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The University of Manchester Research
Biophysics of Curly Hair
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Citation for published version (APA):Wortmann, F., & Wortmann, G. (2016). Biophysics of Curly Hair: Why is hair curly, wavy, or straight?.
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Download date:07. Aug. 2019
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Biophysics of Curly Hair
Why is hair curly, wavy or straight?
Franz J. Wortmann, Gabriele Wortmann
School of Materials, University of Manchester, UK
2nd Mancunian Skin Club Annual International Workshop
14-15 April 2016, Manchester, UK
Franz J.Wortmann
Hair formation
Cell death
Spatial separation of celltypes.
Cell DifferentiationSynthesis & self-assemblyof specific proteins
Primary morphological components
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Franz-J.Wortmann
BC Powell & GE Rogers in ‘Formation and Structure of Human Hair’, P Jollès, H Zahn, H Hoecker (eds), Birkhaeuser 1997, p.59-148
Biomaterial
Tissue
Physics & Engineering
Life Sciences
http://naturalnigerian.com/2012/03/hair-101-the-scalp-get-this-right-and-your-hair-will-grow/
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Keratin Material : General Morphology of a Fiber
3Franz J. Wortmann
Basic, ethnic hair types
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Franz-J.Wortmann
straight wavy curly
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Crimp & fibre morphology in fine wool: Early investigations
Other geometries of cell separation lead toless pronounced or no crimp for other typesof wool.
Cell fractions change with fibre diameter:More ortho-, less clear separation – lesscrimp (Orwin & Woods, 1980)
Hypothesis: The side-by-sidestructure leads to the induction offibre crimp in Merino wool.
o-cortex on the outside
p-cortex on the inside
5Franz J.Wortmann
Horio & Kondo, 1953Mercer, 1954
Cortical cell distribution in straight & curled Japanese hair
Swift, 1997Kajiura et al, 2006Nagase et al, 2008
Orientation of IFs
Cell cross-section
para- ortho-type
Bryson et al. observed basically four types of cortical cells:
A: ortho-type – convex sideB: ortho/meso-typeC: para-type – concave sideD: minor component
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Franz-J.Wortmann
Biomechanically, the side-by-side arrangementof o-type & p-type cells will upon keratinisationinduce fibre crimp (Munro & Carnaby, 1999)
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Wool & hair: Cortex compositions
Thermal analysis (DSC) shows distinct differences forthe thermal stability of helical IF proteins in ortho-and para-type cells, leading to unsymmetricalendotherms.
The differences between denaturation temperaturesare distinct for wool and more subtle for human hairs.
Cortical cell fractions are very similar for differenthair types and size-wise in line with expectations forcoarse wool.
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Hair Type ortho I, % ortho II , % para, %
Merino wool 12 56 32
African 11 68 21
Asian 9 60 31
European 10 64 26
This support the hypothesis, that curl is onlyrelated to the lateral segregation of cell typeswith different types of IF orientation.
Wool
Asian Hair
Quadflieg & Wortmann, 2011
IF denaturation & hair self-straightening
Due to the pronounced correlation between straightening ef fect and helix-content, themechanism of self-straightening is identified as the alkali-induced denaturation of α-helical segments in the IFs.
This in turn confirms the role of IFs and their orientation fo r maintaining macroscopichair shape.
http://escovaprogress.com/store/keratin-relaxer/gold-black-definitive-liss/
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Franz-J.Wortmann
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The role of fibre ellipticity for curl formation
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Franz-J.Wortmann
Asian Hair European Hair African Hair
It is intuitively clear that for equal cross-sectional area an elliptical fibre will be easierto bend (across its short axis, b) than theequivalent circular fibre.
As a consequence elliptical fibres canform tight curls with only acomparatively low degree of stress-imbalance upon keratinization.
Round fibres for the same pre-conditionwould just form slight waves.
B = E*II = π ab3/4
Role of the follicle form
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Franz-J.Wortmann
Gel-like, stable, straight form
Increasing metastability due to cell segmentation
Collapse into equilibrium fibre shape upon cross-linking and drying.
African Hair Follicles (Bernard, 2003)
Hair, emerging from a curved follicle, generallyshows retro-curvature.
If this effect is insufficient or absent, dermatologicalconsequences may occur. https://www.dermquest.com/image-library/image/5044bfcfc97267166cd62ae1
pseudofolliculitis barbae
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Follicle activities
11Franz J.Wortmann
Different cortical protein types areformed with lateral segregation.
Langbein, 2003Other source:Thibaut et al., 2007
Adhikari et al., 2016
A huge number of processes occurs in the follicle undergenetic control.
Those contributing to hair form need to relate to
• IF-aggregation• lateral cell segregation
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Biomechanics of hair forms: Primary cases
Franz-J.Wortmann
straight wavy curlystraight
http://stylesatlife.com/articles/different-hair-types/
Medium ellipticity &biased distribution: Slight/medium curl
High ellipticity&bilateral distribution: Strong curl
No or Low ellipticity &random distribution of cell types: Straight Hair
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