Researchers believe that the fibrin scaffold sends signaling cues that mimic native wound healing, binding to growth factors and other molecules found in blood clots. It also attracts an enzyme that breaks down the fibrin, releasing fibrinogen proteins that signal the surrounding cells to migrate in and grow new tissue, says Pins.
The cells appeared to integrate into the host tissue in just a couple of days. After a week, the microthreads began to degrade, and researchers saw that muscle fibers had grown into the area left behind. At 10 weeks, the wound bed was full of human cells, which looked like mature muscle fibers. Page presented the research at a bioengineering symposium at WPI earlier this month.
The researchers are now trying to determine whether the new tissue behaves like normal muscle. Early evidence suggests that the implants also spurred the growth of native muscle cells, though Page says they still need to confirm this.
In addition, mice implanted with microthreads had much less scar tissue than animals left to heal on their own. The microthreads “dramatically reduced the amount of collagen [the major component of scar tissue] deposited in the wound area,” says Page. “Instead of collagen, we see a lot of [well-organized] muscle tissue.”
Page says that while other scientists have been able to repair muscle to a certain extent, the WPI technology healed a much larger area of injury than previous research. This may be because the microthreads help solve one of the major challenges in growing larger swaths of new tissue—drawing in an adequate supply of blood, vital for cell survival. “One of the reasons we wanted to investigate microthreads was, we felt having space between threads would give room for vasculature to form and for muscle cells to grow,” says Page.
Harvard’s Parker, who is growing heart muscle using even smaller fibers, agrees, adding that few people in tissue engineering are taking this approach. “If I put a solid chunk of meat in there, the center will become hypoxic [or oxygen-starved],” says Parker. “If I leave space between the cells, it is easier to recruit local blood vessels.”