Nanotube Adhesive Sticks Better Than a Gecko's Foot

From Rensselaer Research Review Summer 2007

[According to Pulickel Ajayan, the Henry Burlage Professor of Materials Science and Engineering at Rensselaer,] “Several people have tried to use carbon nanotube films and other fibrous structures as high-adhesive surfaces and to mimic gecko feet, but with limited success when it comes to realistic demonstrations of the stickiness and reversibility that one sees in gecko feet. … We have shown that the patchy structures from micropatterned nanotubes are essential for this unique engineering feat to work. The nanotubes also need to be the right kind, with the right dimensions and compliance.”

“Geckos inspired us to develop a synthetic gecko tape unlike any you’ll find in a hardware store,” Dhinojwala says. “Synthetic gecko tape uses ‘van der Waals interactions’ — the same interactions that hold liquids and solids together — to stick to a variety of surfaces without using sticky glues.”

The material could have a number of applications, including feet for wall-climbing robots; a dry, reversible adhesive in electronic devices; and outer space, where most adhesives don’t work because of the vacuum.

How Gecko Toes Stick

From the American Scientist

The powerful, fantastic adhesive used by geckos is made of nanoscale hairs that engage tiny forces, inspiring envy among human imitators

Kellar Autumn

Geckos can run up smooth walls or cross inverted surfaces with seeming ease. How do they do it? Author Autumn describes recent research in his lab and others that tells the tale. It turns out that gecko toe pads are sticky because they contain extraordinary structures that act together as a smart adhesive. But gecko toes work nothing like pressure-sensitive adhesives (found on adhesive tape), which are soft enough to flow and make intimate, continuous surface contact. Instead, gecko toes bear ridges covered with arrays of stiff, hairlike setae. Each seta branches into hundreds of tiny endings that touch the surface and engage intermolecular van der Waals forces. Together, the 6.5 million setae on a 50-gram gecko generate enough force to support the weight of two people. Furthermore, gecko toes detach within milliseconds, stick to nearly every material, and neither stay dirty nor self-adhere.

See also Kellar Autumn's page, which also includes a slide show on the various ways animals have evolved to adhere to surfaces.

Biomimetics

Economist.com reports on Technology that imitates nature.

Engineers are looking increasingly toward nature as an inspiration for technological innovation. The field of biomimetics will soon be more accessible to engineers, as scientists at the Centre for Biomimetic and Natural Technologies at the University of Bath in England are developing a "biological patent" database, wherein natural structures with potential technological significance (like the hook and loop structure that became Velcro) are archived. That a structure exists in nature, having necessarily been tested and refined in order to survive, automatically gives it a leg up on human-generated concepts. A gecko can defy gravity and crawl on the ceiling because of a weak intermolecular attraction between hair-like setae on their feet that, if reproduced synthetically, could yield revolutionary new adhesives. Robotic engineers, especially keen observers of nature, often look to animals to create a robot's pattern of motion that would enable it to negotiate terrain such as the moon too rocky to be traversed by a robot on wheels. While nature has yielded many unlikely technical advances, the Centre's Julian Vincent believes we have only scratched the surface, and that the flow of information between the biological and engineering communities needs to be reversed, so that instead of a newly discovered structure being shopped around for potential use, "biomimetics should be providing examples of suitable technologies from biology which fulfill the requirements of a particular engineering problem.