Domain Coordination Governs Pore Architecture in Transient Double-Network Antibody-Binding Polyprotein Hydrogels

Protein-based hydrogels synthesized from covalently cross- linked globular proteins are an emerging class of biomaterials, yet their dense nanoscale network architecture severely limits permeability to large biomolecules. Here, we report a general strategy to create highly permeable polyprotein hydrogels by photochemically cross-linking engineered octameric repeats of antibody-binding Protein A or Protein L in the presence of a transient alginate network, which can function as high-capacity affinity matrices. We demonstrate that the coordination capacity per domain controls the cross-linked shell that forms around growing pores during competitive gelation, with higher coordination (Protein L) producing a denser shell and more numerous but smaller pores and lower coordination (Protein A) yielding larger pores. The resulting hydrogels enable rapid and deep penetration of antibodies throughout the entire material volume while retaining high functional-domain density. When used as model affinity matrices, these materials display exceptional binding capacity, near-quantitative recovery, and excellent operational and shelf stability. This work establishes a molecular design rule for tuning porosity in folded-protein biomaterials and opens a route to next-generation, fully protein-based scaffolds with programmable permeability and function.