Laser-Induced Breakdown Spectroscopy for the Analysis of Cobalt—Chromium Orthopaedic Wear Debris Particles

Abstract

Laser-induced breakdown spectroscopy (LIBS) is investigated for the quantitative analysis of individual cobalt–chromium wear particles generated in vivo from human artificial knee joints. As implemented, the LIBS technique provided a measurement of the absolute chromium and cobalt masses for individual wear particles, which enabled calculation of chromium-to-cobalt mass ratios and the equivalent spherical diameter on a particle-to-particle basis. Using a multiple analyte emission line spectral filtering process, absolute cobalt and chromium mass measurements were made as low as 40 and 20 fg, respectively, corresponding to a particle diameter of approximately 200 nm. The size of the wear debris ranged from approximately 200 to 800 nm, with a mean diameter of 385 nm. In addition, the wear particles exhibited a depletion of cobalt with respect to the bulk composition of the cobalt–chromium alloy. The cobalt depletion exhibited a strong correlation with size, with the larger particles characterized by a more significant depletion of cobalt. All synovial fluid samples were inactivated with 10% bleach to reduce risks of infection by bloodborne pathogens. Control wear debris was generated from manual abrasion of pristine cobalt–chromium alloy specimens and analyzed with the LIBS technique to address the potential effects of bleach addition. No statistical differences were recorded between the particle suspensions treated and untreated with bleach. Overall, the LIBS method was successfully implemented for the quantitative analysis of cobalt–chromium wear particles.