Characterization of moving fronts in cross-linked amylose matrices by image analysis

The purpose of this work was to characterize swelling and solvent concentration gradients in large matrices by image analysis. Tablets prepared by direct compression of cross-linked amylose (CLA), a polymer used for controlled release of drugs, with 10% diltiazem HCl were studied. Matrices corresponding to 3 different degrees of cross-linking were compared. The technique was simple and precise. It permitted the characterization of the changes occurring at the surface as well as inside the tablets during water sorption. The solvent penetrated all sides of the tablets. Three-dimensional swelling was recorded. Axial swelling was more pronounced than radial swelling for the 3 types of CLA. Augmenting the degree of cross-linking from 6 to 11 significantly increased the degree of swelling and solvent transport kinetics in CLA tablets. The equilibrium swelling state was attained much after the solvent penetration fronts had met.