A new deformation model of hard alpha-keratin fibers at the nanometer scale: implications for hard alpha-keratin intermediate filament mechanical properties.
The mechanical behavior of human hair fibers is determined by the interactions between keratin proteins structured into microfibrils (hard alpha-keratin intermediate filaments), a protein sulfur-rich matrix (intermediate filaments associated proteins), and water molecules. The structure of the microfibril-matrix assembly has already been fully characterized using electron microscopy and small-angle x-ray scattering on unstressed fibers. However, these results give only a static image of this assembly. To observe and characterize the deformation of the microfibrils and of the matrix, we have carried out time-resolved small-angle x-ray microdiffraction experiments on human hair fibers stretched at 45% relative humidity and in water. Three structural parameters were monitored and quantified: the 6.7-nm meridian arc, which is related to an axial separation between groups of molecules along the microfibrils, the microfibril's radius, and the packing distance between microfibrils. Using a surface lattice model of the microfibril, we have described its deformation as a combination of a sliding process and a molecular stretching process. The radial contraction of the matrix is also emphasized, reinforcing the hydrophilic gel nature hypothesis.
Kreplak
L
L
Laboratoire pour l'Utilisation du Rayonnement Electromagnétique, Bât 209D, Centre Universitaire Paris-Sud, 91898 Orsay Cedex, France. kreplak@lure.u-psud.fr
Franbourg
A
A
Briki
F
F
Leroy
F
F
Dallé
D
D
Doucet
J
J
D006197:Hair / Q000648:ultrastructure; D006801:Humans; D007633:Keratins / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry; D020894:Microfibrils / Q000378:metabolism; D012542:Scattering, Radiation; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction; D014965:X-Rays
D008055:Lipids; D014867:Water; D007633:Keratins