Nanoindentation of Hair Cortex and Medulla Regions

Abstract

Reports related to cuticle damage and hair’s mechanical properties are of interest to dermatologists in treatment of hair disorders. Apart from tensile test, few studies were reported on mechanical properties of hair, especially nanomechanical properties of cortex and medulla regions. Inner diameter of hair fiber (8–12 µm) is considered as medulla and it exists in hair at the beginning of the anagen phase. This study is aimed for quantitative comparison of nanomechanical properties between cortex and medulla and also with respect to donor age by performing nanoindentation on fiber cross sections using two different instruments. The medulla and cortex regions revealed hardness values of 70–170 MPa and 200–312 MPa, respectively. Similarly lower values of indentation modulus were observed for medulla compared to cortex because medulla has poorer orientation of microfibrils compared to the surrounding cortex. This study also found a linear correlation between hardness and indentation modulus especially for medulla region. This could be due to the fact that organization of the microfibrils increases from the medulla center to medulla periphery. It is also found that donor age has no influence on cortex modulus and hardness. The findings of this study will be useful for dermatologists in estimating the hair disorders and for estimating dye uptake of keratin fibers in textiles.