Article

The Effect of Hydration on the Mechanical Behaviour of Hair

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Abstract

Human hair is a biological material constantly exposed to different external factors,such as humidity, sunrays, temperature, chemical treatments, etc. All these treatments influence and modify its physical behaviour. Studying the biophysical properties of human hair is very important in both dermatology to provide useful markers for the diagnosis of hair disorders and in cosmetics to develop better hair-care products. Water is one of the external factors whose action on the mechanical behaviour of hair is the most visible. To understand the role of water in the biophysical behaviour of hair, it is essential to study its influence on alpha-keratin, which composes the major part of the structure of hair. The influence of water on the biomechanical behaviour of hair has been studied using relaxation tests. The generalised Maxwell model was used to analyse rheological results. The results indicate a modification of the rheological behaviour of hair before and after immersion in water and during ambient airdrying. Finally, a correlation between the rheological results and the chemical bond structure of hair is discussed.

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... The salt bridges are affected by water and pH changes, and they contribute to the overall structure stabilization. The hydrogen bonds located between the α-keratin helix are also influenced by the presence of water, which can penetrate the polypeptide chains and caused it to break [34]. ...
... Hair keratins are composed of three stratified layers: cuticle, cortex, and medulla (Fig. 11). The cuticle with a thickness between 1.5 and 5.0 μm consists of flat overlapping cells that protect the inner hair parts and is responsible for its rigidity [34]. The cortex complex and multi-scale fibrillar system, which is about 90 % of the fiber weight plays a major role on hairs' mechanical properties [34,81] while the medullar (which is not always present) has a (Placeholder1) negligible effect. ...
... The cuticle with a thickness between 1.5 and 5.0 μm consists of flat overlapping cells that protect the inner hair parts and is responsible for its rigidity [34]. The cortex complex and multi-scale fibrillar system, which is about 90 % of the fiber weight plays a major role on hairs' mechanical properties [34,81] while the medullar (which is not always present) has a (Placeholder1) negligible effect. The cortex [74]. ...
Article
This review explores the potential of animal-based fillers and fibers as eco-friendly alternatives to conventional synthetic ones. Examining materials such as wool, silk, feather, hair and beak, the review elucidates their chemistry, structure, properties and sources, emphasizing biodegradability and renewability. It also discusses the compatibility of these materials with polymer matrices and their mechanical, acoustic and thermal performances. The review critically analyzes environmental and ethical implications, presenting challenges and opportunities in the emerging field. By addressing ecological and performance aspects, it contributes to global efforts in fostering sustainability in materials science. Future research to address gaps and enhance the design, manufacture and application of animal-based reinforcements in various industries are clearly outlined at the end of the review.
... In addition, McMichael et al. stated that weathering from different hair care techniques and genetic susceptibility can cause hair fragility that results in breakage [83]. Water content and hydrogen bonding play major roles in the mechanical properties of hair [35,84,85]. In this study, the potential of Olaplex ® and K18 ® commercial products to rebuild internal bonds compromised by the bleaching process was explored, thereby enhancing the mechanical properties of hair, in particular, the fiber's mechanical strength and extensibility. ...
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The increasing demand for effective hair care products has highlighted the necessity for rigorous claims substantiation methods, particularly for products that target specific hair types. This is essential because the effectiveness of a product can vary significantly based on the hair’s condition and characteristics. A well-defined bleaching protocol is crucial for creating a standardized method to assess product efficacy, especially for products designed to repair damaged hair. The objective of this study was to create a practical bleaching protocol that mimics real-world consumer experiences, ensuring that hair samples exhibit sufficient damage for testing. This approach allows for a reliable assessment of how well various products can repair hair. The protocol serves as a framework for evaluating hair properties and the specific effects of each product on hair structure. Color, brightness, lightness, morphology, and topography were primarily used to understand the big differences in the hair fiber when treated with two repair benchmark products, K18® and Olaplex®, in relation to the Bleached hair. The devised bleaching protocol proved to be a fitting framework for assessing the properties of hair and the unique characteristics of each tested product within the hair fiber. This protocol offers valuable insights and tools for substantiating consumer claims, with morphological and mechanical methods serving as indispensable tools for recognizing and validating claims related to hair. The addition of K18® and Olaplex® demonstrated an increase in hair brightness (Y) and lightness (L* and a*) in relation to the Bleached samples, which were considered relevant characteristics for consumers. Olaplex®’s water-based nature creates a visible inner sheet, effectively filling empty spaces and improving the disulfide linkage network. This enhancement was corroborated by the increased number of disulfide bonds and evident changes in the FTIR profile. In contrast, K18®, owing to the lipophilic nature of its constituents, resulted in the formation of an external layer above the fiber. The composition of each of the products had a discrete impact on the fiber distribution, which was an outcome relevant to the determination of spreadability by consumers.
... These conclusions remain true for hair fibers that are dry, wet, or coated with products. 39,[42][43][44][45] It is for these reasons that the cosmetic industry has done a lot of research and development to create products that will strengthen and fortify the natural structure of curly hair. 2,4 The results in the current study display similar trends to previous studies. ...
