Automatic Actin Filament Quantification and Cell Shape Modeling of Osteoblasts on Charged Ti Surfaces

Featured Application In medical implantology the human biosystem interacts with the artificial biomaterial. For permanent implants, e.g. titanium, it is of importance that cells immediately accept and occupy the material surface. To get deeper insights into molecular mechanisms of the cell behavior at the interface is of great importance. The future aim is to find an optimum in material surface design for tissue-integrated, long living implants. Surface charges at the cell-biomaterial interface are known to determine cellular functions. Previous findings on cell signaling indicate that osteoblastic cells favor certain moderately positive surface charges, whereas highly positive charges are not tolerated. In this study, we aimed to gain deeper insights into the influence exerted by surface charges on the actin cytoskeleton and the cell shape. We analyzed surfaces with a negative, moderately positive, and highly positive zeta (zeta) potential: titanium (Ti), Ti with plasma polymerized allylamine (PPAAm), and Ti with a polydiallyldimethylammonium chloride (PDADMA) multilayer, respectively. We used the software FilaQuant for automatic actin filament quantification of osteoblastic MG-63s, analyzed the cell edge height with scanning ion conductance microscopy (SICM), and described the cellular shape via a mathematical vertex model. A significant enhancement of actin filament formation was achieved on moderately positive (+7 mV) compared with negative zeta-potentials (-87 mV). A hampered cell spreading was reflected in a diminished actin filament number and length on highly positively charged surfaces (+50 mV). Mathematical simulations suggested that in these cells, cortical tension forces dominate the cell-substrate adhesion forces. Our findings present new insights into the impact of surface charges on the overall cell shape and even intracellular structures.

Automated summary

Through studying the impact of different surface charges on osteoblastic cell behavior, it was found that moderately positive surface charges can enhance actin filament formation, while highly positive surface charges can hinder cell spreading, resulting in a decrease in actin filament number and length. Our findings provide new insights into the influence of surface charges on overall cell shape and intracellular structures.