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Gecko Feet

Gecko Feet Photo Credit: David Clements. Shimbathesnake, from Wikimedia Commons

Engineers are trying to imitate the amazing properties of the gecko's toes. Here's why.


Transcript

What lizards can teach engineers. I'm Bob Hirshon and this is Science Update.

Right now, geckos are best known for hawking car insurance. But they're also marvels of engineering. That's because gecko toes are packed with millions of tiny, spatula-shaped hairs, which allow the lizards to scamper effortlessly across ceilings and drop at will.

Electrical engineer and computer scientist Ron Fearing of the University of California at Berkeley is leading an effort to create artificial microfibers that act like gecko feet.

Ron Fearing:

And they don't slip, it's very high friction. But it doesn't quite work like the gecko because if you try to pull it off, it just pulls off really, really easily, actually much easier than the gecko.

That could provide good traction for tires and shoes. But a material that sticks and releases like gecko feet may have more colorful applications as well, from pain-free adhesive bandages to wall-climbing robots. I'm Bob Hirshon for AAAS, the science society.


Making Sense of the Research

Nature is a great engineer, in part because useful natural materials have millions of years to evolve and improve. Among many other things, scientists have attempted to imitate the strength and flexibility of spider silk, the hardness of human tooth enamel, and the fiber-optic properties of sea sponges.

This is often easier said than done, because natural materials can have seemingly contradictory properties—which makes them extremely useful but tough to copy. For example, take the surface of gecko feet: It's sticky enough to allow geckos to climb walls and ceilings, without using any kind of glue. Yet it releases its grip just as easily, which makes the gecko nimble on its feet and able to drop to the ground in an instant.

Basically, if humans could make this material, the next Spider-Man movie could save a lot of money on special effects. Fearing's team has gotten part way there. They've identified for sure what makes gecko feet stick so well: The unique spatula shape of the tiny, angled hairs, each only 200 billionths of a meter wide, allows each hair, or seta, to interact with individual molecules on the surface of the wall or ceiling. These interactions produce chemical attractions between the hair and the surface, which allow the hair to stick.

Because geckos pack so many setae into a small area (a million could fit easily in the area of a dime), the total effect of these chemical forces is amazingly strong. How strong? For the gecko, it means that it can hang its entire body from a ceiling by a single toe. Mathematically, if an average gecko used all of its 6.5 million setae at once, it could support over 290 pounds. (To put that in perspective, the average weight of a pro football player is about 250 pounds).

Just knowing how the gecko does it, however, doesn't make it easy to imitate. Because the hairs are so small, it takes a tremendous technological effort just to make them the right size. Furthermore, it's an enormous undertaking to make enough hairs, and pack them tightly enough, to simulate the surface of a real gecko foot. Their current model packs 42 million fibers per square centimeter. Finally, making the fiber material behave exactly like gecko setae has proven tricky. That's why they've figured out how to create friction, like a gecko, but not how to create the right adhesion. Fearing suspects that unlike gecko setae, his team's artificial fibers have a tendency to straighten out too easily, which breaks the chemical bond with the surface.

What they have now might already be useful, since high-friction treads can help tires and shoes navigate slippery surfaces. But it's that combination of stickiness, friction, and quick release that the researchers are really after. If they succeed, people may someday literally be climbing the walls.

Now try and answer these questions:

  1. What are the useful properties of gecko feet?
  2. Where do these properties come from?
  3. What's challenging about creating a material that resembles the surface of gecko feet?
  4. What applications can you imagine for this sort of material?

You may want to check out the October 20, 2006 Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: the truth about star naming, a practical plan for getting rid of fossil fuels, imitating gecko feet, worms in your diet, and why we have a bias against foreigners.


For Educators

Other Science Update radio programs about imitating nature include:


Engineers have been working to imitate spider silk for decades. Find out why, and how, in the National Geographic News articles Artificial Spider Silk Can Be Used for Armor, More, Lab Spins Artificial Spider Silk, and Gene for Key Spider Silk Protein Found

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