Taking a cue from nature, British scientists have come up with a reusable adhesive tape they say is strong enough to dangle a man from the ceiling by the palm of his hand. The researchers modeled their tape on the hairy feet of the gecko, the wall-scrambling lizard famed for its gravity-defying stunts.
In 2000, Bob Full of the University of California, Berkeley, and Kellar Autumn of Lewis & Clark College in Oregon made the first measurements on the strength of the millions of tiny hairs on gecko feet that give the lizard its power to stick (ScienceNOW, 8 June 2000). Using all of its hairs at the same time, a gecko could support 280 pounds. Autumn and colleagues later demonstrated that the gecko gets its grip from intermolecular van der Waals forces between the submicrometer gecko hairs and solid surfaces (ScienceNOW, 27 August 2002). A number of research teams have been trying to develop adhesive tapes based on the same principle.
The new tape, developed by nanotechnologist Andre Geim and colleagues at the University of Manchester, is composed of a dense array of microscopic plastic pillars on a flexible layer of plastic. Each pillar adheres with less than a micronewton--holding a good-sized apple against the force of gravity requires one newton of force--but they work together making a strong bond between tape and surface. The pillars themselves are flexible enough to allow them to bend so they can stick to uneven surfaces but are not so flexible that they would clump together and fail to stick. The backing tape is also pliable enough to ensure that the maximum number of pillar tips come into contact with the surface. And because there's no goo, the tape can be reused many times. Geim reports the findings in the July issue of Nature Materials.
Full says the development is very exciting. "Uses are nearly unlimited," he says, "In addition to a general adhesive, it can be used to move computer chips in a vacuum, pick up small fibers, and design novel bandages. It can be like Velcro without needing the other side!" Moreover, he says, geckos are just one of many creatures with such adhesive arrays. Spiders and insects could provide the model for other adhesives with different uses, he says. "This is only the beginning if we wish to match nature."