Rescue crews arrive on the scene of a collapsed mine and drill a borehole several hundred meters down to a small cavern. They put a cylindrical, camera-equipped robot made of metal into the hole that will descend and search for survivors. As the robot crawls downward, the ground shifts, collapsing the borehole to half its diameter, crushing the bot. Now what? If the robot had been made of deformable polymers, it could have simply lengthened and narrowed its shape, like a worm, and continued on its mission.
Such “soft” robots exist today only in the laboratory, but advances in materials science, control theory, energy storage and flexible electronics could change that. Pliable automatons could soon be available to perform demanding tasks in mines, factories, as well as inside the human body.
In building soft robots, engineers are copying the movements of octopuses, worms and other invertebrates. Why spend the time and money to reproduce a human hand using actuators, cables and motors, when a pneumatically powered polymer tentacle could do the job cheaper and more efficiently? In one such attempt, researchers at Cornell University fashioned a “universal gripper” from a small ball filled with air and coffee grounds. When the gripper came into contact with an object, it conformed to that object's shape. By vacuuming out the air inside the ball, researchers made the ball slowly stiffen, delicately grasping the object. Alternatively, a similar robot could be made out of soft polymers that expand, contract and bend in response to electric currents.
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Conventional, vertebrate-inspired robots may be faster and stronger than their pliable counterparts, but soft robots powered by air pressure or electric currents could be more effective at manipulating a wider variety of items and more adaptable to moving in diverse settings. Their rubbery composition might also make them more likely to survive being toppled or trampled on a factory floor.
Researchers at Harvard University's Whitesides Research Group have made a variety of shape-shifting polymer robots, including a meter-long quadruped that looks like a pair of Ys joined at the stems. Air pumped into valves in the robot's layers of pneumatic channels causes the creature to inflate, bend and move various legs to inch along. Equipped with its own battery and air compressor, the robot has undulated and crawled across the lab floor, through snow and even across a hot grill. In 2011 the researchers built a much smaller, tethered version that squeezed through a space just a few centimeters high. “The range of opportunities is much larger if you can operate them untethered, and we've crossed that crucial line,” says George M. Whitesides, a renowned Harvard chemist and materials scientist. The scientists are also improving the robot's speed with more efficient transfer of compressed air through internal channels, rather than having parts of the bot “bulge in unproductive ways,” Whitesides notes.
Inspired by the progress, investors are in the process of licensing the technology and recently launched a start-up company, Soft Robotics, to devise biomedical devices. An elastomer robot could, for example, help doctors perform a biopsy or angioplasty by delicately grasping tissue or anchoring to vascular walls without damaging them.
Within the next decade commercial products may make their debut as wearable support devices—artificial muscles that provide physical assistance to people who have motor impairments or who work lifting heavy items, say, in warehouses, according to the inaugural issue of the journal Soft Robotics. The Defense Advanced Research Projects Agency is also interested in funding development of soft robots for reconnaissance missions and as prosthetics, as part of the agency's Maximum Mobility and Manipulation program.
The success of soft robotics still depends on advances in a number of technologies, however. North Carolina State University researchers are tackling the materials angle by developing a water-based hydrogel that can be patterned, folded and used to manipulate objects. Hydrogels, which use water as their swelling agent, are elastic, translucent and potentially biocompatible. In one experiment, researchers injected copper ions into a V-shaped segment of hydrogel that caused the V to flex like a pair of tweezers. In another, a chemical reaction caused an X-shaped piece of hydrogel to fold in the shape of a four-pronged grabber.
The greatest advantage of soft robots may also be the easiest to overlook. A piece of polymer, some air tubes and a small power source are likely to cost a fraction of what it takes to make a moving, metallic robot. The savings could lead to pervasive use—if people are willing to accept robots that look more like cephalopods than the Jetsons' humanoid maid Rosie.
