Development of a three-point cantilever bending technique to study the mechanical properties of hair styling ingredients.

BACKGROUND: The mechanical properties of hair treated with styling ingredients is an important aspect to determine if products will be efficacious when used by the consumer. Measurement techniques have been proposed in earlier work; however, these are mostly aimed at hairspray systems and not the myriad of styling products available to the modern-day consumer. AIM: In this article, experimental and data analysis guidelines are proposed for the evaluation of styling ingredients using a three-point cantilever bending technique. Most of the experiments were carried out on polysaccharide-based ingredients-guar hydroxypropyltrimonium chloride (Guar HPTC) and cassia hydroxypropyltrimonium chloride (Cassia HPTC)-to establish basic characterization concepts of the polymer-fiber assemblies. METHODS: A three-point cantilever bending technique was developed using a texture analyzer housed in a temperature and humidity-controlled chamber. Scanning electron microscopy (SEM) studies were conducted to monitor the fracture mechanics of polymer-fiber assemblies. RESULTS: Fundamental studies were carried out to determine the effect of concentration, molecular weight (MW), and chemistry of the polysaccharides on the calculated indices, which characterize the stiffness, flexibility, elasticity, and plasticity of the treated hair. Experiments were conducted in a controlled temperature and humidity environment, which allowed us to monitor the behavior of the polymer-treated hair from 40-90% RH. Studies were also conducted on polymer blends and conventional styling polymers to provide guidance of the performance of naturally-derived polymers to their synthetic counterparts. CONCLUSIONS: A detailed description is provided for a user-friendly, quick method to measure the mechanical properties of styling ingredients on hair. We provide guidelines for three-point cantilever bending tests of straight hair tresses treated with conventional and naturally-derived styling polymers. Indices were developed to characterize the force-distance curves and were designated as E1, F1, position of F1, post-fracture gradient, toughness, E10/E1, and F10/F1. These indices provide an overall characterization of the stiffness, flexibility, elasticity, and plasticity of polymer-treated hair.

Investigation of the interactions of cationic guar with human hair by electrokinetic analysis.

OBJECTIVE: Cationic guar is an important polysaccharide used as a hair conditioning agent in personal care products. In this article, we report streaming potential data demonstrating its behaviour as it interacts electrostatically with hair. Several cationic guar variants with different molecular weights (MWs) and charge densities (CDs) were examined. METHODS: All experiments were carried out with a custom-designed streaming potential instrument so that in situ, real-time data were monitored during the treatment of a hair plug with aqueous solutions of cationic guar and subsequent treatment with anionic surfactants-sodium laureth sulfate (SLES) and cocamidopropyl betaine (CAPB)-commonly found in contemporary shampoo formulations. RESULTS: The MW of the cationic guar variants plays an integral role in determining the thickness of the adsorbed polymer layer on the hair surface while CD influences the zeta potential. Data were also generated for the treatment of hair with a cationic flexible polymer (polyquaternium-28) and cationic conditioning surfactant (behentrimonium chloride) to provide a frame of reference. The deposition behaviour on hair of high MW cationic guar variants is distinct from these conventional molecules in terms of its electrokinetic properties. We also examined the electrokinetic behaviour of cationic guar on hair types from different racial backgrounds. While the cationic guar treatment yielded similar results for the different hair types, anionic surfactant treatment resulted in quicker sorption and desorption from African, European 65% grey, and Mulatto hair as compared to Chinese, European dark brown, and Indian hair. CONCLUSION: We introduce an in situ technique for measuring the dynamic sorption/desorption of charged molecules on the surface of human hair. Evaluation of a series of cationic guar species revealed varying behaviour depending on the MW and CD of the polysaccharide. Our data also demonstrate differences in the desorption properties of typical shampoo surfactants for hair from diverse racial backgrounds.

