Region-Dependent Testing And Study Of Cartilage Flexion And Creep Properties In The Knee Joint

Joint disease is considered one of the world’s major disabling diseases,and according to the World Health Organisation,approximately 400 million people worldwide suffer from joint disease.However,the current limitations in the knowledge of the mechanical properties of articular cartilage make it difficult to assess the challenges in treating articular cartilage repair and the design of bionic cartilage.The study of cartilage mechanical properties and the acquisition of precise mechanical characteristics of cartilage are essential for resolving joint diseases! Existing research on articular cartilage lacks the mechanical property distribution of an intact part of the cartilage,which makes the design of intact cartilage isotropic and does not consider the area-dependent load-adapted design of articular cartilage,and lacks a basis for evaluation.It could lead to a stress shielding effect during the service of the bionic or regenerative cartilage material,which could eventually reduce the service performance of the material and even seriously endanger joint health and life safety.This study focuses on the need for a realistic basis for the design and preparation of bionic engineering and the urgent need for research on articular cartilage;based on the lack of parameters of articular cartilage performance indicators for intact parts and the lack of a theoretical basis for the design of differences in the mechanical properties of different regions of the same articular cartilage.A series of experimental studies on the regiondependence of knee cartilage reveals the regional distribution of the mechanical properties of knee cartilage in terms of friction and wear scoring,three-point flexural composite loading,and creep,providing a theoretical basis for the development of bionic knee cartilage and the evaluation of the physical properties of new treatment strategies by cartilage tissue engineers.The main contents of the paper are as follows:(1)Combined with 3D reverse engineering to optimize the experimental selection and experimental design scheme,ensuring the repeatability and scientific validity of the design scheme.To enhance the experimental reliability,nanoindentation experimental testing to determine the cartilage material and the preservation scheme using PBS buffer as cryoprotectant at-20°C.(2)The friction wear scratch test on typical areas of articular cartilage demonstrated significant differences in the mechanical properties of cartilage in different areas of the same articular cartilage.It clarified the significance of subsequent experimental studies.It also reveals that the friction factor decreases sequentially in four typical regions: medial condylar cartilage(MC),lateral condylar cartilage(LC),distal patellar cartilage(DTP),and proximal patellar cartilage(PTP).A series of characterization tools confirmed that the pattern was attributable to a significant density gradient difference between regions of cartilage.(3)Dynamic monitoring of load and structural morphology under three-point bending reveals the mechanism behind the simultaneous enhancement of bone structural load-bearing capacity by the cartilage layer of the knee joint,clarifies the distribution of the simultaneous enhancement of bone structural load-bearing capacity by the cartilage layer in different regions of the same knee joint and the underlying principles,and quantifies the numerical indexes of load enhancement in each region.The test results show that,at a specific scale,there is little difference in the load-bearing capacity of the hard bone in different regions of the same size.However,the composite bone with the cartilage layer attached shows a significant load-bearing capacity gradient.The cartilage layer effectively relieves the impact load on the hard bone,directs the load transfer to the hard bone attached to the cartilage,and slows down the accelerated damage caused by stress concentration.The cartilage layer affects how hard bone cracks expand,making the crack progression more tortuous and complex.(4)Based on the nanoindentation dot matrix test,curvature variability,and the principle of the five-point sampling method,a region-dependent creep study of articular cartilage was carried out to obtain the complete Knee cartilage creep property distribution cloud from the micro-and nano-scale.The experimental results showed that the creep resistance of the cartilage of the medial condyle surface was the strongest,and that of the proximal patellar surface was the weakest in the whole knee cartilage.The experimental data obtained can be used as a complementary study for predicting cartilage damage and artificial joint materials.The results show a significant regional distribution of the mechanical properties of knee cartilage and a significant gradient difference in the density of cartilage throughout the knee joint.