Controlled release of diclofenac sodium from pH-responsive carrageenan-g-poly(acrylic acid) superabsorbent hydrogel

In this paper, controlled release of diclofenac sodium (DS) from pH-sensitive carrageenan-g-poly(acrylic acid) superabsorbent hydrogels was investigated. The hydrogels were prepared by graft copolymerization of acrylic acid (AA) onto kappa-carrageenan, using ammonium persulfate (APS) as a free radical initiator in the presence of methylene bisacrylamide (MBA) as a crosslinker. Infrared spectroscopy was carried out to confirm the chemical structure of the hydrogel. Moreover, morphology of the samples was examined by scanning electron microscopy (SEM). The synthesized hydrogels were subjected to equilibrium swelling studies in simulated gastric and intestinal fluids (SGF and SIF). Hydrogels containing drug DS, at different drug-to-polymer ratios, were prepared by direct adsorption method. The loading yield was found to depend on both the impregnation time and the amount of encapsulated drug. In vitro drug-release studies in different buffer solutions showed that the most important parameter affecting the drug-release behaviour of hydrogels is the pH of the solution. The mechanism involved in release was Fickian (n <= 0.43, n = 0.348) and Super Case II kinetics (n > 1, n = 1.231) at pH 1.2 and 7.4, respectively.