From a loved ones comforting words to a mother’s shout of warning, human voices are the main way people communicate. Scientists in the US are currently undergoing extensive research looking into producing working lab-grown vocal cords from human tissue.
Vocal cords consist of one or two small bands of smooth muscle tissue within the larynx. The muscle tissue is lined with a material called mucosa. When air passes through them, the folds vibrate hundreds of times per second to make sounds.
Diseases such as cancer can destroy the delicate folds within the muscle, and for many patients there is not much scope for treatment. Sometimes vocal cords become too scarred and stiff to work properly meaning they must be removed.
“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.”
The vocal cord tissue is highly specialised, being flexible enough to vibrate, but strong enough not to be damaged by millions of hours of use. As the lab-grown tissue would have to display these same characterisics, the task of creating it in a lab is very challenging.
The US team have collaborated with doctors in Japan, who have grown tissue from healthy connective tissue taken from four patients whose voice boxes had been removed for medical reasons, and one dead human donor. After weeks of study positive results were showing as two cell types began to assemble into layers that resembled the structure of healthy vocal cords.
Scientists implanted the freshly grown tissue into one side of voice boxes taken from dogs, and attached them to an artificial windpipe to send air through them. Humidified air was blown over the tissue which vibrated, producing sounds that sounded similar to those made by natural dog.
As transplant rejection can cause many issues, follow-up studies using mice were used. Mice have similar immune systems to human which can mimic the immune system of a human. The research showed that the tissue transplants were not rejected during the three-month trial.
Scientists are unlikely to use tissue from patients to grow replacement voice boxes as there is too little tissue available that is free of diseased or cancerous cells. Doctors believe that they can create vocal cords from stem cells that are turned into muscle cells to form the cords.
While the research is just the first step on a lengthy journey towards clinical use, the results have proven to be extremely promising, providing a solid basis for future study. More clinical studies are needed to ensure that they work well and do not aggravate an immune response, and the whole process must be performed with cells suitable to be implanted in humans.