Synthesis And Characterisation Of Calcium Phosphate Nanoshells Using DOPA and DPPA Liposome Templates
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Date
2012-01
Authors
Yeo, Chiew Hwee
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Abstract
Calcium phosphates (CaPs) are very useful biomaterials in bone tissue engineering due to their excellent biological properties. The major difficulties facing in most of the synthesising methods are the size and the shape-controlling of CaP particles. Therefore, the aim of this project is to synthesise CaP nanoshells by using liposomes as template in order to control the particle size and the shape of the CaP particles. The effectiveness of liposomes (1, 2 dioleoyl-sn-glycero-3-phosphate (sodium salt) (DOPA) and 1, 2-dipalmitoyl-sn-glycero-3-phosphate (sodium salt) (DPPA)) as template were firstly investigated in this project. The results showed that both liposomes formed spherical structures of unilamellar liposomes, in which fulfil the morphology and the size requirement of templates of CaP nanoshells by using suitable preparation method. The effect of concentrations of sodium hydroxide (NaOH) (0.025 M, 0.050 M, 0.075 M, 0.100 M or 0.125 M) and calcium ions (Ca2+) (0.050 M, 0.100 M, 0.150 M or 0.200 M) to the properties of CaP nanoshells prepared using DOPA and DPPA liposome templates were then studied. NaOH plays the role as a base solution to increase the pH, and thus, control the supersaturation of the mixture of CaP nanoshells. In addition, Ca2+ is another main parameter to influence the electrostatic localisation with liposome template and the growth of the CaPs on the liposome template. The morphology, final calcium-to-phosphorus (Ca/P) molar ratio, particle size, particle size distribution, zeta potential, functional group and phase of CaP nanoshells were evaluated by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM),energy dispersive X-ray spectrometer (EDX), Zetasizer nano ZS, Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). From the investigation of different concentrations of NaOH and Ca2+, the best results in this project showed that spherical CaP nanoshells with Ca/P molar ratio of 0.97 were formed at pH of 10.52 by using DOPA liposome template when 0.100 M of NaOH coupled with 0.100 M Ca2+ were used. In contrast, the needle or irregular shaped particles were observed in the CaP nanoshells prepared with DPPA liposome template. CaP nanoshells prepared using DOPA and DPPA liposome templates were indicated as poorly crystalline (favorable in biomedical application) or amorphous in FTIR and XRD analyses. Results showed that the CaPs prepared without template had large and unstable of agglomerated and crystallised particles due to the homogenous nucleation growth, in which involved growth mechanism of nucleation-aggregation-agglomeration. In addition, from growth mechanism, it was found that the stability of liposome template can influence the heterogeneous nucleation growth of CaP nanoshells, in which is an important factor in the synthesis of CaP nanoshells.
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Calcium phosphate