Human skin has superb sensitivity to feel even the most delicate of touches, but the birthday suit doesn't hold up too well to sharp objects or the passage of time. Now, an artificial "super skin" could combine both super-stretchy durability and a touch-sensitive surface for bionic humans and their robotic brethren.
The transparent skin can stretch out to more than twice its normal length before snapping back into place — and it can do so repeatedly without wrinkling. Its embedded sensors make it suitable for creating better smartphone and computer touch screens, bandages capable of sensing pressure, and sensitive skin on the prosthetic limbs of both humans and robots.
"This sensor can register pressure ranging from a firm pinch between your thumb and forefinger to twice the pressure exerted by an elephant standing on one foot," said Darren Lipomi, a postdoctoral researcher at Stanford University.
Lipomi worked on a team led by Zhenan Bao, a chemical engineer at Stanford University, to make the stretchy sensor skin out of carbon nanotubes. First, they sprayed the nanotubes onto both sides of a thin layer of silicone. Then they stretched the material out so that the nanotubes formed into tiny structures resembling springs.
"After we have done this kind of pre-stretching to the nanotubes, they behave like springs and can be stretched again and again, without any permanent change in shape," Bao said.
The silicone layer sandwiched between the nanotube films stores electrical charge like a battery. That allows the carbon nanotubes to act like electrodes and sense any changes in the electrical charge caused by any pulling or squeezing.
For now, Bao's group wants to make the new sensor skin even more sensitive. The researchers previously built a sensor capable of detecting the pressure caused by a dead fly's body, but focused on making the latest sensor skin more transparent and stretchy.
"We did not spend very much time trying to optimize the sensitivity aspect on this sensor," Bao said. "But the previous concept can be applied here. We just need to make some modifications to the surface of the electrode so that we can have that same sensitivity."
A paper on the research appeared in the online Oct. 23 issue of the journal Nature Nanotechnology.