A few months ago, we reported on the development of a material that uses the same technique employed by gecko feet to allow its adhesion to be turned on and off at will. This allows fragile components, like those used in the manufacture of semiconductors, to be carefully picked up and put down without suction or residue-leaving adhesives. Now researchers at the University of Pennsylvania (UPenn) have developed a gripper, also inspired by the gecko and also tunable, that they claim is much simpler, making it easy and cheap to mass produce.
The material developed by scientists atGermany's Leibniz Institute for New Materials (INM) that we looked at in Marchmimics the microscopic mushroom-shaped, hair-like projections known as setaethat are found on gecko feet. So, just like gecko feet, the manmade microscopicpillars created by the INM team temporarily bond to surfaces at the molecularlevel thanks to the van der Waals force. To switch the stickiness off, thestructure of the pillars is altered electronically. The problem is that makingthese complicated structures is, well, complicated.
"Other researchers have mimicked [gecko setae]structures to achieve tunable adhesion, but they are tough to make," says UPenn graduate student HelenMinsky. "You can make a few of these structures, but, if youwant to make larger arrays of them, it becomes much tougher. The angles and theflared tip means you can’t just slip them out of a mold."
So although they also took inspiration from thegecko, Minsky and Kevin Turner, the Gabel Family Term Associate Professor in the School ofEngineering and Applied Science’s Department of Mechanical Engineering andApplied Mechanics, have taken a different approach.
They created a simple cylindrical poststructure that consists of a hard plastic core surrounded by a softer siliconerubber shell. While the structure doesn't mimic the mushroom shape of thegecko's setae, it achieves the same result through the soft rubber conformingto the surface and the stress from lifting being concentrated on the stiffinner core. The adhesion is switched off through the application of lateralforce, which shifts the stress to the edges and allows a crack to form and thebond to break.
"When it comes to tunable adhesion, everyone is familiar with thegecko, and everyone tries to copy it," says Turner. "The problem isthat it’s really hard to manufacture complex structures as well as nature.We’ve come up with a strategy that can achieve similar adhesion behavior but ismuch easier to make."
The researchers have created prototype grippers that are a fewmillimetres in diameter and are designed to grip smooth surfaces, such asglass. However, they claim their experiments and simulations indicate that thecomposite structure will work in the same way when scaled down to microscopicsizes.
Turner and Minsky's study appears in thejournal Applied Physics Letters.
Source: UPenn
