Unveiling tablet structural changes: A micro computed tomography analysis of aqueous coating effects

Tablet coating with aqueous solvents represents a well-established environmentally sustainable alternative to coatings based on organic solvents. However, this practice requires a careful evaluation of potential quality issues, such as increased porosity and crack formation stemming from possible tablet components interaction with water. In this work, a preliminary study on the compression of quaternary mixtures of one model drug and three common excipients was performed to investigate the behaviour of the mixtures and the relevant components during compression. Obtained tablets were coated with a hypromellose aqueous solution followed by an enteric coating with a poly(methyl acrylate-co-methyl methacrylate-co-methacrylic acid) dispersion. At each step, tablet porosity was measured by X-Ray microcomputed tomography (XµCT). XµCT evidenced significant changes in the structure of some tablets upon coating. The mechanical characteristics of the mixture components play a crucial role in the observed porosity increase (up to 12%) after the coating. Materials with remarkable plastic densification upon compression afforded higher structural changes with swelling and cracking formation. XµCT has proven to be an essential technique for identifying morphological changes that could compromise the quality of the tablets.