A new radioisotope tracing method of UHMWPE wear particle dispersion using 97Ru

A new method of radioisotope labelling, using the reaction 92Zr(12C,α3n)97Ru, has been demonstrated. The method places radioactive 97Ru tracer atoms into ultra-high molecular weight polyethylene (UHMWPE). The radioisotope 97Ru (half-life t1/2=2.9 days) was implanted in 5 mm×5 mm UHMWPE samples to a maximum depth of 5 μm. The radioisotope is identified via a characteristic gamma-ray emission from its daughter 97Tc at 216 keV. The new method is advantageous since the concentration profile of the 97Ru label is almost constant starting at the surface. In order to show the efficacy of the method for wear measurements on prostheses, the labeled UHMWPE samples were worn in a model system. The model system involved bi-directional sliding actuation on a steel block. Debris transport, via the two pathways linking the polymer with the articulating steel surface and with the lubricant, respectively, has been quantified. Surface roughness of the steel and the load on the steel were varied. Changing the surface roughness of the steel from (110±30) to (340±90) nm increased the amount of debris dispersed in the lubricant from (21±3)% to (67±3)%. Furthermore, changing the load from 1 to 5 kg also increased debris transport along this pathway.