Scientists have developed the first adhesive tape that sticks to a surface as firmly as the toes of a gecko and also possesses similar self-cleaning properties.
Using such a tape, food packagings or bandages might be opened and closed several times, said researchers from the Karlsruhe Institute of Technology in Germany and the Carnegie Mellon University in Pittsburgh.
When moving forwards, the gecko's toes drag across a part of the surface. As a result of this lateral friction contact, larger dirt particles are removed.
Smaller particles deposit among the setae on the sole and in the skinfolds below.
In an experiment, the researchers showed that both mechanisms provide for 95 per cent of the self-cleaning effect.
"This effect is determined by the ratio between particle size and setae diameter," said Dr Hendrik Holscher of KIT's Institute of Microstructure Technology (IMT).
For their experiments, the scientists used elastic microhairs of variable size. Instead of dirt particles, they employed glass spheres of micrometre size and distributed them on a smooth plate.
To simulate the steps made by a gecko, they pressed an artificial adhesive tape covered by microhairs onto the plate, shifted it laterally, and lifted the tape off again. This "load-drag-unload" cycle was repeated several times. In parallel, adhesive force was measured.
When the diameter of the spheres exceeded that of the microhairs, the adhesive force disappeared after the first contact - as in case of an ordinary adhesive tape.
After eight to ten test cycles, however, the gecko-inspired adhesive tape reached 80 to 100 per cent of its original power again.
"In the long term, this effect might be used to develop a low-cost alternative to hook and loop fasteners," Holscher said.
"Such a tape might be applied in the sports sector, in medicine, automotive industry or aerospace technology," added Metin Sitti, Professor of the Carnegie Mellon University.
When the size of the spheres was smaller than the diameter of the microhairs, the researchers succeeded in restoring one third of the original adhesive force only.
"For the perfect gecko-inspired adhesive tape, we therefore need fibres in the nanometre range, which are smaller than most dirt particles," said Dr Michael Rohrig, IMT scientist.