Preprint
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Hair is one of the key characteristics that classify us as mammals. It is a natural polymeric composite that is primarily composed of tight macro-bundles of keratin proteins, which are highly responsive to external stimuli, including pH, temperature, and ionic solvent content. The external responsive behavior displayed by hair is similar to the behavior displayed by hydrogels and other natural fibrous gel systems like collagen and fibrin. Hair and its appearance play a significant role in human society. It is a highly complex biocomposite system, which has been traditionally challenging to characterize and thus develop functional personal care products for consumers. Over the last few decades, a significant societal paradigm shift occurred among those with curly hair. They began to accept the natural morphological shape of their curls and style their hair according to its innate, distinct, and unique material properties. These societal and cultural shifts have given rise the development of new hair classification systems, beyond the traditional and highly limited ethnicity-based distinction between Caucasian, Mongolian, and African. L’Oréal developed a hair typing taxonomy based on quantitative geometric parameters displayed among the four key curl patterns – straight, wavy, curly, and coily (kinky). However, the system fails to capture the complex diversity of curly and kinky/coily hair. Acclaimed celebrity hair stylist, Andre Walker, developed a classification system that is the existing gold standard for classifying curly and kinky/coily hair, however the system relies upon qualitative classification measures, making the system vague and ambiguous to the full diversity of phenotypic differences. The goal of this research is to use quantitative methods to identify new geometric parameters, which will be more representative of curly and kinky/coily hair curl patterns. These new parameters will therefore provide more information on the kinds of personal care product ingredients that will resonate best with these curl patterns, and thus maximize desired appearance and overall hair health. The goal is also to correlate these new parameters with its mechanical properties. This was accomplished by identifying new geometric and mechanical parameters from several types of human hair samples. Geometric properties were measured using scanning electron microscopy (SEM), photogrammetry, and optical microscopy. Mechanical properties were measured under tensile extension using a texture analyzer (TA) and a dynamic mechanical analyzer (DMA), which bears similarity to the common act of brushing or combing. Both instruments measure force as a function of applied displacement, thus allowing the relationship between stress and applied stretch ratio to be measured as a hair strand uncurls and stretches to the point of fracture. From the resulting data, correlations were made between fiber geometry and mechanical performance. This data will be used to draw more conclusions on the contribution that fiber morphology has on hair fiber mechanics and will promote cultural inclusion among researchers and consumers possessing curly and kinky/coily hair.
... The water content and absorption profiles could be drastically altered by daily routines or cosmetic procedures that affect the keratin structure of hair [41,42]. Despite water influencing several properties of hair, its effect is more notorious on the mechanical behavior of hair fibers [43]. The capacity of proteins to bind water is related to the proteins' composition and conformation. ...
Article
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The perming of hair is a common styling procedure with negative impact on the overall properties of the hair fibers. Usually, this process uses harsh chemicals to promote the disruption of disulfide bonds and the formation of new bonds to change the shape of hair. Here, we explored bovine serum albumin (BSA), silk fibroin (SF), keratin and two fusion recombinant proteins (KP-UM and KP-Cryst) as new perming agents. A phosphate buffer prepared at different pH values (5, 7 and 9) was used to apply the proteins to virgin Asian hair, and a hot BaByliss was used to curl the hair fibers. To assess the potential of the protein formulations for hair styling, the perming efficiency and the perming resistance to wash were measured. Furthermore, the fiber water content was evaluated to assess if the proteins protected the hair during the styling process. Despite all of the proteins being able to assist in the curling of Asian hair, the best perming efficiency and perming resistance to wash results were observed for BSA and keratin. These proteins showed perming efficiency values close to that measured for a commercial perming product (chemical method), particularly at pH 5 and 9. The increase in the hair’s internal and external water contents revealed a protective effect provided by the proteins during the application of heat in the styling procedure. This study shows the potential of proteins to be used in the development of new eco-friendly hair styling products.
... The water molecules tended to migrate to amorphous region of polymer structure, providing extra free volumes for the structural relaxation [24]. Considering such molecular interactions, moisture might weaken the effective bonding including hydrogen-bond network and other intermolecular cross-links in keratin [25,26]. In contrast, the excessive cross-linking including hydrogen bonds reduced molecular relaxations for the keratin at dry state, which increased the brittleness and rigidity of keratin to lead to brittle fracture of D-samples, i.e., relatively "flat" surface with high magnification, as shown in Fig. 3e, f. ...
Article
Buffalo horn sheath is one of the typically natural composites with balanced strength and toughness. It demonstrates a structural hierarchy with stacked and corrugate-shaped lamellae, longitudinally sutured scaly cells and unidirectional keratin fibers. This work clarifies the influences of protein secondary structure, anisotropy microstructure, and moisture on flexural properties of sheath. From distal to proximal sections of sheath, flexural strength and modulus decrease, which may relate to the varied secondary structure. The mechanical properties are demonstrated to be enhanced along longitudinal direction correlated to the anisotropic microstructure. Besides, the strength and modulus can be weakened by the plasticization of moisture induced by rehydration. The fracture modes, which include matrix failure, interface dissociation and fiber breakage, are further correlated with the effects of anisotropy and moisture to illustrate damage patterns of horn sheath under different conditions. This study may provide reference to the structure-property relationship of natural composites and design strategy of bioinspired composites with tubular shape and anisotropy.
... The cortex represents the major part of the hair mass (>90% dry weight). 7 It is composed of cortical cells and the CMC. Cortical cells are tightly packed with macrofibrils, which have a hierarchical structure starting from keratin in a α-helical fold. ...
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Brillouin microscopy is a new form of optical elastography and an emerging technique in mechanobiology and biomedical physics. It was applied here to map the viscoelastic properties of human hair and to determine the effect of bleaching on hair properties. For hair samples, longitudinal measurements (i.e. along the fibre axis) revealed peaks at 18.7 GHz and 20.7 GHz at the location of the cuticle and cortex, respectively. For hair treated with a bleaching agent, the frequency shifts for the cuticle and cortex were 19.7 GHz and 21.0 GHz, respectively, suggesting that bleaching increases the cuticle modulus and ‐ to a minor extent ‐ the cortex modulus. These results demonstrate the capability of Brillouin spectroscopy to address questions on micromechanical properties of hair and to validate the effect of applied treatments. This article is protected by copyright. All rights reserved.
