Tocopheryl acetate nanoemulsions stabilized with lipid-polymer hybrid emulsifiers for effective skin delivery

Tocopheryl acetate is used as the oil component of nanoemulsions using a mixture of unsaturated phospholipids and polyethylene oxide-block-poly(epsilon-caprolactone) (PEO-b-PCL). This study investigates the effects of the lipid-polymer composition on the size and surface charge of nanoemulsions, microviscosity of the interfacial layer, and skin absorption of tocopheryl acetate. The lipid-polymer hybrid system exhibits excellent colloidal dispersion stability, which is comparable to that of polymer-based nanoemulsions. If lipids are used as emulsifiers, nanoemulsions show poor dispersion stability despite a good skin absorption enhancing effect. The amount of tocopheryl acetate absorbed by the skin increases with an increased lipid-to-polymer ratio, as determined using the hairless guinea pig skin loaded in a Franz-type diffusion cell. An 8:2 (w/w) mixture of unsaturated phospholipids and PEO-b-PCL exhibits the most efficient delivery of tocopheryl acetate into the skin. Our results show that tocopheryl acetate is absorbed almost twice as fast by the lipid-polymer hybrid system than the nanoemulsions stabilized with PEO-b-PCL. This study suggests that the lipid-polymer hybrid system can be used as an effective means of optimizing nanoemulsions in terms of dispersion stability and skin delivery capability. (C) 2012 Elsevier B.V. All rights reserved.