Parameter-dependent stress states and their effects on properties of press-coated tablets

Press-coated tablets (PCTs) are a modern dosage form designed to circumvent the negative effects of liquid and heat exposure that may damage drug substances during common wet coating processes for tablets. However, the production process is complex and the mechanical properties of the formulations of the different compartments may lead to challenges regarding processability, distribution of properties, and mechanical stability of the PCTs. In this study, materials with markedly different deformation properties were combined to elucidate the stress distribution during press coating and to assess the effects of process parameters and core geometry on the final PCT properties. Thorough structural investigations of all PCT compartments and the in-die analyses of axial and radial stress were applied. The simplistic approach to unify effects on the core properties by relating the punch force only on the projection area of the core only applies to the recovered core diameter and fails for further parameters. It accordingly requires more consideration of the complex stress states. The radial stress analyses clarify the anisotropy within the compression process of PCTs. It explains the findings on the distributions of porosity across different coat compartments and on the compactibilities of the recovered core. Finally, the breaking pattern of PCTs were explained with structural findings and the deduction of acting residual stresses.