The key to the surgical technique, demonstrated in rats so far, is to emulate the normal agonist-antagonist pairing of muscles (think biceps and triceps) at the amputation site so that the muscles and nerves surrounding a prosthetic can sense and transmit proprioceptive information about the artificial limb and how much force is being applied to it. The researchers published their work today (May 31) in Science Robotics.
“We’re talking about a dramatic improvement in patient care,” Hugh Herr, an MIT professor of media arts and sciences and a coauthor of the study, said in a statement. “Right now there’s no robust neural method for a person with limb amputation to feel proprioceptive positions and forces applied to the prosthesis. Imagine how that would completely hinder one’s ability to move, to successfully balance, or to manipulate objects.”
Herr, himself a double-amputee, and his team operated on seven rats, cutting through muscles and nerves in their hind legs. The researchers then grafted on paired muscles, wiring them up to severed nerves. After healing for four months, the rats’ new muscles were contracting and relaxing in tandem, as in naturally paired muscles, and sending electrical signals that reflected the amplitude of the artificial stimulation Herr and his colleagues applied.
“In the past, the limb was amputated and cremated, and all those great tissues were thrown away,” Herr told Popular Science. “Even in my case—both my legs are amputated below the knee, and my amputations were done 30-some years ago in a really silly way, in a conventional way—in principle we can do a revision on my limbs and get muscles from another part of my body and create these pairs.”
Herr added that he and his team plan to translate this surgical technique into humans and that he will serve as the first study subject.