Loading of vitamin E into silicone hydrogel by supercritical carbon dioxide impregnation toward controlled release of timolol maleate

•Supercritical impregnation was applied for loading vitamin E into silicone hydrogel.•Loading of vitamin E in supercritical CO2 is more effective than that in liquid solution.•Supercritical impregnation achieves timolol maleate diffusion in vitamin E rich region.•Timolol maleate diffusivity in hydrogel is reduced significantly by loading vitamin E.

Supercritical CO2 impregnation was applied to loading of vitamin E into silicone hydrogel for development of controlled release system of timolol maleate, hydrophilic ocular drug for glaucoma. Vitamin E was loaded into the silicone hydrogel to reduce the diffusivity of timolol maleate. Supercritical impregnation accomplishes the large amount of loaded vitamin E into the silicone hydrogel at the low concentration in supercritical CO2 compared with that by ethanol liquid solution. The loading of vitamin E 0.49 g g−1-hydrogel by the supercritical impregnation results in the significant reduction of the diffusivity of timolol maleate in the silicone hydrogel to 1.4 × 10−5 mm2 min−1 much smaller than of that without vitamin E, 13 × 10−5 mm2 min−1. The release system of timolol maleate in silicone hydrogel with the low diffusivity is obtained from the effective loading of vitamin into the silicone hydrogel using the supercritical impregnation.

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