Self-Healing Muscle Grown in Lab

Biomedical engineers at Duke University have grown living skeletal muscle that resembles real tissue.  It contracts rapidly and powerfully, integrates into the host quickly and for the first time ever; it demonstrates the ability to heal itself both inside the laboratory and inside an animal.
The study conducted at Duke University has tested the bioengineered muscle on a living mouse. The fresh technique they used has allowed for real-time monitoring of the muscle’s integration and maturation inside a living animal.  Both the lab-grown muscle and experimental techniques are important steps toward growing viable muscle for studying diseases and treating injuries, said Nenad Bursac, associate professor of Biomedical Engineering at Duke University.  “The muscle we have made represents an important advance for the field…It’s the first time engineered muscle has been created that contracts as strongly as native neonatal skeletal muscle,” Bursac said.

Long, colorful strands of engineered muscle fiber have been stained to observe growth after implantation into a mouse. (Image courtesy of Duke University)

A team led by Bursac and graduate student Mark Juhas, have discovered that preparing better muscle requires two things, well-developed contractile muscle fibres and a pool of muscle stem cells, known as satellite cells.  Every muscle has satellite cells on reserve, that are ready to activate upon injury and begin the regeneration process. The key to the team’s success was successfully creating the microenvironments, called niches, where the stem cells await action.
“Simply implanting satellite cells or less-developed muscle doesn’t work as well…The well-developed muscle we made provides niches for satellite cells to live in and when needed to restore the robust musculature and its function,” said Juhas.  To test their engineered muscle, the team ran it through trials in the laboratory. They stimulating it with electric pulses, measured its contractile strength, thereby showing that it was more than 10x stronger than any previously engineered muscles.  Next they damaged it with a toxin that was found in snake venom.  This was to prove that the satellite cells could activate, multiply and then heal the injured muscle fibres.  After these tests, then they moved it out of a dish environment and into living tissue, a mouse.

Greg Palmer, an assistant professor of radiation oncology in the Duke University School of Medicine, assisted the team.  The engineers next inserted their lab-grown muscle into a small chamber, which was placed on the backs of live mice. A glass panel then covered this chamber. Every two days for a two week period, Juhas looked upon the implanted muscles through the window to ascertain the progress.  The muscle fibres were genetically modified to produce fluorescent flashes during calcium spikes, which cause muscle to contract. The researchers could then watch the flashes become brighter as the muscle grew stronger.  “We could see and measure in real time how blood vessels grew into the implanted muscle fibres, maturing toward equalling the strength of its native counterpart,” said Juhas.
The engineers are now starting work to see if their biomimetic muscle can be used to repair muscle injuries and disease.  “Can it vascularise, innervate and repair the damaged muscle’s function?…That is what we will be working on for the next several years,” said Bursac.