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The physical properties of alpha-keratin fibers
... Human hair is a hot topic of debate on its electrical conductivity properties (1)(2)(3)(4)(5). To better understand the electrical properties of hair, the architecture of human hair is to be carefully examined (6)(7)(8). ...
... α-Keratin protein is the major component of human hair (including wool), horns, nails, hooves, and claws of mammals (5,7,8). Eminent hair experts have provided ample proof that α-keratin protein in hair is an insulator (4,5,(13)(14)(15) It has been demonstrated that resistivity value of hair changes with water content. The wool-water system with 7% water content, exhibited a resistivity of 3 × 10 12 ohm cm at room temperature; whereas, at 25% of water content, the resistivity decreased to 6 × 10 6 ohm cm at room temperature. ...
... The wool-water system with 7% water content, exhibited a resistivity of 3 × 10 12 ohm cm at room temperature; whereas, at 25% of water content, the resistivity decreased to 6 × 10 6 ohm cm at room temperature. It has been concluded that even at high moisture content, α-keratin is a poor conductor of electricity (4,5,(13)(14)(15)(16)(17)(18)(19)(20). The scientists considered hair as a proton semiconductor to explain the limited electrical conductivity of a keratin-water system, which is the same as that of ice, nylon-water, and cellulose-water system (4,5,14,(21)(22)(23)(24)(25)(26). ...
Electrical conductivity of human hair is a debatable issue among hair experts and scientists. There are unsubstantiated claims that hair conducts electricity. However, hair experts provided ample evidence that hair is an insulator. Although wet hair exhibited drastic reduction in resistivity; scientists regarded hair as a proton semiconductor at the best. Here, we demonstrate that hair filaments generate electricity on absorbing water vapor between 50 degrees and 80 degrees C. This electricity can operate low power electronic systems. Essentially, we are exposing the hydrated hair polymer to a high temperature (50 degrees-80 degrees C). It has long been speculated that when certain biopolymers are simultaneously hydrated and exposed to high temperature, they exhibit significant proton hopping at a specific temperature regime. This happens due to rapid movement of water molecules on the polymer surface. This lead us to speculate that the observed flow of current is partly ionic and partly due to "proton hopping" in the hydrated nano spaces of hair filament. Such proton hopping is exceptionally high when the hydrated hair polymer is exposed to a temperature between 50 degrees and 80 degrees C. Differential scanning calorimetry data further corroborated the results and indicated that indeed at this temperature range, there is an enormous movement of water molecules on the hair polymer surface. This enormously rapid movement of water molecules lead to the "making and breaking" of innumerable hydrogen bonds and thus resulting in hopping of the protons. What is challenging is "how to tap these hopping protons to obtain useful electricity?" We achieved this by placing a bundle of hair between two different electrodes having different electro negativities, and exposing it to water vapor (water + heat). The two different electrodes offered directionality to the hopping protons and the existing ions and thus resulting in the generation of useful current. Further, by continuously hydrating the polymer with water vapor, we prolonged the process. If this interesting aspect of polymer is exploited further and fine tuned, then it will open new avenues for development of sophisticated polymer-based systems, which could be used to harvest electricity from waste heat.
... Weak fibres that break during processing decrease fibre length in the top and increase carding losses and combing noilage (Rottenbury et al. 1981;Whiteley 1987;Rogan 1988). The physical properties of a-keratin fibres, including wool, have been reviewed by Feughelman (1982). Most studies which have measured the strength of wool fibres have considered their resistance to longitudinal (extension) forces, but compressional and torsional forces may also be applied to fibres. ...
... The longitudinal strength of single wool fibres can be measured by determining the load required to break fibres or by comparing the stress (load)-extension curves of fibres (Collins and Chaikin 1965;Yeates et al. 1975;Feughelman 1982;Hunter et al. 1983). The strength of wool for processing purposes has traditionally been assessed on staples using a subjective method (Roberts et al. 1960;Rottenbury 1979). ...
... No clear association has been established between protein composition and strength of wool fibres, despite many observations of differences in the proportions of the constituent proteins in 'sound' and 'tender' wool and in wool fibres weakened by a variety of treatments. The cortex of wool fibres can be regarded as a two-phase structure consisting of highly organized cylindrical rods embedded in an amorphous matrix (Feughelman 1982(Feughelman , 1987. These two components correspond to the microfibrils (intermediate filaments) which are composed of the low-sulfur proteins, and the matrix which is composed of the high-sulfur and high-tyrosine (or high-glycine-tyrosine) proteins (Gillespie 1983;Powell and Rogers 1986). ...
This review outlines the factors that may influence the strength of wool fibres and the associated changes in structure and protein composition that have been observed in weakened fibres. The strength of a wool staple is dependent on the intrinsic strength of the fibres that it contains and the total cross-sectional area of fibre being tested. The minimum fibre diameter and the rate of change of diameter along a staple are important determinants of strength. Different sheep kept under similar conditions show a large range of staple strengths. Estimates of heritability for staple strength are sufficiently high (0.17 to 0.49 in Merinos; 0.20 to 0.58 in Romneys) to prompt the establishment of selection programmes in both breeds. A variety of physiological and environmental factors influence the strength of wool fibres. Nutrient supply exerts a major influence via effects on fibre diameter. In addition, there are specific effects of some amino acids (methionine and lysine), trace elements (copper and zinc) and vitamins (folic acid). Seasonal effects are important in breeds which exhibit a large annual rhythm of wool growth, e.g. Romneys, but not in Merinos. Pregnancy and lactation influence fibre strength through competition for essential nutrients but hormonal factors may also be involved. Fibre strength may also be influenced by stress involving excessive secretion of glucocorticoids and by various parasites and diseases which can influence nutrient supply and cause stress. No clear association has been established between the strength of wool fibres and the proportions of the constituent proteins. The content of high-tyrosine proteins in the matrix of weak fibres is frequently, but not invariably, reduced. Likewise, fibre strength has been associated with the proportions of components of the high-sulfur proteins in some studies, but not in others. Thus in Romneys, but not Merinos, tender (weak) wool contained a higher proportion of orthocortex than sound wool, and hence contained less ultra-high-sulfur proteins. Weak fibres produced by specific nutritional treatments in adult sheep and lambs show a loss of cuticle scale pattern and malformed or degraded fibres.
... Human hair exhibits a complex morphological fine structure (Fraser and MacRae, 1980;Zahn et al., 2003). Fig. 1 shows a generalized, graphical representation of the morphological structure of a typical keratin fiber and how it differentiates on the various structural levels from the micro-to the nanometer scale ( Marshall et al., 1991;Feughelman, 1997). ...
... The inset figure shows the idealized two-phase filament/matrix structure of the cortex. Adapted (Wortmann, 2009) from Marshall et al. (1991) andFeughelman (1997). The inset shows the two-phase model as developed by Feughelman (1959). ...
... The positive value of DC R p for a-keratin shows that non-polar surface area is exposed upon denaturation ( Richardson and Makhatadze, 2004). This is consistent with the structure of the helical coiled-coil structure in the IFs, where the specific heptad sequence of the helical segments of the monomer provides a hydrophobic strip, leading to helix aggregation through apolar interactions ( Fraser et al., 1982;Feughelman, 1997). One consequence of a positive DC R p is furthermore ( Richardson and Makhatadze, 2004) that, if for different helical proteins an increase of denaturation temperature is observed, this should be accompanied by an increase in denaturation enthalpy. ...
