Scientists discover light-controlled muscles: a new hope for people with paralysis and amputations

MIT researchers have developed a way to help people with amputation or paralysis regain limb control. Credit: Steph Stevens

MIT scientists have made an exciting breakthrough that could help people with paralysis or amputations regain control of their muscles.

Traditional neuroprosthetic systems use electrical currents to stimulate muscle contractions, but this method often leads to rapid muscle fatigue and poor control.

Now, MIT researchers have developed a new technique using light instead of electricity, which promises better muscle control and less fatigue.

In their study, published in Science Robotics, the researchers used an approach called optogenetics. This method involves genetically engineering cells to produce proteins that respond to light.

When these proteins are exposed to light, they can control the activity of the cells.

Although this technique is not yet ready for humans, the MIT team is working on ways to safely introduce these light-sensitive proteins into human tissue.

The study was led by MIT professor Hugh Herr and graduate student Guillermo Herrera-Arcos. They experimented with mice that had been genetically modified to produce a light-sensitive protein called channelrhodopsin-2.

By implanting a small light source near the tibial nerve, which controls the lower leg muscles, they were able to stimulate muscle contractions using light.

One major advantage of this optogenetic approach is its ability to control muscle contractions more precisely.

Traditional electrical stimulation (FES) tends to activate the entire muscle at once, leading to sudden, forceful contractions that wear out the muscle quickly. In contrast, the light-based method allows for a gradual increase in muscle force, similar to how our brain naturally controls muscles.

This results in smoother, more controlled movements and significantly reduces muscle fatigue.

The researchers measured the muscle force generated by both the traditional FES method and their optogenetic technique. They found that while muscles fatigued after only 15 minutes of FES stimulation, the optogenetic method allowed muscles to be stimulated for over an hour before becoming fatigued. This improvement could make a huge difference for people relying on neuroprosthetic systems.

To further refine their technique, the researchers created a mathematical model that links the amount of light used to the muscle force generated. This model helped them design a closed-loop controller, which adjusts the light stimulation based on feedback from sensors measuring muscle force. This ensures precise control of muscle contractions.

The team is now focused on overcoming the challenge of safely delivering light-sensitive proteins into human tissue. Previous attempts triggered immune responses that inactivated the proteins and caused muscle damage. Herr’s lab is working on designing new proteins and delivery strategies to avoid these issues.

If successful, this light-based method could provide a minimally invasive way to help people with strokes, limb amputations, spinal cord injuries, and other conditions affecting limb control.

This innovative approach has the potential to transform clinical care for many individuals with limb impairments.