... Thus, when keratin is arranged in its wrapped alpha-form, hair possesses "cohesion provided by net-works, such as catenated cystine cross-linkages, interactions between side chain groups, hydrogen bonds between neighboring groups, and hydrophobic interactions" [35]. In fact, "although hydrogen bonds are rather weak because of their lower energy when compared with covalent bonds, a high number of inter-peptide bonds can initiate substantial changes to the mechanical behaviour of single and dense hair fibril systems" [36]. However, when keratin is in its beta-form, hair is stretched. ...
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ConspectusHair is a natural polymeric composite primarily composed of tight macrobundles of keratin proteins, which are highly responsive to external stimuli, similarly to the hydrogels and other natural fibrous gel systems like collagen and fibrin.Hair and its appearance play a significant role in human society. As a highly complex biocomposite system, it has been traditionally challenging to characterize and thus develop personal care products. Over the last few decades, a significant societal paradigm shift occurred among those with curly hair, accepting the natural morphological shape of their curls and styling their hair according to its innate, distinct, and unique material properties, which has given rise to the development of new hair classification systems, beyond the traditional and highly limited race-based distinction (Caucasian, Mongolian, and African). L'Oréal developed a hair typing taxonomy based on quantitative geometric parameters among the four key patterns─straight, wavy, curly, and kinky, but it fails to capture the complex diversity of curly and kinky hair. Acclaimed celebrity hair stylist Andre Walker developed a classification system that is the existing gold standard for classifying curly and kinky hair, but it relies upon qualitative classification measures, making the system vague and ambiguous of phenotypic differences. The goal of this research is to use quantitative methods to identify new geometric parameters more representative of curly and kinky hair curl patterns, therefore providing more information on the kinds of personal care products that will resonate best with them and thus maximize desired appearance and health, and to correlate these new parameters with its mechanical properties. This was accomplished by identifying new geometric and mechanical parameters from several types of human hair samples.Geometric properties were measured using scanning electron microscopy (SEM), photogrammetry, and optical microscopy. Mechanical properties were measured under tensile extension using a texture analyzer (TA) and a dynamic mechanical analyzer (DMA), which bears similarity to the common act of brushing or combing. Both instruments measure force as a function of applied displacement, thus allowing the relationship between stress and applied stretch ratio to be measured as a hair strand uncurls and stretches to the point of fracture. From the resulting data, correlations were made between fiber geometry and mechanical performance. This data will be used to draw more conclusions on the contribution that fiber morphology has on hair fiber mechanics and will promote cultural inclusion among researchers and consumers possessing curly and kinky hair.
Preprint
Full-text available
Hair is one of the key characteristics that classify us as mammals. It is a natural polymeric composite that is primarily composed of tight macro-bundles of keratin proteins, which are highly responsive to external stimuli, including pH, temperature, and ionic solvent content. The external responsive behavior displayed by hair is similar to the behavior displayed by hydrogels and other natural fibrous gel systems like collagen and fibrin. Hair and its appearance play a significant role in human society. It is a highly complex biocomposite system, which has been traditionally challenging to characterize and thus develop functional personal care products for consumers. Over the last few decades, a significant societal paradigm shift occurred among those with curly hair. They began to accept the natural morphological shape of their curls and style their hair according to its innate, distinct, and unique material properties. These societal and cultural shifts have given rise the development of new hair classification systems, beyond the traditional and highly limited ethnicity-based distinction between Caucasian, Mongolian, and African. L’Oréal developed a hair typing taxonomy based on quantitative geometric parameters displayed among the four key curl patterns – straight, wavy, curly, and coily (kinky). However, the system fails to capture the complex diversity of curly and kinky/coily hair. Acclaimed celebrity hair stylist, Andre Walker, developed a classification system that is the existing gold standard for classifying curly and kinky/coily hair, however the system relies upon qualitative classification measures, making the system vague and ambiguous to the full diversity of phenotypic differences. The goal of this research is to use quantitative methods to identify new geometric parameters, which will be more representative of curly and kinky/coily hair curl patterns. These new parameters will therefore provide more information on the kinds of personal care product ingredients that will resonate best with these curl patterns, and thus maximize desired appearance and overall hair health. The goal is also to correlate these new parameters with its mechanical properties. This was accomplished by identifying new geometric and mechanical parameters from several types of human hair samples. Geometric properties were measured using scanning electron microscopy (SEM), photogrammetry, and optical microscopy. Mechanical properties were measured under tensile extension using a texture analyzer (TA) and a dynamic mechanical analyzer (DMA), which bears similarity to the common act of brushing or combing. Both instruments measure force as a function of applied displacement, thus allowing the relationship between stress and applied stretch ratio to be measured as a hair strand uncurls and stretches to the point of fracture. From the resulting data, correlations were made between fiber geometry and mechanical performance. This data will be used to draw more conclusions on the contribution that fiber morphology has on hair fiber mechanics and will promote cultural inclusion among researchers and consumers possessing curly and kinky/coily hair.
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Many studies on hair deal with the improvement of cosmetic products using SEM or AFM measurements. This paper proposes a new method, which uses an interferometer to compare two topographic images from the same area of a sample. The repositioning method combined with topographic tools, allow a precise observation of the cuticle evolution before and after treatment. The outlined tracking zone method and interferometry can also be used during pull experiments. (c) 2008 Elsevier B.V. All rights reserved.
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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.
