Diffusional release of a dispersed solute from a spherical polymer matrix

The exact analytical solution and an approximate solution based on the variational formulation method have been obtained for the release kinetics of a solute from a spherical polymeric matrix in which the initial solute loading A is above the solubility limit C-s. Comparisons between these new solutions and previously reported approximate solutions based on either pseudo-steady state assumptions or the refined integral method indicate that the approximate solutions are very accurate when A/C-s is much larger than unity. However, as drug loading decreases, deviations between the approximate solutions and the exact solution increase so that the approximate solutions are least accurate in the limit A/C-s --> 1.