Nonlinear viscoelastic characterization of human vocal fold tissues under large-amplitude oscillatory shear (LAOS)

Abstract

Viscoelastic shear properties of human vocal fold tissues were previously quantified by the shear moduli (G′ and G″). Yet these small-strain linear measures were unable to describe any nonlinear tissue behavior. This study attempted to characterize the nonlinear viscoelastic response of the vocal fold lamina propria under large-amplitude oscillatory shear (LAOS) with a stress decomposition approach. Human vocal fold cover and vocal ligament specimens from eight subjects were subjected to LAOS rheometric testing with a simple-shear rheometer. The empirical total stress response was decomposed into elastic and viscous stress components, based on odd-integer harmonic decomposition approach with Fourier transform. Nonlinear viscoelastic measures derived from the decomposition were plotted in Pipkin space and as rheological fingerprints to observe the onset of nonlinearity and the type of nonlinear behavior. Results showed that both the vocal fold cover and the vocal ligament experienced intercycle strain softening, intracycle strain stiffening, as well as shear thinning both intercycle and intracycle. The vocal ligament appeared to demonstrate an earlier onset of nonlinearity at phonatory frequencies, and higher sensitivity to changes in frequency and strain. In summary, the stress decomposition approach provided much better insights into the nonlinear viscoelastic behavior of the vocal fold lamina propria than the traditional linear measures.

Nonlinear rheological characteristics of single species bacterial biofilms

“…In the past decade, LAOS has become a canonical technique for quantifying the rheological characteristics of polymers, soft solids, gels, emulsions and various other complex fluids and materials 48,54 . The techniques have also been successfully applied to understand the intracycle strain dependent hardening/softening or thickening/ thinning of biological materials, examples of which include: mucus of the gastropod 55 , hagfish slime 56 , fibrobalst cells 57 , fibrin/collagen gels 58 , vocal fold tissues 59 , pluronic/hyaluronic acid 60,61 , Xanthan gum 62 and blood 63 . For biofilms, LAOS provides us with the ability to determine the nonlinear material response of biofilms when subjected to large shear.…”

Mechanics of human vocal folds layers during finite strains in tension, compression and shear

“…They highlighted the non-linear behaviour of this tissue showing a J-shape stress-strain curve upon loading, and thus, an increasing tangent longitudinal modulus E t z from 10 kPa to 2000 kPa [22,24,9,30,21]. Viscoelastic properties of this layer were also investigated using either standard shear Dynamic Mechanical Analysis (DMA), i.e., within the linear regime [7,6,14,37], or more recently using Large Amplitude Oscillatory Shear (LAOS) [5]. These works allowed to characterise the shear storage G and loss G moduli (DMA) of the lamina propria, as well as its cyclic and finite strains shear behaviour (LAOS) within the (x, y) plane.…”

Ovine Vocal Fold Tissue Fatigue Response to Accumulated, Large-Amplitude Vibration Exposure at Phonatory Frequencies

“…Among the time points of 30, 1,040, 2,080, and 4,160 s, the duration of 30 s was chosen to quantify the initial tissue viscoelastic response before fatigue, but after achieving the "preconditioned" state, or stabilization of the cyclic stress-strain response. This stabilized state has been found to be achieved following around 100 cycles of largeamplitude oscillatory shear at 100 Hz for the human vocal fold lamina propria (Chan, 2018). The duration of 30 s at the lowest testing frequency (100 Hz) would correspond to 3,000 cycles of shear, well past the preconditioned state.…”

“…For each vocal fold mucosal specimen, accumulated, large-amplitude vibration exposure was applied in a controlled-strain, simple-shear rheometer previously validated for the nonlinear deformation and linear viscoelastic characterization of vocal fold tissues (Chan, 2018;Chan & Rodriguez, 2008), at one of four frequencies in a physiological range (100, 150, 200, and 230 Hz), covering the male and female phonatory range for typical conversational speech (Titze, 2006). The continuous vibration exposure applied to each specimen was in the form of large-amplitude, translational, sinusoidal simple-shear deformation of the specimen between the upper plate and the lower plate of the rheometer (see Figure 1).…”

“…The frequency of continuous vibration exposure covered the typical male and female mean speaking fundamental frequency range, at 100, 150, 200, and 230 Hz (Titze, 2006). The continuous vibration exposure was delivered with a simple-shear rheometer, capable of precise, large-amplitude nonlinear translational shear deformation of vocal fold tissues at phonatory frequencies (Chan, 2018), as well as measurements of the corresponding changes in tissue viscoelastic response (Chan & Rodriguez, 2008), as functions of the frequency and duration of vibration exposure. The ex vivo ovine data could provide some preliminary insights on how tissue fatigue response may contribute to vocal fatigue at phonatory frequencies.…”