Caffeine release from fully swollen poly(ethylene oxide) hydrogels

Abstract Diffusion of uniformly dispersed caffeine in water-swollen poly (ethylene oxide)-based hydrogels was studied by assaying the release of solute from thin slabs into a finite volume of solution at 37° C. Fractional release followed a time 0.5 relationship for a range of thicknesses between 1 and 5 mm and different polymer compositions with equilibrium water uptake of 118–530 parts per hundred dry polymer. Values of the diffusion coefficient, D p , were calculated from the experimental results by assuming the hydrogel to be (1) an infinite sheet and (2) a rectangular parallel-epiped. Both bound and free water were identified in differential calorimetry scans of the hydrogel. The diffusion coefficient found for the various water contents obeyed the Davis relationship and this equation appears to represent the diffusion characteristics of these PEO hydrogels quite accurately.