It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Wednesday, January 29, 2025
Bad hair bears! Greasy hair gives polar bears fur with anti-icing properties
An international team of scientists has discovered the anti-icing secret of polar bear fur – something that allows one of the planet’s most iconic animals to survive and thrive in one of its most punishing climates. That secret? Greasy hair.
After some polar sleuthing, which involved scrutiny of hair collected from six polar bears in the wild, the scientists homed in on the hair “sebum” (or grease) as the all-important protectant. This sebum, which is made up of cholesterol, diacylglycerols, and fatty acids, makes it very hard for ice to attach to their fur.
While this finding sheds fascinating new light on our understanding of polar bear – and even Inuit – ecology, it may also have a suite of unrelated applications, with a similar concoction of artificially made sebum promising to be useful as an anti-ice surface coating, or in next-gen ski skins used by skiers and snowboarders.
Julian Carolan, PhD Candidate from Trinity College Dublin’s School of Chemistry and the AMBER Research Ireland Centre, is the first author of the journal article, which has been published today as the cover story in leading international journal Science Advances.
He said: “We measured ice adhesion strength, which is a useful measure of how well ice sticks to fur; 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. We then compared the performance of the polar bear hair with that of human hair and two types of specialist human-made ‘ski skins’.
“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. 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.”
That finding led the team to perform a detailed chemical analysis of polar bear sebum. As well as identifying the key components (cholesterol, diacylglycerols, and fatty acids), they were surprised to find “squalene” was absent. This fatty metabolite is present in human hair, and in the hair of other aquatic animals, like sea otters, which suggests its absence in polar bear hair is very important from an anti-icing perspective.
Dr Richard Hobbs, Assistant Professor and Royal Society-Science Foundation Ireland University Research Fellow in Trinity’s School of Chemistry and the AMBER Research Ireland Centre, is a senior author of the journal article. He added: “Animals living in polar habitats have emerged as a source of inspiration for the development of new anti-icing materials.
“For example, Anne Kietzig’s group at McGill recently found that the hierarchical structure of Gentoo penguin feathers afforded them anti-icing properties that relied on the feather structure rather than the preen oil coating. Our work shows that polar bear fur provides an alternative strategy to produce an anti-icing surface based on the characteristic blend of lipids present in their fur sebum or hair grease.
“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. Despite having thick layers of insulating blubber and fur, and spending extensive periods in water at sub-zero temperatures, it seems that the fur grease provides a natural route for polar bears to easily shed ice when it forms due to the low ice adhesion on their fur.
“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.”
In addition to the structural explanations, these interesting discoveries also help us better understand hunting behaviours – both of polar bears and of native Inuit populations.
Prof. Bodil Holst, University of Bergen, is a senior author of the journal article. She added: “One of the polar bears’ main hunting strategies is ‘still hunting’, where they lay motionless beside a breathing hole on sea ice waiting 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.
“Our findings also help us 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.”
Notably, the traditional Inuit preparation method protects the sebum on the fur by ensuring the hair-covered side of the skin is not washed. This is unlike, for example, a fox skin, which would traditionally be cleaned by rubbing the hair side with soapstone or dry clay.
A polar bear's insulating fur shown under infrared heat imaging
A polar bear's insulating fur shown under infrared heat imaging taken with a FLIR E75 24o (FLIR Systems OÜ, Estonia) Svalbard Archipelago, Norway.
Polar bear fur’s natural ability to resist ice formation could pave the way for safer, more sustainable solutions to prevent ice buildup across industries such as aviation and renewable energy, according to researchers at the University of Surrey.
An international study published in Science Advances has explored the anti-icing properties of polar bear fur in extreme Arctic conditions, revealing a unique mix of lipids in the fur’s sebum – an oily substance produced by the skin - that drastically reduces ice adhesion. In the face of climate change, this natural design could help prevent ice buildup on infrastructure such as frozen wind turbine blades or aeroplane wings.
Key to this discovery are the advanced quantum chemical simulations carried out by the University of Surrey’s computational chemistry team, which investigated molecular interactions between the fur’s sebum and ice.
Dr Marco Sacchi, Associate Professor at Surrey’s School of Chemistry and Chemical Engineering, is co-author of the study who led the group:
“We found that specific lipids in the sebum, such as cholesterol and diacylglycerols, exhibit very low adsorption energies on ice. This weak interaction is what prevents ice from adhering to the fur.”
Experiments confirmed these theoretical findings, measuring ice adhesion strength before and after the fur’s natural oils were removed. Researchers found that untreated polar bear fur performed on par with high-performance fluorocarbon coatings used in sports and industry. However, when it was washed to remove the sebum, ice adhesion was four times higher than unwashed samples.
The study also explored the fur’s hydrophobicity – its water-repelling properties – and how it delays the onset of freezing in the harsh Arctic, where temperatures drop below -40°C. Yet these properties alone could not explain the superior anti-icing performance.
Using techniques such as gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS/MS), and nuclear magnetic resonance (NMR), the team found it was a unique mix of lipids – particularly an abundance of cholesterol and diacylglycerols – responsible for this ability.
Commenting on the revelation, Dr Sacchi said:
“It’s fascinating to see how evolution has optimised the sebum’s composition to avoid ice adhesion. We found squalene, a common lipid in other marine mammals, was almost entirely absent in polar bear fur. Our computational simulations revealed squalene strongly adheres to ice, and this absence significantly enhances the fur’s ice-shedding properties.”
Led by the Norwegian Polar Institute and the University of Bergen – with contributions from Trinity College Dublin, University College London, and the National Museum of Denmark – the research also highlights the importance of Indigenous knowledge of the Arctic and builds on that. Inuit communities have long recognised the unique properties of polar bear fur, using it in tools and garments.
Dr Sacchi added:
“Our findings highlight the power of interdisciplinary collaboration. We combined experimental evidence, computational chemistry and Indigenous Arctic insights to uncover a fascinating natural defence mechanism – which could transform how we combat ice in everything from aviation to renewable energy.”
Dr Sacchi’s computational team at Surrey included Dr Neubi F. Xavier Jr. and Adam Pestana Motala, who carried out the molecular modelling that underpins the study’s conclusions.
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