Controlling spatiotemporal mechanics of globular protein-polymer hydrogel via metal-coordination interactions

Mechanical properties of hydrogels are dependent on their spatial and temporal structural properties. Several attempts have been made to tune the mechanical properties of hydrogels either through controlling spatial or temporal design elements. However, controlling both elements simultaneously still proves to be extremely difficult and elusive. This goal could be achieved by combining the function and structure of globular proteins with the versatility of synthetic polymers to form a hybrid hydrogel. In this study, a physically crosslinked protein-polymer hydrogel (PPH) was synthesized. As a model globular protein, bovine serum albumin (BSA) was used together with poly(methacrylamide) to control hydrogel spatiotemporal mechanics. In order to control the temporal hierarchy (crosslinking kinetics) we used the coordination sites of BSA to create metal-coordination crosslinks, while the folding-unfolding of BSA triggered by specific metal ions was exploited to define the network architecture (spatial hierarchy). Mechanical properties, relaxation times, and microstructure were found to be affected by the nature of metal ions in the PPHs. It is anticipated that understanding of spatiotemporal mechanics will facilitate the development of novel PPHs with fine-tuned mechanical properties.