Synthesis of calcium phosphate nanostructured particles by liquid flame spray and investigation of their crystalline phase combinations

Calcium phosphate-based (CaP-based) bioceramics have been widely applied in biomedical applications (such as dental roots, hard (bone) tissue engineering, drug delivery, gene delivery, bioimaging, coating metallic implants, etc.) for the last two decades. This is because of their excellent biomedical properties, which include biocompatibility, bioactivity, osteoconductivity, and osteoinductivity, as well as favorable (micro- and nano-)mechanical, surface, and physio-chemical properties. In pursuit of the desired properties for the targeted bioapplicatoins, different synthesized CaP compounds are prepared in several phase combinations. Therefore, bi-, tri-, and multiphasic formulations of CaP-based (nano)particles have recently attracted intense interest due to their ability to adjust the major (bio)properties of the biomaterial by changing the ratio among the phases. Thus, developing simple, cheap, up-scalable, reproducible, and high-speed synthesis methods of the CaP nanoparticles with different ratios of phases offers an interesting research area.
In this study, calcium phosphate powder has been successfully synthesized in different phase compositions by liquid flame spray (LFS). LFS is an ultra-short synthesis time aerosol method and meets the above-mentioned criteria. Calcium nitrate tetrahydrate (Ca(NO3)2⋅4H2O, Merck) and ammonium phosphate dibasic ((NH4)2HPO4, Sigma-Aldrich) have been used as the sources of Ca and P, respectively. The solvent was ethanol and deionized water, with an ethanol-to-water volume ratio of 40-60. By changing the ratio of the precursors, different phase combinations of calcium phosphate nanoparticles have been synthesized. The synthesised powder was collected from the flame with an electrostatic precipitator (ESP). Eventually, the effect of the Ca/P ratio on the crystallographic and structural properties of the synthesized powder was investigated by different characterization methods. Subsequently, the crystalline phase recognition and crystallite size of the synthesized powder were investigated by means of X-ray diffraction (XRD) analysis. Moreover, the morphological shape and size of the synthesized particles were determined from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) micrographs.