Snake Origins (3.16.04) - A famous Saint Patrick's Day legend explains why Ireland has no snakes. Now biologists are using DNA to explain why snakes have no legs.
Running Out of Reptiles (8.15.00) - The World's reptiles could be going the way of the dinosaurs.
For now the gecko might be best known for peddling car insurance. But as this ScienCentral News video reports, the lizard has also been put to work in the lab, where scientists want to turn their Spider-Man-like sticking powers into new materials for us.
Sticky, But Not Gooey
Geckos are renowned for their ability to stick to almost any surface (they can't stick to Teflon®) with relative ease— they can hang from a tree branch by one toe, and combined, the bottoms of their feet could theoretically support the weight of a 250-pound man. But if their feet are so sticky, how come they aren't covered in dirt and sand by the end of the day?
"Geckos live in some of the dirtiest places on earth— sandy deserts, dusty places— and their feet don't get dirty," says Kellar Autumn, a biologist at Lewis and Clark University. "In fact we found that they get cleaner and cleaner with repeated use."
Given that geckos also don't groom their feet, Autumn wanted to know how they stay so clean. He's been studying the lizard for the past 17 years and in 2002 showed that geckos can stick to most surfaces because of so-called " van der Waals forces"— attractive forces between the molecules in gecko feet and the molecules of the surface they are sticking to. The molecules have areas of slight positive or negative charge that attract each other, sort of like mini magnets. Since gecko toes are covered with as many as 2 million tiny hairs, and each hair then splits into 100 to 1,000 tiny branches, the number of mini magnets is immense.
But in a new study published in Proceedings of the National Academy of Sciences, Autumn reports that it seems the same mechanism that helps geckos stick also helps keep dirt off their feet. That's because while those millions of hairs combined create enough force to allow geckos to climb walls, the force created by just the few hairs that would touch any single piece of dirt is too weak, so the dirt falls off. In other words, geckos' feet are self-cleaning.
This microscopic image shows the spatulae that split off from the setae on the bottom of a gecko's foot. image: Kellar Autumn & Ed Florance
"Each gecko foot-hair (seta) splits into hundreds of nano-tips (spatulae) that get so close to a surface that they bond at the atomic level (van der Waals force)," explains Autumn. "Gecko spatulae also form van der Waals bonds with dirt particles, but only a few spatulae can adhere to a single piece of dirt. When that dirt particle gets close to another surface— say the wall the gecko is walking on— attractive forces pull the particle off the gecko spatulae and they become cleaner. Our mathematical models suggest that it would take between 26 and 59 spatulae attached simultaneously to each piece of dirt to prevent self-cleaning— and that simply doesn't happen very often. In most cases only a few spatulae attach to any one dirt particle, and the attraction on that same particle to the wall is much, much stronger."
What This Means To You
Autumn and other scientists have been working on creating synthetic gecko hairs for some time now. If they succeed, he hopes the result will be a new adhesive that is incredibly strong, but also clean and re-usable.
"If our models are accurate, self-cleaning in gecko setae is largely a consequence of the structure (size and shape) of the setae and not their chemical nature. This suggests that the self-cleaning phenomenon we've discovered could be applied to synthetic adhesives made from a wide variety of materials," he says, adding, "You can imagine larger patches of gecko adhesive being used for mundane things like Post-it‚ notes that are reusable, or Band-Aids‚ that are waterproof and don't cause your child pain when you pull them off."
Teenagers could tape posters to their walls without angering their mothers about ruining the paint job. Rock climbing could become a lot safer and easier (if perhaps less challenging). Since the process works in a vacuum, there could also be applications for adhesives in outer space. And because synthetic gecko hairs would be so small, Autumn thinks they could be used in nano-surgery.
Such products won't be available for years, though, since creation of these synthetic hairs is still in the early stages of development. Ron Fearing, professor of engineering at University of California, Berkeley who is working with Autumn, molded tiny synthetic gecko hairs with an atomic force microscope. Two types of hairs he created— one from silicone rubber and one from polyester— stick to surfaces as well as gecko hairs do. There is also a group of scientists in England working toward the same goal.
delicious
digg
magnolia
reddit
newsvine
netscape
netvibes
