The current study examined the in vitro pulmonary toxicity of titania nanotubes induced by the morphological and crystalline changes associated with post-synthetic thermal processing. A549 lung carcinoma cells were exposed to untreated, amorphous titania nanotubes and those treated at 200, 400, 600 and 800 °C, respectively. The cytotoxic action of the untreated and annealed TNTs was assessed using a battery of cytotoxicity assays that examined cellular metabolic and prolific activity and membrane integrity, in addition to the production of intracellular reactive oxygen species (ROS). Toxicity effects due to the period and dose of exposure were determined by exposing the A549 cell line to various TNT concentrations during different incubation periods. The untreated, amorphous and annealed TNTs elicited an overall dose-dependent increase in toxicity. As the annealing temperature increased from 200 to 800 °C, the nanotubular structure of TNTs fragmented and a crystalline phase composition developed. Crystalline nanoparticles also began to grow among the walls of disintegrated TNTs, and crystallite and particle size increased progressively. In comparison to amorphous TNTs, those of anatase, rutile or anatase/rutile mixed-phase composition exerted notable in vitro pulmonary toxicity. Rutile-rich TNTs possessing fragmented nanotube walls and larger particle size induced the greatest loss in viability of A549 lung carcinoma cells, presumably due to the domination of the rigid rutile crystal arrangement. The current study thus highlights the necessity for material manufacturers to consider the effects of post-synthetic processing on the possible toxicity profile of nanomaterial containing products and devices. [Figure not available: see fulltext.].
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