A Mechanistic Assessment of Enzyme-Induced Degradation of Albumin-Crosslinked Hydrogels

Pepsin-induced degradation of albumin-crosslinked hydrogels was studied as a function of the degree of albumin incorporation in the network and the concentration of pepsin. The degree of albumin incorporation, which represents the sum of chemical crosslinks and physical entanglements in the network, was controlled by changing the concentration of initiator in the monomer solution and the degree of vinylic functionality on albumin. Swelling characterization studies showed that the degree of hydrogel swelling decreased as the concentration of chemical initiator for the polymerization increased or as the degree of vinylic functionality on albumin increased. This indicated that the degree of albumin incorporation in the network increased by raising either the concentration of chemical initiator or the degree of albumin functionality. The rate and mechanism of gel degradation was also dependent on the degree of albumin incorporation in the network. A low degree of albumin incorpora tion resulted in a predominance of surface degradation while a high degree of albumin incorporation resulted in a predominance of bulk degradation. The transition from surface degradation to bulk degradation occurred at lower con centrations of chemical initiator when the degree of vinylic functionality on albumin was high. However, when the degree of vinylic functionality on albumin was low, the transition from surface degradation to bulk degradation was observed at higher concentrations of chemical initiator. The rate of gel degradation became slower as the concentration of pepsin was reduced. The results suggest that the rate and mechanism of hydrogel degradation was de pendent on the steric constraints imposed by polymer chains of the network and on the conformational constraints of the albumin crosslinker.