Papers by Keyword: Calcium Deficient Hydroxyapatite

Abstract: In this work, nanosized calcium deficient hydroxyapatite (nCDHA) was synthesized by the precipitation method, and then utilized as an adsorbent for removal of Fe (II), Cu (II), Ni (II) and Cr (VI) ions from aqueous solutions after characterizing it by various techniques as scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and BET method. A possible structure of synthesized nCDHA was proposed. The adsorption study indicated that the adsorption equilibrium is well fitted with Langmuir isotherm model with the maximum adsorption capacities followed the order of Fe (II) > Cu (II) > Ni (II) > Cr (VI) with the values of 137.23, 128.02, 83.19 and 2.92 mg/g, respectively. The ion-exchange mechanism was dominant for the adsorption of metal ions onto nCDHA at initial metal concentrations lower than 0.01 mol/L. Along with the ion-exchange mechanism, there was an additional precipitation occurred on the surface of nCDHA in the case of Fe (II) and Cu (II) at initial concentrations higher than 0.01 mol/L.

Abstract: In current research three different prepared calcium deficient hydroxyapatite samples were evaluated for dental application. Lyophilized (lyoCDHAp), spray dried (spCDHAp) powders and wet precipitates (pCDHAp) were characterized by XRD, FTIR, SEM and BET analysis. Results showed, that various drying processes did not affect initial crystallinity, phase and chemical composition of samples. Small agglomerates (up to 2 μm) beside separated particles for lyoCDHAp and spCDHAp were observed in SEM analysis. LyoCDHAp and spCDHAp powders could be used as desensitizing component in the dentifrice, while pCDHAp could be more resorbable due to smaller particle size and induce remineralization of caries sites in the enamel.

Abstract: The effect of excess calcium and aging media on calcium phosphate biomaterials mechanical strength was studied. The variation of excess calcium and sample type has shown different performance when they are being aged in the moist environment (ME) and the simulated body fluid (SBF). The calcium phosphates were synthesized via low temperature hydrothermal method and sampled to two types of powder-water (3:2) mixture and paste for 90 days of the aging time. Two mechanical tests were applied, compression and diametrical tensile test, while XRD to evaluate phases. Scanning electron micrograph showed the paste samples that soaked in SBF was better entanglement of the particles, better compression strength but with degradation and diametrical tensile strength improvement by aging. Calcium hydroxide and ammonium di-hydrogen phosphoric was traced in all the samples along with calcium deficient hydroxyapatite as the main phase.

Abstract: The difficulty of beta tricalcium phosphate (β-TCP) crystallization in aqueous media opens the question whether β-TCP can be produced using an alternative pathway. Amorphous calcium phosphate (ACP) is metastable in an aqueous environment and prefers a more stable apatite phase. Others have transformed a crystallized calcium deficient hydroxyapatite (Ca-def HAp) into β-TCP, but automatic transformation from ACP to Ca-def HAp followed by transformation to β-TCP has not been addressed. This work shows the formation of Ca-def HAp after different aging times of ACP and the subsequent transition to β-TCP. An amorphous phase with a Ca/P ratio of 1.5 was synthesized, rinsed, filtered and excess fluid removed for maturation. The resulting apatite was monitored with X-ray diffraction at different temperatures. Heating at 700 °C then investigated the transition to β-TCP. It was found that Ca-def HAp formed at short aging times produced a combination of alpha and beta phases, but a longer aging time led to pure β-TCP.

Abstract: The effect of structure and composition of calcium phosphate (CaP) nanoparticles namely hydroxyapatite (HA), calcium deficient hydroxyapatite (CDHA) with Ca/P ratio ranging from 1.33 to 1.61 and tricalcium phosphate (β-TCP), on the efficiency of nanoparticles as an ideal drug carrier have been investigated. Ibuprofen, an anti-inflammatory drug was chosen for this study. The CaP nanoparticles were prepared by microwave accelerated wet chemical synthesis method and were characterized by X-ray powder diffraction, infrared spectroscopy, and electron microscopic techniques. The loading and release profiles of ibuprofen from the nanocarriers was studied using UV-Vis spectroscopy. Maximum loading of the drug was observed in β-TCP (75%) followed by CDHA of Ca/P ratio 1.5. Both samples have same Ca/P ratio but have different crystal structure. Low amount of drug loading was observed in HA and other CDHAs which have Ca/P ratio different from 1.5. Although, all the samples exhibits sustained release of ibuprofen for about 7 days, the maximum release was also shown by β-TCP (26%). Among HA and CDHAs, the amount of ibuprofen release increases with increasing Ca/P ratio. The loading and release profile of ibuprofen drug seems to be strongly related to the Ca/P ratio and structure of CaP nanocarriers.

