Mixture Theory Modeling Dynamic Finite Deformation of Hydrated Soft Tissue

Yun Ge, Purdue University

Abstract

Hydrated and highly fibrous soft biological tissues are often injured as the result of sports injuries, motor vehicle collisions involving civilians, blunt force traumas, ballistic impacts and blast wave involving soldiers. When these injuries happened, the tissues are under large deformation. The dynamic impact experiments show that large stress also is built in the tissues. The tissues response is nonlinear and inelastic and sensitivity to strain-rate under dynamic loading. These dynamic behaviors are because of tissues multiphase structures and inertia which carries a significant part of the applied load at high strain rates. To represent these rate-dependent, viscoelastic behaviors of soft tissue, a volume-fraction base biphasic material model based on dynamic mixture theory was developed in this dissertation. In this model, the tissue is a mixture of a porous permeable solid domain filled with interstitial fluid. This model has only three parameters: shear modulus and bulk modulus which describe the isotropic hyperelastic solid phase, specific permeability which governs the transition response between solid deformation and fluid flow. To our knowledge, this is the first time to develop a logical model which can capture both large deformation and a wide range of loading rate mechanical properties of hydrated tissue. The model was implemented in finite element software COMSOL-Multiphasics and verified with analytical solutions of mechanical response of a cylindrical dish tissue specimen under confined compression. The model is able to exhibit viscous behavior, stress-relaxation, without intrinsic viscosity in both solid and fluid phases. The model also captures the dynamic response of tissues: significant strain-rate sensitivity, nonlinear stress-strain relationship and radial inertia effect, nonlinear deformation during the dynamic impact. Further, a viscoelastic mixture theory model was proposed to account intrinsic viscosity in solid phase. Since there are large amount of tissue intracellular water trapped in the solid phase, there is a possibility that the solid phase behaves certain level of viscosity. The model shows good curvefits with the porcine skeletal muscle data under dynamic unconfined compression. The results of this work encourage the potential to model response of hydrated soft tissue in a greater number of dynamic experimental testing configurations than previous models. They also provide a basis for more advanced mixture theories and diffusion models in studying mechanism of tissue injury.

Degree

Ph.D.

Advisors

Chen, Purdue University.

Subject Area

Mechanical engineering|Engineering|Biomechanics

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