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# Design of a Mechanical Larynx With Agarose as a Soft Tissue Substitute for Vocal Fold Applications

[+] Author and Article Information
J. Q. Choo, C. K. Chui, T. Yang, S. H. Teoh

Department of Mechanical Engineering, National University of Singapore, Singapore 117576, Singapore

D. P. C. Lau

Department of Otolaryngology, Singapore General Hospital, Singapore 169608, Singapore

C. B. Chng1

Department of Mechanical Engineering, National University of Singapore, Singapore 117576, Singaporeg0900645@nus.edu.sg

1

Corresponding author. Present address: Control and Mechatronics Laboratory, National University of Singapore, EA-04-06, 9 Engineering Drive 1, Singapore 117575, Singapore.

J Biomech Eng 132(6), 065001 (Apr 26, 2010) (7 pages) doi:10.1115/1.4001161 History: Received October 04, 2009; Revised January 21, 2010; Posted February 02, 2010; Published April 26, 2010; Online April 26, 2010

## Abstract

Mechanical and computational models consisting of flow channels with convergent and oscillating constrictions have been applied to study the dynamics of human vocal fold vibration. To the best of our knowledge, no mechanical model has been studied using a material substitute with similar physical properties to the human vocal fold for surgical experimentation. In this study, we design and develop a mechanical larynx with agarose as a vocal fold substitute, and assess its suitability for surgical experimentation. Agarose is selected as a substitute for the vocal fold as it exhibits similar nonlinear hyperelastic characteristics to biological soft tissue. Through uniaxial compression and extension tests, we determined that agarose of 0.375% concentration most closely resembles the vocal fold mucosa and ligament of a 20-year old male for small tensile strain with an $R2$ value of 0.9634 and root mean square error of $344.05±39.84 Pa$. Incisions of 10 mm lengthwise and 3 mm in depth were created parallel to the medial edge on the superior surface of agar phantom. These were subjected to vibrations of 80, 130, and 180 Hz, at constant amplitude of 0.9 mm over a period of 10 min each in the mechanical larynx model. Lateral expansion of the incision was observed to be most significant for the lower frequency of 80 Hz. This model serves as a basis for future assessments of wound closure techniques during microsurgery to the vocal fold.

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## Figures

Figure 1

Mechanical larynx model

Figure 2

Perspex channel. Lg denotes the glottal width. Lo denotes the membranous vocal fold length. εo denotes the variable glottal aperture.

Figure 3

Agarose vocal fold phantom attached on the vocal fold frame

Figure 4

Coronal profile of the vocal fold used in this study is outlined by solid black lines. Vocal fold thickness is represented by Cc. Vocal fold depth is represented by FH. All dimensions are indicated in millimeters.

Figure 5

Vocal fold mold and vocal fold profile displacer

Figure 6

Schematic 3D overview of the mechanical larynx model and experimental setup, drawn with CAD-SOLIDWORKS . Mechanical larynx model is encircled and an enlarged view is shown in Fig. 1.

Figure 7

Comparison between experimental data of various concentrations of agarose (N=5)

Figure 8

Mapping of agar concentrations to that of vocal fold cover and ligament. Constants C1–C7 are determined based on the constitutive logarithmic and polynomial equations. Determined constants for constitutive modeling of 0.375% agar are C1=−0.005244, C2=4.342×105, C3=−9.541×104, C4=2.051×105, C5=1.372×104, C6=1636, and C7=−4047. R2 is 0.9999. RMSE is 91.15. Determined constants for constitutive modeling of 0.5% agar are C1=0.7437, C2=5.774×105, C3=−1.768×105, C4=3.167×105, C5=1.402×104, C6=2955, and C7=−9196. R2 is 0.9999. RMSE is 116.9.

Figure 9

Measurement of crack length. Certain images are processed in contrast to provide sharper appearance of cracks. Lo denotes the known length of the vocal fold phantom. CLupper denotes the measurement of upper crack length.

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