Study of extracellular matrix in vocal fold biomechanics using a two-phase model

Abstract

The extracellular matrix (ECM) of the vocal fold tissue consists primarily of fibrous and interstitial proteins. The purpose of this study was to investigate the effects of selective enzymatic digestion of two ECM proteins, namely elastin and versican, on the elasticity of rabbit vocal fold tissue. Quasi-static, sinusoidal, uniaxial tensile tests were performed. The data were analyzed within the framework of a model of the ECM as a two-phase composite material consisting of collagen fibrils as the reinforcing fibers and noncollagenous ECM proteins as the matrix. To validate the two-phase model, the regression parameters for the fibers' volume fraction and shear modulus in a different animal model were compared with corresponding published data. The proposed model was then used to analyze rabbit vocal fold tissues. The mean value and the standard deviation of the fiber volume fraction were found to be 8.49 ± 3.75 % for the control samples (n = 4), 0.59 ± 1.13 % after elastin removal (n = 4), and 8.22 ± 1.06 % after versican removal (n = 4). The results suggest that elastin removal may lead to a reduction in tissue stiffness, through counteracting the reinforcement of collagen fibrils.

Fig. 1

A rabbit hemilarynx and the orientation of the vocal fold sample used for mechanical tensile tests

Fig. 2

Schematic of the tissue sample under uniaxial loading, and one representative volume element (RVE) for unidirectional composite materials, and the equivalent cylindrical assemblage

Fig. 3

Representative elastic van Gieson (EVG) and 1,9-dimethylmethylene blue (DMMB) staining of rabbit vocal folds in coronal sections. The scale bar is 200µm

Fig. 4

The variation of Cauchy stress versus stretch for one porcine vocal fold sample under uniaxial traction testing for verification; Regression curves from three models: single-phase solid Fung model, fiber-reinforced Fung model, and fiber-reinforced Gent model

Fig. 5

The variation of Cauchy stress versus stretch for one rabbit vocal fold sample under uniaxial traction testing in the control solution; Regression curves from fiber-reinforced Fung and Gent models

Fig. 6

The variation of Cauchy stress versus stretch for rabbit vocal fold samples (m = 4) using the average values reported in Table 2, for three different protocols (R1 & R2 denote first and second rounds, respectively)