To gain insight into the thermal stability of intermediate filaments and matrix in the biological composite structure of α-keratins, the thermal denaturation performance of human hair fibers was investigated by Modulated Differential Scanning Calorimetry (MDSC) in the dry and the wet state. Denaturation enthalpy ΔH(D) in water was found to be independent of heating rate (11.5J/g) and to be approximately double as high as in the dry state (5.2J/g). The lower enthalpy (dry) and its dependency on heating rate are attributed to effects of pyrolysis. The stepwise change of reversing heat capacity ΔC(p) marks the denaturation process as a classic two-stage transition. The increase of ΔC(p) with heating rate reflects a continuous shift of the nature of the denaturation of the α-helical material, first, into random coil and then towards random β-materials for lower heating rates. Denaturation temperatures follow Arrhenius relationships with heating rate, yielding activation energies of 416kJ/mol (dry) and 263kJ/mol (wet), respectively. A decrease of activation energy (wet) for high heating rates supports the hypothesis of systematic changes of the pathway of denaturation.
... The torsional properties of hair were examined by an automated torsion pendulum (Textile Research Institute, Princeton, NJ, U.S.A) equipped with a laser micrometer for dimensional analyses [7]. A 4.5 gram weight was attached to the bottom of single hair fibres (n = 30), wound 360°and released. ...
... The elastic modulus of hard water-treated virgin hair was 19% (P < 0.001) higher than that of soft water-treated hair, and this was accompanied by a 5% (P < 0.009) increase in break stress. This indicates that calcium and magnesium made the hair more resistant to extension and breakage by contributing to the existing coulombic interactions (salt links) that would be disrupted by water otherwise [7]. tensile properties of virgin hair were unaffected by calcium and magnesium content, presumably because the inherent hydrogen and coulombic interactions within the fibre were intact at 50% RH. ...
... It should be noted that the stiffening effect of calcium and magnesium on bleached hair in the wet state would likely manifest with additional bleaching treatments. We believe this to be true because additional bleaching would reduce disulphide linkages [8], and the stiffness of the fibre would then become more dependent on the contribution of the coulombic interactions within the fibre [7]. As we have shown, calcium and magnesium can add to these interactions. ...
Synopsis Human hair can extract significant levels of calcium and magnesium, water hardness metals, from tap water immediately following chemical treatments and during hygiene practices. We have previously shown that this uptake is primarily a function of the condition of the hair. Depending on the extent of chemical damage, the hair can extract notable amounts of water hardness metals even from soft water. As water hardness metals concentrate primarily in the cuticle layers of the hair fibre, it is hypothesized that their presence will affect the structural properties that are chiefly driven by the cuticle. We examined hair mechanics and styling by technical measures of single-fibre torsional and tensile properties, combability and style retention as a function of the calcium and magnesium content of virgin and bleached hair. Our work has indicated that water hardness can affect hair properties. Fibre stiffening was induced by the presence of water hardness metals inside the fibres of both virgin and bleached hair. A reduction in combing forces was also observed, and this effect is believed to be a result of the stiffening. The style retention of virgin hair was improved by water hardness metals, whereas that of bleached hair was slightly reduced. ICS © 2011 Society of Cosmetic Scientists and the Société Française de Cosmétologie.
... The value measured by indenting the longitudinal section, the transverse elastic modulus, E⊥, is close to, but lower than, the axial measured modulus, indicating an anisotropy within the fibre (Breakspear et al., 2018). In general, the cortex of Monilethrix af fected hairs was found to have lower Young's moduli than Control hair, most noticeably in the axial direction, supporting the theory (Feughelman, 1982) that this component may be dominated by the KIF; disruption to this highly ordered structure, as noted for Monilethrix hair, then leads to a decrease in resistance to deformation. Likewise, in transverse section the properties of the matrix (KAP) component of the hair fibre dominates and the relatively lower drop in modulus value observed in transverse sections indicates that the matrix of Monilethrix affected hairs is less affected. ...
... Experimental data acquired at RH = 45%. Gosline, 2004;Feughelman, 1982); the value for the Young modulus of matrix is evaluated with the equation published previously (Breakspear et al., 2019) from the values of axial and transverse moduli measured on Control fibre at 45% relative humidity (plotted in Fig. 11) as 2.8 GPa. ...
Utilising the AFM nanoindentation technique for the study of hair cross- and longitudinal sections, the mechanical anisotropy of human hair fibres affected by a rare congenital condition, Monilethrix, has been investigated for the first time. Supported by X-ray microdiffraction data, and applying a model based on an ideal composite material consisting of rods (KIFs) and matrix (KAPs), to Monilethrix affected fibres it has been shown that the results could be grouped into clearly different classes, namely: almost isotropic behaviour for Monilethrix affected hairs and anisotropic behaviour for Control hair. Moreover, AFM nanoindentation of hair cross sections has demonstrated, also for the first time that hairs affected by Monilethrix have a continuous, and not periodic, weakness within the cortex. This has been attributed to disruptions in the KIF-KIF, KIF-intermacrofibrillar matrix or KIF-desmosome complexes within the hair shaft, as suggested by X-ray microdiffraction examination. Hairs from a patient exhibiting no obvious phenotype exhibited similar mechanical weakness despite the otherwise normal visual appearance of the fibre. This further supports a hypothesis that the beaded appearance of Monilethrix hair is a secondary factor, unrelated to the inherent structural weakness.
... Mechanical properties of α-keratin fibers are primarily dependent on the matrix in which intermediate filaments are embedded. [1] Tensile properties of twisted hair samples revealed that twisting followed by untwisting and giving 10 min time for relaxation has resulted in the properties same as of virgin hairs. However, twisting alone reduced the properties of hair such as moduli, strength, and strain values. ...
... Stress-strain plot of a human hair is normally split into three regions, [21,22] but the plots are split into four regions in this study [ Figures 3 and 4]. Postyield incremental modulus until ~33% strain is reported in the literature [1,19,23,24] as the third region, but the fourth region, that is, decrease of postyield modulus between ~33% and 45% strain is not discussed earlier. A brief structure-property correlation is provided below considering the cortical cell as a composite comprising of crystalline and amorphous domains [23] for detailed understanding of all four regions and four tensile properties described in this study. ...
Background
Hair tensile properties play a crucial role in cosmetology regarding functionality and quality. Commonly, scalp positions are subjected to varying magnitudes of environmental and physical stimuli and correspondingly different hair balding patterns are observed.
Aim
This study is aimed at comparing the tensile properties of hair from four different scalp positions and quantifying the differences using statistical methods. Further, the second aim is to investigate the structure–property relationship with respect to the tensile properties obtained from hair in order to obtain a better understanding of the heterogeneous and composite structure of hair.
Materials and Methods
Hair samples were subjected to tensile testing and position wise data was compared using relative rating and grey relational analysis. Scanning electron microscopy was used to study the fractography of tensile specimens.
