Due to its biocompatibility, bioactivity and high durability properties, hydroxyapatite (HA) has a wide range of applications in medical cases such as bone defect treatment and bone tissue regeneration. Biological apatite as the most important integrity of the mineral part of hard tissues consists of tiny hydroxyapatite crystals in nanoregime. It seems that using the artificial hydroxyapatite with similar structure and chemical composition to biological apatite could increase its durability inside the natural hard tissues. The aim of the present work was the synthesis of nano structured hydroxyapatite via different routes, comparison of their characterization and enhancement of the bioactivity and bioresorbability of prepared hydroxyapatite by controlling its crystal size and chemical composition. Nano structured hydroxyapatite was prepared by mechanical activation and sol-gel routes. X-ray diffraction technique (XRD), Fourier transform infra red spectroscopy (FTIR) and transmission electron microscopy (TEM) were used to characterize the prepared hydroxyapatite powders. The synthesized powder was soaked in simulated body fluid (SBF) for various periods of time in order to evaluate its bioresorbability and bioactivity after immersion in SBF. Atomic absorption spectroscopy (AAS) was used to determine the dissolution rate of calcium ions in SBF media. Results showed that the mechanical activation prepared HA powder had nano scale structure with mean size of 29 nm and the sol gel prepared HA powder had nano scale structure with mean size of 25 nm. Ionic dissolution rate of prepared nano structured powders was higher than the conventional HA (with micron size) and were similar to biological apatite. It could be concluded that bioactivity behavior of hydroxyapatite powder is affected by its crystalline size. By using the nano structure HA powder with less than 50 nm crystalline size, the optimum bioactivity and bioresorbability would be achieved.

Keywords: Hydroxyapatite, Nano structure, Mechanical activation, Sol-gel, Bioactivity, Bioresorbability.

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