Titanium　dioxide　(TiO2)　nanotubes　can　accelerate　the　adhesion　and　differentiation　of　osteoblasts,　yet　little　is　known　how　this　nano-modified　implant　surface　affects　osseointegration　at　molecular　level　in　vivo.　The　aim　of　this　study　was　to　investigate　the　effects　of　TiO2　nanotubes　with　different　diameters　(30　nm,　70　nm　and　100　nm)　on　biological　attachment　mechanism　of　implants　to　bone　in　vivo　by　studying　the　gene　expression　and　bone　formation　around　the　implants.　The　histological　features　and　fluorochrome　labeling　changes　of　bone　around　implants　on　the　non-decalcified　sections　(at　3,　5　and　8　weeks　after　implantation)　were　investigated　by　using　traditional　light-　and　fluorescent　microscopy,　and　the　gene　expression　of　alkaline　phosphatase　(ALP),　osterix　(Osx),　collagen-I　(Col-1)　and　tartrate-resistant　acid　phosphatase　(TRAP)　was　examined　by　using　real-time　PCR　at　1,　2,　3,　4　and　5　weeks　after　implantation.　Comparing　with　machined　titanium　implants,　a　significant　increase　in　bone　implant　contact　(BIC)　and　gene　expression　levels　was　found　in　the　bone　attached　to　implants　with　TiO2　nanotubes,　especially　with　70　nm　diameter　nanotubes.　At　the　same　time,　the　sequential　fluorescent　labeling　images　illustrated　dynamic　bone　deposition.　In　conclusion,　TiO2　nanotubes　can　modulate　bone　formation　events　at　the　bone　implant　interface　as　to　reach　favorable　molecular　response　and　osseointegration;　in　addition,　the　diameters　of　nanotubes　can　be　precisely　controlled　in　order　to　obtain　better　bone　formation.　(C)　2011　Elsevier　Ltd.　All　rights　reserved.