Gecko's Sticky Secret Is A Hairy One
Sun Herald
Sunday June 15, 2003
Is it only geckos that hang on to surfaces with their hairs?
No, skinks and some insects use a similar trick, but geckos are the best at it.
PEOPLE have long pondered how geckos climb sheer walls - even Greek philosopher Aristotle wondered about it in the fourth century BC.
Now British scientists have made an adhesive tape based on the way geckos cling to surfaces.
The breakthrough came last year when US researchers discovered the geckos' secret.
Rather than making their feet sticky with a kind of biological glue, as some insects do, or relying on the surface tension of water, like frogs, geckos' feet are completely dry and very hairy.
Barely half a micrometre wide (that's less than a thousandth of a millimetre), the hairs are packed in tightly there are about 2 million per gecko. To give even more points with which to contact the surface, each seta (hair) branches into roughly 1000 tips called spatulae.
When objects are this small, interactions between individual molecules become significant. Gecko setae hold on to a surface using what is called V an d er W aals forces . This is a weak electrostatic force, where positive attracts negative.
It's a bit like the way your hair might stick to a plastic comb on a dry day, only on a much, much smaller scale.
Regardless of how smooth a surface looks, geckos find plenty to grab on to because their hairs are small enough to fit between particles.
This created a problem for the scientists how do they make such fine hairs? They have to be thin but not fragile, flexible rather than stiff, and they can't stick to each other.
After a great deal of trial and error, described in a recent edition of Nature Materials, Professor Andre Geim and his team of nanotechnologists at the University of Manchester made a piece of film covered in tiny plastic pillars. They called it ``gecko tape".
``We have proven that the gecko mechanism is scalable," Geim said. This means the more hairs, the more weight can be supported.
The team hopes to solve the problems of durability and matting that their prototype suffers by making the hairs out of keratin. This, like human hair, is what gecko setae are made of.
As for the applications of gecko tape, Geim said: ``For the moment, you can imagine everything you want that requires any tackiness."
But one question remains: if geckos hang on so tightly, how come they're not stuck permanently?
``It's the same way you unstick Velcro tape," Geim said. ``Geckos peel their feet from one edge when they want to move."
HANGING BY THREADS
* A gecko climbs up a pane of glass.
* Its feet are covered with ridges for gripping even the smoothest surface.
* They might look like figerprints, but at 270-times actual size, it's clear each ridge is a carpet of fine hairs.
* The hairs are less than a thousandth of a millimetre wide. The tip of each hair splits into 1000 tiny branches small enough to hang onto individual molecules in the glass.
* This 40g toy hangs from a horizontal piece of glass in the laboratory of Professor Andre Geim who covered its hand with gecko-tape.
© 2003 Sun Herald