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 in improving the mechanical properties of human hair fibers. Human hair fibers, both undamaged and chemically damaged by bleaching, were analyzed. The study found that the control group (damaged fibers without active treatment) showed a significant decrease in the natural logarithm of Young's modulus (ln(E)) compared to virgin fibers. In contrast, the active group (damaged fibers with active treatment) showed an increase in ln(E) compared to both the control and placebo groups, indicating the active's effectiveness in improving fiber strength. The study also noted a radial decrease in ln(E) in the active group, consistent with Confocal Raman Spectroscopy results, suggesting variation in active permeation. The analysis highlighted the advantage of FV-AFM over traditional Tensile Tester methods, as the latter did not show significant differences between groups. Additionally, a correlation was found between higher adhesion forces and decreased ln(E), possibly due to differentiated adhesive structures with low cystine content.