This is part of IEEE Spectrum's SPECIAL REPORT: WINNERS & LOSERS 2009, The Year's Best and Worst of Technology.
Armed and READY
Jonathan Kuniholm wears a prototype of the prosthetic arm created by the DARPA Revolutionizing Prosthetics project.
It’s October at Duke University, in Durham, N.C., and Jonathan Kuniholm is playing ”air guitar hero,” a variation on Guitar Hero , the Nintendo Wii game that lets you try to keep up with real musicians using a vaguely guitarlike controller. But the engineer is playing without a guitar. More to the point, he’s playing without his right hand, having lost it in Iraq in 2005. Instead he works the controller by contracting the muscles in his forearm, creating electrical impulses that electrodes then feed into the game. After about an hour he beats the high score set by Robert Armiger, a twoâ¿¿armed Johns Hopkins University engineer who modified Guitar Hero to train amputees to use their new prostheses.
Armiger’s research is part of a nationwide effort to create a neurally controlled prosthetic arm. That arm has been the focus of much media attention, but that focus obscures the truly groundbreaking research typical of the Revolutionizing Prosthetics 2009 (RP2009) program.
The U.S. Defense Advanced Research Projects Agency (DARPA) is pouring at least US $71.2 million into the program in the hope that it will let amputees do what most people take for granted: make gestures, test the water in a teacup, turn a key, even peel the shell off an egg. Words like bionic and thought -controlled have been thrown at the project, but they don’t do justice to the sheer ordinariness of its purpose. DARPA isn’t looking for a superstrong ”Six Million Dollar Man” arm; it just wants an arm that moves exactly like a real one does.
Yet even making just a garden-variety arm requires a herculean effort, not only in the field of mechatronics but in neuroscience, electrical engineering, cognitive science, signal processing, battery design, nanotechnology, and even behavioral science. This four-year project is wildly ambitious even by the standards of the Pentagon’s mad-science wing. After the program concludes at the end of 2009, many of the arm’s various technologies will go into FDA clinical trials and then out into the world.
But some of the RP2009 technologies have already begun to filter out. In October, a Canadian hospital announced that it had used part of the control mechanism of the DARPA arm to steer regular, nonrevolutionized prosthetic arms in two patients. Simply borrowing that one technology has made huge improvements in commercially available prosthetic devices.
DARPA’s device is the world’s first truly neurally controlled prosthetic arm. To keep it from being the last, its designers are explicitly creating it with other designers in mind. The program’s engineers want a quasi–open source platform for hardware and software, so that the RP2009 specifications will replace the Babel-like confusion of scattered prosthetic-arm designs with a platform everyone can use to finally push the technology into the 21st century.
The Revolutionizing Prosthetics program has been testing control technologies on volunteers around the country: at the Rehabilitation Institute of Chicago; at OrthoCare, in Oklahoma City; and at the Johns Hopkins University Applied Physics Laboratory (APL), in Laurel, Md. RP2009 team leader Stuart Harshbarger says the investigations will likely extend later this year to the Salt Lake City Veterans Affairs hospital, one of the military’s major rehab centers for amputees.
Such centers are reeling under the burden posed by the wars in Iraq and Afghanistan, where improvements in body armor have saved the lives but not always the limbs of many soldiers who would have died in earlier wars. The number of such amputees stood at 1214 on 1 August 2008, compared with 4809 deaths and 33 116 injuries, making for a ratio of amputations to deaths that’s roughly twice as high as in any previous war.
Those numbers have turned amputee research from a backwater to a high priority. In 2005, DARPA set up the prosthetic-arm project and put it in the hands of Geoffrey Ling, a neuroscientist trained at Georgetown University, in Washington, D.C., who is also a colonel in the U.S. Army.
Ling split the program into two distinct parts. The part headed by Dean Kamen’s New Hampshire–based Deka Research and Development Corp. had a 2007 deadline for creating a sophisticated mechanical limb by making the most of existing technologies, using noninvasive control mechanisms.
The complementary four-year program has a 2009 deadline to reinvent prosthetics from the ground up so that they can be biologically controlled. The goal is to restore sensory feedback to amputees so that they can again perceive heat, cold, pressure, and the position of a limb in space. All these faculties must fit inside a package that has the look, weight, strength, dexterity, natural movement, and toughness of an arm [see illustrations, ”Custom Built”].
Ling tapped APL to oversee this nationwide ”Manhattan Project” for prosthetic arms. Over 30 universities and research institutions are collaborating on the project, all of them leaders in their fields. ”I thought it was going to be like herding cats,” says Harshbarger, Ling’s APL counterpart, who directs the 2009 effort. But countering stereotypes of academic competitiveness, these 300â¿¿odd researchers have been working together in lockstep, project first and egos last, to make the endeavor succeed.
Creating an arm that actually interfaces with an amputee requires an encyclopedic understanding of countless disciplines including power management, neural integration, and anatomy. APL built two mechanical prototypes, both of which were marvels of modern engineering. The Rehabilitation Institute of Chicago (RIC) developed surgical techniques to reroute existing nerves in amputees so that they interface with the electronics in the prosthetic arm. Chicago-based Sigenics developed implantable electrodes to wirelessly transmit the electrical signals from residual muscles directly to the prosthetic limb. Researchers at the University of New Brunswick, in Canada, developed signal-processing algorithms to decipher the noisy biopotentials from the reinnervated muscle in real time. Researchers at the University of Utah developed brain-penetrating electrodes to tap nerve impulses at their source. Johns Hopkins University has developed what it calls the Virtual Integration Environment, in which an amputee can practice by ”driving” a virtual arm with nerve signals.