Bionic leg and a new neuroprosthetic interface allow amputees to walk faster and more naturally

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 system, speeding up walking ability and making walking more natural.

The new system increased walking speed by 41% in seven below-knee amputees,compared to many others that did not have it, and improved its performance in real-world environments such as stairs, slopes and paths with obstacles.

Proprioception is a sixth sense that informs us of the position of our body parts in space. The new interface allows neural control information to be transmitted to the prosthesis and returns the user’s proprioceptive sensation.so it doesn’t feel like something foreign and improves the way you regulate 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 by Nature Medicine.

Herr noted that no previous study has been able to demonstrate “this level of brain control” over a prosthesis, which produces a natural gait at a pace similar to that of a non-amputee.

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

Surgical amputation of a limb causes a considerable 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 several muscle-sensing electrodes and a small computer that decoded the signals.

Herr explained that When the patient thinks about moving his bionic limb he feels the muscles move naturally like 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 is 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 as a function of speed.

In fact, when the person moves the prosthesis “feel that movement with a sense of natural proprioception“, the researcher highlighted.

The study focused on proprioceptive muscle input, which arises from receptors in muscles and joints throughout the body and sends information to the central nervous system.

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

The brain is “so adaptable” that it only needs a small amount of proprioception to control a very complex prosthesis, Herr added.

These results suggest that even Partial restoration of neuronal 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 it.”.

The study published today is, according to Herr, “a decisive step, if you will, toward that long-term goal of complete neural control and embodiment.”