The Study Of Poroelastic Behavior Of Defective Articular Cartilage

Articular cartilage of the knee joint is composed of two phase porous materials by solid and liquid,not only increasing the joint lubrication between bone and bone and also have effect on buffering pressure by its deformation,plays an important role on human exercise.However,the degeneration and defect of articular cartilage due to external load and internal pathological changes are the main pathological features for early arthritis.Location,depth,size of cartilage defect and so on are also different,and the mechanics properties of degenerated cartilage will change.These changes will have further influence on cartilage internal pore pressure and flow velocity,and change of pore pressure and velocity distribution inside cartilage directly affect the metabolism of cartilage cells and collagen fiber structure and the content of protein matrix,which related to cartilage degeneration mechanism.However,the theory of related mechanical behavior is unclear,as a point to study in this paper.Simplified analytical models and finite element models of healthy and disease cartilage are derived and further finite element models of real human cartilage are constructed to explore the change rule.Articular cartilage is carried on the stress relaxation experiments to explore the parameters change rule.The more detail works and main conclusions are as follows:???Using poroelasticity theory respectively establish simplified analytical models and finite element models of healthy and hollow cylinder cartilage,then using Matlab program to calculate analytical results,solutions from the calculation models are consistent with the finite element calculations.The results show that:?1?Under confined boundary condition,healthy cartilage pore pressure decreases from inner to surface,and velocity increases from inner to surface;?2?The pore pressure of the hollow cartilage model increases at first and then decreases from internal to surface.?3?Under confined boundary condition,the pore pressure of healthy cartilage model decreases from inner to surface,and the flow velocity increases from inner to surface.?4?And the pore pressure of healthy cartilage increases from internal to surface,and the flow velocity decreases to zero.???The idealized cartilage model is established according to the literature to study the femoral cartilage defect and degradation.Furthermore,finite element simulation models of human femoral cartilage are established for analysis by using MRI images.The models with different geometrical defect and physical property are studies by using the control variable method.Compare the changes of pore pressure and flow velocity of healthy cartilage and defect cartilage under pulse displacement.?1?The results show that pore pressure and flow velocity decrease with increase of the defect radius.?2?With the increase of the defect depth,the pore pressure around the defect decreases,and the flow velocity increase when the defect is not fully penetrated.?3?As the defect position moves from the outside to the inside,the change of pore pressure and flow velocity of the cartilage around defect are decrease.?4?The articular cartilage models with the change of the physical parameters are set.With the decrease of elastic modulus of articular cartilage,the pore pressure and flow velocity around the cartilage defect area decreased.?5?With the increase of permeability,pore pressure is mostly unaffected and the flow velocity increases.???In this paper,the mechanical properties of porcine cartilage were studied for the next step of preparation of porous elastic replacement material for cartilage.The viscoelastic mechanical properties tests of pig cartilage layers are conduct,according to the viscoelastic theory about three parameters model.The laws of viscoelastic mechanics parameters of cartilage layers stress relaxation experiments are analyzed.Stress relaxation test was performed on the joint cartilage specimen with changed area defect,and the change rule of cartilage viscoelastic parameters are studied.?1?For the same strain of cartilage specimen,the spring stiffness and the relaxation time and viscosity increase gradually as the depth increases.?2?For the same layer of cartilage,the spring stiffness and the relaxation time and viscosity increase gradually as the strain increases.?3?Under the same strain,spring stiffness E₁ of Kelvin model decreases and spring stiffness E₂ that in parallel with it increase with the increases of the defect area..Viscosity changes little,and the relaxation time decreases with the increase of the defect area.