Lab pioneering arms controlled by thought


The Pentagon wants to get one thing straight: It is not building a "bionic" arm like the one test pilot Steve Austin got in The Six Million Dollar Man TV series more than 30 years ago.

True, the government is paying the Johns Hopkins Applied Physics Laboratory $30.4 million to spearhead development of a thought-controlled mechanical arm for the growing number of soldiers who lose their own in battle or accidents.

But the new device won't give wearers super powers to carry back into combat. The APL's mission is to replace missing limbs with natural-looking arms and hands that soldiers can "feel" and operate with their brains, just like the real thing.

"We're not trying to improve the capability. We're restoring function," says Stuart D. Harshbarger, project manager for the APL. "It's more than just a little challenge - it's hard to top the human limb."

But it's worth the attempt. "A lot of these folks are still in their 20s. They have a lot of life ahead of them. ... They [the Pentagon] felt it was important to do whatever is possible to give them back a full range of abilities," Harshbarger said.

Although it sounds like science fiction, team members have already taught a mechanical hand to play rock-paper-scissors. And a Tennessee amputee managed to wreck a prototype thought-controlled arm trying to pull-start his lawnmower. So engineers know the concept works.

To move it to reality, the Defense Advanced Research Projects Agency (DARPA) has broken the job into two parts. The APL, based near Laurel, hopes to have the arm's thought-control and sensor systems ready for clinical trials in four years with an international team of 30 corporate, government and academic partners.

In a parallel, two-year effort under an $18.1 million contract, DEKA Research and Development Corp. of Manchester, N.H., will lead a team developing the arm's mechanical and cosmetic components.

The target price for the final product is $30,000 to $50,000 a copy. "It's going to cost about the same as a new car, to be honest," Harshbarger says.

There's a growing market for these sci-fi prosthetics - a result of improved body armor and prompt battlefield medical care in Iraq and Afghanistan. They save soldiers who would have died in past wars - but more of those are amputees.

Through January, the Pentagon says, 387 military personnel from the two conflicts had been treated at Army hospitals for the loss of hands, feet, arms or legs. Some are multiple amputees.

"We suddenly found ourselves with a number of young Americans who are badly injured and didn't have the prostheses they would need, or we would want them to have, in an ideal world," said Col. Geoffrey S.F. Ling, a physician and veteran of Iraq and Afghanistan who manages the program for DARPA.

"What's available commercially is woefully inadequate," he says. "We also set the bar really high. We want to give them back their lives."

The APL, best known for developing classified weapons for the military and interplanetary missions for NASA, may seem an unlikely candidate for this work. But over the years it has developed expertise in miniaturization and the abilities to extract weak signals from noisy environments and build sophisticated guidance systems - all valuable in building a high-tech arm.

Nor is the APL a stranger to prosthetics. In decades past, it helped develop rechargeable, motor-driven prosthetic arms for amputees who had difficulty using older, body-powered models. It also built a tabletop mechanical arm to spoon-feed paralyzed patients.

To carry out the current project, called the Revolutionizing Prosthetics Program, the lab will have to outdo its earlier efforts. "Even for DARPA, this is a significant challenge," Harshbarger said.

DARPA sponsors the Defense Department's cutting-edge scientific research. That means it puts big money (the Bush administration wants $2.9 billion next year) into projects with the highest risk of failure but the greatest potential payoff.

"DARPA-hard," they call it - projects that are technologically challenging, hard to administer or just too fantastic to attract a critical mass of private money and brainpower. Some DARPA successes: the Internet and the Global Positioning System.

When the prosthetic arm project came up, Harshbarger recalls, APL Director Richard Roca said that the lab had managed complex missions to Pluto and Mercury but quipped, "I'm not sure you guys can do this."

Modern, computerized prosthetic "C-legs" have enabled soldiers to walk normally and return to duty - even as paratroopers. But the arm and hand are far more complex, scientists say. And while today's best prosthetics offer amputees more than simple hooks or cosmetic hands, they're still far from ideal.

For example, a German company called Otto-Bock Healthcare (a partner in the new project) makes a three-fingered hand with a simple pinch grasp. The wrist can rotate, and the elbow can open and close.

Its movements are controlled by myoelectric signals that originate in the patient's own muscles, picked up by electrodes on the skin. Users contract biceps if they have them (or back or chest muscles if they don't) to generate an electrical signal that activates the artificial limbs. To tighten a grip, they repeat the contraction.

