Polar bears need all the help they can get to survive their frosty Arctic environment. One of their biggest survival secrets appears to be greasy hair. The sebum–or hair grease–on their fur makes it very difficult for ice to stick. The findings are detailed in a study published January 29 in the journal Science Advances, and could help chemists and engineers develop new anti-ice coatings for more durable fabrics, skis, snowboards, and more.
Polar animals as inspiration
Polar bears have a thick layer of fat below two layers of fur that help trap their internal body heat. According to Polar Bears International, these layers keep them so warm that adult males can quickly overheat when they run. Ice also does not accumulate on it, despite the bears spending nearly all of their time in and around freezing cold water.
“Animals living in polar habitats have emerged as a source of inspiration for the development of new anti-icing materials,” Richard Hobbs, a study co-author and chemist at Trinity College in Dublin, said in a statement.
To learn more about how, the team collected hair from six polar bears in the wild. They measured the adhesion strength of ice to get a sense of how well it can stick to fur. Next, they looked at hydrophobicity–the process that dictates whether water can shed before it freezes. Finally, they analyzed the freezing delay time, or how long it takes for a single drop of water to freeze at certain temperatures on a particular surface. They then compared the performance of polar bear hair with human hair and two human-made ski skins.
A polar bear’s insulating fur shown under infrared heat imaging taken with a FLIR E75 24o (FLIR Systems OÜ, Estonia) Svalbard Archipelago, Norway. CREDIT: © Jon Aars, Norsk Polarinstitutt.
“The sebum quickly jumped out as being the key component giving this anti-icing effect as we discovered the adhesion strength was greatly impacted when the hair was washed,” Julian Carolan, a study co-author and doctoral student at Trinity College, said in a statement.
“Unwashed, greasy hair made it much harder for ice to stick. In contrast, when the polar bear hair was washed and the grease largely removed it performed similarly to human hair, to which ice sticks easily whether it is washed or greasy.”
A cool concoction
After pinpointing the hair grease as the key component for keeping ice off of polar bear fur, they performed a detailed chemical analysis of the sebum. They first identified the key components–cholesterol, diacylglycerols, and fatty acids. This mixture is what makes it difficult for the ice to attach to the fur.
However, the team was surprised to see that a fatty metabolite called squalene was missing. Squalene is present in human hair and in aquatic mammals, including sea otters–who don’t live in icy conditions, but still need fur that keeps them warm. It is suggested that the absence of the squalene in the polar bear hair was critical from an anti-icing perspective.
It also offers insight into some of the ways other animals living in polar environments have adapted to keep ice off of their fur and feathers. For example, the structure of Gentoo penguin feathers repels ice, all without the fatty grease that polar bears use.
[ Related: Polar bears adapted to the Arctic just 70,000 years ago. ]
Grease as a hunting tool
This grease also helps explain more about the hunting strategies of polar bears and Indigenous Inuit populations. Polar bears deploy “still hunting,” where they lay motionless next to a breathing hole in the ice. There, they wait for seals to surface.
“Still hunting frequently develops into an ‘aquatic stalk’ with the polar bear using its hind paws to slide into the water to pursue its prey, and the lower the ice adhesion, the less noise generated and the faster and quieter the slide,” Bodil Holst, a study co-author and experimental physicist
at the University of Bergen in Norway, said in a statement.
Inuit peoples will also take subtle steps to mimic the polar bear’s still hunting. Their traditional fur preparation methods also protect the sebum.
“Inuit hunting stools are sometimes shod with polar bear fur on the feet to avoid noise when moving on the ice, while people also sometimes wear ‘polar bear trousers’, ensuring the entire contact area with the ice is covered in low ice-adhesion polar bear fur for optimal noise reduction,” said Holst.
In addition to learning more about these masters of adaptation, it can help us develop new and safer materials that deflect ice.
“We expect that these natural lipid coatings produced by the bear will help us to develop new more sustainable anti-icing coatings that may replace problematic ‘forever chemicals’ like PFAS that have been used as anti-icing coatings,” said Hobbs.
