Exogenously triggered, enzymatic degradation of photopolymerized hydrogels with polycaprolactone subunits: experimental observation and modeling of mass loss behavior

Degradation plays an important role in the evolution of the extracellular matrix secreted by chondrocytes encapsulated in PEG-based hydrogels. For this study, macromonomers were synthesized by methacrylating both ends of polycaprolactone-b-poly(ethylene glycol)-b-polycaprolactone (PEG-CAP) tri-block copolymers. These divinyl molecules were photopolymerized to form hydrogels with PEG-CAP crosslinks that were subsequently degraded upon exogenous addition of a lipase enzyme. The rate of degradation and subsequent mass loss depends on both the length of the polycaprolactone units and the concentration of enzyme. Control gels that did not receive lipase did not significantly degrade on the time scale of these experiments. A model was developed to predict mass loss using enzyme kinetics and a previously described statistical treatment of bulk network degradation. The model was used to predict mass loss profiles at the specific conditions used, and also to demonstrate the importance of potential changes in reaction rate and enzyme stability on temporal mass loss.