Experimental methods to identify dynamic mechanical properties of vocal fold tissue

This paper describes various experimental methods to characterize the mechanical properties of vocal fold tissue. Uniaxial traction testing was performed, using small hooks to grip small tissue samples. Digital image correlation (DIC) was used to estimate the local surface deformation of porcine vocal folds in quasi-static traction tests. The mechanical stiffness and the loss factor were determined from measured data by regression of the observed nonlinear stress-stretch behavior using an eight-chain hyperelastic model. In another approach, an inverse identification method was used to measure the mechanical properties of rubber samples and porcine vocal folds. A tailored finite element model was used to compute the surface displacement field for a range of elastic modulus and Poisson ratio values. The parameter values minimized the mean square difference between calculated and measured strain data. Two different wave propagation techniques were also investigated, one based on Rayleigh waves and the other based on longitudinal waves and a transfer function method. The frequency dependent viscoelastic properties of silicone rubber samples, with elastic characteristics similar to those of human vocal folds, were measured. Atomic force microscopy (AFM) was also used to measure the viscoelastic properties of the same synthetic materials through microindentation. The results from these methods were found to be in very good agreement. The ultimate goal is to validate these methods through cross comparisons with commonly used rheometry methods, and to assess the accuracys and limitations of each method.