Hydrothermal conversion of Malaysian coral to hydroxyapatite, a bone substitute: synthesis, characterization and in-vitro solubility studies
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Date
2005
Authors
Samsudin, Mimi Rahayu
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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