The future of prosthetics is in your mind
February 24, 2010
Robotics has long fascinated the mind of the public. Androids, bionic men and exoskeletons populate both the large and small screens. But until recently, the technology seen in pop culture has not been manifested in daily life. Now, the Department of Defense is revolutionizing the field of prosthetics and turning science fiction into science fact.
The Defense Advanced Research Projects Agency is working in unison with the Department of Veterans Affairs and the DEKA Research and Development Corporation to manufacture and study advanced upper-extremity prosthetics to benefit Soldiers, other servicemembers and civilians.
While DARPA is spearheading the research for the program, DEKA will manufacture prototypes, and the VA will work with both agencies to provide patients, medical experts and conduct clinical studies.
"You'll find 50 percent of people who need upper-extremity prosthetics don't even use them," said Col. Geoff Ling, program manager of the Revolutionizing Prosthetics program at DARPA.
"They just put it in the closet. They'd rather have a rubber hand that looks like a hand so nobody's staring at them, but that doesn't do anything at all," because the arm and hand prosthetics currently on the market are cumbersome, he said.
The Revolutionizing Prosthetics program was created to give Soldiers and other servicemembers who have experienced limb loss the most advanced replacements available, and to give them the choice to return to active duty.
"The whole idea of any of these programs is to return choice to the patient. You don't have to go back to active duty, but if you want to, it gives you enough level of function that you can," Ling said.
The program has two development tracks: one track developed a sophisticated, myoelectric arm-an arm that responds to electrical signals from remaining muscle-to perform complex functions like personal hygiene, Ling explained. Eventually, the program personnel want users to be able to control this arm with signals from the brain. The second track developed a "strap and go" arm users control with techniques that don't require invasive procedures.
Ling, a board-certified neurologist and critical-care doctor, said the program targets upper-extremity prosthetics, because lower-extremity prosthetics were very good, while the upper limbs needed further development.
"The upper extremity was a bugaboo," Ling explained. "Even the VA couldn't handle that one. And the reason for that is because the arm, which is really quite an amazing appendage, really has only one function, and that's to move your hand where it wants to go."
That's where the difficulty manifests, he said. The human hand has 21 points of articulation, which all move independently. Developing the technology for upper-extremity prosthetics is a vastly different task than developing the lower extremities, because of the complex movements involved.
"When you get hurt in your arm, you don't lose (an arm) and keep your hand, you always lose your hand...so you lose the most complex part. That becomes very daunting," Ling said.
During the early 2000s, DARPA experimented with determining how the brain codes signals for motor movement, and how to use that data to control external devices, like a prosthetic arm. In the experiment, researchers at the Human Assisted Neuro Device program at Duke University trained chimpanzees to play a computer game for a reward.
"All the while, they are measuring the firing of the brain using electrodes, little electrodes, that are associated with the arm movements over an area of the brain we call the motor strip," Ling said.
The experiment determined that the brain uses an initiation code to begin a motor activity. Doctors and scientists were eventually able to play the game for the chimpanzee with the computer and calculated initiation codes, based solely on the motor signals from the chimp's brain, Ling said.
In the second part of the experiment, scientists from the University of Pennsylvania added a robotic arm. The chimpanzee was able to work the arm with his mind alone.
"At that point, we had our paradigm shift. No more myoelectric, that is, triggering these switches with your back muscles. (Instead, you would be) thinking like you normally would think," Ling said.
With the technology in place, DARPA was able to push for the development of the arm itself. Even as they are researching more advanced prosthetic arms, DARPA's goal is to get a highly functional arm and hand unit out as soon as possible, Ling said. DEKA took on that responsibility and created the arm for the program's second track. They had a prototype ready to test in two years.
Currently, DEKA is conducting clinical optimization trials with the VA, which is supplying patients and prosthetic specialists, Ling explained.
