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Flowerlike porous B-type carbonated hydroxyapatite (CHAp) microspheres have been synthesized by a novel bubbletemplate route. Their pore sizes can be well regulated in a wide range from microscale to nanoscale by smartly constructing a kind of CO 2 bubble as a template and precisely adjusting the system pressure. We studied the formation of a porous structure of CHAp microspheres and the effect of the system pressure on their morphologies. Most of all, the control of the pressure over the pore sizes of bubble-template porous CHAp microspheres was investigated. The results suggested that the gathering and growth of the CO 2 bubbles generated the formation of the porous structure of CHAp microspheres, and along with the increase of system pressure, the surface of the microsphere got denser and the flakes, which assembled the porous structure, became smaller. In addition, with the increased pressure, the average pore sizes of bubble-template CHAp microspheres gradually decreased from microscale to nanoscale. Furthermore, the relation between the pressure P and the pore size r was derived from the Laplace equation, the Kelvin equation, and the Clapyeron equation.

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Flowerlike porous carbonated hydroxyapatite (CHAp) microspheres have been synthesized by employing different chelating ions: disodium ethylene diamine tetraacetate (Na2EDTA) and trisodium citrate (Na3CA) and constructing a CO2 bubble as a novel template. By adjusting the concentration of the chelating ions or the surface tension of the solution, the pore size of the porous CHAp could be well controlled. With an increase of the concentration of the chelating ions, the pore size decreased by degrees, and at the same concentration, the pore size obtained via citric acid (CA) was obviously much smaller than that obtained via ethylenediaminetetraacetic acid (EDTA). On the other hand, with the increased surface tension, the pore size decreased gradually, and this control relation was confirmed by the Laplace equation, the Kelvin equation, and the Clapyeron equation. Most importantly, according to the important effects of the chelating ions and the CO2 bubble in the self-assembly, the self-assembled process and mechanism were further investigated. First, the bubbles gathered into the stable spherical foams and the calcium ions were orientatedly attached onto the bubble surface by the chelating ions. Next, the nucleation emerged in the plateau borders and the orientated release of calcium ion from the bubble surface caused the orientatedly self-assembled growth of CHAp flakes along the interfaces between the bubbles. Finally, the flakes interconnected into the porous structure and the porous microsphere formed. In addition, a better and further explanation on the pore size control by the concentration of the chelating ions was given according to the self-assembled process and mechanism.