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

The swelling of hydrating HPMC tablets has been studied by NMR microsc opy. The technique is non-invasive and has allowed both dimensional ch anges in the core and in the developing surface hydrated layer to be s tudied. Hydration at the edges of the tablet occurred to a greater ext ent than in the centre of the tablet surfaces, giving rise to a convex shaped hydrated layer. Gel layer development occurred to the same ext ent in both axial and radial directions, and was similar in all HPMC t ypes. The predominantly axial swelling reported for all HPMC types, wa s shown to result almost equally from growth of the hydrated surface g el 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.