یک فرآیند سنتز جدید ژل-سل (فرآیند تولید مواد جامد از مولکول های کوچک) با دمای پایین برای هیدروکسی آپاتیت نانوبلوری پایدار حرارتی A novel low temperature sol–gel synthesis process for thermally stable nano crystalline hydroxyapatite

۱٫ Introduction In past few decades, synthetic hydroxyapatite (HA:Ca10(PO4)6(OH)2) has been extensively used as a bone substitute material due to its chemical and structural similarity with natural bone mineral [1–۳]. The HA which can be derived from natural sources or synthesized by various methods is regarded as a good bioactive substance, since it forms a strong chemical bond with the host bone tissue, and hence it is recognized as a good bone graft material. However, the particle size of the natural apatite in the bone mineral is in the nano scale with a very large surface area. Synthetic HA particles (HAp) on the contrary have low surface area and present strong bonding properties [4]. Many researchers have attempted to engineer its properties such as bioactivity, solubility and sinterability by controlling its composition, morphology and particle size [5–۷]. During recent years, a number of different techniques, such as precipitation, sol–gel, hydrothermal, multiple emulsion, biomimetic deposition, electrodeposition [8–۱۰], have been applied for the synthesis of HA. The sol–gel method is preferred due to its low synthesis temperature, high product purity, homogenous molecular mixing and the ability to generate nano sized particles compared to other alternatives [11]. Sol–gel method for the preparation of HAp can usually form fine-grain microstructure containing a mixture of nano-to-submicron particles with crystalline structure. It has been reported that these crystals are very efficient to improve the contact and stability at the artificial/natural bone interface observed in vitro and in vivo environments [12]. The synthesis of HAp by sol–gel method requires a correct molar ratio of 1.67:1 between Ca and P in the final product [13]. Moreover there are a lot of different calcium and phosphorus precursors used for HAp synthesis, as reported sol–gel processes in the literature. Besides, bioactivity of Ca–P based materials is dependent on many factors such as the synthesis procedure, precursor reagents, impurity contents, crystal size and morphology, concentration and mixture order of reagents, pH and temperature. Selection of the route of synthesis depends on the application [3,5,11–۱۳]. In this work, a novel, low temperature alcohol based sol–gel method for the synthesis of pure nano-HAp was developed using Ca(NO3)2.4H2O and NH4H2PO4 as calcium (Ca) and phosphorus (P) precursors. The advantages of this novel technique over the previous studies [3,14–۲۶] concerning sol–gel synthesis of HAp most importantly include: (a) carrying out the reaction at room temperature, (b) obtaining the gel formation without any dispersant and (c) forming nano sized HAp without using any grinding process. The structure of nano-HAp synthesized with this novel method was investigated using FTIR, XRD, DTA/TGA, SEM and TEM. We have found that pure HAp phase with hexagonal-crystal structure could be synthesized at room temperature with nanometer size.