ABSTRACT
Objective To study the damage propagation and evolution mechanism of cartilage under compressive loads.Methods The fiber-reinforced porous elastic model of cartilage with micro-defect was established by using finite element method,and the process of damage evolution under compressive loads was simulated and analyzed with parameters.The patterns of stress and strain distributions on cartilage matrix and collagen fiber at different damage extension stages were obtained.Results The strain in the surface and forefront of cartilage damage increased significantly with the increase of compression displacement,and they were obviously in positive correlation;in the process of damage evolution,there was a trend that cartilage extended to the deep and both sides simultaneously;cracks and damage in cartilage extended preferentially along the fiber tangent direction.With the aggravation of cartilage damage,the lateral extension speed was significantly faster than the longitudinal extension speed.Conclusions The process of cartilage damage extension has a close relationship with the distribution of fibers.The damages in matrix and fiber promote each other.The evolution speed and degree of cartilage vary constantly in different layers and at different stages.These results can provide the qualitative reference for prediction and repair of cartilage damage,as well as the theoretical basis for explaining pathological phenomena of damage degeneration and its clinic treatment.
ABSTRACT
Objective To study the damage propagation and evolution mechanism of cartilage under compressive loads.Methods The fiber-reinforced porous elastic model of cartilage with micro-defect was established by using finite element method,and the process of damage evolution under compressive loads was simulated and analyzed with parameters.The patterns of stress and strain distributions on cartilage matrix and collagen fiber at different damage extension stages were obtained.Results The strain in the surface and forefront of cartilage damage increased significantly with the increase of compression displacement,and they were obviously in positive correlation;in the process of damage evolution,there was a trend that cartilage extended to the deep and both sides simultaneously;cracks and damage in cartilage extended preferentially along the fiber tangent direction.With the aggravation of cartilage damage,the lateral extension speed was significantly faster than the longitudinal extension speed.Conclusions The process of cartilage damage extension has a close relationship with the distribution of fibers.The damages in matrix and fiber promote each other.The evolution speed and degree of cartilage vary constantly in different layers and at different stages.These results can provide the qualitative reference for prediction and repair of cartilage damage,as well as the theoretical basis for explaining pathological phenomena of damage degeneration and its clinic treatment.
ABSTRACT
Objective To study the damage propagation and evolution mechanism of cartilage under compressive load. Methods The fiber-reinforced porous elastic model of cartilage with micro-defect was established by using finite element method, and the process of damage evolution under compressive load was simulated and analyzed with parameters. The patterns of stress and strain distributions on cartilage matrix and collagen fiber at different damage extension stage were obtained. Results The strain in surface and the forefront of cartilage damage increased significantly with the increase of compression displacement, and they were obviously in positive correlation; in the process of damage evolution, there was a trend that cartilage extended to the deep and both sides simultaneously; cracks and damage in cartilage extended preferentially along the fiber tangent direction. With the aggravation of cartilage damage, the lateral extension speed was significantly faster than the longitudinal extension speed. Conclusions The process of cartilage damage extension has a close relationship with the distribution of fibers. And the damage in matrix and fiber promote each other. The evolution speed and degree of cartilage vary constantly in different layers and at different stages. These results can provide the qualitative reference for prediction and repair of cartilage damage, as well as the theoretical basis for explaining clinical pathological phenomena of damage degeneration and treatment.
ABSTRACT
Objective To investigate the mechanical properties of both artificial cartilage and host cartilage by establishing the in vitro model of tissue engineered cartilage for repairing defects. Methods The agarose gel as an artificial cartilage was implanted in a deep cartilage defect connected with biological adhesive to set up the in vitro model of tissue engineered articular cartilage defects. Under the compression load, the instant mechanical behavior of the repair area was studied using the digital image correlation technology. Results There was no cracking phenomenon occurred at the interface during the compression process. The Strain distributions at middle layer of the repair area were obtained when the cartilage thickness appeared changes with 3.5%, 5.6%, 7.04% and 9.0% by the compression, respectively. When the compressing change increased from 3.5% to 9%, the maximum compressive strain of host cartilage was increased by 75.9%, and the maximum tensile strain of artificial cartilage was increased by 226.99% in the vertical direction of cartilage surface. In the direction parallel with cartilage surface, the maximum tensile strain at the interface was increased by 116.9%, and the increment was far more than that at the host cartilage area and artificial cartilage area. For shear strain at the repair area, the direction of shear strain at the interface changed oppositely with the compression increasing. Conclusions The repair effect of tissue engineered cartilage was uncertain due to the mechanical environment of the repair area. After the tissue engineered cartilage was implanted in the defect, the repair area was under the influence of complex strain states. The strains changed greatly at the interface both with the host cartilage and artificial cartilage as the compression increasing. The strain in the vertical direction of cartilage surface at the interface might change from compressive stain to tensile strain, which was significantly increased in the direction parallel with cartilage surface. The strain direction at the interface could even be changed oppositely, and the shear strain appeared rapidly increase. The complex strain states lead to such great changes in mechanical environment of the defect area, and may cause cracking at the interface, and even further affect the repair process. Therefore, attention should be given to this complex mechanical environment during cartilage defect repair process in clinical treatment.