Scientists create bioengineered vocal cord tissue capable of transmitting sound

A team of researchers, primarily from the University of Wisconsin-Madison (UW), reported in the journal Science Translational Medicine their successful attempt at creating bioengineered vocal cord tissue capable of transmitting sound once implanted inside an animal’s voice box, or larynx. Better still, the lab-grown proved to be nearly as functional as naturally present vocal cord tissue, and in later mice experiments, appeared to be tolerated well by a human immune system.

Their “proof of principle” study may be considered the first step of many toward alleviating difficult-to-treat voice impairments, or dysphonia, present in approximately 20 million Americans to date.

According to senior study author Dr. Nathan Welham, a speech-language pathologist at UW, research efforts to create functional vocal fold (VF) mucosa, the formal term for the two vocal cords we each possess, have been slow-moving. "Voice is a pretty amazing thing, yet we don't give it much thought until something goes wrong," said Welham, also an associate professor of surgery in the UW School of Medicine and Public Health, in a statement. "Our vocal cords are made up of special tissue that has to be flexible enough to vibrate, yet strong enough to bang together hundreds of times per second. It's an exquisite system and a hard thing to replicate."

Instead of relying on stem cells, as with earlier attempts to create bioengineered VF tissue, Welham and his colleagues instead used human VF cells from a cadaver and donors who needed to have their healthy larynxes removed as the seed for their lab-grown tissue. After isolating and purifying the cells, they then planted them on a 3D collagen scaffold and grew them the same way that scientists have grown artificial skin and “other mucosal systems.” Two weeks later, the tissue’s structure began resembling the genuine article and it passed physical tests of viscosity and elasticity with flying colors.

They then took things further with a series of animal experiments. First, they replaced one vocal cord of a noble decreased dog’s larynx and ran what might be best thought of as miniature wind-tunnel tests on both cords, finding that the artificial tissue “generated vibratory behavior and acoustic output that were indistinguishable from those of native VF tissue.”

Then, they transplanted their tissue onto mice that were gifted human immune systems resembling either the original larynx-cell donors or completely foreign hosts. In either case, the tissue was well-tolerated to the same degree, validating previous research showing that the area around the vocal cords may be especially tuned to accepting donor tissue. "It seems like the engineered vocal cord tissue may be like cornea tissue in that it is immunoprivileged, meaning that it doesn't set off a host immune reaction," explained Wetham.

About the only noticeable drawback seen by the team was the artificial VF tissue’s less complex underlying fiber structure. As human vocal cords are known to take approximately 13 years to reach full maturity, however, that finding isn’t particularly surprising, and the researchers are optimistic that they can find a workaround for it in the lab.   

While Wetham and his team’s findings are undoubtedly encouraging, it will take years of further experimentation and a dedicated framework around VF tissue gathering for the reality of bioengineered VF tissue to come to pass. As it stands now, healthy VF donor cells are difficult to come by, since most vocal cords are removed due to cancer, and a sort of banking system to collect them en mass would be needed in the future. Similarly, advances in stem cell technology may also be able to provide abundant VF tissue someday as well.

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