Analysis of swelling behavior of poly(methacrylamide-co-methacrylic acid) hydrogels and effect of synthesis conditions on water uptake

An investigation of water uptake behavior of a novel pH-sensitive poly(methacrylamide-co-methacrylic acid) hydrogel system was carried out with two major objectives. First was to study the effect of various synthesis conditions like reaction temperature, initiator content and degree of dilution of feed mixture on the water absorbency of resulting hydrogels and the second was to interpret the water uptake data by various kinetic models. The 2.25 times dilution of the reaction mixture resulted in the formation of hydrogels with highest water uptake of 1423 ± 21% in the simulating intestinal fluid of pH 7.4 at 37 °C. Likewise, the optimum synthesis temperature and initiator concentration were found to be 80 °C and 11.04 × 10−2 mM, respectively. The kinetic models proposed by Peppas and Hopfenberg were applied on the water uptake data to obtain the best fit. The enthalpy of mixing ΔHmix was also evaluated for hydrogels with varying concentrations of monomer acid in the feed mixture. Finally, the gels demonstrated sharp change in their water absorbency and mesh size of networks with pH of the swelling media, thus suggesting their strong candidature for being used as oral drug-delivery systems along the gastrointestinal tract.