| As the most representative biomaterials, hydroxyapatite(HAP) has been of great interest in the fields of materials and neoteric biomedicine engineering science. HAP is the biocompatible and bioactive material that has been widely used in medical applications as implants or as coatings on prostheses. However, HAP has properties of low dense, low strength and poor mechanism, which limited its applications on a large extent. In order to solve these problems, many investigations have been carried on such as coating materials, composite materials, and nanomaterials. Some research revealed that properties of HAP are largely dependent on their microstructural features, such as particles size, degree of particles size agglomeration and sintered densities. Therefore, the preparation of fine,single distribution and sinerable HAP particle is the most important step in achieving a highly sintered ceramic material with desirable microstructure. In this paper, diverse preparation methods which are suit to be used in the lab were applied, namely co-precipitation method, hydrothermal method, microemulsion method, template method, to synthesize hydroxyapatite nanoparticles in a systematic and all-round way, and basically realized the controllability of the sizes and appearances of the as-synthesized hydroxyapatite nanoparticles. Some mechanism of HAP growth was simply discussed. The main research works were as follows:Firstly, hydroxyapatite nanoparticles were successfully synthesized in water solution system by homogeneous co-precipitation method with calcium nitrate and diammonium hydrogen phosphate as precursors. The influences of factors, namely pH value, ageing time, reaction temperature, sintering temperature, the charging pattern and rate, on the characteristics of the as-synthesized particle, namely particle size, crystalline, particle size distribution, purity, were investigated, and the simple technological condition to prepare hydroxyapatite nanoparticles was founded.Secondly, the process of the synthesis of HAP nanorods by homogeneous precipitation under hydrothermal conditions with calcium nitrate and diammonium hydrogen phosphate as precursors was researched. It was found that hydrothermal temperature and reaction time had a great impact on the size of HAP micro-crystal, which stand that increasing the temperature would be helpful for the HAP micro-crystal to grow along the a axis and prolonging the reaction time would be helpful to grow along the c axis. It was also found that pH value had a notable influence on the size and composition of HAP micro-crystal, which stand that an increasing pH value would go against the growth of HAP micro-crystal along the c-axis, and only when the pH value equaled or was higher than 8．7, the products was pure HAP ,without any doping CaHPO. HAP nanorods of high crystallinity and good dispersity, which had a typical diameter and length range of 19-38nm and 17-343nm, respectively, as well as a slenderness ratio of 2-18, were synthesized under optimized conditions.Thirdly, Rod-like hydroxyapatite nanoparticles were successfully synthesized in the reverse micelles (Triton X-100+Tween 80 ) /cyclohexane/ (butanol + hexanol) /water phase) system, which was stabilized by non-ionic surfactants, and the particles are 20-25 nm in diameter, and 28-64 nm in length, respectively. The produced particles have a narrow particle size distribution and a good agglomeration, and the best HLB value is 13．5．Furthermore, another reverse micelles system (TX-100 + CTAB/ butanol+ hexanol/ cyclohexane/ water) was used as template to prepare the hydroxyapatite nanoparticles. Due to the different stabilization functions of the two emulsifiers on the W/O interfacial film, agglomeration between the particles can be effectively prevented to some extent, and the products also displayed a better dispersion than that of the first one. Fourthly, Emulsion methods have been shown to be one of the techniques that are capable of preparing ceramic powders with controlled particle size and distribution, uniform shape, lowered degree of agglomeration, and a high degree of chemical purity. The combination of reverse microemulsion method and hydrothermal method would realize the control of particle size, morphology, and structure in molecular degree. The present study is aimed at investigating the effect of pH value and CTAB in the water phase of microemulsion on the HAP crystal growth using emulsion technique under hydrothermal conditions.Finally, vesicle and microemulsion ordered system were taken as two soft templates and the growth mechanics of hydroxyapatite nanoparticles were studied. The appearances of the synthesized hydroxyapatite nanoparticles can be effectively controlled by variating the experimental parameters. Some significant results were found as followed: In CTAB/SDS vesicle system, when reaction temperature is 25℃for 24h. The gained crystals have lamellar-rolling structure and exhibit nanoclusters due to low potential energy. In microemulsion (cyclohexane/ SDS, CTAB/butanol/water) system, when reaction temperature is 25℃for 24h. The gained crystals exhibit nanoribbon in shape and a mean width 15-20 nm. In microemulsion ( cyclohexane/TX-100/butanol/water phase) system, when reaction temperature is 25℃for 24h and pH was 8, The appearance of gained crystals was mostly rod-like with length 50-120 nm and diameter 20-30 nm ,and nanosphere were obtained with the mean diameter of about 30-40 nm when pH was 9．HAP has been of interest because of their mineral components being similar to bone and teeth of human body. With the increase of development of global elder people, the research for HAP biomaterials would has more valuable and prosperous outlook.
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