Muscle injuries may soon be treatable using grown muscles derived from stem cells. By simply taking a sample from a person’s muscle tissue and growing stem cells from it, scientists could theoretically produce brand new muscle that can be implanted back into the patient after a debilitating injury.

Engineers from Duke University have recently achieved a closer step to this goal. In a new study, the researchers describe how they found a way to isolate stem cells from mouse muscle then grow new muscle fibers from them, producing muscles that are 10 times stronger than muscles previously made in labs — about as strong as real muscles.

“For 15 years, people have tried to make artificially grown muscle with the same strength as real muscle,” lead researcher Nenad Bursac told Quartz. “And this is more than 10 times stronger than anything made in the lab before.”

The researchers initially experimented using petri dishes, then moved on to living mice. They inserted a small chamber onto the back of the mouse, attaching the muscle to the body. They were able to observe through a glass “window” implanted on the backs of mice as the muscle began to receive blood supply from the body, and grew three times stronger. “We got them to grow into strongly contracting fibers,” Bursac said. “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.”

Meanwhile, the muscle stem cells are also self-healing. “The stem cells don’t just build these fibers,” Bursac told Quartz. “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.”

The scientists moved on to creating human muscles as well, claiming that they are the first to complete trials with human muscle. But several problems remain before they’ll be able to complete this process in humans. For example, multiplying stem cells is difficult in humans; there is a limited amount that can be extracted before they lose their potency. “The cells in the center of the muscle would die from lack of nutrients,” Bursac explained. “You need to make a vasculature system that could sustain life while the muscle was outside the body.”