The Man/Machine Interface Just Got an Upgrade

The vast majority of people living with prosthetic arms have very limited movement. They can't do much more than a few grasps with their replacement hands using the remaining working muscles in their arms or shoulders; this leads to 40 to 50 percent of recipients ditching their prosthetics altogether.

A new study on six volunteers has the potential to advance prosthetic technology in a way that will allow amputees to perform more day-to-day tasks than ever before: When the patients thought of their new prosthetics as phantom limbs, they were able tosuccessfully perform everyday movements, like pinching and rotating.

The research, most of which was done at the University Medical Centre Gottington, looked into a system that connects robotic prosthetics to amputees by rewiring their neurological pathways. Bioengineer Dario Farina and a team of scientists developed a novel sensor technology that converts electrical signals from the brain into commands that a prosthetic can respond to. These signals come from nerve cells called motor neurons that live in the spine. Motor neurons have axons, fibers that are directly in control of the body's muscles.

The group of volunteers had amputations either above their elbows or below their shoulders. In a press release, Farina, who is now at the Imperial College London, explained that the new treatment centers on the nervous system—aka the motor neurons and their axons—as opposed to muscles, which is the current gold standard for prosthetics.

Another lead scientist on the study, Ivan Vujaklija, tells Tonic that the team surgically redirected peripheral nerves that made the original limb move by connecting them to any remaining muscle. This procedure is known as targeted muscle reinnervation (TMR). Until now, these muscles—though intact after the amputation—had little to no physical ability. "Here, newly innervated muscles can be seen as biological amplifiers of nerve activity which originates back in the spinal cord and in essence contains the idea of motion the brain would like the limb to carry out," Vujaklija explains. This allows an amputee's remaining muscles to be more receptive to nerve signals, which is pivotal to the new prosthetic's success.

With their new robotic limbs and rejuvenated system of connections, the volunteers were trained to use the prosthetics via physiotherapy. After this, they were able to engage in a wider variety of movements than those made possible by the robotic prosthetics currently on the market. In fact, patients were even able to radially move their new extremities: They were opening and closing their hands and moving their wrists horizontally.

So what comes next? For starters, there will be clinical trials within a larger group of recipients who have more traumatic amputations than those studied previously. This would allow researchers to not only test the robotic prosthetics' effectiveness, but also improve upon their current model.

In 2014, a series of studies reported that patients that were able to control prosthetics with their minds and even feel with them as a result of connecting the artificial limbs to remnant nerves.  And in January, scientists at the Johns Hopkins Applied Physics Laboratory (APL) explained in a press release that they had developed a customized prosthetic that is implanted directly into a patient's marrow; this increased the prosthetic's range of motion enough to allow the recipient to carry out some day-to-day activities. Farina's team suggests that their preliminary model may be available to the public in as little as three years.