Geckos Can Turn Their Sticky Toe Hairs On and Off When Hanging Out

Geckos have the amazing ability to stick to almost any surface--hanging vertical on walls and even upside down on ceilings. Now, though, scientists have taken a closer look at this creature's talent and have found that the animal can turn the "stickiness" of its toe hairs on and off in order to be able to run while still adhering to surfaces.

"Since the time of the ancient Greeks, people have wondered how geckos are able to stick to walls-even Archimedes is known to have pondered this problem," said Alex Greaney, one of the researchers, in a news release. "It was only very recently, in 2000, that Kellar Autumn and colleagues proved unequivocally that geckos stick using van der Waals forces."

Van der Waals forces are weak atomistic level forces. Geckos take advantage of these forces through a system of branched hairs, called seta, on their toes. These seta can deform to make contact with even very rough surfaces, resulting in millions of contact points that can carry a small load.

Yet geckos don't just stick. They have to be able to unstick themselves in order to move across a surface. That's why scientists investigated the process a bit more closely.

"Understanding the subtleties of the process for switching stickiness on and off is groundbreaking," said Greaney. "By using mathematical modeling, we've found a simple, but ingenious, mechanism allows the gecko to switch back and forth between being sticky or not. Geckos' feet are by default nonstick, and this stickiness is activated through application of a small shear force. Gecko adhesion can be thought of as the opposition of friction."

The findings reveal how geckos can unstick without expending energy. This, in turn, may result in practical applications for the process, such as creating climbing robots and synthetic adhesives.

"While we don't envision Mission Impossible sticky gloves, which are inspired by or based on the concept of gecko adhesion, we envision that robots will use gecko adhesion in extreme environments in the future," said Greaney.

The findings are published in the Journal of Applied Physics.