Mechanical properties characterization of human hair fibers cortex region by multiparametric Atomic Force Microscopy mapping

This study utilized Atomic Force Microscopy (AFM) to evaluate the effectiveness of a cosmetic active ingredient in improving the mechanical properties of human hair fibers. The research compared virgin hair fibers with chemically damaged ones, treated with and without the active ingredient. The AFM analysis revealed that the control group showed a significant decrease in the natural logarithm of the Young's modulus (ln(E)) compared to virgin fibers, while the active ingredient group showed an increase in ln(E) compared to both the control and placebo groups. This indicated that the active ingredient effectively improved the Young's modulus of damaged fibers. Additionally, a radial decrease in ln(E) was observed in the active group, consistent with Confocal Raman Spectroscopy results, suggesting varied active ingredient permeation. The study highlighted the advantage of FV-AFM analysis over traditional Tensile Tester methods, which did not show significant differences between groups. A correlation was found between decreased ln(E) and higher adhesion forces, possibly due to distinct adhesive structures with low cystine content.