Highly Hydrophilic TiO 2 Nanoparticles as Stabilizers of Pickering Emulsions with Photosensitive Lipophilic Compounds: Synthesis and Application.

Pickering emulsions are a very promising system for encapsulating and photoprotecting active ingredients. The highest photoprotection efficiency can be achieved when bare TiO 2 nanoparticles are used as stabilizers. However, the main problem when using highly hydrophilic TiO 2 nanoparticles is their inability to adsorb at the oil-water interface. Here, we developed emulsions stabilized by bare, highly hydrophilic TiO 2 nanoparticles for the encapsulation and photoprotection of active lipophilic compounds. Emulsion stabilization occurs due to the formation of hydrogen bonds between hydroxyl groups on the particle surface and the carbonyl groups of the oil molecules. The stability and rheological properties of emulsions are explained by the properties of the initial hydrosols. The resulting Pickering emulsions demonstrated effective UV protection of α-lipoic acid. Our results pave the way for the formulation of Pickering emulsions with a widely used cosmetic oil and show for the first time the possibility of photoprotection of a lipophilic active substance using unmodified TiO 2 nanoparticles.