Device could create real-life Spiderman
Engineers have used the adhesive power of water to create a device capable of sticking to glass, wood and even brick. Photo: AFP/GETTY
Engineers at Cornell University, in New York, have invented a palm-sized device that uses the adhesive power of water to create a reversible adhesive bond capable of sticking to glass, wood and even brick.
The researchers, whose work was funded by the US military, hope to use their invention to develop gloves and shoes that will allow the wearer to climb up even the blankest of walls.
The technology was inspired by the Palmetto tortoise beetle from Florida, which uses surface tension from tiny droplets of oil secreted by glands at the top of its legs to clamp its shell down onto a leaf when it is under attack from ants.
Once attached, the beetle is capable of holding loads 100 times its own weight.
Professor Paul Steen, a biomolecular engineer at Cornell University, found that by pumping tiny droplets of water through microscopic holes in a flat plate, he could exploit the surface tension of the water to "glue" the plate to another surface.
Using an electrical field to pump the water through the holes, he was also able to reverse the process, allowing the plate to become unstuck on demand simply by changing the electric field.
While each droplet is only able to hold a small force, together they are able to hold a far greater force. An early version of the device can hold weights of around one ounce using water droplets about a sixth the size of a pinhead.
Professor Steen has found that the more droplets there are between surfaces, the stronger the adhesion becomes.
He found that by making the holes, and so also the water droplets, smaller it was possible to get more droplets on the surface of the device and so increase the amount of weight it is possible to hold.
He believes that by using microscopic water drops, around 1,000 times smaller than the width of a human hair, it would be possible to create a 3 inch wide pad that could hold up weights up to 20 stone.
He said: "What we have is the ability to make strong but reversible bonds and this idea of creating clothing that can give a Spiderman type ability comes from that.
"At the moment the only way it is possible to climb up the side of buildings is to use suction cups which require ungainly and heavy vacuum pumps and a lot of power. We are exploiting the cohesion of water rather than having to create the suction ourselves.
"Epoxy-strength adhesive that is switchable doesn't exist, but we realised the beetle was showing us the way. Our inspiration comes from the beetle, but our control of the "bond" is quite different."
The device consists of a flat plate covered in holes with a small reservoir of water beneath. When an electrical field is applied from a common 9 volt battery, water is pumped through the holes to form droplets on the surface that then cling to any surface they touch.
The water molecules act like a bridge between the two surfaces binding them together at the edges of each droplet.
During testing Professor Steen and his colleague Michael Vogel found that it was possible to adhere to wood, plastic, glass, metal, brick and sandpaper.
Their research has been funded by Defence Advanced Research Projects Agency (DARPA), which is the research and development wing for the US military.
Such a device could prove useful for special forces looking to scale buildings quickly as the ability to reverse the grip of the device makes it easy to release limbs independently.
With such small power demands, the device could easily be incorporated into clothing, according to Professor Steen.
"At the moment we don't know what DARPA envisages the end use of our research will be, but having the ability to stick and release a load easily could have a number of uses."
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