Study On The Pore Size Control And The Self-assembled Mechanism Of Porous Carbonated Hydroxyapatite Prepared By The Bubble-template Self-assembled Route

Carbonated hydroxyapatite (denoted CHAp), as a functional biomaterial, inherits the excellent properties from hydroxyapatite (denoted HA), and can be widely applied in many fields such as biochemistry, biomedicine, environmental engineering, and chemical catalysis, etc..Porous CHAp was synthesized through two routes of template-directed self-assembly. The first one is that experimental reagents, and different chelating ions: Ethylene Diamine Tetraacetic Acid (EDTA) and Citric Acid (CA) were used. Another one is that natural collophanite was used. XRD, FT-IR, and SEM were employed to analyze the chemical composition and morphology of the productions. The results showed that the flowerlike porous CHAp microsphere which assembled by the nano-size flakes was obtained. There was B-type CHAp by laboratorial route and was A-type by natural collophanite.The pore size control of the porous CHAp microsphere prepared through the experimental route by the concentration of the same chelating ions was studied. The results showed that with the increased concentration of the chelating ions, the pore size decreased gradually, and the decreased trend became slow. On the other hand, at the same concentration, the pore size of the porous CHAp prepared by CA was obviously much smaller than that prepared by EDTA. This control route has advantages in simply obtaining the porous CHAp with the pore in a smaller size.The bubble stability model in solution was constructed and the formation of porous structure was studied to investigate the precise pore size control of CHAp by the adjustable pressure or surface tension. In addition, the theoretical control relation was derived. The results revealed that gradually with the increase of system pressure, and the pressure was higher, the average pore size of porous CHAp microspheres was larger, the surface of the CHAp microsphere was denser and the flakes became smaller. On the other hand, this regular was the same with the relation between the surface tension of the initial mixed solution and the pore size. Furthermore, the control relation between the system pressure and the pore size, and that between the surface tension and the pore size were agreemet with the equation 4-7 and 4-9, respectively. The control of the pore size by the surface tension and that by the system pressure could form an integrated controlled system to adjust the pore size of porous CHAp.According to the important effects of the chelating ions and the CO₂ bubble in the self-assembled growth, the self-assembled process and mechanism was further investigated. Firstly, the calcium ions were orientatedly attached onto the bubble surface by the chelating ions. And then, the nucleation emerged in the plateau borders and the orientated release of calcium ion from the bubble surface caused the CHAp flakes to orientatedly self-assembly grow along the interfaces between the bubbles. Finally, the flakes interconnected into the porous structure and the porous microsphere formed. In addition, the pore size control by the concentration of the chelating ions was better explained via the self-assembled process and mechanism.