Published: August 7, 2009
CLEMSON — Scientists from Clemson University and the University of Calgary have discovered that gravity triggers the remarkable ability of geckos to grip the slickest of surfaces, clinging at any angle on nearly any surface.
Scientists knew how geckos attached themselves to surfaces but did not know what caused them to deploy their unique gecko grip. The findings of evolutionary biologists Anthony Russell of Calgary and Timothy Higham of Clemson were published in the Aug. 5 online edition of the Proceedings of the Royal Society B. (http://rspb.royalsocietypublishing.org/content/early/2009/08/03/rspb.2009.0946.abstract)
A gecko’s foot is very special. Unlike squirrels that use claws, ants that secrete a sticky fluid or octopi that use suction cups, geckos use a mat of hairs, called setae. On its toes are pads covered with millions of the microscopic hairs that have even tinier split ends, called spatulae. This intricate design enables an electric force that attracts molecules to each other — the van der Waals force — to supply the energy to hold a gecko to a surface. The process was discovered in 2002, confirming a 40-year-old hypothesis.
"Scientists have figured out mechanism that allows geckos to cling to surfaces, but we had no answer for what caused them to trigger it," said Higham, a former Calagary student now an assistant professor of biological sciences at Clemson. "We found that body orientation is the key."
When a gecko is set on a slope of 10 degrees or more, out come the grippers. In their study, Russell and Higham tested a team of geckos climbing at a series of angles. Three of six geckos studied deployed their adhesive ability at 10 degrees. At 30 degrees all six used the traction mechanism. The three that applied the traction at 10 degrees slowed, the three that didn't kept their quickness.
Using the traction system comes at a cost: speed. Being surer-footed also means being slower-footed. The choice comes into play when avoiding danger. The system may play a role in survival.
For evolutionary biologists, studying animals in the field and laboratory offers insights into how special behaviors and systems evolved to solve problems: escaping danger, gathering food, storing and using energy, attracting a mate, raising young.
The ability to stick to and release from virtually any surface and do so over and over again intrigues material scientists. Applying gecko-tech could create shoes and tires that grip better and not wear out; design bandages and sutures that would stick better to wounds; give a better grip for tools in all kinds of environments, including space; and develop adhesives that could replace glues, solders, even Velcro.
“There are hundreds of species of geckos that use adhesion and there is considerable variation in the pattern of hairs on their toes,” said Higham. “This variation presents so many possibilities to learn from geckos and make use of it.”