Simulation And Experimental Study Of Mechanical Properties For Defect Articular Cartilage

Knee articular cartilage is an important tissue of the human body,which is frequently used in daily activities and has a large bearing capacity and high probability of injury.However,due to the complex structure of articular cartilage and poor self-healing ability,its repair treatment has been a major problem,one of the important reasons is the mechanical properties of cartilage has undergone great changes after the injury.Therefore,in-depth study of the mechanical properties of defect articular cartilage is of great significance for its repair treatment.In this paper,the mechanical behavior of defect articular cartilage was studied from two aspects of experimental study and numerical simulation,and the changing regularity of mechanical properties of defect cartilage was obtained,which provided some references for the pathological study and repair of articular cartilage diseases.In this paper,the experimental study on the creep behavior of defect articular cartilage under compressive loading was carried out.In the experiment,digital image correlation technique was used to analyze the strain field of the collected images,and the variation of creep in each layer around the defect of articular cartilage was obtained under constant load.The study found that the existence of damage affect the creep around the cartilage defects.Under constant stress,the creep strain values of each layer gradually increase with the increasing of time,while the rate of strain change gradually decreases as the time increasing until it tends to be gentle.The creep strain value of each layer around the defect cartilage gradually increases with the increasing of cartilage defect depth.The creep strain value at the bottom corner of the defect is larger than the creep strain value at the middle of bottom of the defect.In this paper,micro-defect two-dimensional numerical models of fiber-reinforced and porous-viscoelasticity was established by using ABAQUS software,which takes into account the relationship between fiber distribution,porosity and permeability with the change of cartilage depth.Comparing the numerical calculation results with the experimental results,it is found that the trend of both is consistent,which proves the validity of the numerical calculation model.On the basis of the model,the effect of initial defect shape on cartilage damage evolution under rolling load was analyzed,and the initial shapes were set as rectangular section,100° trapezoidal section,80° trapezoidal section and semicircular section respectively.The results show that the pathways of damage evolution of cartilage with various initial notch shapes are similar,the damage starts from the notch bottom corner,preferentially expands to the deeper depth along the fiber tangential direction,when expands to a certain depth,expands upward along the tangential direction of the adjacent fibers,and finally produces cartilage fragments under the load.Notch shape affects only the initial stage of cartilage damage evolution and has little effect on the middle and late stage of damage evolution.From the analysis of maximum shear strain value,interstitial flow rate and interstitial fluid pressure,their values decreased with the increase of cartilage damage.The interstitial fluid pressure of the cartilage with rectangular cross-section gap is larger than the cartilage with other cross-sectional shape,stress,strain and interstitial flow rate are less than cartilage with other cross-sectional shapes,so it is recommended to use a cylindrical notch shape to repair.The simulation also found that the cartilage fragments gradually increased with the increase of initial damage depth,the mechanical properties of surface and middle layer damaged cartilage tend to be consistent,and that of deep damaged cartilage is very different.Secondly,taking the cartilage with rectangular cross-section gap as an example,the variation regularity of fluid field of damaged cartilage load was analyzed under compressive.It was found that the interstitial hydraulic pressure and interstitial flow velocity of the articular cartilage increased with the increasing of the load at the linear loading stage,which gradually decreased with the increasing of time at the constant loading stage.The interstitial flow velocity around cartilage defect was always larger than that of undamaged part,and the interstitial fluid at the site of cartilage injury flows around with the stress concentration area at the bottom corners on both sides as the center,the most obvious of which is the flow to the cartilage surface and the central area of injury.In this study,when the articular cartilage damages,it can achieve self-protection and delay the injury by adjusting the mechanical properties of solid and liquid.