Synthesis, characterization, and drug release properties of poly(N-isopropylacrylamide) gels prepared in methanol-water cononsolvent medium

Abstract

Poly(N-isopropylacrylamide) (PNIPAM) hydrogels were simply prepared by free radical polymerization in different methanol-water mixture. A scanning electron microscopy study revealed that the freeze-dried hydrogels were macroporous. The swelling ratios in water at 20°C of the resulting hydrogels followed the order: X 0.43>X 0.21>X 0.76 ≈ X 0.57>X 0.31>X 0.13>X 0.06>X 0, where X m denotes a gel prepared in a methanol-water mixture with m mole fraction of methanol (x m). Below the lower critical solution temperature, the swelling ratio values of all of the hydrogels gradually decreased with the increase in the temperature. The complete collapse of the PNIPAM chain of all the gels occurred at about 38°C, whereas the same was observed at about 35°C for the conventional gel prepared in water. The swelling ratio values of all the PNIPAM gels in the methanol-water mixtures with different x m values at 20°C passed through a minimum in the cononsolvency zone. The deswelling rates of the hydrogels decreased in the following order: X 0.43> X 0.31> X 0.21> X 0.57> X 0.76 â≈ X 0.13> X 0.06> X 0. The reswelling rates of these hydrogels decreased in the following order: X 0> X 0.31> X 0.06 ≈ X 0.13 > X 0.76> X 0.57> X 0.21> X 0.43. The release rates of the Tramadol Hydrochloride drug at 37°C from the drug-loaded hydrogels were almost same for all of the hydrogels. © 2012 Wiley Periodicals, Inc.