Progress in Hydrogels Based on Regenerated Silk Fibroin

Regenerated silk fibroin (RSF) is a fibrillar protein obtained from Bombyx mori silkworm silk. Recently, RSF-based hydrogels have attracted extensive research interest, which has yielded an improved understanding in the gelling mechanisms, physical and mechanical properties as well as the applications in regenerative medicine and tissue engineering. Mechanistically, RSF hydrogel networks can be formed via two pathways, chemical cross-linking including enzymatic cross-linking, and physical cross-linking through conformational transition, during which thermodynamically more stable beta-sheet structures are induced. An advantage of RSF hydrogels is that the physical and mechanical properties of hydrogels can be further controlled by the beta-sheet content in the conformation on top of concentration and cross-linking density. RSF can be mixed with other polymers and/or inorganic components to prepare composite hydrogels for a wider spectrum of mechanical properties. Furthermore, we summarize most recent applications of RSF hydrogels in biomaterials, including controlled drug release, muscle, tendon and bone tissue engineering.