Abstract
Synthesis of hydroxyapatite (HA) through sol–gel process in different solvent systems is reported. Calcium nitrate tetrahydrate (CNTH) and diammonium hydrogen phosphate (DAHP) were used as calcium and phosphorus precursors, respectively. Three different synthesis reactions were carried out by changing the solvent media, while keeping all other process parameters constant. A measure of 0.5 M aqueous DAHP solution was used in all reactions while CNTH was dissolved in distilled water, tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) at a concentration of 0.5 M. Ammonia solution (28–30%) was used to maintain the pH of the reaction mixtures in the 10–12 range. All reactions were carried out at 40 ± 2°C for 4 h. Upon completion of the reactions, products were filtered, washed and calcined at 500°C for 2 h. It was clearly demonstrated through various techniques that the dielectric constant and polarity of the solvent mixture strongly influence the chemical structure and morphological properties of calcium phosphate synthesized. Water-based reaction medium, with highest dielectric constant, mainly produced β-calcium pyrophosphate (β-CPF) with a minor amount of HA. DMF/water system yielded HA as the major phase with a very minor amount of β-CPF. THF/water solvent system with the lowest dielectric constant resulted in the formation of pure HA.
Highlights
Hydroxyapatite [Ca5(PO4)3OH] (HA), denoted as [Ca10(PO4)6(OH)2] in order to show the hexagonal crystal unit cell consisting of two entities, is an important and extensively studied material because of its wide range of applications, especially in the biomedical field [1]
Diffractograms for different samples are reproduced in figure 2, where characteristic peaks for HA are shown with red arrows and peaks for β-calcium pyrophosphate (β-CPF) are marked with black arrows at their corresponding 2θ angles
Samples were compared with database, matched with cards for HA (PDF-04-014-8416) and β-CPF (PDF-00-009-0346), and diffractograms are provided in the electronic supplementary material
Summary
Hydroxyapatite [Ca5(PO4)3OH] (HA), denoted as [Ca10(PO4)6(OH)2] in order to show the hexagonal crystal unit cell consisting of two entities, is an important and extensively studied material because of its wide range of applications, especially in the biomedical field [1]. Critical importance in bone tissue engineering applications due to its similar crystallography with 2 minerals of natural bones, bioactivity and non-toxicity, which are essential properties of a material suitable for bone regeneration [4]. Bone contains about 70% calcium phosphate by weight, which makes it an important material especially for hard tissue development. Bone has a fairly complex, hierarchical [13], three-dimensional structure encompassing self-assembled discrete building blocks composed of collagen triple helices, mineralized by bioapatite nanocrystals [14,15], which is formed by a cell-mediated process
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