Self-Healing Muscles

Biomedical engineers at Duke University have been able to grow living skeletal muscles in the lab that look and act like the real thing. It's a first step in growing human muscle that can treat injuries and disease.

DURHAM - All of us take our muscles for granted. 

We shouldn’t.

Typing this article and other simple acts like picking up a pen, sitting in a chair, or even walking across the room, require muscles to fire constantly; contracting and releasing, moving our skeletons, which moves our bodies.

Skeletal muscles, which attach to the skeleton and facilitate movement, comprise 45% of the body. They are the body’s largest organ grouping and work amazingly well. So well, in fact, we forget about it, until there’s a problem. On the minor side, all of us damage our muscles in some way almost everyday. If you overdo your workout in the gym, or pull a muscle working in the yard, the aches and pains you feel are muscles dying.

Fortunately, skeletal muscles are regenerative. In other words, the muscles heal themselves, which means those aches and pains go away quickly.

But in the case of more serious injuries, surgery is needed to replace the injured muscle with a muscle taken from another part of the body. It is not always successful and, in the case of major muscle injury, such as damage from a disease, it is not always possible.

Doctors have always dreamed that the best way to help those patients with serious muscle damage would be to harness the self-regenerating power of muscles in a big way — implanting a muscle and letting it grow. Thanks to research at Duke University, the dream may become a reality.

“The goal is to make one that is large in size and can enable walking and other activities that require a lot of force and a lot of contraction,” said Dr. Nenad Bursac, Associate Professor of Biomedical Engineering at Duke. “Building a big muscle is a big challenge because these cells require a lot of oxygen, a lot of nutrients. Metabolically, we say they are very active.”

It’s a big idea, but all big ideas start small. Which is why Dr. Bursac is so excited about what we are watching on a laptop in the lab. On the screen is a fleshy, fuzzy-looking object that resembles a tiny barbell. It appears to be floating in something and is bending back and forth.

“You’re looking at an individual skeletal muscle that is about a half-inch long,” adds Dr. Bursac. “It is moving because it is reacting to impulses. First, we worked with creating these in the lab and testing these in the lab. Once we optimized a model, we went to testing it in an animal.”

Tests revealed the lab-grown, living skeletal muscle is amazingly life like. It is 10 times stronger than previous engineered muscles. The engineered muscle also contracts powerfully and quickly and integrates itself into the body with other muscles.

Duke graduate student Mark Juhas shows a series of images with original muscle cells on the top row and the lab-grown muscles on the bottom row. The images look identical.

“Basically, we’re showing here they have a similar outer layer of connective tissue and the interior has these connected, semi-striated muscle fibers,” explains Juhas. “Most important, we are showing how we maintain a pool of satellite cells, otherwise known as stem cells, which are important as we move on because that’s what facilitates muscle growth.”

The experiment at Duke was a breakthrough in muscle therapy because it is the first time muscles engineered in a lab provided an environment where satellite cells, or stem cells, were able to survive, and then activate and grow.

“Even though muscles are one of the most regenerative organs in the body, the ability to preserve satellite cells and then regenerate hasn’t been shown outside of the body before," says Dr. Bursac. "So this is the first time we were able to generate the muscle that does have these cells and then be able to repair itself.”

The lab-engineered muscle was then placed in the back of a living, walking mouse. Scientists monitored the muscle through a specially-designed window. And because they had genetically modified the muscle to flash when it was contracting, scientists were able to watch the muscle grow stronger.

“We actually saw a maturity over time, or an increase in this flash over time, showing we are improving our muscle,” adds Juhas.

Researchers are now working to see if their engineered muscle can be used to repair actual muscle injuries. The long-term goal is to take a biopsy of an injured human muscle and be able to grow a new muscle in the lab that could then be transplanted back into the patient.

“This isn’t something that will be available tomorrow, or next year,” warns Dr. Bursac. “It’s not something we will be able to do for many years because the most important issue we still must address is vasculature. We need to make sure we can get blood, nutrients and oxygen to the muscles so they can regenerate properly. If we can do that, we can open the door to many therapies.”

Dr. Bursac admits the therapy will start small. If further tests in animals prove successful, the first human muscles to be replaced may be a dysfunctional facial muscle, which causes a droopy eyelid. If that is successful, researchers will move on to larger muscles.

“It is very exciting and very promising but there is a lot more work to do,” adds a smiling Dr. Bursac, as he points to the video of the tiny muscle, glowing and contracting as it fires and grows. It is something nobody has been able to do before.

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