Effects of clinically relevant alumina ceramic wear particles on TNF- α production by human peripheral blood mononuclear phagocytes

Abstract

The recent introduction of microseparation of the components of ceramic-on-ceramic hip prostheses during hip simulations has produced clinically relevant wear rates, wear patterns and wear particles. This provided an opportunity to determine the response of primary human peripheral blood mononuclear cells to clinically relevant alumina ceramic wear particles in vitro. Alumina ceramic wear particles were generated in a hip joint simulator under microseparation conditions. The particles showed a bi-modal size distribution with nanometer sized (5– 20 nm ) and larger particles (0.2– >10 μm ). The particles were cultured with human peripheral blood mononuclear cells obtained from six different donors at particle volume to cell number ratios of 1, 10, 100 and 500 μm 3 . After 24 h incubation the viability of the cells and the levels of TNF- α were determined. The response to the microseparation wear particles was compared to that of commercially available alumina powder with a uniform morphology and mean size of 0.5 μm . All six Donors PBMNC produced significantly elevated levels of TNF- α when stimulated with 100 μm 3 of the alumina powder per cell. Volumetric concentrations of 10 and 1.0 μm 3 per cell failed to stimulate a significant response by the cells from any of the six donors. Three of the six Donors PBMNC secreted significantly elevated levels of TNF- α when stimulated with 100 μm 3 of the microseparation wear particles, whereas the other three failed to respond to the wear debris at this concentration. All of the Donors PBMNC produced significantly elevated levels of TNF- α when stimulated with 500 μm 3 of the microseparation wear particles per cell. Thus, a greater volume of the microseparation wear particles was required to activate the PBMNC than the alumina powder. This was probably due to the microseparation wear particles having fewer particles in the critical size range (0.1– 1 μm ) for macrophage activation compared to the alumina powder. It can be concluded that alumina ceramic wear particles generated under microseparation conditions are capable of inducing osteolytic cytokine production by human mononuclear phagocytes. However, the volumetric concentration of the particles needed to generate this response is extremely high and given the low wear rates ( <4 mm 3 per million cycles) of ceramic-on-ceramic bearings, even under severe microseparation conditions, it is unlikely that this concentration threshold will be achieved in vivo.