Interpenetrating polymer networks (IPNs) based on N-vinyl pyrrolidone (NVP) : gelatin (Ge), and a copolymer of NVP - acrylic acid (AA) : gelatin (Ge) were prepared using N-N'methylenebisacrylamide (BIS) (0.5, 1% w/w) and glutaraldehyde (GLU) (0.5% v/v) as cross-linkers, respectively, by gamma irradiation technique. GLU was incorporated after irradiation to crosslink the gelatin chains, whereas BIS was placed in the respective solutions before irradiation. Several samples were prepared by varying the composition of gelatin to NVP or by changing the ratio of NVP : AA in preparing IPNs. The swelling behavior of the hydrogels was investigated as a function of variable doses, crosslinker (BIS) concentration, copolymer composition (NVP : AA ratio) or Ge : NVP ratio and pH of the immersion medium (3, 7.4, and 11). As expected, the swelling ratio increased with increasing acrylic acid content and decreased with increasing BIS content. No definite trend in the swelling behavior was observed as a function of dose. The interpenetration of the polymeric chains was established by morphological and thermal characterization. Scanning electron microscopy of IPNs showed a hybrid of coral and honeycomb structures as compared with the crosslinked polymers based on Ge and NVP (G(x) and PVPx). (c) 2007 Wiley Periodicals, Inc.