Methods: Titanium discs with smooth (acid-pickled, PT) and rough (sand-blasted, large grit, acid-etched, SLA) topographies were supplied by Institut Straumann AG. Samples were cleaned and sterilized by argon-gas glow discharge treatment. Osteoclasts were isolated from the long-bones of neonatal rats and rabbits, plated on the titanium substrata and incubated for various times in serum-containing medium. Preparations were then fixed and processed for fluorescence or scanning electron microscopy. Filamentous actin and nuclei were labeled using fluorescent probes.
Results: Fluorescence microscopy revealed that, after 2 h incubation, fewer rat osteoclasts attached to PT than to SLA surfaces. Osteoclasts spread on both substrata; however, quantification revealed that the extent of spreading was significantly greater on PT. Osteoclasts adhere to substrata via podosomes—dynamic, actin-containing structures that self-organize into rings, belts and sealing zones, which are essential for resorption. The percentage of osteoclasts exhibiting actin rings or belts on SLA was significantly less than on PT (58% versus 71%, respectively, p<0.05). Scanning electron microscopy of rabbit osteoclasts incubated for 24 h confirmed increased spreading on PT. In addition, osteoclasts on PT exhibited extensive ruffling on the basolateral (dorsal) aspect of their plasma membranes; whereas, osteoclasts on SLA had relatively smooth basolateral membranes. As well, osteoclasts on SLA appeared to conform to surface irregularities, especially in the cell periphery.
Conclusion: This is the first report that surface topography of titanium affects the spreading and cytoskeletal organization of authentic osteoclasts. A lower incidence of actin rings and belts was observed in osteoclasts plated on SLA, consistent with inhibition of resorptive activity in response to roughened topography.