WASHINGTON—At the urgent request of the Pentagon, scientists and engineers are rushing to create an artificial arm that works like a flesh-and-blood one for the growing number of soldiers who are losing their limbs in the Iraq war.
"The goal is to develop an arm that moves like a real biological arm, feels like a real biological arm and looks like a real biological arm," said Greg Clark, a bioengineer at the University of Utah in Salt Lake City.
If it works as hoped, the bionic arm not only will be deft enough to handle small objects, such as shirt buttons, but it also will deliver sensory feedback to the patient's brain. Amputees will feel what they're touching, just as if they were using their own hands.
Clark heads one of several dozen teams of biologists, physicists and electronic engineers whom the Defense Advanced Research Projects Agency has sponsored to produce such a bionic device by 2009.
"It's a challenging and daunting responsibility," Clark said. "Today's artificial arm is so much trouble, so cumbersome, that people put it on the closet shelf and don't use it.
"The new arm will be different. It can make many types of movements all at once. It can reach out in space, the elbow bends, the wrist rotates and the hand takes on the shape of the object it's going to pick up. This will mean a lot to an amputee. People who lost limbs want to feel whole again."
Advances in battlefield armor and medical care have increased the need for and the feasibility of a more realistic prosthetic device. Fewer soldiers are dying, but more are returning gravely wounded.
"Although our war fighters suffer fewer fatalities, they still endure horrible injuries, and today one of the most devastating battlefield injuries is loss of a limb," said Col. Geoffrey Ling, a doctor who heads the Revolutionizing Prosthetics Program for DARPA.
DARPA assigned management of the four-year $55 million project to the Applied Physics Laboratory at Johns Hopkins University in Baltimore. In turn, the laboratory subcontracted with 28 government, university and private organizations to design and construct sample arms. One or more winners will be selected in time for clinical testing on patients in 2009.
A key part of the Revolutionizing Prosthetics Program is linking the bionic arm to the remaining nerves in what's left of a soldier's arm. That's the part that Clark's Utah team is working on. In a telephone interview, he explained how it's supposed to work:
When a healthy person wants to move an arm, hand or finger, the brain sends electronic signals down long nerves to the spinal cord, then along other nerves to the appropriate muscles. The signals are tiny electric pulses, measuring less than a tenth of a volt. If the pulses are slow, say one per second, the muscle is relaxed. If the pulses speed up, say to 10 or 20 a second, the muscle is activated.
When a limb is amputated, the connection between brain and arm is broken. But the nerves from the brain to the stump of the arm remain.
"It's like a telephone wire without a phone," Clark said. "The wire is still there. We're going to listen in."
To do so, Utah bioengineers connect the ends of the nerves to an array of tiny electronic connectors called electrodes. The electrodes fit in a pill-sized box implanted in the patient's upper arm or shoulder. The electrodes relay the signals from the nerves to a small computer hanging on the patient's belt. The computer translates the signals into electronic commands to move the muscles in the bionic arm.
"The electronic pulses are the same as the biological wire normally receives," Clark said. "We wiretap the nerves. The brain can't tell the difference."
With such a system, he said, it will be easier for patients to learn how to control their artificial arms since they'll be using signals that their brains already know.
Other research teams are working on designing and fabricating artificial arms, fingers and joints for the new prosthetics. One system would direct signals straight from the brain, instead of using nerves in the arm, to an implanted control device.
Eventually, DARPA hopes that the technology can be adapted for people who've lost their feet or legs.
For more information online, go to www.darpa.mil/dso/thrust/biosci/revprost.htm
(c) 2006, Knight Ridder/Tribune Information Services.
PHOTO (from KRT Photo Service, 202-383-6099): BIONICARM
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