The toepads of a gecko rely on a quantum effect to maintain their adhesiveness

Self-cleaning sticky tape takes lead from geckos' toes

A self-cleaning adhesive tape inspired by geckos’ feet can stay sticky even on dusty and dirty surfaces.

By mimicking a gecko’s toepad, researchers from the USA and Germany have managed to create a dry material covered in clinging microscopic hairs that automatically rids itself of larger dust particles through friction, while smaller grains disappear into grooves between the hairs.

The tape could be used as an alternative to Velcro or to produce first aid bandages that can be opened and closed several times, say the researchers, and the work could even lead to new methods for printing electronics on complex surfaces.

"Our work has implications for use of this synthetic gecko-adhesive in a variety of industry sectors including defence, consumer products, sports, automotive, medicine, aerospace and robotics applications," said Professor Metin Sitti, a mechanical engineer from Carnegie Mellon University (CMU) and author of a paper that appears in the Journal of the Royal Society Interface today.

It took scientists many years to fathom how geckos are able to scurry up vertical walls and even hang upside down from ceilings. The lizards employ no glue or suction devices. Instead, millions of tiny hairs on each toe exploit an electrical quantum effect that maintains a firm grip even on polished glass.

Molecules and atoms exert a weak attraction when they are brought extremely close together due to Van der Waals forces, which involve the random movement of electrons. Because of the large number of microhairs on its feet, the gecko is able to apply the effect until it greatly outweighs gravity.

The new sticky material developed by the team, which includes researchers from the Karlsruhe Institute of Technology in Germany, employs artificial elastic mushroom-shaped microhairs to mimic the toepads of the gecko.

"We performed contact self-cleaning experiments with three different sizes of mushroom-shaped elastomer microfibers and five different sizes of spherical silica contaminants,” said Prof Sitti.

“Using a load-drag-unload dry contact cleaning process similar to the loads acting on the gecko foot during climbing, our fully-contaminated synthetic gecko-adhesive could recover lost stickiness and lost adhesion at a rate comparable with that of the gecko.”

Prof Sitti is also using his work with geckos to inspire new methods to print electronics on complex surfaces. Along with researchers, Prof Sitti developed a reversible adhesion method for printing electronics on a swath of complex surfaces such as clothing, plastic and leather.

His team designed a square polymer stamp with pyramid micro-tips that allows them to control adhesion strength.

"We are very close to commercialising the gecko-inspired synthetic adhesives for use in many industry sectors," said Prof Sitti, also founder and president of nanoGriptech, a 2009 CMU spinoff company.

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