Time-dependent adhesive interaction of osteoblastic cells with polished titanium alloyed implant surfaces.

Aim: Design optimization and surface modifications of orthopedic implants are focused on adhesive properties depending on specific applications. To obtain an in vitro understanding of the adhesion interaction of bone cells on implant surfaces the time-dependent adhesion behavior of osteoblastic cells was studied. Materials and Methods: MG-63 osteoblastic cells were seeded on discs of polished titanium alloy (Ti6Al4V) and allowed to adhere for various time periods (1 to 48 h). Using a spinning disc device and a confocal laser scanning microscope (LSM) the shear stress required to detach the bone cells from the substrate was determined. An approximation of the adhesion force was calculated from measurements of cell height and contact radius. Results: Shear stress ranged from 40.4 N/m(2) to 82.4 N/m(2) showing an increase in cell adhesion reaching a maximum after 6 h before decreasing significantly. Using the cell height and contact radii, measured for the various time periods, the lowest adhesion force of 232 nN was approximated after 1 h cell adhesion and analogous to the adhesion strength measurements, the highest of 664 nN after 6 h. Generally, cell adhesion decreased at incubation times longer than 6 h before an increase after 48 h was observed once again. Conclusions: Differences in adhesion behavior over time indicate dynamic cell-substrate interactions because of cell migration and proliferation processes. The study stresses the importance of calculating the adhesion force rather than shear stress to gain more expressive data regarding cell adhesion.