Fig. 2

Photoprotection of PDA NPs sunscreen on UV-induced skin damage of Balb/c mice. (A) Schematic diagram of the commercial sunscreen or PDA NPs sunscreen applied topically in the dorsal skin of Balb/c mice. Mice were exposed to UVR (UVA + UVB) for 9 weeks. Meanwhile, several randomly selected UVR skin-damaged mice were treated with either (1) commercial sunscreen (vehicle group) or (2) prepared with different concentrations of PDA NPs (2.5 wt%, 5 wt%, and 10 wt%, PDA sunscreen group). (B) Quantifications of the skin severity scores of dorsal skin in Balb/c mice after experimental treatments. The results were calculated by the sum of scores in each term referred to four-point Likert scale, including the symptoms of erythema/hemorrhage, edema, scaling/dryness, and excoriation/erosion. (C) Representative photographic and H&E staining images of Balb/c mice in each group. (D) Quantitative analysis of epidermal thickness measured in H&E staining. (E, F) Representative immunofluorescent images and quantification of filaggrin (FLG) signal in the dorsal skin of Balb/c mice after different experimental treatments. FLG were stained with Cy3 and nuclei were stained with Hoechst 33,258 (blue). (H) Quantification of transepidermal water loss (TEWL) evaluated by Tewameter with colorimeter MPA-580(Courage & Khazaka, Cologne, Germany). N = 4 in each group. All data represent the mean ± SD. *p < 0.05, **p < 0.01 and ***p < 0.001.