Researchers have created artificially grown muscle that’s as strong and good at self-repair as the real thing. One day this could mean lab-grown replacements for permanently injured human muscle. But the advances are already being used to test the toxicity and effectiveness of new drugs.
In a paper published today (paywall), biomedical engineers from Duke University describe how they isolated stem cells from mouse muscle, then grew them into new muscle fibers. “We got them to grow into strongly contracting fibers,” lead researcher Nenad Bursac told Quartz. “This is the first time we’ve seen muscle fibers contract so strongly in the lab. It was comparable to the contracting forces you’d see in an actual mouse muscle.”
The fibers were also self healing. “The stem cells don’t just build these fibers,” Bursac says. “They sit next to the muscle fibers, and if there’s an injury—if a muscle is torn, and some fibers die—these cells jump in and fuse to rebuilt the lost tissue.”
By injecting the engineered muscle with snake toxin, which killed large portions of it, the researchers were able to observe this process as it occurred. After running the tests in a petri dish, they repeated the experiment using a living mouse. “We put a little chamber on the back of the mouse, with the muscle attached inside,” he says, “and then covered it with a glass plate, so we could observe.” Within two weeks, he says, the muscle was being fed with a healthy blood supply from the mouse’s body. During that same period, the muscle contractions grew three times stronger. “For 15 years, people have tried to make artificially grown muscle with the same strength as real muscle,” Bursac says, “and this is more than 10 times stronger than anything made in the lab before.”
While the research published today used mice, Bursac says his team has already moved on to run the same successful trials with human muscle. “I think we’re the only group with active contracting human muscle,” he says, “and it’s very important for drug testing. If you’re testing a drug that’s supposed to improve muscle function, it improves pre-clinical testing if you use something physiologically similar to native muscle.” They’ve even found that stem cells from people with certain genetic diseases can yield muscle with the same clinical symptoms.
Grow your own
To replace an injured muscle, doctors would need to take a little bit of muscle tissue from the patient, cultivate stem cells from it, use those to grow new tissue, and then transplant that back into the patient. How soon will this be possible? First, researchers need to figure out how to get more stem cells. “With the mice, we could take as much tissue as we wanted,” Bursac says, “But working from a reasonably sized human biopsy, you don’t get many stem cells. You can expand them more and more, but they lose their potency.”
Many researchers are working on how to multiply stem cells without them losing their potency, so Bursac expects this problem to be overcome soon. The task of feeding a growing muscle in the lab poses a larger hurdle. Muscles require a lot of blood flow to survive. Since Bursac’s method requires muscle to be grown in the lab before being transferred to a human body, growing a piece larger than a millimeter would require some novel technology to provide the artificial muscle with an artificial blood supply. “Let’s say you’re rebuilding a facial muscle,” he says. “For a human, that’s a large muscle mass. The cells in the center of the muscle would die from lack of nutrients. You need to make a vasculature system that could sustain life while the muscle was outside the body.”
Once this challenge is met, though, this kind of artificial muscle will be ready for clinical use almost immediately. “The vasculature problem is Nobel-Prize worthy. It could take us 10 or 15 years to solve,” he says. “But it’s hard to say… and if someone comes up with an answer next year? We could be using them to repair human injury within three.”