Marina Slawinski & Daniel Collison, “Shape Programming of Protein Hydrogels Using Metal Cations”
Mentors: Ionel Popa & Luai Khoury, Physics
The ability to program a temporary shape in biomaterials that can revert to their original shape in response to a stimulus is referred to as shape programming, which is essential to the future of medicine and soft robotics. Here we use hydrogels made from covalently cross-linked pure proteins, which we program into new shapes using adsorption of cations. We synthesize bovine serum albumin (BSA) hydrogels through a photoactivated reaction with a primary covalent cross-linking network via tyrosine amino acids. Incubation in solutions of divalent metal cations (Zn2+ and Cu2+) induces the formation of a secondary physical cross-linking network via ionic interactions with histidine amino acids. The dual cross-linking stiffens the hydrogel, allowing for temporary shape morphing and restoration with the addition and removal of the secondary network. Following incubation in Zn2+ and Cu2+ solutions, force-clamp rheometer measurements revealed an increase in Young’s modulus directly related to the concentration of the solution. The addition of the secondary network allowed us to program complex shapes, while diffusion of adsorbed cations removed the secondary network and restored the original shape. The shape manipulation of BSA hydrogels at room temperature in response to different aqueous solutions explores the possibilities to engineer responsive and biocompatible tissues, whose stiffness and form react to their environment.