| Medical porous titanium can be adjusted porosity and mechanical properties to match the bone tissue as titanium implant for reduce the stress shielding phenomenon. In addition, the porous structure is beneficial to osteoblast proliferation and differentiation, which can increase the bone ingrowths. Higher porosity of the porous titanium in a certain range (30%-90%) is more conducive to lead the tissue growth into the pores. However with the porosity increase, the mechanical property of porous titanium will rapidly decrease in order to could not meet the bearing demand of hard tissue replacement materials. Therefore the problem for us is to look for a porous titanium implant with a high mechanical property as well as a high porosity. In this paper, double-layers porous titanium (DPT) with high porosity of outer layer and high mechanical property was fabricated with NH4HCO3as a pore-forming agent by adding pore-forming agent method. Moreover, the rare earth reinforced DPT was successfully fabricated with LaF3as an additive. The porous titanium was analyzed by scanning electronic microscopy (SEM), X-ray energy dispersive spectroscopy (EDX) and X-ray diffraction (XRD) to characterize surface morphology, composition and crystal structure. Also used the mechanical test machine to determine compressive strength (CS), bending strength (BS) and elastic modulus (EM) of porous titanium, and determine the shear strength of DPT. The biological properties of porous titanium were evaluated by biomineralization after alkali-heat treatments.In this paper, the effect of titanium powder particle size, adding amount of pore agent and LaF3, gradient structure on the mechanical properties of porous titanium was investigated. Porosity and open porosity of porous titanium reduced with the decrease of the particle size of titanium powder, when had the same adding pore-forming. The porosity and open porosity of porous titanium prepared on A group particle size of titanium powder (31.5μm) was65.0%-72.8%and70.5%-79.7%respectively. The porosity and open porosity of porous titanium prepared on B group particle size of titanium powder (18.1μm) was62.3%-65.2%and62.2%-70.5%respectively. When the particle size of titanium powder was9.8μm (C group), the porosity and open porosity of porous titanium was further reduced, that was58.9%-61.7%,57.8%-63.6%respectively. With the decrease of the particle size of titanium powder, pore, size of porous titanium reduced in a small range which homogeneously distributed and was interconnected. Pore size distribution of porous titanium prepared by A, B and C group particle size of titanium powder was100-255μm,90-240μm and90-225μm, respectively. The LaF3exert little influence on morphology of the porous titanium.The mechanical test indicated that the LaF3-doped porous titanium presents best biomechanical compatibility when the content of LaF3lie in0.05wt%in the bigger particle size of titanium powder (31.5μm,18.1μm) and0.3wt%in the smaller particle size of titanium powder (9.8μm). The mechanical properties of porous titanium with minimum particle size of titanium powder were best. The CS, EM and BS of singer porous titanium (SPT) C-L30(titanium powder particle size of9.8μm, with0.3wt%adding amount of LaF3) with60%high porosity and90-240μm pore size were157.84±16.00MPa,3.73±0.39GPa, and66.6±12.10MPa, respectively. The mechanical properties of DPT with high density of inner layer and the same high porosity in outer layer as singer layer porous titanium (SPT) were better than (SPT). With the decrease of the particle size of titanium powder, the mechanical properties of DPT reinforced. The mechanical properties of DPT with the lanthanum fluoride in the outer layer were better than that DPT which did not add lanthanum fluoride. The CS, EM and BS of PT2050(Titanium powder particle size is9.8μm) which had60%porosity in outer layer and pore size was90-240μm were203.51±14.20MPa,2.91±0.09GPa and53.22±9.93MPa, respectively. Moreover, the CS, EM and BS of C-L2050with0.3wt%LaF3in outer layer which maintained the same high porosity and large pore size in the outer layer could be further improved, were234.8±13.52MPa,3.82±0.63GPa and59.31±6.10MPa, respectively. Therefore, through selecting the titanium powder particle size, adding the proper amount of LaF3and designing gradient structure, the medical porous titanium with high porosity, large pore size and high strength can be prepared which had the mechanical properties matching the nature bone.There is new composite of sodium titanate (Na2Ti3O13ã€Na2Ti5O11ã€Na2TiO3and NaTi3O2) and rutile TiO2were found on the surface of porous titanium after alkali-heat treatment. In biomimetic mineralization condition, the porous titanium after alkali-heat treatment can induce hydroxyapatite (HA) forming on its surface in SBF. The adding of rare earth LaF3in porous titanium reduced the deposition of HA on surface. |
