Papers by Keyword: Ca/P Ratio

Abstract: Hydroxyapatite (HA) is one of the most common ceramic materials used for bone substitutions or reconstructions [1]. HA synthesis from natural sources is convenient relative to synthetic HA preparation while ensuring a similarity with viable bone tissue in terms of chemical composition and some other properties. One of the most important markers used for hydroxyapatite identification and differentiation from other calcium phosphates is the Ca/P ratio [2]. In order to perform a proper identification, this ratio should be evaluated with high accuracy, which involves a correct determination of the elemental concentrations. This study was made on a series of samples, derived from bovine osseous tissue, thermaly treated at 1000, 1100 and 1200°C. Establishing the influence of sample preparation on the Ca/P ratio assessment from the energy dispersion spectrometry (EDS) coupled with scanning electron microscopy determinations was intended. The samples were prepared by two completely different methods: mechanical fracture (without further preparation) and milling followed by homogenization. Regardless the sample preparation method, the analytical results represents the five measurements average performed on different spots.The EDS results showed that, within the same group, the compositional dissimilarities between the samples treated at different temperatures do not exceed 10% regardless of the sample preparation technique. For the same thermal treatment temperature, slight differences between the elemental chemical compositions of differently prepared samples were observed. The most important effect was a 20% decrease of the average Ca/P ratio for the samples prepared by milling and homogenization in regard to the mechanical fractured ones. Thereby, heat treated bovine bone samples’ milling and further homogenization for performing semi quantitative EDS analysis allows the Ca/P ratio assessment with a better accuracy.

Abstract: Calcium polyphosphate (CPP) bioceramics with different Ca/P ratios were fabricated. It was shown that the contents of CPP in the sintered ceramics decrease with the increasing Ca/P ratios (0.5-1.0) of the precursors. The higher the Ca/P ratios of precursors were, the more complex the phases of polymerization were. The compressive strengths of ceramics sintered at the same temperature showed a linear decreasing tendency with the increasing Ca/P ratio.

Abstract: Calcium phosphate ceramics (CPC) have been attractively used in different areas of biomedical applications, such as substances of artificial hard tissue replacement implants, drug delivery system due to their biocompatibility and bioactivity. In this work, three calcium phosphate powders between Ca/P molar ratio 1.50-1.67 were synthesized by aqueous precipitation method, using the mixture of Ca(NO3)2·4H2O and H3PO4 solutions to ammonia solution. During the precipitation reaction, Ca/P molar ratio was adjusted by controlling pH of the solution between 8.0 and 10.5 by the addition of ammonium hydroxide solution. All powders were treated at 800 oC for 2 hrs. The calcined powders were immersed in pH 7.4 distilled water at 37°C for 3 and 7 days. Decomposition and related dissolution with the various Ca/P ratios were investigated by XRD, FTIR, and TEM observation.

Abstract: The effect of Ca/P ratio on surface dissolution of hydroxyapatite [Ca10(PO4)6(OH)2, HA] in distilled water was investigated. The stoichiometric HA powder and desired Ca/P ratio achieved by adding either Ca3(PO4)2 for a Ca/P ratio of 1.62 or CaO for a Ca/P ratio of 1.72 were used as starting materials. Dense HA ceramics were obtained by sintering at 1200 oC for 2 h in air with under moisture protection. The sintered specimens were then placed into 40 ml of pH 7.4 distilled water. After immersing for certain period of time at 37 oC, crystal structure, weight loss and microstructure of the specimens were investigated. As increasing the immersion time, circular cavities similar to that normally attributed to osteoclast resorption lacunae were observed. As a result, it was found that the dissolution of HA along the grain boundary and subsequently microstructural disintegration was more distinct in 1.62 and 1.72 samples compared to pure HA.