Researchers from Pittsburgh, Pennsylvania say they've successfully tested a way to repair and regenerate human muscle mass by implanting scaffolding material made of animal cells.

Damaged muscles grew stronger and showed signs of regeneration in 3 out of 5 men whose previous traumatic leg injuries were surgically implanted with an extracellular matrix (ECM) that was derived from pig bladder cells, according to a new study conducted by medical teams at the University of Pittsburgh's School of Medicine and the McGowan Institute for Regenerative Medicine.

Findings from the ongoing trial were published April 30 in the journal Science Translational Medicine.

"This new study is the first to show replacement of new functional muscle tissue in humans, and we're very excited by its potential," lead study investigator Stephen F. Badylak, a professor of surgery at Pitt and deputy director of the McGowan Institute, a joint effort of Pitt and university medical center, said in a news release. "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."

Dr. Badylak explained when a large volume of muscle is lost, which typically happens because of traumatic injury, the body cannot generate enough tissue to replace it. So, instead, the injured area forms scarring that leaves area strength and function significantly impaired.

The pig bladder matrix, Badylak said, has been used for many years as the basis for hernia repair and skin ulcer treatment products.

In actuality, it is the biologic structure left behind after the animal cells themselves have been removed.

Previous research lead Badylak's team to believe the matrix could be used to regenerate lost muscle by placing the material in the injury site, where it would prompt the body to assign stem and other progenitor cells to rebuild healthy tissue.

For the Muscle Tendon Tissue Unit Repair and Reinforcement Reconstructive Surgery Research Study, which is sponsored by the United States Deptartment of Defense, and is continuing to enroll new participants, five men who had lost at least 25 percent of leg muscle volume and function at least six months earlier underwent a specialized regimen of physical therapy for between 12 to 26 weeks, until their function and strength leveled off for at least two weeks.

Then, the study's lead surgeon J. Peter Rubin, professor and chair of plastic surgery at the University of Pittsburgh Medical Center as well as Pitt School of Medicine, implanted a "quilt" of compressed ECM sheets that filled the trail subjects' injury sites.

Within 48 hours of the operation, the participants resumed physical therapy for up to 26 additional weeks.

The study reported three of the participants, two of whom had thigh injuries, while the third had a calf injury, were stronger by 20 percent or more six months after the surgery.

One thigh-injured patient improved on a "single hop test" by 1,820 percent, while the other saw a 352 percent improvement in a chair lift test and a 417 percent improvement in the single-leg squat test.

Biopsies and scans indicated muscle growth had indeed occurred.

Meanwhile, the two remaining participants with calf injuries did not have such dramatic results, but nonetheless experienced improved limited function and said they generally felt better.

"This work represents an important step forward in our ability to repair tissues and improve function with materials derived from natural proteins. There will be more options to help our patients," Rubin said.