Abstract: This work presents a systematic framework to achieve the desired diffusional release of drug from a non-erodible polymeric matrix.The model of this representation is a boundary value problem based on Fick's second law.The solution of this governing equation is divided into two phases.Phase I is a Stefan problem with a moving diffusion front while Phase Ⅱ begins after the moving diffusion front has disappeared. The main objective of the present study is to investigate analytically the complete release process of a solute from a non-erodible matrix up to a time corresponding to the absence of the diffusion front.This solution may serve as a basis for modeling more complicated systems.

Key words: diffusional release, moving diffusion front, exact solution, cumulative mass release