The anisotropic hyperelastic biomechanical response of the vocal ligament and implications for frequency regulation: A case study

Abstract

One of the primary mechanisms to vary one's vocal frequency is through vocal fold length changes. As stress and deformation are linked to each other, it is hypothesized that the anisotropy in the biomechanical properties of the vocal fold tissue would affect the phonation characteristics. A biomechanical model of vibrational frequency rise during vocal fold elongation is developed which combines an advanced biomechanical characterization protocol of the vocal fold tissue with continuum beam models. Biomechanical response of the tissue is related to a microstructurally informed, anisotropic, nonlinear hyperelastic constitutive model. A microstructural characteristic (the dispersion of collagen) was represented through a statistical orientation function acquired from a second harmonic generation image of the vocal ligament. Continuum models of vibration were constructed based upon Euler-Bernoulli and Timoshenko beam theories, and applied to the study of the vibration of a vocal ligament specimen. From the natural frequency predictions in dependence of elongation, two competing processes in frequency control emerged, i.e., the applied tension raises the frequency while simultaneously shear deformation lowers the frequency. Shear becomes much more substantial at higher modes of vibration and for highly anisotropic tissues. The analysis was developed as a case study based on a human vocal ligament specimen.

Morphological basis for the evolution of acoustic diversity in oscine songbirds

“…The inhomogeneous composition provides a basis for anisotropic behaviour of labia, i.e. the labial layers cause a direction-dependent stress response to deformation, which is likely to facilitate the production of frequencies within the range in stereotyped fashion [33]. Stereotypy of song may constitute an important sexually selected feature [34,35], and the make-up of the labia influences the potential for maintaining a given frequency and for generating precise continuous sweeps of a wide frequency range.…”

Validation of a flow–structure-interaction computation model of phonation

“…The stress–strain relationship in physiological VFs is typically hyperelastic (Kelleher et al, 2013a). In contrast the constitutive behavior of the physical replica and the computation model used here is linear elastic.…”

Fracture Toughness of Vocal Fold Tissue: A Preliminary Study

“…The variations of physical properties, such as stiffness and fracture toughness, along the anterior-posterior direction are dictated by the tissue microstructure 3, 10 . An organization of elastic fibers, such as elastin and collagen, provides tissue stiffness and its extent of deformation 10 .…”

“…An organization of elastic fibers, such as elastin and collagen, provides tissue stiffness and its extent of deformation 10 . In contrary, high-damping extracellular matrix components, such as hyaluronic acids and glyco-samino-glycans, mainly contribute to tissue flexibility.…”

“…The difference between the toughness values of coronal and transverse slicing highlights the tissue anisotropy and the contribution of collagen fibrils (see Miri et al 7 ). The longitudinal direction has the strongest stiffness compared to other directions because of the spatial orientation of collagen fibrils 3, 10 . Therefore, tissue exhibits its highest toughness when sliced in the coronal plane.…”