Chemical unfolding of protein domains induces shape change in programmed protein hydrogels

Abstract

Programmable behavior combined with tailored stiffness and tunable biomechanical response are key requirements for developing successful materials. However, these properties are still an elusive goal for protein-based biomaterials. Here, we present a new method based on protein-polymer interactions, to manipulate the stiffness of protein-based hydrogels made from bovine serum albumin (BSA) by using polyelectrolytes such as poly(Ethelene)imine (PEI) and poly-L-lysine (PLL) at various concentrations. This approach confers protein-hydrogels tunable wide-range stiffness, from ~ 10 - 60 kPa when treated with PEI, without affecting the protein mechanics and nanostructure. We ascribe the increase in stiffness to the synergistic effect of the non-covalent electrostatic polymer-protein interaction, as well as the polymer-shell that stabilizes the protein domains nanomechanics. We use the 6-fold increase in stiffness induced by PEI to program BSA-hydrogels in various shapes. By utilizing the characteristic protein unfolding we can induce reversible shape-memory behavior of these composite materials using chemical denaturing solutions. We anticipate this novel approach based on protein engineering and polymer reinforcing will enable the development and investigation of new smart biomaterials and extend protein hydrogel capabilities beyond their conventional applications.