Toxicity of TiO2 nanoparticles (NPs) depends on characteristics of NPs such as nanoparticle shape, size, crystal structure, zeta potential, aggregation and agglomeration tendency, surface characteristics and coatings. However, their effect on toxicity remains unclear due to ambiguous results from different studies. The presented study examined the cytotoxic effect of ten diverse TiO2 NPs without photoactivation in human monocytic cell lines THP-1 differentiated into macrophage-like cells.A set of NPs consists of 5 variants of anatase and 5 variants of rutile nanoparticles differing in their diameter (from 3 to 165 nm). TiO2 samples were characterized in the powder form and dispersed in water and cell culture media. Three cytotoxicity assays were used: MTS, WST-1, and LDH. For all nanomaterials, three independent repetitions were carried out.Overall, cytotoxicity of all NPs was low even at the highest concentration of 256 µg/ml. The viability of cells did not decrease below 60% for WST-1 and MTS assays and 80% for the LDH assay. Besides concentration, crystalline size was identified as the most important cytotoxic factor. Clear nonlinear relationship between crystalline size and cytotoxicity was detected; higher toxicity induced NPs within the size range 20-60 nm. Increased cytotoxicity in given diameter size range would give an answer to inconsistent findings at size and cytotoxicity relationship.Keywords: TiO2, nanoparticles, macrophages, cytotoxicity, nanoparticle size
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