Vocal cords with 'voice' grown in US laboratory
Functional vocal cords with a "voice" have been grown in the laboratory for the first time.
The research offers hope to people whose voices have been lost due to cancer or injury, although the first vocal cord implants are still some years away.
Vocal cords consist of two flexible folds of muscle lined with a delicate membrane, or mucosa, that vibrate hundreds of times per second to create sound.
Scientists in the US succeeded in growing multi-layered cells on a 3D scaffold to produce strong, elastic tissue similar to that of natural vocal cords.
Tests on the lab-grown tissue transplanted into voice boxes removed from dead dogs proved that it could produce the same kind of sound generated by its "real" counterpart.
Lead researcher Dr Nathan Welham, from the University of Wisconsin-Madison, said: "Voice is a pretty amazing thing, yet we don't give it much thought until something goes wrong.
"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."
The tissue was grown from healthy connective and surface lining cells taken from the vocal cords of four patients whose voice boxes had been removed for non-cancer medical reasons, and one dead human donor.
In about two weeks the two kinds of cells self-assembled into layers that closely resembled the structure of natural vocal cords, the researchers reported in the journal Science Translational Medicine.
The tests involved implanting the artificially grown cord tissue into one side of cadaver dog voice boxes attached to artificial windpipe.
When warm, humidified air was blown over the tissue it vibrated. Analysis showed that the sound made had the same acoustic characteristics as that produced by the remaining natural dog vocal cords.
Further work revealed that the tissue was not rejected when transplanted into mice engineered to have human immune systems.
"It seems like the engineered vocal cord tissue may be like cornea tissue in that it is immunoprivileged, meaning that it doesn't set off a host immune reaction," said Dr Welham.
The lab-grown tissue had a fibrous structure that was less complex than that of adult vocal cords. But the researchers say this is not surprising since human vocal cords continue to develop for at least 13 years after birth.
Because cancer-free vocal cord tissue is rare, clinical applications will require cell-banking or the use of stem cells, say the scientists.
Stem cells could be primed to differentiate into vocal cord cells by exposing them to vibration and stretching forces in a "laryngeal bioreactor", according to the team.