Current research on ethnic hair Franbourg, A.; Hallegot, P.; Baltenneck, F. ...
Journal of the American Academy of Dermatology,
06/2003, Letnik:
48, Številka:
6
Journal Article, Conference Proceeding
Recenzirano
This study collected qualitative and quantitative data about the morphology, structure, geometry, water swelling, and mechanical properties of hair fibers from subjects of different ethnic origins. ...X-ray analysis, cross-sectional measurements, tensile testing, and water swelling were performed on samples of hair collected from Caucasian, Asian, and African subjects. No differences in the intimate structures of fibers were observed among these 3 types of hairs, whereas geometry, mechanical properties, and water swelling differed according to ethnic origin. In addition, the behavior of hair fiber under mechanical stress was visualized with environmental scanning electron microscopy. (J Am Acad Dermatol 2003;48:S115-9.)
The mechanical behavior of human hair fibers is determined by the interactions between keratin proteins structured into microfibrils (hard
α-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.
Synchrotron X-ray micro-diffraction studies along the follicle and the hair fibre allowed us to follow the keratinization process and the progressive organization of the keratin: i) molecular ...organization appeared progressively in the follicle; the formation of alpha-helices was completed inside the follicle. ii) supramolecular organization appeared only outside the follicle, far from the bulb; filament structure was observed far from the follicle. Comparisons between structures observed for in vitro and in vivo grown hair, whatever in the bulb or in the fibre, indicate there is no evidence of any structural difference. More, no variation in the transition in vivo/in vitro zone has been observed. In vitro and in vivo fibres exhibited the same structure.
Synopsis
Repetitive hair‐relaxing treatments often applied to African–American hair weaken the hair structure. Therefore hair breakage is a common feature of African–American hair and an important ...cause of hair loss. Recently, by analysing the lipids extracted from human hair, a fraction of free‐ceramide was isolated in which sphinganine was predominant. This study shows that this sphinganine‐derived ceramide (i.e. C18‐dhCer) binds to African–American hair and protects it from weakening caused by chemicals. To show this binding, we used two methods: radioactivity detection with a microimagerTM and secondary ion mass spectrometry.
We evaluated the benefits of C18‐dhCer on African–American hair fibre, relaxed by guanidine hydroxide, using a new method called the Break'in Brush Technique (BBT®). This method determines the hair breakage resistance during a brushing. Using this technique, we have shown less breakage when applying a shampoo with ceramide.
The present study opens new prospects for the development of products able to increase the protection, provide better care and meet the needs of African–American hair thanks to the effect of ceramide binding.
Résumé
L'application régulière de traitement de défrisage affaiblit la structure des cheveux afro‐américains. Pour cette raison, la casse des cheveux afro‐américains est un phénomène fréquent et important.
Récemment, l'analyse des lipides extraits de cheveux humains a permis d'isoler, une fraction enrichie en céramides libres, dans laquelle la shinganine était prédominante. Cette étude montre que ce céramide dérivée de la sphinganine (C18‐dhCer) se fixe aux cheveux afro‐américains et les protège des affaiblissements causés par des traitements chimiques. Pour évaluer cette fixation qualitativement et quantitativement, nous avons utilisé deux méthodes: la détection de la radioactivité grâce à un microimagerTM et l'utilization d'un spectromètre de masse des ions secondaires.
Nous avons évalué les effets bénéfiques du C18‐dh‐Cer sur les cheveux défrisés à la guanidine, en utilisant une nouvelle méthode appelée la technique Break'in Brush (BBT®). Cette méthode détermine la résistance de casse des cheveux durant un brushing. Avec l'utilisation d'un shampooing contenant le céramide, nous avons montré une réduction importante de la casse des cheveux.
Cette étude offre de nouveaux horizons pour le développement de produits permettant d'augmenter la protection des cheveux afro‐américains, de leur offrir de meilleurs soins et de répondre ainsi aux besoins de ce type de cheveux grâce aux effets du céramide.
A new test developed to characterize the bending properties of treated or virgin hair fibers is described. The device consists of a pendulum that bends a sample made up of 39 parallel hair fibers at ...each swinging stroke. Hair bending stiffness can be assessed by the number of strokes observed until the pendulum stops. The mechanical behavior of natural hair fibers is related to their geometric characteristics. The effects of various hair treatments can be assessed by this method.
The mechanical behavior of human hair fibers is determined by the interactions between keratin proteins structured into microfibrils, a protein sulfur-rich matrix 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.
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