Swelling and diffusion studies of calcium polysaccharide gels intended for film coating.

The aim of this paper was to study the swelling and diffusion behaviors of calcium polysaccharide gel (CaPG) films prepared by an interfacial complexation technique, a new gel formation method that allowed calcium ions to diffuse from a source to form gel films with polysaccharide (i.e., alginate or pectin). The dynamic swelling behavior of CaPG films showed that swelling was a function of time. Most CaPG films showed a maximum amount of water absorption during the first few hours. The films swelled less in water and acidic media but extensively swelled in 0.1M NaCl. The rehydration of the dry films in the acidic media or the 0.1M NaCl solution also lead to the extraction of most of the calcium ions from the CaPG within 4h or less. Partitioning and diffusion of a model drug, theophylline (TPL), were measured through CaPG films equilibrated in different media. The partition and diffusion coefficients of TPL through CaPG films were found to vary, depending upon polysaccharide type, concentration and equilibration medium. The results suggest that both partition and pore mechanisms operated concurrently in the transport of TPL through CaPG films equilibrated in different media.