From the Technology Review: "Researchers have repaired large muscle wounds in mice by growing and implanting 'microthreads' coated with human muscle cells. The microthreads - made out of the same material that triggers the formation of blood clots - seem to help the cells grow in the proper orientation, which is vital for rebuilding working muscle tissue. ... We hypothesize that cells migrate along these scaffolds, which act like a conduit. The cells grow into the space where muscle used to be, but they grow in a guided way. Currently, there's not much doctors can do when someone suffers massive injury to a muscle, such as in a car crash or an explosion. Thick bands of scar tissue can form in the wound, leaving the muscle severely and permanently impaired. Scientists are developing numerous approaches to creating replacement muscle, including growing patches of cells in a dish, injecting stem cells into damaged muscle, and implanting cell-seeded scaffolds designed to mimic native tissue. While all of these efforts show promise for certain applications, one of the major challenges has been growing enough cells in the correct structure to heal large muscle wounds. ... Muscle alignment is very important. You want the sarcomeres [the basic functional unit of muscle] to be aligned, that's how you get muscle contractions."