Friction and lubrication behaviour of hip resurfacing metal-on-metal and ZTA ceramic on CFR peek implants with various diameters and clearances. Friction and lubrication behaviour of hip resurfacing Co-Cr-Mo and zirconia toughened alumina ceramic heads against carbon fibre reinforced poly-ether-ether-ketone cups with various diameters and clearances have been investigated using serum-based lubricants.

摘要

Total hip joint prostheses made of CoCrMo heads versus ultra high molecular weightudpolyethylene (UHMWPE) cups have a limited lifetime, mainly due to the wear of theudUHMWPE cups as a result of high friction between the articulating surfaces leadingudto osteolysis and implant loosening with revision surgery becoming inevitable inudmore active patients. Tribology plays an important role in developing the design,udminimizing wear and reducing friction of hip joint prostheses in order to improveudtheir long-term performance, with good lubricating properties. Metal-on-metal hipudresurfacing prostheses have shown significantly lower wear rates compared withudconventional metal-on-polyethylene implants and thus osteolysis is potentiallyudreduced leading to increased lifetime of the prosthesis. Nevertheless, excessive wearudof metal-on-metal joints leads to metal ion release, causing pseudo-tumours andudosteolysis. An alternative approach to such bearings is the use of newly developedudcarbon fiber-reinforced poly-ether-ether-ketone (CFR PEEK) acetabular cupsudarticulating against ceramic femoral heads due to their better wear resistanceudcompared to UHMWPE. In this study, therefore, friction and lubrication propertiesudof large diameter, as cast, Co-Cr-Mo metal-on-metal hip resurfacing implants withudvarious diameters and clearances have been investigated and compared to those ofudthe newly developed zirconia toughened alumina (ZTA) ceramic femoral headsudarticulating against carbon fiber reinforced poly-ether-ether-ketone (CFR PEEK)udacetabular cups with different diameters and clearances. Friction hip simulator wasudused to measure frictional torque and then friction factors were calculated along withudSommerfeld numbers leading to Stribeck analysis and hence the lubricating modeudwas also investigated. This involved using lubricants based on pure bovine serumud(BS) and diluted bovine serum (25 vol. %BS+75 vol. %distilled water) with andudwithout carboxymethyl cellulose (CMC) (as gelling agent). Standard Rheometer wasudused to measure lubricant viscosity ranged from 0.0014 to 0.236 Pas at a shear rate ofud3000 . Pure bovine serum, diluted bovine serum without CMC and with CMCud(25BS+75DW+0.5gCMC and +1gCMC) showed pseudoplastic flow behaviour up toudshear rate of ¿139 above which a Newtonian flow with significant increase inudshear stress was observed. The viscosity flow curves for the 25BS+75DW+2gCMC,ud+3.5gCMC and +5gCMC showed only shear thinning up to a shear rate of 3000 .udThe shear rate application modified the flow behaviour of bovine serum from audpseudoplastic to a Newtonian flow depending on its purity and CMC content. Thisudwill cause a different frictional behaviour depending on joint diameter and clearance,udas seen in this work. The experimental data were compared with theoreticaludivudpredictions of the lubricating regimes by calculating theoretical film thickness andudlambda ratio. The metal-on-metal Biomet ReCaps showed similar trends of Stribeckudcurves, i.e. friction factors decreased from ~0.12 to ~0.05 as Sommerfeld numbersudincreased in the range of viscosities ~0.001-0.04Pas indicating mixed lubricationudregimes above which the friction factor increased to ~0.13 at a viscosity of 0.236Pas.udThe Stribeck analyses suggested mixed lubrication as the dominant mode with theudlowest friction factor in the range ~0.09 - ~0.05 at the physiological viscosities ofud~0.01 to ~0.04 Pas and that such joints can be used for more active patients asudcompared to the conventional total hip replacement joints with 28mm diameter. TheudStribeck curves for all ZTA ceramic-on-CFR PEEK components illustrated a similarudtrend with BS fluids showing higher friction factors (in the range 0.22-0.13) than theuddiluted BS+CMC fluids (in the range 0.24-0.05). The friction tests revealedudboundary-mixed lubrication regimes for the ZTA ceramic-on-CFR-PEEK joints. Theudresults, so far, are promising and suggest clearly that the newly developed ZTAudceramic femoral heads articulating against CFR PEEK cups have similar friction andudlubrication behaviour at optimum clearances to those of currently used metal-onmetaludhip resurfacing implants at the range of viscosities 0.00612 to 0.155Pas. Theseudresults clearly suggest that the ZTA ceramic-on-CFR-PEEK joints showed lowudfriction at the physiological viscosities of ~0.01Pas in the range ~0.1-0.05,udsuggesting that these novel joints may be used as an alternative material choice forudthe reduction of osteolysis. The result of this investigation has suggested that theudoptimum clearance for the 52mm diameter MOM Biomet ReCaps could be ~170¿m.udHowever, 48 and 54mm joints showed lower friction due to clearances to beud>200¿m. For the 52mm ZTA ceramic-on-CFR-PEEK joints the optimum clearanceudseems to be ¿ 630¿m radial clearance. These results suggested that increasedudclearance bearings have the potential to generate low friction and hence no risk ofudmicro- or even macro-motion for the ceramic-on-CFR-PEEK joints. This study foundudno correlation between theoretical predictions and experimental data for all metal-onmetaludand ZTA ceramic-on-CFR PEEK bearings at the physiological viscosityud(0.0127Pas). However, at lubricant viscosity of 0.00157Pas, the theoreticaludprediction of lubrication regime correlated well with the experimental data, bothudillustrating boundary lubrication. As expected, a decrease in viscosity resulteduddecrease in the film thickness.