The degree of functionalization affects in vitro cytotoxiciy of multiwalled carbon nanotubes (CNTs).

The cytotoxicity of multi-walled-CNTs, bare (MW) and differently
functionalized (MW-COOH, MW-NH2, hf-MW-NH2: highly
functionalized) was investigated in human astrocytoma D384
cells and lung carcinoma A549 cells using MTT-assay and
calcein/propidium-iodide (Ca/PI)-staining. CNTs were characterized
by TGA, FT-IR-spectroscopy, NC-AFM to assess thè degree of
purity and functionalization. Cells were exposed to CNTs (1-800 ug/ml) for 24-48 h in medium containing 10%FCS. In D384, MTT data revealed a strong dose-dependent cytotoxicity of pristine-MW, MW-COOH, MW-NH2. At both time-points, MTT metabolism was decreased by 75% at 100 ug/ml. Apparently, A549 cells were less markedly affected showing 50% viability at 10 ug/ml without further exacerbation at 100 ug/ml. At the higher doses, CNTs tended to aggregate forming bundles covering celi surface. In contrast with the MTT data, celi viability was not affected by CNTs at any concentration or exposure time in assays conducted on D384 or A549 cells using Ca/PI-staining. hf-MW water soluble CNTs, characterized by a liquid oil texture showed dose-dependent cytotoxicity in experiments by MTT. Cytotoxic effects were observed at concentrations >100 ug/ml at both
time-points in both celi types, with remarkable loss of celi viability
at 200 and 400 ug/ml (30-50%) that was further exacerbated (about
75%) at 800 ug/ml. Ca/PI-staining partially confirmed thè MTT data
as indicated by dose-dependent decrease (20-60%) in celi viability at 400 and 800 ug/ml. In summary, thè degree of functionalization impacts on CNT cytotoxicity, with dissimilar responses obtained by classica! in vitro tests possibly due to CNT interference with thè dye marker employed.