Image analysis studies of water transport and dimensional changes occurring in the early stages of hydration in...

The purpose of this work was to monitor and quantify water transport and dimensional changes occurring in the early stages of hydration in cross-linked amylose (CLA) matrices using image analysis technique. Samples were prepared by direct compression of CLA-6 powder to obtain matrices of 0.17 cm thickness and 1.295 cm in diameter. A surface gel layer was formed quasiinstantaneously. The gel expansion was then constrained and the material continuity caused the outer gel layer to be in a state of biaxial compression and the internal core in a state of biaxial tension. A diffusion front preceded the gel-glass interface even in the early stages of hydration. A delayed stress-release occurred through a radial expansion of the tablet interior. This relaxation coincided with the time at which the axial diffusion fronts met. The dimensional changes had a marked impact on the kinetics of water uptake in CLA-6 tablets in early stages of hydration.