OBJECTIF: Le guar cationique est un polysaccharide important utilisé comme conditionneur capillaire dans les produits cosmétiques. Dans ce rapport, nous démontrons l'utilisation de la technique du potentiel de streaming pour étudier comment le guar cationique interagit électrostatiquement avec les cheveux. Plusieurs variantes del guar cationique avec différents poids moléculaires et densités de charge ont été examinés. MÉTHODES: Nous avons utilisé un instrument de potentiel de streaming pour les expériences. Les études ont été réalisées en temps réel pour surveiller le traitement de cheveu avec des solutions aqueuses de guar cationique suivi d'un traitement ultérieur avec tensioactifs anioniques comment le sulfate de laureth de sodium et le cocamidopropyle bétaïne, des ingrédients généralement trouvés dans les formulations de shampooing. RÉSULTATS: Le poids moléculaire des variants du guar cationique joue un rôle intégral dans la détermination l'épaisseur de la couche de polymère adsorbée sur la surface des cheveux tandis que le densité de charge influence le potentiel zêta. Des données ont également été générées pour le traitement des cheveux avec un polymère flexible (polyquaternium-28) et tensioactif de conditionnement cationique (behentrimonium chlorure) pour fournir un cadre de référence. Le comportement de dépôt sur les cheveux des variants de guar cationiques à poids moléculaire élevé est distinct de ces molécules conventionnelles en termes de ses propriétés électrocinétiques. Nous avons également examiné le comportement électrocinétique de guar cationique sur des types de cheveux de différents milieux raciaux. Le traitement avec le guar cationique a donné des résultats similaires pour les différents types de cheveux. En contraste avec ceci, le traitement avec le tensioactif anionique a entraîné une sorption et une désorption plus rapides de cheveux africains, de cheveux européens (65% gris) et de cheveux mulâtres en comparaison à les cheveux chinois, européens et indiens. CONCLUSION: Nous introduisons une technique in situ pour mesurer la sorption et la désorption dynamique de molécules chargées à la surface des cheveux humains. L'évaluation d'une série des espèces de guar cationiques ont révélé un comportement variable en fonction du poids moléculaires et densités de charge de le polysaccharide. Nos données démontrent également des différences dans les propriétés de désorption de tensioactifs de shampooing typiques pour les cheveux de diverses origines raciales.

Investigation of the Internal Structure of Human Hair with Atomic Force Microscopy.

The internal ultrafine structure of human hair was explored with atomic force microscopy (AFM). Cross sections of hair were prepared by a proprietary technique that provided a smooth surface for effective imaging in contact-mode AFM. Investigations of virgin hair revealed structural details of cortical and cuticle cells consistent with previous transmission electron microscopy (TEM) studies, in addition to the identification of a boundary region surrounding macrofibrils of the cortex. The effects of bleaching and solvent extraction on the internal structure of hair were also investigated. In the cuticle cell, bleaching causes the most damage to the endocuticle and cell membrane complex, evident by erosion of these components. Similarly, bleaching results in crevices, cracks, and asperities in the cortex of hair. In addition, the cortical cell membrane complex appears compromised along with either lipid or protein structures at the outer boundaries of macrofibrils. In delipidated hair, most structural components of the fiber appear intact with the exception of an overall swollen nature of the various morphological components.

Investigating Film Properties of Polymers Used in Anhydrous Sunscreen Formulations Using Scanning Electron Microscopy (SEM): Polymer/Polymer Interactions and Their Relation to Vapor Transmission.

A mechanistic understanding of the role of polymers in waterproofing anhydrous sunscreen formulations has been hypothesized in the past, but has never been clearly established. In this article, we demonstrate the utility of field emission scanning electron microscopy (SEM) to generate images of sunscreen films in the presence and absence of several polymers. VA/butyl maleate/isobornyl acrylate copolymer was studied alone and in combination with hydroxypropyl cellulose and acrylates/dimethicone copolymer. Anhydrous sunscreen formulations were sprayed onto stratum corneum substrates and left to dry. SEM micrographs of treated stratum corneum sections were then collected at various magnifications. Vapor transmission data were collected using an evaporimeter to understand the permeability of these films in the presence and absence of film formers. Examination of the SEM images reveals that after spraying the product onto a layer of corneocytes, the sunscreen filters formed a hydrophobic barrier over the skin, whereas added polymers formed films over the sunscreen layer. The shape of the film formed by various polymers and its porosity were influenced by chemistry and concentration. When more than one polymer was incorporated in the sunscreen formulation, the interactions between the polymers influenced the formation of the film. Cumulative evaporimeter data indicated that the sunscreen phase had the highest reduction in cumulative evaporation rate (39.3%/h) followed by the addition of a film former to the spray, which reached an additional reduction of 17.9%/h in the best case. This method was also used to examine the film properties of a commercial sun protection factor 30 sunscreen product containing VA/butyl maleate/isobornyl acrylate copolymer. SEM micrographs of the commercial product applied to skin showed the same fingerprint as prototype formulations containing VA/butyl maleate/isobornyl acrylate copolymer. Overall, this method can be used by sun care scientists in the development and optimization of anhydrous sunscreen sprays.

