For the first time, scientists have successfully grown vocal cords in the lab, with tests showing the engineered tissue to be functional, with the ability to transmit sound. While the research is just the first step on a long path towards clinical use, the results are very promising, providing a solid basis for future study.
While vocal cord issues are very common, with around 20 million people in the US suffering from some form of voice impairment, it's a very tricky area of study. Vocal cord tissue is extremely specialized, being flexible enough to vibrate, but strong enough not to be damaged by thousands of hours of use, the cords colliding with one another hundreds of times every second. As engineered replacement tissue would have to exhibit these same properties, the task of creating it in the lab is a difficult one.
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For the new study, conducted at the University of Wisconsin, the researchers worked with vocal cord tissue taken from four patients who had previously had their larynges removed, as well as samples from a cadaver. The tissue cells were grown from the mucosa, before being transferred to a 3D collagen scaffold.
After two weeks of growth on the scaffold, the team tested the qualities of the resulting tissue, finding that a pliable lower layer had formed underneath an upper covering of layered epithelial cells. Further testing revealed that many of the same proteins found in natural vocal cords were present, and a membrane was found to be forming that helps create a barrier against irritants and pathogens in the airway. Overall, the results were similar to what you'd expect from naturally-grown tissue.
The next step was to see if the bioengineered tissue was actually able to transmit sound. To do so, the team transplanted it onto larynges removed from canine cadavers, passing air through attached artificial wind pipes. Once again, the results were promising, with sound being produced and high-speed imaging revealing that the engineered tissue vibrates in a similar way to its natural counterpart.
Continuing their testing, the scientists then grafted the tissue onto laboratory mice engineered to have human immune systems. Once again, the results were positive, with the tissue growing normally and not being rejected.
However, despite the success of the study, perhaps unsurprisingly, the engineered vocal cord tissue isn't quite as good as the real thing. Most notably, its fiber structure is less complex than in natural tissue in adults, which develop over much longer periods of time, for at least 13 years after birth.
According to the researchers, years of further study will be required before clinical applications could be considered, particularly to assess the safety and long-term function of the tissue. That said, given how rare a commodity cancer-free vocal cord tissue is, the research provides a very strong basis for future study.
The results of the study were recently published in the journal Science Translational Medicine.
Source: University of Wisconsin