Good vibrations

How to restore people’s voices

The Economist, Aug 25th 2012 | http://www.economist.com/node/21560837

INJURY, disease or sheer old age mean that as many as 7% of Americans (and, presumably, a similar proportion of the population of other countries) have some kind of voice disorder caused by scarring of their vocal cords. Such scarring makes the cords stiff, and stops them producing sound in the normal way. But that could be overcome if a method were found to restore the cords’ flexibility.

Robert Langer, a pioneering biomedical engineer at the Massachusetts Institute of Technology, and his colleagues think they have one. They have developed a material that mimics the characteristics of natural vocal cords and could thus help restore distorted voices.

The new polymer gel is not intended to heal scarred tissue, but rather to make the whole tissue flexible enough to restore vibrations to normal. To achieve this Dr Langer proposes to inject the gel under the tissue membrane (a thin layer of cells that covers the vocal cords), forming an additional layer within. Patients with different voices could be treated with gels that had different physical characteristics, in order to produce the desired effect.To make their new material, Dr Langer and his team took polyethylene glycol, a substance widely used in the cosmetics industry and thus known to be safe, and altered the chemical linkages between its molecules. This allowed them to control the polymer’s viscosity and elasticity. After some trial and error, as they described on August 20th to a meeting of the American Chemical Society held in Philadelphia, they hit on a mixture which matches the traits of human vocal cords. Laboratory tests have shown that when air is blown through a model of the vocal cords made from this material, the model responds in the way that real cords do.

There is a limitation. The new gel is prone to degradation and in some cases would need to be topped up regularly. But trials on animals suggest the procedure is safe, and human trials are expected to start soon.