Evaluation of gold nanoparticles toxicity towards human endothelial cells under static and flow conditions

A new in vitro model system, adding advection and shear stress associated with a flowing medium, is proposed for the investigation of nanoparticles uptake and toxicity towards endothelial cells, since these processes are normally present when nanoparticles formulations are intravenously administered. In this model system, mechanical forces normally present in vivo, such as advection and shear stress were applied and carefully controlled by growing human umbilical vein endothelial cells inside a microfluidic device and continuously infusing gold nanoparticle (Au NPs) solution in the device. The tests performed in the microfluidic device were also run in multiwells, where no flow is present, so as to compare the two model systems and evaluate if gold nanoparticles toxicity differs under static and flow culture conditions. Full characterization of Au NPs in water and in culture medium was accomplished by standard methods. Two-photon fluorescence correlation spectroscopy was also employed to map the flow speed of Au NPs in the microfluidic device and characterize Au NPs before and after interactions with the cells. Au NPs uptake in both in vitro systems was investigated through electron and fluorescence microscopy and ICP-AES, and NPs toxicity measured through standard bio-analytical tests. Comparison between experiments run in multiwells and in microfluidic device plays a pivotal role for the investigation of nanoparticle-cell interaction and toxicity assessment: our work showed that administration of equal concentrations of Au NPs under flow conditions resulted in a reduced sedimentation of nanoparticle aggregates onto the cells and lower cytotoxicity with respect to experiments run in ordinary static conditions (multiwells).