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Hair Mechanical Anisotropy-What Does It Tell Us?

Steven Breakspear1, Bernd Noecker1, Crisan Popescu1

  • 1Kao European Research Laboratories, KAO Germany GmbH, Darmstadt D-64297, Germany (S.B., B.N., C.P.).

Journal of Cosmetic Science
|February 16, 2019
PubMed

Insights

This study reveals how hair fiber

Area of Science:

  • Materials Science
  • Biophysics
  • Textile Science

Background:

  • Hair fibers exhibit complex mechanical properties influenced by environmental factors.
  • Understanding hair's anisotropic behavior is crucial for material science and cosmetic applications.

Purpose of the Study:

  • To investigate the mechanical anisotropy of hair fibers.
  • To determine the relationship between anisotropy and moisture content.
  • To correlate mechanical anisotropy with hair fiber's internal structure.

Main Methods:

  • Atomic force microscopy and nanoindentation were employed to measure mechanical properties.
  • Young's modulus was evaluated along (longitudinal) and across (transversal) the hair fiber.
  • Anisotropy index (IA) was calculated as the ratio of longitudinal to transversal Young's modulus at varying relative humidity levels.

Main Results:

  • The anisotropy index (IA) of hair fibers varies with relative humidity.
  • A composite material model was used to link IA to the fiber's internal architecture.
  • Results suggest a specific micro-structure of the exocuticle, typically masked by cross-linking, becomes apparent upon moisture absorption.

Conclusions:

  • Hair fiber's mechanical anisotropy is humidity-dependent.
  • The study provides insights into the hair fiber's micro-structure, particularly the exocuticle.
  • Moisture absorption plays a key role in revealing the mechanical properties of the exocuticle.

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