Human adhesives are famed for their fallibility. Gooey glues soon lose their grip, are easily contaminated and leave residues behind. But not gecko feet. Geckos can cling on repeatedly to the smoothest surfaces thanks to the self-cleaning microscopic spatula-shaped hairs (setae) that coat the soles of their feet. Back in 2002, Kellar Autumn found that these dry hairs are in such intimate contact with surfaces that the reptiles 'glue' themselves on by van der Waals forces with no need for fluid adhesives. More recent studies had suggested that geckos might benefit from additional adhesion in humid environments through capillary action provided by microscopic droplets of water sandwiched between setae and the surface. But Autumn wasn't so sure, so he and his lab at Lewis and Clark College and the University of Washington, USA, began testing gecko grip to find out how increasing humidity helps them hold tight Autumn publishes his team's discovery that humidity helps geckos grip tighter by softening the surface of their feet on 15 October 2010 in The Journal of Experimental Biology at http://jeb.biologists.org.
Knowing that geckos replace lost setae when they moult, Autumn, his postdoc Jonathan Puthoff, and Matt Wilkinson collected patches of the 'sticky' hairs from gecko feet and attached them to a mechanical testing device, known as 'Robotoe', that reproduces the way the reptile drags its foot as it contacts a surface. Dragging the setae across two surfaces (one that repelled water and another that attracted water) at different velocities and in environments ranging from 10% to 80% humidity, the team tested whether microscopic water bridges formed in high humidity were helping the geckos hang on. They reasoned that if the reptiles were using microscopic water bridges then the setae would bond more tightly to the surface that attracted water than the surface that repelled water. But when they measured the set
|Contact: Kathryn Knight|
The Company of Biologists