Papers by Keyword: Articular Cartilage

Abstract: Structural organization of articular cartilage is rooted in the arrangement of mesenchymal stem cells (MSCs) into morphologically distinct zones during embryogenesis as a result of spatiotemporal gradients in biochemical, mechanical, and cellular factors that direct the formation of stratified structure of articular cartilage. These gradients are central to the function of cartilage as an articulating surface. Strategies that mimic zonal organization of articular cartilage are more likely to create an engineered tissue with more effective clinical outcome. The objective of this work was to measure the expression of human MSCs encapsulated in engineered gels that simulate stiffness of the superficial, middle and calcified zones of articular cartilage supplemented with zone specific growth factors. Size of the encapsulated cells increased from the gel simulating superficial zone to those simulating middle and calcified zones. Glycosaminoglycans (GAG) content progressively increased from the gel simulating superficial zone to those simulating middle and calcified zones. Human MSCs in the gel simulating the superficial zone showed up-regulation of Sox-9 and SZP whereas those in the calcified gel showed up-regulation of ALP. Results demonstrate that a developmental approach can potentially regenerate the zonal structure of articular cartilage.

Abstract: Articular cartilage is a complicated material to model for a variety of reasons: its biphasic/triphasic properties, heterogeneous structure, compressibility, unique geometry, and variance between samples. However, the applications for a biomimetic, cartilage-like material are numerous and include: porous bearings, viscous dampers, robotic linkages, artificial joints, etc. This work reports experimental results on the stress-relaxation of equine articular cartilage in unconfined compression. The response is consistent with simple spring and damper systems, and gives a storage and loss moduli. This model is proposed for use in evaluating biomimetic materials, and can be incorporated into large-scale dynamic analyses to account for motion or impact. The proposed characterization is suited for high-level analysis of multi-phase materials, where separating the contribution of each phase is not desired.

Abstract: Atomic Force Microscopy (AFM) based nanoindentation is a widely used technique for measuring mechanical properties of living cells, providing information for understanding their mechanobiological behavior. However, very local properties of cell surfaces have not been characterized earlier. The goal of this study was to develop an AFM-based technique to determine local elastic properties of bovine articular chondrocytes. The Youngs modulus of chondrocytes was 19.3 ± 5.6 kPa for spread cells and 10 ± 4.1 kPa for the round cells. The results were compared to previous studies in which different techniques were used to obtain more global properties of chondrocytes. Our findings suggest that using nanosized AFM tips, the very local cell properties can be measured.

Abstract: This study aimed at investigating positive and negative potential effect on phospholipid lubrication for artificial joint. Surface potentials of CoCrMo in saline were measured once per day for 1 week to simulate corrosion of implanted artificial joint. Both +250 mV and-250 mV were applied on CoCrMo. 2mg/ml DPPC liposome was fabricated to produce lipidic adsorption on CoCrMo. Friction tests were carried out on cartilage vs. CoCrMo and UHMWPE vs. CoCrMo. The results showed that superficial potential of CoCrMo in saline changed from-177 mV at 1^st day to 133mV at 7^th day. Lubrication performance of DPPC liposome without potential was declined gradually. Liposome@-250 mV sustained low friction coefficient of both tribopairs whereas liposome@+250 mV greatly increased friction coefficient of UHMWPE vs. CoCrMo from 0.041 to 0.076. It demonstrated that negative potential enhanced adsorption of DPPC liposome, and promoted its lubrication. In contrast, positive potential on CoCrMo due to corrosion deteriorated liposome lubrication.

Abstract: Cartilage with complex structure is a porous viscoelastic material. The direction of arrangement of collagen fibers in different layer regions directly affects the mechanical properties of the cartilage layer region. It is very important to use the method of numerical simulation for studying cartilage damage and repair through experimental measurements of cartilage mechanical parameters of the different layers. Because of the relatively small size of the cartilage, it is very difficult to measure mechanical parameters of cartilages by tensile test. The paper for main problems in the tensile test of cartilages, first by porcine articular cartilage compression testing, measuring the displacement of cartilage areas of different layers, according to the characteristics of the displacement determines the size of areas of different layers of cartilage, and then designed the cartilage and substrate stretching models. Model includes two forms of direct bonding and embedding bonding to simulate stretching process of different layers of the cartilage area in numerical way, displacement fields and stress-strain fields of stretching cartilage in different layer regions are derived. The numerical results show that using the way of embedded bonding can make stress of articular well-distributed without stress concentration, so it is a good way of bonding methods. Paper of the research work laid the foundation for measuring mechanical parameters of cartilage by stretch experiment.

