Tablet and powder mechanics depend on nano and micro scale adhesion, lubrication and structure

Tablets are the most convenient form for drug administration. Despite its ease of manufacturing problems such powder adhesion occur during the production process. This study presents a surface and structural characterization of tablets formulated with commonly used excipients (microcrystalline cellulose (MCC), lactose, mannitol, magnesium (Mg) stearate) pressed under different compaction conditions. Tablet surface analyses were performed with scanning electron microscopy (SEM), profilometry and atomic force microscopy (AFM). The mechanical properties of the tablets were evaluated with tablet hardness test. Tablet surface addition decreased when Mg stearate was present into the formulation. Besides, tablet strength of plastically deformable excipients such as MCC is significantly decreased after addition of Mg stearate. This indicates that Mg stearate affects the particle-particle binding and thus elastic recovery. In contrast, tablet strength of brittle materials like lactose and mannitol is unaffected by Mg stearate. Thus fracture occurs within the excipients and not at particle boundaries, creating new area not previously exposed to Mg stearate. Such uncoated surfaces may well promote adhesive interactions with tools during manufacture. The MCC excipient displayed the highest hardness which is characteristic for a highly cohesive material. This is discussed in the view of the relatively high adhesion found between MCC and a hydrophilic probe at the nanoscale using AFM