Cellular reactions of osteoblasts to micron- and submicron-scale porous structures of titanium surfaces

Osteoblast reactions to topographic structures of titanium play a key role in host tissue responses and the final osseointegration. Since it is difficult to fabricate micro- and nano-scale structures on titanium surfaces, little is known about the mechanism whereby the topography of titanium surfaces exerts its effects on cell behavior at the cellular level. In the present study, the titanium surface was structured in micron- and submicron-scale ranges by anodic oxidation in either 0.2 M H3PO4 or 0.03 M calcium glycerophosphate with 0.15 calcium acetate. The average dimensions of pores in the structured surface were about 0.5 and 2 microm in diameter, with roughness averaging at 0.2 and 0.4 microm, respectively. Enhanced attachment of cells (SaOS-2) was shown on micron- and submicron-scale structures. Initial cell reactions to different titanium surfaces, e.g. the development of the actin-containing structures, are determined by the different morphology of the surfaces. It is demonstrated that on either micron- or submicron-structured surfaces, many well-developed filopodia were observed to be primary adhesion structures in cell-substrate interactions, and some of them entered pores using their distinct tips or points along their length for initial attachment. Therefore, porous structures at either micro- or submicrometre scale supply positive guidance cues for anchorage-dependent cells to attach, leading to enhanced cell attachment. In contrast, the cells attached to a smooth titanium surface by focal contacts around their periphery as predominant adhesion structures, since repulsive signals from the environment led to retraction of the filopodia back to the cell bodies. These cells showed well-organized stress fibres, which exert tension across the cell body, resulting in flattened cells.