the bottom of the defect. To clarify whether joint immobilization inhibits the spontaneous hyaline cartilage regeneration, we conducted this study with 20 rabbits. At 4 or 12 weeks after surgery, the defect in the mobile knees was filled with a sufficient volume of the hyaline cartilage tissue rich in proteoglycan and type-2 collagen, while no cartilage tissues were observed in the defect in the immobilized knees. Type-2 collagen, Aggrecan, and SOX9 mRNAs were expressed only in the mobile knees at each period. This study demonstrated that joint immobilization significantly inhibits the spontaneous hyaline cartilage regeneration induced by the DN gel implantation. This fact suggested that the mechanical environment is one of the significant factors to induce this phenomenon.
• Spontaneous hyaline cartilage regeneration can be induced in an osteochondral defect created in the femoral condyle using a novel double-network hydrogel

  Masashi Yokota, Kazunori Yasuda, Nobuto Kitamura, Kazunobu Arakaki, Shin Onodera, Takayuki Kurokawa, Jian-Ping Gong

  BMC MUSCULOSKELETAL DISORDERS 12 49  1471-2474 2011/02 [Refereed][Not invited]
   

  Background: Functional repair of articular osteochondral defects remains a major challenge not only in the field of knee surgery but also in tissue regeneration medicine. The purpose is to clarify whether the spontaneous hyaline cartilage regeneration can be induced in a large osteochondral defect created in the femoral condyle by means of implanting a novel double-network (DN) gel at the bottom of the defect. Methods: Twenty-five mature rabbits were used in this study. In the bilateral knees of each animal, we created an osteochondral defect having a diameter of 2.4-mm in the medial condyle. Then, in 21 rabbits, we implanted a DN gel plug into a right knee defect so that a vacant space of 1.5-mm depth (in Group I), 2.5-mm depth (in Group II), or 3.5-mm depth (in Group III) was left. In the left knee, we did not apply any treatment to the defect to obtain the control data. All the rabbits were sacrificed at 4 weeks, and the gross and histological evaluations were performed. The remaining 4 rabbits underwent the same treatment as used in Group II, and real-time PCR analysis was performed at 4 weeks. Results: The defect in Group II was filled with a sufficient volume of the hyaline cartilage tissue rich in proteoglycan and type-2 collagen. The Wayne's gross appearance and histology scores showed that Group II was significantly greater than Group I, III, and Control (p < 0.012). The relative expression level of type-2 collagen, aggrecan, and SOX9 mRNAs was significantly greater in Group II than in the control group (p < 0.023). Conclusions: This study demonstrated that spontaneous hyaline cartilage regeneration can be induced in vivo in an osteochondral defect created in the femoral condyle by means of implanting the DN gel plug at the bottom of the defect so that an approximately 2-mm deep vacant space was intentionally left in the defect. This fact has prompted us to propose an innovative strategy without cell culture to repair osteochondral lesions in the femoral condyle.
• Long-term in situ observation of barnacle growth on soft substrates with different elasticity and wettability

  Nafees Ahmed, Takayuki Murosaki, Akira Kakugo, Takayuki Kurokawa, Jian Ping Gong, Yasuyuki Nogata

  SOFT MATTER 7 (16) 7281 - 7290 1744-683X 2011 [Refereed][Not invited]
   

  In this paper, settlement, metamorphosis, and long term growth of barnacles on soft substrates with a wide elasticity range (modulus 0.01-0.47 MPa) as well as with the variation in wettability were investigated for the first time in vitro, in the laboratory environment. Tough double-network (DN) hydrogels and polydimethylsiloxane (PDMS) were used as the soft hydrophilic substrates and hydrophobic substrates, respectively, and polystyrene (PS), a hard and hydrophobic substrate, was used as a control. It was observed that (1) the initial settlement and metamorphosis of cyprid larvae dramatically increase with the substrate elastic modulus while not showing an explicit dependence on the substrate wettability; (2) the growth rate of barnacles on both DN gels and PDMSs does not show an explicit dependence on the elasticity of the soft substrates, while it shows a slightly higher value on the hydrophobic PDMSs than on the hydrophilic DN gels; (3) the growth rate on these soft substrates is explicitly lower than that on the rigid PS substrate at the late stage of the growth; (4) the "self-release'' phenomenon of barnacles was observed for the PDMS substrate with a modulus higher than 0.01 MPa. Based on these observations, the antifouling effects of the soft substrates on barnacles were discussed.
• Hydrogel with cubic-packed giant concentric domains of semi-rigid polyion complex

  Zi Liang Wu, Md Arifuzzaman, Takayuki Kurokawa, Hidemitsu Furukawa, Jian Ping Gong

  SOFT MATTER 7 (5) 1884 - 1889 1744-683X 2011 [Refereed][Not invited]
   

  We report a novel giant oriented structure observed in plate hydrogels synthesized by photo-polymerization of cationic monomers with a cross-linker in the presence of a semi-rigid polyanion as the dopant. The giant structure, formed via self-assembly of the semi-rigid polyion complex, consists of millimetre-scale cubic packed concentric cylindrical domains that are sandwiched by two homeotropically aligned outer layers. A universal relationship between the diameter of the cylinders D and the thickness of the swollen gel T is observed, as D = 0.5T, regardless the change in the concentrations of the polyanion and precursor cationic monomer. This result permits us to induce the giant concentric structure into hydrogels with tunable cylindrical sizes.
• Unidirectional Alignment of Lamellar Bilayer in Hydrogel: One-Dimensional Swelling, Anisotropic Modulus, and Stress/Strain Tunable Structural Color

  Md. Anamul Haque, Gen Kamita, Takayuki Kurokawa, Kaoru Tsujii, Jian Ping Gong

  ADVANCED MATERIALS 22 (45) 5110 - + 0935-9648 2010/12 [Refereed][Not invited]
   

  A novel anisotropic hydrogel, consisting of lamellar bilayers and a polymer network, with unidirectional alignment of the bilayer structure has been synthesized. The unidirectional orientation of bilayer in the gels leads to one-dimensional swelling, strong anisotropy in elastic modulus, and exhibits excellent visible color. The gel shows reversibly tunable structural color under mechanical stimulation and could be the basis for a deformation-based color display.
• 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
• Dual Network Formation in Polyelectrolyte Hydrogel via Viscoelastic Phase Separation: Role of Ionic Strength and Polymerization Kinetics

  Zi Liang Wu, Takayuki Kurokawa, Songmiao Liang, Jian Ping Gong

  MACROMOLECULES 43 (19) 8202 - 8208 0024-9297 2010/10 [Refereed][Not invited]
   

  In this Article, we report a systematic research on a hydrogel with dual networks or 10(4) times difference in mesh sizes. The structure was developed by polymerizing a cationic monomer N-[3-(N.N-dimethylamino)propyl] acrylamide methyl chloride quarternary (DMAPAA-Q) in the presence of a small amount of semirigid polyanion, poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT). During the polymerization, polyion complexes were formed, which caused viscoelastic phase separation (VPS) due to the self-assembly of the semirigid polyion complexes, whereupon the dynamic coupling or phase separation and gelation is crucial for the structure formation. When PBDT was above its overlap concentration (C(PBDT) > C*), a critical concentration of cationic monomer, C(Q) approximate to 1.5 M, was observed, below which VPS occurred and turbid hydrogels with the dual network structure were formed, whereas above which, a transparent, anisotropic hydrogel was formed. It has been elucidated that the critical effect of C(Q) on the VPS process is through the ionic strength mechanism. That is, the abundant unreacted cationic monomer at high C(Q) behaves as a simple salt that screens the electrostatic interaction between the polycation and PBDT and therefore suppresses the occurrence of the phase separation. Furthermore, we investigated the effects of reaction kinetics on the VPS and the microstructure of gels by changing the concentrations of photoinitiator and chemical cross-linker. The dual network gels possess controllable turbidity degrees and mesh sizes corresponding to different quench depths of the phase separation. On the basis of these results, as well as in situ observation of the structure formation during the polymerization, we proposed a detailed mechanism for the formation or dual networks and the anisotropic hydrogels.
• Spontaneous Redifferentiation of Dedifferentiated Human Articular Chondrocytes on Hydrogel Surfaces

  Jing Jing Yang, Yong Mei Chen, Jian Fang Liu, Takayuki Kurokawa, Jian Ping Gong

  TISSUE ENGINEERING PART A 16 (8) 2529 - 2540 1937-3341 2010/08 [Refereed][Not invited]
   

  Chondrocytes rapidly dedifferentiate into a more fibroblastic phenotype on a two-dimensional polystyrene substratum. This impedes fundamental research on these cells as well as their clinical application. This study investigated the redifferentiation behavior of dedifferentiated chondrocytes on a hydrogel substratum. Dedifferentiated normal human articular chondrocyte-knee (NHAC-kn) cells were released from the sixth-passage monolayer cultured on a polystyrene surface. These cells were then subcultured on a chemically crosslinked copolymer hydrogel, that is, poly(NaAMPS-co-DMAAm), and the cells thus obtained were used as the seventh-passage cultivation. Copolymer gels were synthesized from a negatively charged monomer, the sodium salt of 2-acrylamido-2-methyl-1-propanesulfonic acid (NaAMPS), and a neutral monomer, N,N-dimethylacrylamide (DMAAm). These gels were of different compositions because the molar fraction (F) of NaAMPS was varied (F = 0, 0.2, 0.4, 0.6, 0.8, and 1.0). The dedifferentiated NHAC-kn cells spontaneously redifferentiated to normal NHAC-kn cells on neutral (F = 0) and poly(NaAMPS-co-DMAAm) hydrogels of low charge density (F = 0.2). This was deduced from the cell morphology and expression of cartilage-specific genes and proteins. These results should enable us to establish a simple and efficient method for preparing large amounts of chondrocytes by cultivation on the surfaces of neutral and low-charge-density hydrogels.
• 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.
• Hydrogels with Cylindrically Symmetric Structure at Macroscopic Scale by Self-Assembly of Semi-rigid Polyion Complex

  Zi Liang Wu, Takayuki Kurokawa, Songmiao Liang, Hidemitsu Furukawa, Jian Ping Gong

  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 132 (29) 10064 - 10069 0002-7863 2010/07 [Refereed][Not invited]
   

  A hydrogel with cylindrically symmetric structure at macroscopic scale has been developed by polymerization of a cationic monomer in the presence of a small amount of semi-rigid polyanion poly(2,2'-disulfony1-4,4'-benzidine terephthalamide) (PBDT) in a cylinder glass tube. The polyion complex radially aligns in the outer region of the synthesized cylinder gel. On the other hand, it orients in concentric and axial directions in the inner region. To the authors' knowledge, this is the first report of such millimeter-scale ordered structure developed in a polymeric hydrogel. We elucidate that homeotropic alignment on the glass wall is energetically favorable for the semi-rigid polyion complex, resulting in the radial orientation in the outer region. In the inner region, the oriented structures result from the monomer diffusion (due to the heterogeneous polymerization) that induces PBDT orientation perpendicular to the diffusion direction. The structured gels showing sensitive response of birefringence to external force are expected to find applications in optical sensors.
• Artificial cartilage made from a novel double-network hydrogel: In vivo effects on the normal cartilage and ex vivo evaluation of the friction property

  Kazunobu Arakaki, Nobuto Kitamura, Hiroyuki Fujiki, Takayuki Kurokawa, Mikio Iwamoto, Masaru Ueno, Fuminori Kanaya, Yoshihito Osada, Jian Ping Gong, Kazunori Yasuda

  JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A 93A (3) 1160 - 1168 1549-3296 2010/06 [Refereed][Not invited]
   

  This study evaluated the in vivo influence of a poly-(2-Acrylamido-2-methylpropane sulfonic acid)/poly(N,N'-dimetyl acrylamide) (PAMPS/PDMAAm) double-network (DN) hydrogel on counterface cartilage in rabbit knee joints and its ex vivo friction properties on normal cartilage. In the first experiment, the DN gel was implanted in a surgically created defect in the femoral trochlea of rabbit knee joints and the left knee was used as the control. Evaluations using a confocal laser scanning microscopy demonstrated that the DN gel did not affect the surface microstructure (surface roughness, the number of small pits) of the counterface cartilage in viva at 4 and 12 weeks. The histology also showed that the DN gel had no pathological damage on the cartilage matrices and cells at 4 weeks. However, two of the five DN gel-implanted knees showed mild irregularity on the counterface cartilage surface at 12 weeks. In the second experiment, the friction property between the normal and the artificial cartilage was determined using a joint simulator apparatus. The ex vivo mean friction coefficient of the DN gel to normal cartilage was 0.029, while that of the normal-to-normal cartilage articulation was 0.188. The coefficient of the DN gel-to-normal cartilage articulation was significantly lower than that of the normal-to-normal cartilage articulation (p < 0.0001). This study suggested that the PAMPS/PDMAAm DN gel has very low friction coefficient on normal cartilage and has no significant detrimental effects on counterface cartilage in vivo, and can be a promising material to develop the artificial cartilage. (C) 2009 Wiley Periodicals, Inc. J Biomed Mater Res 93A: 1160-1168, 2010
• Brittle, ductile, paste-like behaviors and distinct necking of double network gels with enhanced heterogeneity

  Yasunori Kawauchi, Yoshimi Tanaka, Hidemitsu Furukawa, Takayuki Kurokawa, Tasuku Nakajima, Yoshihito Osada, Jian Ping Gong

  Journal of Physics: Conference Series 184 12016 - (8pp) 2009/08 [Refereed][Invited]
  
• First Observation of Stick-Slip Instability in Tearing of Poly(vinyl alcohol) Gel Sheets

  Yoshimi Tanaka, Hiroyuki Abe, Takayuki Kurokawa, Hidemitsu Furukawa, Jian Ping Gong

  MACROMOLECULES 42 (15) 5425 - 5426 0024-9297 2009/08 [Refereed][Not invited]
  
• Antifouling properties of tough gels against barnacles in a long-term marine environment experiment

  Takayuki Murosaki, Takaya Noguchi, Kazuo Hashimoto, Akira Kakugo, Takayuki Kurokawa, Junji Saito, Yong Mei Chen, Hidemitsu Furukawa, Jian Ping Gong

