Hydrothermal conversion of Malaysian coral to hydroxyapatite, a bone substitute: synthesis, characterization and in-vitro solubility studies

Abstract
The purpose of this study is to synthesize hydroxyapatite, Ca1o(P04)s(OH)z from Malaysian coral of species Porites Jutea, to be used as bone substitute in medicine and dentistry. Coral was characterized using x-ray diffraction (XRD}, fourier transform infrared (FT-IR), x-ray fluorescence (XRF), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). The characterization study involves the determination of coral phases, element content, morphology and thermal stability of coral used in this study. The characterization was carried out in order to ensure that the coral used in this study was suitable raw material. Characterization results revealed that coral was made up of 97.76% calcium carbonate 1n aragonite phase, while the remaining 2.24% belongs to minor and traces element. Thermal analysis of coral showed that about 44% weight loss occurred at 791 oc which was identical to that of commercial calcium carbonate. Coral of this species possessed porous structure with interconnectivity throughout the skeletal. It has a consistent pore size of around 117,...m. Coral was successfully converted into hydroxyapatite, through hydrothermal reaction. Hydrothermal reaction was carried out in a high-pressure batch reactor at temperature range between 150°C - 250°C and pressure of 34 atmospheres, generated by water vapor. Many parameters have been studied in order to find the optimum conditions of hydroxyapatite formation, such as reaction temperature (150°C- 250°C), contact time (1 - 42 hours}, amount of DAP (less and excess than stoichiometric molar ratio) and pH value (pH 9 -11) of initial solution. The formation of single phase hydroxyapatite with excellent thermal stability and minimal carbonate content was obtained at 250°C, 6 hours of contact time, 30% excess of DAP and at pH 9 of the initial solution. At this operating condition, the formation of other phases such as calcium hydroxide and calcium carbonate were not detected. The in-vitro stability studies of hydroxyapatite were performed in phosphate buffer saline (PBS) and de-ionized water at 37°C to determine its solubility in physiological environment. Hydroxyapatite synthesized at optimum conditions was the most stable when immersed in both solutions after 55 hours. .. .....
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Keywords
Bone substitute , Characterization
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