Cell-Material Interaction - Spreading Course Correlates with Surface Charge Cell-Material Interaction - Spreading Course correlates with

To design appropriate materials for tissue engineering, a profound understanding of the cell-material interaction is essential. We are of the opinion that the zeta (ζ) potential has a decisive role in the cell behaviour, outshining wettability. Here we present a comparative analysis of the MG-63 osteoblastic cell spreading behaviour on negatively and positively charged surfaces in the hydrophilic range. The results indicate a correlation of the cells’ spreading area with the surface charge. Thus, the ζ-potential should be considered as a key parameter for cell interactions at the biomaterial interface.


Introduction
Materials that are coated with polymers are currently being widely used in biomedical applications. This involves a high degree of interaction at the cell-material interface. Depending on time and distance of cells to the material surface the four initial adhesion phases were described as surface recognition, early attachment stage, intermediate attachment or membrane adhesion, and late adhesion or spreading phase [1], profoundly influencing the further cell viability, growth and cell function. To select appropriate materials for tissue engineering, a sound understanding of this cellmaterial interaction is indispensable [2]. Considering the biological relevance of these interactions, numerous research groups are focusing on this issue. However, as Vendre et al. [1] stated, the "cellmaterial communication code" is still not fully deciphered to define precise principles that govern the cell-material crosstalk.
Although a variety of material surface properties (chemical, topographical or mechanical [1]) have been reported to contribute to the nature of cell-material interactions, no general rules could yet be developed allowing predictions of cell attachment, spreading, or growth [3]. Considering for example the wettability of a surface, several studies indicate that hydrophilic surfaces promote the cell adhesion [4], while hydrophobic surfaces often inhibit the crosstalk between cells and materials [5]. However, there are also exceptions to the rules [6].
Accordingly, to our opinion, Spriano et al. [7] claimed that systematic studies of diverse materials in the same investigative conditions are still lacking in literature. We assume that not the wettability but the surface charge via ζ-potential strongly affects the cellular behaviour at the interface. Here, we focused on the

Abstract
To design appropriate materials for tissue engineering, a profound understanding of the cell-material interaction is essential. We are of the opinion that the zeta (ζ) potential has a decisive role in the cell behaviour, outshining wettability. Here we present a comparative analysis of the MG-63 osteoblastic cell spreading behaviour on negatively and positively charged surfaces in the hydrophilic range. The results indicate a correlation of the cells' spreading area with the surface charge. Thus, the ζ-potential should be considered as a key parameter for cell interactions at the biomaterial interface.

Cell membranes were stained with the PKH-26 General Cell
Linker Kit (Sigma-Aldrich Chemie, Taufkirchen, Germany) for 5min at 37°C in suspension [14]. 50,000 vital stained cells/cm² were seeded onto the substrates and cultivated for 1, 3 and 12h. Cell areas

Copy@ Barbara Nebe
In our experiments the wettability seemed not to play a decisive role for cell spreading. PSS surfaces were hydrophilic with a WCA similar to PPAAm (68°) [8], but negatively charged as the Ti surface (-82mV [16]). However, the hydrophilic PPAAm with a positive ζ-potential of +8mV [16] displayed the highest initial cell area ( Figure 1 Our positively charged PDADMA surfaces were hydrophilic with WCA values of ~ 40°, but cells ignored this hydrophilic environment and exhibited an impaired spreading behaviour after an initial tendency to spread better than Ti. A reduction of the cell area occurred, demonstrating the additional strong influence of a very high positive ζ-potential with ~ +50mV for PDADMA on the spreading behaviour. Interestingly, the cells seem to favour only a certain spectrum of ζ-potentials, being neither in the negative nor in the highly positive range -independent of the hydrophilicity.

Conclusion
The ζ-potential appears to be of great importance for the cellular spreading as indicator of the cell-material interaction and should be considered as a key parameter when designing and investigating new materials for medical applications.