01 Jun 2006
-
A gecko can grip fast to the smoothest of walls
What drives a gecko lizard up the wall? The answer lies in an amazingly complex surface texture on the creature’s toes that can grip fast to the smoothest of walls – even to glass. Scientists at the ATC have probed the gecko’s secrets and have recreated their own version of lizard sticking power: an artificial surface that grips tightly without glue or pressure.
The results have aroused interest across a number of BAE Systems businesses who have suggested applications ranging from aircraft tethers to ‘Spiderman’ infantry. The gecko’s ability to scurry up vertical walls and windows has bemused people for centuries. The reptile’s antics have inspired flights of fancy such as the familiar wall climbing, comic book characters.
So how does the lizard grip so tightly yet still have the freedom to move? It was once thought that miniature vacuum suckers were at work but the answer turns out to be much more complicated. The soles of each of the gecko’s feet are patterned with millions of tiny hairs with ‘split ends’. At the tip of each is a mushroom shaped cap less than one-thousandth of a millimetre across. These microscopic features ensure that, whatever the roughness underfoot, the lizard’s toes are always in very close contact with the surface beneath– so close that molecular forces of attraction create the grip. The grip is released by a peeling action when the animal lifts its foot, which breaks the bond. The attractive force for each hair is tiny but when multiplied by a few million for all four of the animal’s feet there is more than enough grip to support its weight. And yes…it has been calculated that if human palms were covered with the same material they could support an average person’s weight.
Recognising that such bonding power could have tremendous engineering potential, ATC scientists set out to make their own version of the gecko foot. Some of the applications suggested by BAE Systems businesses include instant repair patches for holed structures (such as fuel tanks and aircraft skins), access panels without fasteners, rapid attachment of armour or stealth panels to platforms, improved crawler robots, personal safety harnesses, new building materials and even the tethering of aircraft to carrier decks.
Using their micro engineering, clean room facilities, the ATC have created layers comprising thousands of microscopic stalks with splayed tips closely resembling the mushroom headed gecko hairs. The strength with which these polymer layers stick to glass has been measured using a purpose built balance. A pull-off force of 3,000 kg per square metre has been measured. This means that a sheet of this artificial gecko material just over 60 centimetres square could be used to suspend the weight of an average family car.
“We have very quickly been able to make artificial gecko bonds as good as any one has managed so far” says Jeff Sargent, materials specialist at the ATC. “We believe the process can be tailored to suit a range of applications depending on the kind of re-adhesion properties needed. We can’t quite imitate the gecko yet in coping with a range of different surface roughness - more work is needed, but we believe our fabrication method can be scaled to achieve this far more readily than methods tried by others” he says.
Jeff and his colleagues already have an eye on possible future enhancements which could lead to a gripping force that can be controlled and varied at will to create and release bonds without moving the surfaces. This would outperform even the athletic gecko.
