Study On Osteoinductivity Of Tantalum And Titanium Surface To Normal And Ovariectomized Rats

Objectives: Tantalum(Ta)serves as a promising biomaterial for bone implants,and many studies have demonstrated that its osteoinductivity is superior to titanium(Ti).Whereas,samples applied in most previous studies underwent surface treatments or structural changes,and the difference regarding osteoinductivity and related mechanisms,which are determined by the intrinsic surface effects of the two materials,remains to be elucidated.Furthermore,reports focusing on performance of the two biomaterials in osteoporosis are rare.In view of this,Ta and Ti substrates with highly polished surface were used in the present study,and influences of the samples on cell osteoblastic differentiation and the related mechanisms were evaluated by using bone mesenchymal stromal cells from normal and ovariectomized rats(NOR-and OVX-rBMSCs).Besides,bone defects were built in femurs of both rats,and in vivo osteoinductive performance of Ta and Ti was measured after implantation.Materials and Methods: SEM,AFM,XPS and ICP-OES,etc were used tocharacterize the surface of Ta and Ti substrates.CCK8 assay,fluorescent staining,ROS detection etc were applied to assess the biocompatibility and effects of the two samples on initial cell behaviors.In addition,ALP activity assay,alizarin red staining,RT-PCR,westernblot and plasmid transfection were utilized to study the osteoinductive performance of the two substrates and the relevant biological mechanisms.Finally,sequential fluorescent labeling and histologic staining were used to evaluate the new bone formation and mineralization on the sample surface in vivo.Results:(1)Ta and Ti substrates revealed featureless surface with low roughness,and no obvious ion release effect was identified for both samples.The major difference between the two substrates lied in the chemical components of their respective surface oxide layer.(2)For NOR-and OVX-rBMSCs,both Ta and Ti substrates were conducive to their initial adhesion and proliferation.Whereas,less apoptotic cells and low ROS production were identified on the Ta surface.Additionally,the cells on Ta substrates demonstrated higher level of ALP activity and extracellular mineralization,enhanced expression of RUNX2?ALP?OCN?COL-I at both gene and protein levels.(3)In comparsion to Ti,NOR-rBMSCs on Ta surface revealed more enhanced gene expression of integrin a5 and integrin b1;OVX-rBMSCs on Ta surface showed higher expression of BMP2 and Smad1.(4)For NOR-rBMSCs,down-regulation of integrin a5b1/ERK1/2 signaling pathway obviously inhibited their osteogenesis on the Ta surface,and up-regulation of the cascade improved the osteoblastic differentiation on the Ti substrates.(5)For OVX-rBMSCs,silence of BMP2/Smad1 pathway apparently suppressed their osteogenic activity on the Ta surface,and over-expression of the signaling promoted their osteogenesis on the Ti substrates.(6)After samples were embedded in the femur defects of NOR-rats,more new bone formation and mineralization was observed around the Ta surface,together with the higher bone-implant contact rate(BIC)at 4,8 w(the difference at 8 w was not statistically significant).(7)Following the implantation in OVX-rats,bone forming activity was more vigorous around the Ta samples;and the Ta surface revealed a slightly better BIC rate compared to Ti(the difference at 4,8 w was not statistically significant).Conclusions:(1)The principle route through which the Ta and Ti substrates function on cells is direct cell-material contact,and the different surface oxide layers on the two sample surfaces serve as the major cause for the diverse results of the following experiments.(2)Ta surface boasts better biocompatibility and osteoinductivity when compared with Ti.(3)For NOR-rBMSCs,the stronger osteoinductive effect of Ta surface is associated with its ability to more sufficiently trigger the expression of integrina5b1/ERK1/2 cascade.(4)For OVX-rBMSCs,the better performance of Ta surface is contributed by its capacity to better activate BMP2/Smad1 signaling.(5)For both NOR-and OVX-rats,the osteoinductivity and early osseointegration of Ta may be better than Ti in vivo.