MECHAVOICE: biomechanics of self-sustained vibrations of the human vocal folds, computer modelling and experimental validation

Human phonation is produced through periodic self-sustained oscillations of the vocal folds excited by air flowing from the lungs. The vibration of the vocal folds modulates the stream of air, producing the primary sound of voice in a narrow oscillating constriction between the two vocal folds, called the glottis. This primary sound signal propagates through the vocal tract, which modifies its quality through acoustic resonances, the so-called formants which occur as peaks in the envelope of the voice spectrum. The formants are determined by the size and shape of the vocal tract cavities and define vowels and the voice timbre. Thus, the final sound quality of human voice is given by the characteristics of the vocal fold vibration and by the vocal tract properties, thereby involving complex fluid-structure-acoustic interactions still poorly understood so far.

This scientific gap leads to clinical plans empirically applied for most routine treatments of vocal disorders, as highlighted by the French Society of Phoniatrics for 10 years. Disorders can be due to dysfunctional pathologies with nodules formation, to surgery sequelae for laryngeal cancer (3500 cases/year in France, 15% of total cancers), or to a laryngeal paralysis. Such pathologies create aero-dynamical and vibration disturbances. In the extreme case of laryngectomy (8000 cases in France), many traumatic complications appear, among them the loss of voice and very high psychological distress. Therefore, the fundamental knowledge on multi-physics processes driving human phonation is highly expected to better interpret clinical findings, develop targeted treatments of laryngeal disorders, and advance in the current challenge of restoring the patients’ vocal abilities by injected biomaterials or artificial voice prostheses.

Addressing these medical and societal expectations, the global aim of the “MechaVoice” project is to develop and validate a 3D biomechanical model of human phonation, able to simulate the multi-scale physiologic deformation of laryngeal tissues under fluid/structure interaction. A particular focus will be given to the specificities of vocal tissue’s structural (microstructural arrangement of collagen and elastin fibrous networks, mass of the different constitutive layers) and mechanical properties (non-linear elasticity, viscosity), to their impact on vocal-fold vibromechanical properties and thereby, on voice quality. The model validation will be based on the design, process and characterization of original fibre-reinforced materials mimicking vocal-fold structural and mechanical features.