Investigation of hair dye deposition, hair color loss, and hair damage during multiple oxidative dyeing and shampooing cycles.

Color fastness is a major concern for consumers and manufacturers of oxidative hair dye products. Hair dye loss results from multiple wash cycles in which the hair dye is dissolved by water and leaches from the hair shaft. In this study, we carried out a series of measurements to help us better understand the kinetics of the leaching process and pathways associated with its escape from the fiber. Hair dye leaching kinetics was measured by suspending hair in a dissolution apparatus and monitoring the dye concentration in solution (leached dye) with an ultraviolet-visible spectrophotometer. The physical state of dye deposited in hair fibers was evaluated by a reflectance light microscopy technique, based on image stacking, allowing enhanced depth of field imaging. The dye distribution within the fiber was monitored by infrared spectroscopic imaging of hair fiber cross sections. Damage to the ultrafine structure of the hair cuticle (surface, endocuticle, and cell membrane complex) and cortex (cell membrane complex) was determined in hair cross sections and on the hair fiber surface with atomic force microscopy. Using differential scanning calorimetry, we investigated how consecutive coloring and leaching processes affect the internal proteins of hair. Further, to probe the surface properties of hair we utilized contact angle measurements. This study was conducted on both pigmented and nonpigmented hair to gain insight into the influence of melanin on the hair dye deposition and leaching processes. Both types of hair were colored utilizing a commercial oxidative hair dye product based on pyrazole chemistry.

Probing the textures of composite skin care formulations using large amplitude oscillatory shear.

Identifying meaningful and measurable rheological parameters that shadow the dynamic shear stresses sustained in the initial application and subsequent spreading of structured cosmetic formulations onto the skin is quite challenging. When applied to non-Newtonian soft solids, traditional oscillatory rheological testing tends to best correlate with the "at-rest" state, or, more fundamentally, with the initial and thermodynamically reversible perturbations in the physiochemical networking that binds components of the amalgamated microstructure. In addition, after yielding, as an applied film is further thinned while spreading on the skin surface, shear rates during flow processes may rapidly and dynamically increase to 104 s⁻¹ , which is a magnitude that is not practically simulated with a standard rotational rheometer. Realistically speaking, it is rare that a single rheological measurement or resultant parameter predicts the sensorial appeal of a complex fluid during the entire scope of a spreading process. Large amplitude oscillatory shear (LAOS) methodology is an augmentation of standard oscillatory rheology, or small amplitude oscillatory shear (SAOS), and delivers a means to dynamically probe the deforming microstructure of a soft solid as it rheologically transitioned from a viscoplastic material to a structured fluid. LAOS rheology was performed on four different prototypes having different skincare textures to produce Bowditch­Lissajous plots (henceforth truncated to Lissajous in the remainder of the document) for subsequent association with previously measured sensorial properties. Insights into the shapes of the curves and their relation to paralleled sensorial analyses are primarily based on the performance of the composite prototypes rather than speculating on the individual contribution of each constituent to the dynamics of the adapting microstructure. Therefore, transitions in the Lissajous trajectories may be used to visually describe changes in the bulk rheology as the physical components of the local viscoelastic environment are controllably sheared. In this work, Lissajous profiles are amassed with smooth and rough surfaces data utilizing standard rheological techniques, including oscillatory SAOS, stress ramps, Brookfield viscometry, and the manifestation of interfacial or complex flow properties, such as wall-slip and shear-banding phenomena. Practical influences on the human stratum corneum, including thermal softening and electrostatic shielding, are also considered. Additionally, outcomes from texture profile analysis are reported and contrasted with the accompanying results. Ultimately, the objective is to make meaningful connections between trends in Lissajous trajectories and paralleled sensorial analyses conducted by a trained expert panel. For the reader, a basic level of rheological knowledge is assumed.

Quantifying hair shape and hair damage induced during reshaping of hair.

The manipulation of hair shape, either to straighten or curl hair, is carried out on a grand scale in the hair care consumer market. Often, such changes are brought about through chemical or physical treatment, resulting in changes to hair chemistry. In this article, we review existing and present new data on methods to assess the efficacy of such treatments, mostly concentrating on imaging technologies used in conjunction with image analysis. In addition, we introduce spectroscopic imaging techniques and fluorescence spectrophotometry as tools to assess the biochemical state of the hair fiber as a result of hair shape modification regimens. Finally, we demonstrate how the structural integrity of the fiber is monitored with dynamic scanning calorimetry and traditional mechanical testing of the tensile properties of hair.

