Scientists implanted thin sheets of scaffolding-like material from pigs into a few young men with disabling leg injuries — and say the experimental treatment coaxed the men’s own stem cells to regrow new muscle.

The research, funded by the Defense Department, included just five patients, a small first step in the complex quest for regenerative medicine.

The researchers described some of the men as improving enough to stop using canes or to ride a bicycle again after years of living with injuries that today have no good treatment.

“The real rush for someone like myself is to see this patient being able to do these things and not struggle and [to] have a smile on his face,” said Stephen Badylak of the University of Pittsburgh School of Medicine. He led the study, which was reported Wednesday in the journal Science Translational Medicine.

Muscles have some natural ability to regenerate after small injuries. But if too much is lost — from a car accident, a sports injury or, for soldiers, a bomb blast — the body can’t heal properly. Hard scar tissue fills the gap. A severe enough injury, called volumetric muscle loss, can leave an arm or leg essentially useless.

The new experiment combines bioengineering with a heavy dose of physical therapy to spur stem cells that are roaming the body to settle on the injury and turn into the right kind of tissue to repair it.

First, surgeons remove the scar tissue. Then they implant something called an “extracellular matrix” derived from pigs.

That’s the connective scaffolding that remains after cells are removed from tissue. (Without cells, the immune system doesn’t reject it.)Such material has been used for many years as a kind of mesh in treatments for skin ulcers and in hernia repair.

What’s new here is that the matrix temporarily fills in the injury, between edges of remaining muscle. As the scaffolding slowly degrades, it releases chemical signals that attract stem cells to the site, Badylak said.

Then physical therapy puts tension on the spot, in turn signaling the stem cells that they need to form strong, stretchy muscle tissue, he said. Without the exercise, Badylak cautioned, those cells won’t get the message to boost muscle mass, and scar tissue could return.

Researchers around the country are exploring different ways to spur the regeneration of various body parts, and many focus on injecting stem cells or tissues grown from them. Wednesday’s approach is different.

“This strategy obviously has some merit,” said professor George J. Christ of the Wake Forest Institute for Regenerative Medicine, who wasn’t involved with the new study. While larger studies must verify the findings, “the concept of physical therapy coupled with these regenerative strategies is going to be really important,” he said.

The Pittsburgh study is continuing, and Badylak would like to test as many as 50 more patients.

— Associated Press