Solute transport in poly(2-hydroxyethyl methacrylate) hydrogel membranes

The swelling, permeation, and release characteristics for benzoic acid, caffeine, propranolol hydrochloride, and diclofenac sodium in crosslinked poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels were examined. Increasing polymer crosslinking density resulted in decreases in the degree of swelling, drug loading, the diffusivity of solute in the hydrogels, and in the rate of drug release. Diclofenac sodium led to an abnormally large degree of swelling as the maximum value is given as 6.5, while the highest for the other three was 1.07. That the logarithmic drug diffusivity was proportional to the reciprocal of hydration indicates that the free volume theory accounts for the transport of solute in the gels. Increasing the concentration resulted in increases in the diffusivities, solubilities, and permeabilities of the solutes in the hydrogels. The drug release kinetics from most wet hydrogel samples can be well-fitted by a Fickian diffusion model. Near zero-order release is observed only for dry samples with caffeine of low loading.