For vocal cords, producing sound is no mean feat. They need to be flexible enough to vibrate, but tough enough to withstand smacking together over a hundred times per second. If our whole bodies were subjected to an equivalent force, we’d be ripped apart.
Now, for the first time, researchers at the University of Wisconsin-Madison have grown this superhero-like tissue in the lab, using human vocal cord cells as their raw ingredients. Their hope is to one day implant these engineered vocal cords into patients so they can recover their voices.
The new technology is nowhere near-ready for use in the clinic, but the idea might not be completely far-fetched: these tissues are both strong and stretchy enough to produce sound.
“It represents hope,” said Dr. Ramon Franco, medical director of the Voice and Speech Laboratory at Massachusetts Eye and Ear, a speciality hospital in Boston, who was not involved in the study. “I have patients who are severely hoarse. There aren’t a lot of options.”
Other engineered organs of the throat have been tested in human clinical trials. These include tracheas, the tubes that lead into the lungs, and larynxes, which hold the vocal cords and allow for breath. But the vocal cords themselves are trickier to engineer because they need to vibrate under so much pressure.
Right now, treatments for damaged vocal cords include injecting steroids or other substances to soften up scar tissue. But this approach usually offers only temporary relief for the millions of Americans with impaired vocal cords. “Often the materials are absorbed by the body after a few months and you’re back at square one,” said Nathan Welham, a speech-language pathologist at the University of Wisconsin School of Medicine, and one of the creators of the new lab-grown tissue.
Welham and his colleagues thought that the best way to repair the damaged tissues might just be to replace them. They collected healthy vocal cords from patients who needed to have them removed (and, in one case, from a cadaver), and used an enzyme that could digest the tissue without killing the cells. They scooped up the cells, and set them up in the exact environment they needed to grow into a three-dimensional replica of the human vocal cord.
To test their newly grown tissue, the researchers made a model of the voice-box in the lab. The larynx looks relatively similar in dogs and humans, so the scientists stuck five dog larynxes onto bits of PVC piping, and blew warm, humid air through them to mimic the way breath passes through the voice-box.
They then swapped the canine vocal cords with their engineered human tissue, and found that it vibrated as well as the original. The sound of their success was less like a voice than it was like the buzzing of a saw — but that’s because there were no bodies in which the vibrations could resonate.
“It doesn’t sound like my voice or your voice,” said Welham. “But if I cut off my head and made voice out into the open air, it would sound like that.”
They also inserted the lab-grown vocal cords into mice equipped with a human immune system, and the tissue wasn’t rejected. Welham and his team reported the findings on Wednesday in Science Translational Medicine.
But if anyone with voice trouble is already hankering after these bioengineered tissues, they should remember that they’ve only been tested on dog larynxes in the lab. “The kinks have to be worked out,” said Franco. “You need to make sure you’re not going to create a tumor. There are so many things that need to be investigated before these things hit the streets.”
Still, for Dr. Maggie Kuhn, a voice expert at University of California, Davis, this new tissue is good news. “The fact that they’re starting animal studies is promising,” she said.