Diffusional release of a dispersed solute from solid and hollow cylindrical polymeric matrix into a finite external...

This study proposes both exact and numerical methodologies to characterize the diffusional release kinetics of a solute from solid or hollow cylindrical polymeric matrices into a limited external environment when the initial solute concentration exceeds its solubility limit. The influence of solute loading and external volume has been simulated for both geometries, and for the hollow cylinder, different inner-to-outer diameter ratios were also examined. A comprehensive understanding of the drug release kinetics was obtained by applying exact analytical and numerical methods to the moving boundaries. The analytical results were aligned with numerical solutions for the solid cylindrical matrix and validated against previous studies on both solid and hollow cylinders under ideal sink conditions. Furthermore, the developed mathematical models were validated using experimental drug release data, showing excellent consistency with experimental observations and robust predictive accuracy. The results demonstrated that whereas higher initial drug loading reduced both the time-dependent and maximum fractional release, increasing the external fluid volume enhanced the release rate and increased the total amount of drug released from both solid and hollow cylindrical matrices; moreover, in hollow cylinders, a higher inner-to-outer diameter results in more sustained, nearly zero-order release profile. Subtle geometric changes can generally greatly enhance release kinetics, providing a flexible approach for maximizing controlled drug delivery systems.