BACKGROUND:The purpose of this study was to investigate the influences of nanoscale wear particles derived from titanium/titanium alloy-based implants on integration of bone. Here we report the potential impact of titanium oxide (TiO2) nanoparticles on adhesion, migration, proliferation, and differentiation of mesenchymal stem cells (MSC) from the cellular level to the molecular level in the Wistar rat. METHODS:A series of TiO2 nanoparticles (14 nm, 108 nm, and 196 nm) were synthesized and characterized by scanning electron microscopy and transmission electron microscopy, respectively. RESULTS:The TiO2 nanoparticles had negative effects on cell viability, proliferation, and the cell cycle of MSC in a dose-dependent and size-dependent manner. Confocal laser scanning microscopy was used to investigate the effects of particle internalization on adhesion, spreading, and morphology of MSC. The integrity of the cell membrane, cytoskeleton, and vinculin of MSC were negatively influenced by large TiO2 nanoparticles. CONCLUSION:The Transwell migration assay and a wound healing model suggested that TiO2 nanoparticles had a strong adverse impact on cell migration as particle size increased (P < 0.01). Furthermore, alkaline phosphatase, gene expression of osteocalcin (OC) and osteopontin (OPN), and mineralization measurements indicate that the size of the TiO2 nanoparticles negatively affected osteogenic differentiation of MSC.