Reversible Temperature-Switching of Hydrogel Stiffness of Coassembled, Silk-Collagen-Like Hydrogels

Recombinant protein polymers, which can combine different bioinspired self-assembly motifs in a well-defined block sequence, have large potential as building blocks for making complex, hierarchically structured materials. In this paper we demonstrate the stepwise formation of thermosensitive hydrogels by combination of two distinct, orthogonal self-assembly mechanisms. In the first step, fibers are coassembled from two recombinant protein polymers: (a) a symmetric silk-like block copolymer consisting of a central silk-like block flanked by two soluble random coil blocks and (b) an asymmetric silk-collagen-like block copolymer consisting of a central random-coil block flanked on one side by a silk-like block and on the other side a collagen-like block. In the second step, induced by cooling, the collagen-like blocks form triple helices and thereby cross-link the fibers, leading to hydrogels with a thermo-reversibly switchable stiffness. Our work demonstrates how complex self-assembled materials can be formed through careful control of the self-assembly pathway.