For the first time, doctors have grown vocal cords from scratch. This could one day restore the ability to speak to those that have lost their voice through surgery or disease.
Doctors built the vocal cords using cells from human donors. The cells were coaxed into forming tissue that mimics vocal fold mucosa – the flaps in the larynx that vibrate to create the sounds of the human voice.
This is the latest success in the rapidly advancing field of tissue regeneration – the list of organs already includes kidneys, windpipes and hearts.
The donated vocal fold cells came from one cadaver and four patients who’d had their larynxes removed surgically for various reasons. The team grew the cells in the lab for two weeks to create 170 vocal folds, around 16 millimetres in length and a millimetre thick.
Researchers tested the vocal cords by attaching them to larynxes extracted from dogs. “We put the larynxes with the folds attached onto a fake windpipe and blew warm air through them,” said Nathan Welham at the University of Wisconsin School of Public Health in Madison, and head of the team behind the work. The result resembled a robotic kazoo, says Welham. “It was an eeee-like sound.”
The sound matches that made by natural human vocal folds in isolation, he explains, but a real human voice is generated through further modulation of sounds by other structures, such as the mouth and throat.
A new voice
Welham and his colleagues created the folds by seeding a 3D collagen scaffold with human vocal fold cells – collagen is the main structural component of organs and tissue. The team used two types of cells – fibroblasts to create the thickest, most elastic tissue in a fold, and epithelial cells to provide the delicate lining that vibrates up to 1000 times a second. “No other tissue in the human body is subject to these biomechanical demands,” says Welham.
When the team tested the folds in mice with human immune systems, the tissues weren’t rejected, suggesting they were immune-privileged, hidden from the immune system.
Welham envisages two possible ways of growing folds for transplant. One would be to have a bank of donated vocal fold mucosa cells, grown on demand to suit each patient’s throat. The other idea would involve producing off-the-peg folds in a variety of shapes and sizes that could suit a wide range of individuals.
Welham hopes each approach would allow easy access to customised folds for people who need them. He expects the lab-grown folds to work better than existing grafts of tissue from other parts of the mouth, which are not designed for the task in hand. Demand for better treatments is there, says Welham, for example, voice impairment already affects about 20 million Americans.
Other researchers welcomed the advance. “It shows we’re getting closer and closer to engineering clinically relevant tissues,” says Harald Ott of Massachusetts General Hospital, whose team earlier this year unveiled the world’s first lab-grown “bio-limb” – a rat forelimb. “Loss of voice has a devastating impact on a patient’s quality of life, so engineering a living, functional replacement for these patients is a very important milestone,” Ott says.