Stefan M. Paterson

Degradable Hydrogels for Tissue Engineering – Part I: Synthesis by RAFT Polymerization and Characterization of PHEMA Containing Enzymatically Degradable Crosslinks

A nonapeptide, which is sensitive to enzymatic digestion by collagenase, was modified by the covalent attachment of an acrylamido group at the terminal positions. The functionalized peptide was used as a crosslinking agent during polymerization of 2-hydroxyethyl methacrylate (HEMA). Reversible addition-fragmentation chain transfer (RAFT) method was used to obtain a polymer (PHEMA) with an average theoretical molecular weight of 4000 Da, containing enzymatically labile peptide crosslinks. The functionalized peptide was analyzed in detail by 1H and 13C nuclear magnetic resonance (NMR) spectrometry. The polymerization reaction was monitored by near infrared spectrometry, while the resulting polymer was analyzed by size exclusion chromatography and solid NMR spectrometry. The peptide-crosslinked PHEMA was subjected to an in-vitro degradation assay in the presence of collagenase. At the highest concentration of enzyme used in the study, a weight loss of 35% was recorded after 60 days of incubation in the collagenolytic medium. This suggests that crosslinking with enzymatically degradable peptides is a valid method for inducing biodegradability in polymers that otherwise are not degradable.

Improving the cellular invasion into PHEMA sponges by incorporation of the RGD peptide ligand: The use of copolymerization as a means to functionalize PHEMA sponges

A monomer that contained the RGD ligand motif was synthesized and copolymerized with 2-hydroxyethyl methacrylate using polymerization-induced phase separation methods to form poly(2-hydroxyethyl methacrylate)-based hydrogel sponges. The sponges had morphologies of aggregated polymer droplets and interconnected pores, the pores having dimensions in the order of 10 μm typical of PHEMA sponges. RGD-containing moieties appeared to be evenly distributed through the polymer droplets. Compared to PHEMA sponges that were not functionalized with RGD, the new sponges containing RGD allowed greater invasion by human corneal epithelial cells, by advancing the attachment of cells to the surface of the polymer droplets.