Determination of physicochemical properties of delipidized hair.

Using various physicochemical methods of analysis, we examined human hair in its virgin and delipidized state. Free lipids were removed by a solvent extraction technique (covalently bound lipids were not removed) using a series of solvents with varying polarity. We analyzed the surface properties of hair by conducting mechanical combing and dynamic contact angle analysis. In addition, we used inverse gas chromatography surface energy analysis to explore the chemical composition of the hair surface based on interactions of various nonpolar and polar probes with biological molecules residing on the hair surface. Further, we investigated the importance that free lipids play in the internal structural properties of hair using dynamic scanning calorimetry and tensile strength measurements. The microstructure of the hair surface was probed by atomic force microscopy, whereas the lipid content of hair's morphological components was determined by infrared spectroscopic imaging. We also monitored the water management properties of virgin and delipidized hair by dynamic vapor sorption, which yielded unique water sorption isotherms for each hair type. Using all these techniques, differences were found in the chemical composition and physical behavior of virgin and delipidized hair. To better understand the influence of hair lipid composition on hair styling treatments, we conducted mechanical analyses of hair shaped into omega loops to determine the stiffness, elasticity, and flexibility of hair-polymer assemblies. Although there were no discernible differences between untreated virgin and delipidized hair, in terms of stiffness and elasticity, we found that treatment with hair styling agents produced different effects depending on the hair type used. Likewise, streaming potential measurements were carried out to monitor the binding capacity of rinse-off treatments on virgin and delipidized hair. Using this technique, we monitored the surface potential of hair and found significant differences in the binding behavior of cationic polymers and surfactants (polyquaternium-55 and quaternium-26) on both hair types.

Influence of various environmental parameters on sweat gland activity.

The choice of environmental conditions when conducting antiperspirant studies greatly affects the quantity of sweat output. Our initial goal in this work was to develop an in-house procedure to test the efficacy of antiperspirant products using replica techniques in combination with image analysis. To ameliorate the skin replica method, we conducted rheological studies using dynamic mechanical analysis of the replica formulation. In terms of sweat output quantification, our preliminary results revealed a considerable amount of variation using the replica technique, leading us to conduct more fundamental studies of the factors that influence sweating behavior and how to best design the experimental strategy. In accordance with the FDA's protocol for antiperspirant testing, we carried out gravimetric analyses of axillae sweating under a variety of environmental conditions including temperature and humidity control. Subjects were first acclimatized in an environmentally controlled room for 30 min, and then placed in a sauna for an additional 30 or 45 min, depending on which test we administered. In Test 1 (30 min total in the sauna), the first 10 min in the sauna was another equilibration period, followed by a 20 min sweat production stage. We monitored axillae sweating during the last 20 min in the sauna by gravimetric analysis. At time (t) = 30 min in the sauna, skin replicas were taken and later analyzed using imaging and image analysis techniques. Test 1 was carried out on over 25 subjects, both male and female, from various racial backgrounds. In Test 2, subjects spent 45 min in the sauna after the initial 30-min period in the environmental room. During the 45 min, we obtained gravimetric readings of absorbent pads placed in the axillae. We conducted studies at various temperature and relative humidity settings. We also studied the influence of several external parameters on sudoriferous activity. Test 2 was a range-finding experiment on two subjects to determine the optimized environmental conditions for the hot room procedure. In addition to the replica and gravimetric techniques, we also measured flux density to determine the onset of firing of sweat glands to ensure that our environmental preconditioning step (30 min in the environmental room) brought subjects to the point that their sweat glands were activated. Although flux density measurements are usually carried out to determine transepidermal water loss (TEWL), we found that they can be equally useful for monitoring the onset of sweat production. Thermal infrared imaging experiments were also carried out allowing us to generate full-body images of subjects containing anatomical thermal distribution data with high accuracy. Overall, we conclude that our in-house hot room procedure offers much potential as an effective and cost-efficient screening tool for narrowing copious antiperspirant formulations to a select few for expensive clinical evaluation.

Fluorescencia de los tejidos queratinosos / Fluorescence in keratin tissues

Utilizando una técnica de fluorescencia, registramos mapas de los fluoróforos presentes en varios tipos de tejidos queratinosos. Descubrimos que la fluorescencia de todas las muestras analizadas tienen rasgos en común. Observamos el aminoácido triptófano en todos los tejidos. Asimismo, nos parece que la máxima principal es debido a las kinureninas que son productos metabólicos y degradativos del triptófano. Esta máxima constituye un conglomerado de varias moléculas como L-kinurenina, 3-hidroxikinurenina y N-formilkinurenina. La proporción de kinureninas que tiene el triptófano depende del tipo de tejido y del grado de pigmentación. También, la longitud de onda de excitación y emisión depende de estos parámetros...

