A new artificial skin developed by U. California-Berkeley researchers could eventually provide prosthetic and robotic limbs with one of the five human senses: touch.
Using inorganic materials – in this case, semiconductors – Ali Javey, UC Berkeley associate professor of electrical engineering and computer science, and his team of engineers were able to create an “e-skin” that is sensitive to pressure because of electric conductivity similar to human nerves. The researchers described their creation in a study published online Sept. 12 in the journal Nature Materials.
“The goal was to create a material system that could function similar to the human skin, being able to detect touch,” Javey said in an e-mail.
The e-skin consists of multiple thin layers including a base, parallel strips of germanium and silicon nanowires that conduct the electricity and transistors that control the conductivity in the nanowires, which are topped with pressure-sensitive rubber, according to the study.
For an initial test, researchers placed a mold of the “Cal” letter C on a 7-by-7 square centimeter prototype of the skin and applied pressure. According to the study, the e-skin “felt” the letter with an accuracy of 84 percent.
Previous attempts at producing a useful artificial skin have used organic materials because of their flexibility. However, the organic materials require a much higher level of electricity – more than 10 volts, as opposed to two or three – to function, rendering them impractical for most real applications, according to Javey.
“Low voltage is, of course, important for portable sensors (like e-skin) to enable longer battery life times,” Javey said in the e-mail. “Additionally, inorganics are often more chemically stable than organics, which presents yet another advantage of the current work.”
According to the study, the development of the e-skin “is of profound interest for robotic and prosthetic applications.”
The benefits of the skin to people with prosthetic limbs are likely not immediate. However, such a skin could be incorporated with a robotic platform, enabling robots to hold a delicate item without breaking it or to hold a heavy item without dropping it.
Pieter Abbeel, a UC Berkeley assistant professor of electrical engineering and computer science, said he is interested in the benefits of the artificial skin to robotic dexterity. Abbeel’s own research focuses on programming robots to complete simple household tasks, such as folding towels and pairing socks.
According to Abbeel, it is difficult for a robot to coordinate the image from its camera with the motion of its “limbs.”
“First off, it is very hard to ensure the robot’s perception of 3-D through its cameras (is) perfectly matched with its notion of where it is moving its hands,” Abbeel said in the e-mail. “Secondly, often when grasping an object, the hand will enclose the object, making it very hard to see what’s happening. The incorporation of high quality tactile sensing could greatly enhance current robots’ performance.”
A prosthetic arm works in a similar fashion and would benefit in many of the same ways, said Tony LaFrance, a certified prosthetist and orthotist at Laurence Orthopedic in Oakland.
“Skins” currently made for prosthetics are merely for cosmetic purposes, Lafrance said. Made of vinyl, the skins have no ability to transmit feeling or touch.
“They are a far way from being a skin,” he said. “There isn’t anything that is integrated or moving or anything remotely close to that. It’s just basically a fancy glove.”
Like a robot, a prosthetic arm – whether it has a hook or a hand at the end of it – can grab and hold an object based only on what its user can see. Therefore, Lafrance said the feedback that “e-skin” could provide to people who use prosthetics would be invaluable.
“Right now it’s all visual,” he said. “This would be a huge new area.”