Dual Cross-Link Networks To Preserve Physical Interactions Induced by Soaking Methods: Developing a Strong and Biocompatible Protein-Based Hydrogel

The engineering of natural protein-based hydrogels with outstanding mechanics and functionalities is an eternal pursuit in biomaterials science. Soaking methods have recently been used to simply and efficiently tune the macroscopic mechanical properties of hydrogels consisting of natural polymers (proteins or polysaccharides). However, the high concentration of salts or organic solvent within the soaked hydrogels is harmful to cells. Once the salts were eliminated, however, these hydrogels experience mechanics attenuation and swelling, limiting their applications as biomaterials. Here we utilize dual cross-link networks to address these problems by preserving the physical interactions formed during the soaking treatment. As an example, a dual cross-link gelatin–chitosan hydrogel is prepared by a click reaction and hydrophobic interactions, which achieve an unusual combination of abundant water content (>87%), strong mechanics (ultimate strength ∼1.8 MPa), antiswelling properties (swelling ratio of 11.25% in PBS for 7 days), thermal stability, and biocompatibility. We expect that this strategy can be generalized for the development of tough, biocompatible, and environmentally stable protein-based hydrogels.