For the first time ever, scientists have been able to successfully regenerate damaged leg muscles through a new stem cell technique that uses material from pig bladder tissue. Researchers at the University of Pittsburgh School of Medicine and the McGowan Institute for Regenerative Health tested out the procedure on five men.

Results from the small, preliminary trial -- and prior animal studies -- were published today in Science Translational Medicine. The research was sponsored by the U.S. Department of Defense.

The procedure involves surgically implanting a "quilt" of sheets of the cells from connective tissue of a pig's bladder. The process causes the body to regenerate stem cells at the injury site, which repairs scar tissue and helps the person to regain muscle strength and movement.

"We can take the type of injury that normally would form nothing other than scar tissue and form a brand new skeletal muscle that's functional, that contracts," Dr. Steve Badylak at the University of Pittsburgh's department of surgery, told CBS News' Ko Im.

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Over time the transplanted tissue melds with the patient's real muscle tissue, explained Badylak. "They get these signals," he said. "They say, okay, I get it, I'm supposed to line up like this, and they recruit their own new blood supply, their own new nerves and they basically start forming new tissue this way."

Pig bladder cells have been used for years to repair damaged and missing tissue of patients. In the past, doctors have employed the technique to fix hernias and treat skin ulcers. Last year, a surgeon in Delray Beach, Fla., grew a man's missing finger using the material. And some researchers are in the early stages of harvesting the tissue to grow vital organs for transplant.

The researchers of this trial report the procedure was highly effective on three of the five men, all of whom sustained injuries six months prior and had lost 25 percent of leg muscle volume. The five men underwent regular physical therapy for 12 to 26 weeks prior to the surgery, and resumed regular sessions 48 hours after the procedure for an additional 26 week

Six months later the surgically treated leg muscles were at least 20 percent stronger in three of the men. One man with an injured thigh muscle showed a 1,820 percent improvement on the "hop test." Another man demonstrated a 352 percent improvement on the chair lift and a 417 percent improvement for a single leg squat. Biopsies and scans of the injured tendons showed muscle regrowth had occurred in all five men.

Nick Clark, one patient enrolled in the study, injured his calf in a skiing accident almost 10 years ago. "Because of complications of that severe break there was a lot of internal bleeding inside these muscle compartments and that caused swelling," Clark told CBS News.

After his initial recovery, Clark found the muscle didn't work the same way. "I couldn't push off my left foot at all. I had no balance," he explained. Since undergoing the procedure, Clark says his balance has improved. He can also put weight on his leg, jump and he no longer needs to wear an orthotic. "I wanted to try it, I wanted to see if it works for me and I'm happy that it has," he said.