# Morphological Dynamics of Leukemia Cells on TiO\({}_{2}\) Nanoparticle Coatings Studied by AFM
## 3 Results and Discussion
### Time-Dependent Morphology of Leukemia Cells on TiO\({}_{2}\)-m Coatings
(**a**) Two-dimensional and (**b**) three-dimensional topography images. The green mask in (**b**) indicates the expanse of the cell membrane. (**c**) Height profile taken along the dashed line in (**a**), revealing that the cell adopts the underlying surface topography. (**d**) Three-dimensional representation of the zoomed area indicated by the dashed square in (**a**). (**e**) Height distribution function calculated for the zoomed image shown in (**d**). The height \(z=0\) nm corresponds to the lowest height value within the zoomed region in (**d**). Figure 4a,b shows a representative leukemia cell after 40 min of contact with the TiO\({}_{2}\)-m coating. Here, some pseudopodia (white arrows in Figure 4a) and protuberances (red arrow in Figure 4b) in the cell membrane can be identified. The latter is probably the result of the endocytosis of immobile TiO\({}_{2}\)-m nanoparticle aggregates protruding from the coating surface. The red arrow in Figure 4b points to one of the membrane protuberances, which is located inside the cell close to the membrane boundary and has a height of close to 1.5 \(\upmu\)m (red arrow in Figure 4c). This observation is a further indication that the cell internalizes immobile TiO\({}_{2}\)-m particle aggregates, consistent with previously reported results [15]. Aside from these protrusions, the membrane morphology recorded in the center of the cell has become rather homogeneous but still exhibits some corrugations and granular features, as can be seen in Figure 4d. Consequently, the height distribution in Figure 4e has further decreased in width with all height values now lying below 600 nm. Finally, after 60 min of contact, the cell shown in Figure 5a,b has reverted to a mostly ellipsoidal shape but still exhibits membrane protrusions (indicated by the red arrow in Figure 5b). Notably, there are almost no more TiO\({}_{2}\)-m nanoparticle aggregates visible right at the membrane boundary but either clearly outside or inside the cell, with the latter being another indicator of TiO\({}_{2}\)-m getting internalized into the cytoplasm by membrane structures, such as pseudopods, which envelop the surrounding aggregates completely. Regarding the membrane morphology in the center of the cell, a slightly corrugated topography with a homogeneous distribution of surface features can be seen in Figure 5d. This is also reflected in the height distribution function shown in Figure 5e, which exhibits a small width but has a visible shoulder at higher \(z\) values, corresponding to the few yet pronounced membrane protrusions. Figure 3: Representative AFM image of an acute lymphoblastic leukemia cell cultured on the TiO\({}_{2}\)-m coating for 20 min. (**a**) Two-dimensional and (**b**) three-dimensional topography images, showing cell contraction without defined anchor points. (**c**) Height profile taken along the dashed line in (**a**). The red arrows indicate some TiO\({}_{2}\)-m nanoparticle aggregates close to the membrane boundary. (**d**) Three-dimensional representation of the zoomed area indicated by the dashed square in (**a**). (**e**) Height distribution function calculated for the zoomed image shown in (**d**). The height \(z=0\) nm corresponds to the lowest height value within the zoomed region in (**d**). Figure 4: Representative AFM image of an acute lymphoblastic leukemia cell cultured on the TiO\({}_{2}\)-m coating for 40 min. (**a**) Two-dimensional and (**b**) three-dimensional topography images. (**c**) Height profile taken along the dashed line in (**a**). The white arrows in (**a**) indicate pseudopodia formation. Protrusions inside the cell can be identified close to the membrane boundary (red arrows in (**b**,**c**)), which may result from internalization of TiO\({}_{2}\)-m nanoparticle aggregates. (**d**) Three-dimensional representation of the zoomed area indicated by the dashed square in (**a**). (**e**) Height distribution function calculated for the zoomed image shown in (**d**).