Last month, the journal Materials Science and Engineering published the team’s findings in an article entitled, ‘Structure and mechanical behavior of human hair.’ The researchers’ rational for the project is fairly straight forward, “The understanding of the mechanical behavior of hair under various conditions broadens our knowledge in biological materials science and contributes to the cosmetic industry,” they write in the article abstract.
Biomimetics
The researchers set out to better understand how hair functions in hopes that this information has wider applications. Besides being valuable to the hair care industry, the university has suggested this new data could even inspire new biomimetic materials for body armor.
“Nature creates a variety of interesting materials and architectures in very ingenious ways,” points out Marc Meyers, lead author on the article, in an item from UC San Diego. He goes on to explain, “we’re interested in understanding the correlation between the structure and the properties of biological materials to develop synthetic materials and designs — based on nature — that have better performance than existing ones.” (Meyers is a professor of mechanical engineering at the UC San Diego Jacobs School of Engineering.)
Structure
The researchers found that it's the differential response to speed, between hair’s cortex and matrix, that allows hair to tolerate phenomenal levels of stress and strain.
“At the nanoscale, the cortex fibrils in hair are each made up of thousands of coiled spiral-shaped chains of molecules called alpha helix chains,” explains the UC San Diego press item. “As hair is deformed, the alpha helix chains uncoil and become pleated sheet structures known as beta sheets. This structural change allows hair to handle a large amount deformation without breaking.”
To a degree the change is reversible, but after a point hair cannot recover. “This is the first time evidence for this transformation has been discovered,” Yang Yu, a nanoengineering PhD student and an author on the article, says.
Behavior
Water and heat were found to have a distinct effect on hair’s behavior. At temperatures over 140 degrees Fahrenheit, according to the press item, hair is permanently damaged, breaking “faster at lower stress and strain.”
In high humidity hair can be deformed up to 80% without breaking. For dry hair that figure drops to 50%. “Water essentially 'softens' hair — it enters the matrix and breaks the sulfur bonds connecting the filaments inside a strand of hair,” explains the item.
The researchers are now at work to better understand how water alters the properties and behaviors of hair, including why washing takes hair back to its original shape.