In a report published recently in the journal Science Translational Medicine, it was revealed that scientists at the University of Wisconsin-Madison have succeeded in growing functional vocal cord tissue in the laboratory. This is a major breakthrough as it may go a long way restoring the voice to people who have lost their vocal cords to cancer surgery or other injuries. The report said that Dr. Nathan Welham, a UW speech-language pathologist, and colleagues from several disciplines were able to bioengineer vocal cord tissue that was able to transmit sound.
Statistics reveal that almost 20 million Americans suffer from voice impairments; many of these people may have damaged vocal cord mucosae, the specialized tissues that vibrate as air moves over them, giving rise to voice. For short term, injections of collagen and other materials can be helpful, but for people who have had larger areas of their vocal cords damaged or removed, there was no substantial treatment option.
Welham, an associate professor of surgery in the UW School of Medicine and Public Health opined that voice is something we do not realize the value of unless something goes wrong with it. Our vocal cords comprises of special tissue that need to be flexible enough to vibrate and also strong enough to bang together hundreds of times per second. It is an exquisite system and quite a hard thing to replicate.
For their experiment Welham and his fellow colleagues started with vocal cord tissue from a cadaver and four patients who had their larynxes removed but did not have cancer. Cells from the mucosa were isolated, purified and grown. A 3-D collagen scaffold was then applied to it – similar to a system used to grow artificial skin in the laboratory. It took two weeks for the cells to grow together and form a tissue with a pliable but strong connective tissue beneath, and layered epithelial cells on top. When proteomic analysis was carried out, it was found that the cells produced many of the same proteins as normal vocal cord cells. Physical testing also revealed that the epithelial cells had also begun to form an immature basement membrane that is instrumental in creating a barrier against pathogens and irritants in the airway.
Welham remarked that the lab-grown tissue was quite like vocal cord tissue and in materials testing it was found that it did have the qualities of viscosity and elasticity similar to normal tissue. In order to see if these bio-engineered tissues could transmit sound, the researchers transplanted the bioengineered tissue onto one side of larynges removed from cadaver dogs. The larynges were attached to artificial windpipes and warm, humidified air was blown through them. The tissue produced sound and high-speed digital imaging showed the engineered mucosa vibrating like the native tissue on the opposing side. Acoustic analysis also revealed that the two types of tissue had similar sound characteristics.
As a final leg of their experiment, the researchers decided to find out if the tissue would be rejected or accepted by mice that had been engineered to have human immune systems. The tissue grew and was not rejected in mice.
Of course, these lab made tissues were not as good as the real thing – human vocal cords keep developing till at least 13 years after birth. So, the similar complexing in its fiber structure cannot be expected.
Clinical applications of this study are still years away, but Welham is of the opinion that this proof-of-principle study is a robust benchmark along the route to replacement vocal cord tissue. Of course, further promising work need more testing of safety and long-term function.