Viscoelastic shear properties of human vocal fold mucosa: Measurement methodology and empirical results

Abstract

A standard method for the empirical rheological characterization of viscoelastic materials was adopted to measure the viscoelastic shear properties of human vocal-fold mucosal tissues (the superficial layer of lamina propria). A parallel-plate rotational rheometer was employed to measure shear deformation of viscoelastic tissue samples, which were deformed between two rigid circular plates rotating in small-amplitude sinusoidal oscillations. Elastic and viscous shear moduli of the samples were then quantified as a function of oscillation frequency (0.01 to 15 Hz) based on shear stresses and strains recorded by the rheometer. Data were obtained from 15 excised human larynges (10 male and 5 female). Results showed that the elastic shear modulus mu and the damping ratio zeta of human vocal-fold mucosa were relatively constant across the range of frequencies observed, while the dynamic viscosity eta decreased monotonically with frequency (i.e., shear thinning). Intersubject differences in mu and eta as large as an order of magnitude were observed, part of which may reflect age-related and gender-related differences. Some molecular interpretations of the findings are discussed.

A Flow Perfusion Bioreactor System for Vocal Fold Tissue Engineering Applications

“…The shear elastic moduli of both the PEGDA and PEGTA hydrogels were within the range of that of the human VF LP. 48 Polymeric materials may fail under cyclic loading. The scaffolds made of HA, Ge, and PEGTA were mechanically stable under continuous phonation-induced stimulation.…”

Influence of hydrogel mechanical properties and mesh size on vocal fold fibroblast extracellular matrix production and phenotype

“…To demonstrate that the initial mechanical properties of the selected hydrogels are within a stiffness range appropriate for VF LP tissue engineering [40], the time-zero elastic compressive modulus of each hydrogel at 40 Hz (nearer adult phonatory threshold) is presented in Fig. 2D. …”

“…In evaluating the initial mechanical properties of each PEGDA hydrogel relative to those of the VF LP, hydrogel elastic compressive moduli data at 40 Hz (mechanical measures above 40 Hz being neglected due to data quality limitations) were compared to literature values of LP elastic shear moduli at similar frequencies [40]. The fact that PEGDA hydrogels can be considered homogenous and isotropic was used in these comparisons [28,41].…”

“…During mechanical testing, samples were immersed in silicone oil to prevent hydrogel dehydration. Following application of a 0.01 N preload, each hydrogel was subjected to 10 µm cyclic compression (~1% cyclic strain) at frequencies of 0.01-100 Hz (100 Hz being the system maximum) The higher frequency testing conditions were selected to approach the frequencies of cyclic LP loading experienced during phonation [40]. The elastic and viscous compressive moduli of each hydrogel formulation were extracted from the resulting stress-strain data.…”

“…Discs, 1 cm in diameter, were cored from each hydrogel formulation. Fluorescently labeled dextrans (10,20,40,70 or 150 kDa, Sigma) were dissolved at 0.01 mg ml −1 in HBS-azide and added at 1 ml per hydrogel disc (3 discs per dextran mol. wt.).…”