Tokay gecko looking threatening

Researchers create new synthetic gecko foot

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An international team of researchers have developed a double-sided synthetic gecko foot which works under damp conditions, and changes its properties in response to acidity.

Geckos can effortlessly adhere to any surface except Teflon, even in slippery rainforests and on slick surfaces like glass windows. This remarkable property is thanks to van der Waals forces between the surface and the bristly, elastic hairs on their feet.

Since this gift was explained in 2002, scientists have been trying to replicate the sticky quality of gecko feet by creating artificial bristles from carbon nanotube arrays, polymers manufactured in microfibres and other materials. Recreating gecko feet could be helpful in the development of dry glues, as well as in biomimetic robotics.

Previously, scientists have developed adhesives inspired by gecko feet which can stick and unstick to surfaces, adapting to changes in light, temperature and magnetic field. For instance, Stickybot – a robot developed at Stanford University – is capable of climbing up glass using feet that mimic those of geckos.

Despite some success, these synthetic gecko feet tend to fail under damp conditions.

Scientists based at the Chinese Academy of Sciences, the University of Salento and Imperial College London have created a double-sided adhesive which not only mimics a gecko’s ability to stick and unstick to surfaces, but works in humid conditions.

The method integrates nanostructured hydrogel fibres on an inorganic membrane. The hydrogels work underwater, swelling and shrinking in response to changes in pH. These expansions and contractions alter the friction and stickiness levels of the synthetic foot.

The team then created a double-faced membrane with hydrogel nanofibres on both sides, where the two faces of the material can stick and slide independently of each other. Their experiments showed that the material exhibits ultra-high friction and adhesion in acidic liquids, but rapidly switched to ultra-low friction and stickiness in an alkaline environment.

“For the first time, we report the design, synthesis, and testing of a novel double-sided synthetic construct that relies on nanohydrogel brushes to provide simultaneous friction switching on each side of the membrane,” the researchers report in the Journal of Physical Chemistry C.

The researchers hope that this could be incorporated into biosensors, such as to track the acidity of lakes, or could be a useful component in underwater robotics.

“This novel design opens a promising route for the development of new solutions for intelligent devices, which can adapt to multistimulus-responsive complex environments.”

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