Vocal cords that produce realistic sounds have been grown in the lab from human cells.
The work marks a first step towards better treatments for patients who lose their voices to injury or disease.
Vocal cords are formed by two bands of smooth muscle tissue that are lined with a material called mucosa. When air passes through them, the folds vibrate hundreds of times per second to make sounds.
But diseases such as cancer can destroy the delicate folds and for many patients, the medical treatments are limited. Some patients with damaged vocal cords have viscous materials injected to make the folds more pliable. Others improve with voice coaching.
Researchers in the US took a different approach and grew layers of vocal cord cells onto scaffolds that produced tough elastic tissue similar to those within the natural voice box. When doctors tested the lab-grown tissue in voice boxes taken from dead dogs, they found they produced the same sounds as the natural tissue.
“Voice is a pretty amazing thing, yet we don’t give it much thought until something goes wrong,” said lead researcher Nathan Welham at the University of Wisconsin-Madison. “The ability to vibrate and make sounds is pretty remarkable and unique to this part of the body.”
“When the tissue is damaged it doesn’t recover and regenerate normally and we don’t have great solutions at present to deal with that,” Welham added. “It’s an exquisite system and a hard thing to replicate.”
Working with doctors in Japan, the US team grew tissue from healthy connective tissue and lining cells taken from the vocal cords of four patients whose voice boxes had been removed for medical reasons, and one dead human donor.
After two weeks in the lab, the two cell types began to assemble into layers that resembled the structure of healthy vocal cords. Details of the research are reported in the journal Science Translational Medicine.
To test the freshly-grown tissue folds, scientists implanted them into one side of voice boxes taken from dogs, and attached them to an artificial windpipe to send air through them.
When humidified air was blown over the tissue it vibrated, producing sounds that had the same characteristics as those made by natural dog vocal cords. High speed digital imaging showed that the cords vibrated like natural tissue too.
In follow-up studies using mice with human-like immune systems, the researchers showed that the tissue transplants were not rejected during a three month trial.
The lab-grown tissue has a simpler structure than adult vocal cords, but the researchers said that was expected since human vocal cords can take 13 years to fully develop.
Scientists are unlikely to grow replacement voice boxes from vocal cord tissue donated from patients. There is too little of the tissue available that is free of diseased or cancerous cells. But doctors believe that instead they can create vocal cords from stem cells that are turned into muscle and lining cells to form the cords.
Lab-grown replacements for damaged vocal cords are still years away, Welham said. More studies are needed in animals to show that they work well and do not provoke an immune reaction, and the entire process must be performed with clinical grade cells before the implants can be trialled in humans.