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Abstract
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.
Highlights
The main function of articular cartilage (AC) is to serve as a bearing material for the synovial joints
Using the diffusion tensor MRI (DT-MRI) techniques, Meder et al (2006) and de de Visser et al (2008b) reported that the principal component of the diffusion tensor near the articular surface appeared to be oriented at around 70–75° to the normal to the articular surface while in the deep zone it appeared to be at approximately 20°, agreeing with the orientations found in this study (Fig. 2)
This study showed that middle zone (MZ) and deep zone (DZ) fibrils considerably contribute to the fluid pressurization by constraining the lateral deformation of cartilage (Figs. 4 and 5)
Summary
The main function of articular cartilage (AC) is to serve as a bearing material for the synovial joints. Its unique load-bearing and lubrication properties are due, in part, to its composition which includes a solid phase of collagen fibrils enmeshed with proteoglycans and a fluid phase (Lu and Mow, 2008). Fluid pressurisation is believed to be one important reason that AC exhibits a very low-friction coefficient (Krishnan et al, 2004). The SZ and MZ layers are thicker (50%) and well developed (Clark, 1991). Such an inhomogeneous distribution of collagen fibrils may have important effects on the mechanics of AC
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