Imagining a bionic future

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.

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