  Biofouling Taylor & Francis 25 (7) 657 - 666 0892-7014 2009/07 [Refereed][Not invited]
   

  In marine environment, the antifouling properties against marine sessile organisms (algae, sea squirts, barnacles, etc.) were tested on various kinds of hydrogels in a long term. The results demonstrate that most hydrogels can ensure at least 2 months in marine environment. In particular, mechanically tough PAMPS/PAAm DN and PVA gels exhibited amazing antifouling activity against marine sessile organisms, especially barnacles as long as 330 days. The antifouling ability of hydrogels to barnacles is explained in terms of an "easy-release" mechanism in which the high water content and the elastic modulus of the gel are two important parameters.
• Direct Observation of Damage Zone around Crack Tips in Double-Network Gels

  Qiu Ming Yu, Yoshimi Tanaka, Hidemitsu Furukawa, Takayuki Kurokawa, Jian Ping Gong

  MACROMOLECULES 42 (12) 3852 - 3855 0024-9297 2009/06 [Refereed][Not invited]
  
• A Novel Double-Network Hydrogel Induces Spontaneous Articular Cartilage Regeneration in vivo in a Large Osteochondral Defect

  Kazunori Yasuda, Nobuto Kitamura, Jian Ping Gong, Kazunobu Arakaki, Hyuck Joon Kwon, Shin Onodera, Yong Mei Chen, Takayuki Kurokawa, Fuminori Kanaya, Yoshihiro Ohmiya, Yoshihito Osada

  MACROMOLECULAR BIOSCIENCE 9 (4) 307 - 316 1616-5187 2009/04 [Refereed][Not invited]
   

  We have developed a novel method to induce spontaneous hyaline cartilage regeneration in vivo for a large osteochondral defect by implanting a plug made from a double-network hydrogel composed of poly(2-acrylamido-2-methylpropanesulfonic acid) and poly(N,N'-dimethylacrylamide) at the bottom of the defect, leaving the cavity vacant. In cells regenerated in the treated defect, type-2 collagen, Aggrican, and SOX9 mRNAs were highly expressed and the regenerated matrix was rich in proteoglycan and type-2 collagen at 4 weeks. This fact gave a significant modification to the commonly established concept that hyaline cartilage tissue cannot regenerate in vivo. This study prompted an innovative strategy in the field of joint ON gel surgery to repair an osteochondral defect using an advanced, high-function hydrogel.
• True Chemical Structure of Double Network Hydrogels

  Tasuku Nakajima, Hidemitsu Furukawa, Yoshimi Tanaka, Takayuki Kurokawa, Yoshihito Osada, Jian Ping Gong

  MACROMOLECULES 42 (6) 2184 - 2189 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.
• Antifouling activity of synthetic polymer gels against cyprids of the barnacle (Balanus amphitrite) in vitro

  Takayuki Kurokawa

  Biofouling 25 (3/4) 313 - 320 0892-7014 2009/02 [Refereed][Not invited]
  
• 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][Not 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.
• Friction between like-charged hydrogels-combined mechanisms of boundary, hydrated and elastohydrodynamic lubrication

  Shinsuke Oogaki, Go Kagata, Takayuki Kurokawa, Shinya Kuroda, Yoshihito Osada, Jian Ping Gong

  SOFT MATTER 5 (9) 1879 - 1887 1744-683X 2009 [Refereed][Not invited]
   

  The friction between two like-charged polyelectrolyte gels in pure water is measured by using a normal strain-controlled rheometer with a parallel-plates geometry. The effects of normal stress, gel elasticity and sample thickness on the velocity dependence of friction between the gels are investigated. The frictional stress demonstrates strong velocity dependence (liquid-like) when the gel is soft and thick, while it demonstrates a weak or even no velocity dependence (solid-like) when the gel is rigid and thin. The former is interpreted by a combined mechanism of boundary lubrication and hydrated lubrication, wherein the thickness of the lubricating layer is velocity-independent, due to the formation of an electric double layer at the soft and repulsive interfaces. On the other hand, the latter is interpreted by a combined mechanism of boundary lubrication and elastohydrodynamic lubrication, wherein the thickness of the lubricating layer is velocity-enhanced by the water entrainment during sliding. The friction of the soft, thick sample is related to micro-contact while that of the rigid, thin sample is related to macroscopic geometric effect. This work may contribute to the science of friction between two soft and repulsive interfaces in water.
• Tear Velocity Dependence of High-Strength Double Network Gels in Comparison with Fast and Slow Relaxation Modes Observed by Scanning Microscopic Light Scattering

  Hidemitsu Furukawa, Rikimaru Kuwabara, Yoshimi Tanaka, Takayuki Kurokawa, Yang-Ho Na, Yoshihito Osada, Jian Ping Gong

  MACROMOLECULES 41 (19) 7173 - 7178 0024-9297 2008/10 [Refereed][Not invited]
   

  To investigate the mechanical strength of double network (DN) gels in a wide dynamical range, the gel solvent was replaced with viscous solvents-ethylene glycol and glycerol-and with their mixtures with water. The viscosity dependence of fracture energy in a tearing test was weak but demonstrated the existence of characteristic tear velocity for maximum fracture energy as a function of solvent viscosity. Fast and slow relaxation modes in the gels' dynamics were simultaneously observed by scanning microscopic light scattering, which reveals that the DN-gel structure stays unperturbed by the solvent change. These results implied that the solvent viscosity weakly affect the toughness and structure of the DN gels. Further, we demonstrated that the effect of solvent viscosity on the fracture energy can be incorporated into a scaled tear velocity that distributes over 6 orders of magnitude. We concluded that the viscous friction between polymer and solvent is not particularly significant for the energy dissipation of DN-gel fracture.
• Localized yielding around crack tips of double-network gels(a)

  Yoshimi Tanaka, Yasunori Kawauchi, Takayuki Kurokawa, Hidemitsu Furukawa, Takaharu Okajima, Jian Ping Gong

  MACROMOLECULAR RAPID COMMUNICATIONS 29 (18) 1514 - 1520 1022-1336 2008/09 [Refereed][Not invited]
   

  Double-network (DN) gels, a type of interpenetrating polymer network (IPN) consisting of rigid and flexible polymer components, exhibit two outstanding mechanical behaviors: yielding deformation of the entire specimen in tensile tests and quite high fracture energy in tearing tests. In this study, atomic force microscope (AFM) measurements were conducted on DN gels to determine the local Young's moduli immediately below the fracture surfaces E-f and below the usual molded surfaces E-m, and compare the local modulus with bulk Young's moduli measured before and after the yielding deformation, denoted as E-h and E-s, respectively. E-m and E-h are around 0.1 MPa; E-f and E-s, around 0.01 MPa, one order lower than the former two moduli. The order relation indicates that yielding deformation occurred locally around the crack tip of the DN gel during fracture. This supports the basic assumption of phenomenological models recently proposed to explain high fracture energy of DN gels.
• Friction of a soft hydrogel on rough solid substrates

  Taiki Tominaga, Takayuki Kurokawa, Hidemitsu Furukawa, Yoshihito Osada, Jian Ping Gong

  SOFT MATTER 4 (8) 1645 - 1652 1744-683X 2008 [Refereed][Not invited]
   

  We investigated the sliding friction between a soft hydrogel and rough and weakly adhesive solid substrates in a water environment. Polyvinyl alcohol (PVA) hydrogels of different elastic moduli and two sets of glass substrates with different contact angles to water, all of which varied in their surface roughness, were used. The friction measurement was performed by using a strain-controlled parallel-plate rheometer. With an increase in substrate roughness, the friction in the low velocity region increased slightly, while it decreased significantly above a critical velocity on a surface with a roughness larger than 1 mm. Below this critical velocity, the frictional stress changed with the glass substrate surface energy, while above this critical velocity, it was not sensitive to the glass substrate surface energy. The velocity-dependence of friction on rough surfaces is explained in terms of surface contact dynamics and is characterized by two velocities, i.e., nu(f) and nu(drainage). The former is determined by the cooperative diffusion constant of the gels, and the latter is by the surface roughness of the substrate and the normal pressure applied on the gel.
• A novel resistivity measurement technique for scaled-down Cu interconnects implemented to reliabitity-focused automobile applications

  Takayuki Kurokawa

  International Electron Devices Meeting, Iedm 2006
• 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.
• Creation of hydrogels with ultra high mechanical strength [XIII]: The necking phenomenon in double network gels

  Yasunori Kawauchi, Rikimaru Kuwabara, Hidemitsu Furukawa, Yang-Ho Na, Yoshimi Tanaka, Takayuki Kurokawa, Jian Ping Gong, Yoshihito Osada

  Polymer Preprints, Japan 55 (2) 3214 - 3215 2006 

  We have recently synthesized DN gels with ultra high mechanical strength. The DN gels consist of polyelectrolyte gels as the 1st network and neutral gels (or linear polymer) as the 2nd network. The previous research with dynamic light scattering proposed that the 1st network has inhomogeneous structure with large voids, where such voids structure is important for the strength enhancement of DN gels. When poor solvent is used to introduce much inhomogeneous structure inside DN gels, the necking phenomenon was observed in the DN gels. We think the research of this new phenomenon leads to clarify the mechanism of strength enhancement of DN gels.
• Hydrated lubrication and friction of gels - Its richness and complexity

  Jian Ping Gong, Go Kagata, Takayuki Kurokawa, Yoshihito Osada

  Polymer Preprints, Japan 55 (2) 4257 - 4259 2006 

  Biological connective tissues, such as cartilage, corneal stroma, are essentially hydrogels consisting of fibrous collagen and proteoglycans. Few are known of the surface properties of the hydrogel, although we observe fascinating tribological behavior of biological soft tissues, such as the extremely low friction between animal cartilages. We consider that the role of solvated polymer network existing in extracellular matrix as a gel state is critically important in the specific frictional behavior of cartilages. In order to elucidate the general tribological features of solvated polymer matrix, friction of various kinds of hydrogels have been investigated, and very rich and complex frictional behaviors are observed. The friction force and its dependencies on the load are quite different depending on the chemical structures of the gels, surface properties of the opposing substrates, and the measurement condition, which are totally different from those of solids. Most importantly, the coefficient of friction of gels, μ, changes in a wide range and exhibits very low values (μ ≈ 10-3 -10-5), which can not be obtained from the friction between two solid materials.
• Surface friction of endothelial cells and the effect of glycocalyx

  Chen Y.M, Tominaga T, Kurokawa T, Gong J.P, Osada Y

  Polymer Preprints, Japan 55 (1) 1904  2006 [Refereed][Not invited]
   

  We have systematically studied the frictional behavior of hydrogels, and found that polymer brushes on gel surface can dramatically reduced the surface friction of gels. Endothelial cell (EC) surface is covered by a layer of glycocalyx, with negatively charged hair-like structure. It is interesting to note that the blood cells can smoothly flow in a capillary although its diameter is about few micrometers. We hypothesize that the phenomenon correlates to surface structure and function of ECs. Studying surface friction behavior of EC is helpful for understanding the low friction mechanism observed in vessel. Here, the effect of glyocalyx on surface friction of EC was investigated. We found that removing of glyocalyx with heparinase increased the surface friction, while enhancement amount of glycocalyx with transforming growth factor-β (TGF-β ) decreased the surface friction. The results suggest that glycocalyx plays an important role in reducing surface friction of EC. 1 1
• Surface Friction of Gels [28] -The effect of surfactants on the surface friction of gels

  Kamada K, Tominaga T, Kurokawa T, Tada T, Furukawa H, Gong J.P, Osada Y

  Polymer Preprints, Japan 55 (2) 3216 - 3217 2006 [Refereed][Not invited]
   

  The effect of surfactants on the surface friction for hydrogels sliding on glass were investigated. By using various surfactants and varying their concentrations, the surface friction between gels and glass was measured. It was found that the surfactants contribute to the reduction in the surface friction between gels and glass (Fig.1). However, surfactants don't contribute to the reduction in the surface friction between glass and glass (Fig.2). We think that gels are so soft that they can change their form to be fitted with the surface of glass by loading. Thus surfactants layer is formed continuously between gels and glass, so the surface friction is reduced. On the other hand, the glass is too hard to behave like as gels (Fig.3).
• Elastic-hydrodynamic transition of gel friction

  T Kurokawa, T Tominaga, Y Katsuyama, R Kuwabara, H Furukawa, Y Osada, JP Gong

  LANGMUIR 21 (19) 8643 - 8648 0743-7463 2005/09 [Refereed][Not invited]
   

  We report the surface sliding friction of a high strength gel against a glass substrate under a normal pressure range of 0.01-2.5 MPa. The friction of the gel swollen with different viscous solvents is investigated over a wide velocity range. A velocity-viscosity conversion relationship is established. From the velocity-viscosity conversion relationship, a master curve that is characteristic to the elastic-hydrodynamic transition is observed. The results indicate that the adsorption model proposed by our previous work is valid even under a pressure up to MPa orders, which is the order of pressure that a cartilage sustains in the articular joints.
• Effect of polymer entanglement on the toughening of double network hydrogels

  H Tsukeshiba, M Huang, YH Na, T Kurokawa, R Kuwabara, Y Tanaka, H Furukawa, Y Osada, JP Gong

  JOURNAL OF PHYSICAL CHEMISTRY B 109 (34) 16304 - 16309 1520-6106 2005/09 [Refereed][Not invited]
   

  The mechanical strength of double network (DN) gels consisting of highly cross-linked poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) as the first component and linear polyacrylamide (PAAm) as the second component has been investigated by varying the molecular weight of the second polymer PAAm, M-w. The experimental results reveal that, for toughening of the DN gels, (1) M-w is one of the dominant parameters, (2) there is a critical value of M-w = 10(6) for a remarkable enhancement: (3) the fracture energy of DN gels with a M-w, larger than 101 reaches a value as high as 10(3) J/m(2). By plotting the strength of DN gels (fracture stress sigma and fracture energy G) against a characteristic parameter of c[eta]. where c is the average concentration of PAAm in the DN gels and [eta] is the intrinsic viscosity of PAAm. it is found that the dramatic increase in the mechanical strength of the DN gels occurs above the region where linear PAAm chains are entangled with each other. Thus, we conclude that the entanglement between the second component PAAm plays an important role of the toughening mechanism of DN gels. This result supports the heterogeneous model, which predicts the presence of "voids" of the first network PAMPS with a size much larger than the radius of the second polymer PAAm.
• Determination of fracture energy of high strength double network hydrogels

