Developing Hyper-Viscoelastic Constitutive Models of Porcine Meniscus from Unconfined Compression Test Data

Abstract

This study examined the time dependent mechanical properties of porcine meniscus under unconfined compression condition. The ramp-hold compression tests with different ramping displacement rates and long-term compression tests with very low displacement rate were performed on porcine meniscus specimens. The time dependent mechanical response of porcine meniscus was described by hyper-viscoelastic constitutive model due to its simplicity and can be easily implemented to finite element models. Inverse iterative finite element analysis procedure was used to obtain the material parameters of hyper-viscoelastic models of meniscus in two stages. In the first stage, the long-term hyperelastic material parameters of meniscus were obtained from the compression test data with very low displacement rate. The long-term hyperelastic material parameters were used as known parameters in the second stage, and the time dependent material parameters were determined from the ramp-hold compression tests with different ramping displacement rates. It can be seen from the force-time curves of ramp-hold experimental data that the mechanical properties of meniscus is highly time-dependent. The instantaneous modulus is more than 50 times higher than the long-term elastic modulus. The third-order reduce polynomial hyper-viscoelastic model established in this study can well describe the mechanical behavior of porcine meniscus under compression load. This model can be used in the finite element study of meniscus biomechanics.