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Gecko tape is an experimental material developed in 2003 by an international team of scientists from the UK and Russia. It is a tape surface covered with nanoscopic hairs intended to maximize surface area. Gecko tape has not yet been perfected, but when it is, it could allow humans to walk on walls and ceilings like geckos.
The gecko is an impressive creature. It can support its entire weight on a horizontal wall with only a single toe, which is minuscule compared to its body size. It can move faster than a meter per second along a molecularly smooth surface such as polished glass. The secret is in the van der Waals force, an intermolecular force that emerges when molecules behave like small magnets that get attracted towards each other. To exploit it well requires a lot of surface area, which gecko feet have.
Gecko feet are covered in little hairs, which use capillary action as well as the van der Waals force to stick to walls. Each hair is about 200 to 500 nanometers wide. Only in the past decade or so has it become possible for scientists to fabricate an artificial material like gecko tape with hairs of such small size. The adhesive power of a centimeter of gecko foot is about 10 Newtons, similar to that of gecko tape.
Gecko hairs are made of keratin, but scientists used the fiber polyimide to create their gecko tape because it is easier to work with at that scale. Originally, they used a silicon wafer as the substrate for the hairs in gecko tape, but it was found that flexible substrates are able to better compensate for uneven surfaces, increasing the adhesion power many times over.
A problem with the artificial gecko tape is that, unlike with genuine geckos, it runs out of sticking power after a few uses. This is because polyimide is not hydrophobic like keratin, and atom-thin films of moisture on surfaces cause its hairs to eventually get wet and cluster together. Keratin hairs on gecko feet allow the animal to run across moist ground and then immediately up a flat surface such as glass, much to the amazement of materials scientists. The gecko tape project is part of a larger field called biomimetics, in which scientists and engineers use animals as inspiration for new materials and devices.
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