Jesse Sullivan

Combining carbon nanotubes with a polymer produces a material that looks, feels, and functions like human skin. For instance, it generates electricity in response to pressure or force, so you can measure pressure applied to its surface, says National Institute of Aerospace's Cheol Park, a development team leader. Carbon nanotubes also enhance the piezoelectricity of the polyimide and make the polymer stronger, he says. The artificial skin is intended to cover a metallic prosthesis and appear more natural than previous efforts. The polyimide skin is flexible, stretchable, lightweight, and tough. It was initially intended for airplane pressure sensors.

The synthetic skin could lead to dexterous prosthetic arms that let users feel, shake hands, and manipulate small objects. Researchers at Oak Ridge National Laboratory (ORNL), NASA, and NIA, Hampton, Va., say a patch of the synthetic skin may be ready by year end. The project is part of Darpa's Revolutionizing Prosthetics program, which aims to build an arm that can touch, feel, and respond to direct brain control by 2010.

Targets on skin
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Embeded temperature sensors under the polyimide layer let the skin transfer heat signals as quickly as possible from polymer surface to sensors. Researchers at ORNL are trying to make nanotube-embedded polymers that conduct heat as well as human tissue does, says ORNL nanomaterial researcher Ilia Ivanov.

Park says another challenge is to deliver pressure signals to the brain. Neuroscientists at the Rehabilitation Institute of Chicago say one way might be to redirect the arm nerves of amputees to their chest muscles, letting them use the chest to control a prosthetic arm and even feel some pressure applied to the limb. They found that patients could sense touch, heat, cold, and pain on the skin of the chest as if it were on the skin of the missing hand.