Atomic Force Microscopy Analysis and Confocal Raman Microimaging of Coated Pellets

Polymer-coated pellets with different coating thicknesses have been studied regarding coating morphology and drug release properties with atomic force microscopy (AFM) and confocal Raman microscopy. The results were compared with those from scanning electron microscopy (SEM) and drug release profiles, which have been measured previously for these systems and found to vary depending on coating thickness. Results from AFM studies indicated that these pellets differ in the amount of crystalline material on the surface of the coating. The amount was found to be highest on the pellet with the thinnest coating. Confocal Raman microscopy studies confirmed that the active component (remoxipride hydrochloride monohydrate) is present at or close to the surface and that the amount is higher for the thinnest coating. AFM studies in aqueous media showed that the crystalline material on the surface was almost instantaneously dissolved and released into the liquid. AFM has proven to be a powerful tool in the study of the surface of dry formulations and in the study of the controlled release mechanism of a pharmaceutical in a liquid cell. The method can be combined with Raman, giving the added possibility to identify the chemical composition in selected small areas of the coating surface.