Transport of Vitamin E from Ethanol/Water Solution into Contact Lenses and Impact on Drug Transport.

Purpose: Contact lens-based drug delivery has many advantages over eye drops including higher bioavailability and sustained release. Commercial contact lenses release drug rapidly necessitating integration of control-release mechanisms into the lenses such as incorporation of vitamin E diffusion barriers. In prior publications, vitamin E barriers are loaded by placing the lenses in vitamin E-ethanol solution, followed by the ethanol extraction. In this article, we investigate feasibility of manufacturing vitamin E barriers by soaking contact lenses in vitamin E dissolved in ethanol-water solutions to minimize swelling. Methods: Contact lenses are soaked in solutions of vitamin E dissolved in ethanol-water mixtures. The dynamics of vitamin E transport into the measured and fitted to diffusion equation to determine diffusivity and partition coefficient. Vitamin E loaded lenses are imaged and transport of hydrophilic drug timolol is measured. Results: The partition coefficient of vitamin E increases more than 5 and 10-fold when the water content in the loading solution reaches 15% and 25% (v/v), respectively. The solubility of vitamin E in the solutions decreases as water fraction increases but the increase in partition coefficient allows for loading > 20% vitamin E in the lens. The barriers manufactured by this approach are effective at sustaining release of glaucoma drug timolol. Conclusions: Vitamin E barriers can be incorporated into contact lenses by soaking in solutions of vitamin E in water and ethanol. Vitamin E barriers extended hydrophilic drug release and the reduced swelling is beneficial in minimizing the possibility of lens damage during loading of vitamin E.