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Scientists unlock secret of gecko adhesive and discover how to climb up glass walls
PORTLAND, Ore. -- Geckos, nature's supreme climbers, can race up a polished glass wall at a meter per second. And they can even do it upside down. Moreover, they can support their entire body weight from a wall with only a single toe.
In this week's issue of Nature, a team of scientists, led by biologists Kellar Autumn of Lewis & Clark College in Portland, Ore., and Robert Full at the University of California at Berkeley, reports the first direct measurement of the adhesive function that makes it possible for the gecko to master these amazing feats.
The discovery is inspiring engineers to design tiny robots that may one day aid search and rescue missions and to create the world's first dry, self-cleaning glue that will work in outer space and under water.
In addition to Autumn and Full, the interdisciplinary team includes engineer Thomas Kenny, Department of Mechanical Engineering, Stanford University; and engineer Ronald Fearing, Department of Electrical Engineering and Computer Science, University of California at Berkeley.
Geckos have millions of seta, microscopic hairs on the bottom of their feet that function as a unique adhesive, Autumn explains. These tiny setae are only as long as two diameters of a human hair. That's 100 millionth of a meter long. Like the split ends of a hair, each seta ends with 1,000 even tinier pads at the tip. These tips, called spatulae, are only 200 billionths of a meter wide -- below the wavelength of visible light.
Using a microscopic force sensor designed by Kenny and a system using a fine aluminum wire designed by Fearing, the scientists took a single seta from a Tokay gecko (Gekko gecko) and measured the tiny forces of adhesion for the first time.
"We got a nasty surprise when we tried to touch the end of the hair to a surface," Autumn says. "It wouldn't stick. But when we manipulated it in a particular way, simulating the movements of a gecko's foot, we discovered that the seta is 10 times more adhesive than predicted from prior measurements on whole animals," Autumn said. "In fact, the adhesive is so strong that a single 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. Our discovery explains why the gecko can support its entire body weight with only a single finger."
"Geckos have developed an amazing way of walking that rolls these hairs onto the surface and then peel them off again, just like tape. But it's better than tape," Full says.
"When the gecko attaches itself to a surface, it uncurls its toes like a party favor that uncurls when you blow into it," Autumn says. "But," he adds, "getting yourself to stick isn't really that difficult. It's getting off the surface that is the major problem. When a gecko runs, it has to attach and detach its feet 15 times a second.
The measurements reject two proposed forms of adhesion: suction and chemical bonding.
"We believe that the seta sticks using only intermolecular forces," Autumn said. "These are weak electrodynamic forces that operate over very small distances."
"The intermolecular forces come into play because the gecko foot hairs get so close to the surface," Full says. "The hairs allow the billion spatulae to come into intimate contact with the surface, combining to create a strong adhesive force," he says. "Our calculations show that van der Waals forces could explain the adhesion, though we can't rule out water adsoprtion or some other types of water interaction."
Moreover, the scientists discovered that the gecko adhesive works in a vacuum and under water, leaves no residue and is self-cleaning.
The scientists clogged the gecko hairs with debris, but five steps later the hairs were clean.
Autumn foresees countless applications for synthetic gecko adhesive--from vacuum areas of clean rooms to outer space.
Currently, the scientists are working with Fearing at Berkeley to design and fabricate synthetic gecko setae. "We will now see if we can fabricate the gecko hair to produce the first dry, self-cleaning glue."
The scientists are also working with IS Robotics in Boston to design tiny robots that can climb on walls and even upside down.
Because geckos treat an obstacle like any other surface and crawl right over it, gecko robots might be useful in search and rescue missions.
The diverse gecko, with its 850 species, has a worldwide range. Most species are nocturnal, effective climbers and energy efficient.
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Download photographs and movies of geckos and their foot hairs at http://www.lclark.edu/~autumn/private/u38j47aOt
Contact:
Jean Kempe-Ware
Director of Public Relations
Lewis & Clark College
(503) 768-7963 (office)
(503) 771-0954 (home)
(503) 701-3211 (cell)
[email protected]
Kellar Autumn
Assistant Professor of Biology
Lewis & Clark College
(503) 768-7502
[email protected]
Robert Full
Professor of Integrative Biology
Director Poly-PEDAL Laboratory
Department of Integrative Biology
University of California at Berkeley
(510) 642-9896
[email protected]
Bob Sanders
Senior Science Writer
University of California at Berkeley
(510) 643-6998
[email protected]
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