Like the rubber nubs on the bottom of kids' socks, the microscopic structures on the bear's paw pads provide some extra friction.
The scientists report November 1 in the Journal of the Royal Society Interface. Pad protrusions may prevent polar bears from sliding across the ice.
says Ali Dhinojwala, a polymer scientist at Akron University in Ohio, who has also studied the adhesive power of gecko feet (SN: 8/9/05).
Nathaniel Ordorff, a materials scientist at Akron who focused on ice, adhesion and friction, was interested in that work.
Joe Dhinojwala's lab did it on geckos, but "we can't really keep geckos on ice," he says. So he turned to the polar bear.
Ordorf worked closely with Dhinojwala, an animal biologist at Syracuse University in New York, and Austin Garner.
Comparison of the claws of a polar bear, brown bear, American black bear and a sun bear. All but Sun Bear's paw pads were bumpy.
But the bulges of polar bears looked a bit different. The team found that for a given diameter, their bumps are longer.
This extra height translates to greater traction on lab-produced snow, the use of a 3-D printed model of the bumps shows.
Until now, scientists didn't know that the size of the collision could make the difference between a catch and a slip, says Dhinojwala.