Dilute gels with exceptional rigidity from self-assembling silk-collagen-like block copolymers

Abstract

Rheological data on monodisperse block copolymer hydrogels are rare because the amounts produced with various methods usually are not sufficient for materials testing. By biotechnological means, expression of a block copolymer encoding gene in the yeast Pichia pastoris, we produced enough protein block copolymer for a study of the macroscopic properties of several gels. To study the effect of block order on the mechanical properties of self-assembling block copolymer hydrogels, we tested gels of two molecules with complementary triblock organization: CS^ES^EC and S^ECCS^E, in which the S^E block self assembles at low pH while the C block remains a random coil. Dynamic mechanical spectroscopy revealed differences in gelling kinetics and mechanical properties. The gels displayed non-linear elasticity comparable to that of actin gels and other networks of cross-linked semiflexible polymers. Moreover, exceptionally high storage moduli, exceeding 40 kPa, were reached already at concentrations as low as 1.5 wt%, without any additional crosslinking agent. Increasing the temperature of a CS^ES^EC gel led to stiffening until 50 °C, above which it melted.