August 13, 2014
Secrets Behind Gecko’s Amazing Adhesive Skills Revealed In New Study
redOrbit Staff & Wire Reports - Your Universe Online
The uncanny ability of geckos to adhere to nearly any surface and even walk on ceilings is the result of a biological mechanism in their toes that the lizards can instantly turn on or off, according to new research appearing in the latest edition of the Journal of Applied Physics.
Geckos, along with spiders and some insects, appear to defy gravity with the way they are able to scale walls and cling to high surfaces, the Oregon State University researchers explained. This unique skill, it turns out, is the result of tiny branched hairs on the bottom of their feet known as “seta” that can be activated or deactivated at a moment’s notice.
These seta allow geckos to run at great speeds, evade predators and keep themselves alive – all without expending any extra energy. The new study examines the mechanics behind this unique adhesion system, which evolved independently in geckos, spiders and insects and has been around for several millions years, they added.
“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,” study co-author and assistant professor of engineering Alex Greaney explained in a statement Tuesday. “It was only very recently, in 2000, that Kellar Autumn and colleagues proved unequivocally that geckos stick using van der Waals forces.”
According to Stefan Sirucek of National Geographic, the van der Waals forces occur when electrons in one atom generate a magnetic field that stimulates and attracts the electrons in a second, neighboring atom. This phenomenon allows the gecko to use a system known as “dry adhesion” in order to attach to surfaces.
While van der Waals forces are the weakest type of interatomic forces there are, Greaney explained that geckos “are able to take advantage of them because of a remarkable system of branched hairs called 'seta' on their toes. These seta and their hierarchy can deform to make intimate contact with even very rough surfaces – resulting in millions of contact points that each are able to carry a small load.”
Greaney added that the angle and flexibility of the seta also play an important role in the adhesive process, which expends a minimal amount of energy. In fact, geckos are capable of darting across a ceiling with millions of seta on their feet becoming sticky as needed. The process which allows them to run at speeds of 20 body-lengths per second, and the forces provided by these foot-based hairs could support 50 times the geckos’ own bodyweight.
“Understanding the subtleties of the process for switching stickiness on and off is groundbreaking,” he said. “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 nonsticky, and this stickiness is activated through application of a small shear force. Gecko adhesion can be thought of as the opposite of friction.”
“What’s amazing is just how finely balanced and finely tuned this whole system is. We understand it at one level, and as we learn more and more about it, it turns out there’s a really subtle interplay of things going on,” Greaney, who co-authored the paper along with Congcong Hu of the OSU Computational Materials Research Group, told Sirucek.
While the seta have already served as the inspiration for robots capable of scaling walls, space-age adhesive materials and other types of technology, the researchers believe that their work will actually improve upon the design of tools based on the reliable suction produced by gecko feet, added Washington Post reporter Rachel Feltman.
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