Utilizing fluorescence, we generated excitation-emission matrices, which provided us with a map of fluorophores present in keratin tissues. Our findings suggest that all of the tested keratin substrates have features in common. We monitor the quantity of tryptophan as well as some of its metabolic and degradation products, the kynurenines. The peak due to kynurenine fluorescence is dominant and is a conglomerate of several molecular species including L-kynurenine, 3-hydroxykynurenine and N-formylkynurenine. The ratio of tryptophan to the kynurenines depends on the type of tissue and the amount of pigmentation present. The emission wavelength also greatly depends on these factors...

Tryptophan fluorescence in hair-examination of contributing factors.

Various types of hair, including white (unpigmented), Piedmont (yellow-colored), blonde, brown, curly black of African origin, straight black of Chinese origin, and chemically processed (bleached) hair, were studied by using fluorescence spectroscopy. Fluorescence measurements were obtained by using a single- or double-grating fluorescence spectrophotometer and a bifurcated fiber optics accessory to measure the spectra directly from the surface of the hair. The results have shown that all types of hair share similar fluorescence characteristics, as recorded by excitation at 290 nm, 320 nm, 350 nm, and 380 nm, with emissions that could be ascribed to chromophores such as tryptophan (Trp), N-formylkynurenine, kynurenine, and 3-hydroxykynurenine. The relative intensities of fluorophore emissions were found to be dependent on factors such as melanin content and the history of UV light or thermal exposure. Trp fluorescence was also found to be dependent upon the state of the hair matrix. Softening of hair keratin by chemical reduction (breakage) of disulfide bonds or by hydration, leads to a 50%-100% increase in Trp emission intensity. Conversely, stiffening of the hair matrix by re-oxidation of reduced hair with hydrogen peroxide, or drying of wet hair, produces a decrease in fluorescence intensity. The results were interpreted by invoking the behavior of certain enzymes, which demonstrate Trp quenching by neighboring disulfide bonds or by hydrogen bonding with alanine residues, or with certain side-chain amino acids.

Spectrofluorescent characterization of changes in hair chemistry induced by environmental stresses.

Hair is frequently exposed to environmental stresses and chemical insults that result in damage to its internal structure and its outer cuticular components. Spectrofluorescence is a useful tool to monitor the health of biological tissues as it can measure the level of tryptophan (Trp), which is representative of protein integrity. In addition to Trp fluorescence, several other fluorophores are also present in hair and are believed to be attributed to kynurenenine, N-formylkynurenine, and 3-hydroxykynurenine, which are known metabolic and degradation products of Trp that are affected by environmental stresses normally experienced by hair. In this work, we were able to construct an endogenous fingerprint of fluorescent compounds present in hair by employing a range of excitation wavelengths from 270 nm to 450 nm with a resolution of 2 nm. As a result, we generated surface plots of fluorescence emission as a function of excitation and emission wavelengths (excitation-emission matrices). Thus, we were able to profile the levels of various structural molecules in hair before and after exposure to UV irradiation and thermal straightening irons as well as to chemical treatment such as bleaching and straightening.

Molecular dynamic simulations of eicosanoic acid and 18-methyleicosanoic acid langmuir monolayers.

The conformational and dynamical properties of Langmuir monolayers of 18-methyleicosanoic acid (18-MEA) and the parent material, eicosanoic acid (EA), are compared using molecular dynamics simulations. The effects on various properties, including film thickness, tilt angle, and order parameter, of the methyl group at the 18 position in 18-MEA were investigated as a function of film-packing density. NVT simulations were run as a function of decreasing areal-packing density similar to experimental Langmuir-Blodgett film compressions and expansions. We find that the order parameters and film thickness for 18-MEA monolayers were markedly different from those of EA. The order parameters for methylene groups for both 18-MEA and EA are greater in the middle region of the chain than at the ends in high-density films. This trend becomes reversed in lower density films. Significantly, our simulations show that the order parameters for methylene groups near the CH3 and carboxyl termini in 18-MEA are comparatively independent of film density in contrast with those of EA. Our findings show that the presence of the methyl group at the 18-position in 18-MEA induces unique intermolecular structural correlations compared to EA.