Investigation of critical factors affecting mechanical characteristics of press-coated tablets using a compaction...

Press-coated tablets have become an indispensable dosage form in chronotherapeutic drug delivery. Drug release from press-coated tablets has been extensively studied, yet there is little knowledge about their mechanical characteristics. This study aimed to systematically investigate the effects of critical factors on the structure, layer adhesion, and delamination tendency of the tablets. Material elasticity was found to play an important role in determining tablet structure in that excessive elastic mismatch between core and shell materials caused tablet defects during decompression and ejection. Unlike bilayer tablets, the overall strength of press-coated tablets was more affected by binding capacity of coating materials than by the core properties. Shell/core ratio was another factor affecting tablet integrity against external stresses. To mitigate the risk of delamination, poor layer adhesion must be compensated by increasing the coating thickness or enhanced by optimizing the formulation and process (e.g., core plasticity/brittleness, initial core solid fraction, and compression speed). X-ray micro-computed tomography revealed the presence of a shell-core gap and inhomogeneous density distribution within the tablet where the side coat appeared as the least dense and weakest region. These findings will enable the improvement of tablet quality and widen the application of press coating in industrial manufacturing.