Hydrogels for colon-specific oral drug delivery: Synthesis and characterization

Hydrogels have been synthesized by free radical co-polymerization of acrylamide and maleic acid in the presence of poly(N-vinyl-2-pyrrolidone) in aqueous medium. The presence of a small amount of maleic acid in the polymer network increased the swelling capacity appreciably, thus changing the Fickian swelling behavior to a non-Fickian one. The hydrogels showed good response to pH, ionic-strength and valency of counterions in the external media. The hydrogels demonstrated minimum swelling in the strongly acidic range 1-2 and maximum swelling was observed in the neutral or slightly alkaline medium (7-8). The amount of maleic acid in the hydrogel affected its swelling behavour in a rather unusual way. At pH 7.0, the equilibrium swelling increased up to 123 mM of maleic acid in the system and then started decreasing, while at a low pH, a continuous decrease was observed. The hydrogels underwent a number of deswelling swelling cycles with a pH change from 1.0 to 8.0, respectively. The hydrogels demonstrated temperature-dependent swelling behavior partially, and activation every for the sample with and without maleic acid was found to be 33.1 and 19.9 kJ mol(-1). Finally, the pH - dependent swelling behavior makes them suitable for a drug delivery device along the gastrointestinal (GI) tract.