An advanced model for composite planar three-layer matrix-controlled release devices: Part I. Devices of uniform material properties and non-uniform solute load

A general model capable of simulating the operation of a polymer-based, solvent-activated, symmetrical three-layer (ABA), or equivalently two-layer (AB with the B surface blocked), matrix-controlled release (MCR) device, is presented and used for a parametric investigation of predicted release kinetics covering a much wider range of conditions than previously studied. The model can account adequately for (i) polymer–solvent–solute sorption and transport interactions, including solvent-induced osmotic effects, (ii) fast or slow (Fickian) solvent penetration relative to solute release and (iii) embedded solute loads exceeding the limit of solubility in the fully swollen matrix. The results obtained for the case of identical A and B layers differing only in solute load are reported here. They reveal important possibilities of markedly alleviating the main problems of non-uniformity of dose rate and initial “burst effect”, which normally characterize the operation of single-layer (monolithic) MCR devices, by use of properly designed ABA systems of the aforementioned type. The comparative analysis of MCR performance data has been put on a firm theoretical basis by the introduction of (i) the concept of efficiency of an MCR system and (ii) examination of the evolution of the fractional solute rate as a function of the fractional amount released rather than as a function of time.