  Y Tanaka, R Kuwabara, YH Na, T Kurokawa, JP Gong, Y Osada

  JOURNAL OF PHYSICAL CHEMISTRY B 109 (23) 11559 - 11562 1520-6106 2005/06 [Refereed][Not invited]
   

  The fracture energy G of double network (DN) gels, consisting of poly(2-acrylamido-2-tnethylpropanesulfonic acid) (PAMPS) as the first network and poly(acrylamide) (PAAm) as the second network, was measured by the tearing test as a function of the crack velocity V. The following results were obtained: (i) The fracture energy G ranges from 10(2) to similar to 10(3) J/m(2), which is 100-1000 times larger than that of normal PAAm gels (10 J/m(2)) or PAMPS gels (10(-1) J/m(2)) with similar polymer concentrations to the DN gels. (ii) G shows weak dependence on the crack velocity V. (iii) G at a given value of V increases with decreasing of cross-linking density of the 2nd network. The measured values of G were compared with three theories that describe different mechanisms enhancing the fracture energy of soft polymeric systems. A mechanism relating to a heterogeneous structure of the DN gel is convincing for the remarkable large values of G.
• Toughening of Hydrogels with Double Network Structure

  Takayuki Kurokawa

  e-Journal of Surface Science and Nanotechnology 3 8 - 11 1348-0391 2005/02 [Not refereed][Not invited]
  
• The toughening mechanism of double-network gels and structural inhomogeneity of 1st network

  Rikimaru Kuwabara, Hidemitsu Furukawa, Yang-Ho Na, Yasunori Kawauchi, Yoshimi Tanaka, Takayuki Kurokawa, Jian Ping Gong, Yoshihito Osada

  Polymer Preprints, Japan 54 (1) 1307  2005 

  We have developed double network hydrogels with extremely high mechanical strength, which are consist of polyelectrolyte 1st network and neutral 2nd network interpenetrated with each other. From the result of DLS, we have found that the 1st network has an inhomogeneous structure with large voids in the 1st network. In this study, we investigated the structural inhomogeneity of 1st network and its effect on the mechanical strength of DN gels. The experimental results showed that the remarkable high mechanical strength of DN gels only exhibits in case of inhomogeneous structure of 1st network. The toughening mechanism of DN gels was discussed in terms of composite materials and the structural imhomogeneity.
• Creation of hydrogels with ultra high mechanical strength [XI]: Strength enhancement in double network gels by controlling inhomogeneous structure of 1st network gel

  Yasunori Kawauchi, Rikimaru Kuwabara, Hidemitsu Furukawa, Yang-Ho Na, Yoshimi Tanaka, Takayuki Kurokawa, Jian Ping Gong, Yoshihito Osada

  Polymer Preprints, Japan 54 (2) 4688 - 4689 2005 

  We have recently synthesized DN gels with ultra high mechanical strength. The DN gels consist of polyelectrolyte gels as the 1st network and neutral gels (or linear polymer) as the 2nd network. The previous research with dynamic light scattering proposed that the 1st network has inhomogeneous structure with large voids, where such voids structure is important for the strength enhancement of DN gels. In the present study, the inhomogeneous structure was altered by using poor solvent to introduce the phase-separated structure inside DN gels. It is found that there is a maximum peak of the fracture energy, depending on the degree of the inhomogeneous structure. This result suggested that the inhomogeneous structure related to the strength enhancement of DN gels has an appropriate size.
• Creation of hydrogels with ultra high mechanical strength (X) -role of the 2nd network entanglement on the toughening of double network gels (X)

  Mei Huang, Rikimaru Kuwabara, Yang-Ho Na, Hiroyuki Tsukeshiba, Yoshimi Tanaka, Takayuki Kurokawa, Hidemitsu Furukawa, Jian Ping Gong, Yoshihito Osada

  Polymer Preprints, Japan 54 (1) 868  2005
• Mechanically strong hydrogels with ultra-low frictional coefficients

  Takayuki Kurokawa

  Advanced Materials 17 (5) 535 - 538 0935-9648 2005 [Refereed][Not invited]
  
• Surface friction of gels [26] -The effect of surfactants on the surface friction of gels

  Kamada K, Tominaga T, Kurokawa T, Tada T, Furukawa H, Gong J.P, Osada Y

  Polymer Preprints, Japan 54 (2) 4666 - 4667 2005 [Refereed][Not invited]
   

  The effect of surfactants on the surface friction of gels was investigated. By using various surfactants and varying their concentrations, the surface friction of gels was measured. It was found that the surfactants also contribute to the reduction in the surface friction of gels. It is similar to the case of solid surface. The frictional behavior below critical micelle concentration (CMC) is different from that above CMC. No large reduction in the frictional stress is observed below CMC. On the other hand, the large reduction in the frictional stress is observed above CMC. The effects of the difference of hydrophilic groups and the different length of hydrophobic groups of surfactants on the surface friction of gels were also discussed.
• Structural characteristics of double network gels with extremely high mechanical strength

  Takayuki Kurokawa

  Macromolecules 37 (14) 5370 - 5374 0024-9297 2004/06 [Refereed][Not invited]
  
• Inhibitory effects of hydrogels on the adhesion, germination, and development of zoospores originating from Laminaria angustata

  Yoshinori Katsuyama, Takayuki Kurokawa, Tatsuo Kaneko, Jian Ping Gong, Yoshihito Osada, Norishige Yotsukura, Taizo Motomura

  Macromolecular Chemistry and Physics 203 (8) 163 - 169 1022-1352 2002/06/10 

  The inhibition of germination and development of zoospores originating from Laminaria angustata originated on various kinds of hydrogels is studied. The effects of the water content of the gel (the degree of swelling), the electrical nature (neutral, positive charge, negative charge), the charge density, the counterions of hydrogels on the inhibition of zoospore germination and development of gametophytes are phenomenologically investigated. Among the gels investigated, poly(acrylic acid) (PAA) gel showed a dramatic inhibition to germination, and might serve as a novel, environmentally safe inhibitor of zoospore adhesion.
• Effect of surface roughness of hydrophobic substrate on heterogeneous polymerization of hydrogels

  Mao Peng, Takayuki Kurokawa, Jian Ping Gong, Yoshihito Osada, Qiang Zheng

  Journal of Physical Chemistry B 106 (12) 3073 - 3081 1089-5647 2002/03/28 [Refereed][Not invited]
   

  Theoretical analysis predicted that a gas layer is trapped between an aqueous solution and a rough hydrophobic substrate, and that the volume of the gas increases with the hydrophobicity and the surface roughness of the substrate. The heterogeneous structure formation of hydrogel on hydrophobic substrate is explained in terms of the retardation of the radical polymerization by residual oxygen trapped at the hydrophobic surface. The polymerization of 2-acrylamide-2-methyl' 1-propanesulfonic acid (AMPS) aqueous solution on Teflon substrate is experimentally studied by using a novel real time laser sheet refraction (RT-LSR) technique, and it is elucidated that residual oxygen in the trapped gas phase obviously retarded the polymerization of AMPS on the Teflon surface and lead to the formation of heterogeneous structure of the gel. The higher the oxygen concentration, the rougher the Teflon surface, the more significant of the substrate effect, which is in agreement with the theoretical prediction.

MISC

• 新規塞栓物質としてのカチオンパイゲルの基礎的実験

  金 芝萍, 長内 俊也, 山崎 和義, 藤村 幹, 野々山 貴之, 黒川 孝幸  脳血管内治療  6-  (Suppl.)  S133  -S133  2021/11
• ハイドロキシアパタイト複合化ダブルネットワークゲル上での骨髄間葉系幹細胞の骨分化能評価

  甲斐原 拓真, 王 磊, 津田 真寿美, 野々山 貴行, 黒川 孝幸, きょう 剣萍, 岩崎 倫政, 田中 伸哉, 安田 和則  日本整形外科学会雑誌  95-  (8)  S1561  -S1561  2021/08
• 経時的応力計測可能なラメラ構造二重膜ヒドロゲルを用いたヒト関節靱帯における内部応力解析

  門間 太輔, 黒川 孝幸, 河村 太介, 瓜田 淳, 松井 雄一郎, 岩崎 倫政  日本整形外科学会雑誌  93-  (3)  S1042  -S1042  2019/03
• 経時的応力計測可能なラメラ構造二重膜ヒドロゲルを用いたヒト関節靱帯における内部応力解析

  門間 太輔, 黒川 孝幸, 河村 太介, 瓜田 淳, 松井 雄一郎, 岩崎 倫政  日本肘関節学会雑誌  26-  (1)  S4  -S4  2019/02
• 経時的応力計測可能なラメラ構造二重膜ヒドロゲルを用いたヒト関節靱帯における内部応力解析

  門間 太輔, 黒川 孝幸, 河村 太介, 瓜田 淳, 松井 雄一郎, 本谷 和俊, 岩崎 倫政  日本関節病学会誌  37-  (3)  256  -256  2018/10
• 経時的応力計測可能なラメラ構造二重膜ヒドロゲルを用いたヒト関節靱帯における内部応力解析

  門間 太輔, 黒川 孝幸, 河村 太介, 瓜田 淳, 松井 雄一郎, 岩崎 倫政  日本整形外科学会雑誌  92-  (8)  S1921  -S1921  2018/08
• 新規技術を用いた新しい研究アプローチ 高分子ハイドロゲルによる癌幹細胞へのリプログラミング誘導技術

  津田 真寿美, 鈴鹿 淳, 王 磊, 仙葉 慎吾, 油谷 幸代, 黒川 孝幸, 近江谷 克裕, 安田 和則, グン 剣萍, 田中 伸哉  日本病理学会会誌  107-  (1)  217  -217  2018/04
• 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
• ハイドロゲルを用いた癌幹細胞新規誘導法の開発

  鈴鹿 淳, 津田 真寿美, 王 磊, 仙葉 愼吾, 油谷 幸代, 黒川 孝幸, 近江谷 克裕, 安田 和則, きょう 剣萍, 田中 伸哉  生命科学系学会合同年次大会  2017年度-  [1P  -0964]  2017/12
• Tough double-network hydrogel as an artificial cartilage

  北村 信人, 黒川 孝幸, 安田 和則, グン 剣萍  整形・災害外科  60-  (11)  1409  -1415  2017/10
• 合成ハイドロゲルが誘導する軟骨分化促進機序の解明

  仙葉愼吾, 後藤佳子, 北村信人, 北村信人, 黒野定, 近江谷克裕, 津田真寿美, 津田真寿美, 黒川孝幸, 黒川孝幸, 田中伸哉, 田中伸哉, GONG Jian Ping, GONG Jian Ping, 安田和則  再生医療  16-  267  2017/02/01  [Not refereed][Not invited]
  
• 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
• PCDMEゲルの口蓋閉鎖床への応用

  金子 知生, 黒川 孝幸, 三古谷 忠, 飯田 順一郎  日本矯正歯科学会大会プログラム・抄録集  75回-  264  -264  2016/11
• 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  シンポジウム2016-  237  -237  2016/11
• 合成PAMPSゲルはタンパク質レザバーとして機能し、軟骨細胞ATDC5細胞に軟骨形成分化を誘導する(Synthetic PAMPS gel functions as protein reservoir, which induces a chondrogenic differentiation of chondrocytic ATDC5 cells)

  仙葉 愼吾, 後藤 佳子, 北村 信人, 黒野 定, 近江谷 克裕, 津田 真寿美, 黒川 孝幸, グン・チェンピン, 田中 伸哉, 安田 和則  日本生化学会大会プログラム・講演要旨集  89回-  [1T18  -405)]  2016/09
• Synthetic PAMPS gel functions as protein reservoir, which induces a chondrogenic differentiation of chondrocytic ATDC5 cells(和訳中)

  仙葉 愼吾, 後藤 佳子, 北村 信人, 黒野 定, 近江谷 克裕, 津田 真寿美, 黒川 孝幸, グン・チェンピン, 田中 伸哉, 安田 和則  日本生化学会大会プログラム・講演要旨集  89回-  [1T18  -05(1P  2016/09  [Not refereed][Not invited]
  
• ハイドロキシアパタイト複合化PAMPS/PDMAAmダブルネットワークゲル人工軟骨の関節内におけるin vivo骨接着性評価

  和田 進, 北村 信人, 野々山 貴行, 木山 竜二, 仙葉 愼吾, 小野寺 純, 横田 正司, 後藤 佳子, 比嘉 浩太郎, 黒川 孝幸, Gong Jian Ping, 安田 和則  日本整形外科学会雑誌  90-  (8)  S1598  -S1598  2016/08
• 軟骨基質高分子を複合化したダブルネットワークゲルの生体材料特性評価 軟骨再生誘導材料としての可能性

  比嘉 浩太郎, 北村 信人, 後藤 佳子, 黒川 孝幸, 和田 進, 野々山 貴行, Gong Jian Ping, 金谷 文則, 安田 和則  日本整形外科学会雑誌  90-  (8)  S1726  -S1726  2016/08  [Not refereed][Not invited]
  
• PAMPSゲルによるATDC5細胞のインスリン非依存性軟骨分化誘導シグナルの解明

  後藤 佳子, 北村 信人, 和田 進, 安田 和則, 木村 太一, 津田 真寿美, 田中 伸哉, 仙葉 慎吾, 黒川 孝幸, グン・チェンピン  北海道整形災害外科学会雑誌  57-  (2)  287  -287  2016/04
• ハイドロゲルの細胞基盤への応用,その優位性 (特集 再生医療の発展に待たれる三次元細胞培養用の培地,足場材料開発)

  柴田 優輝, 黒川 孝幸, 龔 剣萍  Material stage  15-  (11)  5  -10  2016/02
• バイオミネラリゼーションにより複合化したハイドロキシアパタイトコーティングPAMPS/PDMAAmダブルネットワークゲルの骨接着性の評価

