Objective      To investigate the effects of different-diameter TiO

2

nanotubes prepared by anodization on the adhesion

proliferation and osteogenic differentiation of Sprague-Dawley rat mesenchymal stem cells (rMSCs).       Methods      The isolated rMSCs were characterized by osteogenic di

fferentiation and flow cytometry. TiO

2

nanotubes having diameter of 30

70 and 100 nm were fabricated by anodization with different voltages. The topography and hydrophilicity of the nanotubes were accessed with scanning electron microscopy (SEM) and contact angle test

respectively. MTT assay was applied to evaluate the cell adhesion and proliferation on different substrates. Cell morphologies were observed by confocal microscopy. The activity of alkaline phosphatase and mineralization of rMSCs on plane titanium and TiO

2

nanotubes (diameter=30

70 and 100 nm) were also detected during osteogenic differentiation. The expression of Runx2 and OSX was analyzed by real-time PCR in 14 d after osteogenic differentiation.       Results      The osteogenic differentiation of rMSCs was successfully induced

and CD29 positive cells were 99.65%. TiO

2

nanotubes of different diameters were generated. The TiO

2

nanotubes of 70 nm diameter were more hydrophilic (

P

0.05) and exhibited better cell adhesion and proliferation compared with other substrates (

P

0.05). The cells cultured on the TiO

2

nanotubes of 30 nm diameter displayed much higher activity of alkaline phosphatase than those on other substrates in 7 d after osteogenic induction (

P

0.05)

higher mineralization in 21 d after osteogenic induction (

P

0.05) and more Runx2 and OSX gene expression in 14 d after osteogenic induction (

P

0.05).       Conclusion      TiO

2

nanotubes with different diameters have different influences on rMSCs as compared to plane titanium. The TiO

2

nanotubes of 70 nm diameter are more advantageous for adhesion and proliferation of rMSCs

while TiO

2

nanotubes of 30 nm diameter facilitate osteogenic differentiation.