| Porous titanium can induce bone to ingrow into porous structure, which enhances the interface intensity. Body fluid can flow in connected pores, which accelerates the course of bone healing and remodelling. Therefore, porous titanium shows great potential for the bone implant application. Titanium wire was used as material to sinter porous titanium in present dissertation. An equation to design and predict the porosity of porous titanium preform was given by means of theoretical design and calculation, and the effect factors on the porosity of porous titanium preform were analyzed. The final forming and vacuum sintering process was studied. The compressive deformation process and compressive properties were studied, and the relationship between porosity and compressive yield strength was given. On the base of thermodynamics and dynamics analysis, the silicon-containing hydroxyapatite (Si-HA) was prepared on titanium by a biomimetic method. The bioactivity of Si-HA coating was assessed through in vitro cell experiment and in vivo implantation experiment. The results are summaried as follows:The calculated results of the porosity of the porous titanium preform showed that the porosity could be controlled by changing the diameter of the titanium wire (dTi), minimum screw diameter (D) and helix angles (θ1 andθ2).The results of the forming of porous titanium showed that the two-direction-shaping method and the cyclic pressure method made the pore uniform. The obtained biomedical porous titanium had a 3-dimemsion and helix pore structure. The range of porosity was 53%-72%, the range of pore size was 150-600μm, and the range of open-cell percent was 90%-100%. The compressive yield strength ranged 160-60MPa, and Young's modulus was 5-2GPa.The compressive deformation process was studied. The result showed that when the porosity is larger than 67%, the compressive process includes three stages: elastic stage, plateau stage and densification stage. When the porosity is less than 67%, the compressive process includes two stages: elastic stage and densification stage.The relationship between the porosity and the compressive yield strength was studied. The result showed that the compressive yield strength was reduced with the increasing of the porosity. The elastic collapse and the plastic collapse of pore structure were contributed to the compressive yield strength. f was introduced to assess the contribution of the elastic collapse in the stage of yielding. The experimental results showed that the value of f was 0.15, which indicated that the percent of the elastic collapse contributed to the compressive yield strength was 15%, and the percent of the plastic collapse contributed to the compressive yield strength was 85%.The process of mixed alkali (Ca(OH)2 + NaOH) and heat treatment of the titanium surface was studied. Ca2+ was introduced into the surface and the active layer of the surface had a network porous structure after mixed alkali treatment. The phases on the surface were CaTiO3 and rutile mainly. Surface Ca content, the temperature and the time of the heat treatment affected the morphology, the phases constitute and the distribution of the active layer. With the increasing of the temperature and time of heat treatment, the amount of CaTiO3 increased, the network porous structure of the surface was broken, and the shape of rutile changed into a cosh. The more the surface Ca content had, the more CaTiO3 congregated in a flake shape on the surface.The bioactivity of the surface layer was assessed by immersing it in a simulated body fluid (SBF). Influential factors for the bioactivity were the temperature of the treatment temperature, which should be within a range of 580-600℃, and the surface Ca content, which should be at 0.87 at.%. The optimal process of the mixed alkali and heat treatment was applied to porous titanium, and the active layer was uniform all over the porous titanium.The calculated result of thermodynamics and dynamics probability analysis of Si-HA and the experimental result showed that the single phase of Si-HA could be obtained preferentially on the condition of the range of pH value being 7.0-8.0 and the nominal concentration of SiO32- in the immersion solution being less than 5mM. A Si-HA coating was prepared on titanium by a biomimetic method. The surface of the Si-HA coating was porous, and there was coralloid gibbosity on the surface. Si concentration was descent in Si-HA coating from outside to inside. When the Si content increased, the coating became denser and thinner. The introduction of Si in the coating could enhance the shearing strength. The biomimetic method was applied to porous titanium, and the Si-HA coating was uniform all over the porous titanium.The in vitro cell experimental result showed the introduction of Si could enhance the bioactivity and accelerate the biomineralization. The amount of Si content did not show distinct difference in cell attachment on the coating in the early culture stage. After 5 days culture,the most cells were observed on the Si-HA coating with 0.50 wt.% Si, indicating that the surface has the best bioactivity.The in vivo implantation experimental result showed that the Si-HA coating could induce the ingrowth of new bone into porous titanium toward the directions of marrow cavity and muscle. The new bone was well integrated with the Si-HA coating, which testified the better osteoinduction of the Si-HA coating. |
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