Scientists have developed an insulator that mimics the structure of individual polar bear hairs and may have many real world applications in the architecture and aerospace sectors.
For polar bears, the insulation provided by their fat, skin, and fur is a matter of survival in the frigid Arctic.
For engineers, polar bear hair is a dream template for synthetic materials that might lock in heat just as well as the natural version.
"Polar bear hair has been evolutionarily optimised to help prevent heat loss in cold and humid conditions, which makes it an excellent model for a synthetic heat insulator," said Shu-Hong Yu, a professor at the University of Science and Technology of China (USTC).
"By making tube aerogel out of carbon tubes, we can design an analogous elastic and lightweight material that traps heat without degrading noticeably over its lifetime," said Yu.
Unlike the hairs of humans or other mammals, polar bear hairs are hollow. Zoomed in under a microscope, each one has a long, cylindrical core punched straight through its centre.
The shapes and spacing of these cavities have long been known to be responsible for their distinctive white coats. However, they also are the source of remarkable heat-holding capacity, water resistance, and stretchiness, all desirable properties to imitate in a thermal insulator.
"The hollow centres limit the movement of heat and also make the individual hairs lightweight, which is one of the most outstanding advantages in materials science," said Jian-Wei Liu, an associate professor at USTC.
To emulate this structure and scale it to a practical size, the research team manufactured millions of hollowed-out carbon tubes, each equivalent to a single strand of hair, and wound them into a spaghetti-like aerogel block.
Compared to other aerogels and insulation components, they found that the polar-bear-inspired hollow-tube design was lighter in weight and more resistant to heat flow.
It was also hardly affected by water -- a handy feature both for keeping polar bears warm while swimming and for maintaining insulation performance in humid conditions.
As a bonus, the new material was extraordinarily stretchy, even more so than the hairs themselves, further boosting its engineering applicability.
Scaling up the manufacturing process to build insulators on the metre scale rather than the centimeter one will be the next challenge for the researchers as they aim for relevant industrial uses.
"While our carbon-tube material cannot easily be mass produced at the moment, we expect to overcome these size limitations as we work toward extreme aerospace applications," said Yu.
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