In-Vitro Dosimetry Model for Toxicity Ranking of Metal Oxide Nanoparticles

There is a debate in the nanosafety community regarding whether cellular toxicity of engineered nanoparticles (NPs) should be ranked on the basis of delivered dose (i.e., NP mass settled per suspension volume) or administered dose (i.e., initial NP mass concentration). Calculation of delivered dose with sufficient confidence for in-vitro toxicity ranking of NPs requires quantification of NP sedimentation considering fundamental suspension properties of NPs in cell culture media. Accordingly, we developed a first principles “particles in a box” sedimentation model, which accounts for the particle size distribution, fractal dimension and permeability of agglomerated NPs. The developed sedimentation model was evaluated against both external and our own experimental sedimentation data for metal-oxide NPs, demonstrating significantly improved estimates of settled NP mass over other simplified sedimentation calculations with the assumption of impermeable and/or monodispersed NP agglomerates. The model was then applied to calculate the delivered NP doses in different cell culture media for the dose-response analyses of seven metal oxide NPs that were identified toxic from a library of twenty-four NPs in our previous studies. Hierarchical hazard ranking of the identified seven toxic NPs, according to the their EC₅₀, was not measurably different when determined on the basis of either delivered or administered doses. In contrast, simplified sedimentation calculations based on the assumption of monodispersed impermeable NP agglomerates led to significant underestimation of the settled NPs mass and thus distorted toxicity ranking.