2007 Full Paper Macromolecular Chemistry and Physics wileyonlinelibrary.com © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/macp.201500265 Anisotropic Gelation Induced by Very Little Amount of Filamentous Actin Kazuhiro Shikinaka,* Manami Misu, Hidemitsu Furukawa, Akira Kakugo, Jian Ping Gong In this paper, the hydrogel is created with oriented structure by addition of very little amount of dopant, filamentous actin (F-actin), which is 1/50 000 of lower critical concentration for nematic phase in F-actin aqueous solution. The orientation mechanism of polymer network differs depending on the concentration of F-actin. Further- more, it is first exhibited that the role of polyelectrolyte for the emergence of anisotropy of gel is differed depending on its concentration by using digestion method to F-actins, experimentally. Dr. K. Shikinaka Graduate School of Engineering Tokyo University of Agriculture and Technology 2-24-16, Naka-cho, Koganei, Tokyo 184-8588, Japan E-mail: k-shiki@cc.tuat.ac.jp M. Misu, Prof. J. P. Gong Faculty of Advanced Life Science Hokkaido University Kita 10 Nishi 8, Kita-ku, Sapporo 060-0810, Japan Prof. H. Furukawa Graduate School of Science and Engineering Yamagata University 4-3-16, Jonan, Yonezawa 991-8510, Japan Dr. A. Kakugo Faculty of Science Hokkaido University Kita 10 Nishi 8, Kita-ku, Sapporo 060-0810, Japan and it contributes to the formation and smooth motion of muscle fibers. [4] In our previous paper, we have been successful to syn- thesize anisotropic gels with high water content by tem- plate polymerization of cationic monomer in the presence of poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT), which has both rigidity and water solubility. [6–9] This gel shows birefringence even when the concentra- tion of PBDT is as low as 0.02 wt% which is 1/140 of lower critical concentration for nematic phase in PBDT aqueous solution. To the best of our knowledge, such an anisotropic gel, which shows birefringence with a very small amount of mesogen, has never been synthesized previously. This template-polymerization method was represented as a new way to introduce optical anisotropy into synthesized gels by using a small amount of dopant. Moreover, our previous results also indicated that the cross-linking reac- tion in the presence of the anisotropic structure is essen- tially important for the anisotropic self-orientation and it was suggested that a self-orientation process by inter- molecular interaction or cross-linking reaction as shown in this studies has many analogies with the formation of well-ordered structure in living organisms. In living organisms, well-ordered structures are mainly consisted of actins. Actin, which is a globular protein, 1. Introduction Tissues in living organisms contain a large amount of water and could be defined as a soft and wet gel-like state. These biological gels have a well-ordered structure, such as a liquid-crystalline (LC) structure, which plays a crucial role in the normal functioning of the living organisms. [1–5] For example, myosin shows the LC structure in sarcomere, Macromol. Chem. Phys. 2015, 216, 2007−2011