  和田 進, 北村 信人, 野々山 貴行, 木山 竜二, 仙葉 愼吾, 比嘉 浩太郎, 黒川 孝幸, Gong Jian Ping, 安田 和則  日本整形外科学会雑誌  89-  (8)  S1585  -S1585  2015/09
• PAMPSゲルはATDC5細胞の軟骨分化においてBMP/Smadシグナル経路を活性化する

  後藤 佳子, 北村 信人, 木村 太一, 仙葉 愼吾, 黒川 孝幸, Gong Jian Ping, 田中 伸哉, 安田 和則  日本整形外科学会雑誌  89-  (8)  S1708  -S1708  2015/09
• 抗菌性ゲルのスクリーニング

  柴田優輝, 黒川孝幸, 野々山貴行, 中島祐, 相沢智康, 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  49th-  6  2015  [Not refereed][Not invited]
  
• PAMPS/PDMAAmダブルネットワークゲルが誘導する関節軟骨自然再生に対してヒアルロン酸ナトリウムの関節内投与が与える効果

  福井 孝明, 北村 信人, 横田 正司, 後藤 佳子, 安田 和則, 黒川 孝幸, ぐん 剣萍  北海道整形災害外科学会雑誌  56-  (1)  144  -144  2014/12
• ATDC5細胞におけるPAMPSゲル誘導軟骨分化特異的シグナル伝達経路の解明

  後藤佳子, 北村信人, 木村太一, 仙葉慎吾, 黒川孝幸, GONG Ping, 田中伸哉, 安田和則  日本整形外科学会雑誌  88-  (8)  S1529  -S1529  2014/08/29  [Not refereed][Not invited]
  
• 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]
  
• 2F13 Effects of double-network gel component PAMPS on chondrogenic differentiation in ATDC5 cells

  TSUCHIYA Hitoshi, MAEDA Eijiro, KUROKAWA Takayuki, GONG Jian Ping, KITAMURA Nobuto, YASUDA Kazunori, OHASHI Toshiro  バイオエンジニアリング講演会講演論文集  2014-  (26)  481  -482  2014/01/10
• J044024 High Toughness and Self-healing Properties of High Viscoelastic Hydrogel

  KUROKAWA Takayuki, SUN Taolin, IHSAN Abu Bin, GONG Jian Ping  Mechanical Engineering Congress, Japan  2013-  "J044024  -1"-"J044024-3"  2013/09/08  

  Biological soft tissues, such as tendons, ligaments, muscles, cartilages, usually contain 50-85% of water and exist in a gel-like state, exhibit high toughness and excellent mechanical properties. It has been extensively discussed in the literature that load-bearing biological materials such as bone, teeth and nacre have acquired some interesting mechanical properties, one of which is the tolerance of crack-like flaws acquired during tissue function, growth, repair and remodeling. A structure is said to be flaw tolerant if pre-existing flaws do not propagate until it ultimately fails through a uniform rupture near the theoretical strength of material. Numerous studies in the literature have addressed flaw tolerance in elastic structures, so far there has been little investigation on time-dependent, viscoelastic systems, in spite of its importance to biological materials. A central hypothesis adopted in these studies is that the load-bearing biological materials have been evolved to tolerate crack-like flaws at multiple size scales. The optimal state of a material which induces the maximum strength corresponds to a uniform distribution of stress at failure even in the presence of crack-like flaws. In this state, the material fails by uniform rupture, rather than by crack propagation. Here, We report on the roles of ionic association in polyampholyte gel, serves as reversible sacrificial bond that break and reform dynamically giving some extraordinary properties to this novel viscoelastic hydrogel in contrast to conventional elastic hydrogels, for instances, high toughness and resistance against crack propagation by forming huge blunting at the crack tip.
• Hydrogel with Unidirectional Alignment of Lamellar Bilayer : Its Structural Color and Mechanical Response

  SATO Koshiro, HAQUE Md. Anamul, KAMITA Gen, YUE YouFeng, KUROKAWA Takayuki, GONG Jian Ping  The Pigments,Paints and Printing Inks  86-  (8)  290  -294  2013/08/20  [Not refereed][Not invited]
   

  A lot of animals and plants have structural color consisted of ordered structure. Recently attempts to introduce this ordered structure into polymer are attracting extensive attention in the field of sensor. We pay attention to dodecylglyceryl itaconate (DGI) that can form periodically ordered bilayer structure in water. This review describes synthesis, anisotropic structure and mechanical properties, and stress/straininduced change in structural color of a photonic hydrogel with ordered structure consisting of DGI and acrylamide.
• PAMPS/PDMAAmダブルネットワークゲルが誘導する関節軟骨自然再生に対してヒアルロン酸ナトリウムの関節内投与が与える効果

  福井 孝明, 北村 信人, 黒川 孝幸, 横田 正司, ぐん 剣萍, 安田 和則  日本整形外科学会雑誌  87-  (8)  S1320  -S1320  2013/08
• DNゲルによるATDC5細胞の軟骨分化誘導に関する力学的機序の解明 1細胞の力学的特性の変化とアクチン修飾タンパク質発現との関連

  前田 英次郎, 堤 健博, 黒川 孝幸, 北村 信人, Gong Jian Ping, 安田 和則, 大橋 俊朗  日本整形外科学会雑誌  87-  (8)  S1408  -S1408  2013/08
• Optical and mechanical properties of a hydrogel based on lamellar bilayers

  Takayuki Kurokawa, Md. Anamul Haque, Jian Ping Gong  Kobunshi Ronbunshu  70-  (7)  309  -316  2013/07  [Not refereed][Not invited]
   

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

  Takayuki Kurokawa, Md. Anamul Haque, Jian Ping Gong  Kobunshi Ronbunshu  70-  (7)  309  -316  2013/07  [Not refereed][Not invited]
   

  In this highlight, we introduce a novel anisotropic hydrogel with a perfect ID photonic crystal structure based on the uni-axial alignment of lamellar bilayers. The polymerized lamellar bilayers were stacked periodically and entrapped in a Polyacrylamide matrix. This hydrogel shows perfect one-dimensional swelling and magnificent structural color by multilayer interference according to Bragg's law of diffraction. Owing to the softness and large deformability, the color of the gel can reversibly be tuned by compressive mechanical stimulation over the entire visible wavelength range. The single-domain lamellar bilayers not only diffract light, but also serve as reversible sacrificial 'bonds' that dissociate upon deformation, exhibiting large hysteresis as an energy dissipation mechanism. This gives the gel high tensile strength and fatigue resistance. Both the molecular dissociation and lipid-like mobile nature of DGI molecules in the bilayers dramatically enhance the resistance against crack propagation by showing an extra-ordinary blunting effect, which gives the gel very high toughness. ©2013, The Society of Polymer Science,.
• 海の生き物に学ぶ低環境負荷型抗付着材料の創製 : フジツボに対するハイドロゲルの抗付着効果

  黒川 孝幸, 龔 剣萍, 室﨑 喬之, 野方 靖行  PEN  3-  (11)  3  -8  2013/02  [Not refereed][Not invited]
   

  海辺を散歩するとフジツボ類や貝類、藻類等の岩場にへばりついて生きている生物をよく見ることができる。これら海洋付着生物は海洋資源として有用な反面、汚損生物として負の側面も持ち合わせている。例を挙げると、船底に付着する事で水の抵抗が増し船の燃費を増大させる、養殖漁網の網の目を詰まらせる事で養殖魚を窒息死させる、取水口を詰まらせる事で臨海発電所の冷却機能を低下させる等があり、海洋付着生物は世界中のあらゆる海に関わる産業に大きな経済的損失を与えている
• Double‐Networkゲル上で培養したATDC5細胞の軟骨分化メカニズム

  前田英次郎, 堤健博, 黒川孝幸, 北村信人, GONG Jian Ping, 安田和則, 大橋俊朗  バイオエンジニアリング講演会講演論文集  25th-  (25)  221  -222  2013/01/08  [Not refereed][Not invited]
  
• Hyaluronic Acid Enhances Induction Effects of Synthetic Hydrogels on Chondrogenic Differentiation of ATDC5 Cells In Vitro

  YOSHIKAWA Katsuhisa  Japanese Journal of Joint Diseases  32-  (1)  9  -15  2013  [Not refereed][Not invited]
   

  Introduction: Recently, we reported that PAMPS and PDMAAm gels induce the chondrogenic differentiation of ATDC5 cells in vitro in maintenance medium without insulin. We hypothesized that hyaluronic acid (HA) affects the in vitro induction effects of PAMPS and PDMAAm gels on the chondrogenic differentiation of ATDC5 cells, depending on the concentration. The purpose of this study was to test this hypothesis.Methods: This study consisted of three sub-studies: the first was performed to assess the fundamental effects (without HA) of the PAMPS gel, PDMAAm gel, and polystyrene dish surfaces on the chondrogenic differentiation of ATDC5 cells cultured in maintenance medium and in differentiation medium (containing insulin). The second and third sub-studies were performed to analyze the effects of HA supplementation (three concentrations) of the two media on the chondrogenic differentiation of ATDC5 cells cultured on PAMPS and PDMAAm gels, respectively. At 7 days of culture, the gene expression of cartilage markers was examined using real-time polymerase chain reaction analysis.Results: On the PAMPS gel with the maintenance medium, HA at concentrations of 0.01 and 0.10 mg/mL significantly increased the expression of Col-2 mRNA and aggrecan mRNA in comparison to those without HA. In the cells cultured in the differentiation medium, HA at a concentration of 0.01 mg/mL significantly increased mRNA expression of Col-2 and aggrecan genes in comparison to those without HA. On the PDMAAm gel with the maintenance medium, HA at a concentration of 1.00 mg/mL significantly reduced the expression of these genes in comparison to those without HA.Conclusion: Mechanical signals from each hydrogel surface significantly affect the chondrogenic differentiation of ATDC5 cells, and HA affects the mechanical signals from each hydrogel surface, depending on the concentration.
• Hydrogels as feeder-free scaffolds for long-term self-renewal of mouse induced pluripotent stem (mips) cells.

  Yang Jing Jing, Liu Jian Fang, Kurokawa Takayuki, Kitada Kazuhiro, Gong Jian Ping  Journal of Tissue Engineering and Regenerative Medicine  2012/11/20  

  Expanding undifferentiated induced pluripotent stem (iPS) cells in vitro is a basic requirement for application of iPS cells in both fundamental research and clinical regeneration. In this study, we intended to establish a simple, low cost and efficient method for the long-term self-renewal of mouse induced pluripotent stem (miPS) cells without using feeder-cells and adhesive proteins. Three scaffolds were selected for the long-term subculture of miPS cells over two months starting from passages 14 to 29: 1) a gelatin coated polystyrene (Gelatin-PS) that is a widely used scaffold for self-renewal of mouse embryonic stem (mES) cells; 2) a neutral hydrogel poly(N,N-dimethylacrylamide) (PDMAAm); and 3) a negatively charged hydrogel poly(2-acrylamido-2-methyl-propane sulfonic acid sodium salt) (PNaAMPS). Each passaged miPS cells on these scaffolds were cryopreserved successfully and the revived cells showed high viability and proliferation. The passaged miPS cells maintained a high undifferentiated state on all three scaffolds and a high level of pluripotency by expressing differentiation markers in vitro and forming teratomas in SCID mice with derivatives of all three germ layers. Compared to Gelatin-PS, the two hydrogels exhibited much better self-renewal performance in terms of high proliferation rate and level of expression of undifferentiated gene markers as well as efficiency in pluripotent teratoma formation. Furthermore, the PNaAMPS hydrogel demonstrated a slightly higher efficiency and simpler operation of cell expansion than the PDMAAm hydrogel. To conclude, PNaAMPS hydrogel is an excellent feeder-free scaffold because of its simplicity, low cost and high efficiency in expanding a large number of miPS cells in vitro. Copyright © 2012 John Wiley & Sons, Ltd.
• ヒアルロン酸はPAMPS/PDMAAmダブルネットワークゲルのATDC5細胞に対するin vitro軟骨分化誘導効果を促進する

  北村信人, 黒川孝幸, 福井孝明, 吉川勝久, GUN Tyenpin, 安田和則  日本整形外科学会雑誌  86-  (8)  S1133  -S1133  2012/08/25  [Not refereed][Not invited]
  
• 埋植されるPAMPS/PDMAAmダブルネットワークゲルシートの厚さがそのin vivo硝子軟骨再生誘導能に与える効果

  松田英敏, 北村信人, 黒川孝幸, 新垣和伸, GONG Jian Ping, 金谷文則, 安田和則  日本整形外科学会雑誌  86-  (8)  S1139  -S1139  2012/08/25  [Not refereed][Not invited]
  
• 羊膝関節の広範囲骨軟骨欠損における高機能ゲルプラグを用いたin vivo軟骨自然再生誘導

  横田 正司, 北村 信人, 新垣 和伸, 小野寺 伸, 近藤 英司, 安田 和則, 黒川 孝幸, Gong Jian Ping, きょう 剣萍  北海道整形災害外科学会雑誌  54-  (1)  81  -82  2012/08  [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
• ダブルネットワークゲルを用いた誘導によってin vivoで自然再生した軟骨組織の遺伝子発現プロファイル:正常関節軟骨との比較

  今淵隆誠, 北村信人, 小野寺伸, 近藤英司, 權赫準, 安田和則, 近江谷克裕, 黒川孝幸, GONG Jian Ping  北海道整形災害外科学会  122nd-  2  2012  [Not refereed][Not invited]
  
• 大腿脛骨関節の骨軟骨欠損に対する高機能ゲルプラグを用いた硝子軟骨自然再生誘導

  横田正司, 北村信人, 新垣和伸, 小野寺伸, 近藤英司, 黒川孝幸, GONG Jian Ping, 安田和則  日本整形外科学会雑誌  85-  (8)  S1263  -S1263  2011/08/25  [Not refereed][Not invited]
  
• PAMPS/PDMAAmダブルネットワークゲルが培養ATDC5細胞の軟骨分化に与える効果—PAMPSおよびPDMAAmゲルの効果との比較—

  北村信人, 権赫準, 近江谷克裕, 黒川孝幸, グン剣萍, 安田和則  日本整形外科学会雑誌  85-  (8)  S1264  -S1264  2011/08/25  [Not refereed][Not invited]
  
