10 Emerging Technologies
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PROSTHETICS Mating robotics with the nervous system creates a new generation of artificial limbs that work like the real thing. By Corie Lok
Conventional leg prostheses frequently leave their users, especially above-the-knee amputees, stumbling and falling or walking with abnormal gaits. Hugh Herr, a professor at MIT’s Media Laboratory, is building more-reliable prostheses that users can control more precisely. Some of the latest prosthetic knees on the market already have microprocessors built into them that can be programmed to help the limbs move more naturally. But Herr has taken this idea one step further. He has developed a knee with built-in sensors that can measure how far the knee is bent, as well as the amount of force the user applies to it while walking. This artificial knee – recently commercialized by the Icelandic company Össur – also contains a computer chip that analyzes the sensor data to create a model of the user’s gait, and adapt the movement and resistance of the knee accordingly.
Now Herr is working to distribute those sensors beyond the knee joint, using them to detect not just the mechanical forces of the body but also neural signals from the muscles near the joint. This work is part of an emerging discipline called biomechatronics, in which researchers are building robotic prostheses that can communicate with users’ nervous systems. In five to seven years, predicts Herr, spinal-cord injury patients will move their limbs again by controlling robotic exoskeletons strapped onto them (or at least they will in research settings). Biomechatronics is receiving more attention now in part because of the Iraq War, which is sending a high number of U.S. soldiers home with crippling injuries. Herr, who leads the Media Lab’s biomechatronics group, is part of a new $7.2 million research project run by the U.S. Department of Veterans Affairs (VA) to develop new technologies for amputees who lost limbs as the result of combat injuries.
Herr, a double leg amputee, plans on becoming his own first test subject for his latest prosthetic ankle prototype. By early next year, at least three small sensors will be implanted into the muscles of one of his legs below the knee. As Herr flexes his leg muscles in ways that once moved his ankle, these sensors will measure electrical activity in the muscles and transmit that information to a computer chip in the prosthetic ankle, which will translate those impulses into instructions for the ankle’s motors. Herr hopes to be able to move the ankle by firing up the residual muscles near the joint and feeling it respond, just as he would with a natural joint. Nor will communication be just one way. Herr should also be able to sense the ankle’s position through vibrations emanating from the joint. “We regard this work as extraordinarily promising,” says Roy Aaron, a professor of orthopedics at Brown Medical School who is heading up the VA project.
Having lost his lower legs to frostbite while mountain climbing as a teenager, Herr says he’s looking forward to trying out the device. “I think it will be quite profound to control my ankles again,” he says. Herr’s vision for the field is to combine biomechatronics with tissue engineering and create limbs made of both artificial materials and human tissue. Says Herr, “I think, inevitably, we’ll end up with hybrid devices.”