Electron microscope characterization of drug release from methacrylic acid-ethyl acrylate copolymer-coated cross-linked alginate-gelatine beads

Drug release from alginate-based beads is generally a fast process influenced by parameters such as bead production technique and drug physicochemical properties. In a previous report new cross-linked alginate-gelatin beads were developed, with the ability to successfully prolong drug release. The present work is focused on scanning electron microscopy analysis of the morphological modifications of cross-linked alginate-gelatin beads occurring throughout enteric coating with a methacrylic acid-ethyl acrylate copolymer and in vitro release studies. The coating material remains unchanged in gastric pH conditions irrespective either of the irregular thickness of the coating layer or related changes observed in the inner matrix. In phosphate buffer pH 7.4 the coating dissolves immediately and the cross-linked matrix tends to swell influencing drug release. However, beads maintained their shape throughout the dissolution test, presenting a prolonged drug release profile. The cross-linking bonds contribute to the particle keeping its shape throughout release. Microscopical analysis confirms that matrix modification by the cross-linking reaction is crucial for the controlled release of the model drug (pindolol) from alginate beads.