The first-ever working vocal cords able to produce realistic sound have been grown from scratch in a lab, promising hope to people who have lost their voice due to illness, injury or invasive surgery.
The vocal chords are actually, in theory, fairly simple: two bands of smooth muscle lined with delicate folds of mucosa. As air is forced by them, the lining can vibrate at speeds of up to 1000 times a second, allowing humans to produce a wide range of nuanced sounds. But many diseases and surgeries can damage the delicate lining, leaving patients with limited vocal ability.
Now, a team from the University of Wisconsin School of Public Health in Madison has grown working replicas from scratch. They took a 3D collagen scaffold and used two different types of cell to create the artificial cords — fibroplasts that were grown into smooth muscle and epithelial cells that were coaxed into becoming the delicate lining. The donated cells were taken from one dead donor body and the larynxes removed from patients through necessity.
The resulting vocal cords were grown in the lab for two weeks, reaching sizes of around 16 millimetres in length and 1 millimetre in thickness. They were then implanted into the voice boxes taken from dogs, where they were tested by blowing air through them with a fake windpipe. The result, according to the researchers, was a kind of "eeeee" sound, not unlike that made by a kazoo.
That might sounds like a failure, but it's actually roughly how a vocal cord should sound given that set-up. Humans can shape that sound using subtle variations in the throat and mouth to produce the rich, textured sounds of the voices that we're used to. The research is published in Science Translational Medicine.
The team also checked that their lab-grown cords were biologically viable by inserting small sections into mice with human-like immune systems. They weren't rejected, which suggests they should sit well enough in humans too.
But that's a way off yet: the team reckons that extensive animals testing, stem cell research and trials would be required before lab-grown vocal cords find their way into any human voice box.