Fig. 7. Doxorubicin loaded nanotubes reduce the viability and size of human glioblastoma spheroids. The viability of glioblastoma spheroids formed from 1000 U-87 cells is reduced by doxorubicin and doxorubicin loaded nanotubes, as measured using the PrestoBlue assay after seven days (a) and 14 days (b). Doxorubicin loaded PEG nanotubes (15 μg mL⁻¹) mediated a reduction in viability which correlates with a reduction in the growth rate of the spheroid as determined by spheroid diameter (c), with 4 μg of doxorubicin causing complete dissociation of the spheroid after three days in culture (n = 6, error bars represent ± standard deviation, * represents statistical significant difference to control (one way ANOVA with Tukey's multiple comparison test (P ≤ 0.05))). After 14 days of culture, brightfield microscope images show untreated control spheroids (d) or spheroids cultured with doxorubicin loaded PEG nanotubes (15 μg mL⁻¹) (e) (scale bars represent 500 μm).