Modification of the swelling behavior of a hydrophilic polymer as an approach to maintaining a constant gel layer thickness

Abstract

The objective of the present study was to screen some ionic polymers that can modify the swelling and erosion characteristics of a hydrophilic polymer (HPMC) and thereby help provide constant drug release. It was hypothesized that the hydrophilic polymer's swelling rate and erosion of matrices could be modified by adding an ionic polymer, as the two will form a hydrogen bond. Methocel™ K4M (HPMC) was selected as the hydrophilic polymer. NaCMC, Eudragit® S100, and Eudragit® L100 were selected as anionic polymers. Eudragit® RSPO, Eudragit® RLPO and Eudragit® EPO were selected as cationic polymers. Various techniques were used to characterize the rate of swelling, gel layer thickness, and erosion of matrices of HPMC-ionic polymer combinations (3:1 ratio). Fourier-transform infrared spectroscopy was used to study HPMC-ionic polymer interaction. A texture analyzer was used to investigate the change in gel layer thickness and firmness of matrices during dissolution study over time. The stereo microscopic examination provided a structural change in matrices during swelling. Of all the matrices, the HPMC-Eudragit® RSPO combination showed simultaneous swelling and matrix erosion, resulting in constant gel layer thickness (diffusional path length) for 12 h.