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A chemically cross-linked filamentous actin (F-actin) gel consisting of globular actin (G-actin) as repeating units was prepared. The F-actin gel was cross-linked by covalent bonds, and the main chain is represented by the self-assembly of G-actin with a high-ordered hierarchical structure. The gel exhibited good mechanical performance with a storage modulus >1 kPa and undergoes reversible sol-gel transitions in response to changes in the salt concentration (chemical-induced sol-gel transition) as well as to shear strain (mechanical-induced sol-gel transition). Therefore, the gel exhibits self-repairing ability through dynamic polymerization and depolymerization across the structure hierarchies under repeated shear stress.

A thermoresponsive 3D microtubule hydrogel (MT gel) was prepared by simultaneous polymerization and chemical cross-linking of tubulins. The main chain of this gel is composed of cross-linked MTs, which consists of a cylindrical assembly of tubulin covalently connected by polyethylene glycol. This gel, which contains 10 mg/mL of tubulin, exhibits a storage modulus G' as high as 1 × 10(3), which is 10 times higher than the loss modulus G'' over a wide range of frequencies. The MT gel exhibits a reversible sol-gel transition by temperature changes at 4-37 °C via depolymerization and polymerization of the MT network. Notable effects of the presence of the cross-linkage on the process of polymerization and depolymerization of tubulin were experimentally observed, and the role of the cross-linkage was discussed.

Novel electro-conductive and mechanically-tough double network polymer hydrogels (E-DN gels) were synthesized by polymerization of 3, 4-ethylenedioxythiophene in the presence of a double network hydrogel (DN gel) matrix. The E-DN gels showed not only excellent mechanical performance, having a fracture stress of 1.4-2.1 MPa, but also electrical conductivity as high as 10−3 S cm−1, both under dry and water-swollen states. The fracture stress and fracture energy of the E-DN gel was increased by 1.7 and 3.4 times, respectively, as compared with the DN gel. From scanning electron microscope and AFM observations, it was found that electro-conductive poly(3,4-ethylenedioxythiophene) (PEDOT) was incorporated into DN gel matrix, apparently due to the formation of a poly-ion complex with sulfonic acid group of the DN gel network. Thus, PEDOT incorporated into the DN gel matrix greatly improves not only electronic conductivity, but also mechanical properties, reinforcing the double network gel matrix. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 [ABSTRACT FROM AUTHOR]