Study On Mechanical State For Tissue-Engineering Repaired Cartilage Under Compressive Load

There is no nerves、blood vessels and lymphatic vessels in cartilage,the ability to repair is limited and cartilage tissue becomes the predilection site in clinical diseases.At present,the cartilage tissue engineering as a kind of ideal method of repairing cartilage has become a hot issue of orthopaedic researches.Although it can eliminate the clinical symptoms partly,some phenomenon such as graft’s and host cartilage’s degradation and modified properties may appear because the implanted cartilage tissue has bad integration with the surrounding host cartilage.All of them are related with the mechanical state,so researching the influence of implanted cartilage’s shape and properties,the characteristics of loads on defect restoration’s mechanical state have an important significance.Based on the compression state of the human body and with the help of finite element simulation software,this paper analyzed and compared the mechanical properties of defect restoration’s mechanical state under different factors.The main contents and results are as follows:The finite element software ABAQUS is used to establish two-dimensional finite element model of articular cartilage under the condition of compression.In the model,two phase structure of the cartilage,viscoelastic characteristics,different layers of collagen fibers,changes of void ratio and permeability are considered.Models contains a complete cartilage,different cross section shapes of the defect(rectangular,trapezoidal,circular arc form)and different repair depths(superficial,middle,deep and full-thickness layer)cartilage.For different cross section shape of cartilage defect model,host cartilage is hierarchical and the material of every layer is regarded as transversely isotropic,while the artificial cartilage is the isotropic material.And using the part of subroutine calls and property in the software,the definition of osmotic pressure and void ratio are realized with FORTRAN language program.On this basis,how factors including the cross section shape of cartilage defect,the repaired depth,elastic modulus,poisson’s ratio,amount of compression,the compression rate affect the Mises stress,axial strain and pore pressure,the liquid velocity and porosity is researched.The finite element model is used to simulate the cartilage’s mechanics experiments of other scholars,simulations show the consistency with experiment on the mechanical properties’ regularities of distribution in the cartilage,namely strain in the cartilage decreases with the increase of the cartilage’s depth and it enhances the reliability of the model.Simulation results show that the cross section shape of defect and depth of the repair willaffect the mechanical properties of cartilage,bearing capacity in rectangular defect shape is higher,the exchange of nutrition is more sufficient;When the defect is above the deep zone,the deeper the repaired is,the worse the repaired effect will be.While when the depth reaches deep zone,the full-thickness is conducive to cartilage’s repair on the contrary.The increase of amount of compression and compression rate will increase the stress and strain of repaired area,which will make stress concentration appears,even make the repaired area cracked.The increase of elastic modulus of artificial cartilage may improve cartilage’s bearing capacity,and reduce the deformation and pore velocity of repaired area simultaneously,which can promote the transfer of nutrients.Artificial cartilage’s poisson’s ratio have little effect on the mechanical properties of cartilage,but the increase of it can significantly increase the stress and strain of repair area,so its increase is bad for repairing.This article mainly researches how factors including the cartilage defects of different shapes and depths,the characteristics of compression load and material properties of artificial cartilage affect the repairment of cartilage in the aspects of simulation.It is relatively comprehensive which can provide certain theoretical reference for the clinical treatment and postoperative rehabilitation training of cartilage’s defect.