Penetration of Titanium Dioxide Nanoparticles through Slightly Damaged Skin in Vitro and in vivo

Purpose Titanium dioxide nanoparticles (TiO ₂ -NPs) have been widely developed for versatile use, but the potential risk form their skin exposure is still unclear. To evaluate this risk, the skin penetration of TiO ₂ -NPs is necessary to be understood first. The aims of this study are to investigated the penetration of TiO ₂ -NPs through slightly damaged skin and intact skin in vitro and in vivo. Methods TiO ₂ -NPs with a diameter of 20 nm was labeled with ¹²⁵ I. The skin of rat was treated with 2% SLS solution and obtained as slightly damaged skin. The ¹²⁵ I labeled TiO ₂ -NPs ( ¹²⁵ I-TiO ₂ -NPs)solution and 0.9% PS solution were added into the donor chamber and receptor chamber of static diffusion cells which clamped the skin at the middle of two half-cells, respectively. During 24 hours, samples were extracted from the receptor chamber and counted for 1 min using γ-counter to detect the radioactivity. The skin penetration of TiO ₂ -NPs in vitro was expressed as the percentage of radioactivity of receptor chamber solution compared with total radioactivity in the donor chamber. Thereafter, the ¹²⁵ I-TiO ₂ -NPs was exposed to the rats. After 1 day and 3 days, the blood and tissues of rats were harvested, weighed and counted for 1 min using γ-counter to detect the tissue radioactivity. The skin penetration of TiO ₂ -NPs in vivo was expressed as the percentage dose per gram tissue (% dose/g). Results In the skin penetration experiment in vitro, the radioactivity of receptor chamber solution through damaged skin was higher than that of through intact skin and was about 2% radioactivity of donor chamber on 24 h. In the skin penetration experiment in vivo, the radioactivity of blood and tissues of rats after exposing to ¹²⁵ I-TiO ₂ -NPs solution though damaged skin or intact skin were less than 0.05% dose/g on 1 d and quickly declined on 3 d. The skin penetration rates of TiO ₂ -NPs through slightly damaged skin and intact skin in vitro and vivo were lower than the rate of free ¹²⁵ I in the TiO ₂ -NPs solution. Conclusions The TiO ₂ -NPs could not penetrate through the damaged skin or intact skin both in vitro and in vivo. It suggested that the TiO ₂ -NPs should be safe when it was applied and contacted with skin.