The anti-icing secret of polar bear fur, the critical factor that allows the animals to survive and thrive in punishing cold climates, has finally been explained.
It is all down to a distinct form of greasy hair.
An international team including researchers at Trinity College Dublin made the discovery following scrutiny of samples collected from six polar bears in the wild, homing in on their hair “sebum” – or grease – as the all-important protectant.
It is made up of cholesterol, diacylglycerols and fatty acids, which make it very hard for ice to attach to their fur.
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The finding sheds new light on the polar bear species but also Inuit ecology. It could lead to a suite of unrelated applications, with a similar concoction of artificially made sebum as an anti-ice surface coating, “or in next-gen ski skins used by skiers and snowboarders”.
Julian Carolan, a PhD student at Trinity’s School of Chemistry and AMBER centre, is first author of a study published on Wednesday as the cover story in the journal Science Advances.
“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,” he added.
“We measured ice adhesion strength, which is a useful measure of how well ice sticks to fur; [known as] hydrophobicity, which dictates whether water can be shed before it freezes; and freezing delay time, which simply shows how long it takes for a drop of water to freeze at certain temperatures on a given surface.”
They then compared the performance of the polar bear hair with that of human hair and two types of specialist human-made “ski skins”.
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.
They were surprised to find “squalene” was absent. This fatty metabolite is in human hair, and that of aquatic animals such as sea otters, which suggests its absence in polar bear hair is very important from an anti-icing perspective.
“Animals living in polar habitats have emerged as a source of inspiration for the development of new anti-icing materials,” said Dr Richard Hobbs, a Trinity academic who contributed to the study.
Their work shows polar bear fur provides an alternative strategy to produce an anti-icing surface from fats in their hair grease compared to penguins, who rely on their feathers to counter the cold.
“This work not only represents the first study of the composition of polar bear fur sebum, but it also resolves the question of why polar bears don’t suffer from ice accumulation,” Dr Hobbs said.
Although polar bears have thick layers of insulating blubber and fur, and spend extensive periods in water at sub-zero temperatures, it seems fur grease provides a natural route for them to easily shed ice when it forms.
[ Ireland had warmest and wettest year on record in 2023 - CSOOpens in new window ]
Prof Bodil Holst, of the University of Bergen, said the findings help to better understand the subtlety of the steps taken by Inuit people to optimise hunting strategies to mimic the polar bear method of “still hunting”.
“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.”
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