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

• Development of novel therapeutics to alter wound healing and regenerate vocal fold tissues relies on quantifying vocal fold mechanical properties.
• In-vivo testing is impractical; in-vitro models are best for aerodynamic studies. Ex-vivo testing is most widely as they allow for adaptation of existing techniques.
• Nanoindentation is suited for testing both functional units and individual tissue layers.
• Combination of testing techniques provides clinically relevant information when testing pathologic conditions of the vocal folds or novel therapeutics.

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 to diseased or 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 critical to optimize biomechanical testing of vocal fold tissues.