A new interface and a bionic leg allow for faster and more natural walking

One goal of research for amputees is that prosthesis can emulate the performance of the lost limb. A new neuroprosthetic interface comes close to achieving this with a bionic leg that fully responds to the nervous systemwhich accelerates walking ability and a more natural walk.

The new system increased by a 41% the walking speed of seven below-knee amputees compared to seven others who did not wear the device, and improved their performance in real-world environments such as stairs, slopes and paths with obstacles.

Proprioception is a sixth sense that informs us of the spatial position of our body parts. The new interface allows neural control information to be transmitted to the prosthesis and returns the user’s proprioceptive sensation, so it does not feel like something foreign and improves the way of regulating movement.

This was explained in a virtual press conference by researcher Hugh Herr from the Massachusetts Institute of Technology (USA) and lead author of the study detailing the procedure published today in Nature Medicine. Herr stressed that no previous study has been able to demonstrate “this level of brain control” on a prosthesis, which produces a natural gait at a pace similar to that of a non-amputee.

To create full range of motion of a limb, muscles act in agonist-antagonist pairs and transmit proprioceptive signals to the central nervous system, providing the person with awareness of position and movement.

Surgical amputation of a limb causes significant deterioration of the neural-muscular architecture at the amputation site, which alters muscle dynamics and proprioception. The team created an interface that surgically connected agonist-antagonist muscle pairs, each with various muscle-sensing electrodes and a small computer that decodes the signals.

Herr explained that when the patient thinks about moving his bionic limb he feels the muscles moving naturally as they did when his leg was intact. “Even though your limb is made of titanium, silicone and all these electromechanical components, it feels natural and moves naturally without you even thinking about it.”

The entire gait cycle and dynamics of the bionic prosthesis are controlled by the brain, which receives information from sensors not only about the position in space, but also the force exerted against the ground or the stiffness depending on the speed.

In fact, when the person moves the prosthesis “feel that movement with a sense of natural proprioception“, the researcher said. The study focused on proprioceptive muscle input, which arises from receptors in muscles and joints throughout the body, which send information to the central nervous system.

MIT researcher and signatory of the article Hyungeun Song also highlighted that with just one 18% of biological neural information was sufficient to restore control of a functional gait, which he considered a “significant scientific discovery”.

The brain is “so adaptable” “A small amount of proprioception is sufficient to control a very complex prosthesis,” Herr said. “These results suggest that even partial restoration of neural signaling may be sufficient to enable clinically relevant improvements in neuroprosthetic functionality.”

For future work, the researchers want to replace the electrodes on the surface of the muscles with small magnetic spheres, which would allow them to more accurately monitor the dynamics of muscle pairings in order to better control the prosthesis.

The team aims to connect the peripheral nervous system with electromechanics and synthetic prosthetics, because “When that neural connection is provided, personification occurs. When you ask the person using the prosthesis what their body is, they include the prosthesis as part of their body.” The study published today is, according to Herr, “a decisive step, if you will pardon the pun, towards that long-term goal of total neural control and personification.”

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