Novel Compounds for Hair Repair: Chemical Characterization and In Vitro Analysis of Thiol Cross-Linking Agents

<b>Introduction:</b> Hair damage from chemical treatments, mechanical stress, and environmental factors can lead to significant degradation in hair quality, necessitating effective solutions for restoration. The aim of this study was to develop and evaluate novel compounds for repairing hair damage through the chemical regeneration of disulfide bridges. <b>Materials and Methods:</b> Three novel thiol-reactive cross-linking agents (APA, STA, SAA) were synthesized and characterized. Their efficacy in repairing hair damage was evaluated through in vitro tensile strength tests on human hair fibers, comparing treated and untreated samples. Cysteine reactivity tests were also performed to assess the capability of these agents to restore disulfide bridges in hair keratin. <b>Results:</b> The tensile strength tests revealed significant improvements in the mechanical properties of treated hair fibers compared to untreated samples. APA demonstrated the highest efficacy in restoring tensile strength and elasticity, showing higher performance in mechanical strengthening. The cysteine reactivity tests confirmed that APA could effectively re-establish disulfide bonds, particularly at higher temperatures. STA, while less effective than APA, showed substantial efficiency in restoring disulfide bonds. When compared to the reference agent, both APA and STA exhibited higher performance in tensile strength and cysteine reactivity, with APA showing the greatest improvement in mechanical properties. <b>Conclusions:</b> Our study successfully revealed the potential of the synthesized thiol-reactive cross-linking agents in repairing hair damage by chemically regenerating disulfide bridges. These findings offer a promising new direction for the development of advanced hair repair treatments in the cosmetic industry.