Hair has strength to weight ratio comparable to steel. It can be extended up to single and a half times its primary length before breaking. “We intended to comprehend the mechanism behind such extraordinary property,” says Yang Yu, a nanoengineeringPh.D student at the UC San Diego and the first author of the study.
“Nature prepares a range of interesting substances and architectures in very ingenious ways. We are interested in comprehending the correlation between the properties and the structure of biological substances to develop synthetic substances and designs based on the nature that have higher performance than existing ones,” says Marc Meyers, a lecturer of mechanical engineering at the UC San Diego Jacobs School of Engineering and the head author of the study.
The scientists investigated at the nanoscale level how a single strand of human hair functions when it is stretched or deformed. The group identified that the hair behaves distinctly depending on how slow or fast it is stretched. The faster the hair is stretched, the stronger it is. ‘Think of an exceedingly viscous substance, like honey,” explains Meyers. “If you deform it fast it becomes stubborn, but if you deform it slowly it readily pours.”
Hair comprises two mains sections – the cortex, which is prepared of parallel fibrils, and the matrix that has an amorphous structure. The matrix is sensitive to the speed at which hair is deformed, while the cortex is not. The combination of such two components, Yu explain is what gives hair the potential to withstand high strain and stress.
And as the hair is extended, its structure transforms in a specific way. At the nanoscale, the cortex fibrils in hair are each prepared of numerous of coiled spiral shaped coins of molecules known as alpha helix chains. As hair is deformed, the alpha helix chains uncoil and become pleated sheet structures called as beta sheets. Such structural change allows hair to handle up a big volume of deformation without breaking.
Such structural transformation is almost reversible and when the hair is stretched under a tiny volume of strain, it can recover its original shape. Extend it further, the structural transformation becomes irreversible. “This is the first time evidence for such transformation has been discovered,” says Yu.
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