Formation of Calcium Phosphate Whiskers in Hydrogen Peroxide (H2O2) Solutions at 90°C

A novel, one-pot technique of synthesizing calcium phosphate whiskers was developed. Commercially available β-tricalcium phosphate (β-Ca₃(PO₄)₂) powders were aged in unstirred 30% H₂O₂ solutions at 90°C for 48 h in ordinary glass media bottles. Resultant samples consisted of whiskers (200 nm wide and 5 μm-long) of a biphasic mixture of octacalcium phosphate (OCP: Ca₈H₂(PO₄)₆·5H₂O) and carbonated apatitic (apatite-like) calcium phosphate (Ap-CaP). As-formed whiskers possessed a Ca/P molar ratio of 1.46 and a BET surface area of 8 m²/g. Upon soaking these whiskers in a Tris-HCl-buffered SBF solution of 27 mM HCO₃⁻ for 6 days, Ca/P molar ratio and surface area values were increased to 1.60 and 52 m²/g, respectively. The technique, owing to its simplicity, may prove useful in providing large amounts of biocompatible short whiskers for numerous technology sectors.     

Brushite Cements from Polyphosphoric Acid, Calcium Phosphate Systems

Brushite cement is more soluble than apatitic cement under physiological conditions. Thus, brushite cement may be resorbable in vivo when used as a bone substitute material. Our group has previously reported the formation of brushite cement from orthophosphoric acid and several calcium phosphates such as β-tricalcium phosphate or nanocrystalline hydroxyapatite. In this study, polyphosphoric acid was investigated as a calcium phosphate cement component. We found that brushite cement was not formed when polyphosphoric acid was mixed with β-tricalcium phosphate but instead monocalcium phosphate monohydrate (MCPM) was formed. Although stronger in compression when tested dry, MCPM is readily soluble under physiological conditions and cement loses structural integrity within hours of aging in water. However, by varying the solid component phases, we have discovered a new route to the formation of brushite cement. The mixture of polyphosphoric acid, water, and tetracalcium phosphate yielded cement composed predominantly of brushite. The mechanical performance, microstructure, and setting time of this cement appeared to be dependent on the composition of the set cement, which in turn was determined by the composition of cement reactants in the cement slurry.     

Phase Evolution during the Formation of α-Tricalcium Phosphate

The formation of α-tricalcium phosphate from monobasic ammonium phosphate and calcium carbonate was investigated using a number of complementary techniques. Differential thermal analysis showed five distinct thermal events attributed to melting of the ammonium phosphate, decomposition of acidic calcium orthophosphate into an amorphous calcium metaphosphate, crystallization of β-calcium metaphosphate, crystallization of β-calcium pyrophosphate, and calcination of calcium carbonate. X-ray diffraction analyses as a function of temperature supported the evolution of these events and phases and also showed the formation of other intermediates, including an amorphous phase, apatite, lime, and β-tricalcium phosphate. Thermal gravimetric analysis (TGA) showed a large weight loss occurring between 150° and 250°C due to reaction between the acidic phosphate liquid and the calcium carbonate. This resulted in an amorphous intermediate with a Ca/P ratio between 0.5 and 1.0 from which both β-calcium metaphosphate and β-calcium pyrophosphate crystallized. Mass spectroscopy indicated that the ammonia and carbon dioxide were evolved in four different steps, while water was evolved in at least five steps. These decomposition steps correlated with those observed by TGA. Scanning electron microscopy indicated the formation of an intermediate phase that coated the calcium carbonate by 250°C. The proposed mechanistic reaction path to alpha-tricalcium phosphate involves the formation and consumption of the following sequence of intermediates: an acidic amorphous condensed phosphate; β-calcium metaphosphate and β-calcium pyrophosphate; lime, apatite, and β-tricalcium phosphate.     

Calcium phytate: Effect of ph and molar ratio on in vitro solubility

Calcium and phytate phosphorus were highly soluble below pH 4 at all molar ratios of calcium (Ca) to phytic acid (PA) studied (0.512.67). As pH is increased above 4, there is a drop in solubility, the magnitude of which depends on the Ca:PA molar ratio. Above pH 6, the greatest calcium precipitation occurred at molar ratios between 4 and 6.5; both lower and higher Ca:PA molar ratios showed higher calcium solubility. In contrast, phytate phosphorus solubility decreased in proportion to the Ca:PA molar ratio, showing essentially complete precipitation above the Ca:PA ratio of 5. The pentacalcium phytate salt probably predominates when calcium is not limiting. Under calcium-limiting conditions, the complexes resolubilize as the pH is increased above 7.     

