Human Hair Keratin Network And Curvature

The study investigated the structural elements related to hair curl patterns by examining human hair samples ranging from straight to tightly curled. It found that the frequency and amplitude of cross-sectional rotations were crucial for describing curliness at the macroscopic level. Transmission electron microscopy revealed that macrofibril organization was strongly related to hair curliness, with curly hair follicles exhibiting retrocurvature regardless of ethnic origin. The study highlighted an intrinsic asymmetry in the proliferative compartment of curly hair, causing delayed differentiation of inner and outer root sheaths and resulting in an elliptical and asymmetric hair cortex. The accumulation of hHa8 keratin on the concave side of curly hair, as opposed to the even distribution in straight hair, suggested that the curly shape of the hair shaft resulted from asymmetric differentiation of the precortex, making hair fiber a shape memory material.