Stanford Researchers Develop Stretchy Skin-Like Pressure Sensor

In a quest to create the perfect artificial skin, Stanford researchers have developed a material that is skin-like in consistency that can also precisely locate in a 2D-plane any applied pressure.

The heart of the technology lies in a unique application of carbon nanotubes. They are sprayed onto a square silicone sheet in tension. When this stretch is released, the tubes coil up along the lines of tension much like springs. This allows them to be stretched in any direction while maintaining their mechanical and electrical properties. What this means in plain English is that the material can be stretched repeatedly and still give accurate and precise pressure readings and locations. A technology like this has multiple uses, but the idea of a smart “skin” for prosthetic limbs seems particularly promising. Such a skin would also require light touch, temperature, and pain sensing capabilities in order to mimic our own native tissue.

Here’s more from the press release:

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 key element of the new sensor is the transparent film of carbon “nano-springs,” which is created by spraying nanotubes in a liquid suspension onto a thin layer of silicone, which is then stretched.

When the nanotubes are airbrushed onto the silicone, they tend to land in randomly oriented little clumps. When the silicone is stretched, some of the “nano-bundles” get pulled into alignment in the direction of the stretching.

When the silicone is released, it rebounds back to its original dimensions, but the nanotubes buckle and form little nanostructures that look like 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.

Stretching the nanotube-coated silicone a second time, in the direction perpendicular to the first direction, causes some of the other nanotube bundles to align in the second direction. That makes the sensor completely stretchable in all directions, with total rebounding afterward.

Additionally, 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. Maintaining the same conductivity in both the stretched and unstretched forms is important because the sensors detect and measure the force being applied to them through these spring-like nanostructures, which serve as electrodes.

The sensors consist of 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, 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.

Press release: Stanford researchers build transparent, super-stretchy skin-like sensor…

Hat tip: Engadget…