A new bionic leg restores agility to amputees: "It feels like part of my body."

Hugh Herr was a teenage mountaineer who lost both of his legs 43 years ago after they froze and suffered tissue damage during a climb on Mount Washington (New Hampshire, USA). The personal tragedy not only redefined his life, but also his purpose: to forever transform the technology used for amputees. Today, he is one of the world's leading experts in bionics; and he has just unveiled a breakthrough that breaks a barrier in prosthetic design that hasn't changed much in decades. Finally, a bionic leg goes beyond restoring mobility.

This engineer, who received the Princess of Asturias Award for research in 2016 , leads the development of advanced bionic leg prostheses that mimic human movement, as well as ankle and foot orthoses, at the Massachusetts Institute of Technology (MIT). He walks, runs—and even climbs at high levels—with the bionic legs he helped design. Along with a team of scientists from the MIT Yang Tan Collective , Herr has managed to go a step further, with an ambition that—like on the mountain—always aims higher. He has created a bionic prosthesis that connects to the body's muscles and nerves; this allows people with above-knee amputations to move with greater agility than with traditional rehabilitation devices.

The new system, called the osseointegrated mechanoneural prosthesis (OMP), incorporates an implant anchored to the femur and a myoneural interface that mimics the behavior of muscles, according to details in the scientific article that Herr and his team published today in the journal Science . Thanks to this technology, the amputee can not only move the prosthesis with greater precision, but also regain sensations such as the position or movement of the lost limb. “Our prosthesis is unique because it is connected directly to the bone and the implant contains cables that transmit neural signals,” Herr explains in a video call with EL PAÍS.

Joining him is young scientist Tony Shu , whose doctoral research shaped and formed the basis of the recently published article. “When I joined the lab at MIT, there were many new avenues open, but during my master's and doctoral studies, we made great strides,” he recalls. The clinical trials involved two people with above-knee amputations. Initially, the scientists were cautious, aiming to restore only walking and basic mobility, but over time, they observed that the participants were able to perform more complex tasks.

In each case, the OMP system enabled superior mobility in a variety of leg movements in real-life situations. Patients were able to move with a naturalness that previously seemed out of reach, such as walking over uneven terrain, rising from a chair smoothly, or kicking a ball . Even with only one motorized joint, the volunteers stated, “The prosthesis feels like part of my body.”

Mimic human muscle power

The system has motors powered by lithium-ion batteries. This allows the motorized prosthesis to generate force, which helps with activities such as climbing stairs. They achieve this by mimicking muscle function, allowing for more agile and voluntary movement. "We were the first to integrate neuromuscular surgery, an osseointegrated implant, and a robotic controller into a single system," says Tony Shu.

One of the main limitations of the prosthesis is that it only involves the knee . The human leg is more than that, as the ankle and foot also perform complex movements. "It doesn't include those additional degrees of freedom," the young researcher acknowledges.

Although the invention still faces certain challenges, researchers are optimistic. Systems that integrate directly with the body—like the OMP, which connects bone, muscle, and nerve—mark the beginning of, perhaps, a new generation of devices. A type of prosthesis that not only restores mobility, but also restores an essential part of the human experience.

For Hugh Herr, the next challenge lies in perfecting the reading of muscle signals, as they currently use implanted electrodes to understand the user's intentions. "In the future, we plan to use magnetic sensors on the skin," he says. The goal is to measure muscle movement and strength more accurately.

“If you're looking for an analogy, think of Formula 1 or space exploration. Those areas push technology to the limits, and then those advances trickle down to the average consumer. We don't expect this prosthesis to ever reach the market, but we do believe several of its components will,” Shu reflects.