pH-responsive CMC/PAM/PVP semi-IPN hydrogels for theophylline drug release

Novel semi-interpenetrating network (semi-IPN) polymeric hydrogels for theophylline drug delivery were prepared using carboxymethyl chitosan (CMC), acrylamide (AM), and polyvinylpyrrolidone (PVP) as synthetic components in the presence of N,N-methylene bisacrylamide as a crosslinker and potassium persulfate as an initiator. The structures of the CMC/polyacrylamide (PAM)/PVP hydrogels were characterized by Fourier transform infrared spectroscopy. Scanning electron microscope observations indicated that the hydrogels had morphologies characterized by a three-dimensional network, with crosslinking rates of 76–82 %. As the PVP content was increased, the porous structure became more compact and the pore size smaller. Investigations of the swelling kinetics of the hydrogels demonstrated that their equilibrium swelling ratios depended on their compositional ratios, ionic strengths, and the pH of the buffer solution. In particular, the hydrogels swelled at pH 7.4 but shrank at pH 1.4, resulting in a larger swelling ratio in alkaline solution than in acidic solution. The swelling ratios of the hydrogels decreased with increasing ionic strength. Studies of the in vitro release of the model drug theophylline from the hydrogels revealed that the drug release profile depended on the pH of the medium and the hydrogel composition. As the PVP content was increased, the drug release rate rose at pH 1.4, whereas the rate decreased at pH 7.4. The reason for the faster drug release at pH 7.4 than at pH 1.4 may be the occurrence different mechanisms at different pH values: non-Fickian behavior in PBS at pH 11.7 and Fickian diffusion in PBS at pH 1.4.