Substrate softness increases magnetic microdiscs-induced cytotoxicity.

Cytotoxicity of nanoparticles is primarily assessed on cells grown in plastic culture plates, a mechanical environment that is a million times stiffer than most of the human tissues. Here we question whether nanoparticles cytotoxicity is sensitive to the stiffness of the extracellular environment. To this end, we compare the metabolic activity, the proliferation and death rates, and the motility of a glioblastoma cancer cell line and a fibroblast cell line exposed to gold-coated Ni(80)Fe(20) microdiscs when grown on a glass substrate or on a soft substrate whose mechanical properties are close to physiology. Our main result is that cells grown on soft substrates take up more microdiscs which results in greater toxic effects, but also that toxicity at similar particle load is more pronounced on soft substrates especially at large concentration of nanoparticles. These results suggest that both microdiscs uptake and their intracellular processing differ between soft and rigid substrates.