Replacement limbs that completely replicate the functions and abilities of real limbs are the current white whale of prosthetics, and we're getting closer: mind-controlled robotics are becoming much more common, tapping into the body's natural actions to allow the wearer control.
Les Baugh, who lost both arms in an electrical accident 40 years ago, has become the first amputee in the world to simultaneously wear and control two robotic arms, performing a variety of tasks just by thinking.
The arms in question are Modular Prosthetic Limbs developed by the Johns Hopkins Applied Physics Laboratory. They require the wearer to first undergo surgery called target muscle reinnervation, which reassigns existing nerves to the tasks required by the prosthetic arms; these nerves will be connected to the arm.
"It's a relatively new surgical procedure that reassigns nerves that once controlled the arm and the hand," explained Johns Hopkins Trauma Surgeon Albert Chi, MD. "By reassigning existing nerves, we can make it possible for people who have had upper-arm amputations to control their prosthetic devices by merely thinking about the action they want to perform."
Before being fitted with the limbs, Baugh had to be trained how to use them. This consisted of a number of tutorials. First, he had to train using the APL's pattern recognition system, which uses pattern recognition algorithms to identify individual muscles, how well they intercommunicate, and their amplitude and frequency; this information is then translated into instructions for controlling a prosthetic limb.
Then, he was fitted with a custom socket. This both connects with the reassigned nerves, and acts as a support bracket for the prosthetic arms. Using this, Baugh was able to practise using the limbs through a virtual-reality version of the limbs, allowing the team to fine-tune the socket.
Only after these training processes and surgery could Baugh be fitted with the limbs -- with which he managed to move several objects. One of these tasks involved moving a cup from one shelf to a higher shelf, requiring the coordination of eight separate motions.
"This task simulated activities that may commonly be faced in a day-to-day environment at home. This was significant because this is not possible with currently available prostheses. He was able to do this with only 10 days of training, which demonstrates the intuitive nature of the control," said APL prosthetist Courtney Moran.
"We expected him to exceed performance compared to what he might achieve with conventional systems, but the speed with which he learned motions and the number of motions he was able to control in such a short period of time was far beyond expectation. What really was amazing, and was another major milestone with MPL control, was his ability to control a combination of motions across both arms at the same time. This was a first for simultaneous bimanual control."
The next step is sending Baugh home with a pair of arms so that he can try and use them in his daily life.
"Maybe for once I'll be able to put change in the pop machine and get pop out of it," he said.