STRUCTURE AND BEHAVIOR OF HYDROPHILIC MATRIX SUSTAINED-RELEASE DOSAGEFORMS .1. THE ORIGIN AND MECHANISM OF FORMATION OF GAS-BUBBLES IN THEHYDRATED SURFACE-LAYER

Gas bubbles are an important feature of the surface hydrated layer of hydrophilic matrix tablets in that they may significantly influence th e performance of these dosage forms. Cryogenic SEM studies on the hydr ated 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 pa rticles within a partially hydrated region at the core/pseudogel inter face, giving rise to discrete air pockets within the pseudogel layer.