Characterization of Mechanical Property Distributions on Tablet Surfaces

Abstract

Powder densification through uniaxial compaction is governed by a number of simultaneous processes taking place on a reduced time as the result of the stress gradients within the packing, as well as the frictional and adhesive forces between the powder and the die walls. As a result of that, a density and stiffness anisotropy is developed across the axial and radial directions. In this study, microindentation has been applied to assess and quantify the variation of the module of elasticity (Emod) throughout the surface of cylindrical tablets. A representative set of deformation behaviors was analyzed by pharmaceutical excipients ranging from soft/plastic behavior (microcrystalline cellulose) over medium (lactose) to hard/brittle behavior (calcium phosphate) for different compaction pressures. The results of the local stiffness distribution over tablet faces depicted a linear and directly proportional tendency between a solid fraction and Emod for the upper and lower faces, as well as remarkable stiffness anisotropy between the axial and radial directions of compaction. The highest extent of the stiffness anisotropy that was found for ductile grades of microcrystalline cellulose (MCC) in comparison with brittle powders has been attributed to the dual phenomena of overall elastic recovery and Poisson’s effect on the relaxation kinetics. As a reinforcement of this analysis, the evolution of the specific surface area elucidated the respective densification mechanism and its implementations toward anisotropy. For ductile excipients, the increase in the contact surface area as well as the reduction and closing of interstitial pores explain the reduction of surface area with increasing compaction pressure. For brittle powders, densification evolves through fragmentation and the subsequent filling of voids.

The use of X-ray microtomography to investigate the microstructure of pharmaceutical tablets: Potentials and comparison to common physical methods

“…However, results for φ UV−VIS and φ theo are based on the examination of whole tablets while φ XMT relates to an analysis volume of (2.53 mm) 2 multiplied by the tablet height taken from the middle of the tablet. Therefore, the measured values by UV-VIS may not necessarily match the exact same values yielded by XMT – especially if IBU is not homogeneously distributed inside the tablet or due to the density distribution from the center to the edge in flat-faced tablets ( Cabiscol et al, 2018 ).…”

Characterisation and Traceability of Calcium Carbonate from the Seaweed Lithothamnium calcareum

“…The fluidity of CaCO 3 is also related to its surface area and porosity. A decrease in the pore size of L. calcareum and oyster shell CaCO 3 increases the compacted density of the material (Table 2), making the tablets fragile, brittle and easily chipped during large-scale production [33]. In terms of porosity, L. calcareum CaCO 3 had the characteristics of an ultra-microporous material, with a pore size of < 7 Å; the form shown in the literature for this type of material is slit or curled [38,39].…”

“…In L. calcareum CaCO 3 , there may have been a greater interaction between the particles as a consequence of their morphology. The flow of CaCO 3 particles is compromised by the cleavage of crystals, which form particles of an anisotropic (rhombohedral) shape, deviating from the ideal spherical shape [33]. The smaller the particle size, the lower the CI and HR, which are features that distinguish L. calcareum CaCO 3 from other carbonates [34,35].…”

Disintegrant Selection in Hydrophobic Tablet Formulations

“…The values of the tablets' dimensions after 1 day storage at RT in sealed bags are an indication of elastic recovery. 34 All other observed changes in dimensions result from the combined effects of elastic recovery and storage conditions. In each storage condition, the percentage change in tablet thickness was z10 fold greater than the change in diameter, indicating a preferential expansion in the axial direction (i.e.…”