In vitro percutaneous penetration of silver nanoparticles in pig and human skin

In this study, the effects of surface charge, dose, and cosmetic vehicle on the penetration of silver nanoparticles (AgNPs) into pig and human skin were compared. AgNPs (20 nm) with varying surface-charges (polyethylene glycol (PEG; neutral), citrate (CIT; negative), and branched polyethylenimine (bPEI; positive) were dosed onto skin in in vitro diffusion cells using an aqueous solution and an oil-in-water emulsion formulation. Samples were analyzed by inductively coupled plasma mass spectroscopy (ICP-MS) and transmission electron microscope (TEM) to assess AgNP skin penetration. The results showed that neutral and positive AgNPs penetrate human skin when applied in a high dose aqueous solution and less with the emulsion vehicle. A mass balance percutaneous penetration study in human skin found the majority of AgNPs were washed from the skin or remained mostly in the stratum corneum (3.4% of the applied dose for AgbPEI and 1.7% for AgPEG). Very little silver was found in the epidermis (1.2% AgbPEI and 0.3% AgPEG) and dermis (0.1% AgbPEI and none detected for AgPEG). These results indicate low dermal penetration of AgNPs that is not greatly affected by surface coating charge. The results will facilitate dermal exposure assessments by better understanding how nanoparticle properties affect skin absorption of nanoparticles found in personal care products.