Enhancement of the bioactivity of alkali-heat treated porous titanium by pre-calcification

The porous titanium with maximal pore size about 239 μm and 40% porosity was prepared by powder metallurgy process. The samples were subjected to NaOH solution and heat treatment, then immersed in Na₂HPO₄ solution and saturated Ca(OH)₂solution to perform pre-calcification. The samples without pre-calcification were soaked in SBF (Simulated Body Fluid) for 28 d to form apatite coatings on surfaces. And the samples subjected to pre-calcification were soaked in SBF only for 4 d for apatite deposition, showing that pre-calcification enhanced the bioactivity of porous titanium remarkably. The mechanism of pre-calcification was explained as follows: during the pre-calcification process, the sodium titanate formed on surfaces of porous titanium by alkali-heat treatments would be hydrolyzed to produce negatively charged Ti-OH group, which absorb Ca²⁺ to surfaces. When samples were soaked in SBF, the Ca-P was supersaturated in shot time and the ion activity near the surfaces increased, which stimulated the nucleation and growth of the apatite crystal. Expect the samples subjected to alkali-heat and pre-calcification treatments, the Ca/P atom ratios of apatite coatings on the porous titanium for other samples were less than that of human bone. The thin coatings with fine crystal did not destroy the pore structure of porous titanium.