It's been two years since the Defense Advanced Research Projects Agency (DARPA) sought out ideas for creating upper-extremity prosthetics for a new generation of amputees—especially those returning from combat in Iraq and Afghanistan. DEKA Research, run by inventor Dean Kamen (famed as the creator of the Segway Personal Transporter), came up with one. The Johns Hopkins University Applied Physics Laboratory (APL), managing a team of over 30 contracted organizations like a virtual corporation, has another.
Robotic Arm
MAJOR INNOVATION Direct neural control—and eventually brain control—of artificial limbs.
WHY IT MATTERS Will provide limb replacements for injured soldiers and others with missing limbs.
ESTIMATED ARRIVAL Clinical trials by 2009, with manufacturing in 2010.
The two groups have had a friendly competition during the first two-year phase. The new limb prototypes, already in clinical trials, are modular marvels of engineering that offer far more movement—degrees of freedom in engineer-speak—than today's artificial limbs, which typically have only three possible movements. The goal is an artificial limb with the same size, weight, and dexterity as a real arm. That means as many as 25 degrees of freedom working in conjunction, so the patient doesn't have to choose between bending an elbow and manipulating fingers but can actually do both at once.
Perhaps more miraculously, as both DEKA and APL enter the next phase of DARPA's Revolutionizing Prosthetics 2009 (RP 2009) program, the limbs can interface directly with an amputee's nerve endings through targeted muscle reinnervation. It's a method developed at Northwestern University and the Rehabilitation Institute of Chicago to let nerve signals actuate unused muscles to control an artificial hand and fingers.
"For someone who lost his arm closer to the wrist, there are more options" for controlling an artificial hand, says Stuart Harshbarger, systems integrator and team leader with the APL group. "If you don't have muscles available, you go to the peripheral nerve itself."
APL places injectable myoelectric sensors (IMES) into the flesh to look for the electrical activity in a muscle contraction and uses it to control the prosthetic arm wirelessly. IMES should go to the FDA for approval soon. "I think we'll see a highly dexterous limb system in the manufacturing transition process in two years," Harshbarger says.
Eventually, these new limbs could interface with the brain itself, a goal that both DEKA and APL are working toward. It is, after all, what everyone envisions going back to The Six Million Dollar Man. Getting direction from the motor cortex of the brain could be the only option for an amputee who also has a spinal injury. The initial goal, though, is a neural interface strategy, such as IMES, that's minimally invasive.
DEKA's project manager, Rick Needham, calls complete, intuitive brain control the researchers' holy grail. He says there's even the potential for permanently attaching a prosthesis to the patient's skeletal system. Much like APL's, DEKA's prototype was also created with a team of organizations and is designed to handle multiple methods of control. DEKA calls its artificial limb design the "Luke Arm," after Luke Skywalker, who gets a fully functional artificial hand in The Empire Strikes Back.
Patient comfort is a major design goal for DEKA. The researchers found that a number of amputees don't even use their prosthetics because the limbs hurt to wear. They create constant pressure because they're attached so tightly. The Luke Arm has a dynamic socket that can adjust, becoming tighter when the user is lifting something and extra support is needed, but looser if the person isn't using the limb.
Needham gives a lot of credit to DARPA and Colonel Geoffrey Ling, the manager of RP 2009, for creating this project, which will benefit not only soldiers but also anyone with a missing arm. "DARPA stepped up and made resources available to make this happen. We appreciate them having the vision to do that," Needham says.
Harshbarger says APL's goal for its artificial limb is to have it settle into a manufacturing cycle similar to those of digital cameras or phones. "Every couple of years, a new generation comes out with new capabilities, more pixels, more bells and whistles, but the price stays about the same." He wants these new limbs to cost no more when manufactured and fitted than an artificial limb costs today. That's not small potatoes: $75,000 to $100,000 by the time a clinician fits the prosthesis. But the much higher level of performance brought about by the new technologies will at last make it feel like money well spent.
