Agnese FRAGASSIAntonietta GRECOMartina DI FRANCESCOLuca CESERACCIU...
539-553页
查看更多>>摘要：Nano-and micro-particles are being increasingly used to tune interfacial frictional properties in diverse applications,from friction modifiers in industrial lubrication to enhanced biological fluids in human osteoarthritic joints.Here,we assessed the tribological properties of a simulated synovial fluid enriched with non-spherical,poly lactic-co-glycolic acid(PLGA)microparticles(μPL)that have been previously demonstrated for the pharmacological management of osteoarthritis(OA).Three different μPL configurations were fabricated presenting a 20 μm×20 μm square base and a thickness of 5 μm(thin,5H μPL),10 μm(10H μPL),and 20 μm(cubical,20H μPL).After extensive morphological and physicochemical characterizations,the apparent Young's modulus of the μPL was quantified under compressive loading returning an average value of~6 kPa,independently of the particle morphology.Then,using a linear two-axis tribometer,the static(μs)and dynamic(μd)friction coefficients of the μPL-enriched simulated synovial fluid were determined in terms of particle configuration and concentration,varying from 0(fluid only)to 6×105 μPL/mL.The particle morphology had a modest influence on friction,possibly because the μPL were fully squeezed between two mating surfaces by a 5.8 N normal load realizing boundary-like lubrication conditions.Differently,friction was observed to depend on the dimensionless parameter Ω,defined as the ratio between the total volume of the μPL enriching the simulated synovial fluid and the volume of the fluid itself.Both coefficients of friction were documented to grow with Ω reaching a plateau of μs~0.4 and μd~0.15,already atΩ~2×10-3.Future investigations will have to systematically analyze the effect of sliding velocity,normal load,and rigidity of the mating surfaces to elucidate in full the tribological behavior of μPL in the context of osteoarthritis.
查看更多>>摘要：The wear profile analysis,obtained by different tribometers,is essential to characterise the wear mechanisms.However,most of the available methods did not take the stress distribution over the wear profile in consideration,which causes inaccurate analysis.In this study,the wear profile of polymer-metal contact,obtained by block-on-ring configuration under dry sliding conditions,was analysed using finite element modelling(FEM)and experimental investigation.Archard's wear equation was integrated into a developed FORTRAN-UMESHMOTION code linked with Abaqus software.A varying wear coefficient(k)values covering both running-in and steady state regions,and a range of applied loads involving both mild and severe wear regions were measured and implemented in the FEM.The FEM was in good agreement with the experiments.The model reproduced the stress distribution profiles under variable testing conditions,while their values were affected by the sliding direction and maximum wear depth(hmax).The largest area of the wear profile,exposed to the average contact stresses,is defined as the normal zone.Whereas the critical zones were characterized by high stress concentrations reaching up to 10 times of that at the normal zone.The wear profile was mapped to identify the critical zone where the stress concentration is the key point in this definition.The surface features were examined in different regions using scanning electron microscope(SEM).Ultimately,SEM analysis showed severer damage features in the critical zone than that in the normal zone as proven by FEM.However,the literature data presented and considered the wear features the same at any point of the wear profile.In this study,the normal zone was determined at a stress value of about 0.5 MPa,whereas the critical zone was at about 5.5 MPa.The wear behaviour of these two zones showed totally different features from one another.
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