story by John Dvorak
photo by Dr. Kellar Autumn
Nature has engineered some brilliant ways of making one thing stick to another. Tree frogs have tiny suction cups on their toes. Snails secrete a mucus that gives them traction. And most Island residents have seen their friendly household geckoes scamper up a window without leaving any trace of residue, like a living Post-It note. But how the gecko, which is not gluey or slimy, can adhere to surfaces smooth as glass has been a mystery since Aristotle first puzzled over their amazing ability in the fourth century BC. In 2002, a team of scientists from UC Berkeley, UC Santa Barbara and Lewis & Clark College solved the 2-millennia-old mystery: Microscopic structures on the gecko’s toe take advantage of a peculiar force at the quantum level.
In the very small realm of atoms, subatomic particles are popping in and out of existence all the time. When two objects are very close together, the narrow space prohibits some types of particles from popping in. Their absence produces, in essence, a quantum vacuum, and the two objects become attracted to each other. But for the phenomenon to occur, the two objects have to be much closer together than, say, your finger can get to anything it’s touching (no matter how hard you press). So how does the gecko get close enough to a surface?
Each toe of a gecko is covered with millions of bristles, called setae, and each is covered with thousands of microscopic hairs. When a gecko touches a wall or a window, these hairs reach into every nook of its surface, and the toe conforms to the microscopic contours. When there’s only the tiniest gap between the hair and the surface, quantum physics does the rest.
The millions of close attachments produce a lot of contact area; it is estimated that a full-grown gecko can press its body against a wall with 300 pounds of force, making the attempt to brush one away with a broom almost hopeless. The tiny hairs have another benefit: A gecko needs to retract them only a minuscule distance to break the quantum attraction and run off.
Aside from chasing bugs by your porch lights or running from a hungry cat, the gecko doesn’t make much use of its technology. But this microscopic marvel has inspired engineers to begin developing adhesive strips that will one day put Velcro to shame. The quantum force that holds a gecko to the wall may also even make possible a microscopic perpetual motion machine.