Article
Résumé Les auteurs ont étudié l'incidence de températures croissantes de 20 à 200°C sur la structure superficielle et profonde du cheveu dans le but de définir une température optimale de séchage permettant de respecter l'intégrité de la fibre de kératine tout en favorisant la permanence de sa déformation. Pour ce faire, diverses techniques ont été mises en oeuvre: microscopie à balayage, dosage de l'eau par la méthode de Karl Fischer, calorimétrie différentielle et diffraction des rayons X. Il apparait une température critique de 140°C en deçà de laquelle les modifications observées sont faibles, réversibles et liées à la perte progressive de l'eau libre. Au delà de 140°C, les modifications structurales sont profondes et irréversibles. Elles se traduisent par un changement d'aspect dû au plissement de la cuticule, les écailles de la cuticule disparaissant peu à peu. Après élimination de l'eau liée, la dégradation totale de la structure interne est obtenue aux environ de 200°C. On peut toutefois sélectionner une température optimale de séchage de 60°C pour laquelle la fixation ultérieure de l'eau par le cheveu sec sera plus lente le rendant moins sensible aux variations hygrométriques. Effects of heat treatment on hair structure
Article
Structurally there are four classes of intermediate filaments (IF) with distinct but closely related axial organisations. One of these, hard α-keratin IF, has been studied to clarify several apparently exceptional features which include the number of molecules in the IF cross-section and the mode by which the axial organisation of its constituent molecules is stabilised. Using the dark-field mode of the STEM at the Brookhaven National Laboratory (USA) mass measurements were obtained from unstained IF isolated from hair keratin. The data thus obtained show that the number of chains in cross-section is about 30 (±3: standard deviation) and is very similar to the numbers determined in previous STEM experiments for the dominant filament type in other classes of IF (about 32). Furthermore, re-analysis of the low-angle equatorial X-ray diffraction pattern reveals, in contrast to earlier work, solutions that are compatible with the number of chains in cross-section indicated by the STEM data. The absence of the head-to-tail overlap between parallel molecules characteristic of most IF may be compensated in hard α-keratin by a network of intermolecular disulfide bonds. It is concluded that native IF of hard α-keratin and desmin/vimentin —and probably many other kinds of IF as well— contain about 32 chains in cross-section, and that the axial structures of these various kinds of IF differ in small but significant ways, while generally observing the same basic modes of aggregation.
Article
A simple quantitative method for determining the amount of mechanical strength contributed by the various types of bonds in hair fiber has been developed. The effects of various types of reagents, such as acids, bases, oxidizing agents, and reducing agents, are discussed. The reaction between various chemical agents and hair fibers has been found to be first- order with respect to the reagent and also with respect to the bonds to be broken. The effect of temperature is discussed. Using the theory of absolute reaction rates, the heats and entropies of activation for the reaction have been calculated. The rate of diffusion into hair has been considered. Using Fick's second law of diffusion, the diffusion coefficient of hydroxyl ion in hair has been calculated. Also applying the theory of absolute reaction rates, the values for the heat and entropy of activation have been calculated.
Article
The stress-relaxation behavior of wool fibers after a pretreatment with a chemical solution is particularly important for evaluating the efficiency of the pretreatment. In this study, three viscoelastic models, including the Maxwell, two Maxwell unit, and modified two Maxwell unit models, were established first. To verify the feasibility of the models, stress-relaxation experiments for wool fibers were performed. The wool fibers were pretreated with a sodium bisulfite solution (1 and 3%) at various temperatures (293, 298, 303, 308, 313, and 318 K). Then, the experimental values were fitted to the three models to obtain the rate constants of relaxation. The activation energy of the wool fibers was calculated with the Arrhenius equation. The results showed that the modified two Maxwell unit model provided the best fit for the experimental data of the wool fibers. The stress-relaxation process of the wool fibers could be divided into two stages, a rapid stage followed by a slow stage. The rapid relaxation of stress was attributed to the weak bonds in the wool fibers, and the following slow relaxation stage was attributed to strong bonds. The Arrhenius equation could describe the stress-relaxation process of the wool fibers very well. Furthermore, the activation energy decreased in the presence of sodium bisulfite. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Article
Synopsis---HUMIDITY has a major influence on hair sets. Experimental results suggest that water affects the mechanical properties of single fibres and these in turn strongly influence the set holding characteristics of hair tresses. The paper discusses the molecular mechanism of WATER BINDING to KERAT1N fibres and the role that hydration plays in the behaviour of single fibre properties. The binding of water appears to be a site binding process, i.e. interactions occur in stoichiometric ratios between the water molecules and the various hydrophilic groups of the protein (carboxylic, amino and peptide groups) and are governed by the mass action law. The effect of water on the mechanical properties of the fibre and, in particular, on its tem- perature-induced shrinkage (i.e. SUPERCONTRACTION) and the strain-stress curve can be adequately represented by means of a polymer-gel model. According to this model keratin is a semicrystalline (partially helical) cross-linked polypeptide network. The polypeptides, irrespec- tive of their conformations, are capable of binding water molecules, although the value of the binding constant depends on the conformation. The elasticity of the network, i.e. the retractlye force of the fibre, is determined by the free energy which is required to disorganize the helical regions into random conformations. Absorption of water changes this free energy of transition and thus affects both f, the elastic force, and T s, the shrinkage or melting temperature of the hair. The experimentally determined dependences of T s and f on humidity and off on tempera-
Article
Human hair fibers experience tensile forces as they are groomed and styled. Hence the behavior of hair under tension is of interest to beauty care science. Previous studies have used optical/scanning electron microscopy to characterize hair tensile response. For the first time, in situ tensile loading experiments on hair with atomic force microscopy (AFM) have been performed. A custom-built AFM sample stage allows loading hair fibers in tension. A technique to locate and image the same control area at different strains is developed. This is used to study morphology changes that occur with deformation. Caucasian virgin, chemically damaged and mechanically damaged hair samples are studied to assess the effects of damaging treatments and the differences between chemical and mechanical damage. Virgin and damaged samples treated with commercial conditioner are also studied to ascertain the effect of conditioner on the tensile response. Mechanisms for the observed results are discussed.
