| As an important carrying tissue of human body,knee cartilage plays an important role in transmitting loads and cushioning vibrations.Articular cartilage is mainly composed of chondrocytes and extracellular matrix.Chondrocytes maintain the balance of each component of cartilage through its own metabolism,proliferation and differentiation.The macromolecular matrix secreted by chondrocytes such as proteoglycans and collagen fibers is the material basis for maintaining the cartilage topology and mechanical properties.The cartilage matrix makes articular cartilage elastic and has good compressive and shear resistance.The regeneration ability of articular cartilage defects is very limited.Although tissue engineering repair has achieved certain results,the long-term repair effect is uncertain.The effect of defect repair is closely related to the complex mechanical microenvironment of cartilage cells in the repair area.A large number of animal experiments and in vitro cell culture experiments show that mechanical forces have a significant impact on the biological function of cells.Due to the limitations of experimental techniques,it is not yet possible to study the microscopic mechanical behavior of chondrocytes in vivo.It is possible to study the complex mechanical behavior of cartilage and chondrocytes by finite element technique.The finite element software COMSOL was used to establish the fiber reinforced solid-liquid coupled biphasic finite element model and the micro-finite element model of chondrocyte in the articular cartilage.Under the conditions of repairing cartilage intermediate layer and deep defect,the factors such as load frequency,load amplitude,material properties of TEC(tissue engineered cartilage,TEC),integration conditions and the number of cells in cartilage lacuna were taken into account.To study the mechanical behavior of cartilage and chondrocyte in defect repair area under cyclic compression load.The simulation results show that the mechanical behavior of the host cartilage surface is greatly affected by the repair of the cartilage interlayer defect.Comparatively speaking,when the elastic modulus of TEC is small(such as 0.1 MPa,0.3 MPa)and the load frequency is 0.5 Hz,the mechanical environment of the repair area is in a more reasonable range.The mechanical microenvironment of the host chondrocyte under the implant was analyzed.The results showed that the liquid flow velocity of the host chondrocyte near the interface increased,the FSS(fluid shear stress,FSS)in the corresponding area increased,and the liquid flow velocity of the deep chondrocyte and extracellular matrix far away from the repair area changed little.After repairing the full-thickness cartilage defect,the mechanical response of chondrocyte to cyclic compression load was studied.It was found that the response of chondrocyte to cyclic compression load varied with the number of cells in deep cartilage lacunae.The mechanical response parameters of chondrocyte vary periodically with load frequency.The shear stress of chondrocyte is less than that of PCM(pericellular matrix,PCM),but the shear strain of chondrocyte is larger than that of PCM,which indicates that PCM has a strong protective effect on chondrocyte and signal transduction.When three cells were wrapped in the cartilage lacunae,the Mises stress of the intermediate cells was significantly greater than that of the upper and lower cells,and the response of the surface chondrocytes to shear strain was greater than that of the deep lacunae cells.In addition,the integration of cartilage defect repair models in vitro under cyclic compression loading was studied by digital image correlation technology experiments.It was found that low frequency and low amplitude loading were beneficial to the integration of host cartilage and TEC interface.This study can provide theoretical guidance for the implementation of cartilage tissue engineering,is the basic research of tissue engineering as a routine operation,and will improve the level of cartilage tissue engineering technology. |
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