Abstract: In recent years there has been increasing interest concerning the synthesis of hollow materials in nanometer to micrometer dimensions. Hollow hydroxyapatite(HAP) microspheres with pores on their surfaces were prepared by a Li-Ca-B glass in situ immersion conversion process in an aqueous phosphate solution at 37°C. The chemical reaction ability of the Li-Ca-B glass was studied by immersing the glass in SBF solution, and the phases of the reaction product were identified by the XRD method. The morphology, composition, phases and thermal property of the hollow HAP microspheres were investigated using by chemical analysis, SEM ,and XRD . The microphere wall consisted of calcium deficient hydroxyapatite (CDHAP) crystals only. Furthermore, the formation mechanism of the hollow HAP microsphere was also discussed.

Abstract: The aim of this study was to investigate the sol gel synthesis of HA/FA nanoparticles and the possible formation of TCP phase or unstoichiometric calcium deficient hydroxyapatite (CDHA) from the precursors with a Ca/P ratio of 1.62. In order to prepare the sol, the solutions of Triethyl phosphite, ammonium fluoride and calcium nitrate in ethanol were used respectively as P, F and Ca precursors. The crystallinity, particle and crystallite size, powder morphology, chemical structure and phase analysis were investigated by SEM, XRD, FT-IR and Zeta sizer experiment. A multiphase compound containing hydroxyapatite (HA) and fluoroapatite (FA) nanoparticles and calcium deficient hudroxyapatite (CDHA) agglomerates was obtained. The size of the crystallites estimated from XRD patterns using Scherrer equation and the crystallinity of HA phase were about 5 nm and 66% respectively. The zeta sizer experiments for the dispersed particles in its own conditions showed an average size of 98 nm.

Abstract: Two biphasic BCP ceramic samples were synthesized by chemical precipitation and microwave curing of calcium deficient hydroxyapatite CDHA under the same pH value and temperature but varied in their initial Ca/P molar ratio. Precipitates were characterization after thermogravimetric analysis, fourier transform infrared spectroscopy, X-ray diffraction, atomic absorption spectroscopy and TEM. Hydroxyapatite (HA) contents were measured for the two biphasic calcium phosphate (BCP) ceramics by sintering the calcium-deficient apatites (CDHA). The results reveal two condensation mechanisms of HPO42- affecting the Ca/P molar ratio after calcination. The X-ray diffraction patterns of BCP powders show the in situ formation of -TCP in the BCP powder. The amount of -TCP phase increases as the initial Ca/P molar ratio decreases due to more calcium deficiency in CDHA structure. The influence of HPO42- incorporation on increasing -TCP phase content after calcination is evaluated. TEM micrographs proved the effect of microwave curing during the preparation process on reducing of particle size to nanoscale range and the destruction of CDHA to finer HA and -TCP particles upon calcination.

Abstract: The biological behavior of a new bioactive material composed of calcium-deficient hydroxyapatite, octacalcium phosphate, and β-tricalcium phosphate was investigated by in vitro indirect and direct cytotoxicity, cell adhesion and proliferation tests, and by in vivo subcutaneous and bone implantation in rats. The results of the in vitro studies showed that the material is biocompatible and no cytotoxic. Slightly poorer initial cell adhesion and lower cell proliferation than in control was observed, which were attributed to the reactivity and roughness of the material surface. In vivo results showed that the material is biodegradable and bioactive in bone tissue, but only biocompatible and partially biodegradable in soft tissue.

Abstract: Three types of calcium-deficient apatite fibers (Ca-def AF) were synthesized by a homogeneous precipitation method using starting solution with Ca/P ratios of 1.00, 1.50 and 1.67, and then the resulting fibers were characterized by XRD, FT-IR and SEM. Especially, the microstructure including strain and defect of individual Ca-def AF was examined by transmission electron microscopy (TEM). All the resulting Ca-def AFs had a single phase of apatite, and contained carbonate ions. These fibers were of single crystal, and highly strained. However, when Ca-def AFs were heated to higher than 800 °C, they changed to HAp and TCP biphases. The content of the carbonate group in the Ca-def AFs decreased with heating temperature.