Highlighting the efficiency of ultrasound-based emulsifier-free emulsions to penetrate reconstructed human skin

Objective The cosmetic industry endeavours to strengthen the greener and safer claims of processes to respond to the high demand from customers for natural and environmentally friendly products. High-frequency ultrasonication technology (HFUT) is a physical process enabling the stabilization of emulsions without requiring additional ingredients, such as emulsifying surfactants (ES) to be introduced into the formulations. In this study, key formulation characteristics of an emulsion synthesized by HFUT and a reference emulsion (RE) were compared, as well as the permeation kinetics of caffeine, used as a model active cosmetic ingredient, from both types of emulsions. Methods The pH, droplet size and viscosity of emulsions prepared by the HFUT and the RE were determined and compared. The permeation of caffeine from the HFUT emulsion and the RE applied to the surface of reconstructed human epidermis (RHE) models was compared. Results The ES-free formulations prepared by HFUT displayed a nearly 2-fold lower average droplet size and over 3-fold greater viscosity, compared to the RE. Despite these differences, the absence of ES in the HFUT emulsion did not significantly alter the permeation kinetics of caffeine through RHE. The caffeine steady-state flux, lag time and permeability coefficients differed by 20%-30% only. Conclusion This study demonstrates the potential of the HFUT to yield topical cosmetic products with lower requirements ingredients-wise, without losing efficacy, supporting the possible implementation of the technology in the cosmetic industry.

Automated summary

This study compares the key formulation characteristics and caffeine permeation kinetics of emulsions synthesized by HFUT and a reference emulsion. The HFUT emulsions, which are free of emulsifying surfactants (ES), exhibit a smaller average droplet size and greater viscosity compared to the reference emulsion (RE). However, the absence of ES in the HFUT emulsion does not significantly affect the permeation kinetics of caffeine through reconstructed human epidermis (RHE). The caffeine steady-state flux, lag time, and permeability coefficients differ by only 20%-30%.