STRUCTURE AND BEHAVIOR IN HYDROPHILIC MATRIX SUSTAINED-RELEASE DOSAGE FORMS .2. NMR-IMAGING STUDIES OF DIMENSIONAL CHANGES IN THE GEL LAYER AND CORE OF HPMC TABLETS UNDERGOING HYDRATION

The swelling of hydrating HPMC tablets has been studied by NMR microscopy. The technique is non-invasive and has allowed both dimensional changes in the core and in the developing surface hydrated layer to be studied. Hydration at the edges of the tablet occurred to a greater extent than in the centre of the tablet surfaces, giving rise to a convex shaped hydrated layer. Gel layer development occurred to the same extent in both axial and radial directions, and was similar in all HPMC types. The predominantly axial swelling reported for all HPMC types, was shown to result almost equally from growth of the hydrated surface gel layer and expansion of the ungelled tablet core. The smaller axial expansion observed in E4M tablets was not a result of slower gel layer growth, but was entirely due to a smaller expansion of the core.