NiNPs were purchased from Sun Innovations (Fremont, CA) and were characterized by the manufacturer as a sphere-shaped nanoparticle with a diameter of ~20 nm, metal purity of 99.9% and surface area of 40 to 60 m2/g. Moreover, these NiNPs have been previously described as insoluble in water and possess an oxidation state of zero (Glista-Baker et al., 2014 (link)). A more detailed independent characterization of NiNP size carried out in our laboratory using TEM showed an average mean (±SEM) particle diameter of 25.43 ±11.62 nm with agglomerates ranging from 250 – 600 nm when suspended in 0.1% pluronic F-68 (Sigma, St. Louis, MO) diluted in Gibco’s phosphate-buffered saline (DPBS) (Glista-Baker et al., 2012 (link)). For pulmonary exposure of mice, NiNPs suspended in 0.1% pluronic/DPBS were sonicated in a cuphorn sonicator (Qsonica, Newton, CT) for 2 minutes and vortexed immediately before dosing as described below. A representative TEM image of the NiNPs is shown in Fig. 1A.