The new kind of lab-grown muscle will allow the study of disease and testing new medications in a safe setting outside the human body, said the team, led by Nenad Bursac, Duke University associate professor of biomedical engineering, and postdoctoral researcher Lauran Madden.
"The beauty of this work is that it can serve as a test bed for clinical trials in a dish," Bursac said. "We are working to test drugs' efficacy and safety without jeopardising a patient's health."
The contracting muscles were grown from what is called myogenic precursor cells -- cells that have progressed beyond the early stem cell phase, but hadn't quite yet grown into full muscle tissue. These cells were increased 1,000-fold, seeded into a 3D scaffold and nourished with a culture gel full of nutrients to encourage growth.
Although growing animal muscles in a lab had already been achieved -- we have seen lab-grown meat -- optimising the process to successfully grow human muscle took the team a year.
The resulting muscle tissue was then tested with a variety of external stimuli to see how closely it resembled human tissue.
For the first time, lab-grown muscle tissue robustly contracted in response to electrical stimuli. The nerve signal pathways -- which would allow the nerves to activate the muscle -- were intact and functional.
The team also demonstrated that the effect of drugs on the lab-grown tissue matched the effect seen in human patients. They tested a variety of pharmaceuticals, such as statins, which are used to lower cholesterol, and clenbuterol, an off-label athletic performance enhancer. The statins caused abnormal fat accumulation at high doses, while the clenbuterol had a narrow beneficial window for increased contraction -- both of which effects have been documented in humans.
This could allow future physicians to tailor pharmaceutical treatments to individual patients.
"One of our goals is to use this method to provide personalised medicine to patients," Bursac said. "We can take a biopsy from each patient, grow many new muscles to use as test samples and experiment to see which drugs would work best for each person."
The team is already working towards this goal -- as well as towards growing the muscle tissue, not from a biopsy, but from pluripotent stem cells; that is, "blank" cells that can grow into any other cell, rather than cells that are already on the way to becoming muscle cells.
"There are a some diseases, like Duchenne Muscular Dystrophy for example, that make taking muscle biopsies difficult. If we could grow working, testable muscles from induced pluripotent stem cells, we could take one skin or blood sample and never have to bother the patient again," Bursac said.
The full study can be found online in the open-access journal eLife.