Computational study of human hair provides insights into structure of its poorly understood outer surface

January 16, 2013
When the molecules that comprise human hair’s outer surface (blue) are packed together tightly (top), they are forced to stand erect, resulting in a thicker layer than when they are less tightly packed (bottom). Credit: 2012 American Chemical Society

Human hair is a complex, multi-layered material, the composition of which is only partly established. Hair fibers are sheathed in a thin protective coating called the epicuticle, but despite its industrial importance—the epicuticle is the first surface with which hair products interact—the exact structure of this layer is unknown. Now, a theoretical model of epicuticle structure developed at the A*STAR Institute of High Performance Computing (IHPC) has revealed the likely composition and properties of hair's outer surface. The model, developed by Daniel Cheong and his co-workers at IHPC, is already helping to resolve apparent discrepancies over epicuticle structure.

Previous experimental research has shown that hair's outermost surface consists of a thin monolayer of fatty called 18-MEA, which stand on end like the bristles on a brush. According to Cheong, one study suggested that these molecules attach to the surface around 1 nanometer apart. "Although this distance is frequently cited, it has never been corroborated, as it is very difficult to measure this value experimentally," says Cheong.

To examine the 18-MEA separation distance further, Cheong and his co-workers constructed simplified computational models of the hair surface. They then looked for the separation distance that gave the most energetically stable structure. "Surprisingly, our indicated that the separation distance between the should be around 0.5–0.65 ," says Cheong.

One possible explanation for this apparent disagreement with earlier work could be that bound 18-MEA molecules are indeed spaced 1 nanometer apart; but extra, unbound lipids may pack the space in between to generate the more stable structure, Cheong suggests.

This theory could also resolve apparently conflicting results regarding experimental measurements of the fatty acid layer's thickness, which have ranged from 1.3 nanometers to 2.6 nanometers. The team's model shows that the more tightly the fatty acids are packed, the more upright they stand, which makes the epicuticle appear thicker (see image). Cheong suggests that, in studies where this layer was found to be only 1.3 nanometers thick, the free lipids may have been lost, partly collapsing the fatty acid structure. Tellingly, his model predicts that for fatty acids spaced 1 nanometer apart, the layer would appear 1.3 nanometers deep.

"With this simple model, we can also study the interactions between small molecules and the hair surface," Cheong explains. "This would be important in understanding how potential active ingredients in hair products will behave at the hair surface."

Explore further: Sum Cheong Lung-brand dried fish recalled

More information: Cheong, D. W., Lim, F. C. H. & Zhang, L. Insights into the structure of covalently bound fatty acid monolayers on a simplified model of the hair epicuticle from molecular dynamics simulations. Langmuir 28, 13008–13017 (2012).

Related Stories

New research provides clues on why hair turns gray

June 14, 2011

A new study by researchers at NYU Langone Medical Center has shown that, for the first time, Wnt signaling, already known to control many biological processes, between hair follicles and melanocyte stem cells can dictate ...

Recommended for you

Efficient catalyst developed for producing pronucleotides

April 28, 2017

(—A team of researchers with Merck & Co., Inc. has developed an efficient catalyst for producing pronucleotides, paving the way perhaps to a new class of drugs for combatting viruses and cancer. In their paper ...

Tick protein helps antibiotics combat MRSA super bug

April 27, 2017

A protein derived from ticks enhances the effectiveness of antibiotic treatment for methicillin-resistant Staphylococcus aureus, or MRSA, according to a Yale-led study. The strategy of using the protein in combination with ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.