Zn/Gallic Acid/Polyvinylpyrrolidone Coordination Polymer Nanoparticles as Sunscreen for Broadband UV Protection

Excessive ultraviolet (UV) exposure from sunlight has brought serious threats to human health. Due to their excellent UV absorption and antioxidant properties, natural polyphenols have emerged as green UV filters to replace commercial sunscreens which have alarming biosafety and serious damage to marine environments. However, the commercial application of polyphenols is greatly limited by their narrow wavelength absorption, long-term instability, and deep skin penetration. Herein, broadband UV filters with good antioxidant ability and high security were developed by coordination assembly of gallic acid and Zn2+ with combination of polyvinylpyrrolidone (PVP) (Zn-GA-PVP NPs). Owing to the π–π stacking interaction, ligand-to-metal charge transfer, and the carambola-like morphology, the UV shielding range of Zn-GA-PVP NPs is broadened to entire UVA and UVB region through both absorption and reflection of UV rays. The antioxidant ability of Zn-GA-PVP NPs is protected by PVP, which guarantees that they will negatively generate but effectively scavenge reactive oxygen species upon UV exposure. The abundant phenolic hydroxyl groups and proper particle size allow Zn-GA-PVP NPs to have strong skin adhesion but not to penetrate into the deep skin. Meanwhile, Zn-GA-PVP NPs also show good water resistance and easy mechanical removal because of the amphipathy of PVP. Zn-GA-PVP NPs exhibit a high UV protection effect and good biosafety in a photodamage mouse model. This study provides a promising approach for modifying natural polyphenols to better suit their use in commercial sunscreens.