DIFFUSION AND DRUG RELEASE IN POLYMER-FILMS PREPARED FROM ESTER DERIVATIVES OF HYALURONIC-ACID

The transport properties of thin films formed from hyaluronic acid esters have been studied. The permeabilities of the films to various solutes, the partition coefficients for a series of alkyl parabens, the rate and extent of hydration, and the release of a model compound were used as indicators of transport behavior. All the films tested had permeabilities to small neutral and positively charged solutes that were greater than 1 × 10-5 cm/s. Smaller permeability values were observed for negatively charged solutes, and for solutes with molecular weights greater than 3000 amu. The partition coefficients (Cmembrane/Cbuffer) for a series of alkyl parabens into a benzyl ester film varied from 12 to 41, and increased with increasing alkyi chain length of the paraben, indicating a partial hydrophobic character of the hydrated films. The films hydrated to a significant degree in distilled water (20 to 260% weight increase); the degree of hydration depended on the alcohol used to form the ester. A correlation between the permeability of the films to ethyl paraben and the degree of polymer hydration was observed. The release of a model compound (chlorpromazine) that was physically incorporated into the films was rapid, with complete release occurring in less than 200 minutes. This rapid release is consistent with the high degree of hydration and high permeability of the films. © 1990.