Assessment of implant degradation products using a bioluminescent bacterial toxicity assay
Description
Metallic implanted devices have proven to be an effective means to replace and/or restore function to defective or damaged tissue in the human body such as bone because of their excellent mechanical properties. However, once implanted, orthopedic and dental alloys degrade over time, releasing ions in vivo due to a remarkably aggressive biological environment characterized by extensive chemical activity and highly variable mechanical stresses. This can lead to two harmful consequences: a weakening of the material and host reactions associated with the released degradation products. Thus, the success of metallic implants is heavily dependent on the biocompatibility of released degradation products In this study, a combination of concentration measurement methods and a bacterial bioluminescence toxicity assay were used to provide insight into factors which can dramatically affect the biocompatibility of implanted materials in both orthopedic and dental applications. Initial work established that the Microtox bacterial bioluminescence toxicity assay produces results for simulated corrosion product mixtures consistent with well-known facts regarding biocompatibility and thus demonstrated efficacy of using Microtox as a tool for studying biocompatibility Application of this method, as well as concentration assessment techniques, to degradation products produced in vitro from common orthopedic and dental alloys has shown that corrosion product toxicity can be enhanced by both the release of specific chemical species from metallic materials and selective leaching of the more toxic ions. Also, the influence of saline and protein content on toxicity has been determined for representative environments of orthopedic and dental implants. In order to study synergistic and antagonistic interactions among released ions, a mathematical model has been developed which can predict the toxicity of a mixture behaving additively based on the Microtox data for its individual components. In addition, the interaction between the test bacterium and solid corrosion products has been investigated here and has raised further questions about how solid corrosion products behave in vivo Results of this investigation demonstrate that this methodology shows significant promise as a rapid, uncomplicated, and inexpensive means to preliminarily evaluate existing and newly developed biomaterials. Based on this work, the extension of Microtox to other biomedical applications appears promising