Tuning tissue ingrowth into pro-angiogenic hydrogels via dual modality degradation

The potential to control the rate of replacement of a biodegradable implant by tissue would be advantageous. Here, we demonstrate through the novel approach of overlaying an enzymatically degradable hydrogel with an increasingly hydrolytically degradable environment, tissue invasion can be tuned. Polyethylene glycol (PEG) hydrogels were formed from varying proportions of PEG-vinyl sulfone (PEG-VS) and PEG-acrylate (PEG-AC) monomers via a Michael-type addition reaction with a dithiol containing matrix metalloproteinase susceptible peptide crosslinker. Swelling studies showed that PEG hydrogels with similar initial stiffnesses degraded more rapidly as the PEG-AC content increased. The replacement of subcutaneously implanted PEG hydrogels was also found to be proportional to their PEG-AC content. In addition, it would in many instances be desirable that these materials have the ability to stimulate their neovascularization. These hydrogels contained covalently bound heparin and it was shown that a formulation of the hydrogel that allowed tissue replacement to occur over 1 month could trap and release growth factors and increase neovascularization by 50% over that time.