Microfluidic Device Offers a Testing Ground for Neuromuscular Junctions

The microfluidic chip isn’t much bigger than a quarter, yet shows a lot of promise for the treatment of neuromuscular disorders. (Image courtesy of Sebastien Uzel.)

Engineers have recently developed a microfluidic chip that could open the door to a better understanding of neuromuscular diseases such as amyotrophic lateral sclerosis (ALS). The device is about the size of a quarter and replicates a neuromuscular junction, the connection between nerves and muscles in the human body.

"The neuromuscular junction is involved in a lot of very incapacitating, sometimes brutal and fatal disorders, for which a lot has yet to be discovered," said Sebastien Uzel, who led the work at MIT. "The hope is that being able to form neuromuscular junctions in vitro will help us understand how certain diseases function."

Recreating the Neuromuscular Junction

Other attempts to simulate neuromuscular junctions in the lab have been lacking. Though several experiments have been conducted since the 1970s, none of them have accounted for the complex, three-dimensional environment of the real human body. Uzel and his colleagues set out to address these shortcomings.

They did this by including two important features in their microfluidic device: a 3D environment and a separation of the nerves from the muscles to mimic the natural separation in the body. The team achieved these features by placing muscle and nerve cells within separate, millimeter-sized compartments and then filling the compartments with gel to create the desired 3D environment.

To create the muscle fiber, the team used muscle precursor cells from mice. The team differentiated the cells into muscle cells and injected them into one of the microfluidic compartments; from there, the cells grew and fused into a single strip of muscle.

Similarly, the nerve cells began as motor neurons from a cluster of stem cells. The team first genetically modified these cells to respond to light using a technique called optogenetics. Finally, the engineers differentiated the motor neurons into neural cells and placed them in the second microfluidic compartment.

Neurons (green) send out axons to the muscle fiber (red) in the microfluidic device. The bottom fluorescent image shows this process in action, with about 1 mm of separation between neurons and muscle. (Image courtesy of Sebastien Uzel.)

The last piece of the puzzle was adding a way to sense the force of the muscle. The team fabricated two small, flexible pillars and placed them within the muscle cells’ compartment, allowing the muscle fiber to grow around them. This way, when the muscle contracts, it squeezes the pillars together. By measuring the displacement of the pillars, the researchers could determine the mechanical force of the muscle.

Testing the Device and Imagining the Future

In order to test the microfluidic device, the team first observed axons extending from the neurons toward the muscle fiber. Once an axon had made a connection, the team stimulated the neuron with a burst of light. The result? An instant contraction of the muscle.

This initial success could mean a variety of useful applications of the device. For one, it could help scientists study the effects of repeated stress on muscle performance, leading to healthier exercise protocols. Even more exciting is the potential as a testing ground for drugs designed to treat neuromuscular disorders. But wait, it gets better: someday, the device could even be used to create personalized treatments for patients.

"You could potentially take pluripotent cells from an ALS patient, differentiate them into muscle and nerve cells and make the whole system for that particular patient," said Roger Kamm, a coauthor on the study. "Then you could replicate it as many times as you want and try different drugs or combinations of therapies to see which is most effective in improving the connection between nerves and muscles."

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