Within reach of artificial skin

Engineers at the University of California, Berkley have recently developed artificial skin that could one day mimic the touch and sensitivity of human skin necessary for a robot to undertake this delicate task[i].

They’re calling it ‘e-skin’ and researchers are suggesting it could help with one of the big challenges in robotics – the ability to sense the amount of force required to handle different objects, from fragile eggs to sturdy frypans.

But this research has far more exciting applications than building robots that can make scrambled eggs without smashing in parts of the shell. As technology linking artificial electronics to human nerves advances, it has enormous potential to restore the sense of touch for people with artificial limbs.

“The idea is to have a material that functions like the human skin, which means incorporating the ability to feel and touch objects,” said Ali Javey, Associate Professor of Electrical Engineering and Computer Sciences and head of the UC Berkeley research team developing the artificial skin.

“If we ever wanted a robot that could unload the dishes, for instance, we’d want to make sure it doesn’t break the wine glasses in the process.  But we’d also want the robot to be able to grip a stock pot without dropping it.”

Previous attempts to make artificial skin have used organic materials (that are generally derived from once-living things) that are very flexible but not good electrical conductors.  The researchers at Berkley made a big advance by finding a way to make their e-skin out of artificial, inorganic substances that have the flexibility of organic material but are much better at conducting electrical signals.

Their advances relied on their ability to manipulate nanowires, structures so tiny that scientists ‘grow’ them atom by atom.  They are called nanowires because they can be as small as one nanometer, which is one billionth of a meter and many thousands of times narrower than a human hair.

To make e-skin, nanowires, made from germanium and silicon, are grown on the outside of a cylinder so they can be rolled in an ordered pattern onto material to form the base layer of the artificial skin.  The researchers involved have described this method as a high-tech lint roller in reverse.

In their recently published research, the engineers layered a seven by seven centimetre square of the nanowire matrix with touch sensitive rubber and demonstrated its ability to detect pressure in a range that we use everyday for things like typing on a keyboard.  They also proved it could still work after repeated bending, a durability that is a vital part of being able to successfully apply artificial skin to prosthetic limbs.

While seven centimetres may not sound like a large patch of e-skin, this is the first time ordered nanowires have been used in a functional system like this.

“This is the first truly macroscale integration of ordered nanowire materials for a functional system — in this case, an electronic skin,” said study lead author Kuniharu Takei.

“It’s a technique that can be potentially scaled up. The limit now to the size of the e-skin we developed is the size of the processing tools we are using.”

[i] Takei K, Takahashi T, Ho J C, Ko H, Gillies A G, Leu P W, Fearing R S and Javey A, 2010. Nanowire active-matrix circuitry for low-voltage macroscale artificial skin. Nature Materials; 10, 821-826.