This story is part of a series about advances in prosthetic arms. For more, watch the video of the "Luke Arm" in action.

PHOTO: Dean Kamen: DEKA Research; Robo Hand: Dirk van der Merwe

Dean Kamen's “Luke arm”—a prosthesis named for the remarkably lifelike prosthetic worn by Luke Skywalker in Star Wars—came to the end of its two-year funding last month. Its fate now rests in the hands of the Defense Advanced Research Projects Agency (DARPA), which funded the project. If DARPA gives the project the green light—and some greenbacks—the state-of-the-art bionic arm will go into clinical trials. If all goes well, and the U.S. Food and Drug Administration gives its approval, returning veterans could be wearing the new artificial limb by next year.

The Luke arm grew out of DARPA’s Revolutionizing Prosthetics program, which was created in 2005 to fund the development of two arms. The first initiative, the four-year, US $30.4 million Revolutionizing Prosthetics contract, to be completed in 2009, led by Johns Hopkins Applied Physics Laboratory in Laurel, Md., seeks a fully functioning, neurally controlled prosthetic arm using technology that is still experimental. The latter, awarded to Deka Research and Development Corp., Kamen’s New Hampshire–based medical products company (perhaps best known for the Segway), is a two-year $18.1 million 2007 effort to give amputees an advanced prosthesis that could be available immediately “for people who want to literally strap it on and go.” Kamen’s team designed the Deka arm to be controlled with noninvasive measures, using an interface a bit like a joystick.

On the second floor of the mill complex that houses Deka, a 650-square-meter space is dedicated to realizing the Luke arm. Right past the entrance is a life-sized Terminator figure missing its left arm; in its place is the same kind of harness that patients wear when testing the Deka arm. It’s there for inspiration. The Terminator is in line for its new arm behind volunteers like Chuck Hildreth, who come to Deka to help the engineers prepare for clinical trials.

Hildreth, 44, lost both arms 26 years ago, when he was electrocuted while painting a power substation. His badly burned right arm was so damaged that doctors even had to remove the shoulder blade. They saved part of Hildreth’s less-damaged left arm, amputating about halfway between the shoulder and the elbow.

Since then Hildreth has been wearing—or more accurately, not wearing—a traditional prosthesis. As Kamen discovered when he talked to patients in rehabilitation clinics and at VA hospitals, after the initial shock of amputation wears off, usually within a year or two, patients stop wearing their prostheses. Even extreme levels of amputation don’t much curb this tendency. Wearing the burdensome prosthetic is simply not justified by the small amount of assistance it provides, says Hildreth. “It gets sweaty and slippery,” he says. He’s gotten so used to living without arms that he changes the blades in his lawn mower with his feet.

When DARPA director Tony Tether and Revolutionizing Prosthetics program manager Colonel Geoffrey Ling approached him in 2005, Kamen says he thought they were crazy—“in the good kind of way,” he says. There was no financial incentive to create a next-generation prosthetic arm. The research and development costs were enormous. Unless funded by DARPA, no private company would take such a risk for such a comparatively small market (in the Americas, about 6000 people require arm prostheses each year). Kamen spent a few weeks traveling around the country interviewing patients, doctors, and researchers to get an idea of the current technology—and soon saw the deficit in available arm prosthetics. He was swayed by the discrepancy between the current state of leg prostheses and that of arm prostheses. “Prosthetic legs are in the 21st century,” he says. “With prosthetic arms, we’re in the Flintstones.”

So he set out to reinvent the prosthesis that has been pretty much the same since the U.S. Civil War. Until now, a state-of-the-art prosthetic arm has meant having up to three powered joints. However, since this type of arm is frustrating to control and doesn’t provide that much functionality, most users still opt for the hook-and-cable device which has been around for over a century. In either case, these prosthetics only have three degrees of freedom—a user can move the elbow, the wrist, and open and close some variant of a hook.