Research On Fibril-Reinforced Poroelastic Mechanical Behavior Of Articular Cartilage

Osteoarthritis is a common joint disease and it troubles the patients a lot. It is widely accepted that osteoarthritis is caused by mechanical overloading, so we need to analyze the stress-strain distribution of the joint under load and further, discover the pathological process and raise effective treatment method. Finite element method is the most efficient method to study the stress-strain distribution and more and more biomechanical researchers have used this method to explore the stress distribution of biological tissue. To conduct the FEM analysis, finite element model of the joint is needed and constitutive behavior is one of the most important parts. Joint is normally consists of femur, tibia and articular cartilage. Among these, articular cartilage has the most complex mechanical behavior. It shows obvious nonhomogeneity, anisotropy and viscoelasticity. A lot of mechanical model have been developed these years. The model is more and more precise while the computation cost increases at the same time. So we need to find the best model which require little cost and can explain most experimental phenomenon simultaneously. The fibril-reinforced poroelastic model base on spring is a relative simple and easy to be implemented model which can account for more phenomenon than traditional biphasic proelastic model. In this essay, we implement this model and check it to ensure whether to use this model for further research. The ability of a model to simultaneously account for the relaxation of the reaction force and variation of the lateral displacement under unconfined compression test have been one of the common used rule to validate the model and here, we just use it.This research covers the following contents: 1. Introducing the composition and structure of articular cartilage and explore the relationships between the mechanical behavior and its composition and structure. 2. Implementing the fibril-reinforced poroelastic model based on spring. To implement this model, we should first implement the biphasic poroelastic model, then add the strain dependent permeability and then add the nonlinear spring to represent the fibril. 3. Developing inverse method to get the value of material parameter. The material property of articular cartilage has significant individual variation, so we cann't predicate behavior with the parameter value obtained from another experiment but get the value from the same experiment. Determined the material parameter value, we validate the model.Through this research, we have the following achievement:1. Implementing the fibril-reinforced poroelastic model based on spring and get the distribution of lateral displacement, pore pressure and mises stress under unconfined compression test. 2. Strain-dependent permeability have little effect of the model behavior under unconfined compression test while fibril-reinforcement enhance the ability to explain relaxation phenomenon. 3. Conducting inverse analysis and validate the ability of the model to account for the experiment phenomenon simultaneously. The fibril-reinforced model has the following disadvantages: 1. It can't reflect the stress distribution on unconfined compression test. It is because this model doesn't reflect the actual fibril distribution. 2. It can't explain the relaxation of reaction force. This is because the intrinsic viscoelasticity of the articular cartilage is not considered.