Article
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.
Article
The time-dependent bending recovery of human hair fibers was investigated for a variety of relative humidities and aging times. The data were analyzed on the basis of a viscoelastic filament/matrix model and the Denby-equation, containing the parameter K as the ratio of the elastic bending rigidities of the matrix and the filaments and the Kohlrausch-Williams-Watts (KWW) function as relaxation function. The first stage of the analysis ascertained that the recovery curves shift with aging time on the time scale with the expected aging rate of μ ≈ 1. The second stage showed that the shape factor of the KWW function exhibits a mean value across the aging and humidity range of m = 0.28, which is close to the “universal” value of 1/3. On this basis, it was found that virtually no change occurs for the modulus ratio for low water contents up to about 10%, being constant at K0= 6 .1, while linearly decreasing beyond this threshold. The reduced, characteristic relaxation time drops on the log-time scale from logτr(0) = 0.47 for the dry fiber linearly with water content, covering about two thirds of a decade for 0–20% water content. With the pronounced humidity dependence of the parameters, hair shows what is termed hydro-rheologically complex (HRC) in analogy to thermo-rheologically complex behavior. Using the HRC approach, the dynamical mechanical performance of hair (1 Hz) was calculated for a range of water contents and aging times and found to be in good general agreement with experimental data. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Article
The water content of hair can be evaluated by weighing, the Karl Fischer method, and from electrical properties. However, these methods cannot be used to study the distribution of water in the hair. Imaging techniques are required for this purpose. In this study, a highly sensitive near-infrared (NIR) imaging system was developed for evaluating water in human hair. The results obtained from NIR imaging and conventional methods were compared. An extended indium–gallium–arsenide NIR camera (detection range: 1100–2200 nm) and diffuse illumination unit developed in our laboratory were used to obtain a NIR image of hair. A water image was obtained using a 1950-nm interference filter and polarization filter. Changes in the hair water content with relative humidity (20–95% RH) and after immersion in a 7% (w/w) sorbitol solution were measured using the NIR camera and an insulation resistance tester. The changes in the water content after treatment with two types of commercially available shampoo were also measured using the NIR camera. As the water content increased with changes in the relative humidity, the brightness of the water image decreased and the insulation resistance decreased. The brightness in the NIR image of hair treated with sorbitol solution was lower than that in the image of hair treated with water. This shows the sorbitol-treated hair contains more water than water-treated hair. The sorbitol-treated hair had a lower resistance after treatment than before, which also shows that sorbitol treatment increases the water content. With this system, we could detect a difference in the moisturizing effect between two commercially available shampoos. The highly sensitive imaging system could be used to study water in human hair. Changes in the water content of hair depended on the relative humidity and treatment with moisturizer. The results obtained using the NIR imaging system were similar to those obtained using a conventional method. Our system could detect differences in the moisturizing effects of two commercially available shampoos.
Article
Characterization of friction and wear properties of hair and skin is essential to develop better shampoo and conditioner products and advance biological and cosmetic science. Literature on the tribological characterization of hair and skin is scarce to date. In this study, friction experiments were performed at a range of loads, speeds, and skin area in order to study their effect on skin–hair contact. In addition, friction and wear experiments were performed to simulate skin–hair and hair–hair contacts at nominal conditions. Environmental dependence of hair friction is of importance and the effects of temperature and humidity on the friction of hair against skin were studied. Measurements were made using a flat-on-flat tribometer under reciprocating motion on Caucasian, Asian, and African hair (virgin, chemo-mechanically damaged, and conditioner treated) against polyurethane film (synthetic skin) and against hair. The morphology of hair and skin were measured by atomic force microscopy (AFM) and optical microscopy. Average coefficient of friction values were measured for each ethnicity and hair type, and are discussed. The directionality dependence of friction with respect to hair is also discussed.
Article
Human hair fibers experience tensile forces during grooming and styling processes. The tensile response of hair is hence of considerable interest to the cosmetics industry. In this study, in situ tensile characterization studies have been carried out in an atomic force microscope (AFM) on different hair under different conditions. A custom-built AFM sample stage allows hair fibers to be loaded in tension. A technique to locate and image the same control area at different strains has been developed to study the changes in morphology that occur with deformation. Virgin Caucasian, Asian and African hair were studied to understand the differences between different ethnic hair types. Also, the tensile response and morphological changes of virgin, chemically damaged and conditioner-treated Caucasian hair after soaking were compared against the corresponding dry tensile response. Finally, virgin, damaged and treated Caucasian hair fibers were subjected to fatigue cycling to simulate combing/detangling, and their tensile response studied.
Article
The atomic force microscope fiber probe is used to directly measure the forces and friction between two human hairs under various conditions. It is shown that the forces between the hair fibers in solution can be well explained by a DLVO interaction and that cationic surfactant modifies the interactions in a manner entirely consistent with current views of adsorption behavior. A Coulombic attraction occurs between the crossed hair fibers in air due to the heterogeneity of the surface, and at shorter separations a clear dispersion interaction is observed. Exposure of the hair to a bleaching solution leads to the removal of the adhesion and solely a double-layer interaction. Two crossed hair fibers obey Amontons' classic law of friction, with a linear relation between applied load and frictional force, allowing the determination of a friction coefficient; positively charged surfactant adsorption is shown to reduce the friction coefficient between the fibers in a manner consistent with boundary lubrication by a palisade layer.
