The dependence of enzyme leakage on crosslink density in poly(N‐vinyl‐2‐pyrrolidone) hydrogels with immobilized urease

Urease enzyme was immobilized in hydrogels prepared from vinyl pyrrolidone/water/crosslinking agent ternary mixtures by γ‐irradiation of the solutions at room temperature. Two types of crosslinking agents used, namely ethylene glycol dimethacrylate and trimethylol propane triacrylate, yielded hydrogels with different swelling and crosslink density properties. The activity of immobilized urease was measured at the optimum conditions of temperature and pH over a period of time. It has been determined that for hydrogels with average molecular weights between crosslinks, Mc, above 2000, urease leakage is a serious problem. When Mc is around and below this value, immobilized systems showed a long time activity.