Muscle Transplants Could Enable Mind-Controlled Prostheses—No Brain Surgery Required

Alex Smith was like that He was 11 years old when his right arm was amputated in 2003. A drunken boat driver collided with his family’s boat on Lake Austin, sending him overboard. He hit the propeller, his arm was cut off in the water.

A year later, he received a myoelectric arm, a type of prosthesis that provides electrical signals to the muscles of his remaining limb. But Smith didn’t use it because it was “too slow” and had a limited range of motion. He could open and close his hand, but nothing else. He tried other robotic arms over the years, but they had the same problems.

“They don’t work very well,” he says. “There is a big delay between doing some work and doing the transplant. In my daily life, it became faster to find other ways of doing things.”

Recently, he’s been testing a new system made by Austin-based Phantom Neuro that has the potential to provide lifelike control of prosthetic limbs. The company creates small, flexible muscle implants to allow amputees a wider, more natural range of motion by simply thinking about the gestures they want to make.

“There aren’t many people using robotic limbs, and that’s largely because of how bad the control system is,” said Connor Glass, CEO and founder of Phantom Neuro.

In data shared exclusively with WIRED, 10 participants in a study conducted by Phantom used a wearable version of the company’s sensors to control a robotic arm already on the market, achieving an average accuracy of 93.8 percent across 11 hands and wrists. Smith was one of the participants, and the other nine were strong volunteers, which is common in early prosthetics studies. The success of this study paves the way for the future testing of Phantom implantable sensors.

Current myoelectric prosthetics, like the ones Smith tried, read surface electrodes that sit on a severed stump. Most robotic prostheses have two electrodes, or recording channels. When a person turns their hand, the muscles of their arm contract. That muscle contraction still occurs in the amputated upper limb when bending. Electrodes pick up the electrical signals from those contractions, translate them, and initiate movement in the implant. But surface electrodes don’t always capture stable signals because they can slip and move, reducing their accuracy in real-world environments.