Results
The modulus, yield stress, maximum stress, and work of elongation were in the range of 2–6 GPa, 60–190 MPa, 130–340 MPa, and 30–100 MJ/m³, respectively. The postyield incremental modulus change at around 33% strain correlated well with fracture features wherein significant macrofibril pullout was observed indicating the fourth region in the stress–strain plot.
Conclusion
From the statistical analysis, it was found that there was no significant difference in terms of rating of hair samples from different scalp positions. This may be attributed to the presence of microscopic and nanoscopic structural heterogeneities.
... Tensile behavior of wool fibers under quasi-static loads has been thoroughly studied both experimentally and analytically. The effects of moisture, temperature, non-uniformity, and the extent of crystallization and amorphous orientation in wool fibers have been previously investigated [1][2][3][4]. Various theoretical models have been proposed to explain the tensile behavior of wool fibers in terms of their microstructures [5][6][7][8][9]. ...
... The relationship between yield stresses and strain rates was plotted (Figure 8). Neglecting the effect of gauge length, this relationship was modeled using the popularly employed Cowper-Symonds relation [26], (1) where σ d and σ s are the impact and quasi-static yield stresses, respectively, is the strain rate, and B and q are material constants. It was found that, for Lincoln wool fibers, B = 370 s -1 and q = 0.7. ...
A new testing method using a mini split Hopkinson tensile bar was employed in the impact tests of Lincoln wool fibers. Stress-strain curves of Lincoln wool fibers subjected to impact loadings at strain rates in the order of 102s—1 were obtained, which fill the gap in the impact data for Lincoln wool fibers. For comparison, quasi-static tests were also carried out with a single Lincoln wool fiber using a Micro-Tester. Stress level was observed to increase with increasing strain rates.
... Die Steigung ist der Elastizitätsmodul E (Youngsche Zahl). Das Verhalten innerhalb dieses Bereiches ist keineswegs linear-elastisch und trägt den Namen Hookescher Bereich zu unrecht [10]. Der E-Modul setzt sich eigentlich aus einem zeitunabhängigen elastischen und einem zeitabhängigen viskosen Anteil zusammen. ...
... Der Anstieg der Steifigkeit bei Rückgang des Wassergehaltes ist zeitabhängig. Das Verhalten der Faser kann vereinfacht durch System aus einer Feder, die einen Beitrag von 1.4 × 10 5 N/cm 2 (in Wasser) zur Steifigkeit leistet und einer parallel geschalteten Feder mit Dämpfer beschrieben wer- den [10] . Die Viskosität des Dämpfungselementes hängt dabei von der Feuchtigkeit ab. ...
Im folgenden wird eine Übersicht über die geometrischen und physikalischen Eigenschaften von Haaren gegeben. Unter geometrischen Eigenschaften werden die axiale und die radiale Struktur, sowie die Haarlänge verstanden. Die physikalischen Eigenschaften umfassen die Zug-, Biege- und Torsionssteifigkeit, viskoelastisches Verhalten und Hysterese, sowie den Einfluss von Feuchtigkeit, Temperatur und kosmetischen Behandlungen auf eben diese Größen. Dazu zählen au�erdem die Reibung und die optischen Eigenschaften.
... Many studies [264,265,[268][269][270]311,316,[353][354][355][356][357][358][359][360][361][362][363][364] have been carried out to determine the relationship and agreement between the diameter measurements obtained on different instruments. Most of these studies have found highly acceptable agreement between measurements of different instruments. ...
... thinnest place) [648][649][650][651][652][653] together with the tensile properties (i.e. intrinsic strength) of the fibre structure and material (alpha-keratin) per sé [364,654]. ...
The world has moved away from subjective appraisal of raw wool characteristics and
has entered an era of objective measurement and specification, and the raw wool trade
is rapidly moving towards sale by total description which necessitates the accurate,
rapid and cost effective measurement of all the raw wool characteristics important in
determining price, textile performance and end-use. The development and availability
of new technologies and equipment have enabled the objective measurement of many
more raw wool characteristics than was possible in the past.
Over the past few decades, a considerable amount of research has been carried out
worldwide on the effect of the raw wool characteristics on topmaking and spinning
performance, as well as on yarn properties. This was done in order to gain a better
understanding of, and to quantify, the effects of fibre and processing parameters on
processing behaviour and performance and on the properties of the top and yarn and
even the fabric. An important aim of the research was to improve the processing of
wool and the productivity and cost effectiveness of the various processing stages. This
research led to a better understanding of which raw wool characteristics influence
textile processing behaviour and performance, as well as the product quality and enduse
performance, and ultimately the raw wool price. On the basis of this, technologies
and instruments were developed and commercialised for measuring the key raw wool
characteristics rapidly, accurately and cost effectively. In parallel to this, the associated
test methods were developed and standardised largely under the umbrella of the IWTO,
many of these being adopted and used in raw wool marketing and trading worldwide.
This review covers the research and development carried out over more than half a
century on the development and standardisation of technologies, instruments and test
methods for the measurement of those characteristics determining the price and textile
quality of raw wool and which are therefore important in terms of the global marketing
and trading of raw wool. Research and development in this field is still continuing, but
at a much lower intensity and pace than during the second half of the previous century.
... Human hair Wbers consist of a sulfur-rich outer protective cuticle layer surrounding highly keratinized cortex cells. The structural hierarchy and disulphide cross-linking nature of keratins results in the remarkable mechanical properties of hair Wbers [19, 20, 36, 37]. These mechanical properties (i.e. ...
... Several models were described by others to explain tensile strength properties of hair, including the transition of keratin to -keratin when hair is stretched. Cysteine crosslinkages , coulombic interactions between side chain groups, hydrogen bonds between neighbouring groups, and hydrophobic interactions provide the necessary cohesion in the -keratin arrangement181920. The fact that ch-OSA supplementation partially prevents the loss in tensile strength suggests a structural eVect of ch-OSA on hair Wbers. ...
The appearance of hair plays an important role in people's overall physical appearance and self-perception. Silicon (Si) has been suggested to have a role in the formation of connective tissue and is present at 1-10 ppm in hair. Choline-stabilized orthosilicic acid ("ch-OSA") is a bioavailable form of silicon which was found to improve skin microrelief and skin mechanical properties in women with photoaged skin. The effect of ch-OSA on hair was investigated in a randomized, double blind, placebo-controlled study. Forty-eight women with fine hair were given 10 mg Si/day in the form of ch-OSA beadlets (n = 24) or a placebo (n = 24), orally for 9 months. Hair morphology and tensile properties were evaluated before and after treatment. Urinary silicon concentration increased significantly in the ch-OSA supplemented group but not in the placebo group. The elastic gradient decreased in both groups but the change was significantly smaller in the ch-OSA group (-4.52%) compared to placebo group (-11.9%). Break load changed significantly in the placebo group (-10.8%) but not in the ch-OSA supplemented group (-2.20%). Break stress and elastic modulus decreased in both groups but the change was smaller in the ch-OSA group. The cross sectional area increased significantly after 9 months compared to baseline in ch-OSA supplemented subjects but not in the placebo group. The change in urinary silicon excretion was significantly correlated with the change in cross sectional area. Oral intake of ch-OSA had a positive effect on tensile strength including elasticity and break load and resulted in thicker hair.
