Nanomechanical characterization of human hair using nanoindentation and SEM

Wei, Guohua; Bhushan, Bharat; Torgerson, Peter M.

doi:10.1016/j.ultramic.2005.06.033

Cited by 117 publications

(83 citation statements)

References 12 publications

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“…1B), measured at distances above 800 μm after drying of the follicles (SI Text). Note that the modulus of the developing, dried hair measured from 800 μm on is similar to moduli determined on mature hair (16,28).…”

Section: Resultssupporting

confidence: 60%

“…The stiffness of the hair follicle is expected to extend over several orders of magnitude, due to the differentiation of its soft keratinocytes into a hair fiber with Young moduli in the gigapascal range (16,17). Between these two extremes, the keratinization process of the IF network transforms a living isotropic cell matrix into an inert and anisotropic material (18), bridging length and force scales from the subcellular level to the tissue level.…”

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confidence: 99%

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Keratin network modifications lead to the mechanical stiffening of the hair follicle fiber

Bornschlögl

Bildstein

Thibaut

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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The complex mechanical properties of biomaterials such as hair, horn, skin, or bone are determined by the architecture of the underlying fibrous bionetworks. Although much is known about the influence of the cytoskeleton on the mechanics of isolated cells, this has been less studied in tridimensional tissues. We used the hair follicle as a model to link changes in the keratin network composition and architecture to the mechanical properties of the nascent hair. We show using atomic force microscopy that the soft keratinocyte matrix at the base of the follicle stiffens by a factor of ∼360, from 30 kPa to 11 MPa along the first millimeter of the follicle. The early mechanical stiffening is concomitant to an increase in diameter of the keratin macrofibrils, their continuous compaction, and increasingly parallel orientation. The related stiffening of the material follows a power law, typical of the mechanics of nonthermal bending-dominated fiber networks. In addition, we used X-ray diffraction to monitor changes in the (supra)molecular organization within the keratin fibers. At later keratinization stages, the inner mechanical properties of the macrofibrils dominate the stiffening due to the progressive setting up of the cystine network. Our findings corroborate existing models on the sequence of biological and structural events during hair keratinization.atomic force microscopy | elastic modulus | human hair follicle | biomechanics | X-ray diffraction B iological tissues are structurally complex materials with remarkable mechanics and elastic moduli that can range from a few pascals to several gigapascals (1-3). An active field aims at understanding how the local structural and mechanical properties of bionetworks define its macroscopic mechanics from a molecular scale toward a cellular and tissue scale (4-6). One challenge is that the properties of these networks have to be considered over multiple length and force scales with macroscopic mechanical forces being transduced from the whole tissue scale down to the cellular and molecular level and vice versa.At the cellular level, the last decades witnessed for a considerable advancement toward a better understanding of how the cytoskeleton composed of actin, microtubules, and intermediate filaments (IFs) determines cellular mechanics (1,(6)(7)(8). In vitro studies on isolated cells (6) and reconstituted in vitro bionetworks with controllable architecture and composition (9-12) considerably advanced our knowledge of cytoskeletal mechanics. However, these models are only approximations of the complex tridimensional architecture of most tissues. At the tissue level, the mechanical anisotropy together with the variety of mechanically different constituents usually hamper direct correlations between network architecture and mechanical properties (3, 13). Analytical models and computer modeling allow to theoretically link the macroscopic mechanical properties of the network with parameters of the local network architecture (5, 14, 15).The human hair follicle was used here...

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Section: Resultssupporting

confidence: 60%

mentioning

confidence: 99%

Keratin network modifications lead to the mechanical stiffening of the hair follicle fiber

Bornschlögl

Bildstein

Thibaut

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…Finally, the low estimated contrast in RI between these layers explains why the observed large number of repeating layers does not produce bright colours, as similar structures do in other cases [1,10]. Typical non-iridescent hairs are circular to ovoid in cross section and have large and protruding cuticular scales ( figure 1; electronic supplementary material, figure S2), but may have multi-layered cuticles [11]. Those in human hairs, the most well-studied example, are larger but of the correct thickness and regularity [11] to produce iridescent colours as second-order peaks [12], suggesting that their presence is a necessary, but not sufficient condition for iridescent colour.…”

Section: Discussionmentioning

confidence: 83%

“…Typical non-iridescent hairs are circular to ovoid in cross section and have large and protruding cuticular scales ( figure 1; electronic supplementary material, figure S2), but may have multi-layered cuticles [11]. Those in human hairs, the most well-studied example, are larger but of the correct thickness and regularity [11] to produce iridescent colours as second-order peaks [12], suggesting that their presence is a necessary, but not sufficient condition for iridescent colour. As in barbules from iridescent feathers [1], the additional surface area provided by flattening probably contributes to the enhanced reflection from iridescent hairs.…”

Section: Discussionmentioning

confidence: 99%

“…High specular reflectance relative to diffuse reflectance occurs when light hits a flat and smooth surface. Thus, the small size and flattening of scales on golden mole hairs enhances, while the large protruding scales on non-iridescent hairs ( [11]; figure 1d), decreases, specular reflectance and thereby the expression of colour from the multi-layers.…”

Section: Discussionmentioning

confidence: 99%

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Iridescent colour production in hairs of blind golden moles ( Chrysochloridae )

et al. 2012

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Relative to other metazoans, the mammalian integument is thought to be limited in colour. In particular, while iridescence is widespread among birds and arthropods, it has only rarely been reported in mammals. Here, we examine the colour, morphology and optical mechanisms in hairs from four species of golden mole (Mammalia: Chrysochloridae) that are characterized by sheens ranging from purple to green. Microspectrophotometry reveals that this colour is weak and variable. Iridescent hairs are flattened and have highly reduced cuticular scales, providing a broad and smooth surface for light reflection. These scales form multiple layers of light and dark materials of consistent thickness, strikingly similar to those in the elytra of iridescent beetles. Optical modelling suggests that the multi-layers produce colour through thin-film interference, and that the sensitivity of this mechanism to slight changes in layer thickness and number explains colour variability. While coloured integumentary structures are typically thought to evolve as sexual ornaments, the blindness of golden moles suggests that the colour may be an epiphenomenon resulting from evolution via other selective factors, including the ability to move and keep clean in dirt and sand.

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