For years scientists have tried to make strong, reusable adhesives by mimicking the microscopic hair-like structures on gecko toes that give the lizard its climbing ability. But those structures are hard to make, limiting the adhesives’ size to a few centimeters. Now researchers from the University of Massachusetts, Amherst, have come up with a different gecko-inspired structure that works even better. They have created a reusable adhesive fabric that can be easily and cheaply made tens of centimeters wide and is three times stronger than gecko feet.
Hand-sized patches of the material cling to smooth glass even while holding 300 kilograms of weight, the researchers report in the journal Advanced Materials. This is much more than any other reversible adhesive can hold, they say. The pads can be peeled off and reused over 100 times. Such materials could be used to attach TVs to a wall, make robots that scuttle up walls and windows, and hold together computer and car parts.
A good adhesive needs two conflicting traits, says Ali Dhinojwala, a professor of polymer science at the University of Akron in Ohio. It must be soft so it can conform to a surface, but also stiff enough to hold weight. The fibers on gecko toes fit the bill: they are made of a strong protein, but are thin enough to bend and make close surface contact. That is why Dhinojwala and others have tried to emulate the intricate toe hairs using carbon nanotubes and polymers.
The UMass researchers have taken a simpler approach. They deposit a thin rubbery polymer layer on a fabric made of stiff carbon fibers. The polymer conforms very closely with a surface, sticking to it because of a reversible force of attraction known as the van der Waals force, which also helps gecko toe hairs cling to any surface.
The stiff fabric is the key to the material’s adhesive strength, says UMass biologist Duncan Irschick, who was involved in the new work. The millimeter-thick fabric has a sticking force of about 30 newtons per square centimeter: three times the strength of a gecko’s front two feet. That’s still only about one-third as strong as adhesives made of carbon nanotubes, but the new fabric is much easier and cheaper to make in larger sizes. The researchers showed that it can be used to affix a 42-inch TV to a glass surface, and that it also can be lifted off with a gentle pull and reused over and over without leaving any residue.
Dhinojwala says the work is an exciting concept that bridges gecko-like adhesion with conventional sticky tapes. However, he says, the researchers need to show that their new material can stick to more surfaces than glass—and that it can hold large weights for a long time.
Alfred Crosby, a UMass polymer science and engineering professor who is leading the new work, says the adhesive design should indeed work on a variety of surfaces. The researchers plan to demonstrate that soon and to commercialize the adhesive.