As far as lizards go, geckos are pretty amazing. Terrifically successful -- there are 850 different gecko species -- the gecko body is also quite energy-efficient. One species, the Frog Eyed Gecko from the Gobi desert, can move more than three times as far per unit energy than other creatures of similar size. But what makes geckos truly amazing is their uncanny ability to stick to pretty much any surface. Gecko feet adhesion "leaves no residue, is directional, detaches without measurable forces, is self-cleaning, and works underwater, in a vacuum, and on nearly every surface material and profile." In 2002, biologist Kellar Autumn at Lewis & Clark University in Oregon discovered that the adhesion came from van der Waals Forces, minute molecular-scale attraction, (spider feet work in a similar, albeit simpler, manner). Each gecko foot is covered with millions of tiny hairs, or setae, which branch in to nanoscale tips, or spatulae; each seta is strong enough to lift 20mg. The combined adhesive power of a gecko's four feet is over 90 lbs.
Autumn's lab has continued to work on revealing the secrets of gecko feet, and yesterday unveiled their latest discovery: why gecko feet actually get cleaner in use. It turns out that the solution wasn't in biochemistry, but in biogeometry. The shape and structure of the spatulae will discard small dirt particles even as they continue to adhere to more stable surfaces. The implications of this discovery are wide-ranging. As Autumn puts it:
This means that synthetic self-cleaning adhesives could be fabricated from a wide variety of materials. The possibilities for future applications of a dry, self-cleaning adhesive are enormous. We envision uses for our discovery ranging from nanosurgery to aerospace applications.
Or, as he's quoted in the Times, "We're not talking about just the glue of the future, we're talking about the screw of the future." Working with Ron Fearing at UC Berkeley, Autumn's research has already led to larger-scale synthetic versions of gecko setae. In 2003, they managed to create artificial setae with adhesion on the order of 0.5 Newton per square centimeter; their eventual goal is adhesion force equivalent to gecko setae, 10 Newton per square centimeter.
One feature of systems of millions of tiny attraction points is that they can be both incredibly strong and readily detached. A gecko is able to peel its feet up and run at a good clip, or stand still and be nearly impossible to pull from a window or wall. As Autumn suggests, geckomimetic adhesive could be of enormous value in object construction, as the adhesion force could be quite strong. At the same time, being able to simply peel apart components -- with no chemical residue -- would enhance our ability to design for disassembly, an important part of cradle-to-cradle thinking.