Kinetic Method of Producing Pores Inside Protein-Based Biomaterials without Compromising Their Structural Integrity

Hydrogels made from globular proteins cross-linked covalently into a stable network are becoming an important type of biomaterial, with applications in artificial tissue design and cell culture scaffolds, and represent a promising system to study the mechanical and biochemical unfolding of proteins in crowded environments. Due to the small size of the globular protein domains, typically 2-5 nm, the primary network allows for a limited transfer of protein molecules and prevents the passing of particles and aggregates with dimensions over 100 nm. Here, we demonstrate a method to produce protein materials with micrometer-sized pores and increased permeability. Our approach relies on forming two competing networks: a covalent network made from cross-linked bovine serum albumin (BSA) proteins via a light-activated reaction and a physical network triggered by the aggregation of a polysaccharide, alginate, in the presence of Ca2+ ions. By fine-tuning the reaction times, we produce porous-protein hydrogels that retain the mechanical characteristics of their less-porous counterparts. We further describe a simple model to investigate the kinetic balance between the nucleation of alginate and cross-linking of BSA molecules and find the upper rate of the alginate aggregation reaction driving pore formation. By enabling a more significant permeability for protein-based materials without compromising their mechanical response, our method opens new vistas into studying protein-protein interactions and cell growth and designing novel affinity methods.