Interfacial Assembly of Metal–Phenolic Networks for Hair Dyeing

Fast and facile coating strategies play a key role in surface engineering and functionalization of materials for various applications. Herein, we report a rapid and eco-friendly hair dyeing process for natural gray hair via the 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 advantages (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.