Study On Controlled Synthesis Of Hydroxyapatite Crystal/Particle Under Hydrothermal Condition

Hydroxyapatite (HA) has been a very important biomaterial due to its excellent bioactivity and biocompatibility. In order to develop its research merits and application scope, the preparation of hydroxyapatite nanoparticle/microparticle with various morphology and different spacial structure become one hotspot of biomaterials research. This paper focuses on synthesis of crystal/particles with various morphology or hollow structure microspheres by controlling reaction conditions, introducing different kinds of reaction additives and adopting polymer templates.This paper also investigated the mechanism and model, which is adopted to control the morphology and structure of hydroxyapatite crystal/particles effectively in the hydrothermal conditions. The main content and results are summed up as following:Firstly, the hydrothermal parameters of high crystallization degree and complete crystal shape are achieved by studying on the impact of hydrothermal conditions, such as reaction temperature, pressure, initial pH value, different pH regulator, calcium ion concentration and calcium ion releasing channel and so on, also including the affected degree of these hydrothermal parameters. Fibre-like and big size hexagonal prism-like hydroxyapatite crystal, and controllable crystal size particles are available by adjusting the relative ion concentration of hydroxyapatite components. The function mechanism that hydrothermal conditions impact hydroxyapatite growth unit formation and combination, is elaborated by introducing growth unit model of anion coordination polyhedron.CTAB (Cetyl trimethyl ammonium bromide), SDS (sodium dodecyl sulfate) and PVA (polyvinyl alcohol), three kinds of surfactants are introduced to hydrothermal process to adjust the hydroxyapatite crystal growth habits and crystal morphology. The results indicate that short rod-like hydroxyapatite nanoparticles are achieved by adding positive surfactant-CTAB, while plate-like hydroxyapatite nanoparticle are obtained by introducing negative surfacetant-SDS, and low aspect ratio hydroxylapatite nanoparticles are prepared by introducing nonionic surfacetant-PVA. The mechanism bases on:the formation of Ca-P6O24growth unit of anionic coordination polyhedra is influenced by different surfactant groups with electric charge blocks, which disturbs hydroxyapatite growth unit to join hydroxyapatite crystal and retards the combination velocity of growth unit, and those effects lead to different morphology crystals.The basic amino acid of arginine, acidic amino acid of glutamic acid, and compound amino acid are used as additives to prepare HA nanoparticle with various morphology. The research shows that the Arginine with positive guanidine group is apt to adhere to the P site of (100) face of HA crystal, and the adsorption interaction become stonger with higher concentration, which leads to short rod-like HA nanoparticle with lower aspect ratio. The Glutamic acid with negative carboxy groups prefer to bind on the (100) or (010) face of HA crystal, which leads to plate-like hydroxyapatite crystals. The compound amino acid affects different crystal facet in different pH value, which result in spherical HA particle as the growth speed is almost uniform.The main reaction mechanism lies in:different amino acid groups may absord on different sites of hydroxyapatite crystal, and have different effect on crystal facets, which changed the HA crystal structure and produced various crystal morphology.The effect of STPP (sodium tripolyphosphate) and SHMP (Sodium hexametaphosphate) on hydroxyapatite crystal morphology are studied in hydrothermal preparation. The investigation shows that polyanions, the ions of polyelectrolyte in solution, are easy to adhere to (100) facet of hydroxyapatite crystal, which blocks active sites growth of (100) plane and make (100) facet to be obvious facet. The research also demonstrates that the polyanions with linear type molecular chain have stronger absorption force, and show more obvious effect on crystal morphology than the polyanions with circular type moleculear chain. In addition, the concentration of STPP impacts the morphology of hydroxyapatite crystal. It is preferable to get plate-like hydroxyapatite crystal with higher concentration of polyelectrolyte.The hydroxyapatite microspheres with hollow structure are prepared by adopting template of CS-PAA polymer complex, hydroxyapatite particles nucleating and growing on the hollow CS-PAA polymer microspheres, and the polymer template is removed by calcination. The experiment shows that electrostatic attractive force and repulsive force have played crucial role in the formation of the CS-PAA sphere, and the size of CS-PAA spheres could be tuned by adjust the ratio and concentration of CS-AA in the reaction system. Gelatin, acted as binder to connect the spheres of CS-PAA with hydroxyapatite particles, help hydroxyapatite crystals to nucleate and grow on the polymer microsphere. Finally, the hollow structure hydroxyapatite microspheres are achieved by calcining the CS-PAA polymer template. This preparation method and mechanism of hollow structure hydroxyapatite microspheres, provides an effective approach to produce hollow inorganic microsphere.