The mechanical properties of a cell, as determined by its actin cytoskeleton, are important for nanoneedle insertion into a living cell.

Previously, we reported that a nanoneedle of 200 nm diameter manipulated by an atomic force microscope apparatus could be inserted into a living cell. The insertion probabilities varied according to cell type. However, the nanoneedle was never successfully inserted into artificial liposomes. In the current study, we found that the stress fibers and actin filaments comprising the plasmalemmal undercoat are important, determining factors as to whether a nanoneedle can be successfully inserted into a cell. Depolymerization of microtubules increased both the number of stress fibers and insertion efficiency in NRK cells. These results indicate that the insertion efficiency of a nanoneedle (200 nm in diameter) into a cell with a smaller actin meshwork in its plasmalemmal undercoat is enhanced and the formation of stress fibers obviously contributes to this incremental enhancement. These facts are not only important as technical information to improve the efficiency of cell manipulation but also as observations of the mechanical properties of the native cell cortex.