... Oil can collect airborne pollutants and dust. [27] 2. Too much oil can make hair feel greasy [28,29] 3. Heavy oil can make hair heavy [30] 4. Massaging your hair with oil can increase blood circulation and relax your body [31] 5. Oiling your scalp can prevent dandruff and scalp [32] 6. Oiling your hair and prevents it from becoming brittle and dull [33] 7. Hot oil treatment locks in more moisture and adds shine, volume, and elasticity [34] 8. Oils such as coconut oil and castor oil promote hair growth [35] 9. Oils and moisturize the scalp [36] 10. Hibiscus herbal oil increases circulation follicles stronger and regenerating scalp. ...
... This phenomenon is more pronounced in long strands of hair. 5,6 Damage to the cuticle on the hair surface also affects the tensile properties. 7 Hair is not of vital importance to humans. ...
Hair is exposed to harmful factors such as sunlight, pollution, cosmetic applications, and cleaning every day. With lost moisture, the hair is worn out, loses shine, and exhibits color changes in the case of dyed hair. In this study, the effects of herbal oils on hair were investigated by comparing the properties with measurements. Three different types of hair were used: natural (unprocessed), damaged, and dyed hair. After washing hair with a base shampoo, herbal oils were applied, and brightness, color changes, elasticity, and breaking points were examined. Safflower seed oil, grape seed oil, and rosehip oil were applied to the samples. It was tried to regain the properties that have decreased as a result of shampoo application in the hair with the applied oils. The highest gloss was observed with grape seed oil, and according to color change calculations, the best result was seen with safflower seed oil. Tensile-strain testing was performed for all samples, and rosehip oil gave the best results. The changes in hair fractures were examined with a scanning electron microscope, and grape seed oil was the best for all hair types. When all analyses were evaluated, the best performing herbal oil was grape seed oil. All analysis results showed that herbal oils can be used in the cosmetics industry with different applications.
... The mechanism is as follows: when hair fibers are equilibrated at moisture conditions between 30 and 65 % RH, and then subjected to elongations ranging between 5 and 17 %, mechanical energy appears across the hair fiber in the form of tensile, shear, and Poisson stresses. In this range of deformation, the keratin intermediate filaments in the cortex undergo an alpha to beta transformation (7). This protein phase transition enables the cortex to unfold and relax thereby, allowing for higher elongations while partially dissipating high concentration of mechanical stresses. ...
The role of moisture in the cuticle sheath has so far not been properly explored. In this paper, analysis and experiments are presented indicating that moisture variations in the cuticle sheath have a significant impact on its shear and tensile Modulus and therefore on the overall hair mechanical and cosmetic properties. The analysis indicates that if there is an imbalance in the required moisture content in the cuticle cell inter and intra-layers, steep layer Moduli mismatches and stress concentrations are generated across interfaces. Imbalances of this type often arise when the hair has very low levels of moisture or when it is transiently subjected to high temperatures becoming more sever with tensile extensions. For instance, at high elongations and near the yield point the intermediate filaments in the cortex undergo an alpha to beta transformation. This keratin phase transition occurs at both low or high moisture conditions and causes the cortex tensile Modulus to decrease allowing for higher deformations without severe stress build up. In contrast, at high elongations the cuticle sheath has no such stress dissipation mechanism and high stress concentrations appear across the cuticle cells. Therefore, moisture loss in the cuticle cells accompanied by extensions aggravate stress concentrations resulting in damage at the cuticle cell cement boundaries.
... Multiple methods and techniques are listed in the literature to quantify hair strength. [14] Break load or force is one of the tensile test parameters used extensively in the literature to define hair strength; [15] higher the break load, stronger the hair. Break load is found to have a linear correlation with hair diameter; larger the diameter, higher the break load. ...
Aim:
The aim of this study is to propose a new quantification protocol for determining the change in hair properties on weathering and formulate hair damage protection metric to compare different hair care products.
Subjects and methods:
The study was conducted with 30 participants (nonhair oil users), wherein hair samples were collected and evaluated for (a) average cross-section and mean diameter at different sections of strand and (b) breakage point location on hair extension. Correlation between breakage point and hair mean diameter as function of length was studied. Inferences were extrapolated to characterize the quality of hair samples in (a) another matched group of 30 participants (coconut oil users) and (b) studies on hair swatches with different hair treatments.
Results:
In accordance with the weakest link theory, on extension hair fractured at the section where average mean diameter (or cross section) is the smallest (correlation R2 = 0.86). The weakest link in hair fiber is connected with irregularity in hair strands-characterized by root mean square variability (Rq). We found that tips of hair have ~100% more Rq than the roots. Furthermore, regular coconut oil users have hairs with Rq lower by ~65% in comparison to nonoilers. Hair swatch studies confirmed that coconut oil-wash cycles (n = 20) help reduce Rq by 30%, whereas other hair treatments such as shampoos and conditioners did not lead to much change. A new metric was proposed - hair protection factor - to quantify damage control power of various products.
Conclusions:
Hair breakage is a complex phenomenon with multi-factorial effects. The present work identifies irregularities in mean diameter along hair length as the precursor for hair strength. The weakest link in hair is characterized by the presence of internal defects-preceded by surface irregularities. From root to the tip, cuticle chip-off increases and so does the Rq and tendency to break. Thus, the metric based on Rq can help compare hair care treatments in their promise to control hair damage.
... In this particular, is fundamental to consider that human hair has an outer protective layer, which surrounds the cells of the highly keratinized cortex and a structural hierarchy of disulfide bonds that has influence on the mechanical properties of hair. [1][2][3][4] Changes in growth and hair quality can be induced by protein malnutrition or low intake of oligoelements and vitamins and environmental aggression. 5 These deleterious effects are manifested in the form of difficult combing, brittleness and dryness. ...
Objectives: We evaluated the correlation between metric parameters and laboratory assessments of hair taken from patients undergoing oral supplementation of orthosilicic acid. Material and methods: 34 women aged between 17 and 57 years received an oral dose of 30 mg of orthosilicic acid for five months. Hair samples (pre and post-treatment) were obtained from an area of 1 cm² on the occipital protuberance and submitted to ultrasound bath in a distilled water solution. After that, we tested this water using spectrophotometric technique for measuring the hair ability to preserve proteins during physical stress. Hair growth was also assessed every month, before treatment and during treatment. We applied a questionnaire addressing the perception of patients about their hair. Results: 83% of patients believed that there was overall improvement of hair quality after treatment. 79.41% of patients exhibited increasing in hair growth rate and this increase was of 37.6%. Protein loss analysis showed a improvement in hair quality. Conclusion: We suggest that orthosilicic acid has a beneficial role in the hair, leading to a faster growth rate and an increase in resistance to aggression.
... The disulfide bridge is the major covalent bond, providing great chemical stability and the characteristic mechanical properties of hair. The weaker non-covalent polar bonds also represent an important interaction and, as they can be easily broken by water, they explain the dependence of the mechanical behavior of hair on humidity [5,8,9]. Bornschlögl and co-workers [10] have recently shown and proposed a sequence of events that explain the huge increase in the mechanical stiffening of keratin fibers during the keratinization and cornification process, which occurs above the follicle over the course of just 1 mm. ...
