Structure and mechanical behavior of human hair.
The understanding of the mechanical behavior of hair under various conditions broadens our knowledge in biological materials science and contributes to the cosmetic industry. The hierarchical organization of hair is studied from the intermediate filament to the structural levels. The effects of strain rate, relative humidity, and temperature are evaluated. Hair exhibits a high tensile strength, 150-270MPa, which is significantly dependent on strain rate and humidity. The strain-rate sensitivity, approximately 0.06-0.1, is comparable to that of other keratinous materials and common synthetic polymers. The structures of the internal cortex and surface cuticle are affected by the large tensile extension. One distinguishing feature, the unwinding of the α-helix and the possible transformation to β-sheet structure of keratin under tension, which affects the ductility of hair, is analytically evaluated and incorporated into a constitutive equation. A good agreement with the experimental results is obtained. This model elucidates the tensile response of the α-keratin fibers. The contributions of elastic and plastic strains on reloading are evaluated and correlated to structural changes.
Department of NanoEngineering, University of California, San Diego, La Jolla, CA 92093, United States.
Yang
Y
Yu
Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093, United States; Department of Materials, Eidgenössische Technische Hochschule Zürich, Zürich 8093, Switzerland. Electronic address: wen.yang@mat.ethz.ch.
Wen
W
Yang
Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093, United States.
Bin
B
Wang
Department of NanoEngineering, University of California, San Diego, La Jolla, CA 92093, United States; Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093, United States. Electronic address: mameyers@eng.ucsd.edu.
Marc André
MA
Meyers
D000328:Adult; D001696:Biomechanical Phenomena; D002462:Cell Membrane / Q000648:ultrastructure; D005260:Female; D006197:Hair / Q000033:anatomy & histology* / Q000502:physiology* / Q000648:ultrastructure; D006801:Humans; D006813:Humidity; D007382:Intermediate Filaments / Q000648:ultrastructure; D007633:Keratins / Q000737:chemistry; D017433:Protein Structure, Secondary; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013718:Tensile Strength; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
D014867:Water; D007633:Keratins
Human hair; Keratin; Mechanical properties; Strain-rate sensitivity