Differential cytotoxicity exhibited by silica nanowires and nanoparticles

Silica nanowires are one-dimensional nanomaterials that are being developed for use in biological systems. Unfortunately, little is known regarding the cytotoxic potential of this type of nanomaterial. Here, using two different human epithelial cell lines we have examined the cytotoxicity of silica nanowires over a broad concentration range. The results indicate that silica nanowires are nontoxic at concentrations below 190 µg/ml but exhibit considerable cytotoxicity at higher concentrations. Examination of the mechanisms responsible for nanowire-induced cytotoxicity indicates that apoptotic pathways are not activated. Instead, cytotoxicity appears to be primarily due to increased necrosis in cells exposed to high concentrations of nanowires. In contrast to what was seen with silica nanowires, analysis of silica nanoparticles revealed very little cytotoxicity even at the highest concentrations tested. These results indicate that structural differences between silica nanomaterials can have dramatic effects on interaction of these nanomaterials with cells.