Researchers backed by the Defense Department said Wednesday they had succeeded in coaxing the regeneration of muscle tissue lost in people who suffered traumatic injuries, including wartime bomb wounds, with a new type of treatment that uses material from a pig's bladder.

Implanting the pig material at the wound site enticed the patient's own stem cells - master cells that can transform into various kinds of cells in the body - to become muscle cells and regenerate tissue that had been lost, the researchers said.

The study was small, involving only five male patients, but its results suggested that this procedure could offer new hope to a category of patients, including troops who suffered major war injuries, with scant good treatment options, researchers said.

All five patients, including two U.S. soldiers hurt by improvised explosive devices, had badly damaged leg muscles. The research was backed by $3 million in funding over five years from the Defense Department, said Stephen Badylak of the University of Pittsburgh, a veterinarian, physician, and pathologist who led the study.

Many failures

Thousands of U.S. troops have been left with serious impairments after suffering wounds involving major loss of muscle tissue in roadside bombings and other incidents since 2001 in the Afghan and Iraq wars.

When a large amount of muscle is lost in vehicle crashes, industrial accidents, bomb blasts, or other traumas, the body is unable to replace it and the site forms scar tissue that lacks the functionality of the lost muscle.

Existing treatments include surgery to remove scar tissue or replace it with muscle from elsewhere in the body, but these methods do not yield satisfying results and are difficult for patients, the researchers said.

"Nothing has ever worked," Badylak said.

'Very encouraged'

The study, published in the journal Science Translational Medicine, demonstrated for the first time the regeneration of functional muscle tissue in people with major muscle loss.

"While the number of patients was small, we were very encouraged by the data," said J. Peter Rubin of the University of Pittsburgh, a plastic surgeon who worked on the research team. "And we were seeing very dramatic improvements in quality of life for some of our patients."

Doctors implanted material from a pig's urinary bladder called "extracellular matrix" - the non-cellular component including collagen present within all tissues and organs - to serve as scaffolding for the rebuilding of lost muscle mass.

This material acted as a "homing device" to recruit existing stem cells to rebuild healthy muscle tissue at the site of the injury, the researchers said.