Influence of synovia constituents on tribological behaviors of articular cartilage

The extremely low friction and minimal wear in natural synovial joints appear to be established by effective lubrication mechanisms based on appropriate combination of articular cartilage and synovial fluid.The complex structure of cartilage composed of collagen and proteoglycan with high water content contributes to high load-carrying capacity as biphasic materials and the various constituents of synovial fluid play important roles in various lubrication mechanisms.However,the detailed differences in functions of the intact and damaged cartilage tissues,and the interaction or synergistic action of synovia constituents with articular cartilage have not yet been clarified.In this study,to examine the roles of synovia constituents and the importance of cartilage surface conditions,the changes in friction were observed in the reciprocating tests of intact and damaged articular cartilage specimens against glass plate lubricated with lubricants containing phospholipid,protein and/or hyaluronic acid as main constituents in synovial fluid.The effectiveness of lubricant constituents and the influence of cartilage surface conditions on friction are discussed.In addition,the protectiveness by synovia constituents for intact articular cartilage surfaces is evaluated.

Biomimetic artificial cartilage:fibre-reinforcement of PVA hydrogel to promote biphasic lubrication mechanism

The fibre-reinforced structure in synovial articular cartilage plays an important role in enhancing the fluid load support in the biphasic lubrication mechanism.Poly(vinyl alcohol)(PVA)hydrogel is a potential biomimetic articular cartilage material.In this study,PVA hydrogel was reinforced with PVA fibres to improve its frictional properties.By computational analysis,the position of the PVA fibre layer was examined with a migrating contact condition to reduce the friction coefficient.To improve the fibre reinforcement,a method for fibre placement was developed to retain the initial strain of the fibre in the hydrogel matrix.The experimental results showed that the fibre-reinforced PVA hydrogel with a surface fibre layer had a low friction coefficient of 0.031 in pure water.The fibre-reinforced PVA hydrogel successfully reduced friction coefficient.

Effect of collagen-induced residual stress on the frictional property of articular cartilage

Previous findings,such as split-line of the articular cartilage surface and curving of sliced cartilage specimen,would suggest that residual stress is contained in articular cartilage.This study was performed to determine the effect of collagen fibre-induced residual stress on the biphasic lubrication property of articular cartilage.A fibre-reinforced poroelastic model of articular cartilage was developed in Abaqus.In the model,residual stress was contained in the collagen fibre in the surface layer by applying 1-5%of tensile strain.Reciprocating friction analysis was performed between the model and a sphere at a friction speed of 1.0-10.0 mm/s.Results revealed that the coefficients of start-up and dynamic friction at second friction cycle were lower in residual stress model than in no-residual stress model,with the largest decreases observed at a friction speed of 1 mm/s.It was obse rved that re hydration was promoted in the bearing area in residual stress model.These results suggest that collagen-induced residual stress plays an important role in enhancing the biphasic lubrication property of articular cartilage.

Transitional behaviour between biphasic lubrication and soft elastohydrodynamic lubrication of poly(vinyl alcohol)hydrogel using microelectromechanical system pressure sensor

The soft hydrogel material is expected for a candidate material as biomimetic artificial cartilage with synergisticfunctionalities of adaptive multimode lubrication.In boundary lubrication mode of hydrogel material,the biphasiclubrication mechanism cooperatively exerts its functionality.In hydrodynamic lubrication mode,it is preferable that thelubricating surfaces be impermeable to trap the fluid pressure in contact surfaces,whereas the actual biphasic materiallike a hydrogel is a permeable material with surface porosity.lt is indicated that the interstitial fluid pressurisation inthe permeable biphasic material can contribute to significant fluid load support under lower sliding speed condition.So,the authors examined how the contrary fluid pressure effect appears in the transition from the boundarylubrication mode to soft elastohydrodynamic lubrication mode.In the experiment,a small pressure sensor was utilisedto measure the in-situ fluid pressure in sliding condition.Although the experimental condition of this study wasselective,the result showed a possibility of the negative effect of the biphasic surface,in which the permeable surfacediminished the hydrodynamic fluid pressure.This means that one should manage and enhance the biphasic lubricationabilities in wide operation range when the hydrogel material was used as a load bearing material.

Erratum to: Influence of synovia constituents on tribological behaviors of articular cartilage

Erratum to Friction 1(2):150-162(2013)DOI 10.1007/s40544‐013‐0010‐6 The original version of this article unfortunately contained the incorrect lengend“HA 0.5 wt%+DPPC 0.01 wt%+albumin 1.4 wt%”in Fig.7 on page 155,instead of.

Influence of collagen fibre orientation on the frictional properties of articular cartilage

Articular cartilage has a unique collagen fibre network structure that exhibits both anisotropy and depth dependency.Collagen fibre orientation in a cross-section parallel to the articular cartilage surface may affect the lubrication properties of articular cartilage.The effect of collagen fibre orientation on the frictional properties of articular cartilage was examined through finite element analysis of the friction.Specifically,a three-dimensional fibre-reinforced poroelastic biphasic model was used to determine the influence of collagen fibril orientation on the frictional properties of articular cartilage.The simulations reveal that collagen fibre orientation has a significant influence on the deformation behaviour of articular cartilage in front of and behind the contact area.The coefficient of dynamic friction was lower in the direction parallel to the collagen fibre orientation than in the direction perpendicular to the collagen fibre orientation,regardless of the indenter speed.