Influence of hydroxyapatite particle characteristics on the [K]/[Na] ratio: a human monocytes in vitro study

Research in bone substitutes has shown that calcium phosphates, particularly hydroxyapatite, are well adapted to use in prosthetics. Due to its characteristics that are close to those of bone, hydroxyapatite is used as a coating or bone defect filler. At long term, one of causes of prosthetic failure is bone lysis followed by aseptic loosening. Particles released at the implantation site may be one cause of this phenomenon. It is important to address the loosening problem because longer implantation times are now required due to the increasing life expectancy of the population. To understand these effects and to optimise implantation of hydroxyapatite based prostesis, simulated wear debris produced by hydroxyapatite powders of various shapes, sizes and sintering temperatures were introduced into cultured human monocytes. Monocytes were chosen because they are among the first cells to colonise, the inflammatory site. Cellular alteration caused by the particles is evaluated by measuring intracellular potassium to sodium ratios. Elemental intracellular ionic concentrations were measured in cells close to the physiological state by using cryomethods combined with electron probe microanalysis. This study demonstrated that various powder characteristics influence cellular viability. It was found that needle shaped particles are the most toxic whereas powders with particle size greater than 30 mum are the least toxic. (C) 2003 Elsevier B.V. All rights reserved.