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.