In Situ Forming Poly(ethylene glycol)- Poly(L-lactide) Hydrogels via Michael Addition: Mechanical Properties, Degradation, and Protein Release

Chemically crosslinked hydrogels are prepared at remarkably low macromonomer concentrations from 8-arm poly(ethylene glycol)-poly(L-lactide) star block copolymers bearing acrylate end groups (PEG-(PLLAn)8-AC, n = 4 or 12) and multifunctional PEG thiols (PEG-(SH)n, n = 2, 4, or 8) through a Michael-type addition reaction. Hydrogels are obtained within 1 min after mixing PEG-(PLLA4)8 -AC and PEG-(SH)8 in phosphate buffered saline, quickly reaching a high storage modulus of 17 kPa. Lysozyme and albumin are released for 4 weeks from PEG-(PLLA12)8-AC/PEG-(SH)8 hydrogels. Lysozyme release from PEG-(PLLA12)8-AC/PEG-(SH)2 and PEG-(PLLA12)8-AC/PEG-(SH)4 hydrogels is significantly faster with complete release in 3 and 12 d, respectively, as a result of a combination of degradation and diffusion.