Why geckos have superglue feet
Washington: A new study sheds light on why geckos are able to cling on repeatedly to the smoothest surfaces.
Kellar Autumn 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.
The team discovered that self-cleaning microscopic spatula-shaped hairs (setae) that coat the soles of their feet help the reptiles stick to any surface with utmost ease.
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.
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 setae's adhesion and friction it was essentially the same on the two surfaces.
Knowing that setae are composed of keratin and keratin is softened by high humidity, Autumn wondered whether having softer setae could improve the reptiles'' contact with surfaces and increase their van der Waals adhesion.
Puthoff found that softer, more deformable setae could explain the gecko's improved attachment at high humidity. Not only did increased softness strengthen the contact between the setae and the surface but also it made it easier for the reptile to peel its foot off.
So instead of improving gecko's attachment through microscopic bridges, higher humidity softens the setae that coat the reptile's feet to help them hold fast and peel free with ease.
The study was published on 15 October 2010 in The Journal of Experimental Biology.