How the polar bear stays ice-free
Its thick fur protects the polar bear from the Arctic cold. Although the fur itself is barely warmer than the environment, there is no ice between the hairs. We only now know how this works.
Although polar bears swim in sub-zero temperatures, frolic in the Arctic snow and roll around in it, there is normally no ice in their fur. Until now, nobody knew why this is the case. Now a research team reports that it is due to the special tallow that the large Arctic hunters produce and which surrounds the hair in their fur. More precisely, it is because this tallow lacks a special ingredient.
In the Arctic, where the polar bear lives, temperatures can drop to minus 40 degrees Celsius. Its thick fur and several layers of fat insulate the warm body of the giant mammal so efficiently that the fur is usually at ambient temperature on the outside. And as we humans can also see in freezing rain, ice freezes wonderfully in hair - but not on the polar bear's hair.
In order to find out why this is the case, an international research team led by Julian Carolan from Trinity College Dublin conducted experiments to investigate how well (or poorly) ice crystals adhere to polar bear fur - and then compared the results with high-performance anti-ice coatings for skis, in which mohair fibres are coated with fluorocarbons (PFAS). In fact, the ice had roughly the same difficulty sticking to both materials. The scientists also discovered that the secret lies in the polar bear's sebum. This greasy mass surrounds the hair of every mammal. However, only the polar bear's tallow is also ice-repellent: if it was removed by washing the polar bear's fur, it lost its anti-ice adhesive effect. Ice crystals adhered around four times more strongly to washed polar bear fur than to unwashed fur and were difficult to remove. Human hair behaved in a similar way to the washed fur.
This is strange, however, because one would expect the fat of mammalian hair to adhere poorly to ice. In fact, it is one molecule in particular that makes the difference. When the research team analysed polar bear blubber, they found typical components known from other mammals, including particularly large amounts of cholesterol or long-chain fatty acids. However, one key ingredient was missing: squalene, a long hydrocarbon zigzag chain. It is typically found in the tallow of mammals, especially in aquatic animals such as beavers, sea otters and sea lions.
The team used quantum mechanical calculations to determine how well squalene and the main components of polar bear tallow adhere to ice surfaces. According to the results, squalene binds much more strongly to frozen water than the other molecules contained in the tallow. The absence of this molecule probably contributes significantly to the anti-adhesive effect of polar bear fur against ice crystals.
The fact that they have solved the riddle of the ice-free polar bear fur could, according to the researchers, help to produce biologically inspired ice-repellent materials. This could potentially offer alternatives to coatings made from controversial PFAS, which are difficult to break down and therefore accumulate in soils and waters worldwide - including in the Arctic.
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Original article on Spektrum.de
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