The effect of collagen fibril orientation on the biphasic mechanics of articular cartilage

The highly inhomogeneous distribution of collagen fibrils may have important effects on the biphasic mechanics of articular cartilage. However, the effect of the inhomogeneity of collagen fibrils has mainly been investigated using simplified three-layered models, which may have underestimated the effect of collagen fibrils by neglecting their realistic orientation. The aim of this study was to investigate the effect of the realistic orientation of collagen fibrils on the biphasic mechanics of articular cartilage. Five biphasic material models, each of which included a different level of complexity of fibril reinforcement, were solved using two different finite element software packages (Abaqus and FEBio). Model 1 considered the realistic orientation of fibrils, which was derived from diffusion tensor magnetic resonance images. The simplified three-layered orientation was used for Model 2. Models 3–5 were three control models. The realistic collagen orientations obtained in this study were consistent with the literature. Results from the two finite element implementations were in agreement for each of the conditions modelled. The comparison between the control models confirmed some functions of collagen fibrils. The comparison between Models 1 and 2 showed that the widely-used three-layered inhomogeneous model can produce similar fluid load support to the model including the realistic fibril orientation; however, an accurate prediction of the other mechanical parameters requires the inclusion of the realistic orientation of collagen fibrils.</p

Computational investigation of the time-dependent contact behaviour of the human tibiofemoral joint under body weight

The knee joint is one of the most common sites for osteoarthritis, the onset and progression of which are believed to relate to the mechanical environment of cartilage. To understand this environment, it is necessary to take into account the complex biphasic contact interactions of the cartilage and menisci. In this study, the time-dependent contact behaviour of an intact and a meniscectomized human tibiofemoral joint was characterized under body weight using a computational model. Good agreement in the contact area and femoral displacement under static loads were found between model predictions of this study and published experimental measurements. The time-dependent results indicated that as loading time progressed, the contact area and femoral vertical displacement of both intact and meniscectomized joints increased. More load was transferred to the cartilage–cartilage interface over time. However, the portions of load borne by the lateral and medial compartments did not greatly vary with time. Additionally, during the whole simulation period, the maximum compressive stress in the meniscectomized joint was higher than that in the intact joint. The fluid pressure in the intact and meniscectomized joints remained remarkably high at the condyle centres, but the fluid pressure at the cartilage–meniscus interface decreased faster than that at the condyle centres as loading time progressed. The above findings provide further insights into the mechanical environment of the cartilage and meniscus within the human knee joint

Elastohyrodynamic lubrication in metal-on-metal artificial hip joints with aspherical bearing surfaces and complex structures

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Numerical Simulation Study on the Flow Field Out of a Submerged Abrasive Water Jet Nozzle

In order to optimize the parameters of pre-mixed abrasive water jet cutting technology, make it more efficient in the coal mine gas environment and solve the problem of hard coal and the difficulty of rock drilling, FLUENT software was used to get the isothermal, incompressible, steady flow field out of a submerged abrasive water jet nozzle through numerical simulation, with different particle sizes and different confining pressures under submerged conditions. The results show that, under submerged conditions, the maximum velocity of the abrasive particle outside the pre-mixed abrasive water jet nozzle is about 6 mm far away from the nozzle; the abrasive particle diameter has little influence on the velocity outside the nozzle. The external confining pressure of the nozzle has an important influence on the velocity, which is that the jet velocity of the same position decreases with the increase of confining pressure and the relationship between the confining pressure of different distance from the nozzle exit and the abrasive velocity is exponential function. The results of the simulation laid the foundation for optimizing the nozzle structure, improving efficiency and developing the abrasive water jet nozzle

Effect of polycarboxylate superplasticizer on fluidity and rheology of cement slurry containing silica fume

The effect of polycarboxylate superplasticizer on the fluidity and rheology of cement - silica fume - water paste was investigated. The changes of dispersion degree, yield stress and plastic viscosity of paste with different superplasticizer content were analyzed. The results show that the rheological properties of paste with different superplasticizer content conform to Herschel-Bulkley model. The shear thinning of the slurry is manifested as a typical yielding pseudoplastic fluid characteristic. When the content of superplasticizer is less than 1.0%, the plastic viscosity and yield stress decrease and the fluidity increase with the increase of plasticizer content. When the content of superplasticizer is more than 1.0%, the yield stress decreases slightly and the plastic viscosity increases with the increase of plasticizer content. The fluidity decreases with the increase of yield stress, and there is a good correlation between them