While humans typically gauge our environment in miles or kilometers, the scale of choice for researchers studying the world of atoms and molecules is the nanometer. Objects at the nanometer scale are too small for even high-powered microscopes to see--there are 25.4 million nanometers in one inch. A human hair is about 100,000 nanometers thick. The science of materials made at this tiny scale is nonetheless beginning to open some mighty big doors for people with artificial limbs.

Early in the study of nanotechnology, researchers learned they could reconfigure carbon, the stuff of both pencil lead and diamonds, into a new, ultra-strong and lightweight fiber they named "nanotubes." NASA uses nanotubes in space applications, and if you have an ultra-lightweight carbon bicycle, chances are you are riding on nanotubes. This amazing substance is now part of some important development projects that enhance the lives of those who have lost a hand or arm.

Collaborative efforts between Oak Ridge National Laboratory, NASA, and the National Institute of Aerospace, as well as additional research funded by the U.S. Department of Defense, have developed pressure- and temperature-sensitive, water-resistant materials made with nanotubes for aeronautic, aerospace, and robotic applications. The materials, embedded with sand, arrays of nanotubes, and thin gold wire, have nearly the same heat-conducting ability of human skin and are piezoelectric, generating electricity in response to pressure. Sensors under the skin are able to measure the electric output or temperature changes and send the data to a computer chip to be interpreted into useful information.

In robots, the sensors lying under the artificial skin report the information they collect through wires connected to a computer, which, in turn, allow the human working with the robot to select the appropriate responses. The challenge research teams face in the development of artificial limbs for humans, rather than for robots, is to be able to get the data from the sensors to the wearer's brain so that it can directly respond to the stimulation just as if the body part were real.

Currently, prostheses are manipulated through a cooperative effort between muscles and mechanics. In an artificial hand, for instance, the user tenses the shoulder or remaining arm muscles that are attached to sensors; these sensors, in turn, send an electronic signal to the mechanics of the artificial hand, telling it to open or close. Technology is working to smooth this process and make it faster by linking to nerves instead of muscles.

Advances in artificial skin that allow for more exact data about temperature and pressure changes are only valuable if the person with the prosthesis is able to process and respond to the information. In attempts to address data transfer issues, medical researchers have experienced success with redirecting the arm nerves of amputees into their chest muscles. They have mapped those redirected nerves in the chest to exact places on the hand or fingers where sensations will be received. This has permitted the creation of an electronic connection between the prostheses and the brain so that the subject can, for instance, experience pressure and have the brain send a signal to tell the fingers to withdraw just as the computer would have in a robot.

It is the developers' hope that by 2010, the data transfer technology--electronic circuits and software to manage the process--will be fast enough to allow the limb user to sense and respond to stimulation just as quickly as he/she would if the limb were natural. Through this program's success, a person who has artificial hands will be able to feel the warmth of a baby's bath water and type on a computer keyboard as readily as anyone else does.

Human skin can send message about location of sensations that are 2 millimeters apart. Current artificial skin technology allows detection of pinpricks that are 5 millimeters apart. Researchers are working with nanotechnology to reduce the space between sensor points so that more accurate locations can be identified. When these technologies are successfully debugged and applied, artificial limbs will have the same sensitivity as real skin.

Polyimide, also known as FILMSkin, is being made to look and feel as real as human skin, too. It is lightweight but stretchable, allowing flexibility for movement with the prostheses, and it sheds water just like human skin, which is an important quality in protecting the electronics within. Scientists are currently studying how to use the piezoelectric qualities of the nanotubes to develop ways to power the electronics within the skin by using solar or body heat energy so that batteries are not required.

Progress in nanotechnology has the power to restore not only functional capability, but also dignity to users of artificial limbs. The next two years will see important advances in the technology required to create an artificial skin that will look, feel, and operate like the natural counterpart it is modeled after. A simple handshake sends subtle messages, and soon thousands of prostheses users will be able to detect the strength and warmth behind it.