The first phase of the Pentagon's plan to regrow soldiers' limbs is complete; scientists managed to turn human skin into the equivalent of a blastema — a mass of undifferentiated cells that can develop into new body parts. Now, researchers are on to phase two: turning that cellular glop into a square inch of honest-to-goodness muscle tissue.

Cellthera Inc. and the Worcester Polytechnic Institute (WPI) just got a one-year, $570,000 grant from Darpa, the Pentagon's blue-sky research arm, to grow the new tissues. "The goal is to genuinely replace a muscle that's lost," biotechnology professor Raymond Page tells Danger Room. "I appreciate that's a very aggressive goal." And it's only one part in a larger, even more ambitious Darpa program, Restorative Injury Repair, that aims to "fully restore the function of complex tissue (muscle, nerves, skin, etc.)

after traumatic injury on the battlefield."

Muscles are, of course, famous for their ability to regenerate; they're broken down and rebuilt with every gym workout. But when too much of a muscle is lost — either from injury or illness — "instead of the regenerative response, you get scarring," Page says. He's hoping to get a different result, by carefully growing fresh muscle, outside the body.

Step one will be trying to get those undifferentiated cells to turn into something like muscle cells. That means making sure the cells have myosin and actin — two proteins that are key to forming the cellular cytoskeleton, and to building muscle filaments. Then, Page and his team will try to get those cells to form around a scaffolding of tiny threads, made of biomaterial. Exactly what will be in thread, Page isn't quite sure — maybe collagens, maybe fibrinogens. It's one of many mysteries to unravel, as his team tries to grow body parts from scratch.

Photo: UCI Regeneration Lab