Dr. Linda Resnik, a physical therapist with a clinical background in orthopedics, is overseeing the optimization study at the VA. The study will evaluate design features and collect feedback from Soldiers and other patients so the final version of the arm can meet the needs of the amputees to the fullest, Resnik said.
The DEKA arm weighs, from shoulder to hand, between 8 and 12 pounds-about the weight of a female arm, Resnik said. It uses an "active socket," which for some users has air bladders that can be inflated or deflated to adjust the fit of the arm.
"Probably the most exciting part of it is the hand, because the hand has six different grip patterns, which range from being able to hold a round object, like a tennis ball, to being able to have a fine pinch, picking up a paper clip or using a power tool," Resnik said.
The arm is a powerful device: the elbow joint is able to lift 20 pounds, and the arm has end-point control, meaning the shoulder and elbow move simultaneously to reach an end-point. For example, when a person reaches for a glass of water, the shoulder rotates at the same time the elbow extends, working together to direct the hand to a point in space. Arm prosthetics currently on the market have to move one joint and then the next to reach for things, and the elbow joint can only support about 4 pounds, Resnik explained.
Paul Yarbrough, a former staff sergeant and one of the first subjects in the DEKA arm study, was very pleased with his testing of the arm. "The DEKA arm is pretty unbelievable," he said, explaining the prosthetic functions just like a real arm and hand. It even lets the wearer know how much pressure is being applied to an object in a grip.
Yarbrough joined the Army in 1989 and was injured during a training exercise in 1991. He and his team were simulating how to clear out buildings and were dropped from a helicopter over the hot zone. "It was at night, and when they dropped us, they dropped us by power lines," he said.
"The power line wrapped around my neck and right to the ground," Yarbrough recalled. He lost both his arms due to the electrical burns, and now has prosthetics.
During the accident, Yarbrough was holding a weapon in his left hand and a metal clamp in his right. It had been raining, and his body acted like a conduit-luckily, the accident did not affect his heart, he said.
"It actually burned my right arm completely off, because I was holding the weapon," Yarbrough said. "Then on my left arm, it left me with my thumb and my first finger. And after multiple surgeries and multiple skin grafts, we just decided I could either keep that one thumb and one finger or just go ahead and get it amputated and just start out fresh."
During the time Yarbrough tested the arm, he discovered a few interesting things, the first of which was that he kept forgetting the prosthetic wasn't his real hand.
"The fingers flex so you can see what you're picking up," Yarbrough said. "It is truly a remarkable invention."
Next, Yarbrough noted that the device was a little heavier than he expected, and the reaction time wasn't quite as fast as he had hoped. Resnik thinks those observations are key. The point of the study is to solicit feedback to help improve the arm in future development.
Resnik believes the advantage of all the feedback received during the optimization trial will help build a prosthetic that amputees really want.
Yarbrough is extremely happy with this second-generation prototype despite the weight and reaction time. He said the arm greatly increases his dexterity and independence.
"I actually sewed a button onto a shirt with this thing," he said, amazed. "I don't think I sewed a button when I had hands! That's how incredible this hand is...it's the closest thing I've seen to date to replacing a hand."
The second phase of the Revolutionizing Prosthetics program will bring the technology even closer to seamlessly replacing upper extremities, through the development of a brain-controlled arm, Ling said. After that, the program can develop how to integrate the prosthetic with the remaining biological arm-but all that is for the future.
"I'd like to imagine that Luke Skywalker's arm, or Will Smith in 'I, Robot,' his arm, can become a reality one day. I believe it can be," Ling said.
"This is a testament to taking care of your own. This is a DOD project, you know, that is really meant to take care of the veterans...they are not forgotten by any stretch of the imagination," Ling said. "Our goal is to give them back the choice to stay on active duty."
"I think the future of prosthetics is just tremendous," Yarbrough said. The prototype arm gives him something to look forward to.
Download a brochure about prosthetics at http://www.research.va.gov/resources/pubs/docs/prosthetics-brochure.pdf . A-a,!A