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Stretchable Sensory Material Created with Carbon Nanotubes

Sensory skin material (Steve Fyffe/Stanford)

Stretchable, transparent sensory skin material (Steve Fyffe/Stanford University)

Stanford University chemical engineers have developed a stretchable, transparent skin-like sensor that can be stretched to more than twice its original length and return to its original shape. The material — that can sense pressure from a firm pinch to thousands of pounds — is described online in the 23 October issue of the journal Nature Nanotechnology (paid subscription required).

The elasticity of the sensor material (pictured right) is the latest sensory-skin product from the lab of chemical engineering professor Zhenan Bao, the holder of 35 U.S. patents. The sensor in this material uses a transparent film of single-walled carbon nanoscale tubes (1 nanometer = 1 billionth of a meter) that act as tiny springs, enabling the sensor to accurately measure the force on it, whether being pulled or squeezed.

The sensor, say the authors, can measure pressure ranging from a pinch between a person’s thumb and forefinger, to twice the pressure exerted by an elephant standing on one foot. Darren Lipomi, a postdoctoral researcher in Bao’s lab, notes that despite this wide range of stretching or squeezing, the material returns to its original dimensions. “None of it,” says Lipomi, “causes any permanent deformation.”

The sensors consist of two layers of the nanotube-coated silicone, with the coatings configured face-to-face, and with a layer of a more easily deformed type of silicone between them. That middle layer of silicone stores an electrical charge, much like a battery.

When pressure is exerted on the sensor, the middle layer of silicone compresses, which alters the amount of electrical charge it can store. That change is detected by the two films of carbon nanotubes, which act like the positive and negative terminals on a typical automobile or flashlight battery. The change sensed by the nanotube films is what enables the sensor to transmit a measurable increment of pressure.

The sensors could be used in making touch-sensitive prosthetic limbs or robots, for various medical applications such as pressure-sensitive bandages or in touch screens on computers. The ultimate goal, says Lipomi, is to devise a replacement skin for medical uses, as needed by trauma or burn victims.

Bao’s lab has already developed an artificial sensory skin so sensitive it can detect pressure applied by a 20 milligram fly’s body. Because the researchers focused on transparency and stretchability, the new material does not have that level of sensitivity. “We just need to make some modifications to the surface of the electrode,” says Bao, “so that we can have that same sensitivity.”

Lipomi and Bao demonstrate and describe their discovery further in the following video.


Read more: Nanoscale Implant Surfaces Help Seal Skin Against Infections

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