Study On The Mechanical Behaviors Of Articular Cartilage Damage Repair Based On Transverse Isotropy

Articular cartilage is a special connective tissue,its unique structure and material composition make it have good mechanical adaptability,but the disease and external force impact easily lead to cartilage damage.Because there is no blood supply and lymphatic drainage in cartilage tissue,it is difficult to repair after injury.Traditional injury therapy can only temporarily alleviate the pain,but it is difficult to achieve a satisfactory repairing effect.The effective treatment after injury has become a difficult problem to be solved urgently.In recent years,with the gradual maturity of tissue engineering technology,it is promising to become the most effective method for repairing cartilage defects.However,there is still considerable uncertainty to be found in the long-term effect of cartilage defects repairing with tissue engineering cartilage(TEC),which is closely related to the inferior mechanical properties of TEC that leads to the change of mechanical environment in the repair zone.Therefore,it is important to study the influence of TEC parameters on the changes of mechanical environment in the repair zone.The findings have important guiding significance for clinical repair.In this paper,the mechanical behaviors of articular cartilage defect repair area under the physiological compressive load were studied by using the finite element software ABAQUS.The main research methods and simulation results are as follows:The three-dimensional finite element model of articular cartilage based on transversely isotropy was established.In the model,the solid-liquid biphasic structure of the cartilage,viscoelastic characteristics,the permeability with the depth and strain variations were considered.The effects of different repair shapes(cylindrical,frustum of a cone,elliptical column,orthorhombic prism),repair depths(superficial,middle,deep,full-thickness layer),and material parameters of TEC on the mechanical behaviors of cartilage defect repair area were studied by numerical simulation.The simulation results showed that the shape and depth of cartilage repair had a significant effect on the mechanical behaviors of the repaired area.The distribution of stress field and liquid flow field was the closest to intact cartilage for using the cylindrical-shaped TEC to repair,which was more conducive to the force and nutrient transport in the cartilage repair area.When non-full-thickness defects were repaired,the phenomenon of Mises stress and shear stress concentration occurred at the repair interface,and the high shear stress area extend to the inside of the cartilage at the corner of the defect bottom,which might result in secondary destruction of the cartilage matrix.However,the stress distribution was more reasonable in the full-thickness defect repair,and the shear stress on the cartilage surface was the closest to the intact condition.The distribution of fluid flow field and pore pressure in the whole superficial layer defect repair was the closest to the intact cartilage.Defect repair reduced the bearing capacity and altered the equilibrium time of cartilage.With the increase of TEC elastic modulus,the decrease of bearing capacity of the liquid phase,which led to the increase of the load applied on the solid matrix and the friction force between joint surfaces.It has been proved that TEC with small elastic modulus(eg 0.3Mpa)can reduced the difference of mechanical behaviors between the host cartilage and the TEC in the defect repair area,which was beneficial to the repair.The theoretical analysis showed that the stress state of the solid matrix in different layers of the defect repair area was different.When the repair depth was different,the deformation types of the surface host cartilage were compression for the intact and superficial layer defect repair cartilage;while the other three repair conditions(middle,deep,full-thickness layer)were elongation-type deformation,which might lead to adhesive interface cracking in repair area.When the elastic modulus of TEC was low,the deformation types of the surface layer and the middle layer in the repaired area were the elongation-type deformation,and the region that produced this kind of deformation decreased with the increase of the TEC elastic modulus.Based on the results from the finite element analysis,it is recommended to use cylindrical TEC to repair the defect in clinically.If the patient’s cartilage defect depth beneath the surface layer,it can be considered to extend the defect to the full-thickness.In this paper,we mainly studied the mechanical behaviors of cartilage defect repair area.The research results can provide some theoretical references for the treatment and repair of clinical illness of articular cartilage.