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 setae's adhesion and friction it was essentially the same on the two surfaces. And when the team compared the adhesion of setae that were moving too fast to form water bridges with that of slowly moving feet that could possibly form water bridges, there was no difference. The geckos were not supplementing their van der Waals attachment forces with capillary forces from water bridges. So how were they holding on tighter?
Graduate student Michael Prowse decided to take a closer look at the material properties of the reptile's feet. 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. The team decided to measure the setae's softness and how it changed as the humidity rose.
Repeatedly stretching and releasing a strip of setae at three different rates (0.5, 5 and 10 Hz) in environments ranging from 10% to 80% humidity, Autumn's team measured the force transmitted through the strip to calculate the strip's elastic modulus – how much elastic energy is stored – to see how it changed. As the humidity rose, the elastic modulus decreased by 75% and the strip of setae became softer. So the strip of setae became more deformable as the humidity rose, but could the increased softness explain the gecko's improved attachment under damp conditions?
Puthoff built a mathematical model to see if softer, more deformable, setae could explain the gecko's improved attachment at high humidity and found that it did. 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.
IF REPORTING ON THIS STORY, PLEASE MENTION THE JOURNAL OF EXPERIMENTAL BIOLOGY AS THE SOURCE AND, IF REPORTING ONLINE, PLEASE CARRY A LINK TO: http://jeb.biologists.org
REFERENCE: Puthoff, J. B., Prowse, M. S., Wilkinson, M. and Autumn, K. (2010). Changes in materials properties explain the effects of humidity on gecko adhesion. J. Exp. Biol. 213, 3699-3704.
This article is posted on this site to give advance access to other authorised media who may wish to report on this story. Full attribution is required, and if reporting online a link to jeb.biologists.com is also required. The story posted here is COPYRIGHTED. Therefore advance permission is required before any and every reproduction of each article in full. PLEASE CONTACT email@example.com
When Air is in Short Supply - Shedding light on plant stress reactions when oxygen runs short
23.03.2017 | Institut für Pflanzenbiochemie
WPI team grows heart tissue on spinach leaves
23.03.2017 | Worcester Polytechnic Institute
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
23.03.2017 | Life Sciences
23.03.2017 | Power and Electrical Engineering
23.03.2017 | Earth Sciences