Measurement of Young's Modulus of Vocal Folds by Indentation

Abstract

Objectives-To assess accuracy of the indentation method for stiffness measurements and to estimate the Young's modulus of the vocal fold using this technique. Study Design-Basic science.Methods-Indentation tests were performed using a range of indenter diameters and indentation depths on single and double layer silicone rubber models with a range of cover layer thicknesses with known geometry and Young's moduli. Measurements were repeated on intact vocal folds and isolated muscle and cover layer samples from three cadaveric human larynges.Results-Indentation on single-layer rubber models yielded Young's moduli with acceptable accuracy when the indentation depth was equal to or smaller than the indenter diameter, and both were smaller than the physical dimensions of the material sample. On two-layer models the stiffness estimation was similarly influenced by indenter diameter and indentation depth, and acceptable accuracy was reached when indentation depth was much smaller than the height of the top cover layer. Measurements on mid-membranous vocal fold tissue revealed location-dependent Young's moduli (in kPa) as follows: intact hemilarynx 8.6 (range 5.3 -13.1), isolated inferior medial surface cover 7.5 (range 7 -7.9), isolated medial surface cover 4.8 (range 3.9-5.7), isolated superior surface cover 2.9 (range 2.7 -3.2), and isolated thyroarytenoid muscle 2.0 (range 1.3 -2.7).Conclusions-Indenter diameter, indentation depth, and material thickness are important parameters in measurement of vocal fold stiffness using the indentation technique. Measurements on human larynges showed location-dependent differences in stiffness. The stiffness of the vocal folds was also found to be higher when the vocal fold structure was still attached to the laryngeal framework as compared to when the vocal fold was separated from the framework.

Phonation threshold pressure and onset frequency in a two-layer physical model of the vocal folds

“…study, a ratio of 1:1 was used for the two components of the liquid polymer solution and the silicone thinner solution ratio was varied depending on the desired model stiffness. The Young's modulus of the cured silicone compound was measured using the indentation method with an indenter diameter of 1 mm and an indentation depth of 1 mm (Chhetri et al, 2011). Note that varying composition ratio of the polymer solution may also change the viscosity of the resulting vocal fold model, which was not measured in this study.…”

A Flow Perfusion Bioreactor System for Vocal Fold Tissue Engineering Applications

“…The silicone thinner was added to achieve viscoelastic properties similar to those reported for cadaveric human VF cover, that is, a Young's modulus of around 3.0 kPa. 24 A vacuum pump was used to evacuate the mixture and to remove air bubbles. The mixture was subsequently molded and cured at room temperature for *6 h. The cured replica was removed from the mold, and unnecessary parts were trimmed.…”

A finite element study on the cause of vocal fold vertical stiffness variation

“…Vertical stiffness variation on the vocal fold medial surface was recently reported in both human (Chhetri et al, 2011;Chhetri and Rafizadeh, 2014) and canine (Chhetri et al, 2014;Oren et al, 2014) samples. Using indentation, the local stiffness on the medial surface of both intact vocal folds and combined epithelium and lamina propria layers dissected and separated from the vocal fold muscle was measured.…”