Essential oil-in-water microemulsions for topical application: structural study, cytotoxic effect and insect repelling activity

Essential oils (EOs) extracted from aromatic plants have been well recognized for their insect repellent properties. Although EOs are effective when freshly applied, protective effect usually dissipates quickly due to low chemical stability and rapid volatilization of ingredients. To address this issue, encapsulation in carrier materials at the nanoscale is proposed. In study, oil-in-water (O/W) microemulsions containing geraniol or Citrepel® 75 (citrepel) as oil phase, a mixture water diethylene glycol monoethyl ether (DEGEE) aqueous phase caprylocaproyl polyoxyl-8 glycerides surfactant were formulated structurally characterized. DLS analysis showed that emulsified droplets had polydispersity (PdI<0.3) average hydrodynamic diameter ranging 13.7 ± 0.7–35.2 2.7 nm, depending on composition. Mean viscosity all prepared was 15.7 0.3 cP 23.8 0.2 indicating suitability preparations topical application. EPR spectroscopy using spin probes gave information about rigidity surfactants’ monolayer. cases an outer compact configuration interfacial layer more flexible inner one observed. SAXS measurements revealed significant changes q values related impact citrepel microemulsion formulations. Looking high region spectra, curves affected by presence compounds concentration depended manner. Cytotoxicity studies normal human epidermal keratinocytes (NHKs) confirmed sub-toxic dosage geraniol-in-water citrepel-in-water 56.25 μg active ingredient per cm2 cell Finally, diluted evaluated repellence action against Asian tiger mosquito (Aedes albopictus) showing activity 3 h dose 190 μg/cm2 ingredient. Gaining comprehensive understanding results, promising candidates application based safe