Muscle Mat Magic: MIT Engineers Create Hydrogel Gym for Cellular Fitness

The vibrating platform could be useful for growing artificial muscles to power soft robots and test therapies for neuromuscular diseases.

There is no doubt that exercise is good for the body, including strengthening and toning muscles. But how exactly does exercise enable this?

As we run, lift, and stretch, our muscles experience chemical signals from surrounding cells as well as mechanical forces from impacting tissue. Some physiologists wonder: Is it the body’s natural chemical stimuli or the physical forces of repeated movements or some combination of the two that ultimately prompts our muscles to grow? The answer could be the key to identifying therapies to help people recover from muscle injuries and neurodegenerative disorders.

MITs innovative training pad for cells

Now, MYTH engineers have designed a kind of exercise mat for cells that can help scientists focus on, at the microscopic level, exercises that have purely mechanical effects.

The new design is not that different from a yoga mat: both are rubber, with a bit of stretch. In the case of the MIT mat, it’s made of hydrogel, a soft gelatin-like material about the size of a quarter and embedded with magnetic microparticles.

To activate the mechanical function of the gel, the researchers used an external magnet under the mat to move the embedded particles back and forth, rocking the gel in turn like a vibrating mat. They controlled the frequency of the swing to mimic the forces that the muscles would experience during actual exercise.

Observing the response of muscle cells to mechanical exercise

Then they raised a carpet of muscle cells on the surface of the gel and activated the movement of the magnet. They then studied how the cells responded to exercise while being magnetically vibrated.

The results so far suggest that regular mechanical exercise can help muscle fibers grow in the same direction. These coordinated, trained fibers can also run or contract in sync. The findings show scientists can use a new exercise gel to shape how muscle fibers grow. With their new device, the team plans to create samples of strong, functional muscles, potentially for use in soft robots and to repair diseased tissues.

We hope to use this new platform to see if mechanical stimulation can help guide muscle regrowth after injury or reduce the effects of aging, says Ritu Raman, the British and Alex d’Arbeloff Career Development Professor in Engineering Design at MIT. Mechanical forces play a really important role in our bodies and environment. And now we have a tool to study it.

She and her colleagues recently published their results in a journal Device.

Ramans Lab: Merging Medicine and Robotics

At MIT, the Ramans lab designs adaptive living materials for use in medicine and robotics. The team is engaged in the engineering of functional neuromuscular systems with the aim of restoring mobility in patients with motor disorders and launching soft and adaptive robots. To better understand natural muscles and the forces that drive their function, her group studies how tissues respond, at the cellular level, to various forces such as exercise.

Here, we wanted a way to separate the two main elements of chemical and mechanical exercise to see how muscles respond solely to the mechanical forces of exercise, Raman says.

Creation and testing of hydrogel mat

The team sought a way to expose muscle cells to regular and repeated mechanical forces, while not physically damaging them in the process. They eventually landed on magnets, a safe and non-destructive way to create mechanical forces.

For their prototype, the researchers created tiny micron-sized magnetic rods by first mixing commercially available magnetic nanoparticles with a rubbery, silicone solution. They dried the mixture to form a slab and then cut it into very thin bars. They placed four magnetic rods, each slightly spaced, between two layers of hydrogel, a material commonly used to cultivate muscle cells. The resulting magnet mat was about the size of a quarter.

The team then grew a cobblestone of muscle cells over the surface of the mat. Each cell began as a circular shape that gradually elongated and joined with other neighboring cells to form fibers over time.

The future of muscle cell research with MagMA

Finally, the researchers placed an external magnet on the track under the gel mat and programmed the magnet to move back and forth. Embedded magnets moved in response, rocking the gel and creating forces similar to those the cells would experience during actual exercise. The team mechanically exercised the cells for 30 minutes a day for 10 days. As a control, they grew the cells on the same mat but left them to grow without exercise.

We then zoomed in and imaged the gel and found that these mechanically stimulated cells looked very different from the control cells, Raman says.

The teams’ experiments found that muscle cells that were regularly exposed to mechanical movement were longer compared to cells that were not exercised, which tended to remain circular in shape. Moreover, the trained cells grew into fibers that were aligned in the same direction, while the immobile cells resembled a more random haystack of misaligned fibers.

Revolutionizing muscle stimulation research

The muscle cells the team used in this study were genetically engineered to contract in response to blue light. Typically, muscle cells in the body contract in response to a nerve electrical impulse. However, electrically stimulating muscle cells in the lab could potentially damage them, so the team decided to genetically manipulate the cells to contract in response to a non-invasive stimulus in this case, blue light.

When we light up the muscles, you can see that the control cells are beating, but some fibers are beating this way, some are beating that way, and overall they’re producing very asynchronous jerks, Raman explains. Whereas with aligned fibers, they all pull and hit at the same time, in the same direction.

Raman says the new exercise gel, which she calls MagMA, for activating the magnetic matrix, could serve as a quick and non-invasive way to shape muscle fibers and study how they respond to exercise. She also plans to grow other types of cells on the gel to study how they respond to regular exercise.

There is evidence from biology to suggest that many types of cells respond to mechanical stimulation, Raman says. This is a new tool for studying interactions.

Reference: Mechanical Programming of Anisotropy in Engineered Muscles with Actuable Extracellular Matrices Brandon Rios, Angel Bu, Tara Sheehan, Hiba Kobeissi, Sonika Kohli, Karina Shah, Emma Lejeune, and Ritu Raman October 20, 2023 Device.
DOI: 10.1016/j.device.2023.100097

This study was supported in part by the US National Science Foundation and the Army Research Office of the Department of Defense.