Investigations of percutaneous uptake of ultrafine TiO2 particles at the high energy ion nanoprobe LIPSION

Micronised TiO2 particles with a diameter of about 15 nm are used in sunscreens as physical UV filter. Due to the small particle size it may be supposed that TiO2 particles can pass through the uppermost horny skin layer (stratum corneum) via intercellular channels and penetrate into deeper vital skin layers. Accumulations of TiO2 particles in the skin can decrease the threshold for allergies of the immune system or cause allergic reactions directly. Spatially resolved ion beam analysis (PIXE, RBS, STIM and secondary electron imaging) was carried out on freeze-dried cross-sections of biopsies of pig skin, on which four different formulations containing TiO2 particles were applied. The investigations were carried out at the high energy ion nanoprobe LIPSION in Leipzig with a 2.25 MeV proton beam, which was focused to a diameter of 1 mum. The analysis concentrated on the penetration depth and on pathways of the TiO2 particles into the skin. In these measurements a penetration of TiO2 particles through the s. corneum into the underlying stratum granulosum via intercellular space was found. Hair follicles do not seem to be important penetration pathways because no TiO2 was detected inside. The TiO2 particle concentration in the stratum spinosum was below the minimum detection limit of about 1 particle/mum(2). These findings show the importance of coating the TiO2 particles in order to prevent damage of RNA and DNA of skin cells by photocatalytic reactions of the penetrated particles caused by absorption of UV light. (C) 2004 Elsevier B.V. All rights reserved.