Scientists have grown muscle cells in the laboratory that not only look and act like real muscle, but can also self-repair using stem cells.

Scientists have grown skeletal muscle in the lab that looks and acts like the real thing. In addition to contracting strongly and rapidly, this newly bioengineered muscle has the ability to repair itself from damage.

“The muscle we have made represents an important advance for the field,” said Nenad Bursac, an associate professor of biomedical engineering at Duke University, in a press release. “It’s the first time engineered muscle has been created that contracts as strongly as native neonatal skeletal muscle.”

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To build a muscle that ideally could be used in real-world applications and as a tool for understanding muscular diseases, researchers grew muscle cells in the lab that resembled those that power the movements we make while running, walking, and simply standing up.

The interior of the bioengineered muscle contained densely packed and parallel muscle fibers, similar to what you would see within real muscle. When the researchers stimulated these artificial muscles in the lab, they functioned as well as their natural counterparts, contracting 10 times more strongly than previous bioengineered muscles.

The researchers then implanted the lab-grown muscles into a special chamber on the backs of living mice. The scientists covered the area with clear glass that allowed them to monitor the muscles as they matured and integrated into the animal’s body. Transplanted muscle can survive only if the body can provide it with oxygen-rich blood through the blood vessels.

“We could see and measure in real time how blood vessels grew into the implanted muscle fibers, maturing toward equaling the strength of its native counterpart,” said graduate student Mark Juhas, co-author of the study.

The glass window also allowed the researchers to measure the strength of the bioengineered muscle visually. Researchers had genetically altered the muscle cells to emit fluorescent flashes of light during spikes in the cells’ calcium level, which occur just before muscles contract. As the muscles grew stronger, so did the flashes of light.

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In addition, the researchers developed a method that would allow muscle stem cells to repair the new muscle if it got damaged. The trick was to create a pocket—or niche—for these satellite stem cells to occupy in preparation for an injury to the muscle.

“Simply implanting satellite cells or less-developed muscle doesn’t work as well,” said Juhas. “The well-developed muscle we made provides niches for satellite cells to live in, and, when needed, to restore the robust musculature and its function.”

This technique worked—at least in the lab. When researchers damaged the bioengineered muscle cells with a toxin taken from snake venom, the satellite cells came to the rescue, multiplying to heal the muscle fibers.

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Bursac’s team is not the first to grow skeletal muscles in the lab. A group at the University of Pittsburgh has been working on a method for regrowing muscles and tendons in the bodies of people with severe injuries.

However, the Duke study focused on the use of stem-cell pockets to help implanted muscles repair themselves. This could enable the muscles to function normally within the body, where minor damage from exercise and injury is common.

In the Duke study, published online yesterday in Proceedings of the National Academy of Sciences, the researchers worked with a very small amount of bioengineered muscle tissue, far too little to be of use right now for human therapy. They intend to continue their research and see how well the lab-grown muscle integrates with the body once it is transplanted.

“Can it [grow veins and nerves] and repair the damaged muscle’s function?” said Bursac. “That is what we will be working on for the next several years.”

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