Neurons Internalize Functionalized Micron-Sized Silicon Dioxide Microspheres

Abstract

Microparticles have potential as neuron-specific delivery platforms and devices with many applications in neuroscience, pharmacology and biomedicine. To date, most literature suggests that neurons are not phagocytic cells capable of internalizing microparticles larger than 0.5 microns. We report that neurons transport fluorescently labeled silica microspheres with diameters of 1–2 microns into neurons in vitro and in rat brain without having overt effects on cell viability. Using flow cytometry, fluorescence activated cell sorting (FACS), and confocal and electron microscopy, we first found that SH-SY5Y human neuroblastoma cells internalized 1-micron silicon microspheres with surface charges of −70 mV (hydroxyl and carboxyl), −30 mV (amino) and +40 mV (ammonio). Uptake was rapid, within 2–4 hours, and did not affect cell viability 48 hours later. Flow cytometry assays indicate that SH-SY5Y cells internalize 1 and 1.5-micron microspheres at the same rate over a 24-hour incubation period. Electron microscopy confirms that SH-SY5Y cells internalize 1, 1.5 and 2-micron microspheres. Confocal microscopy demonstrated that primary cortical neurons (PCNs) also internalized 1, 1.5 and 2-micron amino microspheres within 4 hours. Finally, we injected 1-micron amino microspheres into rat striatum and found microspheres inside neurons. Overall, neurons can internalize microspheres up to 2 microns in diameter with a range of surface chemical groups and charges. These findings allow a host of neuroscience and neuroengineering applications including intracellular microdevices within neurons.

Induction of Oxidative Stress and Cell Death in Neural Cells by Silica Nanoparticles

“…Depending on the cell-surface charge and hydrophobicity, surface functional groups can affect particle attachment and internalization into cells. 37 Our results may indicate that interactions between the particle surface and cell membrane are necessary, but not sufficient for ROS production and cytotoxicity.…”

“…Furthermore, our data indicated that surface carboxylation and BSA coating decreased cytotoxicity without affecting attachment to the cell surface (Figures C and S9). Depending on the cell-surface charge and hydrophobicity, surface functional groups can affect particle attachment and internalization into cells . Our results may indicate that interactions between the particle surface and cell membrane are necessary, but not sufficient for ROS production and cytotoxicity.…”