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Imagining a bionic future

As researchers and engineers test the limits of science to build better prostheses, they imagine a bionic future in which prosthetic devices look and function like the original limb.
/ Source: contributor

When Paul Selmer lost his right leg below the knee in a hunting accident, a doctor fitted him with a standard prosthesis that required a waist belt to swing the wooden foot with each step. Selmer remembers it feeling like a “sandbag.”

That was 28 years ago. The gallery owner and small-aircraft pilot is now a devotee of a high-tech device called a PROPRIO foot, which utilizes sensors, artificial intelligence and microprocessors.

“I marvel at how far we’ve come and how far we can go,” said Selmer, who was unable to fly newer planes until discovering the PROPRIO. According to the Amputee Coalition of America, Selmer is one of 1.9 million people living with limb loss in the country, many of whom have benefited from breakthrough technological advancements in the past few years.

Recent government, private industry and academic prosthetic research has yielded, among other innovations, a thought-controlled mechanical arm, an artificially intelligent knee, and a hand with articulated fingers that can pinch and grasp objects. As researchers and engineers test the limits of science to build better prostheses, they imagine a bionic future in which prosthetic devices look and function like the original limb.

“Over 10 years the technology will only improve in terms of the size, weight and cost of the devices,” said Ian Fothergill, a prosthetic fitter and clinical manager for Ossur Americas, which designed Selmer’s PROPRIO foot.

Fothergill’s aluminum prosthesis, for example, features sensors that quickly measure real-time motion and gather information about gait and surface angles. Bluetooth technology enables wireless transfer of the data to a software-empowered microprocessor which then directs the components to mimic and anticipate Selmer’s natural movements.

“The next big leap will be in terms of the control system,” Fathergill says. “People will be able to integrate their thoughts into how the device moves.”

This promise of seamless control, as well as cheaper but sturdier materials and technological innovation, is what’s driving the prosthetic market. The American Orthotic & Prosthetic Association estimates that businesses provide $3.5 billion worth of services to orthotic and prosthetic patients annually.

Increased government spending and research, triggered by the number of amputee soldiers returning from Iraq and Afghanistan, has played a significant role in helping to allocate resources for bold new projects.

State-of-the-art innovations for soldiers may also produce encouraging results for those with diabetes-related amputations; the disease accounts for more than half of all lower limb amputations each year. According to the Center for Disease Control, the number of Americans diagnosed with diabetes is expected to increase from 20.8 million to 48.3 million by 2050. The nation’s climbing obesity rate, which is linked to Type 2 diabetes, has already required prosthetics makers to adjust the weight limit of a lower-limb extremity prosthesis from around 225 pounds to 300 to 350 pounds. What began as an experiment in restoring mobility to soldiers may be a boon for long-term public health.

In February 2006 the Defense Research Advancement Projects Agency, or DARPA, committed close to $50 million to the improvement of prosthetic limbs. At the time, 387 soldiers had returned from Iraq and Afghanistan as amputees. As of October 2007, that number reached 751.

The Revolutionizing Prosthetics program set an ambitious deadline of utilizing previous power system, robotics, neuroscience, sensor and actuation technology and research to create a prosthetic arm controlled by neural signals by 2009. The Johns Hopkins University Applied Physics Lab, along with 30 different private, government and university collaborators, was awarded $30.4 million to evaluate the research and develop potential designs. Their efforts yielded two prototypes that have been tested by amputees and in virtual environments.

Proto 2, the second of their designs, was unveiled in August. It is a mechanical arm made of high-strength aluminum alloys, carbon fiber components, and molded devices. The limb, which includes a life-like hand and articulated fingers, is thought-controlled and can perform more than 25 degrees of freedom.  The device allows the wearer to lift upwards of 40 to 50 pounds, open and close its fingers and bend at the elbow and wrist. Powered by a rechargeable battery and 25 different microprocessors and motors, it receives commands from electrodes attached to the residual limb which read electrical signals in the user’s muscles.

