Infrastructure Engineering - Research Publications

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    Computational study on synovial fluid flow behaviour in cartilage contact gap under osteoarthritic condition
    Liao, J ; Miramini, S ; Liu, X ; Zhang, L (Elsevier, 2020-08-01)
    This study numerically investigates the pathological changes of fluid flow in cartilage contact gap due to the changes in cartilage surface roughness and synovial fluid characteristics in osteoarthritic (OA) condition. First, cartilage surface topographies in both healthy and OA conditions are constructed using a numerical approach with consideration of both vertical and horizontal roughness. Then, constitutive equations for synovial fluid viscosity are obtained through calibration against previous experimental data. Finally, the roughness and synovial fluid information are input into the gap flow model to predict the gap permeability. The results show that the rougher surface of OA cartilage tends to decrease gap permeability by around 30%–60%. More importantly, with the reduction in gap size, the decrease in gap permeability becomes more significant, which could result in an early fluid ultrafiltration into the tissue. Moreover, it is demonstrated that the pathological synovial fluid has more deleterious effects on the gap permeability than the OA cartilage surface, as it could potentially increase the gap permeability by a few hundred times for pressure gradients less than 106 Pa/m, which could inhibit the fluid ultrafiltration into the tissue. The outcomes from this research indicate that the change in fluid flow behaviour in contact gap in OA condition could significantly affect the function of articular joints.
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    A coupled contact model of cartilage lubrication in the mixed-mode regime under static compression
    Liao, JJ ; Smith, DW ; Miramini, S ; Gardiner, BS ; Zhang, L (Elsevier, 2020-05-01)
    This study presents a coupled cartilage contact model, in which the contact gap and cartilage tissue are modelled as two poroelastic systems, linked by pressure and normal flux continuity boundary conditions. Using a tibial plug under indentation as a proof-of-concept model, the predictions support the weeping lubrication theory under static compression. Specifically, the interstitial fluid would exude from the underlying cartilage into the contact gap to extend the mixed-mode duration by > 20-fold compared to a no fluid exudation counterpart. Moreover, the traditional contact model, that does not consider the contact gap and cartilage fluid exchange, potentially overestimates the interstitial fluid pressure compared to the proposed coupled model. Parametric studies suggest that the increasing viscosity of synovial fluid prolongs the gap fluid pressurisation, while increasing the asperity stiffness reduces the gap fluid pressure but increases contact gap height.