Skin bioinspired anti-ultraviolet melanin/TiO2 nanoparticles without penetration for efficient broad-spectrum sunscreen

Organic filters in traditional sunscreens usually are limited photodegradation and easily penetrate the stratum corneum and epidermal layer, leading to potential harmful effects. Melanin is a natural ubiquitous pigment that protects living organisms from intense sunlight. Inspired by the structure and function of the mussel adhesive protein, a facile strategy involving oxidative polymerization of dopamine was proposed for surface modification of titanium dioxide (TiO 2 ) to obtain melanin/TiO 2 nanoparticles. The thickness of melanin layers was varied from 1 to 7 nm by changing pH and dopamine concentration. The melanin/TiO 2 nanoparticles with 1-nm-thick melanin layers showed highly efficient UV-shielding ability due to synergistic effect of melanin and TiO 2 . The melanin/TiO 2 nanoparticles were introduced as the sole active ingredient to formulating sunscreen; sun protection factor (SPF) could reach 116.9 and 162.4 with a loading of 10 wt% and 15 wt%, respectively. Most importantly, melanin exhibits a good bioadhesion property and can effectively prevent the penetration of melanin/TiO 2 nanoparticles. Thus, the as-prepared nanoparticles possess excellent UV-shielding capacity and biocompatibility, ensuring their superior performance and safe use in the sunscreen. Graphical abstract Inspired by the structure and function of the mussel adhesive protein, a facile strategy involving oxidative polymerization of dopamine was proposed for surface modification of titanium dioxide (TiO 2 ) to obtain melanin/TiO 2 nanoparticles. The melanin/TiO 2 nanoparticles with 1-nm-thick melanin layers showed highly efficient UV-shielding ability due to synergistic effect of melanin and TiO 2 . Most importantly, melanin exhibits a good bioadhesion property and can effectively prevent the penetration of melanin/TiO 2 nanoparticles. Thus, the as-prepared nanoparticles possess excellent UV-shielding capacity and biocompatibility, ensuring their superior performance and safe use in the sunscreen.