Our voice is used to communicate but it also defines our identity. Thus, a voice alteration or a complete speech loss can cause emotional and social issues. Patients suffering from an advanced stage of laryngeal cancer often have to undergo a total surgical removal of the human voice source, the larynx.
To recover the ability to speak, a prosthesis, mimicking the vocal folds, is usually placed between the trachea and the oesophagus. The exhaled air crosses a small tube and produces a substitute voice. Unfortunately, the created voice is of poor quality: it is weak, with a low fundamental frequency (pitch) and sounds mechanical. It has a huge psychological impact, especially on women, who generally struggle with their new masculine voice. In addition, the limited lifetime of the devices, due to biofilm coming from mucus/material interactions, forces a frequent device replacement.
To date, there is no voice prosthesis lasting more than 3 months and able to reconstruct a natural-sounding human voice.
In this context, bird vocal system should attract attention. First, their vocal repertoire is incredibly diverse, with pitch spanning from 100 to 12 000 Hz, compared to only 85 to 255 Hz in human speech. Moreover, their unique vocal organ, the syrinx, produces sounds from the vibration of membranes, located in the wall of the syrinx. The human vocal folds are perpendicular to the trachea, meaning that even in a resting open position, they are always partially obstructing the trachea. However in birds, the labia are on the walls of the syrinx, meaning that when the syringeal muscles are inactive, the labia are retracted and the two syrinx cavities are almost completely open. To date, the prostheses proposed to laryngectomized patients are mimicking the human vocal folds, with a one-way valve perpendicularly positioned in the tube and always partially obstructing it. The large contact area between the silicone valve and the air increases the chance of colonisation by a mixed biofilm of bacteria and yeasts.
Designing prostheses based on the avian vocal organ would not only provide alternatives to reduce biofilm formation, but could also produce higher frequency sounds, leading to voices that will sound more humane.