LAUSR

Fast and facile coating strategies play a key role in the surface engineering and functionalization of materials for various applications. Herein, we report a safe, rapid, and eco-friendly hair dyeing process for natural gray hair via the optimized formation of metal‒phenolic networks (MPNs). MPNs composed of gallic acid display high performance and the coloration is tunable by varying the metal ion types. MPN-based hair dyeing is tolerant to repeated washing (at least 50 times) with detergent solution without color fading and can be discolored in acidic solution (pH < 2). The mechanism of self-assembled MPNs for hair dyeing is investigated by Raman and UV-vis absorption spectroscopy. Cell studies in vitro and skin toxicity tests in vivo demonstrate the superiority (i.e., biocompatibility and hair regrowth) of MPNs for hair dyeing compared to p-phenylenediamine. The reported strategy for hair dyeing avoids the use of toxic substances present in common hair dyes and has negligible damage to the hair structures and tensile strength.