'Super-skin' developed by Stanford researchers

Who needs Botox when you could have this kind of skin? Researchers at Stanford University's engineering school have created a transparent, elastic skin-like sensor that may have potential uses such as prosthetic limbs and touch-sensitive computer displays. "It can sense pressure from a firm pinch to thousands of pounds. The sensor could have applications in prosthetic limbs, robotics and touch-sensitive computer displays," Stanford said in a news release. The sensor is the latest developed by Zhenan Bao, associate professor of chemical engineering, in her quest to create an artificial "super skin." Many of the possible applications for this "super-skin" include medical ones such as pressure-sensitive bandages. Stanford said the new sensors have carbon nanotubes that can be bent to act as springs, and can be stretched to more than twice their original length and bounce back to their original shapes perfectly. Darren Lipomi, a postdoctoral researcher in Bao's lab and a member of the research team, said the 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." "None of it causes any permanent deformation," he said. Lipomi and Michael Vosgueritchian, graduate student in chemical engineering, and Benjamin Tee, graduate student in electrical engineering, are the lead authors of a paper describing the sensor published online Oct. 23 by Nature Nanotechnology (http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2011.184.html). Bao is a co-author of the paper, which said thin films with these properties can lead to the development of skin-like sensors that:

• stretch reversibly
• sense pressure (not just touch)
• bend into hairpin turns
• integrate with collapsible, stretchable and mechanically robust displays and solar cells
• wrap around non-planar and biological surfaces such as skin and organs without wrinkling.

Nano-springs The key to the new sensor is a transparent film of carbon "nano-springs," created by spraying nanotubes in a liquid suspension onto a thin layer of silicone, which is then stretched. With the nano-springs, the sensor can be stretched is in all directions and then rebounds to its original shape. After the initial stretching to produce the "nano-springs," repeated stretching below the length of the initial stretch does not change the electrical conductivity significantly, Bao said. Nanotube-coated silicone The sensors have two layers of the nanotube-coated silicone, oriented so that the coatings are face-to-face, with a layer of a more easily deformed type of silicone between them. The middle layer of silicone stores electrical charge, like a battery. It compresses and alters the amount of electrical charge it can store, once pressure is exerted on the sensor. When the two films of carbon nanotubes detect that change, they act like the positive and negative terminals on a car or flashlight battery. In turn, the change sensed by the nanotube films allows the sensor to transmit what it is "feeling." * compression When the sensor is compressed or extended, the two nanofilms are brought closer together, which seems like it might make it difficult to detect which type of deformation is happening. But Lipomi said it should be possible to detect the difference by the pattern of pressure. Compression may bring a bullseye-like pattern, with the greatest deformation at the center and decreasing deformation farther from the center. "If the device was gripped by two opposing pincers and stretched, the greatest deformation would be along the straight line between the two pincers," Lipomi said. Sensitivity Bao's group previously created a sensor so sensitive to pressure that it could detect pressures "well below the pressure exerted by a 20-mg bluebottle fly carcass" that the researchers tested it with. While she said the latest sensor is not that sensitive, that is because the researchers were focused on making it stretchable and transparent. She said they did not spend much time trying to optimize the sensitivity aspect on this sensor. "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," she said. — TJD, GMA News