Frog-Inspired Tape Reusable, Doesn't Lose Grip

John Roach
for National Geographic News
October 11, 2007
The toe pads of tree frogs and crickets have inspired a new supersticky—yet reusable—adhesive, scientists report.

The material is the latest example of a boom in adhesives that take their cues from nature's greatest clingers: frogs, lizards, and insects.

For example, several science teams have fabricated adhesives that directly mimic the microscopic, spatula-tipped hairs on gecko feet.

Another breakthrough is "geckel," an adhesive combination of gecko hairs and mussel proteins.

The new adhesive, however, does not exactly imitate the natural structures of frog and cricket toe pads, said Anand Jagota, an adhesion scientist at Pennsylvania's Lehigh University who was not involved in the study.

"[It] captures the physics rather than ... the actual structure," he said.

Lead study author Abhijit Majumder and colleagues at the Indian Institute of Technology in Kanpur describe the new adhesive in tomorrow's issue of the journal Science.

Preventing Cracks

Conventional tape cracks when it is pulled off a surface. The cracks enable removal, but usually also render the tape useless for reapplication, the authors said.

The toe pads of tree frogs and crickets, on the other hand, contain microscopic channel patterns that prevent cracking.

The researchers embedded the same type of microchannels in the new adhesive, which thwarted cracks, said study co-author Animangsu Ghatak.

In addition, the researchers found they could increase the adhesive strength by partially filling the microchannels with fluid. The surface tension of the liquid creates a capillary effect—the ability of one substance to draw another toward it like a sponge soaking up water.

In this case, the elastic adhesive pulls tighter to the surface to which it is attached, increasing its stickiness.

The combined properties of the microchannels and fluids increased surface adhesion of the elastic material by about 30 times, according to the researchers.

And since the material itself is elastic, it is reusable.

"You get stickiness without getting stickiness—in the sense that you get a sticky material that doesn't leave anything behind," said Jagota of Lehigh University.

Reusable Tape

The researchers created a piece of adhesive large enough to hold a cover slip on a microscope slide.

But it can be made bigger and used in several applications, according to Ghatak.

For example, the tape could be used to help baseball and cricket players keep their gloves on, he said, or to keep price tags on supermarket goods.

Another potential use is for the feet of wall-climbing robots.

Jon Barnes studies tree frog adhesion at the University of Glasgow. In a related commentary in Science, he noted that car tires patterned after tree frog toe pads are in production.

Barnes said he expects even more such discoveries in the future.

"In this area of materials science," he wrote, "biomimetics [taking design ideas from nature] is certainly coming of age."

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