Biomaterial surfaces for bone implants are modified to achieve a faster attachment of osteoblasts and thus a better osseointegration and regeneration of the surrounding tissue. In this, the material´s physico-chemical properties play an essential role as they are known to affect the cell physiology at the interface . It has been found out that a positively charged, amino-group containing titanium (Ti) surface can amplify osteoblastic cell functions [2-4] such as the calcium ion (Ca2+) mobilization . We hypothesize that surface charges play a crucial role in the material-cell interaction.To confirm this, we currently investigate the intracellular Ca2+ dynamic on Ti modifications with different surface charges.
We chemically modify plane silicon-Ti arrays (10x10 mm, ZfM, TU Chemnitz) by (i) amino functionalization via coating with the monomer allylamine by a pulsed plasma polymerization process (PPAAm) , (ii) polyelectrolyte multilayers (terminated with polydimethyldiallylammonium chloride using layer-by-layer assembly  and (iii) coatings with collagen-type I, Matrigel (basement membrane-like matrix) and the integrin adhesion peptide sequence Arg-Gly-Asp (RGD). We determine the surface charge by zeta potential measurements and the wettability by water contact angle measurements . To evaluate the surface property-dependent mobilization of intracellular Ca2+, human MG-63 osteoblasts (ATCC) are stained with the calcium dye Fluo 3-acetoxymethyl ester and stimulated with adenosine 50-triphosphate to induce an immediate Ca2+ signal .
Our data have shown, especially for the positively charged PPAAm surface (zetapotential:+ 8.6 mV), a high increase of intracellular Ca2+ ions following an ATP stimulation (mean fluorescence intensity (MFI) level at 188–480 s: 89.1±1.9, mean±sem) compared to cells on uncoated Ti (MFI level at 188–480 s: 51.9±0.6, mean±sem) (n=3) .
Hence, we assume that the influence of a positive zeta potential on the cellular behavior dominates other surface properties like wettability. However, it is important to extend these studies to investigate which properties are favored by osteoblastic cells.
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