Thiol-enhanced metal–polyphenol permanent hair dyeing

Overview

Jiangnan University researchers have developed a novel, efficient strategy for permanent hair dyeing using metal-polyphenol networks (MPNs). While MPNs are attractive for their non-toxic properties, they traditionally suffer from poor coloring effects due to limited deposition on and within hair fibers. This new method overcomes these limitations by using thioglycolic acid (TGA) to reduce disulfide bonds in hair into highly reactive thiol groups. These thiol groups form Fe-S bonds with iron ions, which significantly enhances the interfacial and internal deposition of MPNs, resulting in rapid, high-darkness coloration that is resistant to washing.

Technical specifications

• Mechanism: Utilizes thioglycolic acid (TGA) to create thiol groups on hair fibers, which then react with Fe2+ to form Fe-S bonds.
• Performance: Enables rapid coloration at low temperatures (40 °C) and achieves high darkness levels comparable to natural black hair.
• Durability: The resulting MPN coating shows robust resistance to shampoo washing.
• Hair Health: The connection of thiol groups to MPNs through Fe-S bonds helps restore the hair's mechanical and structural properties to states similar to natural white hair.
• Versatility: The strategy is universal for various polyphenolic compounds, including tea polyphenol, tannic acid, and gallic acid, and shows potential for simultaneous hair dyeing and perming.

Technology readiness level

3. This technology is currently at the research and proof-of-concept stage. It has been demonstrated in a laboratory setting at Jiangnan University, with findings published in a peer-reviewed journal in 2025. The study confirms the mechanism and effectiveness on natural white hair samples, but there is no evidence of commercial deployment or market availability.