Biocorrosion and uptake of titanium by human osteoclasts

All metals in contact with a biological system undergo corrosion through an electrochemical redox reaction. This study investigated whether human osteoclasts (OC) are able to grow on titanium and aluminum, and directly corrode the metals leading to the release of corresponding metal ions, which are believed to cause inflammatory reactions and activate osteoclastic differentiation. Scanning electron microscopy analysis demonstrated long-term viable OC cultures on the surface of titanium and aluminum foils. Atomic emission spectrometry investigations showed significantly increased levels of aluminum in the supernatant of OC cultured on aluminum; however, all measurements in the supernatants of cell cultures on titanium were below detection limits. Despite this, confocal microscopy analysis with Newport Green DCF diacetate ester staining depicted intense fluorescence throughout the cytoplasm and nucleolus of OC cultured on titanium foils. Comparable fluorescence intensities were not observed in monocytes and control cells cultured on glass. The present study demonstrated that human osteoclast precursors are able to grow and differentiate toward mature OC on titanium and aluminum. Furthermore, it established that the mature cells are able to directly corrode the metal surface and take up corresponding metal ions, which subsequently may be released and thereby induce the formation of osteolytic lesions in the periprosthetic bone, contributing to the loosening of the implant.