Nanomechanical characterization of human hair using nanoindentation and SEM.

Human hair is a nanocomposite biological fiber with well-characterized microstructures. Nanomechanical characterization of human hair can help to evaluate the effect of cosmetic products on hair surface, can provide a better understanding of the physicochemical properties of a wide variety of composite biological systems, and can provide the dermatologists with some useful markers for the diagnosis of hair disorders. The paper presents systematic studies of nanomechanical properties of human hair including hardness, elastic modulus and creep, using the nanoindentation technique. The samples include Caucasian, Asian and African hair at virgin, chemo-mechanically damaged and treated conditions. Hair morphology was studied using scanning electron microscopy (SEM). Indentation experiments were performed on both the surface and cross-section of the hair, and the indents were studied using SEM. The nanomechanical properties of hair as a function of hair composition, microstructure, ethnicity, damage and treatment are discussed.