Page 1 of 5 Licensee OAPL (UK) 2014. Creative Commons Attribution License (CC-BY) FOR CITATION PURPOSES: Dembinski D, Oren L, Gutmark E, Khosla S. Biomechanical measurements of vocal fold elasticity. OA Tissue Engineering 2014 Feb 22;2(1):3. Review Competing interests: None declared. Conflict of interests: None declared. All authors contributed to conception and design, manuscript preparation, read and approved the final manuscript. All authors abide by the Association for Medical Ethics (AME) ethical rules of disclosure. Tissue Engineering & Modelling Biomechanical measurements of vocal fold elasticity DR Dembinski 1 , L Oren 1* , E Gutmark 2 , SM Khosla 1 Abstract Introduction Accurate characterization of the elastic properties of vocal fold tissue is important in phonosurgical correction of vocal fold pathology and development of physiologic phonation models. This paper examines the work to date attempting to characterize the elastic response of the vocal fold tissue, focusing on three commonly used biomechanical testing modalities in the field: longitudinal elongation, linear skin rheometry, and microindentation. It is hoped that a thorough review of current literature in the field will identify strengths and weaknesses associated with each testing technique and suggest directions for future work. Conclusion While much progress has been made in the characterization of vocal fold elasticity, there is still work to be done to make elasticity measurements practical for clinical applications. Introduction The sound produced by the vibratory process of the human vocal folds is largely dependent on the tissue’s elastic properties. For example, voice properties such as pitch and acoustic intensity are determined (in part) by the tissue strain 1 . Alteration of local elastic parameters in the vocal fold tissue often results in perceivable speech pathology, often requiring phonosurgical correction. Accurate characterization of the inherent elastic parameters of the vocal folds, particularly the Young’s modulus and shear modulus of the tissue, may help refine surgical techniques used to repair vocal fold pathology and improve computer simulations of the phonation cycle. There have been several studies that aimed to characterize the elastic characteristics of vocal fold tissue using varying biomechanical methods. However, due to the non-linear soft- tissue characteristics of the tissue, the estimates of the tissue elasticity are inconsistent, with reported values varying over several orders of magnitude 2 . Difficulties in accurate estimation of vocal fold elasticity arise from a variety of sources, including but not limited to, differences in tissue composition, testing modality, and specimen type and preparation. They can also stem from differences in the Young’s modulus estimation technique. The elastic characteristics of the vocal folds are commonly studied using several models, including human, canine, porcine, and synthetic specimens. While human samples generate the most clinically relevant data, it is often difficult and expensive to procure fresh specimens, resulting in significant tissue decomposition that affects measured elasticity values. Canine specimens are the preferred animal model used in speech science because of their similarities, both anatomically and acoustically, with human specimens 3 . They also allow for testing immediately postmortem, minimizing tissue decomposition and allowing for more accurate elasticity measurements. Porcine larynges have been indicated as valid experimental models because they vibrate at a frequency similar to that of human larynges and they are easily obtainable 4 . However, variations in anatomy, including the presence of two sets of oscillating vocal folds, prevents direct comparison of these samples to their human counterparts 5 . Synthetic models are also constructed, mostly out of silicone, based on available literature data regarding anatomical structure and tissue composition 6 . Elastic characteristics of these models are often difficult to correlate to human samples because of their inorganic composition. The following work presents a review of the data available in the literature regarding vocal fold elasticity. The data was primary collected using three biomechanical techniques: longitudinal elongation, linear skin rheometry, and microindentation. Each one of these methods is subsequently described and major findings from each study are tabulated and summarized. Longitudinal elongation The first attempt to characterize the elastic properties of vocal fold tissue was made by Ishizaka and Kaneko 7 who used the longitudinal elongation technique (longitudinal elongation results are summarized in table 1). In the traditional longitudinal elongation test, the tissue of the vocal fold is excised from the larynx and is fixed to the testing apparatus at its anterior/ posterior ends. The tissue is then subjected to a controlled, stepwise tension, and the corresponding forces are recorded. The tissue can be kept more viable by suspension in an aerated solution, such as a Krebs- Ringer solution. Cyclic stress-relaxation testing allows for generation of hysteresis curves, from which the stiffness of the tissue, which is measured by its Young’s modulus, can be extracted. Ishizaka and Kaneko reported a constant stiffness value of 3.7kPa for a sample of the human vocal fold 7 . Perlman et al. 8 isolated canine vocal fold specimens and used longitudinal elongation to determine elastic parameters of the tissue. The measurement of the initial length of the specimen was determined in two ways: it was measured in situ and immediately post dissection, allowing *Corresponding author Email: orenl@ucmail.uc.edu 1 University of Cincinnati, Department of Otolaryngology-Head and Neck Surgery, Cincinnati, Ohio 2 University of Cincinnati, Department of Aerospace Engineering, Cincinnati, Ohio