Direct Piercing of Ag Nanowires into Living Macrophages: Implications for Nanotoxicity

High aspect ratio nanomaterials, such as nanowires, are known to exhibit unique properties and have a wide range of applications owing to their geometry and small diameters. Prior work has indicated that silver nanowires (AgNWs, more than 15 mu m long) could lead to frustrated phagocytosis in lung macrophages, whose characteristics differ from those among the micro and macro-wires with the same chemical compositions. This work unveils whether other pathways occur upon exposure of living cells to AgNWs. Using high-resolution laser scanning confocal microscopy, the precise locations of AgNWs with respect to cells can be visualized upon exposure of a macrophage cell line, NR8383 cells, to AgNWs. Cellular membranes and intracellular components, such as actin, are also tagged to allow direct and detailed visualization of cellular components with respect to AgNWs during exposures. Direct piercing of AgNWs into cells was captured, where a portion of wires was poked into a cell without significant structural perturbation of its local surroundings. While AgNWs were predicted to be able to poke through the cell membrane from computation studies, direct piercing has not been experimentally observed until the present work. Other scenarios include frustrated phagocytosis and failed attempts by AgNWs to pierce due to the membrane wrapping of the invading portion of the AgNWs resisting their entry. The comprehensive studies of AgNW-cell interactions are of fundamental importance in understanding nanocytotoxicity and nanotoxicity. The knowledge gained shall facilitate the development of preventive measures for the potential adversarial impacts of nanowires on the environment and human health, thus enabling broader applications of nanomaterials.