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Inspired by geckos' toes, a new super-sticky tape is so strong that it can stick a person to the ceiling by just one hand. With a few tweaks, the prototype adhesive could have limitless applications - tyres with more grip, surgical tape and sticky gloves for rock climbers.
Geckos are famed for their wall-climbing antics and their ability to hang from the ceiling by a single toe. They can do this because their digits are covered in millions of tiny hairs that bond with any surface.
"Gecko feet are optimized for sticking through evolution," says Andre Geim of the University of Manchester, whose team have produced a postage-stamp-sized piece of synthetic gecko-tape .
The sample adhesive glued a toy Spiderman to the underside of a horizontal glass plate for several hours. "In theory, Spiderman should be able to stick forever," says Geim.
The tape is covered in millions of protruding plastic polymer 'hairs'. Each one is just two thousandths of a millimetre high, allowing them to get extremely close to the molecules that make up a surface. On dry surfaces the hairs are subject to weak attractions called van der Waals forces that occur between molecules. On wet ones, suction-like capillary action grips the hairs, Geim's team believes.
Because there's no glue, the surface is left clean when the tape is removed. Like its inspiration, the new tape is waterproof and re-useable.
"You could use it to hang pictures without leaving any marks," says Metin Sitti, a mechanical engineer from Carnegie Mellon University, Pittsburgh, who is also designing gecko-inspired adhesives. There are no harmful residues, so you could use it to rejoin tissue during surgery, he says.
"It shows the importance of biological inspiration," says biologist and gecko enthusiast Bob Full from the University of California, Berkeley. The applications "are nearly unlimited".
The sticking point
"We joked that we should have made more tape and suspended one of the students out of the window," Geim quips, "but this would have been a waste of resources - of the tape, not the student." A one-metre-squared piece of gecko tape would cost tens of thousands of pounds to produce, so the team needs to find methods for cost-effective mass production.
The prototype tape only stayed sticky for seven or eight attachments. Geckos, on the other hand, re-use their gummy feet throughout life.
To make the tape more re-useable, "we need techniques that will mimic the true complexity of gecko hairs," says Sitti. Gecko hairs have split ends, or " hairs on hairs", he explains. The challenge is to manufacture theses delicate structures synthetically.
Different materials could also be used to improve hair strength. Kevlar, the material used to make bulletproof vests, might provide an alternative, speculates Sitti.
1. Geim, A. K. et al. Microfabricated adhesive mimicking gecko foot-hair.
Nature Materials, published online, doi:10.1038/nmat917 (2003).
File Date: 06.02.03
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