What good is a super human prosthetic arm in an arm wrestling competition, if the metallic parts give it away? That’s why DARPA continues to fund projects aimed at the development of a highly realistic prosthetic “skin.”
The new artificial skin will incorporate many more sensors and will cover the metallic prosthesis, leading to a more natural-looking bionic arm. The skin-a rubbery polymer called polyimide that has been infused with tiny carbon nanotubes-is flexible, stretchable, lightweight, and tough. Initially designed for airplane pressure sensors, the polymer is durable, resistant to high temperatures, and piezoelectric. That is, it generates electricity in response to pressure or force, so you can measure pressure applied to its surface, says NIA’s [National Institute of Aerospace’s] Cheol Park, who is leading the pressure-sensor development. Carbon nanotubes enhance the piezoelectricity of the polyimide and make the polymer stronger, he says.
Temperature sensors will be embedded under the polyimide layer. The trick is to transfer heat as quickly as possible from the polymer surface to the sensors. Again, carbon nanotubes, which conduct heat along their length unusually well, will play a key role. Researchers at ORNL are trying to make nanotube-embedded polymers that conduct heat as well as human tissue does, says Ilia Ivanov, a nanomaterials researcher at ORNL. They will impregnate the polymer with an array of vertically aligned nanotubes, which will transfer heat from the skin surface to the temperature sensors underneath. Ivanov says the heat transfer should be fast. In 2006, researchers showed that a heat pulse travels 20 times as fast in a polymer containing the nanotube arrays than in the pure polymer.
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