Fabrication And Biocompatibility Evaluation Of A Novel Porous Tantalum-Niobium Alloy

1IntroductionAfter more than half a century of continuous improvements in the orthopaedic biomaterial field, stress shielding phenomena and binding forces between bone and implants still challenge traditional matellic implant materials, which are widely used in arthroplasty and spinal fusion and traumatic surgery. Porous metal maintains several biomaterial properties, including a high volumetric porosity, low modulus of elasticity and open-cell structure, for bone ingrowth. Niobium has excellent biocompatibility and non-toxicity. At the same time, Niobium ions has the potential to promote alkaline phosphatase(ALP) activity, as well as calcification of normal human osteoblasts.We synthesized a novel porous tantalum-niobium alloy with compatible pore size, open-cell structure and low Youngs modulus. Then we made a further research on biocompatibility of porous tantalum-niobium alloy in vivo and in vitro in order to support it to be used in vivo. 2Fabrication and Characterization of porous tantalum-niobium alloyObjects:The aim of this study is to investigate the fabrication method and characterization of porous tantalum-niobium alloy.Methods:Porous Ta-Nb alloys are prapred by combination of powder metallurgy(P/M) technique and the sponge impregnation technique. Porous Ta-Nb alloys of three contents (5%,10%and15%) are sucessfully prapared. Porosity, pore structure, microstrure, mechanical property and elastic mudulus of the material is characterized and observed by scanning electron microscope (SEM), optical microscope (OM) and universal testing machine. During optimizing and choosing the suitable process, the optimistic method to fabricate the porous Ta-Nb alloy is expected.Results:The porous Ta-Nb alloys possess a porsity of55%, an open porsity of95%and a pore size of400μm though SEM and OM. The results reveal that these porous parameters are independent of the Ta-Nb alloy content. It is indicated from compression test and transverse test that when the Nb content is10%, the optimum mechanical property is obtained, including a porsity of55%, an open porsity of95%, a pore size of400μm, a compressive strength of83.43MPa, a elasticity modulus of2.54GPa and a bending strength of109.11MPa.It is noticed that all compression curves have good plasticity plateau.Conclusion:Porous Ta-Nb alloys are sucessfully prepared by applying P/M technique and the sponge impregnation technique. When the Nb content is10%, the optimum properties of the porous materials are reached. 3Molecular Biocompatibility of Porous Tantalum-Niobium Alloy on Mouceblast in VitroObjects:The aim of this study is to investigate the biocompatibility of porou tantalum-niobium alloy on mouse osteoblast MC3T3-E1in vitro.Methods:First, we incubate mouse osteoblast MC3T3-E1with different chroma of leaching liquor of porous tantalum-niobium, porous tantalum and dense tantalum-niobium to evaluate their safety, at the same time, blank and positive control groups are set up. Then, MC3T3-E1cells are cultured on surface of three kind of metallic disc. The adherency and proliferation of mouse osteoblast are analyzed by staining with acridine orange. Cell proliferation and morphology are assessed after1day,3days and7days of incubation by SEM. The expression of type I collgen, ALP, osteocalcin(OC), Ki67, intergina5, cbfα1and TGF-β mRNA are measured following mouse osteoblasts MC3T3-E1cultured on three kind of metal at3d,6d,9d,12d using QPCR.Results:The leaching liquor of PTaNb does not induce toxicity to MC3T3-E1cells.4hours after culture on the surface of three materials, the number of cells adhered on PTaNb and PTa are greater than cells on DTaNb. MTT test showe cells proliferation on PTaNb and PTa are also greater than cells on DTaNb, while there is no statistical difference between PTaNb and PTa. SEM observation reveals proliferation and morphology of MC3T3-E1. Cell number increase with time, and entire surface of PTaNb and PTa samples are covered with cells having numerous filopodia. Cells were also found to have migrated into the pores. The trend of temporal expression of mRNA is almost the same on PTaNb and PTa. The level of integrinβ1, Cbfα1、TGF-βmRNA are higher on PTaNb and PTa than on DTaNb (P<0.05), while the level of ALP mRNA on PTaNb were higher than on PTa and DTaNb.Conclusion:PTaNb has excellent biocompatibility and can improve the adherency, proliferation and cell function of osteoblast. The possible molecular mechanism is promoting ALP、Cbfα1、TGF-β and integrinα5activity. 4In vivo Biocompatibility of PTaNb Alloy on New Zealand RabbitsObjects:The aim of this study is to evaluate the biocompatibility of PTaNb alloy via animal experiment, and to investigate the potential of PTaNb to be a novel substitution of implant.Methods:PTaNb,PTa and DTaNb rods are implanted into6mm diameter holes in the distal part of femur of36New Zealand rabbits.X-Ray radiography is conducted at the end of2weeks,6weeks and12weeks to minitor the implant conditions. The animals are sacrificed6weeks and12weeks after surgery to evaluate bone ingrowth by histology and SEM. Then, the specmen are fixed with PMMA to conduct push-out test.Results:None materials causes any adverse effects or inflammatory reactions. No dislocation or loosening are observed in all three group.6weeks after surgery, new bone are observed on both end of PTaNb rods and PTa rods, while no similar reaction on DTaNb rods. SEM investigation show PTaNb and PTa rods are integrated tightly on the host bone. New bone grow very well on the surface and penetrate into deeper pores. With regard to DTaNb, there is a thin layer of fibrous membrane between host bone and implants. In push-out test, DTaNb exhibit worse bonding strength than PTaNb and PTa. There are no statistical difference on the average maximam push-out force between PTaNb and PTa.Conclusion:PTaNb has similar good biocompatibility and osteointegration activity to PTa, and it is suitable for clinical application.