The Preparation Of Hydroxyapatite Bio-materials And Evaluation Of Its Bioactivity

Hydroxyapatite, with scientific name of 2-hydroxyl-6-phosphoric acid -10-calcium and chemical formula of Ca₁₀(PO₄)₆(OH)₂, is usually abbreviated as HA. The HA is the predominant mineral component of human hard tissues (i.e. skeleton, teeth), possessing excellent biocompatibility and bioactivity. It can be used as perfect biomaterial for hard tissue repair and substitute, so the research and development about HA have progressed very fast in recent years.This dissertation mainly focused on the preparation techniques of HA micro-powders and evaluation of the bioactivity of porous HA ceramics, and the determining method of Ca and P contents in the HA products by using chemical analysis was also improved at the same time. First, the HA nanopowder was successfully prepared using both homogeneous precipitation and sol-gel method with the help of orthogonal design method optimizing approach, and the effects of reactant molar ratio (or Ca/P), reaction temperature, starting reactant concentration and sintering temperature on the purity, phase and size of HA powder were analyzed in detail. Secondly, the contents of Ca in the calcium-phosphate system were measured by our improved EDTA complex titration; the contents of P element in the products were accurately measured by using phosphomolyybdate-quinoling precipitate method. The porous HA bioceramics were prepared and the effect of pore-making agent and its amount on the pore size and uniformity of the HA ceramics was investigated as such. Finally, the bioactivity of HA porous ceramics was reasonably evaluated by in vitro test. The XRD, FT-IR were used to analyze the phase and composition; the particle size and morphology of HA ceramic samples as well as the pore distribution and microstructure were observed by TEM and SEM, respectively. The microscopic changes on the surface and cross section of the HA ceramics before and after soaked in static SBF have been studied by the above apparatuses. It has been confirmed that the reactant molar ratio (Ca/P) and sintering temperature remarkably affect the purity, phase and morphology of HA microparticles. In order to obtain the HA powder with high purity and good crystallite, it is necessary to adjust Ca/P=1.67 for homogeneous precipitation method and Ca/P=1.72 for sol-gel method, respectively. Moreover, newly-prepared reactant solutions are strongly suggested to be used in the whole process. Sintering temperature is an important factor that affects the phase and purity, so it should be strictly controlled. If the sintering temperature is too high, HA will decompose and CaO will appear; if the sintering temperature is too low, the precursors can not be totally transferred to HA phase. The sintering temperature should be controlled at 900°C for homogeneous precipitation method and 550°C for sol-gel method, respectively, so as to achieve better HA microparticles. The relatively ideal porous HA ceramic sample with suitable size and distribution can be prepared using stearic acid as pore-making agent whose proportion is about 35% under the pressure of 10MPa and sintering temperature of 500°C. It is shown by the EDS analysis that the composition and amount of bone-like apatite on the surface of bulk HA ceramics change with the changing of soaking time in static SBF. When soaked for 24h, the spherical bone-like apatite can be seen; after soaked for 14d, the needle-like bone-like apatite appears. Therefore, the good bioactivity of the porous HA ceramics prepared in our lab has been verified. At the same time the feasibility of in vitro test for evaluating bioactivity of bioceramic has also been confirmed.