IMPACT OF A TIO2 [NANO] COSMETICS GRADE ON THE CUTANEOUS MICROBIOTA: NANOPARTICLES BEHAVIOR IN EMULSION AND BACTERIOTOXICITY

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Rowenczyk, Laura | Barreau, Magalie | Picard, Celine | Duclairoir-Poc, Cécile | Hucher, Nicolas | Orange, Nicole | Feuilloley, Marc, G J | Grisel, Michel

Edité par CCSD -

International audience. TiO2-nanoparticles (NP) commonly used in cosmetics as physical UV-filters, are surface-modified by applying a first coating in order to quench photo-produced radicals. In addition, a second coating is sometimes added to raise their dispersibility in emulsion. Whereas European regulation mentions the obligation to demonstrate the safety of NP, very few studies took interest on their behavior in use. During formulation and storage, NP are exposed to a variety of environmental conditions which can accelerate aging and induce particles aggregation, adsorption of formula’s compounds or coatings deterioration. Consequently, a crucial question remains their safety while layered on skin and particularly their effect on the skin microflora. We will present the impact of TiO2-nanoparticles on the skin microflora in relation to their physicochemical properties in cosmetic emulsions during aging.A series of cosmetic emulsions were formulated with using conventional cosmetic ingredients, with or without Nanoparticles (NPs): one without NPs considered as blank, and two with hydrophilic and hydrophobic commercial TiO2-NPs, respectively. An emulsification process was developed and optimized to obtain a blank emulsion, physically stable, with improved NPs dispersions in emulsion. Then, emulsions were submitted to accelerate aging.Particles were extracted from the fresh/aged emulsions by original protocols allowing recovering particles with possible adsorbed compounds or cleaned surfaces.Skin bacteria growths were evaluated in emulsions or dispersions to check the toxicity of nanoparticles in use. Then, because of NP opacity, protocols were adapted to measure their effect on bacteria virulence toward skin cells.Microscopic and macroscopic characterizations revealed comparable structures and functional properties between the three fresh emulsions. Then, during aging, different behavior were registered and could be related to nanoparticle coating nature.Extracted NP from the fresh/aged formulas showed quick surface modifications in terms of chemical structures and physical properties that might be caused by adsorption or deterioration at their surfaces.For fresh emulsions, both nanoparticles did not have any impact on skin bacteria strains, S. aureus and P. fluorescens. In the case of aged emulsions, part of NPs seemed to allow the S. aureus growth, whereas others still remained with no effect on microflora. Finally, bacteria generation times and virulence toward skin cells differed depending on NPs surface treatments and exposition time.This work dealt with the impact of nanoparticles on skin microflora along cosmetic emulsion shelf-life. This new approach allows taking into account their safety when used in emulsion.First, through innovative extraction and characterization protocols, it was highlighted that chemical nature and physical properties of nanoparticle surfaces might be altered once in emulsion. These physicochemical observations were related to microbiological tests on skin representative bacteria. Effect of some of the NPs on bacteria growth and virulence evolved after aging. Finally, modification of NPs surface treatment seemed to have an effect on skin microflora.

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