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“The two electron fields do a kind of quantum dance with each other and draw the gecko and the wall together.”
In the 17th century, a Hindu warlord called Shivaji purportedly strapped gecko lizards to his hands in order to scale the walls of the cliff-top fortress where his father was imprisoned. While the story is suggestive more of tall tale than of technological innovation, the ability of the gecko to zip across walls and ceilings without slipping or leaving a trail of slime is real. Now, biomedical products based on the special properties of gecko feet may be only a few years away.
In January, scientists at the University of California, Berkeley, announced that they had made a material that closely mimics gecko grip. The so-called gecko tape adheres not when it’s pressed, but when it slides across a surface. Ron Fearing, the UC Berkeley engineer who developed the new material, says that because it requires virtually no force to apply or remove, and works on wet surfaces, the material could be used for a wide range of medical applications, from holding dentures in place to replacing clamps in operating rooms. “This sort of material can cause a lot less damage,” he says.
Fearing is not the only researcher studying the gecko with an eye on biomedicine. Researchers at the Massachusetts Institute of Technology announced in February that they had developed a tape that replicates the nanoscale hairs on gecko toes. Unlike Fearing’s material, the MIT tape comes with a layer of ordinary glue. The biodegradable, hybrid tape could be used to patch intestines after surgery or very small incisions following minor operations. “It’s a really exciting field of nanotechnology and biomimicry,” says Jeff Karp, director of the Laboratory for Advanced Biomaterials and Stem Cell-Based Therapeutics at the Harvard-MIT Division of Health Sciences and Technology.
Gecko research is picking up speed. Made of the same polymer used to make Zip-Lock bags, the new material from UC Berkeley comes less than eight years after scientists first discovered definitively how it is that geckos do what they do. When Fearing’s collaborator, Kellar Autumn, a biology professor at Lewis and Clark College in Portland, Oregon, set out to decode gecko traction in 2000, serious scientists still thought it was because moisture in gecko toe pads was able to stick to microscopic films of water. But with the aid of hydrophobic semiconductors, Autumn proved that geckos walk on walls because millions of tiny branching hairs on gecko feet (there are over 40 million per square centimeter) take advantage of a molecular-level phenomenon called van der Waals force. In short, it’s the shape of the gecko hairs, not a natural glue or a hydrophilic reaction, that gives geckos their peculiar gift.
Seen through an electron micrograph, the tips of the hard hairs on geckos’ feet fork into billions of tinier nanoscale hairs made of beta-keratin, the same substance found in birds’ beaks. When these structures, which scientists call spatulae, make contact with a surface, van der Waals force kicks in. Imagine the electrons whizzing around an atom making a kind of cloud. Now, imagine the electron cloud on a gecko’s hairs pulsing at a particular frequency harmonizing with the wall’s electron cloud. “The two electron fields do a kind of quantum dance with each other and draw the gecko and the wall together,” Autumn explains.
This spring, Fearing and his team will take his “gecko tape” to Autumn’s lab in Oregon and test it on a device of Autumn’s creation that he’s dubbed the Robotoe. It’s a machine designed to simulate the motion of a gecko down to the nanometer scale. Fearing’s material will be tested for how well it attaches and detaches as it moves across a surface. The researchers will also be using the Robotoe to solve an outstanding riddle of the gecko that could be important if gecko tape is going to find biomedical applications: How is it that gecko feet are self-cleaning? Unlike other animals, geckos waste hardly a minute removing dirt from their soles.
After that, Autumn says, scientists will have to figure out how to make large swaths of gecko tape that stay sticky. Currently, Fearing’s gecko tape loses adhesion as it grows with size. When these problems are solved, a whole slew of biomedical applications, such as adhesives for prosthetic limbs, could soon follow. Gecko gloves and the ability to climb walls like a lizard, or a 17th century Hindu prince, might not be far behind.
