Biofabricating multifunctional soft matter with enzymes and stimuli-responsive materials

Methods that allow soft matter to be fabricated with controlled structure and function would be beneficial for applications ranging from flexible electronics to regenerative medicine. Here, the assembly of a multifunctional gelatin matrix is demonstrated by triggering its self-assembly and then enzymatically assembling biological functionality. Triggered self-assembly relies on electrodeposition of the pH-responsive hydrogelator, 9-fluorenylmethoxycarbonyl-phenylalanine (Fmoc-Phe), in response to electrical inputs that generate a localized pH-gradient. Warm solutions of Fmoc-Phe and gelatin are co-deposited and, after cooling to room temperature, a physical gelatin network forms. Enzymatic assembly employs the cofactor-independent enzyme microbial transglutaminase (mTG) to perform two functions: crosslink the gelatin matrix to generate a thermally stable chemical gel and conjugate proteins to the matrix. To conjugate globular proteins to gelatin these proteins are engineered to have short lysine-rich or glutamine-rich fusion tags to provide accessible residues for mTG-catalysis. Viable bacteria can be co-deposited and entrapped within the crosslinked gelatin matrix and can proliferate upon subsequent incubation. These results demonstrate the potential for enlisting biological materials and mechanisms to biofabricate multifunctional soft matter.