Copyright 2000 Plain Dealer Publishing
Co.
The Plain Dealer
June 11, 2000 Sunday, FINAL / ALL
SECTION: NATIONAL; Pg. 23A
LENGTH: 571 words
HEADLINE: GECKOS HAVE FEET THAT STICK LIKE TAPE, BIOLOGISTS DISCOVER
BYLINE: By JEFF NESMITH; COX NEWS SERVICE
DATELINE: WASHINGTON
BODY:
Geckos, the small lizards that chirp through tropical nights,
appear to invoke an obscure molecular force when they scurry along
vertical surfaces or even upside down in seeming defiance of the
law of gravity.
The tens of millions of microscopic hairs on geckos' toes are
so fine that they are able to interact with the molecules of the
surfaces over which they are moving, said biologist Robert Full
of the University of California, Berkeley. He and collaborators
from Stanford University and Lewis and Clark College described
their gecko studies in this week's issue of the journal Nature.
Geckos can race over a piece of polished glass and crawl upside
down on the ceiling of a room. A gecko can even hang from the
ceiling by a single toe.
Yet their hand-like hairy feet do not have suction cups or glands
that produce any known form of glue.
"Geckos have developed an amazing way of walking that rolls
these hairs onto the surface and then peels them off again, just
like tape," Full said in a telephone interview. "But
it's better than tape."
If the observations and calculations hold up, a century-old mystery
is solved and a possible new principle has been found for creating
an adhesive that is both dry and extremely strong.
Using high-speed video cameras to record the mechanics of gecko
locomotion, the scientists discovered that the creatures attach
their toes to surfaces by "unrolling" them - somewhat
like a "Happy New Year" party toy unrolls when someone
blows through it.
Then they lift the toes by peeling them from the surface, like
peeling off adhesive tape, Full said.
Both actions, happening 15 times a second, are necessary for the
tips of the hairs to invoke the molecular force and withdraw from
it, Full said.
The force that Full and his collaborators believe the lizards
are using is called the "van der Waals force."
Named for the Dutch physicist who discovered it, the force causes
molecules to cling together, like magnets. But it works only at
extremely small distances. As the space between two molecules
increases by, say, the diameter of an atom, the attraction between
them weakens at an exponential rate.
Full and his collaborators believe that when the gecko plants
his hairy little toe on the surface of a mirror, the extremely
fine toe hair gets close enough to the molecules of the mirror
to establish a van der Waals force attraction.
In fact, the contact between the hairs and the molecules of the
mirror becomes so intimate that, for a split second, the hairs
are actually "part of" the mirror, Full said. And that's
about as sticky as anything gets.
The hairs on the bottom of a gecko foot are known as setae, pronounced
"SEE-tee." A gecko has around 500,000 of these hairs,
each about one-tenth the diameter of a human hair, on each foot.
The tip of each of the setae is further divided into several hundred
to 1,000 even tinier hairs called spatulae, the scientists said.
"These billion spatulae, which look like broccoli on the
tips of the hairs, are outstanding adhesives," said Full,
a professor of biology at UC Berkeley.
In fact, all the tiny hairs on the four feet of a single gecko
could theoretically produce enough holding power to lift nearly
100 pounds, the scientists calculated.
When the angle at which the hairs are pushed into the surface
is changed, they appear to lose touch with the molecular van der
Waals force and easily disengage.