Functional assessment of the ex vivo vocal folds through biomechanical testing: A review

Abstract

The human vocal folds are complex structures made up of distinct layers that vary in cellular and extracellular composition. The mechanical properties of vocal fold tissue are fundamental to the study of both the acoustics and biomechanics of voice production. To date, quantitative methods have been applied to characterize the vocal fold tissue in both normal and pathologic conditions. This review describes, summarizes, and discusses the most commonly employed methods for vocal fold biomechanical testing. Force-elongation, torsional parallel plate rheometry, simple-shear parallel plate rheometry, linear skin rheometry, and indentation are the most frequently employed biomechanical tests for vocal fold tissues and each provide material properties data that can be used to compare native tissue verses diseased for treated tissue. Force-elongation testing is clinically useful, as it allows for functional unit testing, while rheometry provides physiologically relevant shear data, and nanoindentation permits micrometer scale testing across different areas of the vocal fold as well as whole organ testing. Thoughtful selection of the testing technique during experimental design to evaluate a hypothesis is important to optimizing biomechanical testing of vocal fold tissues.

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

“…As shown in some of our previous studies on the linear viscoelastic properties of the vocal fold cover and the vocal ligament, different samples from different subjects may show somewhat different magnitudes of the storage and loss moduli as affected by factors such as age, gender, and smoking [5, 6, 22]. Such inter-subject differences in viscoelastic properties of the vocal folds have also been observed in other studies [23]. Nonetheless, to accurately discern the effects of such factors on the critical strain amplitude for the onset of nonlinearity, and on other linear and nonlinear tissue behavior would require well-designed rheological tests focusing specifically on these factors, with enough number of samples in each condition to ensure adequate statistical power.…”

Automated Indentation Mapping of Vocal Fold Structure and Cover Properties Across Species

“…Biomechanical testing methods to compare physiologically relevant mechanical properties of laryngeal tissues are limited. Unique laryngeal geometry and pliability of vocal fold tissues create a challenging environment for biomechanical testing approaches . Indentation biomechanical testing techniques show promise in both animal models and engineered vocal fold products to objectively assess material stiffness and elasticity .…”

“…Unique laryngeal geometry and pliability of vocal fold tissues create a challenging environment for biomechanical testing approaches. [1][2][3] Indentation biomechanical testing techniques show promise in both animal models and engineered vocal fold products to objectively assess material stiffness and elasticity. [4][5][6][7][8] Comparison between excised human and canine vocal fold cover layers identified similar stiffness and elastic properties measured via Young's modulus.…”

Impact of medialization laryngoplasty on dynamic nanomechanical vocal fold structure properties

“…A number of recent dynamic models have shown promise for the assessment of VF properties, including force‐elongation measurement, linear skin rheometry, simple‐shear parallel plate rheometry, torsional parallel plate rheometry, and indentation . Recently, our group described the utility of a nanoindentation‐based method using dynamic nanomechanical analysis (nano‐DMA) to precisely explore VF biomechanics on a micrometer scale .…”