Study On The Bioreactor Design Under Bionic Load And The Mechanical Behavior Of Articular Cartilage

Articular cartilage is a major tissue that bears mechanical load,and its physiological environment is complex.Deformities,trauma or degenerative diseases often cause cartilage defects,and gradually grow up to be a major problem affecting human health in modern society.The demand for articular cartilage repair is further increasing.At present,the research of articular cartilage is focused on tissue engineering construction.On one hand,using bioreactors to simulate natural conditions in vivo,including the stress and the physiological environment,to provide seed cells adequate mechanical stimulation for cell proliferation and differentiation.On the other hand,assessing the mechanical properties of articular cartilage by numerical simulation and finite element analysis,to predict the process of growth,development,injury and repair of cartilage.In this thesis,the mechanical biological background of engineered cartilage and the research status of tissue engineering bioreactors are reviewed.The application of mechanical stimulation in cartilage tissue engineering and bioreactors is investigated.Then this study designs a biaxial composite loading bioreactor based on the mechanics and kinematics of biaxial loading.At the same time,this study also invents a synchronous unidirectional rolling and sliding bioreactor.This thesis considers the heterogeneity,permeability and viscoelastic properties of the cartilage and establishes the two-dimensional and three-dimensional finite element models of articular cartilage based on the walking and standing status of human.Using ABAQUS software,setting material parameters of models,and adding calcified cartilage and subchondral bone to the current mechanical model of articular cartilage.Referring to the motion mode of the normal gait cycle in human knee joints to set boundary conditions and study on the simulation of the mechanical behavior of articular cartilage,including Mises stress,true strain,pore pressure,porosity and liquid flow status,to summarize the effects of different mechanical conditions and parameters on the mechanical behavior of articular cartilage.This thesis finds that the Mises stress,true strain,pore pressure,porosity and fluid flow status change significantly in a standing state when the standing time is increased.In the process of walking,the change of rolling and sliding speed will also affect the above parameters.The rolling speed affects the Mises stress status of cartilage while the sliding speed does not obviously affect the Mises stress status.When the compressive load does not exceed the physiological condition,rotary load has no observable effect on the mechanical parameters.However,Mises stress,pore pressure and maximum tensile strain of articular cartilage increase when subjected to a high rotational and compressive load.Therefore,native articular cartilage can maintain sufficient adaptability for the normal physiological load during walking.People should avoid walking with weight to reduce overload of articular cartilage.Besides,when people are standing for a long time,the maximum stress area is shifted gradually to the lower part of cartilage which is stronger,probably to avoid the damage of hyaline cartilage.The mutual extrusion between the articular cartilages generates a special flow pattern in articular cartilage,which is beneficial to the metabolism.Exchange of substances during the metabolism process of articular cartilage exists not only in the synovial fluid,but also in the blood supply of calcified cartilage and subchondral bone.This study serves as a theoretical reference and provides experimental devices for the study of self-assembled engineered articular cartilage.It lays a good foundation for the subsequent experimental research.