Modulated degradation of hydrogels with thermo-responsive network in relation to their swelling behavior

Hydrogels consisting of poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide-co-butyl methacrylate) and a novel biodegradable cross-linker were synthesized with different concentrations of ammonium peroxodisulfate (APS) as a free radical initiator by photo-induced radical reaction. The swelling ratio of the hydrogels decreased rapidly in proportion to temperature. In vitro enzymatic degradation of the hydrogels was examined in buffer solution containing papain at different temperatures. The enzymatic degradation of the hydrogel prepared with higher APS concentration was observed to proceed at 30°C, however, the hydrogel was not degraded above 35°C. Such an on-mloff switching degradation in response to temperature was not observed for hydrogels prepared with lower APS concentration. It is considered that modulated degradation of hydrogels with a thermo-responsive network is achieved by controlling the cross-link density and eliminating the entanglement of polymeric main chains.