• 現代ものづくり考 ゲル--物性の研究と再生医療への応用

  黒川 孝幸, Gong Jian Ping  未来材料  11-  (8)  2  -4  2011/08  [Not refereed][Not invited]
  
• Surfactant-induced friction reduction for hydrogels in the boundary lubrication regime

  Kosuke Kamada, Hidemitsu Furukawa, Takayuki Kurokawa, Tomohiro Tada, Taiki Tominaga, Yukihiro Nakano, Jian Ping Gong  JOURNAL OF PHYSICS-CONDENSED MATTER  23-  (28)  2011/07  [Not refereed][Not invited]
   

  We studied the ability of surfactants to reduce friction by boundary lubrication for a bulk hydrogel sliding on a solid surface in an aqueous solution. A piece of negatively charged polyelectrolyte hydrogel was slid across solid surfaces with various levels of hydrophobicity, using a strain-controlled parallel-plate rheometer in water. A dramatic reduction in the sliding friction, especially in the low velocity region, was detected by the addition of a surfactant to the water medium. This friction reduction was only observed in gel-solid friction but not in solid-solid friction, indicating that the soft and wet nature of the gel surface was crucial for this surfactant-induced friction reduction. This phenomenon reveals that surfactants can remain at the gel-mated interface, thus preventing direct interfacial interaction between the sliding surfaces, and significantly decreasing the frictional stress. The reported dramatic reduction in friction highlights the frictional characteristics of soft and wet hydrogel materials.
• Robust bonding and one-step facile synthesis of tough hydrogels with desirable shape by virtue of the double network structure

  Junji Saito, Hidemitsu Furukawa, Takayuki Kurokawa, Rikimaru Kuwabara, Shinya Kuroda, Jian Hu, Yoshimi Tanaka, Jian Ping Gong, Nobuto Kitamura, Kazunori Yasuda  Polymer Chemistry  2-  (3)  575  -580  2011/03  [Not refereed][Not invited]
   

  Robust bonding of a hydrogel in aqueous environment, either to another hydrogel or to a solid, is one of the major unsolved issues for the practical applications of hydrogels in various fields. Here we report robust bonding between a pair of hydrogel sheets, containing over 90 wt% of water, by applying the double-network (DN) structure. In the optimal condition, the peeling energy of the united gel sheets reaches 1200 J m-2, which is comparable to the bulk fracture energy of a normal type of tough DN gels. This hydrogel bonding technique is also applied to form tough bonding between hydrogel and plastic plates. Furthermore, based on this technique, we have developed a facile method to synthesize robust double network hydrogels with any desirable free-shape from micro-gel precursors. These novel techniques will substantially merit the applications of the tough hydrogels in various fields, such as an artificial meniscus. © The Royal Society of Chemistry 2011.
• Ethos Fosters Serendipity

  KUROKAWA Takayuki  高分子  60-  (2)  82  -82  2011/02/01  [Not refereed][Not invited]
  
• 表面粗さをもつハイドロゲルの摩擦評価とゲル-ガラス界面の観察

  八島慎太郎, 古川英光, 黒川孝幸, 黒川孝幸, 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
• 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
• One-dimensional Swelling of an Anisotropic Hydrogel by Controlled Two-dimensional Diffusion of Water

  HAQUE Md. Anamul, MAKI Uchiumi, YOUFENG Yue, KUROKAWA Takayuki, GONG Jian Ping  高分子学会予稿集(CD-ROM)  60-  (2 Disk1)  2011
• ヒツジ膝関節の広範囲骨軟骨欠損における高機能ゲルプラグを用いたin vivo軟骨自然再生誘導

  横田正司, 北村信人, 新垣和伸, 小野寺伸, 近藤英司, 黒川孝幸, GONG Jian Ping, 安田和則  北海道整形災害外科学会  121st-  17  2011  [Not refereed][Not invited]
  
• Gene expression, glycocalyx assay, and surface properties of human endothelial cells cultured on hydrogel matrix with sulfonic moiety: Effect of elasticity of hydrogel

  Jing Jing Yang, Yong Mei Chen, Takayuki Kurokawa, Jian Ping Gong, Shin Onodera, Kazunori Yasuda  JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A  95A-  (2)  531  -542  2010/11  [Not refereed][Not invited]
   

  We measured the gene expression, glycocalyx content, and surface properties of human coronary artery endothelial cells (HCAECs) cultured on poly(sodium p-styrene sulfonate) (PNaSS) hydrogels with various levels of elasticity ranged in 3-300 kPa. We found that all HCAECs reached confluence on these hydrogels while retaining the similar expression of EC-specific markers to that on polystyrene (PS), a widely used scaffold in cell culture in vitro. Real-time polymerase chain reaction (PCR) and glycosaminoglycan (GAG) assay showed that the amount of EC-specific glycocalyx secreted by HCAECs cultured on PNaSS gels was higher than that cultured on PS, and it increased with an increase of gel elasticity. Furthermore, the HCAECs cultured on PNaSS gels showed excellent property against platelet adhesion and lower surface friction than that on PS. The platelet adhesion and surface friction of HCAECs cultured on PNaSS gels also depend on the elasticity of gels. The largest amount of EC-specific glycocalyx, excellent blood compatibility, and the lowest friction were observed when the elastic modulus of the gel was larger than 60 kPa. Overall, HCAECs cultured on these hydrogels have better properties than those cultured on PS scaffold, demonstrating the PNaSS gels can be used as potential tissue engineering material for blood vessels. (C) 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 95A: 531542, 2010.
• Study on the Sliding Friction of Endothelial Cells Cultured on Hydrogel and the Role of Glycocalyx on Friction Reduction

  Yong Mei Chen, Takayuki Kurokawa, Taiki Tominaga, Kazunori Yasuda, Yoshihito Osada, Jian Ping Gong, Kimiko Yamamoto, Joji Ando  ADVANCED ENGINEERING MATERIALS  12-  (11)  B628  -B636  2010/11  [Not refereed][Not invited]
   

  We investigate the sliding friction of HUVEC monolayers cultured on PNaSS gel, intending to elucidate the role of glycocalyx on the surface of ECs in friction reduction. Three sets of HUVEC monolayers are investigated: an as-cultured HUVEC monolayer; a HUVEC monolayer treated with TGF-beta(1), which increases the glycocalyx by 148%; and a HUVEC monolayer treated with heparinase I, which reduces the glycocalyx by 57%. When being slid on a flat, glass surface, the frictional stress of the HUVEC monolayer decreases in the order: heparinase-I-treated> as-cultured> TGF-beta(1)-treated samples. The results suggest that glycocalyx may play a role in reducing the friction of endothelial cell monolayer.
• ハイドロゲルの海洋付着生物に対する抗付着効果―2―フジツボキプリス幼生の探索行動とその着生率との関係

  小川知哉, 室崎喬之, 角五彰, 黒川孝幸, GONG Jian Ping, 野方靖行  高分子学会予稿集(CD-ROM)  59-  (2 Disk1)  ROMBUNNO.1PC131  2010/09/01  [Not refereed][Not invited]
  
• ハイドロゲルの海洋付着生物に対する抗付着効果‐1‐フジツボキプリス幼生の付着密度とそのモデル

  室崎喬之, 野口隆矢, 角五彰, 黒川孝幸, GONG Jian Ping, 野方靖行  高分子学会予稿集(CD-ROM)  59-  (2 Disk1)  ROMBUNNO.3J14  2010/09/01  [Not refereed][Not invited]
  
• PAMPSおよびPDMAAmゲルはPAMPS/PDMAAmダブルネットワークゲルと同じ関節軟骨自然再生誘導能を有するか

  小川宗宏, 北村信人, 新垣和伸, 黒川孝幸, GONG Jian Ping, 田中康仁, 高倉義典, 安田和則  日本整形外科学会雑誌  84-  (8)  S1061  -S1061  2010/08/25  [Not refereed][Not invited]
  
• ヒツジ膝関節骨軟骨欠損における高機能ダブルネットワークハイドロゲルを用いたin vivo軟骨自然再生誘導

  横田正司, 北村信人, 新垣和伸, 近藤英司, 小野寺伸, 黒川孝幸, PING Gong Jian, 安田和則  日本整形外科学会雑誌  84-  (8)  S1229  -S1229  2010/08/25  [Not refereed][Not invited]
  
• Spontaneous Redifferentiation of Dedifferentiated Human Articular Chondrocytes on Hydrogel Surfaces

  Yang Jing Jing, Chen Yong Mei, Liu Jian Fang, Kurokawa Takayuki, Gong Jian Ping  Tissue Engineering Part A  16-  (8)  2529  -2540  2010/08/05  [Not refereed][Not invited]
   

  Chondrocytes rapidly dedifferentiate into a more fibroblastic phenotype on a two-dimensional polystyrene substratum. This impedes fundamental research on these cells as well as their clinical application. This study investigated the redifferentiation behavior of dedifferentiated chondrocytes on a hydrogel substratum. Dedifferentiated normal human articular chondrocyte–knee (NHAC-kn) cells were released from the sixth-passage monolayer cultured on a polystyrene surface. These cells were then subcultured on a chemically crosslinked copolymer hydrogel, that is, poly(NaAMPS-co-DMAAm), and the cells thus obtained were used as the seventhpassage cultivation. Copolymer gels were synthesized from a negatively charged monomer, the sodium salt of 2-acrylamido-2-methyl-1-propanesulfonic acid (NaAMPS), and a neutral monomer, N,N-dimethylacrylamide (DMAAm). These gels were of different compositions because the molar fraction (F) of NaAMPS was varied (F¼0, 0.2, 0.4, 0.6, 0.8, and 1.0). The dedifferentiated NHAC-kn cells spontaneously redifferentiated to normal NHAC-kn cells on neutral (F¼0) and poly(NaAMPS-co-DMAAm) hydrogels of low charge density (F¼0.2). This was deduced from the cell morphology and expression of cartilage-specific genes and proteins. These results should enable us to establish a simple and efficient method for preparing large amounts of chondrocytes by cultivation on the surfaces of neutral and low-charge-density hydrogels.
• 高強度ダブルネットワークゲル

  黒川 孝幸, 剣萍  化学工学 = Chemical engineering  74-  (7)  338  -340  2010/07/05  [Not refereed][Not invited]
  
• 気液界面を利用したリング状微小管集合体の形成(Fabrication of ring-shaped microtubule assemblies using contact with air)

  田村 圭輝, 角五 彰, 黒川 孝幸, 壟 剣萍  日本細胞生物学会大会講演要旨集  62回-  140  -140  2010/05
• Formation of a strong hydrogel-porous solid interface via the double-network principle

  Takayuki Kurokawa, Hidemitsu Furukawa, Wei Wang, Yoshimi Tanaka, Jian Ping Gong  ACTA BIOMATERIALIA  6-  (4)  1353  -1359  2010/04  [Not refereed][Not invited]
   

  A method for binding a tough double-network (ON) hydrogel and a porous solid utilizing the double-network principle is proposed. The effects of the pore size of the solid and the structure of the DN gel in the pores on bonding strength were investigated by a peeling test. Porous solids with pore sizes of the order of several microns afforded strong gel-substrate interfaces. Under optimal conditions a bonding strength as high as similar to 1000 N m(-1) was reached. The results obtained were compared with the strength of the bulk DN gel, and discussed in terms of the double-network principle at the bonding interface. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
• 大荷重下におけるDNゲルの保水力評価

  渡鍋貴仁, 黒川孝幸, 田中良巳, 古川英光, GONG Jang Ping  高分子ゲル研究討論会講演要旨集  21st-  2010
• 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
• 圧力に対するDNゲルの保水能評価

  渡鍋貴仁, 田中良巳, 黒川孝幸, 古川英光, 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  44th-  2010
• イオン結合を有した高粘性,自己回復ゲルの創製

  黒田慎也, 黒川孝幸, 古川英光, 郁秋明, 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  44th-  2010
• 共焦点レーザ顕微鏡を用いたハイドロゲル-ガラス界面の3次元イメージング

  八島慎太郎, 古川英光, 黒川孝幸, 黒川孝幸, 角五彰, 角五彰, PING Jian  高分子学会予稿集(CD-ROM)  59-  (1 Disk1)  2010
• 準剛直高分子電解質を用いた配向ハイドロゲルの創製

  澤田大輔, 呉子良, 楊薇, 古川英光, 黒川孝幸, 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  44th-  2010
• ハイドロゲルの表面摩擦~共焦点レーザ顕微鏡を用いたソフト界面の直接観察~

  八島慎太郎, 古川英光, 黒川孝幸, 黒川孝幸, 角五彰, 角五彰, GONG Jian Ping  高分子学会予稿集(CD-ROM)  59-  (2 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
• 海洋中でのフジツボに対するゲルの付着阻害効果とそのメカニズム

  室崎喬之, 野口隆矢, 角五彰, 黒川孝幸, 古川英光, GONG Jiang Pin, 長田義仁, 野方靖行, 松村清隆, 伏谷伸宏  高分子学会予稿集(CD-ROM)  58-  (2 Disk1)  ROMBUNNO.3L2-14  2009/09/01  [Not refereed][Not invited]
  
• 家兎膝関節骨軟骨欠損における高機能ダブルネットワークゲルを用いたin vivo軟骨自然再生誘導

  北村信人, 新垣和伸, 黒川孝幸, GONG Jian Ping, 長田義仁, 安田和則  日本整形外科学会雑誌  83-  (8)  S1195  -S1195  2009/08/25  [Not refereed][Not invited]
  
• 摩擦界面の直接観察によるゲルの摩擦メカニズムの解明

  太田優子, 古川英光, 武富直之, 富永大輝, 黒川孝幸, 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-  20  2009/02/03  [Not refereed][Not invited]
  
• DNゲルの力学物性における水の役割

  板垣裕子, 黒川孝幸, 古川英光, 田中良巳, GONG Jian Ping, 勝本之晶  高分子ゲル研究討論会講演要旨集  20th-  2009
• ハイスループットスクリーニングを目的としたDNゲル合成システムの構築

  大井彰, 黒川孝幸, 古川英光, GONG Jiang Ping  高分子ゲル研究討論会講演要旨集  20th-  2009
• 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
• ゲル-固体界面の接着~DN構造形成によるゲル-固体界面の高強度接着~

