Effect of particle size on macrophage-osteoclast differentiation in vitro

To determine whether particle size affects macrophage-osteoclast differentiation in vitro, latex beads of 0.1, 1, and 10 microm in diameter were added to a murine macrophage-UMR106 osteoblast-like cell coculture system. The extent of osteoclast differentiation was determined by assessing the number of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells on glass coverslips and the extent of lacunar resorption on dentine slices. The addition of particles, 1 and 10microm in size, to the cocultures resulted in a significant increase in the number of TRAP-positive osteoclast-like cells and in the resorption pit surface area compared with findings in control cultures to which no particles had been added. Particles 0.1 microm in size also stimulated osteoclast formation relative to the control; however, the difference was not significant. These results indicate that particles, particularly these 1 and 10microm in size, sizes which were phagocytosable, significantly enhanced the process of macrophage-osteoclast differentiation and suggest that particle size plays an important role in periprosthetic osteolysis.