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March 05, 2012

Sixteen 16 square inches of DARPA Geckskin can stick to glass and support 700 pounds

The Z-Man programs aims to develop biologically inspired climbing aids to enable warfighters to scale vertical walls constructed from typical building materials, while carrying a full combat load, and without the use of ropes or ladders.

Geckos, spiders and small animals are the inspiration behind the Z-Man program. These creatures scale vertical surfaces using unique systems that exhibit strong reversible adhesion via van der Waals forces or hook-into-surface asperities. Z-Man seeks to build synthetic versions of these biological systems, optimize them for efficient human climbing and use them as novel climbing aids.

“Geckskin” is one output of the Z-Man program. It is a synthetically-fabricated reversible adhesive inspired by the gecko’s ability to climb surfaces of various materials and roughness, including smooth surfaces like glass. Performers on Z-Man designed adhesive pads to mimic the gecko foot over multiple length scales, from the macroscopic foot tendons to the microscopic setae and spatulae, to maximize reversible van der Waals interactions with the surface.

Recent activities include:

* Fabrication of Geckskin (stiff fabric impregnated with an elastomer) that “drapes” over a surface to maximize compliance with the surface while reducing compliance in the load direction, thus enabling increased adhesion.

* A proof-of-concept demonstration of a 16-square-inch sheet of Geckskin adhering to a vertical glass wall while supporting a static load of up to 660 pounds.


AMHERST, Mass. - For years, biologists have been amazed by the power of gecko feet, which let these 5-ounce lizards produce an adhesive force roughly equivalent to carrying nine pounds up a wall without slipping. Now, a team of polymer scientists and a biologist at the University of Massachusetts Amherst have discovered exactly how the gecko does it, leading them to invent "Geckskin," a device that can hold 700 pounds on a smooth wall.

Advanced Materials - Biomimetics: Looking Beyond Fibrillar Features to Scale Gecko-Like Adhesion




Gecko-inspired reversible adhesive materials with unprecedented force capacities are described by D. Irschick, A. Crosby, and co-workers. A simple scaling parameter, which describes both natural and synthetic reversible adhesive systems, leads to the development of unpatterned synthetic adhesive materials. Adhesive force capacities as high as 2950 N are achieved, not with fibrillar features, but through an integrated design with inextensible, draping fabrics, inspired by the skin-tendon morphologies found in the tokay gecko. The image presents an arm of a tokay gecko in front of a draping fabric.

Advanced Materials - Looking Beyond Fibrillar Features to Scale Gecko-Like Adhesion

12 pages of supporting material



Hand-sized gecko-inspired adhesives with reversible force capacities as high as 2950 N (29.5 N cm-2) are designed without the use of fibrillar features through a simple scaling theory. The scaling theory describes both natural and synthetic gecko-inspired adhesives, over 14 orders of magnitude in adhesive force capacity, from nanoscopic to macroscopic length scales.

Beyond its impressive sticking ability, the device can be released with negligible effort and reused many times with no loss of effectiveness. For example, it can be used to stick a 42-inch television to a wall, released with a gentle tug and restuck to another surface as many times as needed, leaving no residue.

Previous efforts to synthesize the tremendous adhesive power of gecko feet and pads were based on the qualities of microscopic hairs on their toes called setae, but efforts to translate them to larger scales were unsuccessful, in part because the complexity of the entire gecko foot was not taken into account. As Irschick explains, a gecko’s foot has several interacting elements, including tendons, bones and skin, that work together to produce easily reversible adhesion.

Now he, Bartlett, Crosby and the rest of the UMass Amherst team have unlocked the simple yet elegant secret of how it’s done, to create a device that can handle excessively large weights. Geckskin and its supporting theory demonstrate that setae are not required for gecko-like performance, Crosby points out. "It’s a concept that has not been considered in other design strategies and one that may open up new research avenues in gecko-like adhesion in the future."

The key innovation by Bartlett and colleagues was to create an integrated adhesive with a soft pad woven into a stiff fabric, which allows the pad to "drape" over a surface to maximize contact. Further, as in natural gecko feet, the skin is woven into a synthetic "tendon," yielding a design that plays a key role in maintaining stiffness and rotational freedom, the researchers explain.

Importantly, the Geckskin’s adhesive pad uses simple everyday materials such as polydimethylsiloxane (PDMS), which holds promise for developing an inexpensive, strong and durable dry adhesive.

The UMass Amherst researchers are continuing to improve their Geckskin design by drawing on lessons from the evolution of gecko feet, which show remarkable variation in anatomy. "Our design for Geckskin shows the true integrative power of evolution for inspiring synthetic design that can ultimately aid humans in many ways," says Irschick.
A card-sized pad of Geckskin can firmly attach very heavy objects such as this 42-inch television weighing about 40 lbs. (18 kg) to a smooth vertical surface. The key innovation by Bartlett and colleagues was to create a soft pad woven into a stiff fabric that includes a synthetic tendon. Together these features allow the stiff yet flexible pad to “drape” over a surface to maximize contact. (Credit: Photo courtesy of UMass Amherst)

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