Scientists May Have Unlocked Secret of Sticking Power of Lizard's Feet
NEW YORK, June 8, 2000They scuttle up vertical walls and can cling to a ceiling with a single toe.
The sticking power of geckos has long befuddled scientists dating as far back as 2,300 years ago when the Greek philosopher Aristotle first pondered how the mostly nocturnal lizards managed their trick.
Now a team of mechanical engineers and biologists have zeroed in on geckos and found their gripping power is even stronger than expected. They determined a single gecko about two inches in length is capable of holding onto about 90 pounds about the weight of two small children.
And, surprisingly, the force that geckos use to maintain such gripping power appears to be made up of one of the weakest bonds in nature.
There are countless possibilities, says Kellar Autumn, a biologist at Lewis and Clark College in Oregon and lead author of the latest gecko study, published in this weeks journal Nature. You could manufacture toys that crawl up walls. The adhesive could be used in nanosurgery or you can even imagine astronauts using gecko tape to stick things to satellites.
Examine a geckos toe closely and youll see several flaps of skin known as lamellae. Put those flaps under a microscope and millions of tiny hairs called setae (pronounced see-tee) are visible at the flaps fringes. Electron microscopy further reveals that, sprouting from the tips of each of these tiny hairs are thousands of tiny, slightly curved pads called spatulae. One gecko hosts billions of spatulae at the tips of its toes.
Why such intricacy? Autumn believes its designed to ensure maximum contact between the geckos toe and the surface its crawling on. The more surfaces there are, the better the chance that some of them will make close contact with a surface. And close contact is important since Autumn and his colleagues suspect that the forces that make geckos feet cling operate at a molecular level.
It fluctuates very rapidly, explains Autumn. Its throwing a positive charge here, a negative charge there.
When the atoms of one molecule are placed very closely to the atoms of another molecule, the fluctuation in charge attracts the nearby atoms. This happens because fleeting negative charges at one end of an atom attract fleeting positive charges from nearby atoms and vice versa. Because the charges are constantly shifting, the attraction is very weak. But the cumulative effect of a slight attraction between molecules in the geckos billions of spatulae and the surface add up.
Our measurements showed a single hair-like seta could lift an ant, says Robert Full, a co-author of the study and a professor of integrative biology at the University of California at Berkeley. And just think, the gecko has 2 million setae.
IS Robotics Inc. has already taken this information and fashioned wall-crawling robots that curl and uncurl their toes as they scuttle.
Imagine tossing a swarm of these high-speed gecko robots into a burning building, says Full. They could crawl over any surface and find people so firefighters wouldnt have to risk their lives going into the fire.
The current gecko robot models use a glue-like adhesive to achieve their stick. But glue can be problematic since it doesnt work as well when its dirty and it can eventually wear out. Autumn and Full are eager to replicate the geckos adhesive mechanism since it seems to be virtually problem-free.
Super Gecko Glue
Ruling out those possibilities is what led Autumn and Full to believe that Van Der Waals forces are the main source of grip. Now the real test will be in trying to replicate it.
As Full says, Animals like the gecko are like libraries of information. They have some of the best secrets out there.