LAUREL, Maryland – Jonathan Kuniholm's right arm terminates in a carbon-fiber sleeve trailing cables connected to a PC. He has no right hand, unless you count the virtual one on a display in front of him. The CG hand, programmed to look like silvery stainless steel, moves through a sequence of motions: spherical grasp, cylindrical grasp, thumb to forefinger – all in response to signals from Kuniholm's muscles picked up by electrodes in the sleeve.

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Kuniholm and his fellow engineers at Johns Hopkins University's Applied Physics Laboratory, or APL, are at work on the most ambitious prosthetics project in history. They seek the field's holy grail – to build an artificial human arm that acts, looks and feels to its user like his native arm, and to do it with astonishing speed by the end of 2009.

To get there from here, they'll have to achieve major breakthroughs in neurological control systems and robotics. But they have a more immediate task, which is to assemble the next prototype, called Proto 2, in time for Kuniholm to show it off this week at the 25th Darpa Systems and Technology Symposium in Anaheim, California.

Darpa has called on engineers at 28 companies and research institutions in six countries to help. It all comes together in this workshop, where the APL engineers seek to integrate pattern-recognition software, custom-built computer chips, electric motors and other actuation systems into a seamless whole that a user can don in the morning and use to accomplish daily tasks like tying his shoes, typing, throwing a ball, even playing a piano, with hardly a thought.

Darpa program managers launched Revolutionizing Prosthetics 2009 two years ago to help soldiers like Kuniholm who were returning from combat in Iraq or Afghanistan missing all or part of an arm. Most of the amputees, Kuniholm included, have elected to use simple, body-operated hooks whose basic technologies date back to World War I instead of the current generation of myoelectric arms that read muscle signals from electrodes on the skin. The higher-tech arms are slower, heavier and more difficult to operate than hooks, whose design has changed little in almost 100 years.

Hedging its bets, Darpa is also funding the less-ambitious Revolutionizing Prosthetics 2007 project. That effort, intended to produce the best prosthetic arm possible with currently available technology, is headed by Deka Research and Development, the Manchester, New Hampshire, company run by Segway inventor Dean Kamen. Deka aims to unveil its completed arm by the end of this year, while APL will push past this year's prototypes in an attempt to advance the state of the art.

For now, both Deka and APL are based on cutting-edge myoelectric control systems pioneered by Todd Kuiken at the Rehabilitation Institute of Chicago, or RIC. Conventional myoelectric controls use electrodes on the surface of the skin to read muscle signals from some part of a user's body unaffected by his amputation – his back for example – and pass the signal on to an artificial limb. The user twitches her back, and the limb moves in response.

But moving one's back muscles to operate an arm is counterintuitive, so in 2002 Kuiken improved on this system by surgically rerouting nerves from the arm stump of amputee Jesse Sullivan to muscles in his chest. Sullivan's re-enervated chest muscles now twitch in response to his attempts to move his missing arm, and surface electrodes pick up that muscle activity to use as a control signal. Kuiken has also had success in rerouting sensory nerves to give artificial limbs some degree of tactile feedback to their wearers.

But surface electrodes, removed as they are from the muscles they monitor, lack the resolution to gather more than the most obvious signals – like bending the elbow or rotating the wrist. To perform complex movements, users must perform combinations of gross movements to activate pre-programmed actions, like common hand grasps, much the way computer users activate macros to perform sets of keystrokes.

To gather signals required for finer control, Revolutionizing Prosthetics 2009 engineers will turn to rice-size injectable myoelectric sensors, or IMES – devices being developed by RIC scientists Richard Weir and Jack Schorsch, and Philip Troyk of the Illinois Institute of Technology. Once embedded in the muscles to be read, the IMES devices will send much clearer signals, and many more of them. Ultimately, though, scientists will have to attach tiny electrodes directly to nerves, or go right to the source with electrode arrays on the brain to give a user full dexterity. Both options are being explored by APL's research partners.

The engineers and managers working at APL appear not a bit daunted by the challenge. In fact, they seem energized by it, keeping up a playful banter with one another as they work. "Talk to the hand!" cried an engineer when another interrupted his work at an inopportune moment.

"It's been tremendously rewarding and exciting for me," said manager John Bigelow, who found it hard to stay motivated in his previous job, building navigation and weapons systems for military aircraft. He jumped at the chance to work on Revolutionizing Prosthetics 2009. "For me it's just a case of doing something that can give back."

Project head and electrical engineer Stuart Harshbarger sees prosthetics as a lifelong calling, sparked by a mowing accident that took his grandfather's feet and with them his will to live, and by a neighbor who refused to let a missing arm deter him from such demanding tasks as pruning his own trees. Of course, Kuniholm, who lost his hand in 2005 while serving as a Marine in Iraq, has the biggest incentive of all to complete the project.

While Kuniholm works to train pattern-recognition software to correctly interpret his commands and turn them into motion on his screen, engineer Mike Bridges, seated at a workstation around the corner, puts another of Proto 2's components through its paces. In response to commands issued by Bridges' computer, the Proto 2 arm attached to a mannequin executes a series of eerily fluid and lifelike motions: a salute, a swimming stroke, a hand raised to the mouth as though eating. A bright red and yellow emergency stop switch sits at the ready in case the arm runs out of control.

Power for the arm comes from a set of heavy cables running down the mannequin's back plugged into a heavy power supply on the floor. The final version of the arm will have to enclose its power supply entirely within the arm, with no increase in weight over a flesh-and-blood limb. Ordinary batteries and electric motors won't be up to the task, so engineers at Vanderbilt University are working on a pneumatic actuation system, powered by steam that's produced by hydrogen peroxide reacting with an iridium catalyst.

In another part of the APL workshop, engineers Eric Faulring and Chad Dize hunch over a brightly lit workbench and pick apart the chrome inner workings of Proto 2's hand, whose wrist trails artificial tendons like white and yellow fishing line. This so-called extrinsic hand attaches to a device known as a collaborative robot, or cobot, shaped like a forearm that's resting on the bench nearby.

The cobot's motors are designed to pull the tendons in the hand to actuate the fingers the same way muscles in a native forearm pull tendons. The team is also working on an intrinsic version of the arm, with motors enclosed within the hand, to see if they can improve on nature's design.

Kuniholm is all for augmenting the natural abilities of his missing hand. When a visitor commented that the Proto 2 hand's lack of side-to-side motion in the wrist might make it difficult to operate a computer mouse, Kuniholm replied, "Why do I need a mouse? Why can't I plug my arm right into a USB port?"