Laponite-based nano-emulsions of amazonian essential oils

This study investigated the behaviour of essential oil-in-water emulsions (O/W) containing Bursera graveolens, and Ocotea quixos essential oils. To enhance their topical administration and stability, Laponite (a synthetic, hectorite-like clay) was added at different concentrations to the continuous phase. All formulations were assessed in terms of time-stability, particle size, zeta potential, antioxidant activity, rheological properties, and in vitro cytotoxicity. Despite the excellent encapsulation capacity of essential oils, the addition of 3 % w/w Laponite accelerated emulsion instability at extreme conditions. In contrast, this inorganic ingredient significantly improved the rheological properties for topical administration. High-resolution transmission electron microscopy (HR-TEM) was used to characterize the morphology of the emulsions, showing a layer of Laponite particles around the essential oil droplets, a typical feature of Pickering emulsions. Cytotoxicity studies confirmed that O/W emulsions were not toxic for cells, a result strengthened by 3 % w/w of Laponite. In conclusion, O/W microemulsion from Bursera graveolens and Ocotea quixos essential oils proved stable and safe as topical formulations. Rheological performance and in vitro cytotoxicity can be modulated by the addition of Laponite, although its concentration must be optimised.