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http://www.nytimes.com/2005/08/30/science/30geck.html
Gravity-Defying Geckos Teach Scientists a Lesson
By DENISE GRADY
Published: August 30, 2005
The scientific quest to make artificial gecko feet has
taken a leap forward.
Geckos, lizards that are notorious for their sticky
feet, can run up walls and across ceilings, and hang
tauntingly by one toe. They have no suction cups,
hooks or glue on their feet, so how do they do it?
The soles of geckos' feet are covered by 500,000
minute hairs, and the tip of each hair splits into
hundreds more. Top, a lizard's hairs are magnified 595
times.
Five years ago, researchers at the University of
California, Berkeley; Stanford; and Lewis and Clark
College found the secret: 500,000 minute hairs cover
the sole of each foot, and the tip of each hair splits
into hundreds more. The hairs are so elastic that they
can bend or squish to conform to microscopic nooks and
crannies under the creature's feet, even on the glass
walls of an aquarium.
As a result, the tiny hairs touch so much surface area
so closely that weak forces of attraction between
molecules in the hairs and in whatever surface the
animal is walking on add up and become sufficient to
let the gecko hang on. The connection breaks when the
gecko shifts its foot enough to change the angle
between the hairs and the surface.
The discovery intrigued scientists, who immediately
realized that if synthetic gecko-foot hairs could be
made, they might be a great adhesive - strong,
glue-free, dry, reusable and, unlike suction cups,
capable of working in a vacuum like outer space.
Engineers envisioned robotic instruments that could
climb walls or grab objects without dropping them, and
rovers that could maneuver rugged terrain on distant
planets. Such adhesives could also be used to stick
components together in electronic devices.
The National Science Foundation takes these ideas so
seriously that it gave a $400,000 grant to scientists
at the University of Akron and Rensselaer Polytechnic
Institute to try making imitation gecko feet.
In a recent issue of the journal Chemical
Communications, the team reported that it had indeed
produced synthetic hairs, with 200 times the sticking
power of the ones made by nature.
Although the scientists have tested only minute
amounts of the material, they estimate that if its
properties hold up on a larger scale, a dime-size
patch of it could support 2 to 22 pounds, depending on
how densely the hairs were packed.
"Think of it almost like nano-Velcro," said Ali
Dhinojwala, an associate professor of polymer science
at the University of Akron.
The synthetic hairs - one ten-thousandth the width of
a human hair - are made of highly flexible carbon
cylinders, or nanotubes, embedded in a plastic base
like bristles in a hairbrush.
The tubes are strong and practically unbreakable,
Professor Dhinojwala said, adding that other groups
had tried making the tubes of plastic, but it turned
out to be too weak.
He said people had asked him whether the new material
could be fashioned into gloves and shoes for rock
climbers.
"I'm a little hesitant on going too fast," Professor
Dhinojwala said. "Nature has had more time than we
have had. I would hesitate to extrapolate. But the
imagination is there."
Gravity-Defying Geckos Teach Scientists a Lesson
By DENISE GRADY
Published: August 30, 2005
The scientific quest to make artificial gecko feet has
taken a leap forward.
Geckos, lizards that are notorious for their sticky
feet, can run up walls and across ceilings, and hang
tauntingly by one toe. They have no suction cups,
hooks or glue on their feet, so how do they do it?
The soles of geckos' feet are covered by 500,000
minute hairs, and the tip of each hair splits into
hundreds more. Top, a lizard's hairs are magnified 595
times.
Five years ago, researchers at the University of
California, Berkeley; Stanford; and Lewis and Clark
College found the secret: 500,000 minute hairs cover
the sole of each foot, and the tip of each hair splits
into hundreds more. The hairs are so elastic that they
can bend or squish to conform to microscopic nooks and
crannies under the creature's feet, even on the glass
walls of an aquarium.
As a result, the tiny hairs touch so much surface area
so closely that weak forces of attraction between
molecules in the hairs and in whatever surface the
animal is walking on add up and become sufficient to
let the gecko hang on. The connection breaks when the
gecko shifts its foot enough to change the angle
between the hairs and the surface.
The discovery intrigued scientists, who immediately
realized that if synthetic gecko-foot hairs could be
made, they might be a great adhesive - strong,
glue-free, dry, reusable and, unlike suction cups,
capable of working in a vacuum like outer space.
Engineers envisioned robotic instruments that could
climb walls or grab objects without dropping them, and
rovers that could maneuver rugged terrain on distant
planets. Such adhesives could also be used to stick
components together in electronic devices.
The National Science Foundation takes these ideas so
seriously that it gave a $400,000 grant to scientists
at the University of Akron and Rensselaer Polytechnic
Institute to try making imitation gecko feet.
In a recent issue of the journal Chemical
Communications, the team reported that it had indeed
produced synthetic hairs, with 200 times the sticking
power of the ones made by nature.
Although the scientists have tested only minute
amounts of the material, they estimate that if its
properties hold up on a larger scale, a dime-size
patch of it could support 2 to 22 pounds, depending on
how densely the hairs were packed.
"Think of it almost like nano-Velcro," said Ali
Dhinojwala, an associate professor of polymer science
at the University of Akron.
The synthetic hairs - one ten-thousandth the width of
a human hair - are made of highly flexible carbon
cylinders, or nanotubes, embedded in a plastic base
like bristles in a hairbrush.
The tubes are strong and practically unbreakable,
Professor Dhinojwala said, adding that other groups
had tried making the tubes of plastic, but it turned
out to be too weak.
He said people had asked him whether the new material
could be fashioned into gloves and shoes for rock
climbers.
"I'm a little hesitant on going too fast," Professor
Dhinojwala said. "Nature has had more time than we
have had. I would hesitate to extrapolate. But the
imagination is there."
