Microscopical investigations on the epicuticle of mammalian keratin fibres

Abstract

The existence of a thin chemically resistant layer, the epicuticle, close to the surfaces of all undamaged mammalian keratin fibres has been known since 1916. The identification of such a specific structure within the fibre cuticle has remained elusive. Now, through transmission electron microscope investigations of stained transverse sections of hairs from various animal species, the epicuticle has been tentatively identified as a sharply defined and continuous layer approximately 13 nm thick covering the entire outwardly facing intracellular surface of every cuticle cell. The staining behaviour of the epicuticle leads one to suppose that it is rich in cystine and that thioester‐bound lipids might be present within its bulk. With the atomic force microscope it was established that the undamaged outer surface of all mammalian keratin fibres, even including those from the monotremes, were longitudinally striated. The lateral spacing of the striations was always in the range 0.29–0.39 µm. Striations only occurred on the freely exposed outer surfaces of the original undamaged fibres; evidently arising by some, as yet undefined, interaction in the follicle with the cuticle of the inner root sheath. By stripping off fatty acids known to be covalently attached to the fibre's outer surface, the striations were shown to reflect a corresponding irregularity of the epicuticle's surface.

Atomic force microscopy imaging of hair: correlations between surface potential and wetting at the nanometer scale

“…Such striations are likely due to an artefact that appears during the scanning by the tip (probably remaining optical interferences) since they are also observed on the liquid part. These striations are thus certainly different from the ones observed by Swift and colleagues on different mammalian fibers, which present a typical spacing always in the range from 0.3 to 0.4 µm [27,28].…”

Wetting and electrical properties of the human hair surface: Delipidation observed at the nanoscale

“…Several techniques have been used to obtain information about the structure of human hair such as optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) [2][3][4][5] or X-ray diffraction [6]. In the last decade, atomic force microscopy (AFM) appeared to be a convenient tool for imaging the surface of hair samples; this non-destructive technique is nearly unique to perform local investigations [7][8][9][10], especially by revealing many details of the cuticle structure [11,12].…”

“…Such a branch lowers the melting temperature with respect to that of the corresponding linear chain acid from 82 to 56 • C [14,15]. The presence of this fatty acid has also been proven to be essential for maintaining the structural integrity of the cuticular cell membrane complex (the cuticle cement) [16], and at the surface its absence has a negative impact on the tribological properties of hair [12,17].…”

Unzipping the cuticle of the human hair shaft to obtain micron/nano keratin filaments

“…Human hair/wool shaft consists of two major components: envelop cuticle scales on the surface and inside cortical cells. The detailed substructure is described as follows: the cuticle includes the epicuticle, the A-layer, the exocuticle, the inner layer, and the cell membrane complex (CMC) containing covalently bonded 18-methyleicosanoic acid [6][7][8] ; the cortex consists of macrofibrils that contain intermediate filaments that contain polypeptide -helices. 9,10 The cortex has filament morphology with diameter being 5 m in order, the macrofibril 0.5 m, the intermediate filament <10 nm and the -helix 2 nm, a diameter similar to that of carbon nanotubes.…”