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(ɛ-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.