Investigating Reactions of the Surface of Human Hair to Chemical or Cosmetic Treatments

Human hair is composed of three elements. The cuticule is the outer surface of the hair shaft; it is a very hard keratinous substance. The next element is the cortex which is a more fiberous keratin. The third element is the medulla, a soft keratin-rich material.

Means to Generate High Resolution Surface Images of Hair

To investigate the reaction of the hair surface to chemical or cosmetic treatment, a tool is needed to image the surface with high resolution. Offering easy sample preparation and high resolution imaging possibilities, the Mercury 100 AFM is a well suited instrument for such studies.

The integrated scientific-grade optical microscope provides superior optical access, easy cantilever alignment, and high resolution cantilever survey. An integrated video camera supports precise positioning of the cantilever on the sample area of interest. The cantilever be can easily placed on the hair.

The diameter of the hair is approximately 50 µm and the width of the cantilever is 25 µm. The aim of these studies is to show, the surface structures of different coloured hair. The difference between untreated and bleached blonde hair should also be demonstrated, which will be very interesting as it shows how the different hair will respond to cosmetic treatments.

Investigation of Different Human Hair Samples using WITec AFM

Different human hair was fixed to microscopic slides coated with double-sided adhesive tape. On the left is a brown untreated hair with crenulated cuticule borders (scan range: 30 µm x 30 µm). On the right a natural white hair is imaged (scan range: 40 µm x 40 µm). Clearly visible are the platelets of the keratin, which are wrapped around the hair shaft in several layers.

On the left, an untreated blonde hair (scan range: 35 µm x 35 µm), on the right, a bleached one (scan range: 15 µm x 15 µm). Clearly visible is the complete loss of the scale-like structure after the bleaching process.

Factors Which Governs the Surface Topography of Human Hair

The thickness of the cuticle cells varies with the different colours: 300 nm to 400 nm for the brown hair, between 300 nm and 500 nm for the blonde hair, while the cuticle cells of the white hair are approximately 700 nm thick. Chemical treatment (bleaching) or the preparation of the hair with hair care products lead to significant differences in the surface topography.

Combining the Mercury 100 AFM with the Digital Pulsed Force Mode provides additional information about the sample surface such as adhesion, stiffness or viscosity. Line A shows completely untreated hair. Line B shows hair after shampooing and line C after being treated with conditioner.

In the topography of the unwashed hair, the borders of the cuticule seem to be frayed and some particles are visible. The washed hair shows a smoother result but the hair treated with conditioner is even more so and the platelets of keratin are wrapped closely around the hair shaft.

There is a remarkable change in adhesion. The untreated hair shows different areas with more adhesion (bright) and less adhesion. These are the regions with the accumulation of contaminants.

In the washed hair, only the regions at the borders of the crenelated follicle show more adhesion. The hair treated with conditioner shows a nearly uniform surface. Differences in stiffness are only visible on the untreated hair in contaminated areas.

Only the untreated hair shows significant differences in viscosity. The brighter areas which also show particles are more viscous. The washed hair and the hair with conditioner seem to show nearly the same results with respect to viscosity.

This information has been sourced, reviewed and adapted from materials provided by WITec GmbH.

For more information on this source, please visit WITec GmbH.

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