Topographic characterization of cellulose bilayered tablets interfaces

The introduction of bilayer tablets into the pharmaceutical industry has enabled the development of pre-determined release profiles of active ingredients. During production, however, these bilayer tablets have the tendency to fracture by capping, thought to be caused by internal tensile stresses normal to the plane of fracture. Bi-layered tablets of the widely used excipient microcrystalline cellulose (MCC) have been manufactured and using a developed tensile stress method have been deformed until fracture. The topography of the fracture surfaces at the interface have been obtained using laser profilometry. The overall geometric shape of the topographic profile has shown to provide an insight into the magnitude of stress field that the MCC particles present at the interface have endured. The die wall friction has also shown to have significant implications in the development of the stress fields in bi-layer tablets. Examination of the X-ray tomography of a tablet manufactured using an unlubricated punch and die set indicates that the retardation force of the die contributes to the formation of an inherent crack at the interface of the adjacent layers during either the unloading or more likely at the ejection stage of the compaction process. This crack will act as a local stress concentrator significantly weakening the tablet strength.