“Our philosophy is to try to get access to much wider signals and interpret from signals what the person is trying to do with their limb,” said APL project manager Stuart Harshbarger, referring to how the limb system’s electrodes pick up muscle signals which then trigger movement in the prosthetic. Previous myoelectric models have required the user to “map” muscle movements to prosthetic functions like bending the wrist or elbow.

Reading nerves
Researchers have enabled communication between the prosthetic device and the wearer through a technology known as Targeted Muscle Reinnervation, or TMR, which involves taking remaining nerves from the amputated limb and placing them, in this case, in the pectoral area of the chest where electrode sensors read signals for movement. Proto 2 also incorporated injectable myoelectric sensors which serve a similar function as electrodes but can be implanted or injected into the body.

“We look at these signals with pattern recognition software and then we’re able to allow the limb system to interpret these patterns,” said Harshbarger. “The limb learns what the patterns are and the person has to think only about the movement.” The team hopes a future model, which will incorporate sensory feedback, will be tested by the Food and Drug Administration and be publicly available by 2009.

Harshbarger believes the technological advancements of the project will benefit not only amputees, but also people affected with mobility-limiting diseases like Parkinson’s or spinal cord injuries.

“An [amputee] who is healthy and given the right tools can live a healthy and productive life,” he said. “Without those tools, it really changes your outcome.”

Since upper extremity limb loss accounts for a majority of all amputations each year, and thus draws fewer research dollars, the government hopes its investment will improve technology for arm and hand prostheses.

In addition to the Proto 1 and 2, an array of groundbreaking prosthetic devices have been developed by private companies and academic researchers in the past year, including a myoelectric prosthetic device with motors in each finger joint, a motor-powered ankle-foot, and an artificially intelligent knee. Creators of the devices have puzzled over how to provide power to a prosthetic limb without adding weight, how to most efficiently enable neural or nerve communication between the device and the wearer, and how to provide the functionality and appearance of a native arm.

More projects are underway; in late September, the Department of Defense awarded Idaho State University with an $842,000 grant to build a “smart” prosthetic hand capable of grasping, lifting and twisting as well as responding to sensory and visual feedback.

Yoky Matsuoka, a recently appointed MacArthur Fellow and an associate professor of Computer Science and Engineering at the University of Washington, is aiming beyond DARPA’s four-year deadline with visions of an anatomically correct and life-like robotic hand that could be transplanted on an amputee. Made of composites and metals with a polymer exterior, the hand would connect directly to the nervous system and allow an amputee to use it instinctively.

Paul Selmer, the small airplane enthusiast, is eager to see what new technologies are developed next, but said the most revolutionary innovation in his life switching from a wool sock liner to a custom-made silicone gel liner. For years, Selmer followed his fitter’s instructions and placed wool socks between his prosthesis and his stump to provide cushioning, but often developed painful sores. The new liner not only cushions the bone protrusion but it also draws sweat away from his body, helping to prevent chafing.

“I used to spend two or three days waiting for sores to heal up, but with this technology, I can just keep going,” he said.

Jeff Brandt, CEO of Ability Prosthetics & Orthotics and Selmer’s prosthetist, pointed to another low-key revolution in the field: customization. Brandt, who studied with the prosthetics researcher responsible for developing TMR technology, expects a permanent shift towards bionic technology. When treating amputees daily, however, Brandt said that the ability to customize their prostheses through the use of scanner technology has fundamentally changed his ability to provide precise-fitting and comfortable prostheses to his patients. Scanner technology allows Brandt to take digital images of a patient’s residual limb for the mold, which he can then modify with software.

“Our field has never been standardized,” said Brandt. “But now you can be very accurate about where you want modifications. Fifty years ago you had guys that were true craftsmen and could take a block of willow wood and carve a leg out of it. With technology, you can actually help the patient heal now.”