Article
The natural surface of human hair (epicuticle) consists of a bilayer of heavily cross-linked proteins toward the individual cuticle cell inside combined with a monomolecular, hydrophobic layer of mixed fatty acids to the outside (F-layer), which is generally assumed to be homogeneous. Wetting force profiles along segments of hair from female test persons with lengths equivalent to about 1 month of growth (approximately 10 mm) are presented. In a multistep analysis, applying curve smoothing as well as Fourier and principal components analysis, for hair lengths comprising daily and weekly growth (2 mm) pronounced systematic changes are observed in the profiles, which show that the wettability curves are nonstochastic in nature and that hair exhibits a strongly nonhomogeneous surface. Specifically, a compound daily rhythm is observed for wettability, which through its typical bimodality can be linked to continuous changes of the hair surface during wake and sleep phases. The data set furthermore suggests systematic monthly changes, which may be related to the menstrual cycle. In consequence, the results not only provide proof for the inhomogeneity of the immediate hair surface but also lead to the hypothesis that it preserves a rather detailed and long-term, individual chronobiological record, through a specific, spatially modulated distribution of hydrophobic (lipids) and hydrophilic (proteins) regions, "written" by the composition of the cell membrane of the cuticle cell prior to apoptosis.
Article
Synopsis Examination of very long hair (length > 2.4 m) using a large range of evaluation methods including physical, chemical, biochemical and microscopic techniques has enabled to attain a detailed understanding of natural ageing of human hair keratin fibres. Scrutinizing hair that has undergone little or no oxidative aggression – because of the absence of action of chemical agents such as bleaching or dyeing – from the root to the tip shows the deterioration process, which gradually takes place from the outside to the inside of the hair shaft: first, a progressive abrasion of the cuticle, whilst the cortex structure remains unaltered, is evidenced along a length of roughly 1 m onwards together with constant shine, hydrophobicity and friction characteristics. Further along the fibre, a significant damage to cuticle scales occurs, which correlates well with ceramides and 18‐Methyl Eicosanoic Acid (18‐MEA) decline, and progressive decrease in keratin‐associated protein content. Most physical descriptors of mechanical and optical properties decay significantly. This detailed description of natural ageing of human hair fibres by a fine analysis of hair components and physical parameters in relationship with cosmetic characteristics provides a time‐dependent ‘damage scale’ of human hair, which may help in designing new targeted hair care formulations.
Article
A method is described for the minimization of a function of n variables, which depends on the comparison of function values at the (n + 1) vertices of a general simplex, followed by the replacement of the vertex with the highest value by another point. The simplex adapts itself to the local landscape, and contracts on to the final minimum. The method is shown to be effective and computationally compact. A procedure is given for the estimation of the Hessian matrix in the neighbourhood of the minimum, needed in statistical estimation problems.
Article
The animal cell cytoskeleton consists of three interconnected filament systems: actin microfilaments, microtubules and the lesser known intermediate filaments (IFs). All mature IF proteins share a common tripartite domain structure and the ability to assemble into 8-12nm wide filaments. At the time of their discovery in the 1980s, IFs were only considered as passive elements of the cytoskeleton mainly involved in maintaining the mechanical integrity of tissues. Since then, our knowledge of IFs structure, assembly plan and functions has improved dramatically. Especially, single IFs show a unique combination of extensibility, flexibility and toughness that is a direct consequence of their unique assembly plan. In this review we will first discuss the mechanical design of IFs by combining the experimental data with recent multi-scale modeling results. Then we will discuss how mechanical forces may interact with IFs in vivo both directly and through the activation of other proteins such as kinases.
Article
Mineralized biological tissues offer insight into how nature has evolved these components to optimize multifunctional purposes. These mineral constituents are weak by themselves, but interact with the organic matrix to produce materials with unexpected mechanical properties. The hierarchical structure of these materials is at the crux of this enhancement. Microstructural features such as organized, layered organic/inorganic structures and the presence of porous and fibrous elements are common in many biological components. The organic and inorganic portions interact at the molecular and micro-levels synergistically to enhance the mechanical function. In this paper, we report on recent progress on studies of the abalone and Araguaia river clam shells, arthropod exoskeletons, antlers, tusks, teeth and bird beaks.
Article
We have used an atomic force microscope to provide quantitative real-time analysis of human hair morphologic changes under ambient conditions. This form of microscopy combines the lateral resolution of an electron microscope and the flexibility of a light microscope. Three experiments were performed: a study of hair morphology in air versus water, a kinetic study of hair hydration, and a determination of how pH changes affect hair morphology. The overlapping keratinized cells that form the hair cuticle spread out between 50 and 150% when hydrated, compared to a total shaft diameter change of 10%. This hydration reaches a saturation point within the first few minutes after immersion. Also, hair swells much more at higher pH.
