A friend forwarded this to me.
Sorting Out The Science Of Stickiness : Adhesion Biology Research Crosses
Numerous Disciplinary Lines. Summary Of A Symposium At The Society For
Integrative And Comparative Biology's Annual Meeting In Anaheim, Calif.,
Jan. 2-6, The Natural Engineering Wonders Of Adhesion.
By Ricki Lewis ,The Scientist 16[3]:14, Feb. 4, 2002
A gecko's remarkable movements also reflect smaller scale events. "These
animals have turned their hind feet back into hands, which facilitates
locomotion in a variety of directions," said Anthony Russell, a professor of
biological sciences at the University of Calgary.
Each gecko digit sports thousands of hair-like setae that branch into
thousands more, ending in spatula-like tips. After many experiments that
pulled and pushed the extensions, Kellar Autumn, a professor of biology at
Lewis and Clark College in Portland, Ore., discovered that the setae of
these "stubborn creatures" wouldn't stick without a small and increasing
push, which boosts the adhesive force as more spatula tips form.2 "The
animal needs only to attach 10% of its setae to generate maximal observed
foot force. A gecko's worth of setae is very adhesive," Autumn said. The
lizard's highly symmetrical stance also contributes to its agility, said
Russell. "Gecko digits are more similar in size and spread more than those
of other lizards. The trend toward symmetry of pads came about before
adhesion was invented," he added. Gecko locomotion may therefore be an
"exaptation," a new use for an existing capability.
Autumn and Russell also observed that sticking setae pop off when displaced
from the surface by more than a 30-degree angle. Geckos attach using van der
Waals forces, the weak attraction that occurs as two materials approach one
another. If the surfaces are large, the forces add up. "Geckos stick due to
geometry, and not the chemistry of the surface," Autumn concluded.
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