Johns Hopkins Unveils Proto 2
November 2007 Issue
In response to the plight of World War II amputees, the National Academy of Sciences (NAS) established the Artificial Limb Program in 1945 to promote scientific research to improve prosthetic device design. Emphasis was placed on investigating the movement of normal human limbs, so prostheses could be designed to appear as lifelike as possible.
More than half a century later, U.S. troops injured in Iraq have required limb amputations at twice the rate of past wars. To assist veterans, the Defense Advanced Research Projects Agency (DARPA) Revolutionizing Prosthetics program invested in a beta design of an upper-limb prosthetic from a team led by the Johns Hopkins University (JHU) Applied Physics Laboratory (APL) in Laurel, Maryland.
The new limb research, funded by a $54 million grant from DARPA, has shown seven degrees of freedom and promises 27 degrees of freedom.
"This is the largest DARPA project we've ever been awarded," says Dan Tyler, department head of the university's National Security Technology Department, which develops technologies to enhance the survivability, sustainability, and performance of U.S. troops.
During the first phase of funding, researchers developed Proto 1, a prototype of the first fully integrated prosthetic arm that can be controlled naturally, provide sensory feedback, and allow for seven degrees of freedom. It was fitted for clinical evaluations conducted by team partners at the Rehabilitation Institute of Chicago (RIC) in January and February of 2007. (Editor's note: More information about Proto 1 can be found at 'Bionic' Amputees Display Thought-Controlled UE Prostheses )
"For risk reduction, we produced a seven-degree-of-motion [arm] and fitted it on a double amputee. He loved it so much and DARPA got so enthused that they are paying us extra money this year to transition the seven-degree-of-motion arm to industry to have them start to produce it so it can be used commercially by our partner on the project, Otto Bock," Tyler says.
APL, which was responsible for much of the design and fabrication of Proto 1, has created the second upper limb, a prosthetic prototype that offers 27 degrees of freedom as well as the strength and speed of movement approaching the capabilities of the human limb. It was developed for phase II of the DARPA project, which began October 1. In fact, the team showed off the prosthesis in late August at DARPAtech, a systems and technology symposium held in Anaheim, California.
The limb is built for a transhumeral, or a complete shoulder disarticulation, and is integrated into the central nervous system. Internal components are made of aluminum and composite-graphite materials. The limb will also include a synthetic cosmetic cover. The goal is to have the finished limb weigh in at seven pounds, says Dexter Smith, the laboratory's biomedicine business area executive.
Tyler says the limb combines more than 80 individual sensory elements for feedback of touch, temperature, and limb position. Multiple sensors are used. There are myoelectric sensors on the surface of the skin and implantable myoelectric sensors (IMES) that go into the muscle.
In addition, the team used targeted muscle reinnervation to deliver the full range of motion, Tyler says. To work, it needs to be wired directly to the central nervous system.
"There are two reasons why," he says. "If you are using muscles with the IMES to control the arm, it's very unnatural. If you go directly into the peripheral nerves or the cortex of the patient, he feels like he is just moving his arm. It's completely natural and normal."
Another reason for the neural integration as opposed to myoelectric is the existence of pressure and temperature sensors in the hand, which deliver feedback signals - or afferent signals - that go back to the brain, Tyler says.
Chris Lake, the southwest clinical director of the Irving, Texas-based office of Advanced Arm Dynamics, says the prototype would improve the lives of patients by providing sensory feedback and streamlined use of the limb. To address the spectrum of prosthetic needs, today's user must combine different prosthetic options, adaptive equipment, and custom-made adaptations to meet the basic functional capacity of the human hand, he says. "New technologies will allow multiple grasping patterns in one device, whereas prior options require the interchange of several different devices, often interrupting the spontaneous flow of upper-limb function as the individual retools' the prosthesis for a different task."
Tyler says the hand is motorized using two techniques. To get the range of freedom, the team used co-bionics - or neuro-stimulation devices - that are in the lower half of the limb
coupled into the fingers, almost like tendons, to make them move. Currently, the hand cannot be detached. It provides all needed functionality, and it doesn't need additional adaptive equipment, he says.
Smith says final prototypes will be completed in two years.
"I definitely think that advances in prosthetics and integrating neurology is going to become commonplace," says Mark L. Edwards, the director of prosthetics education at Northwestern University's Feinberg School of Medicine. "Surgical techniques and integration with computer technology is going to let patients function at a very high level."
However, Edwards says the cost for a high-tech prosthetic device is prohibitive. In addition, patients may not want to undergo additional surgeries after suffering an amputation unless there are viable or functional improvements.
A prosthesis also must be durable. Since emerging devices are often designed with high-tech microprocessors, water and dirt can cause major problems.
"A prosthesis has to encompass many environments - shower, work, and recreational activities - so for a prosthesis to be durable is an important feature," Edwards says. "One of the main problems that people have with wearing upper-limb prostheses today is the cosmetic covering... It's not very durable, it stains, and it is costly to replace. That's a drawback."
But the entrance of new devices into the marketplace provides additional career opportunities to practitioners.
"It's going to require that practitioners have more knowledge of the other sciences that are going to affect them, such as engineering and biomechanics," Lake says. "It's going to create opportunities for them to specialize in a specific type of technology."
Lake says the breakthrough at JHU is a concrete sign of the future of upper-limb prosthetics. These new devices coming online will offer tremendous potential to the wearer: more flexible motions; better control; greater continuity from one task to another; and improved aesthetics. In short, it will come closer to the performance of the natural human hand.
But he noted that a high-tech prosthetic hand is not a "plug-and-play" device like a radio.
"We can't hand people a box and send them on their way," Lake says. "Each patient presents unique fitting challenges in terms of the shape and condition of the residual limb. Multiple adjustments and fine-tuning will be necessary to accommodate the user's personal physiology, lifestyle, and individualized movement patterns.
"In addition, the psychological side cannot be overlooked," Lake adds. "Prosthetic users need emotional support that acknowledges their sense of loss while helping them overcome obstacles that impact their daily lives."
Mary Rose Roberts is a Chicago-based freelance writer who focuses on emerging technologies. She can be reached at firstname.lastname@example.org
Editor's note: The O&P EDGE has been providing readers with ongoing coverage of the Revolutionizing Prosthetics program. Additional stories can be found in the archives.