Titanium particles inhibit osteoblast adhesion to fibronectin-coated substrates

To illuminate the effect of titanium particles on osteoblast function, we c ompared the adhesion force of neonatal rat calvarial osteoblasts on fibrone ctin-coated glass after incubation with titanium particles (80% had diamete rs of less than 5 mu m). 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 mu g/ml) was significantly affected by the presence of particulate debris . The adhesion force of the cells incubated with titanium particles for les s than 3 hours was not significantly affected by exposure to the particles; after 4 hours, however, it was significantly reduced relative to that of c ontrols. Aspiration of particle-challenged osteoblasts into the micropipett e demonstrated that the particles were not stripped from the cell surface a nd therefore confirmed that the osteoblasts had ingested them. During aspir ation, the particles traveled through the cytoplasm rather than on the cell surface. When the osteoblasts were exposed to the particles and cytochalas in D, they exhibited much lower adhesion forces than did the controls or th e cells exposed to titanium particles only; this indicates an important rol e of actin filaments in the osteoblastic response to particles. Staining fo r 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 fibron ectin were significantly reduced as early as 4 hours after exposure to part icles compared with levels in controls, and this effect continued to 72 hou rs. These data indicate that direct exposure of osteoblasts to titanium par ticles, which we propose to be ingested by the osteoblasts, can significant ly decrease osteoblast adhesion force; this may lead to decreased cellular activity and gene expression of fibronectin and collagen type I in the pres ence of titanium wear debris.