Preperation And Biological Evaluation Of Graded Porous Titanium With Bioactivity

Porous titanium has excellent biocompatibility and can reduce the Young’s modulus because of the pore structure. Meanwhile, the pore structure can provide much space for tissue ingrowth, which can strengthen the bonding between the implant and tissue. However, the mechanical properties such as compressive strength will be decreased as the too high porosity. Further more, the titanium is a biologically inert material. Thus, how to solve the contradiction between porosity and compressive strength, and how to activate the porous titanium with comples topography is a problem to be solved.The space holder method is a fabrication process that can produce porous materials. As this method is simple, low cost and no expensive equipment needed, meanwhile, the size, shape and porosity can be adjusted by choosing the space holder particles, it was used to preparation of porous titanium implants in this paper. The optimized process parameter can be determined through investigating the process parameters by fabricating the porous titanium with sole porosity. And the effect of the parameters on the porosity and mechanical properties were also investigated. Then, the graded porous titanium with higher porosity in outer layer was fabricated and the mechanical properties were characterized. Subsequently, electrochemical treatments and chemical treatments were conducted to activate the surface and the biological activity of the treated porous titanium was studied in vitro and in vivo. In addition, the full-defect model in the bearing part was established by creating defects in the middle femur of the dogs. Then, the double graded porous titanium implants were used to repair the defect and the results were invested at different time. In this study, steel plates and screws were used to fix the implants. Finally, porous HA/Ti was processed using titanium and hydroxyapatite powder by space holder method, and the mechanical properties and biological activity of the porous composites were investigated.Firstly, the impact of addition of space holder, sintering temperature and holding time on porosity, compressive strength and Young’s modulus were studied in this paper. When the addition of space holder was35%、40%/50%and60%, the porosity of porous titanium was 50%、58%、67%and72%, the compressive strength was160MPa、105MPa、40MPa and25PMa, the Young’s modulus was2.68GPa、2.00GPa、0.75GPa and0.55GPa, respectively. When sintering temperature increased and the holding time extended, the compressive strength increased.In this study, graded porous titanium scaffolds containing the double layer or three layers were prepared at1300℃for2hours. And the porosity in outer layer was approximately67%. Moreover, the compressive strength, flexural strength and Young’s modulus are245.85MPa,64.54MPa and3.98GPa, respectively, matching the bone. The results indicated that the graded porous titanium can be used to repair the hard tissue in bearing part.Multi-level micr-nano porous structure was forming on the surface of porous titanium by electrochemical method and chemical methods, and the results showed that anatase TiO2nanotubes were presented after anodize treatment and heat treatment. And TiO film containing microporous structure was presented after micro-arc oxidation. When the porous titanium was treated in the NaOH solution, plush-like suface containing Na, O, etc was presented. Biomimetic results showed that the three types of modified porous titanium can induce the formation of hydroxyapatite.Animal experiment was conducted to study the effects of the porous titanium before and after modification on bone integration. The results showed that the porous titanium had good conduction capacity and biocompatibility. Anatase nanotubes had significant effect on the growth of bone tissue and promoted bone ingrowth into the pores. When implanted in the animals for6months, the porous titanium with anatase nanotubes showed the higher bonding strength and bone ingrowth area rate than the untreated implants.The full-defects model was established to investigate the bone repair in the part of the bearing part. The double layer porous titanium was used to repair the bone defect. The results showed that the implants were fixed well by steel plate and screws in a month. However, the implants were loose in3and6months. It indicated that the fix method needs to be improved. In addition, the bone induction capability of the porous titanium was investigated through implanting the implants into the muscles. Results showed that the anatase TiO2nanotubes promoted expression of the bone morphogenetic protein (BMP-2). And so did the surface of implants treated by NaOH solution. It indicated that the modified surface had the potentital bone induction ability.Finally, the HA/Ti composites was prepared and the mechanical properties were characterized. The results showed that the compressive strength increased with the addition of the titanium. When the quality ratio of the hydroxyapatite and titanium is1:15, the compressive strength is181.89MPa. Meanwhile, the composites can induce the formation of hydroxyapatite. Moreover, the double layer graded porous composites with excellent mechanical properties can be prepared by adjusting the space holder addition. The graded porous composites with higher porosity in outer layer can be used as a new kind of bone-substitute materials.