Low-Intensity Pulsed Ultrasound Increases Cellular Uptake of Superparamagnetic Iron Oxide Nanomaterial: Results from Human Osteosarcoma Cell Line U2OS

Purpose: To determine whether low-intensity pulsed ultrasound (LIPUS) is able to facilitate the uptake of a superparamagnetic iron oxide (SPIO) nanomaterial by cells that do not express high endocytosis capacity. Materials and Methods: The human osteosarcoma cell line U2OS and a silica-coated SPIO functionalized peripherally with amines groups (overall diameter 8 nm) were used in this study. Adherent U2OS cells were labeled with SPIO by incubating with culture media containing the SPIO at 4.5 mu g[Fe]/mL. LIPUS with the same parameters as those used in clinical application to accelerate bone fracture healing (1.5 MHz, duty cycle 1:4, spatial-average temporal-average intensity 30 mW/cm(2)) was applied to the cells at the beginning of the labeling process for 0, 0.5. 1, or 3 hours. The total incubation time with SPIO was 12 hours. SPIO labeling efficiency was evaluated with Prussian blue staining and a blueness measurement method, and magnetic resonance imaging (MRI) of cell pellets via measuring areas of SPIO-induced signal void. Results: Both Prussian blue staining and in vitro MRI demonstrated that LIPUS application increased the SPIO nanomaterial labeling efficiency for U2OS cells in an exposure-duration-dependent manner. Conclusion: This study is a proof of concept that LIPUS can facilitate the cellular take-up of SPIO nanomaterial.