New artificial skin could make prosthetic limbs and robots more sensitive

The sensor is sensitive enough to easily detect this Peruvian butterfly (Chorinea faunus) with transparent wings and red-tipped tails, positioned on a sheet of the sensors.

The light, tickling tread of a pesky fly landing on your face may strike most of us as one of the most aggravating of life's small annoyances. But for scientists working to develop pressure sensors for artificial skin for use on prosthetic limbs or robots, skin sensitive enough to feel the tickle of fly feet would be a huge advance. Now Stanford researchers have built such a sensor.

By sandwiching a precisely molded, highly elastic rubber layer between two parallel electrodes, the team created an electronic sensor that can detect the slightest touch.

"It detects pressures well below the pressure exerted by a 20 milligram bluebottle fly carcass we experimented with, and does so with unprecedented speed," said Zhenan Bao, an associate professor of chemical engineering who led the research.

The key innovation in the new sensor is the use of a thin film of rubber molded into a grid of tiny pyramids, Bao said. She is the senior author of a paper published Sept. 12 online by Nature Materials.

Previous attempts at building a sensor of this type using a smooth film encountered problems.

"We found that with a very thin continuous film, when you press on it, the material does not have room to expand," said Stefan Mannsfeld, a former postdoctoral researcher in chemical engineering and a coauthor. "So the molecules in the continuous rubber film are forced closer together and become entangled. When pressure is released, they cannot go back to the original arrangement, so the sensor doesn't work as well."

"The microstructuring we developed makes the rubber behave more like an ideal spring," Mannsfeld said. The total thickness of the artificial skin, including the rubber layer and both electrodes, is less than one millimeter.

The speed of compression and rebound of the rubber is critical for the sensor to be able to detect – and distinguish between – separate touches in quick succession. ...

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