Nanometer size wear debris generated from ultra high molecular weight polyethylene in vivo

Ultra high molecular weight polyethylene (UHMWPE) wear debris is a major cause of long-term failure of total hip replacements. UHMWPE wear particle sizes range from submicron to several millimeters, but the particles below 10 μm exhibit the highest biological activity. Some in vitro wear particles, produced in joint simulators, were shown to be smaller than 0.2 μm and recently even in vitro particles as small as several tens of nanometers have been detected. This study brings the first evidence that nano-sized wear particles with sizes below 0.05 μm are produced in vivo. UHMWPE wear nanoparticles were revealed by high-resolution, field emission gun scanning electron microscopy (FEGSEM) in the periprosthetic tissues of two different patients. Purity of the isolated wear nanoparticles was confirmed by energy-dispersive analysis of X-rays (EDS) and infrared spectroscopy (IR). Morphology of wear nanoparticles was determined by image analysis of FEGSEM micrographs. The average equivalent diameters of wear particles in the first and the second patient were 18.5 and 21.2 nm, respectively. Nanoscale wear debris could only be reliably detected if the isolation protocol included intensive sonication and if higher-than-usual magnifications were employed during FEGSEM analysis.