Nonlinear viscoelastic response of the vocal fold lamina propria under large‐amplitude oscillatory shear.

Abstract

Viscoelastic properties of the vocal fold lamina propria have been reasonably quantified beyond the linear range for describing tissue behavior under uniaxial stretch or tensile deformation, but the same cannot be said for oscillatory shear deformation, which is more relevant for understanding the mechanics of large‐amplitude vocal fold vibration. Previous studies reporting the viscoelastic shear properties of vocal fold tissues have been limited to characterization of the small‐amplitude viscoelastic response in the linear viscoelastic region, partly due to the fact that derivation of the elastic and viscous shear moduli is based on the assumption of linearity, and also because of the lack of a coherent framework for describing any nonlinearities beyond the linear viscoelastic region. Based on a recently proposed rheological framework for quantifying such nonlinearities, this study examined the viscoelastic response of human vocal fold cover specimens subjected to large‐amplitude oscillatory shear, up to a shear strain amplitude of around 1.0. Results indicated that the linear viscoelastic moduli (G′ and G″) cannot adequately describe the tissue response under large‐strain shear deformation, whereas geometrical interpretations of Lissajous–Bowditch curves could unveil nonlinearities that are obscured by the use of G′ and G″, such as the phenomenon of strain stiffening.