We selected 1235 decapeptides from human hair proteins encoded by human genes of keratins and keratin associated proteins. The peptides were linked to glass arrays and screened for their affinity towards a solution of human hair extracted keratin fraction. Based on the physicochemical properties of the peptides, ten variables were studied: content of different types of amino acid side chains (cysteine, hydrophobic, polar, basic, acidic, aromatic rings, amide, alcohol side chains), isoelectric point, and net charge. We found differences statistically significant on the binding affinity of peptides based on their content of cysteine, hydrophobic and polar amino acids, mainly containing alcohols. These results point to the formation of hydrophobic interactions and disulfide bonds between small peptides and human hair keratins as the main driving forces for the interaction of possible cosmetic peptides, namely designed to strength human hair. As so, our results enlighten the nature of the interaction of keratin based materials with human hair, which are claimed to enhance hair fiber strength, and enable a more directed and sustained hair care peptide design.
... In the pre-yield region, referred to as the "Hookean" region load is proportional to tensile extension as a signature of the homogeneous response as well as the resistance of α- keratin to stretching. The resistance is usually provided by the hydrogen bonds those are present between the turns and stabilize the α-helix of the keratin (Feughelman, 1982). The yield regions represent the transition of the responsive region from α-keratin to β-keratin (Beyak et al., 1969). ...
... The mechanical behavior of tendon and ligament are similar. Ligamentum nuchae is almost pure elastin and has remarkable elastic properties [27] as will be shown in Section 8. 1. Fig. 106a shows the stress-strain curve of ligamentum flavum (ligament between lumbar vertebrae) from pig [200]. The ligament has a high ductility and is able to transmit the stress until maximum stress. ...
Most natural (or biological) materials are complex composites whose mechanical properties are often outstanding, considering the weak constituents from which they are assembled. These complex structures, which have risen from hundreds of million years of evolution, are inspiring Materials Scientists in the design of novel materials.Their defining characteristics, hierarchy, multifunctionality, and self-healing capability, are illustrated. Self-organization is also a fundamental feature of many biological materials and the manner by which the structures are assembled from the molecular level up. The basic building blocks are described, starting with the 20 amino acids and proceeding to polypeptides, polysaccharides, and polypeptides–saccharides. These, on their turn, compose the basic proteins, which are the primary constituents of ‘soft tissues’ and are also present in most biominerals. There are over 1000 proteins, and we describe only the principal ones, with emphasis on collagen, chitin, keratin, and elastin. The ‘hard’ phases are primarily strengthened by minerals, which nucleate and grow in a biomediated environment that determines the size, shape and distribution of individual crystals. The most important mineral phases are discussed: hydroxyapatite, silica, and aragonite.Using the classification of Wegst and Ashby, the principal mechanical characteristics and structures of biological ceramics, polymer composites, elastomers, and cellular materials are presented. Selected systems in each class are described with emphasis on the relationship between their structure and mechanical response. A fifth class is added to this: functional biological materials, which have a structure developed for a specific function: adhesion, optical properties, etc.An outgrowth of this effort is the search for bioinspired materials and structures. Traditional approaches focus on design methodologies of biological materials using conventional synthetic materials. The new frontiers reside in the synthesis of bioinspired materials through processes that are characteristic of biological systems; these involve nanoscale self-assembly of the components and the development of hierarchical structures. Although this approach is still in its infancy, it will eventually lead to a plethora of new materials systems as we elucidate the fundamental mechanisms of growth and the structure of biological systems.
... The tensile strength of hair is usually in a range of 120 MPa [4]÷170 MPa [3], but it can be as high as 250 MPa [5] and is linked with the diphase nature of the hair's cortex [6]. As the hair is being stretched [6], α-keratin molecules turn into β-keratin while the matrix from gel turns into sol [7], [8]. ...
The aim of this research was to assess the effect of diet supplementation with zinc and copper, in different chemical forms (organic and inorganic), on the mechanical properties of the hair of healthy English thoroughbred horses. Hairs were taken from 18 horses which had been fed with oats and hay for a period of 110 days. Twelve of the horses had been additionally given a daily dose of 700 g of highquality 44-ingredients Fohlengold St-Hippolyt muesli made by Muhle Ebert Dilheim. Six of them had received the muesli-containing organic zinc and copper (OS), while the other six horses had received the muesli-containing inorganic zinc and copper (IS). The mechanical properties of the hairs before and after the supplementation period were tested in a Synergie 100 (MTS) testing machine. Each of the hairs was loaded at a constant rate of 20 mm/min until rupture. Young modulus (E), breaking stress (Ru) and yield point (Rs) of the particular hairs were determined. No significant changes in the mechanical parameters were observed in the reference group in which the horses were fed with only oats and hay for the whole experimental period of 110 days. The supplementation of the diet with inorganic zinc and copper resulted in an increase in the elasticity and diameter of the hairs and in a simultaneous reduction in their strength. Whereas organic zinc and copper caused an increase in the elasticity and strength of the hairs and a simultaneous reduction in their diameter. It has been shown that the organic form of the supplemented trace zinc and copper (mainly copper) elements has a beneficial effect on the mechanical properties of the hairs since it results in an increase in both their elasticity and strength.
... Hair styles and hair care regimes within the Black population often reflect that their hair looks and behaves differently compared to people of other ethnicities, and these differences have been documented in the literature. [1][2][3][4][5][6][7][8][9][10][11] Usually when hair from people of African descent is studied, all curly hair from this population is grouped together and there are oftentimes a low number of samples in the study. As a result, inter-and intraethnic differences within Black hair are not obtained. ...
... For the context of mechanical or thermal investigations, this complex structure can be simplified as a two-phase, filament/matrix composite, as originally proposed by Feughelman. 4,5 In this model, the partly crystalline, a-helical IFs are identified as the filamentous phase. The matrix, in consequence, contains the IFAPs as major component 6 and also summarily the rest of the morphological components, such as cuticle, cell membrane complex, and so forth. ...
Although human hair as an α-keratinous fiber exhibits a complex morphology, it can be considered as a nano-structured filament/matrix composite for the context of thermal analysis. Using differential scanning calorimetry (DSC) in water, the denaturation performance of the α-helical protein fraction and the effects of reductive treatments were studied. The results are viewed in the context of a previous study for oxidative treatments. It was found that the course of the denaturation process remains generally unperturbed by the treatment, following an irreversible, one-step, first-order process. Arrhenius activation energies and pre-exponential factors were determined from the DSC-curves by applying the principles of the Friedman-method. Comparing activation energy values between reductive and oxidative processes shows the differences of the effects on the components of the composite. In contrast, the values of the rate constant at the denaturation temperature, though showing differences in their trends with cumulative treatments, are very similar. This further emphasizes the theory that the viscosity of the matrix affects strict kinetic control over the denaturation of the α-helical segments. Once the viscosity of the matrix has decreased enough for the denaturation process to occur, this follows a path that is largely independent of the temperature range and of the chemical pre-history. © 2008 Wiley Periodicals, Inc. Biopolymers 89: 600–605, 2008.
