Three-dimensional cell culture systems as an in vitro platform for cancer and stem cell modeling

Figure 1 Schematic diagrams of the traditional two-dimensional monolayer cell culture and three-dimensional cell culture systems. A: Traditional two-dimensional monolayer cell culture; B: Three-dimensional cell culture systems; C: The structure of three-dimensional spheroid with different zones of cells with the models of oxygenation, nutrition, and CO₂ removal. Three-dimensional spheroid from inside to outside. The regions are necrotic zone (innermost), quiescent viable cell zone (middle), and proliferating zone (outermost).