Abstract: Here we reported a combined technique for articular cartilage repair, consisting of bone arrow mesenchymal stem cells (BMMSCs) and poly (dl-lactide-co-glycolide-b-ethylene glycol-b-dl-lactide-co-glycolide) (PLGA-PEG-PLGA) triblock copolymers carried with tissue growth factor (TGF-belat1). In the present study, BMMSCs seeded on PLGA-PEG-PLGA with were incubated in vitro, carried or not TGF-belta1, Then the effects of the composite on repair of cartilage defect were evaluated in rabbit knee joints in vivo. Full-thickness cartilage defects (diameter: 5 mm; depth: 3 mm) in the patellar groove were either left empty (n=18), implanted with BMMSCs/PLGA (n=18), TGF-belta1 modified BMMSCs/PLGA-PEG-PLGA. The defect area was examined grossly, histologically at 6, 24 weeks postoperatively. After implantation, the BMMSCs /PLGA-PEG-PLGA with TGF-belta1 group showed successful hyaline-like cartilage regeneration similar to normal cartilage, which was superior to the other groups using gross examination, qualitative and quantitative histology. These findings suggested that a combination of BMMSCs/PLGA-PEG-PLGA carried with tissue growth factor (TGF-belat1) may be an alternative treatment for large osteochondral defects in high loading sites.

Abstract: As a viscoelastic and nonlinear connective tissue, articular cartilage bears continuous sliding load in the daily activities. The optimized digital image correlation (DIC) technique was applied to investigate the effect of sliding rate and compressive strain on the normal displacement of different layers in pig articular cartilage under sliding load. The normal displacements of different layers in cartilage increase gradually with sliding going on with given sliding rate and compressive strain. Experiments showed that the normal displacement of superficial layer is the largest, the normal displacement of deep layer is the smallest and the normal displacement of middle layer is between superficial layer and deep layer, and found that the normal displacements of different layers in cartilage increase with increasing compressive strains, but decrease with increasing sliding rates. The normal displacement of different layers are different under continuous sliding load.

Abstract: A new biomechanical model of articular cartilage was developed using ABAQUS to investigate the mechanical properties of different layers under different loading rates. It is found that the compressive strain of superficial layer is the largest, the compressive strain of deep layer is the smallest and the compressive strain of middle layer is between the superficial and deep layer under constant loading rate. The compressive strains of different layers increase with increasing loading rates. At the beginning of loading, fluid flows mainly in the superficial layer and flows into the middle and deep layer with the increasing time and the position of the maximum flow moves downward. Void ratio also increases with the loading time.

Abstract: Objective To understand the stresses distribution and process of damage evolution of both matrix and fiber in the defect cartilage under load of compression. The numerical results may provide a reference to both of the design for cartilage alternatives and clinical repair of defect cartilage. Methods The thickness of different layers of cartilage was obtained by a kind of experiment, in which the displacement in different layers zone cartilage under the compression load was obtained by the digital correlation technique. The multi-layer cartilage model with fiber and defect was established by the multi-physics analysis software ANSYS, with the different layers of the cartilage refer to the experimental results. According to the strength condition, the cartilage damage evolution process was simulated by the method of modifying the stiffness of the elements. The influence of the different defect depth to the damage evolution of cartilage was considered in parameter study. Result The simulation results have shown that the stress distribution in matrix was related to the cartilage defect depth. The minimum stress was distributed in the deep areas and below the damage area, stress concentration was located in the both sides of the defect area in the cartilage matrix, and the damaged area developed gradually from surface to deep, the maximum stress located at both sides of defect area. The stress distribution of cartilage fibers related with their location, the compressive stresses are mainly distributed in the middle and deep area, which are greater than those of undamaged. Conclusion In the process of damage evolution, the damaged area gradually developed from the surface to the deep. In the case of defect value of 60%, the maximum equivalent stresses in matrix will be increased in the process of damage evolution; in the case of defect value of 5%, the maximum axial stresses in fibers will be increased in the process of damage evolution.

Abstract: The mechanical properties of articular cartilage serve as important measures of tissue function or degeneration, and are known to change significantly with asteoarthritis. In previous computational studies, the cartilage surface of axisymmetric models was assumed to be flat in order to evaluate the cartilage behaviour. This assumption was inappropriate since the synovial joint possessed curvature geometrical shape and may contribute to the inaccurate in characterising the cartilage properties. Therefore, this study aims to examine the sensitivity of cartilage surface curvature of characterized cartilage biphasic properties using a combination of experimental and computational methods. Axisymmetric biphasic poroelastic finite element models were generated to measure cartilage surface radius and thickness. Based on the results, the smaller cartilage surface of 20 mm radius produced higher difference of the characterised properties where its generate 9% difference in the permeability and 5% difference in the elastic modulus, compared to the flat cartilage. Based on these results, it may indicate that the cartilage curvature will affect the characterised cartilage biphasic properties of elastic modulus and permeability.