Most bionic limbs are controlled by electrical signals generated by muscles moving near the attachment site. But when an arm is amputated above the elbow, the remaining muscles aren’t enough to control every joint in an artificial hand. “The higher the amputation, the more joints you have to replace, and the fewer muscles you have to do it,” says Max Ortiz Catalán, a bionicist at Chalmers University of Technology in Sweden.
Now Ortiz Catalán’s team has developed a bionic system that allowed a man with an above-elbow amputation to control every finger of a robotic arm, as described recently in Science Translational Medicine. To create more muscle signals to prompt the prosthetic, the researchers dissected the nerve bundles that carry signals from the man’s brain to muscles in his upper arm. The fibers were then spread out and attached to new muscle targets in his remaining arm, including muscle tissue grafted from his thigh. They also anchored a titanium fixture into the remaining upper-arm bone, making the prosthesis more comfortable than typical fitted socket attachments.
The man has been using the prosthesis in his daily life for more than three years to grasp objects and pour drinks. “This is the first nerve-based prosthetic hand that the patient can go home with,” says bioengineer Cynthia Chestek.
