Sticky Secrets of the GeckoThe images and information were obtained from the
were obtained from : A gecko can dash up a smoothly polished glass surface as easily as we can fall off a log, sticking and unsticking its feet 15 times a second, travelling at almost 1m / sec (3ft / sec). A gecko has enough sticking power to support it's entire body weight from a ceiling, if it feels like it, by a single toe. Yet it uses no force when pulling away fron a tree to take another step. Even in a laboratory-created vacuum, where suction would do little good, a gecko's foot will still stick. 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, reported (September 8, 2000) the first direct measurement of the adhesive function that makes it possible for the gecko to master these amazing feats. The secret is in the gecko's foot. Whimsical-Looking Appendages
Even more astounding, the hairs blossom at the ends into hundreds of teeny split ends. The submicroscopic, funnel-shaped pads, or spatulae, measure a scant 200 nanometers across -- 200 billionths of a meter, so small they cannot even be seen with visible light. A climbing Tokay moves in such a way that when it presses a foot down, the toe hairs splay out and the spatulae unfurl, shooting out and recoiling like blow-through party toys as the lizard scuttles along.
A million of these suckers could fit onto a dime-sized patch capable of holding up 45 pounds. In theory, a teacher could use one of these patches to stick an unruly kindergartner to the classroom ceiling. Engineers Ronald Fearing at Berkeley and Thomas Kenny at Stanford helped the researchers achieve the first direct measurements of a single gecko foot-hair, the key step in unlocking the animal's adhesive secrets, by constructing a delicate icro-electromechanical force sensor. Many other gecko species sport similar footgear, but the Tokay is considered to have the most elaborate feet of any lizard known, possibly the most advanced dry-adhesive technology in nature outside the insect world. Ants and cockroaches are well-equipped, too. Their feet sport tiny spines or hooks, supplemented by sticky secretions in some species, that work extremely well on nearly any rough or porous surface, even if the surface appears perfectly smooth to the naked eye. Some beetles and kissing bugs have setae very similar to those found in lizards, and their relatively low body weights give them a leg up on the heavier geckos. The Tokays could rely on their claws and muscles to grab on, as do birds and most big climbing animals, but that only would take them so far. Because of their unique foot apparatus, the geckos can generate adhesive forces 600 times greater than mere friction alone. Such stick-on overkill appears to be nature's strategy for overcoming the fact that a gecko has to contend with all kinds of rough, irregular surfaces in its native Southeast Asia habitat. In fact, with each step it takes, a Tokay grabs on with only about 2 percent of its available toe-hairs. Some key details are still being kicked around by the researchers. It's not quite clear, for example, just what kinds of molecular interactions might be going on to explain the lizard's climbing prowess. Besides van der Waals forces, another factor that might be significant has to do with the water content of the setae and attractive forces between the water molecules and the surface. Another puzzle is how the setae -- made of the same keratinous material as human toenails -- manage to stay clean, even when the lizards walk up dirty surfaces. ``You stick a piece of tape to a dirty surface and the tape is worthless
after the first stick,'' Autumn noted. ``As the geckos walk, their feet
get cleaner, not dirtier, and we don't know exactly how they do that.''
HOW THE GECKO STICKS TO A WALLResearchers have discovered that a Tokay gecko can climb a vertical wall, stick upside down or even cling to polished glass without benefit of suction, sticky secretions, electrostatic forces, friction or Velco-like interlocking. Instead, the lizard uses an elaborate array of toe-hairs and a peeling motion to form intermolecular bonds with the surface as it walks.
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