Hydroxyapatite (HA) is a well known candidate for many applications in dentistry and medicine such as bone grafts and coatings for medical implants. Studies have shown that nano-structured HA exhibits improved mechanical properties and biocompatibility. To optimize the benefits of nano-sized precursors, the particles must be of a uniform shape and size and have minimum degree of agglomeration. Biomineralization is among those of new methods for synthesis of nano structured HA. In recent studies, by using a specific bacterial strain of Serratia with over producing phosphatase enzyme, nano crystalline HA has been synthesized. The aim of this study was synthesis of nano crystalline HA using an Iranian bacterial strain. For this purpose, Iranian local strains of Serratia were studied for their enzymatic activity. The strain with higher activity of cell wall associated phosphatase enzyme was selected. The selected strain ( Serratia marcescens PTCC 1187) was cultivated. The pellet of S. marcescens PTCC 1187 was separated and exposed to Glycerol 2-phosphate and Calcium chloride at pH from 7 to 9.5. After 14 days of incubation the white precipitated material was dried and sintered. The characterisation of sintered and unsintered powders was performed by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), fourier transform infrared spectroscopy (FTIR) and thermogravimetery analysis (TG). Results showed that the unsintered powder contained of amorphous materials and crystalline HA. The maximum powder production was occurred at pH 8 and temperature of 37 ?C. According to XRD pattern of sintered powder at 600 ?C all of the characteristic peaks of HA were occurred and the crystallinty of synthesized powder was in the standard range. The grain size based on Williamson-Hall method estimated 25-29 nm. TEM images revealed that the particle size of HA powder was 25-30 nm. The FTIR pattern showed that all of the characteristic peaks of HA were occurred exactly in the same wavelengths of standard HA pattern. Furthermore, in the FTIR pattern of HA powder, the peaks related to CO 3 2- and HPO 4 2- functional groups were observed. The presence of these functional groups shows more similarity between the synthesized powder and biological HA. SEM images indicated that the exist agglomerated clusters had smaller size comparing to previous studies. TEM images confirmed that the shape and size of the particles were relatively uniform and the agglomeration was lower comparing to conventional methods. It has been demonstrated that the nano-sized HA powder was produced in this study with standard crystallinity and low degree of agglomeration. This powder could be used in medicine, dentistry and as vector for pharmaceuticals and biological materials such as genes.