This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
«From the hairs on our head to the soles of our feet, our bodies are composed of cells rich in intracellular fibrous proteins called intermediate filaments (IF): a complex group of 30 or so keratins of 40-70 kd in epithelia; a single protein desmin of 52 kd in muscle; a single protein vimentin of 53 kd in cells of mesenchymal origin; glial fibrillary acidic protein (GFAP), a single protein of 50 kd in astroglia; and a triplet of neurofilament proteins, NF-L, NF-M, NF-H in neuronal cells». This introduction to the review «The Molecular Biology of Intermediate Filaments» written 1985 by Steinert et al.[1a], starts with the hairs on our head, but hair and sheep wool, so-called «hard keratins», were only recently accepted as full members of the IF-family, although decisive criteria for the membership such as diameter of the filaments (7-11 nm), supercoiled α-helical structure, and molecular weight of the proteins subunits have been fulfilled by wool and other keratin fibres. When α-keratins were finally recognized by sequence comparison as intermediate filaments in 1982 by Geisler and Weber[2a] the lack of reconstitution of isolated microfibrillar proteins from wool in filaments in vitro posed a special problem as all other proteins of this family readily form filaments. By adopting a new procedure for preparing wool proteins and hair proteins without carboxymethyl groups, it was possible to achieve polymerization in vitro in dilute solutions into filaments that have the same structure as the in situ keratin filaments in wool and hair. These results open the way for a more sophisticated analysis of the chemical quality of wool and hair by assessing the yield and geometry of reconstituted filaments.
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.
Objective:
The process of moisture sorption and desorption by human hair was analysed for extracting hints on the hair structure.
Methods:
The isotherms of moisture sorption and desorption by hair were recorded for untreated and chemically treated (permed and bleached) hair. Data of swelling were also considered.
Results:
By examining the swelling and moisture sorption of keratin fibres, it is possible to conclude that hysteresis is quite improbably caused by capillary condensation. The mobility of the protein chains and the strength of the bonds binding water molecules to the active sites inside the matrix are proposed as causes instead. The concept of "breaking symmetry", derived from moisture sorption-desorption data, and the method of evaluating this parameter, is proposed as a way of characterizing the chemical treatment of hair. The results show that bleaching produces a larger breaking of symmetry than perming, and this is suggested to be due to new hydrogen bonds, created as a result of the chemical treatment, replacing the original disulfide bonds, which are of different strength compared to the bonds of untreated hair. The quantitative sorption data matched well to the model of grains of matrix enveloped in layers of water molecules at increasing relative humidity, up to 100 %. The analysis suggested that, aside from the glass transition event occurring at around 60-70 % relative humidity, there is another, less examined, transition occurring at around 30 % relative humidity, assigned to the opening of the hair inner structure, and accommodation of more water molecules. Both transitions are reflected by corresponding changes in the fibre mechanical behaviour.
Conclusion:
The moisture sorption-desorption by hair was shown not only to allow a quantitative differentiation among various cosmetic treatments of the hair, but also to provide valuable information on the structure of the fibre.
This chapter attempts to familiarize the reader with the science of hair and hair care, while outlining approaches and techniques for evaluating both consumer and technical aspects of performance. The development of hair care products is strongly marketing driven, and consequently the language of the industry is that of the consumer. As such, despite the identification of now commonplace attributes, which are prominently displayed in packaging and advertising, there are often complex or muddled relationships back to the science. Here, an attempt has been made to present current thinking in these areas, while highlighting how a successful product is the combination of strong technical performance, good aesthetics, and a compelling marketing message.
Keratin is the main protein in hair strands. The process of dyeing hair with permanent dyes is quite complex and involves oxidative reactions between precursors, such as p‐toluenediamine (PTD) and p‐aminophenol (PAP), and coupler agents, in alkaline and oxidative medium, inside the hair. The electrochemical behaviour of native and denatured human hair keratin, assessed by using a keratin multilayer film adsorbed on glassy carbon electrode, and its interaction with hair dye precursors, PTD and PAP, by using electrochemical techniques, was investigated. Native and denatured keratin electrochemical oxidation showed two oxidation peaks; the first was first attributed to the cysteine amino acid residues, and the second to the cysteine and methionine amino acids residues. The PTD‐ and PAP‐keratin‐hair dye interactions induced damage, causing the unfolding of the keratin morphological structure, and new additional peaks of the cysteine and tyrosine amino acid residues were revealed. Dyeing to unfold: The electrochemical behaviour of human hair keratin and its interaction with hair dye precursors, p‐toluenediamine and p‐aminophenol, is investigated by using electrochemical techniques. The electrochemical oxidation of keratin occurs through the oxidation of the cysteine and methionine amino acid residues. The interaction between keratin and hair dye precursors induces damage, which causes the morphological structure of keratin to unfold.
This chapter describes tensile, bending and torsional testing including different parameters of each of these deformations and how these are affected by different types of hair including different types of hair damage. Expanded data sets are included for elastic moduli and other parameters of these deformations. A new section describing the historical development for assessing and measuring hair fiber curvature along with a new method for curvature has been developed and applied to more than 2,400 persons from more than 20 different countries. This method and data are featured in this section. Methods to determine the different dimensions of hair fibers including axial (length and curvature) and transverse dimensions (diameter, cross-sectional area and ellipticity) are described with much expanded data sets. Information on hair fiber friction (both high load and low load friction) and how friction varies with fiber diameter, comb composition and hair damage are included. Mechanical fatiguing, extension cycling and their effects on hair damage including scale lifting are described in the final section on the physical properties of hair fibers.
This chapter attempts to familiarize the reader with the science of hair and hair care, while outlining approaches and techniques for evaluating both consumer and technical aspects of performance. The development of hair care products is strongly marketing driven, and consequently the language of the industry is that of the consumer. As such, despite the identification of now commonplace attributes, which are prominently displayed in packaging and advertising, there are often complex or muddled relationships back to the science. Here, an attempt has been made to present current thinking in these areas; while highlighting how a successful product is the combination of strong technical performance, good aesthetics, and a compelling marketing message.
The chapter begins by describing the complex chemical and physical structure of wool. It then reviews the different structure-property models of strength which attempt to explain the shape of the stress-strain curve in terms of wool's known structure. The alternative methods of measuring fibre strength are discussed as well as the difficulties associated with measuring strength in non-uniform fibers. Finally the chapter looks at the way in which a range of environmental, processing and service conditions affect the tensile failure properties of wool.
Most land mammals produce in addition to hair another form of hard keratin — nail, claw or hoof — and occasionally a third form, either horn or quill. Although the so-called horny keratins — nail, claw, hoof, horn and quill — are similar to hair in ultrastructure and composition, their functions are very different. The horny keratins are derived embryologically from the epidermis; the morphology of these keratins is given in Chap. 17, this Vol. Baden and Fewkes (1983) also recently reviewed the morphology, ultrastructure and growth of the human nail.
