The effect of cell density, proximity, and time on the cytotoxicity of magnesium and galvanically coupled magnesium–titanium particles in vitro

Abstract Magnesium (Mg) and galvanically coupled magnesium–titanium (Mg–Ti) particles in vitro have been reported previously to kill cells in a dosage‐dependent manner. Mg–Ti particles kill cells more effectively than Mg alone, due to the galvanic effect of Mg and Ti. This study further investigated the in vitro cytotoxicity of Mg and Mg–Ti in terms of particle concentration, cell density, time, and proximity. Cell density has an effect on cell viability only at low particle concentrations (below 250 µg/mL), where cell viability dropped only for lower cell densities (5000–10,000 cells/cm²) and not for higher cell densities (20,000–30,000 cells/cm²), showing that the particles cannot kill if there are more cells present. Cytotoxicity of Mg and Mg–Ti particles is quick and temporary, where the particles kill cells only during particle corrosion (first 24 h). Depending on the percentage of surviving cells, particle concentrations, and ongoing corrosion activity, the remaining live cells either proliferated and recovered, or just remained viable and quiescent. The particle killing is also proximity‐dependent, where cell viability was significantly higher for cells far away from the particles (greater than ∼1 mm) compared to those close to the particles (less than ∼1 mm). Although the increase of pH does affect cell viability negatively, it is not the sole killing factor since cell viability is significantly dependent on particle type and proximity but not pH. Mg and Mg–Ti particles used in this study are large enough to prevent direct cell phagocytosis so that the cell killing effect may be attributed to solely electrochemical reactions. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1428–1439, 2018.