Analyzing the Surface Topography of Human Hair Using AFM Instrument

Human hair consists of three elements of which the cuticle is a very hard keratinous substance in the outer surface of the hair shaft and the cortex, which is a more fibrous keratin. Medulla, a soft keratin-rich material, is the third element. A high resolution instrument is required to image the hair surface to gain insights into the reaction of the surface to chemical or cosmetic treatment. With high resolution imaging and easy sample preparation possibilities, the Mercury 100 AFM is an ideal tool for such studies.

Key Features of Mercury 100 AFM

The Mercury 100 AFM is an integrated scientific-grade optical microscope, providing easy cantilever alignment, superior optical access, and high resolution cantilever survey. A video camera integrated into the microscope facilitates positioning the cantilever accurately on the sample area of interest. It is easier to place the cantilever on the hair, as illustrated in Figure 1.

An integrated video camera supports precise positioning of the cantilever on the sample area of interest.

Figure 1. An integrated video camera supports precise positioning of the cantilever on the sample area of interest.

Hair Analysis with Mercury 100 AFM

The cantilever has a width of 25µm, while the diameter of the hair is roughly 50µm. This article presents the results of the analysis to show the surface structures of different colored hair as well as the difference between untreated and bleached blonde hair, which will be interesting as it demonstrates the reaction of different hair to cosmetic treatments.

In this analysis, different human hair was attached to microscopic slides that were coated with double-sided adhesive tape. Figure 2 illustrates the image of a brown untreated hair with crenulated cuticule borders at a scan range of 30µm x 30µm and Figure 3 depicts a natural white hair at a scan range of 40µm x 40µm. As can be seen in the images, the platelets of the keratin that are wrapped around the hair shaft in several layers are clearly visible.

Brown hair.

Figure 2. Brown hair.

White hair.

Figure 3. White hair.

Figure 4 shows an image of an untreated blonde hair at a scan range of 35µm x 35µm and Figure 5 illustrates an image of a bleached one at a scan range of 15µm x 15µm, clearly showing the complete loss of the scale-like structure after treated by the bleaching process.

Blond hair.

Figure 4. Blond hair.

Bleached blond hair.

Figure 5. Bleached blond hair.

The thickness of the cuticle cells differs with various colors. The cuticle cells of the brown hair have a thickness range of 300-400nm, while the thickness of the cuticle cells for blonde hair is in the range of 300-500nm and roughly 700nm for the white hair. Chemical treatment (bleaching) or the preparation of the hair with cosmetic products causes significant changes in the surface topography.

Hair Analysis Using Mercury 100 AFM in Conjunction with Digital Pulsed Force Mode

The combination of the Mercury 100 AFM and the Digital Pulsed Force Mode yields additional data about the surface of hair samples, including viscosity, stiffness and adhesion (Figure 6). Line A depicts a completely untreated hair and Line B illustrates hair after shampooing, whereas Line C shows hair treated with conditioner.

Nanoscale surface properties of human hair at scan range of 15µm x 15µm.

Figure 6. Nanoscale surface properties of human hair at scan range of 15µm x 15µm.

In the topography of the unwashed hair, the borders of the cuticle appear to be frayed and some particles are observable. The washed hair yields a smoother result, but the conditioner treated hair is even more so as the platelets of keratin are wrapped tightly around the hair shaft. A remarkable change is observed in adhesion. The image of the untreated hair reveals different areas with less adhesion and more adhesion (brighter areas). These are the regions with the buildup of contaminants.

In the washed hair, more adhesion is shown by only the regions at the borders of the crenelated follicle. The conditioner treated hair illustrates a nearly homogenous surface. Variations in stiffness are only observable on the untreated hair in contaminated areas. Only the untreated hair exhibits considerable differences in viscosity, with more viscous particles (brighter areas). The washed hair and the conditioner treated hair seem to show almost the same results in terms of viscosity.

Conclusion

The results clearly demonstrate the advantage of using the Mercury 100 AFM to perform hair analysis. Furthermore, additional information about the surface of human hair such as viscosity, stiffness and adhesion can be obtained using the combination of the Mercury 100 AFM and the Digital Pulsed Force Mode.

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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