A Bioinspired Strategy Toward UV Absorption Enhancement of Melanin-like Polymers for Sun Protection

Due to the complexity of the structure within melanin and synthetic polymers (i.e., polydopamine, PDA), it is a challenge to regulate the ultraviolet (UV) absorption. In nature, melanocytes can biosynthesize more pheomelanins than eumelanins via protein and gene overexpression for photoprotection when the UV irradiation is enhanced. During this biosynthetic pathway, L-cystine, transported by xCT gene, can be involved to form a new monomer structure incorporating a benzothiazole group, finally resulting in the formation of UV absorption-enhanced pheomelanin. Inspired by this, we have proposed a facile strategy to regulate the UV absorption of PDA by introducing the benzimidazole (BI) unit through the thiol-Michael addition reaction during the polymerization process. It was further found that the introduction of BI units not only significantly increased the content of chromophores and auxochromes, but also effectively restricted the red-shift of the absorption spectrum via interrupting the conjugated microstructure within PDA, both of which contribute to UV absorption enhancement. These UV absorption-enhanced PDA nanoparticles could be used to fabricate bio-inspired sunscreens for efficient sun protection. This work will provide a facile strategy to regulate UV absorption of melanin-like materials and open new horizons for the design and construction of bioinspired sunscreens.