Multifunctional Amino Acid-Assisted Hair Dyeing with Metal-Polyphenol Networks

Metal-phenolic networks (MPNs) have been considered an alternative to the commercial hair dyes. However, it is still challenging to dye white hair black without damaging the hair because the deposition of MPNs is restricted on the surface of the healthy hair. Herein, we develop a novel damage-free strategy that not only promotes surface deposition of MPNs, but also favors internal formation of MPNs. Firstly, basic amino acids that can help open the hair cuticle penetrate into the hair. Then the numerous amino and carboxyl groups of the amino acids serve as coordination sites for Fe 2+ absorption, which facilitates the interfacial and internal growth of MPNs, thereby deepening the color of the dyed hair. As the intake of amino acids increases in the hair, the amount of Fe that enters into the hair increases to enhance the coloration. The dyed hair is capable of withstanding repeated washing with shampoo for at least 15 times without fading. Moreover, the surface MPNs bring about good resistance to UV damage, light fastness, and antioxidant properties, while the amino acids to some extent can repair the potential damage to hair.