Abstract
Single cell force microscopy was used to investigate the maximum detachment force (MDF) of primary neuronal mouse cells (PNCs), osteoblastic cells (MC3T3), and prokaryotic cells (Staphylococcus capitis subsp. capitis) from different surfaces after contact times of 1 to 5 seconds. Positively charged silicon nitride surfaces were coated with positively charged polyethyleneimine (PEI) or poly-D-lysine. Laminin was used as the second coating. PEI induced MDFs of the order of 5 to 20 nN, slightly higher than silicon nitride did. Lower MDFs (1 to 5 nN) were detected on PEI/laminin with the lowest on PDL/laminin. To abstract from the individual cell properties, such as size, and to obtain cell type-specific MDFs, the MDFs of each cell on the different coatings were normalized to the silicon nitride reference for the longest contact time. The differences in MDF between prokaryotic and eukaryotic cells were generally of similar dimensions, except on PDL/laminin, which discriminated against the prokaryotic cells. We explain the lower MDFs on laminin by the spatial prevention of the electrostatic cell adhesion to the underlying polymers. However, PEI can form long flexible loops protruding from the surface-bound layer that may span the laminin layer and easily bind to cellular surfaces and the small prokaryotic cells. This was reflected in increased MDFs after two-second contact times on silicon nitride, whereas the two-second values were already observed after one second on PEI or PEI/laminin. We assume that the electrostatic charge interaction with the PEI loops is more important for the initial adhesion of the smaller prokaryotic cells than for eukaryotic cells.
Highlights
The first quantitative studies on cell adhesion were performed with a simple wash assay
After calibrating the coated cantilevers, single primary neuronal mouse cells (PNCs), MC3T3, or Scc cells were attached to the front of the cantilevers
Our results are in line with cell adhesion models in which the initial phase of adhesion is dominated by the electrostatic interaction between negatively charged cell membranes and positively charged surfaces, without specific adhesion molecules playing a role
Summary
The first quantitative studies on cell adhesion were performed with a simple wash assay. The samples were rinsed after different cell attachment periods. The remaining cells were stained and counted [1]. For the continuous registration of cell adhesion quartz crystal microbalances and thickness shear mode sensors have been developed. They permit statements to be made on the kinetics of cell adhesion using mass and complex elasticity effects as well as viscoelastic effects at the cellular interfaces to the sensor surface [2]. In interdigitated electrode structures (IDES), cell adhesion is registered via the electric impedance, which changes when the number of cells or their degree of spreading alters the electrochemically effective surface of the IDES [3–5]
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