Non-invasive evaluation of hair interior morphology by X-ray microscope

Abstract

Lots of trials have been performed to obtain better microscopic images of hair structure. Although scanning electron microscopy (SEM) and transmission electron microscopy (TEM) provide detailed images of hair, artificial processing may modify the original images during sample preparation. To overcome this limitation, we applied newly-developed X-ray microscopy with an 80-100 nm spatial resolution to produce a detailed view of the morphological change of hair interior. This X-ray microscopy permits us to penetrate a hair shaft without any artificial change and also provides precise images of hair interior with fine resolution. We evaluated the interior morphological change of Japanese standard hair tress No. 8 by various treatments such as ultraviolet (UV) irradiation, heating, hair dyeing, decolorizing bleaching agents and permanent waving. Internal morphological images were relatively similar in both heated and UV-irradiated hair. They revealed coarsening of cuticles and dehydration of cortex and medulla. When compared with TEM, X-ray microscopy provides more intact images in the cuticle and may be a useful tool in observing fine cracks of hair cortex. Additionally, X-ray images were intact and not influenced by any processing procedures. In observing the external and internal structure of hair, its resolution seems to be somewhat lesser than TEM and there are also several remaining weaknesses to be improved. Hopefully, forthcoming technology will solve these problems in the near future.