Synthetic Melanin Hair Dye

Hair dyeing has become an indispensable demand and fashion choice in people's daily lives. The issues of allergy, carcinogenicity, and gene mutation caused by the commonly used chemical hair dye, which mostly comprises p-phenylenediamine and other substances, are becoming noticeable. As a result, there is an urgent need for innovative materials to replace aniline in commercial hair dye. A biomimetic fabrication of polydopamine (PDA) inspired by natural melanin has been reported to have excellent hair dyeing effects. A strong alkaline oxidative environment or metal ion catalysis are usually indispensable for dopamine polymerization. However, excessive alkalinity will make the hair rough and affect its quality, and metal ions may be poisonous. As a result, developing a new type of mild, efficient, safe, and non-toxic synthetic melanin hair dye is an urgent concern. The more reactive melanin monomer 5,6-dihydroxyindole (DHI) may just conduct rapid polymerization by air oxidation, in contrast to DA, which requires demanding oxidation conditions to initiate polymerization. Herein, this work reported a hair dye material that polymerized DHI in situ on the surface and inside of hair under mild conditions. The L value of dyed hair is 30, and L=20 after washing 30 times. The results of the synthetic melanin hair dye to adhere uniformly to the hair surface have been demonstrated by electron microscopy, and some monomers and oligomers will also reach the cortical layer of the hair to polymerize. The poly-DHI (PDHI) structure can engage in a Michael addition reaction with the disulfide bond in the hair to form a covalent coupling due to its high reducibility and highly reactive double bond. The findings of skin sensitization tests demonstrate that using DHI polymerization to dye hair won't affect human skin or health, even at the greatest concentration permitted. Finally, it can be obtained an efficient, durable, and safe melanin hair dye, which provides an innovative design strategy and a dependable tool platform for the development of a new generation of hair dyes.