Fig. 6

Long term toxicity and penetration into mouse or pig skins. After repeated dosing for total six times in half a month, the skin was collected and subjected for H&E staining. A Representative H&E staining images of mouse skin. B Quantitative analysis of epidermal thickness. No obvious epidermal thickness was increased after long-term application of ZIF-8. C–F Penetrations of (C, E) ZIF-8, ZnO, and (D, F) TiO₂ into (C, D) mouse and E, F pig skin. Skin was treated with glycerol, ZIF-8, ZnO, and TiO₂ for 6 h, then the Zn²⁺ and Ti⁴⁺ in skin were detected by ICP-MS. ZnO easily penetrated mouse and pig skin, but not for ZIF-8 and TiO₂