Development and safety assessment of a gold nanoparticles-containing cosmetic cream: dermal absorption and in vitro toxicological profile

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Abstract
Gold nanoparticles (AuNPs) are used in cosmetic formulations due to their physicochemical stability and potential skin benefits. Despite their popularity, the possibility of skin absorption raises concerns about their safety. This feature is especially important for higher concentrations of smaller AuNPs. To overcome this problem we produced larger AuNPs with a diameter of 75.24 ± 16.12 nm using an optimised ultrasonic spray pyrolysis (USP) method. Upon stabilisation with polyvinylpyrrolidone (PVP), the AuNPs were incorporated into a multicomponent cosmetic cream at a low concentration (25 ppm). Physicochemical characterisation of the AuNPs, both in the dried state and within the cream, showed a predominantly spherical and irregular morphology, as well as good dispersion and colloidal stability. The AuNPs were integrated into the cream formulation well, showing no structural, colour, or fragrance changes in the cream matrix. The biocompatibility of the AuNPs cream was evaluated thoroughly using a battery of in vitro tests. The dermal absorption assay using human skin in Franz diffusion cells (OECD TG 428) demonstrated no penetration of AuNPs through the skin. The caffeine control confirmed assay sensitivity. The viability studies, as assessed using L929 mouse fibroblast cells, U937 human monocytic cells and human peripheral blood mononuclear cells (PBMCs), did not show the cytotoxic effect of AuNPs, even at high concentrations. Genotoxicity was not detected in the stimulated PBMCs using the cytokinesis-block micronucleus assay (OECD TG 487). However, the U-SENS™ assay (OECD TG 442E) indicated a positive reaction, most probably due to the presence of sensitising components in the cream`s formulation. When the AuNPs were tested separately the result was negative. In conclusion, our results are consistent with a favourable safety profile of the tested AuNPs-containing cream under the evaluated conditions. However, quantitative dose-bridging and margin-of-safety analysis are needed to substantiate product safety further for real-world use.

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