Study On The Mechanical Environment Of The Chondrocytes In The Articular Cartilage Repair Zone Under Compressive Loading

The delicate and scientific structure of articular cartilage to cope with the functional differences.Collagen fibers constitute the basic framework of cartilage,chondrocytes were distributed among the fibers,superficial were spindle-shaped,middle and deep level cells are oval or round,Chondrocytes are the only units that maintain the normal metabolism of articular cartilage.without innervations,blood vessels,lymph cells provide nutrition,therefore,chondrocytes must rely on synovial fluid in the cartilage and outside the exchange to completed the acquisition of nutrients,metabolic waste discharge of physiological activities.After joint injury was caused by external force or degenerative,as the main chondrocytes for anaerobic respiration,and metabolic rate is slow,as long as it can not migrate,so damage can not be repaired.Conventional joint injury therapy can not produce hyaline cartilage that comparable to normal cartilage in the structure,function.With the clinical application of tissue engineering,it was becoming the most effective way to solve this problem.However,due to the difference of the mechanical properties between implanted cartilage and host cartilage,the mechanical environment and the surrounding flow field of the repairing area changed.This will inevitably lead to changes in gene expression of chondrocytes,metabolic abnormalities,ultimate cause failure resulting in repairing.In this paper,the mechanical environment and flow field of articular cartilage and chondrocytes in repair zone under hydrostatic and cyclic compressive loading were studied.The main research methods and simulation results are as follows:The whole model of repaired cartilage and the cartilage cell microcosmic model was established by COMSOL software.The host cartilage is characterized by its solid-liquid biphasic properties,fiber-reinforced properties,elastic modulus with depth of cartilage,permeability with depth and strain,and so on.The effect of artificial cartilage with different elastic modulus on the mechanical environment of cartilage and chondrocytes in defect repair area was studied by numerical simulation.The simulation results show that the liquid pressure and equivalent stress of the solid matrix increase with the loading time,and the stress concentration at the joint surface is the most obvious.This may cause the matrix microstructure and cell stress damage,and may be resulting in repair failure.Artificial cartilage with small elastic modulus(eg 0.3 MPa)will improve the overall mechanical properties of the restoration zone and reduce the stress concentration at the joint surface.Studies showed that in the chondrocyte unit,the pericellular matrix of the cartilage cells have a protective effect,this can made cells subject to excessive stress stimulation.When the artificial cartilage with different elastic modulus was used to repair the defects,the stress distribution of the cartilage cells was affected.The stress of the superficial layer and the middle layer cell increased,especially the superficial layer,the deep layer cell stress decreased slightly.Defect repair has an effect on the flow field distribution around the cells in each layer as well as the liquid flow rate and the fluid pressure on the cells.The way that chondrocytes supply nutrients by liquid flow was changed.By analysis,we can clarify the potential mechanical factors that cause repair failure in clinical repair.