Article
Nanomechanical properties of biological fibers are governed by the morphological features and chemically heterogeneous constituent subunits. However, very little experimental data exist for nanoscale correlation between heterogeneous subunits and their mechanical properties. We have used keratin-rich wool fibers as a model of composite biological fibers; a wool fiber is a simple two component cylindrical system consisting of a core cellular component surrounded by an outer cell layer and their ultrastructure and chemical composition are well-characterized. The core is 16-40 micrometer in diameter and rich in axially aligned keratin microfibrils. Outer cells have multiple laminar layers, 60-600 nm thick and distinctly rich in disulfide bonds. We used an atomic force microscope (AFM) to examine the nanomechanical properties of various structural components using complementary techniques of force-volume imaging and nano-indentation. AFM images of transverse sections of fibers were obtained in ambient environment, and the mechanical properties of several identified regions were examined. The outer cell layer showed a significantly higher mechanical stiffness than the internal cellular core region. Chemical reduction of disulfide bonds eliminated such dichotomy of mechanical strengths, indicating that the higher rigidity of the outer layer is attributed primarily to the presence of extensive disulfide bonding in the exo-cuticle. This is the first detailed correlative study of nano-indentation and regional elasticity measurements in composite biological systems, including mammalian biological fibers.
Article
The potential of genetic engineering gives current importance to the need to clarify the relations between structure, properties and performance of wool. There are at present three different models to explain the tensile stress-strain properties of alpha-keratin fibres: a development by Wortmann and Zahn (W/Z) of Feughelman's series-zone model based on the structure of intermediate filaments and a gel-->sol matrix; a new model by Feughelman (F94) based on a matrix of protein globules surrounded by water; and Chapman's model based on the composite mechanics of microfibrils, characterised by critical and equilibrium stresses for the alpha<-->beta transition, in an elastomeric matrix. This paper examines the arguments related to these theories, with additional attention to the Chapman/Hearle (C/H) treatment. The main area of uncertainty, on which more information is much needed, concerns the chemical and physical structure and properties of the matrix, which is composed of keratin-associated proteins. The conclusion is that the C/H model, which is based on reasonable values of input parameters and gives good agreement with a wide range of experimental results, is most likely to be valid, though it needs some additional refinement and incorporation in a total model, which includes larger-scale structural features.
Article
The mechanical behavior of human hair fibers is determined by the interactions between keratin proteins structured into microfibrils (hard alpha-keratin intermediate filaments), a protein sulfur-rich matrix (intermediate filaments associated proteins), and water molecules. The structure of the microfibril-matrix assembly has already been fully characterized using electron microscopy and small-angle x-ray scattering on unstressed fibers. However, these results give only a static image of this assembly. To observe and characterize the deformation of the microfibrils and of the matrix, we have carried out time-resolved small-angle x-ray microdiffraction experiments on human hair fibers stretched at 45% relative humidity and in water. Three structural parameters were monitored and quantified: the 6.7-nm meridian arc, which is related to an axial separation between groups of molecules along the microfibrils, the microfibril's radius, and the packing distance between microfibrils. Using a surface lattice model of the microfibril, we have described its deformation as a combination of a sliding process and a molecular stretching process. The radial contraction of the matrix is also emphasized, reinforcing the hydrophilic gel nature hypothesis.
Article
DSC thermal analysis has been carried out for human hair samples with various moisture contents to investigate the melting temperature depression behavior of alpha-form crystallites in human hair. This is achieved by adopting a novel technique using silicon oil as the thermal medium, which permits hair samples to retain a range of moisture contents in between completely dry and fully saturated. The results show that the melting temperature of the alpha-form crystallites in human hair varies with moisture content from 205 degrees C for dry hair to 155 degrees C for the hair sample with moisture content of 23%. These experimental results are particularly useful for clarification of the conceptual ambiguities associated with the molecular properties of alpha-helices and alpha-form crystallites. Furthermore, the Flory-Huggins theory was employed to determine the water-helix interaction parameter (chi = 4.5) and the alpha-form crystallinity of human hair (22%), a figure consistent with that obtained by the XRD method (21%).
Article
A Scanning Probe Microscope (SPM) was used to investigate the mechanical properties of the surface of hair and wool fibres. Using stiff cantilevers, penetration was achieved on the fibres under ambient conditions and at increased relative humidity (RH). The Young's modulus of the exocuticle was estimated to be 2.1GPa under ambient conditions, decreasing to 0.6GPa at 96% RH. Contrary to findings by other authors [Crossley, J.A.A., Gibson, C.T., Mapledoram, L.D. , Huson, M.G., Myhra, S., Pham, D.K., Sofield, C.J., Turner, P.S., Watson, G.S., 2000. Atomic force microscopy analysis of wool fibre surfaces in air and under water. Micron 31, 659-667; Gibson, C.T., Watson, G.S., Mapledoram, L.D., Kondo, H., Myhra, S., 1999. Characterisation of organic thin films by atomic force microscopy-application of force vs. distance analysis and other modes. Applied Surface Science 144-145, 618-622; Blach, J., Loughlin, W., Watson, G.S., Myhra, S., 2001. Surface characterization of human hair by atomic force microscopy in the imaging and f-d modes. Journal of Cosmetic Science 23, 165-174], the surface lipid layer could not be penetrated using soft cantilevers in force-distance (f-d) mode in water. Attempts were made to remove the lipid layer from the surface both physically and chemically so as to examine the influence of the lipid on f-d measurements. Using both techniques, it was not possible to remove lipid without damaging the fibre, suggesting that the lipid is an integral part of the surface rather than a discrete surface layer. Adhesion measurements on the surface of wool, nylon and polyethylene, showed that in water and at high RH, the surface of keratin fibres is more akin to a polyamide. At low RH and in liquid paraffin, the surface is more akin to a hydrocarbon, suggesting it is capable of altering its structure in response to different environments.
