DEVELOPMENT OF PRESERVATIVE-FREE COSMETIC EMULSIONS CONTAINING TIO2 [NANO]: EFFECTS OF PARTICLES SURFACE AND STERILIZATION PROCESS
Résumé
Development and physico-chemical characterization of oil-in-water emulsions containing TiO2-nanoparticles (NPs) will be presented. These particles, commonly used in cosmetics as UV-filters, are surface-modified by applying silica or alumina coatings in order to quench photo-produced radicals. In addition, organic coatings may be added to adapt particle polarity and thus, raise its dispersibility in emulsion. These coatings might have opposite effects on the emulsion structure according to their nature and this need to be evaluated.
In this work, formulae had to be developed preservative-free. In Food industry, many sterilization procedures, consisting in total elimination of germs and spores, are frequently employed. On the contrary, in Cosmetics production, chemical pathway remains the main solution. Cosmetic forms often does not allow utilization of several procedures; for instance, emulsion systems filtration could lead to a demixing phenomenon. Moreover, cosmetic actives prohibit the use of radiations. Recently, sterilization of cosmetic emulsions were conducted through an ultra-high temperature treatment. Nevertheless, temperature could accelerate emulsion aging:
in the case of emulsions containing NPs, they could induce particles aggregation, adsorption of formula's compounds and coatings deterioration.
Emulsions were formulated differing only by the presence and type of NPs: one NP-free as blank, and two containing hydrophilic and hydrophobic commercial TiO2-NPs, respectively. Emulsification process was optimized to obtain oil droplets as fine as possible and acceptable NPs dispersions in emulsion. Microscopic and innovative macroscopic characterizations revealed comparable structures and functional properties between the three initial emulsions.
In our case, at a lab scale, packaging-in sterilization, adapted from Appertisation, was used on emulsions.
Formulation of emulsions containing low microbiological charges under the limit determined by the European Pharmacopoeia[6] was already achieved with cautious manipulations using sterile materials. However, microbiologic tests confirmed the absence of any aerobic mesophilic germs in emulsions after sterilization.
For NP-free emulsion, both the microscopic characteristics and the macroscopic properties (viscosity, consistency or spreading quality...) were only slightly modified by the heat treatment. Success of the procedure on emulsions with NPs seemed mainly to depend on the nature of their coating. Impact of the sterilization step on emulsions containing coated NPs will be presented.
This work adapts a Food industry technic on fragile cosmetic emulsions. Favorable microbiological results show the benefit of temperature sterilization on cosmetic emulsions in term of microbiological quality. Even if heattreatment is still not feasible on some emulsions with NPs, it provides some clues on commercial sunscreens sterilization that would permit to overcome preservatives.