Bioluminescent bacterial assays of implant corrosion product toxicity

The toxicities of simulated corrosion product mixtures of common orthopaedic alloys (Ti-6Al-4V, Co-Cr-Mo, and 316L) have been determined using the Microtox(R) bioassay. Toxicities of the individual alloying elements were first determined, and a mathematical model was developed to predict the toxicities of simulated corrosion products containing metal ions mixed in proportion to alloy composition, The actual toxicities were then measured using Microtox(R) and compared to the predicted toxicities in order that mixture behavior could be classified as additive, synergistic, or antagonistic. Since the relation of such tests to implant corrosion processes can be confounded by the occurrence of selective leaching, the predicted and actual toxicities of simulated corrosion products mixed according to proportions characteristic of selective leaching were determined. Cr, Ni, and Co were seen to be the most toxic individual alloying elements. Co-Cr-Mo was found to be the most toxic mixture of both those combined according to alloy composition and those combined according to selective leaching data, The Ti-6Al-4V mixtures were found to behave synergistically while the Co-Cr-Mo and 316L mixtures behaved antagonistically. These experiments demonstrate the utility of employing bioluminescent bacterial assays to investigate biocompatibility of implant materials