Researchers at the K. Lisa Yang Center for Bionics at the Massachusetts Institute of Technology (MIT) have developed a promising new approach to muscle control using optogenetics. This approach could potentially revolutionize neuroprosthetic systems for individuals with paralysis or amputation.
The study, published in Science Robotics, demonstrates how light can control muscles with greater precision and less fatigue than conventional electrical stimulation methods.
Current neuroprosthetic systems rely on functional electrical stimulation (FES), which involves implanting electrodes to stimulate nerve fibres and cause muscle contraction. However, this approach often leads to poor control and rapid muscle fatigue, limiting widespread adoption. FES stimulates the entire muscle at once, which is not how muscles naturally function, resulting in difficulties achieving fine motor control and muscle exhaustion within minutes.
To address these challenges, the MIT researchers turned to optogenetics, which uses light to control genetically modified cells expressing light-sensitive proteins. Their study compared the muscle force generated using the traditional FES approach with their optogenetic method in mice. The mice were genetically engineered to express channelrhodopsin-2, a light-sensitive protein, and a small light source was implanted near the tibial nerve, which controls lower leg muscles.
The results showed that optogenetic control produced a gradual and nearly linear increase in muscle contraction as the amount of light stimulation was increased. This closely resembles how the brain naturally controls muscles, making it easier to achieve precise control than electrical stimulation.
Using data from their experiments, the researchers developed a mathematical model relating light input to muscle force output. This model enabled them to design a closed-loop controller that adjusts light stimulation based on the desired force and the actual force exerted by the muscle, as detected by sensors.
What is optogenetics?
Optogenetics is a revolutionary technique that allows scientists to control the activity of specific cells in living tissue, particularly neurons in the brain, using light.
This is achieved by introducing light-sensitive proteins, called opsins, into the cells of interest. Opsins are light-sensitive proteins that specific wavelengths of light can activate to control the activity of the cells in which they are expressed. These opsins, usually derived from microorganisms like algae or bacteria, can be activated by shining light of a specific wavelength onto the cells, causing them to either become more active or less active, depending on the type of opsin used.
Scientists use genetic engineering techniques to get the opsins into the desired cells. They create a piece of DNA containing the instructions for making the opsin and then insert it into the cells. This can be very targeted so that only specific types of cells, such as certain neurons in a particular part of the brain, receive the opsin. Once the cells have the opsin, the researchers can control their activity by shining light on them through optical fibres implanted in the brain or other methods.
Optogenetics has revolutionized neuroscience research by providing a way to precisely control and study the function of specific brain circuits in living animals. By activating or deactivating particular neurons with light, researchers can see how those neurons contribute to behaviours, sensations, and other brain functions. This has led to many new insights into how the brain works in health and disease. Optogenetics is also being explored as a potential therapy for some neurological disorders, such as blindness or Parkinson’s disease, where it could be used to restore or modulate neural function in a targeted way.
Significantly, the optogenetic approach allowed muscles to be stimulated for over an hour before fatigue set in, a significant improvement compared to the 15-minute limit of FES stimulation.
There are still challenges to overcome before this technique can be applied to humans. The researchers are developing safe methods to deliver light-sensitive proteins to human tissue without triggering an immune response, which could lead to muscle atrophy and cell death. They also design new sensors and light source implantation techniques to refine the system further.
If successful, this optogenetic approach could greatly benefit individuals with paralysis, amputation, or impaired limb control due to strokes or spinal cord injuries. It can potentially change how we approach clinical care for limb pathologies, offering a minimally invasive strategy for regaining muscle control with greater precision and less fatigue.
TLDR:
- MIT researchers have developed an optogenetic approach to muscle control using light instead of electricity
- Optogenetics allows for more precise and gradual muscle control compared to functional electrical stimulation (FES)
- In mice, optogenetic stimulation enabled longer muscle activation before fatigue set in
- Challenges include safely delivering light-sensitive proteins to human tissue and overcoming potential immune responses
- If successful, this approach could revolutionize neuroprosthetic systems for individuals with paralysis or amputation
