Fig. 5. Drug loaded nanotubes reduce the viability of U-87 human glioblastoma cells. Cell viability analysis (PrestoBlue assay) after one day (a) or three days (b) of incubation with PEG or MWCNTs showing that both nanotube types reduce glioblastoma viability when loaded with doxorubicin (n = 4, error bars represent ± standard deviation, positive control = 4 μg mL⁻¹ doxorubicin, * represents statistical significant difference to empty PEG nanotubes (two way ANOVA with Tukey's multiple comparison test (P ≤ 0.05))). (c) Brightfield images taken after three days of culture showing clear association of the MWCNTs with cells whereas PEG nanotubes spread more evenly across the well (nanotube concentration = 15 μg mL⁻¹, scale bars represent 100 μm, images of the positive control are in Fig. S7†).