That humans can engineer muscle tissue in petri dishes is extraordinary, but it isn't enough to heal serious bodily injuries. To do that, you also need tissue that has the ability to grow strong, heal itself, and respond to commands after being implanted in a living animal. Scientists simply aren't there yet. But a new study published in Proceedings of the National Academy of Sciences today brings us one step closer to orthopedic surgery bliss, because scientists were able to engineer mouse muscle that was just as strong as native muscle — and that could heal itself after injury.
"10 times stronger than the best previously published efforts."
To engineer the tissue, scientists mixed gelatin-like hydrogel matrix with cells from newborn mice called progenitor cells. These cells can take on many different forms, but have lost the ability to replicate indefinitely the way stem cells can. The mixture was then cast in small cylindrical molds and grown for two weeks, until the cells aligned and differentiated into strong muscle fibers. "To our delight, the engineered muscle was more than 10 times stronger than the best previously published efforts," says Nenad Bursac, a biomedical engineer at Duke University and co-author of the study, "and its strength was similar to that of native muscle tissues."
But researchers also wanted to make sure the muscle could heal itself, so they injected it with cobra venom — venom that causes muscle membranes to rupture after just 30 minutes. According the Bursac, the engineered muscle was able to fully self-regenerate even after sustaining significant damage, thanks to the pool of functional progenitor cells it contained.
The researchers implanted the muscle into mice and covered it with glass
Once its healing abilities were demonstrated, researchers implanted the muscle in the backs of mice and covered it with a glass window. This allowed the scientists to observe the tissue as the animals walked around. After two weeks, the rodent's capillaries had invaded the engineered muscle and perfused it with blood, allowing it to gain in strength.
Unfortunately, the muscle doesn't have the ability to respond to commands because scientists aren't able to integrate engineered tissue into the neuronal system of an animal host just yet. Moreover, when the researchers tried to construct human muscle using the same technique, they found that its strength was much lower than that of muscle produced using rodent cells.
Bursac's team is now trying to solve these problems, but they think their findings are significant nonetheless. "The most immediate application of human engineered muscle will be to validate if it could be used as a predictive model for drug and toxicology tests in the lab," Bursac says. The researcher also explained that human engineered muscle could be used to model various diseases, "which should allow us to develop better therapies."