Rational Design and Hierarchical Assembly of a Genetically Engineered Resilin-Silk Copolymer Results in Stiff Hydrogels.

Genetically engineered protein polymers, which can combine different unique peptide sequences from natural protein materials, offer great opportunities for making advanced materials with well-defined structures and properties. Here we report for the first time biosynthesis and self-assembly of a recombinant resilin-silk (RS) copolymer consisting of repeating units of silk and resilin blocks. The copolymer in aqueous solution self-assembled into nanoparticles, and the assembled nanoparticles further form nano- to microscale fibers in a time-dependent manner at body temperature, whereas such fibers were not formed upon incubation of the copolymer at either low or high temperatures. In contrast, a resilin-like polypeptide without the silk blocks exhibited a typical thermoresponsive dual-phase transition behavior and was incapable of self-assembling into fibers. More interestingly, the microscale fibers self-assembled from a moderately concentrated RS solution (20 wt %) could interact to give a self-supporting, semitransparent hydrogel with elastic modulus at approximately 195 Pa. Furthermore, photo-cross-linking of either freshly prepared or annealed RS copolymer led to the formation of stiff hydrogels and the material mechanical property was superior upon annealing of the RS solution for a longer time up to 4 h, with elastic modulus ranging from 2.9 to 7.0 kPa. These results not only shed light on the fundamental hierarchical assembly mechanism of a new family of genetically engineered RS copolymer but also suggest future opportunities for these thermoresponsive polymers in fabrication of hydrogel materials with tunable mechanical properties for diverse applications.