The relationship between crosslinking structure and silk fibroin scaffold performance for soft tissue engineering

Biologically active scaffolds with tunable mechano- and bio-performance remain desirable for soft tissue engineering. Previously, highly elastic and robust silk fibroin (SF) scaffolds were prepared via cryogelation. In order to get more insight into the role of ethylene glycol diglycidyl ether (EGDE) on the structure and properties of SF scaffolds, we investigated the fate of SF scaffolds with different usages of the crosslinking agent in vitro and in vivo. Although SF scaffolds with varied EGDE contents showed similar micro-morphology, increasing EGDE from 1 mmol/g to 5 mmol/g resulted in firstly increased and later decreased content of β-sheet conformation, and linearly increased tensile modulus and decreased elasticity. The dual-crosslinked SF scaffolds with EGDE up to 5 mmol/g did not show in vitro cytotoxicity for NIH3T3 fibroblasts. In vivo subcutaneous implantation of SF scaffolds with <3 mmol/g EGDE displayed excellent degradation behavior and tissue ingrowth after 28 days of implantation. However, with ≥3 mmol/g EGDE, SF scaffolds exhibited obvious post-implantation foreign body reactions, probably associated with slow degradation due to excess chemical crosslinks and less mechanical compatibility. These results suggest that an appropriate dosage of crosslinking agent was critical to achieve balanced mechanical properties, degradability in vivo and immuno-properties of the SF scaffold platform for soft tissue engineering.