Formation of calcium phosphate layer on ceramics with different reactivities

Phosphorus Research Bulletin, 1999

Calcium deficient hydroxyapatite with Ca/P atomic ratio comprised between 1.5 and 1.667 were densified by hot pressing. Hot pressed powders were transformed into hydroxyapatite-tricalcium phosphate biphasic ceramics. After hot

Journal of the American Ceramic Society, 2005

Composite (biphasic) mixtures of two of the most important inorganic phases of synthetic bone applications-namely, calcium hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 (HA)) and tricalcium phosphate (Ca 3 (PO 4 ) 2 (TCP))-were prepared as submicrometer-sized, chemically homogeneous, and highpurity ceramic powders by using a novel, one-step chemical precipitation technique. Starting materials of calcium nitrate tetrahydrate and diammonium hydrogen phosphate salts that were dissolved in appropriate amounts in distilled water were used during powder precipitation runs. The composite bioceramic powders were prepared with compositions of 20%-90% HA (the balance being the TCP phase) with increments of 10%. The pellets prepared from the composite powders were sintered to almost full density in a dry air atmosphere at a temperature of ∼1200°C. Phaseevolution characteristics of the composite powders were studied via X-ray diffractometry as a function of temperature in the range of 1000°-1300°C. The sintering behavior of the composite bioceramics were observed by using scanning electron microscopy. Chemical analysis of the composite samples was performed by using the inductively coupled plasma-atomic emission spectroscopy technique.

1999

Two different preparations of biphasic calcium phosphate (BCP) were characterized in vitro: BCP 1 from a mechanical mixture of hydroxyapatite (HA) and b-tricalcium phosphate (b-TCP) powders, and BCP 2 from calcination of a calcium-de®cient apatite (CDA). The structural, physicochemical and mechanical parameters of these two preparations were investigated, and two different macroporous BCP 1 MBCP 1 and BCP 2 MBCP 2 implants were manufactured and implanted in rabbit bone for in vivo bioactivity studies. Scanning electron microscopy observations showed that MBCP 1 implants had a signi®cantly higher degradation rate P 50X0001 than MBCP 2 implants. This was probably caused by the presence of calcium oxide impurities in BCP 1 and the more intimate mixture and stable ultrastructure of BCP 2 . No signi®cant difference about the newly formed bone rate in these two BCP preparations was observed. Very slight variations in sintering conditions appeared to in¯uence the biodegradation behavior of the two MBCP implants despite their identical HA/b-TCP ratios and similar porosity. Precise and complete in vitro characterization enabled us to understand and predict in vivo degradation behavior. # 1999 Kluwer Academic Publishers * BCP 1 consisted of a mechanical mixture of pure commercial HA and b-TCP powders (Merck,

Journal of materials science. Materials in medicine, 1997

The experimental conditions for the synthesis of sub-micrometre, spherical particles of calcium hydroxyapatite [Ca10(PO4)6(OH)2] (HA) and tricalcium phosphate [Ca3(PO4)2] (TCP) are investigated through chemical coprecipitation from the aqueous solutions of calcium nitrate and di-ammonium hydrogen phosphate salts. The precipitation process employed was also found to be suitable for the production of sub-micrometre HA/TCP composite powders in situ. The synthesized pure HA and TCP powders were found to be stable even at 1300 degrees C in air for prolonged heating times. Bioceramic sample characterization was achieved by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and density and surface area measurements. Crystallographic analyses of HA powders were performed by the Rietveld method on the powder XRD data.

Materials Research, 2013

The aim of this study was to characterize calcium phosphate ceramics with different Ca/P ratios and evaluate cell response of these materials for use as a bone substitute. Bioceramics consisting of mixtures of hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) powders in different proportions were pressed and sintered. The physical and chemical properties of these bioceramics were then characterized. Characterization of the biological properties of these materials was based on analysis of cell response using cultured fibroblasts. The number of cells attached to the samples was counted from SEM images of samples exposed to cell culture solution for different periods. These data were compared by analysis of variance (ANOVA) complemented by the Tukey's test. The TCP sample had higher surface roughness and lower density. The adherence and growth of FMM1 cells on samples from all groups was studied. Even though the different calcium based ceramics exhibited properties which made them suitable as bone substitutes, those with higher levels of β-TCP revealed improved cell growth on their surfaces. These observations indicated two-phase calcium phosphate based materials with a β-TCP surface layer to be a promising bone substitute.

Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2008

In this study, we report a new observation on the phase conversion that occurs during the sintering of hydroxyapatite (HA)-tricalcium phosphate (TCP) biphasic ceramics. During the sintering of the HA-TCP mixture powders, a large amount of TCP was converted into HA, as detected by X-ray diffraction. The amount of TCP transformed into HA was 10-90% of that initially added. From the electron probe microscopy analysis, the HA transformed from TCP was found to be Ca-deficient with Ca/P ratios of 1.62-1.64. The dissolution behavior and osteoblastic responses in a series of HA-TCP biphasic ceramics (10-90% TCP) were assessed. The solubility of the HA-TCP biphasic ceramics was intermediate between that of the HA and TCP pure ceramics. However, in the case of the HA-90% TCP biphasic ceramic, the solubility was even higher than that of pure TCP. The cell proliferation and alkaline phosphatase activity of the cells on the biphasic ceramics were lower than those on pure HA, but higher than those on pure TCP. However, particularly in the HA-50% TCP biphasic composition, the cellular responses were significantly higher than those on pure HA. It is considered that the Ca-deficient apatite newly formed from the TCP may affect in some way the solubility and biological properties of the HA-TCP biphasic ceramics.

Glass and Ceramics, 2011

The properties of Ca-deficient hydroxyapatite powder synthesized from calcium nitrate and ammonium hydrophosphate at 60°C, pH = 7, and Ca/P = 1.67, 1.61, and 1.48 are presented. After sintering at 1100°C for 6 h the phase composition of the ceramic based on these powders was represented by tricalcium phosphate (Ca/P = 1.48) or tricalcium phosphate hydroxyapatite (Ca/P = 1.67 and 1.61). The grain size of the ceramic was 100-1000 nm.

Doklady Chemistry, 2007

Synthetic materials based on hydroxyapatite (HA), an analogue of the mineral component of the bone tissue, are used in medicine for the repair of damaged bone tissue . A new repair technology is based on implanting porous ceramic scaffolds containing cultivated cells and proteins into the bone tissue . The formation of new bone tissue is a complex process that includes protein adsorption as an important stage . Scaffolds should be resorbable with time in the human body with gradual replacement by newly formed bone tissue and should ensure a high protein-adsorption capacity. Hydroxyapatite is stable against dissolution by body fluids, whereas tricalcium phosphate (TCP) has a much higher resorption rate compared to that of HA. By varying the component ratio in an HA/TCP composite, one can control the resorption rate. The problems of design of such composite materials have been considered in reviews . Two-phase composites (TCMs) are produced by thermal decomposition of calcium-deficient HA followed by sintering . Using this method, it is difficult to control the component ratio in the material. Some aspects of the influence of the phase composition on the biological behavior of TCMs remain obscure. This study is devoted to the production of TCMs with specified composition and porosity and elucidation of the question of which factor, porosity or phase composition, is more important for protein adsorption.

Journal of Biosystems Engineering, 2014

The aim of this research was to develop and evaluate natural hydroxyapatite (HA) ceramics produced from the heat treatment of pig bones. Methods: The properties of natural HA ceramics produced from pig bones were assessed in two parts. Firstly, the raw materials were characterized. A temperature of 1,200°C was chosen as the calcination temperature. Fine bone powders (BPs) were produced via calcinations and a milling process. Sintered BPs were then characterized using field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared (FTIR) spectroscopy, and a 2-year in vitro degradability test. Secondly, an indirect cytotoxicity test was conducted on human osteoblast-like cells, MG63, treated with the BPs. Results: The average particle size of the BPs was 20 ± 5 μm. FE-SEM showed a non-uniform distribution of the particle size. The phase obtained from XRD analysis confirmed the structure of HA. Elemental analysis using XRF detected phosphorus (P) and calcium (Ca) with the Ca/P ratio of 1.6. Functional groups examined by FTIR detected phosphate (PO4 3-), hydroxyl (OH-), and carbonate (CO3 2-). The EDX, XRF, and FTIR analysis of BPs indicated the absence of organic compounds, which were completely removed after annealing at 1,200°C. The BPs were mostly stable in a simulated body fluid (SBF) solution for 2 years. An indirect cytotoxicity test on natural HA ceramics showed no threat to the cells. Conclusions: In conclusion, the sintering temperature of 1,200°C affected the microstructure, phase, and biological characteristics of natural HA ceramics consisting of calcium phosphate. The CaP based natural ceramics are bioactive materials with good biocompatibility; our results indicate that the prepared HA ceramics have great potential for agricultural and biological applications.

The Journal of Trauma: Injury, Infection, and Critical Care, 2000