A new method, termed dynamic hairspray analysis, was developed to study the mechanical behavior of pre-set hair tresses, untreated and modified by hairspray resins, under a wide range of bending deformations. The technique includes a vertically acting tensile meter designed to measure the force in both compression and extension modes. The instrument, including a sample holder and spraying devices, was housed in an environmental chamber equipped with a humidity controller. The drying of a hairspray was investigated by (a) applying low intermittent deformations to a preformed hair tress in order to determine the properties of untreated hair, (b) treating the fibers with a hairspray, and (c) measuring the changes both in adhesive properties of a hairspray solution on the surface and in mechanical stiffness of the fiber assembly as a function of drying time. This approach allows the simultaneous determination of parameters such as stiffness of untreated and resin-modified hair, duration of tack, maximum value of tack force, and time of drying. In addition to this, the data collected during the experiment provide information about changes in geometrical dimensions of hair after the application of hairspray and after subsequent drying. In order to test the resistance of fixative resins to high humidity, the kinetic measurements of stiffness and tackiness were also performed at 90% RH.
At or near its surface, hair fibers contain a thick protective cover consisting of six to eight layers of flat overlapping scale-like structures called cuticle or scales which consists of high sulfur KAPs, keratin proteins and structural lipids. The cuticle layers surround the cortex, but the cortex contains the major part of the fiber mass. The cortex consists of spindle-shaped cells that are aligned parallel with the fiber axis. Cortical cells consist of both Type I and Type II keratins (IF proteins) and KAP proteins. Coarser hairs often contain one or more loosely packed porous regions called the medulla, located near the center of the fiber. The cell membrane complex, the “glue” that binds or holds all of the cells together, is a highly laminar structure consisting of both structural lipid and protein structures. Hair fibers grow in cycles consisting of three distinct stages called anagen (growth), catagen (transition) and telogen (rest). Each stage is controlled by molecular signals/regulators acting first on stem cells and then on the newly formed cells in the bulb and subsequently higher up in differentiation in the growing fiber. The effects and incidence of hair growth and hair loss (normal and diseased) for both males and females are described in detail. Molecular structures controlling hair fiber curvature (whether a fiber is straight or curly) and the effects of the different structural units of the fiber on stress–strain and swelling behavior are described in detail.
Hair components were extracted in order to macroscopically observe the component most involved in formation of permanent waving by thioglycolic acid. In addition, we investigated the influence of treatment with hydrolyzed keratin on permanent wave formation in hair damaged by repeated bleaching treatment. We found that microfibrils is a mandatory component for the desired shape formation of permanent wave by thioglycolic acid, and plays a major role in the shape formation in primary bond than the cuticle and matrix do. Impregnating damaged hair with hydrolyzed keratin resulted in improvement of both permanent waving efficiency and the damage of hair. We hypothesize that hydrolyzed keratin increasing the efficiency of permanent wave formation by maintaining both the shape formation ability of primary bond and the resistance to gravity at the time of secondary bond.
Human hair is a nanocomposite biological fiber. Healthy, soft hair with good feel, shine, color and overall aesthetics is generally highly desirable. It is important to study hair care products such as shampoos and conditioners as well as damaging processes such as chemical dyeing and permanent wave treatments because they affect the maintenance and grooming process and therefore alter many hair properties. Nanoscale characterization of the cellular structure, the mechanical properties, as well as the morphological, frictional and adhesive properties (tribological properties) of hair is essential if we wish to evaluate and develop better cosmetic products, and crucial to advancing the understanding of biological and cosmetic science. The atomic/friction force microscope (AFM/FFM) and nanoindenter have recently become important tools for studying the micro/nanoscale properties of human hair. In this chapter, we present a comprehensive review of structural, mechanical, and tribological properties of various hair and skin as a function of ethnicity, damage, conditioning treatment, and various environments. Various cellular structures of human hair and fine sublamellar structures of the cuticle are identified and studied. Nanomechanical properties such as hardness, elastic modulus, creep and scratch resistance are discussed. Nanotribological properties such as roughness, friction, and adhesion are presented, as well as investigations of conditioner distribution, thickness and binding interactions.
The cutting behaviour of beard hair has been investigated quantitatively and qualitatively. High speed cutting tests were
conducted on beard hair samples using a purpose built cutting rig (provided by Gillette, UK) to determine the cutting forces.
High speed digital video photography was used to record the cutting process. In parallel with these tests, low speed cutting
tests were undertaken within a scanning electron microscope (SEM) to gain a better understanding of the cutting process. Results
from the high speed cutting tests showed that the peak cutting stresses are influenced strongly by moisture (the cutting stress
for ‘wet’ samples is reduced by about 30% as compared to dry samples) while the effects on the cutting stress of other variables
(subject age, blade approach angle and sample ageing due to prolonged storage) appeared to be less noticeable. The angle of
cut was affected by the distance of the initial contact point (between the hair and the blade) from the base of the hair with
the line of cut shifting towards the hair axis with increasing distance from the base. Qualitative observations from video-recordings
and still images taken during the cutting tests, conducted in-situ within the SEM as well as the high speed cutting rig, showed
four main cutting mechanisms of hair, which are documented in this paper. The distance from the initial contact point to the
base of the hair and the moisture level were the parameters which controlled the mechanism of failure. Qualitative observations
of the sort reported here are a necessary pre-cursor to the development of finite element models to simulate a cutting operation.
Human hair is the subject of a remarkably wide range of scientific investigations. Its chemical and physical properties are of importance to the cosmetics industry, forensic scientists and to biomedical researchers. The fifth edition of this book confirms its position as the definitive monograph on the subject. Previous editions were recognized as “concise and thorough” (Journal of the American Chemical Society), “an invaluable resource” (Canadian Forensic Science Society Journal), and “highly recommended” (Textile Research Journal). Chemical and Physical Behavior of Human Hair is a teaching guide and reference volume for cosmetic chemists and other scientists in the hair products industry, academic researchers studying hair and hair growth, textile scientists and forensic specialists. Features of the Fifth Edition: Recent advances in the classification and characterization of the different proteins and genes in IF and keratin associated proteins in human hair are described. The mechanism and incidence of hair growth and loss and hair density vs. age of males & females are described for Asians, Caucasians and Africans in different scalp regions. Details of hair surface lipids and cuticle membranes provide a better understanding of the surface and organization of the CMC and its involvement in stress strain is presented. Recent evidence demonstrates a more bilateral structure in curly hair and a more concentric arrangement of different cortical proteins in straighter hair. SNPs involved in hair form (curl and coarseness) and pigmentation and genes in alopecia and hair abnormalities are described. The latest biosynthetic scheme for hair pigments and structures for these and the different response of red versus brown-black pigments to photodegradation is described. A new method for curvature on 2,400 persons from different countries and groups is used to assign curvature throughout this book. Additional data for age and effects on diameter, ellipticity, elastic modulus, break stress and other parameters are presented with much larger data sets featuring statistical analyses. Hair conditioning, strength, breakage, split ends, flyaway, shine, combing ease, body, style retention, manageability and feel parameters are defined and described. A new section of different life stages by age groups considering collective and individual changes in hair fiber properties with age and how these affect assembly properties.
