pH sensitive polyelectrolyte complex of O-carboxymethyl chitosan and poly (acrylic acid) cross-linked with calcium for sustained delivery of acid susceptible drugs

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The present study investigates the ability of a polyelectrolyte complex, composed of O-carboxymethyl chitosan (O-CMC) and carbopol cross linked with calcium, as a pH-sensitive carrier for acid susceptible drugs. DSC studies were performed to confirm the formation of O-CMC–carbopol complex. Double endothermic peaks in thermogram of polyelectrolyte beads reflect the molecular changes brought in after cross-linking. FT-IR spectroscopy was used to reveal peak variation of the carboxylic groups as a function of pH 1.2 and pH 6.8. The formation of polyelectrolyte complex, on account of electrostatic interactions between the –COO group of carbopol and the –NH3+ group of O-CMC, was also confirmed by FT-IR studies. Swelling of the O-CMC–carbopol film showed a pH-dependent profile that was affected by calcium ion concentration. The swelling rate was more significant at intestinal pH because the ionization of carboxylic acid group on O-CMC and carbopol creates electrostatic repulsion. Release behavior of drug is relative to the viscosity of solution and the ionic interaction between O-CMC and carbopol. Mucous glycoprotein assay revealed that ionization of carboxylic group on the beads at intestinal pH formed a strong hydrogen bond with mucin, which was responsible for the prominent mucoadhesive property thus prolonging the intestinal residence time.

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