(715c) Hybrid Chemical-Physical Crosslinking in Artificial Protein Hydrogels

Artificial proteins are an important class of macromolecules for the development of engineered hydrogels in which structural and functional information can be encoded at the level of the protein sequence. In this work, we have designed triblock artificial proteins capable of both chemical crosslinking through reactive amino acid residues at the protein termini and physical crosslinking through associative coiled-coil midblock domains. Under the appropriate conditions, the resulting hydrogel is a hybrid network that contains both chemical and physical junctions and behaves as a viscoelastic solid. While the chemical network is essentially permanent, the coiled-coil physical crosslinkers are able to reversibly dissociate, allowing some of the stress that is stored upon network deformation to relax. The level of stress relaxation can be tuned by adjusting the ratio of chemical and physical crosslinking. Swelling the hydrogels in buffer containing denaturant or introducing a point mutation at one of several key residues disrupts coiled-coil formation and results in a purely elastic, rather than viscoelastic, response to an applied strain. This work demonstrates how bulk hydrogel properties such as viscoelasticity can be programed through variation of the protein sequence. Chemical-physical hybrid networks have potential applications as cell culture platforms to study cellular mechanosensing in a viscoelastic environment, as components to sensors or stimuli responsive materials, and for dissipating mechanical energy during stretching to improve hydrogel toughness.