Mass-producible, gecko-inspired gripper material developed by Georgia Tech

Although engineers have understood for years the mechanisms by which gecko lizard feet stick to smooth and rough surfaces alike and have emulated it in strips of rubbery materials, mass production of those dry adhesive materials hasn’t been practical, due to the high cost of producing them.

However, researchers at the Georgia Institute of Technology say they’ve developed a cost-effective way to make gecko-inspired materials, potentially enabling mass production of the versatile gripping strips for manufacturing applications.

“With the exception of things like Teflon, it will adhere to anything,” said Michael Varenberg, an assistant professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering. “This is a clear advantage in manufacturing because we don’t have to prepare the gripper for specific surfaces we want to lift. [It] can lift flat objects like boxes then turn around and lift curved objects like eggs and vegetables.”

The gecko’s foot has ridges on its toes that, when viewed under an electron microscope, reveal spatula-shaped fibrils that protrude a few dozen microns from those ridges. The fibrils make such thorough contact with surfaces down to the nanoscale that weak attractions between atoms on both sides appear to add up enormously to create overall strong adhesion.

Up to now, attempts at similarly constructed, gecko-inspired materials has relied on pouring ingredients onto a template, letting the mixture set to a flexible polymer and then removing it from the mold.

“Molding techniques are expensive and time-consuming processes,” Varenberg said. “And there are issues with getting the gecko-like material to release from the template, which can disturb the quality of the attachment surface.”

In place of a mold, the Georgia Tech researchers’ method formed those ridges by pouring ingredients onto a smooth surface, letting the polymer partially set and then dipping rows of laboratory razor blades into it. After the material sets around the blades, they are drawn out, leaving behind micron-scale indentations surrounded by the desired walls.

Varenberg’s research team used the drawing method to make walls with U-shaped spaces in between them and walls with V-shaped spaces in between. They worked with polyvinylsiloxane (PVS) and polyurethane (PU). The V-shape made in PVS worked best, but polyurethane is the better material for industry, so Vanenberg’s group says it will now work toward achieving the V-shape gecko gripping pattern in PU for the best possible combination.

“Many researchers demonstrating gecko adhesion have to do it in a cleanroom in clean gear,” said Varenberg, who studies surfaces in nature to mimic their advantageous qualities in human-made materials. “Our system just plain works in normal settings. It is robust and simple, and I think it has good potential for use in industry and homes.”

Varenberg and first author Jae-Kang Kim published details of their new method in the journal ACS Applied Materials & Interfaces.
http://www.gatech.edu