The mechanical properties of human hair fiber and the permeation behaviors of some dye molecules into hair have been studied, and are here discussed based on a universal structural model proposed by the authors in the previous paper. The model consists of two structural parts, both of which have two states (Two-part/two-state model). One part of the hair, which has a higher transition temperature (T-c; ca 70 degrees C in water), is assigned to be macrofibril and exo-cuticle; the other part with lower T-c (ca. 0 degrees C in water) is inter-macrofibrillar materials, a cell-membrane complex (CMC) and endo-cuticle. The temperature dependence of the elastic modulus of a human hair in the Hookean region clearly shows two break points, indicating the above-mentioned transition temperatures. We have proposed a viscoelastic model based on the two-part/two-state structural model to understand the mechanical behaviors in the Hookean, yield and post-yield regions. The permeation rate of some dye molecules into hair fiber starts to dramatically increase at the higher transition temperature. Such permeation behaviors can also be understood from a universal structural model. The molecular size of dye is a crucial factor in permeation behaviors. Dye molecules with a size smaller than 1.0 nm migrate much more easily into hair.
A universal structural model for human hair has been proposed in order to understand the physical properties of hair. The model consists of two structural parts, both of which have two states (Two-part/two-state model). The transition temperature (T-c) between the two states of one part is about 70 degrees C, and that of the other part is about 0 degrees C in a water medium. These transition temperatures depend highly upon the water content of the hair. A higher transition temperature is observed in hair having a lower water content. Above the transition temperatures, both parts of the hair are soft and plastic (a melted state); they are hard and elastic (a solid state) below the transition points. One part of hair which has a higher transition temperature (ca. 70 degrees C in water) is assigned to be macrofibril and exo-cuticle consisting of keratinous proteins; the other part with a lower T-c (ca. 0 degrees C) is inter-macrofibrillar materials, a cell-membrane complex (CMC), and the endocuticle of non-keratinous proteins and lipids. This structural model was derived from the results of thermal-setting and relaxation experiments as well as TEM observations after permeating a dye with a high electron density (Erythrosin B).
and normal (cuticle-unremoved) hairs. The analysis of fiber set, based on the theory established in a previous investigation (7), showed that the set obtained for both types of hair is in the same way related to the relaxation of fiber bending stiffness during reduction. The consideration of the differences between the bending relaxation rate of normal and alescaled hairs during reduction suggests that the main role of the cuticle in waving is to reduce the setting ability of human hair by effectively operating as a chemical barrier. It lowers the concentration of the reducing agent through reaction prior to its diffusion into the fiber cortex. A further, minor, and mechanical role of the cuticle for permanent set is discussed.
Nanomechanical characterization of human hair using nanoindentation and nanoscratch provides valuable information about the
hair fiber itself, as well as how damage and treatment affect important mechanical properties of the fiber (Wei and Bhushan,
2006;Wei et al., 2005). In Sect. 4.1, the hardness, Young’s modulus, and creep results for both the hair surface and cross
section are discussed. In Sect. 4.2, the coefficient of friction and scratch resistance of the hair surface is presented for
unsoaked and soaked hair. In Sect. 4.3, stress–strain curves and AFM topographical images of virgin and damaged hair during
tensile deformation are presented.
derivatization (OPA) and a modification of the single~fiber tensile kinetics (SFTK) method. Virgin, medium brown hair from a single source (DeMeo Brothers) was used for all of the experiments. Stress relaxation of hair fibers was monitored to determine the rate of reduction of stress- supporting disulfide bonds by cysteamine and ATG. Levels of cystine and cysteine were monitored by amino acid analysis to determine the rate of reduction of disulfide bonds in the whole fiber. The results of this study indicated that the rate of reduction of both stress-supporting and whole-fiber disulfide bonds by ammonium thioglycolate was faster than the rate of reduction by cysteamine. The kinetic results obtained by stress relaxation were found to agree with the results from amino acid analysis.
Human hair is a nanocomposite biological fiber. Hair care products such as shampoos and conditioners, along with damaging processes such as chemical dyeing and permanent wave treatments, affect the maintenance and grooming process and are important to study because they alter many hair properties. Nanoscale characterization of the cellular structure, mechanical properties, and morphological, frictional, and adhesive properties (tribological properties) of hair are essential to evaluate and develop better cosmetic products, and to advance the understanding of biological and cosmetic science. The atomic/friction force microscope (AFM/FFM) and nanoindenter have become important tools for studying the micro/nanoscale properties of human hair. In this review article, we present a comprehensive review of structural, mechanical, and tribological properties of various hair and skin as a function of ethnicity, damage, conditioning treatment, and various environments.
The structural characteristics of beard hair have been analysed using optical microscopy, scanning electron microscopy and
atomic force microscopy. The cross-sectional profile of beard hair is found to be broadly elliptical. The three main morphological
features cited in previous literature for scalp hair, namely the cuticles, cortex and medulla were observed. A novel and efficient
method has been developed in order to characterise the cross sectional area of an elliptical hair accurately. Quantitative
data are presented for the variation of average cross-sectional area across different facial sites (cheek, chin and neck)
for three different subjects. Tensile tests have been conducted on a variety of specimens to study the tensile stress-strain
behaviour of beard hair in both wet and dry state at a range of cross-head speeds. Application of the area characterisation
method significantly reduced the scatter in the mechanical data. The Young's modulus and yield stress values of beard hair
are affected significantly by the presence of moisture but only to a limited extent by the strain rate. Repeat tensile tests
have been conducted on beard hair samples which were kept in storage for nine months. A drop in the Young's modulus of up
to 30% has been observed indicating an “ageing” effect (due to prolonged storage) on the properties of the hair.
Hair is a non homogenous complex material which can be associated with a polymer. It is made up 95% of Keratin. Hair has a great social significance for human beings. In the High Middle Ages, for example, long hairs have been reserved for kings and nobles.
Most common interest in hair is focused on hair growth, hair types and hair care, but hair is also an important biomaterial which can vary depending on ethnic origin or on age, hair colour for example can be a sign of ethnic ancestry or age (dark hair for Asiatic, blond hair for Caucasian and white hair for old people in general). In this context, different approaches have been conducted to determine the differences in mechanical properties and characterize the fracture topography at the surface of hair depending on its type and its age.
A tensile testing machine was especially designed to achieve tensile tests on hair. This device is composed of a microdisplacement system and a force sensor whose peak load is limited to 3N. The curves and the values extracted from each experiment, allow us to compare the evolution of the mechanical properties from one hair to another.
Observations with a Scanning Electron Microscope (SEM) and with an interferometer were made on different hairs. Thus, it is possible to access the cuticle state and the fracture topography for each category.
This study employs a novel method, gas sorption (1), to quantify the porosity characteristics of hair by determining total pore volume, adsorption pore-size distribution, and the surface area of damaged hair. Damage mechanisms were studied by comparing the different pore volume and surface area resulting from two different types of damage: chemical and UV. Hair color measurement and tensile strength, both reflecting the changes in hair cortex, were also employed in this study. The results suggest that hair damage caused by oxidative bleach and UV oxidation follows different pathways. Chemical damage (oxidative bleach) nearly triples the hair surface area in the first minute of bleaching due to the increase in the number of pores, followed by a sudden drop after 10 min of bleaching from smaller pores breaking down into larger ones. In contrast, UV damage shows an immediate loss in surface area in the first 200 hr of exposure and a gradual increase as exposure time continues.
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