Synthesis of Enzyme-Digestible, Interpenetrating Hydrogel Networks by Gamma-Irradiation

γ-Irradiation was used to prepare cylindrically shaped, enzyme- digestible hydrogels consisting of a moderately swelling albumin-crosslinked poly(vinyl pyrrolidone) (PVP) hydrogel core which formed a semi-interpene trating network (SIPN) at its outer region with a polyelectrolyte homopolymer of acryloxyethyltrimethylammonium chloride (AETAC). In pepsin-free simu lated gastric fluid (SGF), the presence of a SIPN resulted in only a marginal in crease in swelling as compared to the pure PVP hydrogel. In distilled deionized water, however, the swelling of the 2-phase hydrogel system was dramatically increased. The effects of γ-irradiation on the individual constituent polymers that com prised the 2-phase system were studied. Vinyl pyrrolidone (VP) formed PVP which subsequently crosslinked to form an insoluble three-dimensional net work after 4 h of γ-irradiation. Polymers of AETAC (PAETAC) underwent chain scission following 30 min of γ-irradiation. FA became crosslinked as deter mined by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS- PAGE). The swelling properties of albumin-crosslinked PVP and albumin- crosslinked PAETAC hydrogels were also studied as a function of γ-irradiation time and the concentration of FA in the monomer solution. The equilibrium swelling ratios of the prepared hydrogels in pepsin-free simulated gastric fluid (SGF) were dependent on the γ-irradiation time which affected the crosslinking or chain scission of the polymers. Both the PVP and PAETAC hydrogels under went bulk degradation in pepsin-containing SGF.