Titanium particles inhibit osteoblast adhesion to fibronectin-coated substrates

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Abstract
To illuminate the effect of titanium particles on osteoblast function, we compared the adhesion force of neonatal rat calvarial osteoblasts on fibronection-coated glass after incubation with titanium particles (80% had diameters of less than 5 μm). The cells were incubated with the particles for 1.5–72 hours. Using a micropipette single-cell manipulation system, we showed that the adhesion force of the osteoblasts to fibronectin-coated glass (1.0 μg/ml) was significantly affected by the presence of particulate debris. The adhesion force of the cells incubated with titanium particles for less than 4 hours was not significantly affected by exposure to the particles; after 4 hours, however, it was significantly reduced relative to that of controls. Aspiration of particle-challenged osteoblasts into the micropipette demonstrated that the particles were not stripped from the cell surface and therefore confirmed that the osteoblasts had ingested them. During aspiration, the particles traveled through the cytoplasm rather than on the cell surface. When the osteoblasts were exposed to the particles and cytochalasin D, they exhibited much lower adhesion forces than did the controls or the cells exposed to titanium particles only; this indicates and important role of actin filaments in the osteoblastic response to particles. Staining for F-actin also indicated an influence of internalized titanium particulate on cytoskeletal arrangement and cell spreading. Furthermore, with standard Northern blotting techniques, levels of mRNA for collagen type I and fibronectin were significantly reduced as early as 4 hours after exposure to particles compared with levels in controls, and this effect continued to 72 hours. These data indicate that direct exposure of osteoblasts to titanium particles, which we propose to be ingested by the osteoblasts, can significantly decrease osteoblast adhesion force; this may lead to decreased cellular activity and gene expression of fibronectin and collagen type I in the presence of titanium wear debris.