December 16, 2016
New Gecko Gripper can be used in manufacturing and medicine
Waterloo engineers used the gecko for inspiration when inventing a device that can handle the delicate silicon wafers in electronics
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Boxin Zhao reaches for a dispenser, tears off a strip of cellophane tape and sticks it to the top of his desk at the University of Waterloo, deliberately leaving a few centimetres of it flopping over the edge in front of him.
He grabs the overhanging tab of tape and forcefully yanks it towards himself. It doesn’t budge. Then he lifts the tape up and away from himself instead, slowly peeling the strip off the desk with no effort at all.
“When you pull it, it’s very strong,” says Zhao, a chemical engineering professor with a longstanding interest in biomimicry. “When you peel it, it’s very easy.”
Peeling, not pulling.
That is the simple, elegant secret of how geckos seemingly defy gravity to scurry up walls and across ceilings, a “hot topic” in Zhao’s world of surface science for the last two decades.
It is also the inspiration for a new, manmade device with potential applications in fields including advanced manufacturing and medicine.
More than 10 years after he began studying geckos - small lizards known for their unique climbing abilities - Zhao and three colleagues recently developed what they call a Gecko Gripper to pick up, move and put down objects.
Commercializing the Gecko Gripper
They are now working to commercialize their technology, which is especially well-suited to handling delicate materials - such as silicon wafers used in electronic devices - that require a gentle touch.
“We are linking science to manufacturing through engineering,” says Zhao. “There is huge potential for this.”
Common in warm climates throughout the world, geckos have sophisticated pads on their toes that are comprised of flexible ridges topped by hair-like structures, which have at their ends even tinier, nanoscale hair-like structures. The net result is tremendous molecular force.
Powerful microscopes revealed those structures long ago, but it remained a mystery how geckos were able to swiftly attach, detach and reattach in order to walk while upside down. The force required for them to stick, given their body weight, seemed too great for them to overcome for rapid motion.
Slow-motion imagery unlocked gecko mystery
Zhao had a hand in figuring that mystery out about a decade ago. The gecko’s trick, discovered through slow-motion images, is that it can bend its toes backwards – as if “double-jointed” – thereby creating the peeling motion he demonstrated on his desk.
In effect, geckos do not lift their feet up until they have first peeled their toes off the surface, greatly reducing the forces at play. And since they only move one foot at a time, the remaining three keep them firmly fixed.
“To me, this is a beautiful engineering design,” Zhao says. “It’s a very simple mechanism, but it makes a complete difference.”
Working with graduate students at his Surface Science and Bio-nanomaterials Laboratory about five years ago, Zhao developed a rubber structure, complete with hair-like features, that mimics the design of a gecko toe pad and its tremendous adhesion.
The next challenge was replicating the peeling effect to release an object once it has been picked up. After two years of work, his four-member research team recently had its solution, the Gecko Gripper, published in the journal Advanced Materials.
New device mimics gecko toe pad
Shaped like a small wheel, the smart device has eight legs or spokes shooting out from a central hub. On the end of each spoke is a rubber gripper, inspired by a gecko toe pad, to pick objects up.
The breakthrough is that the spokes are made of a special polymer – a liquid crystal network and elastomer – that changes shape, bending backwards like a gecko toe, when it is heated. When cooled after its gripper has released an object using the self-peeling mechanism, each spoke then returns to its original shape.
The brainchild of Hamed Shahsavan, a PhD student supervised by Zhao, in collaboration with professor Antal Jakli and student Seyyed Muhammad Salili of Kent State University in Ohio, this heating-cooling innovation has been successfully used with machines in Zhao’s lab to “pick and place” silicon wafers up to 15 centimetres in diameter.
While avenues of commercialization are explored, research is now focused on using electrical currents to achieve the same bending-back effect borrowed from the gecko. That would provide more control in manufacturing settings.
“We want to improve performance, reduce cost and add a new function,” says Zhao.