A floppy robotic hand that stiffens when air is sucked out, much like a vacuum-packed brick of coffee, may form the basis of a new type of robotic gripping mechanism, US researchers say.The gripper is essentially a latex balloon filled with ground coffee, and is slipped around hard objects. Because it is soft it is able to conform to the object's shape.When a vacuum is applied it contracts and hardens, much like a vacuum-packed brick of coffee, grabbing the object. When the vacuum is released, air rushes in and the hand releases its grip.Researchers at the University of Chicago, Cornell University in New York and iRobot Corp report on the technology in this week's edition of the Proceedings of the National Academy of Sciences.The team says the so-called "universal gripper" could be used on prosthetic limbs, to dismantle explosive devices, move potentially dangerous objects or as robotic arms in factories.The design is based on the transition between two states: a loose state and a jammed state, in which granules of coffee go from a fluid to a solid state.Dr Hod Lipson, an associate professor of mechanical engineering and computer science at Cornell, says the ground coffee grains are like lots of small gears."When they are not pressed together, they can roll over each other and flow. When they are pressed together just a little bit, the teeth interlock, and they become solid," he said.Many materials can do this, including rice or sand, but the team settled on ground coffee because it is a lightweight material.They say the gripper works well with many types of objects, including a raw egg and a coin, objects that can be difficult even for humans to manipulate.The work was supported by the Defence Advance Research Projects Agency (DARPA), through the United States Army Research Office. The researchers have filed for a patent on the technology.To see a video on the coffee balloon gripper, click here.