2.10. Determination of Cell Viability by MTT Assay

To get a first impression of how the cells interact with the developed formulation, a cytotoxicity test was performed. For this study, the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromid (MTT) assay was applied to colourimetrically determine the metabolic activity of the cells after incubation with the drug delivery system [56]. For this, the cell lines A549 and dTHP-1 described above were cultivated in 96-well plates with a concentration of 2 × 10⁴ cells per well. Subsequently, the cells were incubated for 4, 24 and 48 h with a particle concentration of 10, 50 and 100 µg/mL, respectively. To obtain these concentrations, the formulation was redispersed and diluted in RPMI 1640 + 10% FCS. After different periods of time, the supernatant was removed and replaced by MTT reagent incubating for 4 h. In a final step, the supernatant was removed and replaced with DMSO to dissolve the resulting formazan crystals. Cell viability was then determined by measuring the absorbance at 550 nm after 20 min using microplate spectrophotometer. Untreated cells grown in medium and Triton-X treated cells were used a negative and positive control, respectively.