Researchers have been investigating why hair is incredibly strong and how this strength could be incorporated into innovative materials.
Hair has a strength-to-weight ratio comparable to steel and can be stretched up to one and a half times its original length before breaking.
Understanding the mechanism behind this extraordinary property will be key to replicating its effects in materials with a variety of potential applications from body armour to hair care products.
“Nature creates a variety of interesting materials and architectures in very ingenious ways,” said Marc Meyers, a professor of mechanical engineering at the University of California, San Diego, Jacobs School of Engineering.
“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.”
Hair consists of a cortex of parallel fibrils and a matrix, which is an amorphous structure sensitive to the speed at which hair is deformed. The tension between the rigid cortex and responsive matrix in combination enables hair to withstand high stress and strain.
At the nanoscale, the tiny cortex fibres in hair are each made up of thousands of coiled spiral-shaped chains of molecules called alpha helix chains. 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 of deformation without breaking. When stretched by a limited amount, the structural changes are partly reversible but not if stretched too far.
Researchers made a nanoscale examination of how a strand of human hair behaves when it is deformed or stretched and found that hair behaves differently depending on how fast or slow it is stretched.
The speed by which hair is stretched seemed to increase its strength.
“Think of a highly viscous substance like honey,” Meyers explained.
“If you deform it fast, it becomes stiff but if you deform it slowly it readily pours.”
The team also found that the tensile strength of hair was increased by high humidity levels ‘softening’ it. Further studies relating to the effects of water on the properties of human hair are taking place currently.