Investigating the origins of macroscopic variation in differential ethnic hair types
mesheuropmc: integumentary system
In the modern world hair plays a cultural and aesthetic role. The hair care industry accounts for a large portion of the cosmetic and dermatological industry generating large financial sums in sales, and consequently research and development into hair care products is important for companies seeking to increase their market share and profits. Currently there are very few products which specifically target certain ethnicities as the basis of knowledge underlying what nanoscopic and molecular factors cause the variation seen at the macroscale of human hair is circumscribed. Therefore a need exists within this industry to expand the information available on the origins of macroscopic variation in differential ethnic hair types.\ud The work presented in this thesis is the embodiment of five different studies: a bulk X-ray scattering analysis of single hair fibres, a series of skin-core experiments utilising microfocus X-ray scattering, an attenuated total reflectance Fourier transform infrared spectroscopy study of the cuticle surface and a study of the lipids extracted from different spatial locations within hair fibres.\ud The bulk X-ray scattering analysis on single hair fibres showed that the non-keratinous materials; namely the lipids and the amorphous/disordered material and interfaces present are responsible for the largest source of variation seen inter-ethnically at the nanoscopic and supramolecular levels. The lipids were found to be different amongst hair types with respect to their crystalline spacing, the total intensity and thus volume present and also in the preferential structural orientation of the lipid arrangement. The low angle diffuse scatter which is thought to be related to the keratin associated proteins varied with respect to the extent in q range, the angular behaviour and the behaviour of the diffuse scatter under hydration conditions. The azimuthal spread of the reflection arising from the inter-lateral packing of the keratin intermediate filaments was also found to differ between hair types.\ud The skin-core experiments provide information on the textural variation of the hair fibre across the concentric subsections of hair enabling information to be sought on the structural components of the hair. The work presented shows that there are zonal differences in both the keratinous and non-keratinous structures present across the cross-section of the hair fibres both intra and inter-ethnically. The differences seen are in the size and location of specific hierarchical keratinous assembly structures and also in the ultra -structure of the hair fibre as whole.\ud Attenuated total reflectance Fourier transform infrared spectroscopy is a bench top technique that is widely available to investigate the surface structure of materials. The study presented has shown differences related to the keratin conformational structure and the hydrophilic properties of the hair fibres. There are also variations seen in the products of the cysteine containing structures due to weathering which may be due to a difference in the geographical location of the source.\ud Lipids that are present on either the surface of hair fibres or located within the hair fibre account for the largest non-proteinaceous component present in hair. An investigation characterising the lipids preferentially extracted from different spatial locations of the hair fibre has been performed. The work presented has revealed that there is significant variation both intra and inter-ethnically in the total lipid content present, the lipid classes and the fatty acid profiles. The variation in the fatty acid profiles may also possibly be related to the difference in signal seen in the X-ray diffraction study.
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