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Mechanical anisotropy of hair affected by genetic diseases highlights structural information related to differential crosslinking in keratins

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Abstract

Previous work with Atomic Force Microscope (AFM) nanoindentation, on longitudinal and cross-sections of the human hair fibre, allowed for the derivation of a model for the mechanical behaviour of human hair, called the Anisotropic Index. Expanding that research further, and by applying this model, the nanomechanical behaviour of hairs from patients with the disease Trichothiodystrophy (TTD) has been examined and structural insights, gained from combining the AFM results with Differential Scanning Calorimetry (DSC) experiments and tensile measurements, suggests that TTD-affected hairs have a relatively increased amount of Keratin Intermediate Filaments, contained in compartments of differing crosslinking extent. The associated calculations of axial and transverse Young’s Moduli deliver values in good agreement with the measured fibre mechanics. Furthermore, comparing these findings with the results previously obtained from the study of hairs from patients with the disease Monilethrix, it is shown that the Anisotropic Index correlates well with the known deficiencies in both hair types obtained from such patients and allows for discerning between the Control hair and from those affected by the two diseases. AFM nanoindentation along and across the fibre axis and the Anisotropic Index thus appear to reveal structural details of hair not otherwise acquirable, whilst DSC may offer a quick and simple method for distinguishing between different severities of TTD.

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Acknowledgements

The authors wish to thank Dr. Ingrid Hausser of the Institute of Pathology, University of Heidelberg, Germany, for providing the Trichothiodystrophy-affected hair samples used in this study and to Dr. Lutz Langbein, formerly of German Cancer Research Center (DKFZ) Heidelberg, Germany, for fruitful discussions and advice.

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SB conceptualization, methodology, data curation, formal analysis, investigation, and writing. BN conceptualization, methodology, data curation, formal analysis, investigation, and writing. CP conceptualization, methodology, formal analysis, investigation, and writing.

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Correspondence to Crisan Popescu.

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The authors have no competing interests to declare that are relevant to the content of this article.

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Research does not involve Human Participants and/or Animals. The samples used for this work are hair fibres collected from hair-cut salon.

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The authors do not deem any need of informed consent as there are no identifiable personal data/materials used in this work.

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Breakspear, S., Noecker, B. & Popescu, C. Mechanical anisotropy of hair affected by genetic diseases highlights structural information related to differential crosslinking in keratins. Eur Biophys J 52, 53–67 (2023). https://doi.org/10.1007/s00249-023-01635-2

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  • DOI: https://doi.org/10.1007/s00249-023-01635-2

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