EFFECT OF DRUG HYDROPHILICITY AND MEMBRANE HYDRATION ON DIFFUSION IN HYALURONIC-ACID ESTER MEMBRANES

The diffusion of solutes in hydrated polymer membranes may be influenc ed by solute hydrophilicity and membrane hydration. These effects were examined using a panel of six neutral drug molecules and hyaluronic a cid benzyl ester membranes with varying degrees of esterification. The natural logarithm of diffusivity was found to be a function of membra ne hydration for all drugs and membranes studied. A linear relationshi p between the natural logarithm of diffusivity and the inverse of memb rane hydration was observed for the hydrophilic drugs, indicating cons istency with Yasuda's free volume theory. Non-linear relationships wer e observed for hydrophobic drugs, suggesting deviation from the theory . A simple mathematical model was developed, based on parallel diffusi on in hydrophilic and hydrophobic domains, and was found to adequately describe tile diffusion characteristics of both hydrophilic and hydro phobic solutes.