- The principal component of hair is a protein molecule called keratin. All protein molecules consist of long chains of small molecular units, the amino acids, of which there are 20 different kinds. Each keratin molecule in hair consists of many hundreds of amino acid units, arranged in an irregular order, although not a random one by analogy, the letters in this sentence are in an irregular order, but the sentence has meaning. The order in keratin determines how the molecules fit together, giving the hair strength and flexibility.
- Wool fiber: Like all other protein fibers, wool is also derived from the animal hair. Wool is mainly used as a minor blend (up to 10%) with cotton to introduce special properties to the terry fabric. Raw wool contains a wide variety of impurities, which can account for between 30% and 70% of the total mass. The impurities consist of wool grease, secreted from the sebaceous glands in the skin; suint, produced from the sweat gland; dirt and sand. Wool grease consists chiefly of esters, formed from a combination of sterols and aliphatic alcohols with fatty acids. Suints consist primarily of the potassium salts of organic acids.
- The crimped configuration prevents wool fibers from aligning themselves too closely when being spun into yarn. As a result it is possible to have wool textile materials with air spaces. Occupying about two-third of the volume. The warmth of wool fabric is due more to the air spaces in the material then to fiber.
Intrinsic Curvature in Wool Fibres is Determined by the Relative Length of Orthocortical and Paracortical CellsHair curvature underpins structural diversity and function in mammalian coats, but what causes curl in keratin hair fibres? To obtain structural datato determine one aspect of this question, we used confocal microscopy to provide in situ measurements of the two cell types that make up the cortex of merino wool fibres, which was chosen as a well-characterised model system representative of narrow diameter hairs, such as underhairs. We measured orthocortical and paracortical cross-sectional areas, and cortical cell lengths, within individual fibre snippets of defined uniplanar curvature. This allowed a direct test of two long-standing theories of the mechanism of curvature in hairs. We found evidence contradicting the theory that curvature results from there being more cells on the side of the fibre closest to the outside, or convex edge, of curvature. In all cases, the orthocortical cells close to the outside of curvature were longer than paracortical cells close to the inside of the curvature, which supports the theory that curvature is underpinned by differences in cell type length. However,the latter theory also implies that, for all fibres, curvature should correlate with the proportions of orthocortical and paracortical cells,and we found no evidence for this. In merino wool, it appears that the absolute length of cells of each type and proportion of cells varies from fibre to fibre, and only the difference between the length of the two cell types is important. Implications for curvature in higher diameter hairs,such as guard hairs and those on the human scalp, are discussed.
- Crimp and bulk, important wool fiber properties, are thought to be related to differences in the protein composition of the orthocortex and paracortex. Fiber morphological studies have demonstrated that the paracortex has a higher proportion of matrix and cysteine than the orthocortex. While there is some evidence for the differential expression of genes between these cell types in the follicle, this has not been demonstrated satisfactorily in the mature fiber. Using proteolytic digestion of wool fibers, followed by ultrasonic disruption to obtain relatively pure fractions of both cell types, the KAP3 high sulfur protein family was found to be present in higher concentrations in the paracortex. This significant finding provides an explanation for the higher cysteine content reported in the paracortex. This represents an advance in our understanding of protein expression variation in the orthocortex and paracortex, and how this relates to key physical and mechanical properties of wool fibers.