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Biophys J, April 2002, p. 2265-2274, Vol. 82, No. 4

A New Deformation Model of Hard alpha -Keratin Fibers at the Nanometer Scale: Implications for Hard alpha -Keratin Intermediate Filament Mechanical Properties

L. Kreplak,* A. Franbourg,dagger F. Briki,* F. Leroy,dagger D. Dallé,Dagger and J. Doucet*

 *Laboratoire pour l'Utilisation du Rayonnement Electromagnétique (LURE), Bât 209D, Centre Universitaire Paris-Sud, 91898 Orsay Cedex,  dagger L'Oreal Recherche, 92583 Clichy Cedex, and  Dagger Laboratoire de Physique des Solides (LPS), Bât 510, Centre Universitaire Paris-Sud, 91405 Orsay Cedex, France

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.

Biophys J, April 2002, p. 2265-2274, Vol. 82, No. 4
© 2002 by the Biophysical Society   0006-3495/02/04/2265/10  $2.00


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Copyright © 2002 by the Biophysical Society.