  桜井翔太, 王蔚, 黒川孝幸, 古川英光, 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
• DNゲルの表面摩擦におけるHAの潤滑効果~関節並みの高荷重において~

  中野征洋, 黒川孝幸, 古川英光, 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
• 自由成型可能な高強度DNゲルのハイスピード合成

  黒田慎也, 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
• 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
• 準剛直高分子電解質の階層的構造形成によるハイドロゲルの機能化-異方性を導入した超延伸性ダブルネットワークゲルの創製

  澤田大輔, 古川英光, YANG Weig, WU Ziliang, 黒川孝幸, GONG Jian Ping  高分子学会予稿集(CD-ROM)  58-  (1 Disk1)  2009
• ゲルのハイスループットスクリーニング法の構築

  大井彰, 古橋由梨, 黒川孝幸, 古川英光, GONG Jiang Ping, 山田幸司  高分子学会予稿集(CD-ROM)  58-  (1 Disk1)  2009
• 高強度Double-Networkゲルにおける水の役割

  黒川孝幸, 板垣裕子, 古川英光, 田中良巳, GONG Jian Ping  繊維学会予稿集  64-  (1)  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
• イオン性結合を有した新規高粘性ゲルの創製

  黒田慎也, 黒川孝幸, 黒川孝幸, 古川英光, 古川英光, YU Qiu Ming, GONG Jian Ping  高分子学会予稿集(CD-ROM)  58-  (2 Disk1)  2009
• ゲルのハイスループットスクリーニング法の構築

  大井彰, 古橋由梨, 黒川孝幸, 黒川孝幸, 古川英光, 古川英光, GONG Jiang Ping, 山田幸司  高分子学会予稿集(CD-ROM)  58-  (2 Disk1)  2009
• 超高強度Double Networkゲルの力学物性に及ぼす水の影響

  板垣裕子, 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
• 自己修復型イオン結合性ハイドロゲルの創製

  黒田慎也, 黒川孝幸, 古川英光, GONG Jian Ping  高分子学会予稿集(CD-ROM)  58-  (1 Disk1)  2009
• 構造規則性ハイドロゲルの自己修復機能-秩序・無秩序転移によるsacrificial bondの効果

  白倉悠平, 古川英光, 田中良巳, 黒川孝幸, 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
• 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
• Ultrathin tough double network hydrogels showing adjustable muscle-like isometric force generation triggered by solvent

  Songmiao Liang, Qiu Ming Yu, Haiyan Yin, Zi Liang Wu, Takayuki Kurokawa, Jian Ping Gong  CHEMICAL COMMUNICATIONS  2009-  (48)  7518  -7520  2009  [Not refereed][Not invited]
   

  Ultrathin double-network hydrogels, which have super-high toughness under micro-scale thickness (elastic elongation epsilon(b) > 1000%, tensile strength sigma(b) > 2 MPa and tearing energy G similar to B 600 J m(-2)), and solvent-triggered fast and high isometric stress generation, were synthesized by coupling the salt-controlled swelling process and polymer chain pre-reinforced technique.
• Friction properties of polymer gel with high mechanical strength

  島津 英一郎, 江上 正樹, 黒川 孝幸  NTN technical review  (76)  45  -50  2008/10  [Not refereed][Not invited]
  
• ゲルの表面摩擦‐摩擦界面の直接観察による基盤の親・疎水性効果の解明

  太田優子, 古川英光, 武富直之, 富永大輝, 黒川孝幸, GONG Jian Ping  高分子学会予稿集(CD-ROM)  57-  (2 Disk1)  2I02  2008/09/09  [Not refereed][Not invited]
  
• ゲルの表面摩擦におけるHAの潤滑効果 II~関節並みの高荷重において~

  中野征洋, 富永大輝, 黒川孝幸, 古川英光, GONG Jian Ping  高分子学会予稿集(CD-ROM)  57-  (2 Disk1)  3J01  2008/09/09  [Not refereed][Not invited]
  
• 血管内皮細胞の摩擦抵抗低減ゲル

  陳 咏梅, 楊 晶晶, 黒川 孝幸, 長田 義仁, きょう 剣萍  日本バイオレオロジー学会年会抄録集  31回-  37  -37  2008/06
• 血管内皮細胞とゲル間の摩擦挙動―中性ゲル架橋密度の影響

  CHEN Yong Mei, 黒川孝幸, 富永大輝, GONG Jian Ping, 田中賢, 山本貞明, 安田和則, 下村政嗣, 長田義仁  高分子ゲル研究討論会講演要旨集  19th-  27  -28  2008/01/09  [Not refereed][Not invited]
  
• 超高強度ゲルの創製XVIII]:DNゲルの力学物性に及ぼす水の効果

  板垣裕子, 黒川孝幸, 古川英光, 田中良巳, GONG Jian Ping  高分子学会予稿集(CD-ROM)  57-  (1 Disk1)  2008
• 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
• ゲル薄膜の破壊

  阿部広幸, 田中良巳, 黒川孝幸, 古川英光, GONG Jian Ping  高分子ゲル研究討論会講演要旨集  19th-  2008
• 超高強度ゲルの創製(XX)DNゲルのダメージゾーンの直接観察

  YU Qiuming, 田中良巳, 古川英光, 黒川孝幸, GONG Jianping  高分子学会予稿集(CD-ROM)  57-  (2 Disk1)  2008
• 超高強度ゲルの創製[XIX]-自由水と結合水が力学物性に与える影響

  板垣裕子, 黒川孝幸, 古川英光, 田中良巳, GONG Jian Ping, 勝本之晶  高分子学会予稿集(CD-ROM)  57-  (2 Disk1)  2008
• 自由成型可能な高強度DNゲルのハイスピード合成

  黒田慎也, 黒川孝幸, 古川英光, 田中良巳, GONG Jian Ping  高分子学会予稿集(CD-ROM)  57-  (2 Disk1)  2008
• 構造規則性ハイドロゲルの自己修復機能-秩序・無秩序転移によるsacrificial bondの効果

  白倉悠平, 古川英光, 田中良巳, 黒川孝幸, GONG Jang Ping, 長田義仁  高分子学会予稿集(CD-ROM)  57-  (2 Disk1)  2008
• ゲルの表面摩擦におけるHAの潤滑効果 II~関節並みの高荷重において~

  中野征洋, 富永大輝, 黒川孝幸, 古川英光, GONG Jian Ping  レオロジー討論会講演要旨集  56th-  330  -331  2008  [Not refereed][Not invited]
  
• 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.
• 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.
• 血管内皮細胞とゲル間での低摩擦挙動

  CHEN Yong Mei, 黒川孝幸, 富永大輝, GONG Jian Ping, 田中賢, 安田和則, 長田義仁  高分子学会予稿集(CD-ROM)  56-  (2 Disk1)  3U06  2007/09/04  [Not refereed][Not invited]
  
• ゲル上で培養した血管内皮細胞の表面特性解析

  CHEN Y M, 村椿絵美, 田中賢, 黒川孝幸, 富永大輝, GONG J P, 安田和則, 長田義仁  日本バイオレオロジー学会年会プログラム・抄録集  30th-  22  2007/06/06  [Not refereed][Not invited]
  
• ゲルの表面摩擦におけるヒアルロン酸の潤滑効果

  中野征洋, 杜すい, 富永大輝, 黒川孝幸, 古川英光, GONG J.P, 長田義仁  日本バイオレオロジー学会年会プログラム・抄録集  30th-  39  2007/06/06  [Not refereed][Not invited]
  
• ゲルの表面摩擦[31]ヒアルロン酸の潤滑効果

  中野征洋, DU Miao, 富永大輝, 黒川孝幸, 古川英光, GONG Jian Ping, 長田義仁  高分子学会予稿集(CD-ROM)  56-  (1 Disk1)  1PG093  2007/05/10  [Not refereed][Not invited]
  
• 内皮細胞の表面糖衣の摩擦低減効果

  CHEN Yong Mei, 黒川孝幸, 富永大輝, GONG Jian Ping, 田中賢, 安田和則, 長田義仁  高分子学会予稿集(CD-ROM)  56-  (1 Disk1)  3PD178  2007/05/10  [Not refereed][Not invited]
  
• ゲルの表面摩擦[30]流体潤滑膜形成メカニズム

  武富直之, 富永大輝, 黒川孝幸, DU Miao, 古川英光, GONG Jian Ping, 長田義仁  高分子学会予稿集(CD-ROM)  56-  (1 Disk1)  1PH092  2007/05/10  [Not refereed][Not invited]
  
• 20pPSA-43 Gel-gel Adhesion by Double Network Structure

  Saito J, Furukawa H, Tanaka Y, Kuwabara R, Kurokawa T, Gong J.P, Osada Y  Meeting abstracts of the Physical Society of Japan  62-  (1)  366  -366  2007/02/28  [Not refereed][Not invited]
  
• 20pPSA-44 Soft & Wet Matter With Ultra Toughness (2) : Necking Phenomenon in DN gels

  Kawauchi Yasunori, Tanaka Yoshimi, Furukawa Hidemitsu, Okajima Takaharu, Na Yang-Ho, Kurokawa Takayuki, Gong Jian Ping, Osada Yoshihito  Meeting abstracts of the Physical Society of Japan  62-  (1)  366  -366  2007/02/28  [Not refereed][Not invited]
  
• 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]
  
• ゲルの表面摩擦における潤滑層形成メカニズム

  武富直之, 富永大輝, 黒川孝幸, 杜びょう, 古川英光, 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-  25  2007/02/06  [Not refereed][Not invited]
  
• ゲル-固体界面の接着[I]~DN構造形成によるゲル-固体界面の高強度接着

  WANG Wei, 黒川孝幸, 古川英光, GONG Jian Ping, 長田義仁  高分子学会予稿集(CD-ROM)  56-  (2 Disk1)  2007
• 超高強度ゲルの創製[XV]DNゲルのNecking現象と破壊メカニズム

  川内保範, 田中良巳, 古川英光, 岡嶋孝治, NA Yang-ho, 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
• DNゲルのハイスループットスクリーニング法の構築

  大井彰, 黒川孝幸, 古川英光, 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
• 軟骨に匹敵する高強度・低摩擦ゲルの大荷重下での摩擦・潤滑挙動

  黒川孝幸, 古川英光, GONG J.P., 長田義仁  日本バイオレオロジー学会年会プログラム・抄録集  30th-  2007
• ダブルネットワーク構造形成によるゲル-ゲル界面の接着

  斉藤潤二, 桑原力丸, 田中良巳, 黒川孝幸, 古川英光, 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[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
• Double Network構造形成によるゲル-ゲル界面の強力接着

  古川英光, 斉藤潤二, 桑原力丸, 黒川孝幸, GONG Jian Ping, 田中良巳, 長田義仁  ポリマー材料フォーラム講演予稿集  16th-  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
• 軟骨に匹敵する高強度・低摩擦ゲルの大荷重下での摩擦・潤滑挙動

  黒川孝幸, 古川英光, きょう剣萍, 長田義仁  ポリマー材料フォーラム講演予稿集  16th-  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
• ゲルの表面摩擦[28]―ゲルの摩擦に及ぼす界面活性剤の効果―

  鎌田晃輔, 富永大輝, 黒川孝幸, 多田朋弘, 古川英光, GONG Jian Ping, 長田義仁  高分子学会予稿集(CD-ROM)  55-  (2 Disk1)  2PA061  2006/09/05  [Not refereed][Not invited]
  
• 血管内皮細胞の表面摩擦とglycocalyxによる摩擦低減効果

  CHEN Yong Mei, 黒川孝幸, 富永大輝, GONG Jian Ping, 安田和則, 長田義仁  コロイドおよび界面化学討論会講演要旨集  59th-  238  2006/08/30  [Not refereed][Not invited]
  
• 血管内皮細胞の表面摩擦とglycocalyxによる摩擦低減効果

  CHEN Yong Mei, 富永大輝, 黒川孝幸, GONG Jian Ping, 長田義仁  高分子学会予稿集(CD-ROM)  55-  (1 Disk1)  3H01  2006/05/10  [Not refereed][Not invited]
  
• 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
• 超高強度ゲルの創製[XIII]Double NetworkゲルのNecking現象

  川内保範, NA Yang-Ho, 桑原力丸, 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
• ゲルの表面摩擦における潤滑膜形成

  武富直之, 富永大輝, 黒川孝幸, 杜みょう, 古川英光, GONG J.P, 長田義仁  バイオトライボロジシンポジウム  26th-  12  2006  [Not refereed][Not invited]
  
• ゲルの表面摩擦に及ぼす界面活性剤の効果

  鎌田晃輔, 富永大輝, 黒川孝幸, 多田朋弘, 古川英光, GONG J.P, 長田義仁  バイオトライボロジシンポジウム  26th-  13  2006  [Not refereed][Not invited]
  
• ゲルの表面摩擦[26]‐ゲルの摩擦に及ぼす界面活性剤の効果‐

  鎌田晃輔, 富永大輝, 黒川孝幸, 多田朋弘, 古川英光, GONG Jian Ping, 長田義仁  高分子学会予稿集(CD-ROM)  54-  (2 Disk1)  1T03  2005/09/05  [Not refereed][Not invited]
  
• 超高強度ゲルの創製[XI]Double Networkゲルにおける1st Networkの不均一構造制御と高強度化

  川内保範, 桑原力丸, 古川英光, NA Yang-Ho, 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)  54-  (2 Disk1)  2005
• 超高強度ゲルの不均一構造と高強度化メカニズム

  NA Y-H, 桑原力丸, 黒川孝幸, 田中良巳, 古川英光, 柴山充弘, GONG J P, 長田義仁  高分子ゲル研究討論会講演要旨集  16th-  2005
• 超高強度ゲルの創製(IX)-Double Networkゲルの高強度発現メカニズムと1^stnetworkの構造不均一性-

  桑原力丸, 古川英光, NA Yang-Ho, 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)  54-  (1 Disk1)  2005
• 超高強度ゲルの創製(VII)ゲルの不均一構造と高強度化メカニズム

  NA Y-H, 黒川孝幸, 附柴裕之, 田中良巳, 古川英光, 柴山充弘, GONG J P, 長田義仁  高分子学会予稿集(CD-ROM)  53-  (2 Disk1)  2004
• ゲルの表面摩擦特性[24]-溶媒粘性による網目運動制御-

