Lipid nanoparticles as carriers of cyclodextrin inclusion complexes: A promising approach for cutaneous delivery of a volatile essential oil

Abstract

Solid inclusion complexes with cyclodextrins (CD) may be used to overcome volatility and solubility problems of essential oils of pharmacological interest. However, they lack the many dermatological advantages of lipid nanoparticles. This study intends to evaluate the ability of nanostructured lipid carriers (NLC) to encapsulate hydroxypropyl-β-cyclodextrin inclusion complexes of Lippia origanoides essential oil (EO) and to maintain the desirable aspects of lipid colloids interaction with the skin, specifically follicular accumulation and controlled delivery. CD and NLC were also evaluated separately. Thymol (TML) was used as the essential oil marker and to produce control formulations. As expected, CD alone, though effective in overcoming volatility and low aqueous solubility of TML, were ineffective in controlling marker release (˜50% of EO released after 3 h, Hixson-Crowell kinetics). Even though NLC controlled drug release (˜20% EO released after 12 h, zero-order kinetics) enabling TML penetration into the skin (> 40 μg/cm2after 12 h), NLC alone were not efficient in preventing TML volatility, especially at higher temperatures (calculated shelf-life of 2 days at 35 °C). The combined approach resulted in a synergistic effect (˜20% EO released after 12 h; shelf life of 6 days). The lack of statistical difference of TML skin penetration from NLC and NLC-CD suggests the developed system maintained all skin interaction aspects of lipid colloids, including follicular accumulation forming a depot for controlled delivery. In conclusion, lipid nanoparticles demonstrated to be promising carriers for inclusion complexes of this particular volatile essential oil.