Our previous research showed that material surface charges at the interface, deduced from the \(\zeta\)-potential, possess a remarkable influence on diverse cellular functions, among them spreading [33], morphology, membrane integrity, proliferation, and intracellular calcium signaling [34]. According to the cell behavior, three categories of \(\zeta\)-potential were described: negative, moderately positive, and highly positive [34]. Positive charges at the material surface provide unique cues that initiate an intensive cell response. However, it was revealed that these cell reactions occur in a so-called dose-dependent manner. Cells favor only a certain range of moderately positive material surface charges and cannot tolerate high charges around +50 mV [34]. Figure 1 summarizes our current knowledge on cell spreading and cell shape as a response to material surface charge. Here, the cellular behavior on 12 differently charged surfaces is averaged and depicted (see further information in the Supplementary Material for all layers used). For the first cell encounter, electrostatic forces between the material surface and the cells play an important role. These forces originate from the negatively charged pericellular hyaluron coat around the osteoblasts, resulting in an overall net negative cell charge of \(-15.6\) mV [15]. Therefore, rapid cell attachment can be mediated especially by a positive material surface charge. Our results show a strong correlation between the material surface charge and cell spreading within 24 h, which is optimal between +1 and +10 mV (\(\zeta\)-potential). As the cell physiology is adversely affected on highly positively charged material surfaces [33; 34], cells exhibit on these surfaces also an impaired cell spreading course and retain their circular morphology. In this context, it is of interest to take a closer look at the cell shape. For this, the present study aimed to focus on the actin cytoskeleton as a stabilizer of the cell shape. Actin organization is essential for adhesion, cell contact formation and migration, as well as for directed cytoplasmic trafficking, such as signal transduction [35; 36; 37]. In particular, it is reported that the arrangement of the actin cytoskeleton is pivotal for cellular spreading as for the cell length control [38; 39]. Several studies highlight a surface topography-dependent shift in actin filament formation in osteoblasts [40; 41]. Hence, micropillar structures induce actin formation on the plateau of the pillars in a mimicry fashion. Is the charge of a surface also capable of affecting the actin arrangement and thus cell shape? To answer this question, we used three differently charged titanium surfaces, one from each \(\zeta\)-potential category based on [PERSON] et al. [34]. We quantified the actin filament number and length of MG-63 osteoblasts after growing 1 and 24 h on the substrates in an automated approach using our FilaQuant software, which is freely available (version 2011, University of Rostock, Institute of Mathematics, Mathematical Optimization, Rostock, Germany) [40]. Additionally, we wanted to gain a deeper understanding of the influence that surface charges exert on the cells' morphology. To this end, we measured the cell edge height via scanning ion conductance microscopy (SICM) and developed a mathematical vertex model to explain how actin rearrangement, caused by different surface charges, influences the cell shape. Figure 1: Summary of our current knowledge of \(\zeta\)-potential-dependent change in cell area and shape over time on functionalized Ti surfaces. Our previous research showed that surface charges at the interface deduced from the \(\zeta\)-potential possess a remarkable influence on cellular spreading [33] and morphology [34]. Overall, 12 different top layers of the categories of amino polymers, extracellular matrix proteins/peptide motifs, polyelectrolyte multilayers, and metals were deposited on Ti substrates and analyzed corresponding to surface charge and spreading behavior.