Mysteries of gecko feet may lead to biomimetic technologies

• Their feet will stick to virtually any surface, yet collect no grime and never lose their grip, even as they scurry up trees and scamper through dirt.
• A gecko's feet, scientists have discovered, contain a self-cleaning adhesive.
• Unlike artificial adhesives, the millions of microscopic hairs embedded in a gecko's toes counteract the forces of gravity, while at the same time repelling dirt, the scientists reported.
• The findings, the researchers say, may open the door to tape that can be reused endlessly, robotic rovers that run swiftly over the Martian surface or even fumble-free football gloves.
• "We showed that you can dip a gecko's feet in some of the nastiest dirt ever, and after five steps the dirt just falls off," said Dr. Kellar Autumn, a biologist at Lewis & Clark College and an author of the study.
• Autumn uncovered some answers when he found that geckos, instead of using suction or gooey secretions like insects, relied on faint molecular interactions that operate over short distances, called van der Waals' forces.
• A gecko's foot contains millions of minuscule hairs, or setae, with tiny pads at their tips.
• Because they are only 200-billionths of a meter wide, the tips get close enough to any surface to be pulled by the surface's weak molecular forces.
• The combined strength of all the setae on a single gecko, Dr.
• Autumn found, is enough to lift an offensive lineman, about 280 pounds.
• But that discovery led to another crucial question.
• "Nature is a dirty place, so how is it that geckos don't accumulate great gobs of dirt when they walk around?"
• Using a dust made of fine particles, Dr. Autumn's team coated the feet of geckos and watched as the dirt sloughed off after the lizards took five steps on a clean surface.