U.S. researchers said Wednesday that it is possible to rebuild large amounts of muscles severely damaged in traumatic accidents or military wounds by implanted tissues of pig bladders.

Researchers from the University of Pittsburgh tested the experimental technique on five male patients, who had lost between 58 and 90 percent of limb muscle, and found that three of them had a 25 percent improvement in function.

"This new study is the first to show replacement of new functional muscle tissue in humans, and we're very excited by its potential," Stephen Badylak, senior investigator at the University of Pittsburgh.

"These are patients who can't walk anymore, can't get out of a car, can't get up and down from a chair, can't take steps without falling. Now we might have a way of helping them get better," Badylak said.

Large amounts of muscle can be lost as a result of trauma, such as a car accident, a sports injury, or even an explosive device. There is no treatment for such volumetric muscle loss and native muscle is unable to regenerate to that extent, to fully recovery function and tissue volume. Instead, scar tissue can form to fill the gap.

Stem cells have been shown to help damaged tissue regenerate, but in most cases, stem cells should be taken out, isolated and grown into the cell of choice, and then injected back into patients.

Badylak's team, however, used the extracellular matrix (ECM) from pig bladders to attract stem cells to the site of injury to promote regrowth of muscle.

According to the researchers, pig bladder ECM has been used for many years as the basis for medical products for hernia repair and treatment of skin ulcers. It is the biologic scaffold that remains left behind after cells have been removed.