The effects of sedimentation and dissolution on the cytotoxicity of Ag nanoparticles

Nanoparticles (NPs) are being employed for various industrial purposes with increasing frequency, yet the adverse health effects associated with the prolonged exposure of humans and the environment to NPs has not been well-established. Particularly, the effects of the extrinsic (or dynamic) physicochemical properties of NPs in aqueous cell culture media (e.g., hydrodynamic size, aggregation, agglomeration, sedimentation, and dissolution of nanoparticles) on the cytotoxicities of the NPs are barely understood. In this study, to investigate the effects of two important extrinsic properties of Ag NPs, namely the sedimentation and dissolution of Ag NPs, we performed MTT cell viability tests for HeLa cells exposed to Ag NPs with varying extrinsic properties. Ag NPs with different hydrodynamic sizes, sedimentation rates, and dissolution rates were prepared via exposure to NaCl and FBS. Sedimentation of aggregated/agglomerated Ag NPs was found to contribute more significantly to the cytotoxicity of Ag NPs during early periods of exposure, whereas the cytotoxicity was more greatly enhanced later during the exposure period due to the increase in silver ions. Therefore, it is offered that any assessment of NP cytotoxicity should consider the extrinsic properties of NPs, and their time-dependent properties, because the dominant processes affecting NP cytotoxicity may change over time and lead to a misunderstanding or poor prediction of NP cytotoxicity.