Strain and Strain Recovery of Human Hair from the Nano- to the Macroscale

This study investigates the strain and strain recovery of human hair from the nano- to the macroscale using SAXS and SEM. It finds that intermediate filaments (IFs) experience significant deformation, about 70% of the macrostrain, while lipids in the cuticle show much lower strain. The Poisson ratio at the nanoscale is 0.44. Hair can nearly fully recover its structure within approximately 1,000 minutes after mechanical treatment, indicating self-healing properties. SEM micrographs confirm less deformation in the cuticle compared to the cortex. These findings provide insights into the hierarchical structure and mechanical properties of human hair, which could inform hair care product development.