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November 15, 2010

Microthreads Help Grow New Muscles

Mending muscle: Hair-thin threads like the ones shown here were seeded with muscle cells and implanted into wounds to help heal muscle in mice.
Credit: Tissue Engineering/Mary Ann Liebert


MIT 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.



The threads were seeded with human muscle cells derived from tissue discarded during surgery. Prior to seeding, Page's team grew the cells under conditions that pushed them to de-differentiate—or to become more juvenile, less specialized cells—which in turn made them better able to regenerate.

To test the technology in mice, researchers cut out about 30 percent of the animals' tibialis anterior muscle, which lies at the front of the lower leg. They then implanted cell-seeded microthreads into the wound. (The diameter of the thread, about 50 to 100 microns, is five to 10 times the size of the cells.)

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.

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