But the device is slow and cumbersome, says Dr. Todd Kuiken, director of neuroengineering at the Center for Artificial Limbs at the Rehabilitation Institute of Chicago, a partner in the APL program.

"It's not very natural to open and close your hand with your pectoral muscle or back muscle. But that's what [today's] standard of care is," Kuiken explained.

At DARPA, Ling says, most amputees don't like the cable-operated hooks they're offered. "It's Peter Pan stuff," he said. Many opt for a nonfunctional but more cosmetically appealing prosthesis. So the goal for developers is an arm and hand as much like the real thing as possible.

"Make no mistake," Ling says, "I've got more people telling us we're crazy and totally unrealistic than tell me, 'We see what you see.'"

The work will demand breakthroughs on several technical fronts. For example, DARPA wants a limb that works for 24 hours and recharges quickly. But the lithium batteries available today are too heavy - 20 pounds.

One alternative is a system driven by hydrogen peroxide and a catalyst. The chemicals can produce heat and high-pressure gas to drive pneumatic cylinders. But they're noisy, and "DARPA requires a silent product," Harshbarger said.

Weight, too, is critical. DARPA's limit is eight pounds, the weight of a natural arm. But "the perception of weight is much different for an amputee," Harshbarger says. "The prosthesis is not integrated with the skeleton, so it's perceived to be much heavier. It has to be less."

The joints are another issue. Should the arm have tiny motors to move each digit and joint? Or a central power source in the forearm to drive cables that mimic muscles and tendons?

Whatever the engineers decide, the team's goal is an arm with 22 "degrees of freedom." That means 22 ways to move the shoulder, elbow, wrist and fingers. The best prosthetics now in development offer only six.

"Ideally, the device would grant an amputee the fine motor control necessary to thread a needle, use a computer keyboard, play a piano or perform fretwork on a guitar," the agency's planning documents declare.

This demands that the team analyze natural human behavior and then write software to coordinate movements for everyday tasks that people often take for granted - pointing a finger, turning a key or a gripping a tool.

In a lab at the APL, Bobby Armiger, 25, a Hopkins graduate student on a biomedical fellowship, is working on code that "teaches" a mechanical hand to remember a position and return to it quickly.

"We had it playing paper-rock-scissors," he said.

But the biggest nut to crack, Ling said, will be wiring the mind directly into the prosthesis. Engineers will have to interpret motor signals from the brain, then translate them instantly and accurately into deliberate movements. "You don't want to have a delay when you're trying to pick up an object," Harshbarger said.

Researchers at Duke University, working under an earlier DARPA contract, have taught monkeys with wires implanted in their brains to operate a robotic arm by thought alone. Others are trying to embed microelectrodes in nerves, or to coax injured nerve ends to grow into an electronic interface.

The current state of the human art is Kuiken's work at the Rehabilitation Institute of Chicago. His chief test platform is Jesse Sullivan, a former electrical lineman from Tennessee who lost his arms to a 7,000-volt power line in 2001.

Kuiken rerouted Sullivan's severed arm nerves and grafted them to the pectoral muscles on his chest. Then, as Sullivan willed his missing arm to move, Kuiken mapped the twitchy responses from the chest muscles.

That done, Kuiken attached electrodes to the appropriate spots on Sullivan's chest and wired them, through a computer, to the corresponding joints of a mechanical arm and hand.

Sullivan can now operate the prosthesis naturally, with six degrees of freedom, simply by willing it to move. "He says, 'Doc, now I don't have to think about it so much anymore - I just do it,'" Kuiken reports.

But command and control aren't enough to meet DARPA's challenge. Amputees want sensory feedback from their new arms. So the Revolutionizing Prosthetics Program team plans to capture heat, cold, pressure and proprioception data - the signals that keep us aware of our limbs' position in space - and feed them into the users' nervous systems.

Kuiken and Sullivan have already made a start on that. They connected a pressure sensor on Sullivan's mechanical hand to a computerized plunger on his chest. When the hand felt pressure, the plunger pressed on the spot where the stump of Sullivan's sensory nerves was grafted to his skin. And he felt it.

"Psychologically, it's his hand he's feeling," Kuiken says. "It's still rather crude, but it's important information."

If the Revolutionizing Prosthetics Program work succeeds, Ling said, its benefits would not be limited to U.S. military personnel with missing arms. "I can easily see this jumping off to give us a much better [prosthetic] leg."

With research and development paid for by the government, the mechanical arms would become more affordable, and the market for them much larger.

For video of Jesse Sullivan go to

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