Modulating properties of chemically crosslinked PEG hydrogels via physical entrapment of silk fibroin

A variety of polymers of synthetic origins (e.g., poly(ethylene glycol) or PEG) and macromolecules derived from natural resources (e.g., silk fibroin or SF) have been explored as the backbone materials for hydrogel crosslinking. Purely synthetic PEG-based hydrogels are often chemically crosslinked to possess limited degradability, unless labile motifs are designed and integrated into the otherwise non-degradable macromers. On the other hand, SF produced by Bombyx mori silkworm can be easily formulated into physical hydrogels. These physical gels, however, are less stable than the chemically crosslinked gels. Here, we present a simple strategy to prepare hybrid PEG-SF hydrogels with chemically crosslinked PEG network and physically entrapped SF. Visible light irradiation initiated rapid thiol-acrylate gelation to produce a network composed of non-degradable poly(acrylate-co-NVP) chains, hydrolytically labile thioether ester bonds, and interpenetrating SF fibrils. We evaluated the effect of SF entrapment on the crosslinking efficiency and hydrolytic degradation of thiol-acrylate PEG hydrogels. We further examined the effect of adding soluble SF or sonicated SF (S-SF) on physical gelation of the hybrid materials. The impacts of SF or S-SF inclusion on the properties of chemically crosslinked hybrid hydrogels were also studied, including gel points, gel fraction, equilibrium swelling ratio, and mesh size. We also quantified the fraction of SF retention in PEG hydrogels, as well as the influence of remaining SF on moduli and degradation of chemically crosslinked thiol-acrylate PEG hydrogels. This simple hybrid hydrogel fabrication strategy should be highly useful in future drug delivery and tissue engineering applications. (C) 2015 Wiley Periodicals, Inc.