Photon Factory Activity Report 2004 #22 Part B (2005)
Biological Science

4A/2004G387

Structural Analysis of a Single Keratin Fiber by Scanning Microbeam SAXS
Yoshio 1KAJIURA1, Takashi ITOU1, Yuya SHINOHARA2, Yoshiyuki AMEMIYA*2
Kao Corporation, 2-1-3 Bunka, Sumida-ku, Tokyo 131-8501, Japan2
Department of Frontier Sciences, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba, Japan
Introduction
Human hair is one of many keratinous fibers. Its
diameter typically varies between 40 to 150 µm. The
surface of a hair fiber is covered with the thin scale-likecells, the so-called cuticle, and the inside of the cuticle ismainly filled with the cortical cells which are composedof the intermediate filaments (IFs) surrounded by thematrix proteins. There are various fiber shapes in humanhair and it is commonly accepted that the curl shapes ofhair fibers are roughly classified by their origin in thethree major ethnic groups: African hair which has a strong
curl shape, Caucasian hair which is apt to have amoderately waved shape and Asian hair which has acomparatively straight shape. In the case of Merino wool,
it was found that the fiber crimp was associated with thebilateral distribution of the different types of cortical cells[1], the so-called orthocortex and paracortex. Munro andCarnaby [2] showed that the bilateral distribution of theorthocortex and the paracortex could be the cause of thefiber crimp.
Swift [3] has previously observed two cortical cell
types in human hair. He refers to these two cortical cell
types as the human orthocortex and the human paracortex,
and describes that the distribution of these two types
relates to the ethnic origin, having a different degree ofthe fiber curvature.
These results, however, were obtained by transmission
electron microscopy (TEM) observations. Although TEM
is useful for exploring micro- and nano- structures, it ishard to determine the dominant structure over the wholefiber. In addition, TEM needs chemical agents for sample
preparation, which would artificially affect the sample
condition. Moreover, biological materials are apt to bedamaged by the electron beam; therefore, alternative
experimental methods are needed for further
understanding of the human hair structure.
The purpose of the present study is to explore thedifference of the internal structure between the inner andthe outer side of the curvature for curly human hair in theintact condition, and to understand the macroscopic
curvature of the fiber from the aspect of the internal
nanostructure. The experiment was achieved bymeasuring SAXS patterns with an X-ray microbeam,scanning the fiber in the transverse direction.
Experimental
The experiments were performed at BL-4A. Two
dimensional SAXS patterns were measured with a X-ray
microbeam (size : 5 µm) scanning a curly human hairsingle fiber at several positions in the transverse direction
with a 5 to 10 µm step from outer to inner sides of thefiber curvature.
Results and Discussion

Figure 1 shows typical SAXS patterns. Major intensity
maxima, which have been attributed to the lateral packing
between IFs [4, 5], are observed along the equator(indicated by arrows) and clear differences are foundbetween the inner and the outer side (Figures 1(a) and1(b), respectively). The intensity maxima of the former
are stronger and narrower in the azimuth direction,compared to the latter. These differences denote that curly
human hair has a laterally heterogeneous IFs arrangement,
associated with its curved shape. It is noteworthy thatthese differences were observed for African hair, curly
Caucasian hair and also curly Asian hair, but were notdistinguished for less curly (almost straight) Caucasianand Asian hair fibers. We extracted the equatorial
intensity profiles from the 2-dimensional SAXS patternsof the cortex after subtraction of the parasitic scattering,and compared them with those calculated based on the IF
distribution model proposed by Briki et al. [4]. From ananalogy with Merino wool [6], the distribution ofdifferent types of the cortex in human hair is stronglysuggested.

Fig.1 Typical SAXS patterns of a curly human hairfiber. (a) The inner side of the curvature. (b) The outerside of the curvature. Short arrows indicate the major
intensity maxima along the equator.
References[1] M. Horio, T. Kondo, Text. Res. J. 23 (1953) 373-386.
[2] W. A. Munro, G. A. Carnaby, J. Text. Inst. 90 Part1
No.2 (1999) 123-136.
[3] J. A. Swift, in: P. Jollès, H. Zahn, H. Höcker (Eds.),
Formation and Structure of Human Hair, Birkhäuser
Verlag, Basel, 1997, pp.150-175.
[4] F. Briki, B. Busson, J. Doucet, Biochem. Biophys.
Acta 1429 (1998) 57-68.
[5] R. D. B. Fraser, T. P. MacRae, A. Miller, J. Mol. Biol.
10 (1964) 147-156.
[6] Y. Kajiura, et al, J. Appl. Cryst. 38, 420 -425 (2005)• amemiya@k.u-tokyo.ac.jp

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