Spatial Probing of the Properties of the Human Hair Surface Using Wilhelmy Force Profiles

Abstract

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.

Automated Measurement of Spatially Resolved Hair–Hair Single Fiber Adhesion

“…The magnitudes and, to some extent, the shapes of these distributions are reproducible and are predicted in this work from a Hertzian asperity model leveraging a combination of surface-topography measurements using laser profilometry and surface energy measurements via fiber tensiometry. 27 The agreement between the measured and the modeled adhesion forces suggests that surface topography is the main cause of the large distributions in adhesion force. We therefore suggest that future hair care products may take advantage of this phenomenon by strategically manipulating the surface morphology of hair fibers.…”

Atmospheric Pressure Plasma Jet Treatment of Human Hair Fibers

“…The 18-MEA layer is chemically bonded to the amorphous keratin through thioester or ester groups [20,21]. However, 18-MEA layer is described to have a heterogeneous coverage [22][23][24].…”

Characterization of biomaterials

“…As a lot of modern biomaterials are surface modified to obtain different properties on both sides, the Wilhelmy method is not a popular tool. However, there is a key advantage in that the Wilhelmy method is not limited by the sample size and shape and so single fiber can be used to determine the CAs [189,190]. The Wilhelmy method can even be adopted on the nanoscale by making use of a nanotube [191] or AFM probe [192,193] as the cantilever to measure the wetting forces of nanotubes and nanofibers.…”