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Open AccessArticle

Stiffness of Human Hair Correlates with the Fractions of Cortical Cell Types

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R&D—Hair Care Products Research, Kao Corporation, 2-1-3, Bunka, Sumida-ku, Tokyo 131-8501, Japan
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Product Quality Management, Kao Corporation, 2-1-3, Bunka, Sumida-ku, Tokyo 131-8501, Japan
3
R&D—Analytical Science Research, Kao Corporation, 1334, Minato, Wakayama-shi, Wakayama 640-0112, Japan
*
Author to whom correspondence should be addressed.
Cosmetics 2019, 6(2), 24; https://doi.org/10.3390/cosmetics6020024
Received: 30 January 2019 / Revised: 20 March 2019 / Accepted: 21 March 2019 / Published: 1 April 2019
(This article belongs to the Special Issue Recent Advance in Hair Science and Hair Care Technologies)
(1) Background: The objective of this work was to elucidate the hair microstructure which correlates with the stiffness of human hair fibers. (2) Methods: Bending moduli of hair fibers were evaluated for the hair samples from 156 Japanese female subjects. Hair transverse sections were dual-stained with fluorescent dyes which can stain para- and ortho-like cortical cells separately, and observed under a fluorescence light microscope. Atomic force microscopy nanoindentation measurements were performed to examine the modulus inside macrofibrils. (3) Results: The difference in bending moduli between the maximum and the minimum values was more than double. The hair of high bending modulus was rich in para-like cortical cells and the bending modulus significantly correlated with the fraction of para-like cortical cells to the whole cortex. On the other hand, the elastic moduli inside macrofibrils were almost same for the para- and ortho-like cortical cells. (4) Conclusions: Hair bending modulus depends on the fractions of the constitutional cortical cell types. The contribution of the intermacrofibrillar materials, which differed in their morphologies and amounts of para- and ortho-like cortical cells, is plausible as a cause of the difference in the modulus of the cortical cell types. View Full-Text
Keywords: AFM nanoindentation; bending modulus; cortical cell; human hair; fluorescence light microscopy AFM nanoindentation; bending modulus; cortical cell; human hair; fluorescence light microscopy
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Ezawa, Y.; Nagase, S.; Mamada, A.; Inoue, S.; Koike, K.; Itou, T. Stiffness of Human Hair Correlates with the Fractions of Cortical Cell Types. Cosmetics 2019, 6, 24.

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