Developing a Thought-Controlled Robotic Arm

Dr. Albert Chi, a 2003 graduate of the University of Arizona College of Medicine, Tucson, and a trauma surgeon at Johns Hopkins Hospital, Baltimore, MD, is part of a team of engineers and surgeons developing a Modular Prosthetic Limb—a robotic arm and hand that a person can control using their thoughts. Patients wearing the still experimental robotic limb, say they are able to point a prosthetic finger, grasp a ball, and flex their wrist. In addition, they can distinguish between fingers, and detect the difference between soft and hard objects.

Chi began working on brain control algorithms aimed at controlling robotic arms 20 years ago, while studying biomedical engineering at Arizona State University. His faculty adviser was neurobiologist Andrew Schwartz, who first linked the information coming from the sensory and motor neurons in the brain's cortex to a robotic arm and hand.

At Johns Hopkins, he is part of the $150 million Revolutionizing Prosthetics project led by neuro-intensivist Geoffrey Ling, MD. Revolutionizing Prosthetics is funded by the Defense Advanced Research Projects Agency in response to the more than 1,300 men and women who have come home from war in Iraq and Afghanistan as amputees.

“Specialty centers like Walter Reed Army Hospital do a great job as far as getting a lot of these soldiers back to active duty—as high as 16 percent today, up from around 2 percent in 1980,” Chi said. “But there is a huge discrepancy between upper-extremity injury and lower-extremity injury. An upper-extremity injury is pretty much a career-ending injury for you.”

Dr. Ling challenged researchers at Hopkins and the Applied Physics Lab, to come up with an engineering solution, and, he says, what they came up with is the Modular Prosthetic Limb, which is capable of replacing the natural arm's motor and sensory function. The 100 sensors built into the arm are capable of “feeding back” temperature, pressure, joint angles, and acceleration, Chi explained.

In patients who are quadriplegic, the Modular Prosthetic Limb requires cortical implants to convey neuronal information to electronic sensors in the prosthesis. But for patients whose spinal cord is intact, Chi has performed a new surgical technique to control the prosthesis. Called Targeted Muscle Reinnervation, the technique utilizes the still viable nerves and muscles in an amputated limb and reroutes the endings of three nerves in the patient’s stump to adjacent muscles.

The patient's arm is given six months to heal before the patient begins what will be a lifelong routine of 15 to 30 minutes a day of mental imagery exercises, which re-establish the cortical signals that can now be transmitted to electrodes in the Modular Prosthetic Limb.

Chi was commissioned into the Naval Reserve in April, and will now work with amputee patients at Walter Reed, in addition to his work at Johns Hopkins.

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