Sticky gecko toes have little hairs to thank

A gecko's sticky feet hold it suspended upside-down on a sheet of glass.

WASHINGTON (Reuters) -- Tiny little hairs and not any kind of chemical glue help a gecko race up and down vertical surfaces as smooth as glass, researchers reported Monday.

The finding could help scientists invent better adhesives that will work virtually anywhere, the researchers at Lewis and Clark College in Portland, Oregon, the University of California and Stanford University said.

"We have solved a centuries-old mystery of what makes a gecko's toes so sticky," Lewis and Clark's Kellar Autumn, a biologist, said in telephone interview.

Geckos and their ability to climb and hang virtually everywhere are hardly unknown to science, but biologists had not really understood how they did it.

At first it was assumed they had glue on their toes, but close examination with electron microscopes shows they have millions of tiny hairs called setae.

A seta is only about 100 micrometers long -- about the width of two human hairs. Each seta ends with 1,000 even tinier pads at the tip.

One seta can lift the weight of an ant. A million setae, which could easily fit onto the area of a dime, could lift a 45-pound child and a gecko using all of its setae at the same time could support 280 pounds, the researchers said.

Molecular attraction

The tiny pads work through a molecular attraction called van der Waal's forces. "We confirmed it's geometry, not surface chemistry, that enables a gecko to support its entire body with a single toe," Autumn, who studies biomechanics, said.

Microscopic hairs help geckos climb walls.

Van der Waal's force keeps molecules together.

This is good news for Autumn's colleagues, who are trying to invent better adhesives. "It would have been a lot more difficult if there been a particular biochemistry that we had to duplicate," Autumn said.

If they can make hairs small enough, they should be just as strong and sticky.

He does not think even a sandy, silty surface would thwart a hairy-footed robot. "Geckos live all over the world, even in places where it is sandy, and their feet don't get dirty," Autumn said. "We believe the adhesive is self-cleaning."

Most animals and insects with sticky feet need to use water, which employs the capillary effects to get an adhesive bond. Geckos, some other lizards and one kind of beetle are virtually unique in their ability to attain dry stickiness, Autumn said.

The team has started making synthetic gecko foot-hair tips that stick like the real thing, and want to expand their output.

Could a glove equipped with similar tiny hairs help a person cling to a wall like Spider-Man, the cartoon and film character? "I watched 'Spider-Man' on an airplane and I couldn't help thinking we could do better than that someday," Autumn said.

"A personal dream of mine is to see a small-legged robot with adhesive feet walk on the surface of Mars."

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