Current research on ethnic hair.

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.

A new approach to the bending properties of hair fibers.

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.

Histological structure of human nail as studied by synchrotron X-ray microdiffraction.

Three layers (characterized by different orientations of the keratin molecules) from the outer to the inner side of human nail were observed by synchrotron X-ray microdiffraction. These layers are associated with the histological dorsal, intermediate and ventral plates. The hair-like type alpha-keratin filaments (81 A in diameter), are only present in the intermediate layer (accounting for approximately 2/3 of the nail width) and are perfectly oriented perpendicular to the growth axis, in the nail plane. Keratin filaments of stratum corneum (epidermis) type, found in the dorsal and ventral cells, are oriented in two privileged directions; parallel and perpendicular to the growth axis. This "sandwich" structure in the corneocytes and the strong intercellular junctions, gives the nail high mechanical rigidity and hardness, both in the curvature direction and in the growth direction. Lipid bilayers (49 A thick) parallel to the nail surface fill certain ampullar dilations of the dorsal plate and intercellular spaces in the ventral plate. Using X-ray micro-diffraction, we show that onychomycosis disrupts the keratin structure, probably during the synthesis phase.

Study of the keratinization process in human hair follicle by X-ray microdiffraction.

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.