April 2, 2013
Gecko Grips Just As Good In Wet Habitats As In Dry Ones
Brett Smith for redOrbit.com - Your Universe Online
People have always been looking to nature for inspiration for everything from art to medicine. And in a new study by University of Akron researchers, the affable gecko could lead to a new kind of adhesive tape.
According to the study, which appeared in the Proceedings of the National Academy of Sciences (PNAS), geckos can cling to wet hydrophobic surfaces like plant leaves and stems just as well as they can to dry surfaces. However, the tiny lizards did have trouble sticking to wet, slick surfaces like glass.
Previous studies have shown geckos use small toepads with their tiny hairs to grip on to most surfaces. The fact geckos can cling to most surfaces, but not to wet glass, inspired the Akron team to investigate the gecko´s grip capabilities.
For the study, lead researcher Alyssa Stark and colleagues put harnesses on six geckos and put them on four different surfaces with varying "wettability," or degree of water resistance.
The gecko´s feet and toes were submerged in water on glass, plexiglass, transparent plastic, and Teflon.
Stark reported to National Geographic plexiglass and the transparent plastic "mimic the surface chemistry of the leaves geckos are really walking on in their natural environments.”
After the harnessed gecko was placed on the test surface, the team applied a gentle tug on the harness until the animal slipped, allowing the scientists to measure the animal's grip.
According to the report, a film of water that developed between the geckos' toes and wet glass reduced their ability to stick to the surface. However, on the plexiglass and plastic surfaces, the geckos' toes allow the formation of air pockets that allow their feet to stay dry and “sticky.”
The adhesive forces of the gecko toepads are made possible by the thermodynamic theory of adhesion and Van der Waals force, or the sum of attractive and repulsive interactions between two different surfaces. The force allows the lizards to grip on to surfaces in a variety of situations.
“Our findings suggest a level of versatility in the gecko adhesive system previously not accounted for and calls into question interesting evolutionary, ecological, and behavioral predictions,” the study authors wrote.
In their report, the researchers compared their findings "to the contact made by a terrestrial beetle underwater, where trapped air bubbles actually allow dry contact to occur on [water-resistant] surfaces.”
"The geckos stuck just as well under water as they did on a dry surface, as long as the surface was hydrophobic," Stark explained. "We believe this is how geckos stick to wet leaves and tree trunks in their natural environment."
She added the study´s results should have a “very obvious application" in the field of adhesives.
Stark told National Geographic the charismatic lizards have become a quite popular laboratory animal. However, they can often be difficult to work with.
"Part of their defense mechanism is to basically shoot fecal matter at you," she said. It's "pretty high velocity–I've definitely gotten nailed during experiments."