  黒川孝幸, 古川英光, GONG J P, 長田義仁  高分子学会予稿集(CD-ROM)  53-  (2 Disk1)  2004
• ソフト&ウエットマターの界面運動から探る生体運動の秘密(ソフトマターの物理学2003-普遍性と多様性-,研究会報告)

  〓 剣萍, 加々田 剛, 黒川 孝幸, 長田 義仁  物性研究  81-  (2)  198  -199  2003/11/20  [Not refereed][Not invited]
   

  この論文は国立情報学研究所の電子図書館事業により電子化されました。
• ゲルの表面摩擦特性 [21]‐静止摩擦に及ぼす表面緩和の効果‐

  富永大輝, 加々田剛, 黒川孝幸, GONG J P, 長田義仁  高分子学会予稿集  52-  (9)  1913  -1914  2003/09/10  [Not refereed][Not invited]
  
• Double-network hydrogels with extremely high mechanical strength

  JP Gong, Y Katsuyama, T Kurokawa, Y Osada  ADVANCED MATERIALS  15-  (14)  1155  -+  2003/07  [Not refereed][Not invited]
   

  Very strong hydrogels (with a fracture strength of some tens of MPa), as required for both industrial and biomedical applications, have been generated by inducing a double-network (DN) structure for various combinations of hydrophilic polymers. The Figure shows a hydrogel before, during, and after application of a fracture stress of 17.2 MPa.
• ゲルの表面摩擦特性 XVII-動的粘弾性測定によるゲル表面摩擦挙動の評価-

  富永大輝, 黒川孝幸, 加々田剛, GONG J P, 長田義仁  高分子学会予稿集  52-  (3)  525  2003/05/08  [Not refereed][Not invited]
  
• Substrate effect on topographical, elastic, and frictional properties of hydrogels

  T Kurokawa, JP Gong, Y Osada  MACROMOLECULES  35-  (21)  8161  -8166  2002/10  [Not refereed][Not invited]
   

  Cross-linked poly(N,N'-dimethyl acrylamide) hydrogels were prepared on hydrophilic silicon substrates or hydrophobic polystyrene substrates and their topographical elastic properties were investigated by atomic force microscopy (AFM). The gels prepared on the hydrophobic substrate have a much rougher surface morphology with a lower surface elastic modulus than those prepared on the hydrophilic substrate. The topographical and mechanical properties of the gel have little influence on the surface friction, and the lower surface friction observed for the gel prepared on the hydrophobic substrate was attributed to the presence of dangling free polymer chains formed in the course of the polymerization.
• Inhibitory effects of hydrogels on the adhesion, germination, and development of zoospores originating from Laminaria angustata

  Y Katsuyama, T Kurokawa, T Kaneko, JP Gong, Y Osada, N Yotsukura, T Motomura  MACROMOLECULAR BIOSCIENCE  2-  (4)  163  -169  2002/05  [Not refereed][Not invited]
   

  The inhibition of germination and development of zoospores originating from Laminaria angustata originated on various kinds of hydrogels is studied. The effects of the water content of the gel (the degree of swelling) the electrical nature (neural, positive charge, negative charge), the charge density, the counterions of hydrogels on the inhibition of zoospore germination and development of gametophytes are phenomenologically investigated. Among the gels investigated poly(acrylic acid) (PAA) gel showed a dramatic inhibition to germination, and might serve as a novel, environmentally safe inhibitor of zoospore adhesion.
• Effect of surface roughness of hydrophobic substrate on heterogeneous polymerization of hydrogels

  M Peng, T Kurokawa, JP Gong, Y Osada, Q Zheng  JOURNAL OF PHYSICAL CHEMISTRY B  106-  (12)  3073  -3081  2002/03  [Not refereed][Not invited]
   

  Theoretical analysis predicted that a gas layer is trapped between an aqueous solution and a rough hydrophobic substrate, and that the volume of the gas increases with the hydrophobicity and the surface roughness of the substrate. The heterogeneous structure formation of hydrogel on hydrophobic substrate is explained in terms of the retardation of the radical polymerization by residual oxygen trapped at the hydrophobic surface. The polymerization of 2-acrylamide-2-methyl-1-propanesulfonic acid (AMPS) aqueous solution on Teflon substrate is experimentally studied by using a novel real time laser sheet refraction (RT-LSR) technique, and it is elucidated that residual oxygen in the trapped gas phase obviously retarded the polymerization of AMPS on the Teflon surface and lead to the formation of heterogeneous structure of the gel. The higher the oxygen concentration, the rougher the Teflon surface, the more significant of the substrate effect, which is in agreement with the theoretical prediction.
• Surface of Gel as the Extremely Low Friction Material

  KUROKAWA Takayuki, GONG Jian Ping, OSADA Yoshihito  Oleoscience : Journal of Japan Oil Chemists' Society  1-  (9)  929  -934  2001/09/01  [Not refereed][Not invited]
  
• Synthesis of hydrogels with extremely low surface friction

  JP Gong, T Kurokawa, T Narita, G Kagata, Y Osada, G Nishimura, M Kinjo  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY  123-  (23)  5582  -5583  2001/06  [Not refereed][Not invited]
  
• Surface of Gel as the Extremely Low Friction Material

  KUROKAWA Takayuki, GONG Jian Ping, OSADA Yoshihito  Oleoscience  1-  (9)  929  -934,926  2001  [Not refereed][Not invited]
   

  Living organisms can move pliant and smoothly with extremely low frictional coefficients despite of that they have no bearing system. If the mechanism of low friction in the living organism is clarified, one can build up biomimetic machine systems. We have found that the frictional behaviors of hydrogel are totally different from those of soled materials exhibiting frictional coefficient as low as 10<SUP>-3</SUP>.

Books etc

• トコトンやさしいバイオミメティクスの本 (今日からモノ知りシリーズ)

  下村 政嗣, 高分子学会バイオミメティクス研究会 (Contributor滑らかに動く関節の構造)
  日刊工業新聞社 2016/03 (ISBN: 4526075272) 160
• 生物模倣技術と新材料･新製品開発への応用

  岡崎 春香, 中島 祐, 黒川 孝幸, グン 剣萍 (Contributor第6章第1節 生体のもつ精緻な階層構造を模倣したゲルの作成とその人工軟骨、再生医療への応用)
  技術情報協会 2014/07
• IGI Global

  Md. Anamul Haque, Takayuki Kurokawa, Jian Ping Gong (ContributorChapter 4. Tough Bacterial Nanocellulose Hydrogels Based on the Double-Network Technique)
  CRC Press 2012/12
• Technological Advancements in Biomedicine for Healthcare Applications

  Jing Jing Yang, Jian Fang Liu, Takayuki Kurokawa, Nobuto Kitamura, Kazunori Yasuda, Jian Ping Gong (Contributor)
  IGI Global 2012/10

Presentations

• Bio-Inspired Strategies for Enhancing Underwater Adhesion: Lessons from Aquatic Organisms  [Invited]

  Takayuki Kurokawa

  36th International Microprocesses and Nanotechnology Conference (MNC 2023)  2023/11
• 生物に近い材料「ハイドロゲル」の活用

  黒川孝幸

  超異分野学会 北海道フォーラム2022  2022/11  札幌市
• 低エネルギーで実現する海上農園

  黒川孝幸

  マリンテックグランプリ2022  2022/10  東京都
• 高分子ゲルの表面摩擦

  黒川孝幸

  高分子学会高分子表面研究会  2021/11
• ハイドロゲル表面摩擦のダイナミクス

  黒川孝幸

  第10回 CSJ化学フェスタ  2020/10
• 高分子ゲル研究のチュートリアル

  黒川孝幸

  第69回高分子討論会  2020/09
• 高分子ゲルの摩擦

  黒川 孝幸

  第69回高分子学会年次大会  2020/05
• ドナン電位測定による電解質ゲルの活量評価

  黒川孝幸

  日本分析化学会第６８年会  2019/09
• 高分子ゲルの摩擦挙動に影響をおよぼす階層的要因

  34th Summer University in Hokkaido＆北海道高分子若手研究会  2019/08
• Activity Measurement of Polyelectrolyte in Hydrogels by Microelectrode Technique

  Takayuki Kurokawa

  International Congress on Pure & Applied Chemistry (ICPAC Yangon 2019)  2019/08
• Effect of Inhomogeneous Compliance induced by Fiber Orientation in Polyampholyte Hydrogel on Adhesion in Water

  Takayuki Kurokawa

  INTERNATIONAL CONGRESS ON PURE & APPLIED CHEMISTRY (ICPAC) 2018
• Microelectrode technique for measuring electric potential of polyelectrolyte hydrogels

  Takayuki Kurokawa

  MIRAI Scientific Session – MATERIALS SCIENCE
• Effect of Anisotropic compliance on Adhesion in Water

  Takayuki Kurokawa

  First International Conference on 4D Materials and Systems (M01 Gel Symposium 2018)
• 生物に学ぶ水中吸着の工夫

  黒川孝幸

  九州地区高分子若手研究会・夏の講演会  2018/06
• Effect of Fibrous Skeleton in Polyampholyte Hydrogel on Adhesion in Water

  Takayuki Kurokawa

  MIRAI Materials Science Workshop 2018 Spring
• Effect of Fibrous Skeleton in Polyampholyte Hydrogel on Adhesion in Water

  Takayuki Kurokawa

  2018 Meeting of the Adhesion Society & WCARP 6  2018/02
• ネットワーク形成制御によるゲル材料特性の自在制御

  黒川孝幸

  第30回アイオノマーシンポジウム in 千葉  2017/11
• ハイドロゲルの潤滑におけるリンクル表面形状の効果

  黒川孝幸

  第65回レオロジー討論会  2017/10
• Effect of Fibrous Skeleton in Polyampholyte Hydrogel on Adhesion in Water

  Takayuki Kurokawa

  IPC2016 (The 11th SPSJ International Polymer Conference)  2016/12
• Effect of Fibrous Skeleton at Clingfish Suction Pad

  Takayuki Kurokawa

  5th Nagoya Biomimetics International Symposium (NaBIS)  2016/10
• ハイドロゲルの表面摩擦に及ぼす静電相互作用の効果

  黒川孝幸

  第67回コロイドおよび界面化学討論会  2016/09
• 水棲生物に学ぶ粘着表面設計

  黒川孝幸

  日本化学会 第96春季年会（2016）  2016/03
• ウバウオ吸盤に見られる繊維構造の吸着に及ぼす効果

  黒川孝幸

  知の協奏を目指すソフトおよびナノマテリアル研究会2016
• ツイーターイオンゲルのpHによる摩擦制御

  黒川孝幸

  知の協奏を目指すソフトおよびナノマテリアル研究会2016
• ハイドロゲルの表面摩擦特性  [Invited]

  黒川孝幸

  第64回高分子学会年次大会  2015/05
• 自己修復する高靱性ゲル

  黒川孝幸

  第4回CSJ化学フェスタ  2014/10
• 再生医療に応用可能な機能性ゲルの創製

  黒川孝幸

  大阪工研協会 第93回ニューフロンティア材料部会例会  2014/07
• 水系ラジカル共重合による強靱な自己修復ゲルの力学物性

  黒川孝幸

  日本ゴム協会2014年年次大会  2014/05

Association Memberships

• 高分子学会   日本MRS   日本レオロジー学会   高分子ゲル研究会   日本分析化学会   

Research Projects

• Regulation of genome by hydrogel: Spatial analysis of reprogramming of cancer stem cells towards development of therapeutic drugs

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

  Date (from‐to) : 2024/04 -2029/03 

  Author : 田中 伸哉, 津田 真寿美, 黒川 孝幸, 丸山 玲緒, 加藤 達哉
• 消化器内視鏡治療技術におけるアルギン酸ハイドロゲルの応用

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2023/04 -2026/03 

  Author : 山本 桂子, 黒川 孝幸, 渡邊 祐介
• ゲル化されたMSC由来エクソソームの内視鏡的粘膜下層剥離術後食道狭窄に対する効果

  日本学術振興会：科学研究費助成事業 基盤研究(C)

  Date (from‐to) : 2022/04 -2025/03 

  Author : 小野 尚子, 大西 俊介, 黒川 孝幸, 大野 正芳
• Reprogramming of cancer stem cells by high-function hydrogels creates basis to establish novel cancer therapy

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

  Date (from‐to) : 2019/04 -2024/03 

  Author : 田中 伸哉, 津田 真寿美, 高阪 真路, 黒川 孝幸, 前仲 勝実

   

  （研究の骨格）本研究は、研究代表者が高機能ポリマーハイドロゲルを用いることで、極めて短時間にがん細胞のリプログラミングを誘導して、がん幹細胞を同定する方法を見出したことにはじまる。これは従来のがん幹細胞分離同定法とは異なり、がんの種類を問わず24時間以内にがん幹細胞を同定することができる画期的な方法であり、本研究では、この高機能ゲルのどのような物理学的因子ががん細胞の遺伝子発現変化を短時間で誘導するのかについて検討し、高機能ゲルを基盤としたがん幹細胞診断法を開発し、さらにがん幹細胞標的治療薬を大規模スクリーニングにより創出するものである。 （具体的な実績）申請書においてR2年度は２つの目標を設定した。1番目は「がん細胞リプログラミングを誘導する物理的因子の解明と臓器別人工がん幹細胞ニッシェの開発」である。研究代表者らは高機能ゲルの中でも、ダブルネットワークゲル（DNゲル）の構成成分であるpoly-2-acrylamido- 2-methylpropanesulfonic acid (PAMPS) ゲルに着目し、弾性率や荷電状態を変化させることで最も効率的にがん幹細胞性を誘導させ得る条件を明らかにした（論文作成中）。また、２つ目の目標である「高機能ゲルによるエピジェネティカルなゲノム制御機構（メカノメモリー）の探索」は、poly N-(carboxymethl)-N, N-dimethyl-2-(methacryloyloxy) ethanaminium (PCDME)ゲル上で培養したがん細胞を通常培養皿に移して一定時間培養すると幹細胞性が亢進したことから、PCDMEゲルによるがん細胞のリプログラミングの過程でエピゲノムの変化が誘導されることが明らかとなった。
• Fabrication of Soft Photonic Crystals for Novel Functions

