Scientists have successfully grown vocal cord tissue in the lab and shown it can produce realistic sound when grafted into voice boxes that have been attached to an artificial windpipe that blows air through them.
The team also showed that the tissue – engineered from human cells – did not show signs of rejection when transplanted into mice with humanized immune systems.
Writing in Science Translational Medicine, bioengineers at the University of Wisconsin-Madison suggest their work shows in principle that it is possible to restore vocal cord function with lab-grown tissue.
They say that while there is still a way to go before such a procedure can be carried out in human patients, it brings closer the day when people who have lost their vocal cords to cancer or injury can have their voice restored.
The sounds that make up our voice are produced using the lungs and specialized tissues called vocal folds or vocal cords situated inside the voice box or larynx.
Senior author Nathan Welham, a speech language pathologist and associate professor of surgery, says our voice is an amazing thing that we rarely think about until something goes wrong. He explains:
“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.”
Estimates suggest around 7.5 million people in the US have trouble using their voice. Problems can result when the nerves that control the voice box or the vocal cords themselves become damaged through injury, or as a result of surgery, viral infection or cancer.
Prof. Welham says injections of collagen and other materials can temporarily repair damage to the vocal cord mucosae – the specialized tissues that produce voice sounds by vibrating when air passes over them. But this does not help people who have suffered more extensive damage or who have had their vocal cords removed.
For their study, the team used vocal cord tissue from a deceased person and the voice boxes of four living patients who had had them removed but did not have cancer.
They isolated and purified the cells from the vocal cord mucosa and then grew layers of them on a 3D scaffold made of collagen. The system they used is similar to one used to make artificial skin.
Within 2 weeks, they had strong, flexible tissue with the physical properties and feel of vocal cord tissue with cells that contained many of the same proteins as normal vocal cord cells.
To test the tissue’s physical and sound properties, the team transplanted it into one side of voice boxes that had been removed from cadaver dogs. The voice boxes were attached to artificial windpipes that had warm, humidified air blown through them.
Tests showed the lab-grown tissue not only produced sound but it also vibrated in a similar way to the natural tissue on the opposite side of the voice box. It produced what the researchers describe as a “normal mucosal wave.”
Other tests showed the engineered tissue had also begun to grow a type of membrane that is normally found in the airway and protects it from pathogens and irritants.
And finally, the researchers showed that when transplanted into engineered mice with human-like immune systems, the lab-grown tissue was well tolerated and not rejected.
The authors conclude:
“These data suggest feasibility for transplant and survival in the larynx as well as for function, ultimately giving patients back their voices.”
In the following video, Prof. Welham demonstrates various aspects of the research and explains its significance:
In another study published earlier this year, Medical News Today learned of a discovery that could bring closer the day when we can reverse the loss of hearing and balance that results from loss of hair cells in the inner ear. The discovery surrounds the role of two genes that are important for inner ear development.