Tiny robotic hand has the gentlest touch

By Mason Inman (Image: Yu Sun) A tiny pair of robotic tweezers with the most sensitive grip yet can pick up and move individual cells without damaging them, guided by their own sense of touch. They could be used to probe the properties of living tissue, or create microscale and nanoscale devices. The robotic gripper can exert as little as 20 nanoNewtons of force and are the first to be able to feel the strength of their grip on objects so delicately, says Yu Sun of the University of Toronto in Canada, who led their development. “We’re applying very well-known concepts from robotics down to the micrometre scale,” Sun says. Previous pincers are fumbling by comparison, unable to sense such feedback. “You would break the objects being manipulated, or break the microgrippers.” The grippers are the first to not only feel their grip strength, but also when they touch a surface. This allows them to sense when they’ve run into things, helping them get close to cells and other objects without damaging collisions. Those abilities mean that when connected to a microscope and the right software the grippers can work reliably without human control. At their most sensitive, they exert only enough force to support 2 millionths of a gram against the pull of gravity. The tweezers’ arms are about 3 millimetres long, with fine tips able to grasp cells just 10 micrometres across. In trials using pig heart cells, the pincer could pick up and move the cells without damaging them. Holding them with only 100 nanoNewtons of force, the gripper squashed the cells out of shape by only 15%. The grippers are controlled by software that can identify individual cells and move the tweezers into position in just a few seconds. That’s much faster than a person could do, Sun says. The grippers have a kind of sense of touch that lets them know how strongly they are holding a cell. They can grasp a cell with a pre-set force in less than a second. They are the first to not only feel their grip strength, but also when they bump up against a surface. This crucial allows them to move autonomously and sense when they’ve run into things, helping them get close to cells and other objects without breaking the grippers.” In tests the tweezers picked up and arranged cells into a line to show off their skills. They could be used to assess mechanical properties of biological materials and tissues, or to create microscale and nanoscale devices.” But they could have many other uses too, Sun says. “They can grasp silicon parts, and they can put things together,” he adds. “So it’s really a flexible and dexterous hand.” The grippers are cheap too because they are etched from a silicon wafer, using the well-established processes used by the computer industry. When prepared in a batch of about 100, the grippers cost around US$50, Sun says, and if mass produced, might cost about US$10. The tweezers’ ability to feel its own grip strength and movement makes them useful for automated micromanipulation, says Jason Gorman of the National Institute of Standards and Technology in Gaithersburg, US. “It appears that the force sensing is having a significant effect on the manipulation dexterity,” he adds. Their manipulation of the cells is “impressive”. But Gorman agrees that they could be more usefully applied to assembling microdevices – especially complex high-end sensors that can’t be made through the usual fabrication techniques. Journal reference: Journal of Micromechanics and Microengineering (DOI: 10.1088/0960-1317/18/5/055013) Robots – Learn more about the robotics revolution in our continually updated special report. More on these topics:
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