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

  Date (from‐to) : 2017/06 -2022/03 

  Author : Gong Jian Ping

   

  Hydrogels with lamellar structure consisting of stacking of lipid bilayer and neutral gel layer were developed from one-pot polymerization from mixture of polymerizable lipid monomer and neutral monomer. By applying shear flow to the precursor monomer solution above a critical shear rate, the orientation of lamellar can be uniaxially aligned both in sheet or in multi-cylindrical shape. These gels could be classified as soft crystal because they possess crystal-like photonic structure while maintain soft and flexible feature. These gels show unique properties such as structural color, anisotropic swelling and diffusion, anisotropic mechanical properties. The structure color of sheet-shape gel is angle-dependent while that of multi-cylindrical gel is angle-independent. Moreover, the bilayers serve as reversible sacrificial structure to tough the material. Such multi-functional hydrogels have promising applications.
• 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。
• Development of visible particle embolic material used by new concept hydrogel

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

  Date (from‐to) : 2017/04 -2020/03 

  Author : Osanai Toshiya

   

  In this study, we successfully developed a DN gel with X-ray visibility. We used a DN gel composed of poly (N,N'-dimethylacrylamide) and poly (2-acrylamido-2-methylpropanesulfonis acid) as the basic material and prepared DN particles using tantalum (Ta) powder via two-step suspension radical polymerization. The characteristics of the DN particles were evaluated by comparing them with Embosphere, an existing embolization particle material. Furthermore, we used a rat carotid artery embolic model to evaluate the material’s X-ray CT visibility in an in vivo study. We developed a DN gel particle with X-ray computed tomography (CT) visibility by mixing it with Ta powder. This embolization material was visible in X-ray CT scans and safe for use in the body. Moreover, as it remained in the vessels for a long time, it is expected to be more effective than Embosphere®. Thus, the developed material is a promising DN particle embolization material with X-ray CT visibility.
• 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 Grant-in-Aid for Scientific Research (A)

  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。
• 多機能ゲルによる関節軟骨自然再生誘導法の最適化に関わる機序の解明と制御

  日本学術振興会：科学研究費助成事業 基盤研究(B)

  Date (from‐to) : 2015/04 -2018/03 

  Author : 北村 信人, グン 剣萍, 津田 真寿美, 黒川 孝幸, 仙葉 愼吾

   

  軟骨基質高分子であるコンドロイチン硫酸（CS）、ヒアルロン酸（HA）を複合化したCS-DNゲル、HA-DNゲルを皮下および筋肉内に埋植し、その生体内劣化と組織適合性について検討した。埋植前の圧縮力学試験では、HA-DNゲルは破断強度7.90MPa、弾性率0.72MPaと従来のDNゲルより高い値を示し、CS-DNゲルの力学特性（破断強度2.47MPa、弾性率0.35MPa）より有意に高い値を示した（p<0.0001）。家兎10羽を用いた皮下埋植試験では、HA-DNゲルの力学特性は術後6週で有意に低下した（p<0.0001）。一方のCS-DNゲルは皮下埋植により力学特性の有意な変化は認めなかった。別の家兎21羽を用いた筋肉内埋植による生体内適合試験では、HA-DNゲルはほとんど炎症を生じなかったのに対し、CS-DNゲルは術後1週で陰性対照およびHA-DNゲルに対し有意に高い炎症を示した（p<0.0001、ｐ＝0.0043）。術後4週以降の炎症は陰性対照と同等となった。これらのDNゲル上でATDC5細胞を培養したところ、軟骨分化誘導因子（インスリン）の添加なしに、培養3日で2型コラーゲン、アグリカンの有意な発現上昇が認められた。これらの結果から、HA-DNゲル、CS-DNゲルは優れた生体適合性とともに軟骨分化誘導能を有することが明らかとなった。さらにこれら新規DNゲル上でATDC5細胞を培養しゲルが誘導する軟骨分化過程の細胞代謝を解析した。軟骨分化マーカーは培養早期より発現亢進が認められたが、ヒアルロン酸合成酵素やアポトーシス関連遺伝子には一定の挙動認められなかった。LC3、beclin1は培養12～24時間で対照に比べ高い発現を示し分化過程初期にオートファジー制御が関与していることが示唆された。
• Development of long-term stability high-viscosity gel phantom for evaluation of elasticity and safety

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

  Date (from‐to) : 2014/04 -2017/03 

  Author : Suga Mikio, KUROKAWA TAKAYUKI

   

  It has become common in clinical practice to use magnetic resonance elastography (MRE) for noninvasive evaluation of tissue elasticity. To assess quantitativity and repeatability of MRE systems and to compare viscoelastic parameters between different MRE systems, a quantitative phantom is required. We have developed phantoms for this purpose. However, the phantoms were not suitable for clinical practice because the viscosity is lower than those of human tissue. The purpose of this study was to develop a tissue-simulating tough and stable phantom for MRE. To increase the viscosity, 40wt% glycerin was added to phantom. MRE measurements were performed on a 3 T and 0.3 T MRI using a spin-echo (SE) EPI-MRE pulse sequence. The loss tangent (ratio of the loss and storage moduli) of the new gel was significantly larger than that of the polyacrylamide gel by itself. In this study, we successfully increased the viscosity of a phantom by adding glycerin, and assess stability of the phantom.
• Biomimetic Designs of Interfaces

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

  Date (from‐to) : 2012/06 -2017/03 

  Author : Ohzono Takuya, MUROSAKI Takayuki, Gong Jian-Ping, YOSHIDA Ryo, KITAHATA Hiroyuki, SUZUKI Kosuke, KAIDO Masataka, YAMAGUCHI Tomohiko

   

  In this program, our team tried to understand frictional and adhesion properties in the biological systems, which are closely related to the surface properties of common engineering materials, and, based upon the functional elements extracted from the biological examples, tried to propose new designs of functional materials. As results, strong adhesion mechanism of suction pad of cling-fish in water, the effects of the scales with unevenness-period grove structures of firebrat on the frictional properties, and extremely low adhesive interaction between tentacles of live Cypris larva and polyelectrolyte brush surface in sea water determined by scanning probe microscopy are mainly clarified in terms of the relationship between the functions and the surface topography/chemistry. Based upon the results, a design for shape-tunable undulated surfaces with highly variable friction was newly proposed.
• Production of kelp strains which have environment adaptability and development of the cultivation method utilizing bio-flavor

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

  Date (from‐to) : 2013/04 -2016/03 

  Author : YOTSUKURA Norishige, HOSHINO Yoichiro, KUROKAWA Takayuki, KAWAI Tadashi

   

  Gametophyte of six industrial kelp species in Hokkaido were stocked under axenic condition. Zoospores were isolated from eight sporophytes, that were produced by selection or crossing, including individuals that cultured under high water temperature and low nutrient conditions, and the germinations were cultivated. Meanwhile, cellulose was picked as an epiphytic medium for seedling of kelp. In the inspersion experiment of seedling at the field, the growth of sporophytes that were thought to be germination of the seedlings was found after the half a year of execution. Furthermore, AgNa gel was picked as a supported substrate of bio-flavor extracted from kelp. It was confirmed that aroma substances work on attracting of sea urchin in the laboratory experiment. Because efficiency of the substrates containing the substances was confirmed for capture of sea urchin at the field, the application for cultivation of seedling is expected.
• 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 -2016 

  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

  文部科学省：科学研究費補助金(基盤研究(A))

  Date (from‐to) : 2012 -2014 

  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。
• Analyses on physical and biological factors regulating spontaneous articular cartilage regeneration induced by DN gel

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

  Date (from‐to) : 2012 -2014 

  Author : KITAMURA NOBUTO, YASUDA Kazunori, GONG Jian Ping, KUROKAWA Takayuki, KONDO Eiji

   

  This study investigated to develop a clinical applicable DN gel implant and elucidated physical and biological factors regulating the DN gel-induced cartilage regeneration. (1) We developed a 0.5-mm thick gel implant. (2) We found that a 1.0-mm DN gel implant induced in vivo cartilage regeneration in a rabbit model. (3) We observed that DN gel induced in vivo cartilage regeneration regardless of location in which the DN gel was implanted in the joint. (4) We observed that DN gel induced in vivo cartilage regeneration regardless of the size of osteochondral defect. (5) We found that DN gel induced in vivo cartilage regeneration in a sheep model. (6) We found that the hyaluronic acid was a useful molecule to promote cartilage regeneration induced by DN gel.
• Clarification of signal transmission mechanism in mesenchymal cells during spontaneous cartilage regeneration induced by multi-functional synthetic gel

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

  Date (from‐to) : 2011 -2013 

  Author : YASUDA Kazunori, OMIYA Yoshihiro, OHASHI Toshiro, KUROKAWA Takayuki, KITAMURA Nobuto, TANAKA Shinya, SEMBA Shingo

   

  This study discovered several important phenomena and their molecular mechanisms during chondrogenic differentiation and regeneration of mesenchymal cells induced by the PAMPS/PDMAAm gel or soluble proteins:(1) ATP oscillation, which depends on oscillation of both the mitochondrial respiration and the glycolysis, was induced by calcium ion oscillation. The ATP oscillation does not control cell differentiation but controls cell aggregation and tissue formation via controlling secretion of soluble proteins. (2) Young's modulus of a chondrogenic precursor cell increased to a significantly greater degree during differentiation induced by the gel than during differentiation induced by Insulin. (3) Both the BMP-Smad signaling pathway and the IGF-depending signaling pathway were specifically activated during the differentiation induced by DN gel in comparison with that induced by Insulin. (4) The proteomics analysis showed that the gel has a function as a reservoir of soluble factors.
• Analyses on a molecular mechanism of spontaneous articular cartilage regeneration induced in vivo by double-network gel

  Ministry of Education, Culture, Sports, Science and Technology：Grants-in-Aid for Scientific Research(基盤研究(A))

  Date (from‐to) : 2008 -2010 

  Author : Kazunori YASUDA, Yoshihiro OHMIYA, Nobuto KITAMURA, Shin ONODERA, Hyuck Joon KWON, Takayuki KUROKAWA, Yoshihito OSADA, Jian Ping GONG

   

  (1) We clarified genetic characteristics of the articular cartilage spontaneously regenerated by double-network (DN) gel, using microarray. (2) We found that PAMPS, a component of the DN gel, has an ability that can induces the spontaneous articular cartilage regeneration. (3) We observed marker genes in a chondrogenic differentiation process, using multi-colored bioluminescence probes. We discovered a synchronized oscillation phenomenon of cell metabolism in prechondrogenic condensation. (4) We developed the transgenic bioluminescence mouse to be used for in vivo imaging. (5) These results provided important information to clarify a comprehensive mechanism of the spontaneous cartilage regeneration phenomenon.
• Material Innovation for the Age of Life Science-Creation of Soft and Wet Materials

  Ministry of Education, Culture, Sports, Science and Technology：Grants-in-Aid for Scientific Research(特別推進研究)

  Date (from‐to) : 2006 -2010 

  Author : Jian Ping GONG, 田中 良巳, 古川 英光, Akira KAKUGO, Takayuki KUROKAWA, Hidemitsu FURUKAWA, Yoshimi TANAKA, Kazunori YASUDA

   

  Biological tissues, except for the hard skeleton, mainly consist of soft tissues that contain 50-85wt% of water. Creation of soft and wet materials with a high performance as biological soft tissues is essential to the realization of future welfare society. In this study, by controlling the structure of the polymer hydrogels, we have successfully developed various kinds of soft and wet materials having a high toughness and high performance comparable to soft biological tissue. These materials can be applied as alternative materials for soft biological tissues, such as cartilages, tendons, and blood vessels.
• 超低摩擦・超高強度ゲルの創製とメカニズムの解明

  日本学術振興会：科学研究費助成事業 特別研究員奨励費

  Date (from‐to) : 1999 -2004 

  Author : 黒川 孝幸

   

  これまで、さまざまな化学種・荷重・速度域で系統的な一連の研究から、ゲルの摩擦を吸着モデルと反発モデルの2種類で統一的に議論できることを提唱してきた.しかし、それはあくまでもこれまでに得られていた結果から導かれたもので、測定した領域外の荷重や速度での結果を保証するものではない.そこで、以前より広い速度・荷重域にわたって観察することにより、従来の摩擦モデルの妥当性を議論したい.そのためにはサンプルの力学的強度および装置の性能に更なる発展が必要とされた.高い力学的強度を有するダブルネットワークゲル(以下DNゲル)を発明し、最大2.5MPaの大荷重をかけつつ微小な摩擦力を検知することのできる装置を開発することによりMPaオーダーの大荷重下でのゲルの摩擦挙動を観察することが可能となった.本研究は高強度DNゲルをさまざまな粘性溶媒中で膨潤させ、その大荷重下における摩擦挙動を調べることにより、高分子網目の運動性と摩擦との相関を幅広い速度範囲で調べた.溶媒を変えてゲルの摩擦挙動を観察すると、摩擦係数やその速度依存挙動がまったく異なる結果が得られた.ところが、それぞれの溶媒で膨潤したゲルの摩擦係数の速度依存性のプロットを適当な量をずらして重ね合わせるとあるマスターカーブが得られた.このときの速度軸の移動量は溶媒の粘度と相関があることがわかった.また、このように得られたマスターカーブはゲル摩擦の吸着モデルで説明ができる.すなわち粘度の高い溶媒中で摩擦挙動が低速度側にシフトするということはゲルの摩擦のメカニズムにおいてゲルの網目を構成している高分子の運動性が大きく寄与していることを示している.
• Hydrogel with extremely high strength and low friction

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• 特開2021-088160:エラストマー及び繊維構造体を備えたエラストマー複合体  2021/06/10

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• WO2020-085201:擬似皮膚の製造方法  2020/04/30

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• WO2019-065514:高靭性繊維複合エラストマー  2019/04/04

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• WO2018-225166:自己修復材料  2018/12/13

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• EP Patent No.3183387A4:COMPOSITE COMPRISING FABRIC AND POLYAMPHOLYTE HYDROGEL AND PREPARATION METHOD THEREOF  

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