Structure and behaviour of hydrophilic matrix sustained release dosage forms: 1. The origin and mechanism of formation of gas bubbles in the hydrated surface layer

Abstract

Gas bubbles are an important feature of the surface hydrated layer of hydrophilic matrix tablets in that they may significantly influence the performance of these dosage forms. Cryogenic SEM studies on the hydrated layer provide direct visual evidence for the origin and mechanism of formation of these bubbles. Air within the voids of the dry tablet core is observed to be progressively entrapped by swelling polymer particles within a partially hydrated region at the core/pseudogel interface, giving rise to discrete air pockets within the pseudogel layer.