When there is way too much stress: A first look at the failure behavior of vocal fold tissue

Abstract

In normal voice production, linear small‐amplitude vocal fold oscillation occurs only under restricted conditions, such as during oscillation onset and offset. More often than not, phonation in physiological range involves large‐amplitude oscillation that is associated with the development of tissue shear stresses and strains much beyond their linear viscoelastic limit, particularly in the vibrating portion of the vocal fold, i.e., the extracellular matrix (ECM). This study targeted one such large‐strain nonlinear viscoelastic behavior of the vocal fold by attempting to quantify the stress failure response of the vocal fold ECM under shear. Sheep vocal fold ECM specimens were subjected to torsional, steady shear in a controlled‐strain rheometer in vitro, at constant strain rates of 0.01, 0.1, and 1.0 rad/s. Results showed that the vocal fold ECM demonstrated nonlinear stress–strain response, as well as failure response when shear strain reached around 100%. Strain‐dependent and rate‐dependent onset of partial and complete stress failure was observed. A constitutive approach based on a standard‐linear cohesive zone model was formulated to characterize the observed rate‐dependent failure behavior of the vocal fold ECM. These findings have important implications for predicting tissue injury and for establishing stress and strain safety limits for large‐amplitude vocal fold oscillation.