Mixed Mode Thiol−Acrylate Photopolymerizations for the Synthesis of PEG−Peptide Hydrogels

Thiol−acrylate mixed mode photopolymerizations provide an easy, robust, cost-efficient, and cytocompatible reaction scheme for the incorporation of cysteine-containing peptide sequences into PEG hydrogels. With an acrylate:cysteine ratio of 4:1, ∼95% of the peptide is incorporated after 10 min of reaction with ∼5 mW/cm2 of 365 nm light. Specifically, thiol monomers, with thiol-presenting peptide groups in the form of CGGGGG, CRGGGG, CWGGGG, CDGGGG, CSGGGG, and CGGGGC, copolymerized with PEG4600 diacrylate were characterized. The chain transfer constant of acrylates to thiols was determined to range from 1.5 to 2, depending on the amino acid sequence. Complete conversion of the functional groups occurred after ∼40 s for all systems, excluding the tryptophan-containing peptide sequence which had a retarded polymerization, taking ∼60 s. The cross-linking densities of the final gels ranged from 1.5 × 10−2 to 2.0 × 10−2 mol/L when 10 mM of peptide was reacted with 40 mM of acrylate groups. Efficient incorporat...