Preparation of silk fibroin/hyaluronic acid hydrogels with enhanced mechanical performance by a combination of physical and enzymatic crosslinking.

Silk fibroin (SF) from Bombyx mori is a natural polymer with exceptional biocompatibility, low immunogenicity, and ease of processability. SF-based hydrogels have been identified as one of the most attractive candidate scaffolds for tissue engineering and can be fabricated through various physical or chemical crosslinking approaches. However, conventional SF hydrogels may suffer from several major drawbacks, such as structural inhomogeneity, poor mechanical properties or utilization of cytotoxic reagents. Herein, a dually crosslinked SF-based composite hydrogel with enhanced strength and elasticity was fabricated by inducing the formation of uniform and small β-sheet structures by sonication in a restricted enzymatic precrosslinked network. The composite hydrogel not only demonstrated concentration-dependent stiffness variation but also exhibited time-dependent changes in toughness behavior. Moreover, subsequent experimental results revealed that the hydrogels exhibit other advantages, including high water retention capacity and long-term stability under physiological conditions. Finally, a three-dimensional (3 D) construct of the cell-laden hydrogel was fabricated, confirming that the composite hydrogel could provide a biocompatible microenvironment with dynamically changing mechanical properties. The combination of physical and enzymatic crosslinking strategies contributes to a biocompatible composite hydrogel with unique mechanical properties that holds great potential for use in tissue engineering and regenerative medicine.