Influence of shape, adhesion and simulated lung mechanics on amorphous silica nanoparticle toxicity

Prevailing theories suggest that acicular, or fiber-like, particles induce enhanced toxicity over isotropic materials through hindrance of phagocyte-mediated clearance mechanisms and through the aggravation of proximal cells via mechanical interactions. Currently, the degree to which either of these mechanisms operates is not well understood. To gain a more fundamental understanding of acicular particle toxicity, we have synthesized submicron and nanoscale amorphous silica spheres and rods as model materials for shape-driven toxicological experimentation. To accentuate contributions from mechanical damage in vitro, exposure studies were performed in the presence and absence of simulated lung mechanics. To promote and mitigate cell-particle contact-mediated mechanical interactions, the adhesion of the particles to the cell membrane was respectively modified by the physisorption of fibronectin and the chemisorption of polyethylene glycol to the silica particle surface. Lactic acid dehydrogenase (LDH) and interleukin (IL)-8 release were used as endpoints for cytotoxicity and inflammation, respectively. The results indicate that particle exposures in the presence of physiological stretch induce increased LDH release and IL-8 expression regardless of shape. Moreover, it is evident that shape-induced aggregation may play a significant role in mitigating particle clearance pathways.