Article
Human hair is a nanocomposite biological fiber with well-characterized microstructures. Nanomechanical characterization of human hair can help to evaluate the effect of cosmetic products on hair surface, can provide a better understanding of the physicochemical properties of a wide variety of composite biological systems, and can provide the dermatologists with some useful markers for the diagnosis of hair disorders. The paper presents systematic studies of nanomechanical properties of human hair including hardness, elastic modulus and creep, using the nanoindentation technique. The samples include Caucasian, Asian and African hair at virgin, chemo-mechanically damaged and treated conditions. Hair morphology was studied using scanning electron microscopy (SEM). Indentation experiments were performed on both the surface and cross-section of the hair, and the indents were studied using SEM. The nanomechanical properties of hair as a function of hair composition, microstructure, ethnicity, damage and treatment are discussed.
Article
Human hair ( approximately 50-100 microm in diameter) is a nanocomposite biological fiber with well-characterized microstructures, and is of great interest for both cosmetic science and materials science. Characterization of nanotribological and nanomechanical properties of human hair including the coefficient of friction and scratch resistance is essential to develop better shampoo and conditioner products and advance biological and cosmetic science. In this paper, the coefficient of friction and scratch resistance of Caucasian and Asian hair at virgin, chemo-mechanically damaged, and conditioner-treated conditions are measured using a nanoscratch technique with a Nano Indenter II system. The scratch tests were performed on both the single cuticle cell and multiple cuticle cells of each hair sample, and the scratch wear tracks were studied using scanning electron microscopy (SEM) after the scratch tests. The effect of soaking on the coefficient of friction, scratch resistance, hardness and Young's modulus of hair surface were also studied by performing experiments on hair samples which had been soaked in de-ionized water for 5 min. The nanotribological and nanomechanical properties of human hair as a function of hair structure (hair of different ethnicity), damage, treatment and soaking are discussed.
Article
Hair is a proteinaceous fibre with a strongly hierarchical organization of subunits, from the alpha-keratin chains, via intermediate filaments, to the fibre. The chemistry of the different morphological compartments results in exciting physical properties, including the hydrophilic/hydrophobic paradox. The present tutorial review will be of interest for protein- as well as polymer chemists, who want to learn from nature, and also for biochemists interested in the cytoskeleton and particularly in intermediate filaments; it also presents a scientific basis for hair cosmetics.
Article
To investigate the internal structure changes in virgin black human hair keratin fibers due to aging, the structure of cross-sections at various depths of virgin black human hair (sections of new growth hair: 2 mm from the scalp) from a group of eight Japanese females in their twenties and another group of eight Japanese females in their fifties were analyzed using Raman spectroscopy. For the first time, we have succeeded in recording the Raman spectra of virgin black human hair, which had been impossible due to high melanin granule content. The key points of this method are to cross-section hair samples to a thickness of 1.50-μm, to select points at various depths of the cortex with the fewest possible melanin granules, and to optimize laser power, cross slit width as well as total acquisition time. The reproducibility of the Raman bands, namely the α-helix (α) content, the β-sheet and/or random coil (β/R) content, the disulfide (SS) content, and random coil content of two adjoining cross-sections of a single hair keratin fiber was clearly good. The SS content of virgin black human hair from the Japanese females in their fifties for the cortex region decreased compared with that of the Japanese females in their twenties. On the other hand, the β/R and α contents of the cortex region did not change. © 2007 Wiley Periodicals, Inc. Biopolymers 87: 134–140, 2007. 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
Article
Investigations on the mechanical properties of human hair are inadequate. This research explores the break force of anagen hair by forming criteria according to the diameter of hair, gender, age, strain, use of drugs and hair dyes and how these criteria affect the mechanical resistance of hair. The resistances of anagen hair of 120 volunteers were investigated in our biomechanics laboratory. The relationship between the value of break force of hair and hair diameter, gender, age, strain, use of drugs and hair dyes was examined. Tensile tests were applied to each hair with a 50 N load cell device. The statistical evaluation demonstrated a significant difference between the break forces of hairs with different hair diameters. The hairs with a diameter of 51 mum and above had a significantly higher break force than those of 50 mum and below (P=0.000). An insignificant correlation was observed between break force and strain (P=0.554, r=-0.055) whereas the correlation between diameter and strain was statistically significant (P=0.000, r=0.361). The break force of hairs did not show any significant dependency on age, presence of hair dyes, gender and usage of drugs. Yet, a statistically significant difference was observed between the break forces of hairs when compared according to their diameters and strain. More research on the mechanical properties of human hair consistent with biological properties like protein structure, alpha keratin fibers and microfibril-matrix composite behaviors would guide dermatologists for diagnostic symptoms.
Article
Synopsis We report the results of experiments carried out on the stress relaxation of slightly stretched human hair. The results show that human hair is viscoelastic, and that when quickly extended to a moderate degree (0.5–6.5%) and held, the force generated will fall to half its original value in about 15 h. However, the relaxation process is also dependent on extension, so that iso-chronous (constant time) data is non-Hookean. We show that the iso-chronous stress/strain behaviour departs from linearity at about 1% extension and the modulus progressively decreases thereafter according to a power-law relationship with strain. Résumé Nous présentons ici les résultats d’expériences réalisées afin d’étudier la relaxation de la contrainte appliquée sur un cheveu humain légèrement étiré. Les résultats obtenus montrent que le cheveu humain est viscoélastique, et que lorsque’il est étiré rapidement, et de façon modérée (0,5–6,5%), la force nécessaire pour le maintenir étiré diminue de moitié en 15 heures. La relaxation dépend également du degré d’extension, de sorte que les données isochrones (à temps constant) ne suivent pas la loi de Hooke. Nous avons démontré que le comportement isochrone contrainte/cisaillement dévie du comportement linéaire lorsque le cheveu est étiré de 1% environ et que le module décroît ensuite progressivement en suivant une loi de puissance avec le cisaillement.