Effect of the HA/β-TCP Ratio on the Biological Performance of Calcium Phosphate Ceramic Coatings Fabricated by a Room-Temperature Powder Spray in Vacuum

Four calcium phosphate ceramic coatings, the less soluble hydroxyapatite (HA) coating, the more soluble β-tricalcium phosphate (β-TCP) coating, and two biphasic calcium phosphate (BCP) coatings with HA/β-TCP ratios of 70/30 and 30/70 were fabricated by spraying each corresponding powder onto a titanium substrate at room temperature (RT) in a vacuum, in order to investigate the effect of the HA/β-TCP ratio on the dissolution behavior and the cellular responses of the coating. No secondary phases, except for HA and β-TCP, were observed for the coatings in the X-ray diffraction results. The coating compositions were almost the same as those of the starting powders because the coating was conducted at RT. Microscopic examination of the coatings revealed crack-free and dense microstructures. The BCP coatings exhibited dissolution rates intermediate between those of the pure HA and β-TCP coatings. The dissolution rate of the coatings was largely dependent on their HA/β-TCP ratio. The cell proliferation and differentiation results indicated that the cellular responses of the coatings were not proportional to their dissolution rates. The 3HA–7TCP (HA/β-TCP ratio of 30/70) coating exhibited an optimal dissolution rate for excellent biological performance.     

Regulating the multifactor during wet chemical synthesis to obtain calcium phosphate powders with controllable phase purity for bone repair

Calcium phosphate ceramics are widely used as bone repair materials owing to their excellent biocompatibility, bone conductivity, bone induction, and degradability. Although there are many methods for synthesizing calcium phosphate and controlling its phase composition, it is necessary to explore effective preparation methods by understanding the formation of calcium phosphate and its influencing factors. In this study, calcium phosphate powders with controllable phase compositions were synthesized using a wet chemical precipitation method by adjusting the process parameters (aging time, bipolar solution, initial Ca-P molar ratio, capping agent concentration, and system concentration). Subsequently, a certain biphasic proportion of (biphasic calcium phosphate, BCP) products was prepared, and pure (β-tricalcium phosphate, β-TCP) can be obtained according to the customer's requirements. BCP ceramics with desired phase compositions were obtained by pressing and sintering different calcium-deficient powders. Specifically, β-TCP powder with a purity of 99.83 wt% was obtained when the aging time, bipolar solution, initial Ca-P molar ratio, capping agent concentration, and system concentration were 0 h, 50% ethanol, 1, 0.27 M, and 0.0135 M, respectively. The BCP synthesized in this study shows great application potential in the field of bone tissue repair materials.     

Synthesis of chitin calcium phosphate composite in different growth media

This paper presents some results concerning chitin calcium phosphate composites obtained in different growth media. The synthesis of chitin calcium phosphate composite was carried out by phosphorylation, calcification, and soaking in different calcium phosphate growth media. This research is focused on studying and understanding the effect of using different growth media on composite samples. Hydroxyapatite was determined in the composite samples synthesized by using both simulated body fluid (SBF) and calcium phosphorus tris (Ca‐PTris) solution. Calcium/phosphorus (Ca:P) ratio of the composite synthesized by using SBF was found higher than that of composite synthesized by using Ca‐PTris solution as calcium phosphate growth media. The Ca:P ratio of the composite (1.72) immersed in 1.5× SBF for 35 day is similar to the theoretical value of hydroxyapatite (1.67) and closer to the theoretical value of human bone (1.75). POLYM. COMPOS., 29:84–91, 2008. © 2007 Society of Plastics Engineers     

Influence of precursor characteristics on properties of porous calcium phosphate-titanium dioxide composite bioceramics

Highly porous (macroporosity 76–90%) bioceramics containing interconnected pores (>100 μm) with compressive strength between 0.54 and 0.32 MPa were prepared by polyurethane foam replica method. Effect of following variables, i.e., calcium phosphate/anatase ratio (30/70, 50/50, 70/30 wt%) in the ceramic slurry, anatase particle size (15 nm, 180 nm), Ca/P molar ratio of calcium phosphate (1.67 and 1.50 for hydroxyapatite and apatitic-tricalcium phosphate (ap-TCP), respectively), on the bioceramics properties was investigated. Bioceramics prepared using anatase and hydroxyapatite consisted of three high-temperature crystalline phases - β-tricalcium phosphate (β-TCP), rutile and CaTiO₃. In case of anatase and ap-TCP, two phases (β-TCP and rutile) were obtained. Interaction of anatase and hydroxyapatite during sintering caused formation of CaTiO₃ at β-TCP and rutile grain boundaries thus contributing to a denser grain packing. Combination of ap-TCP and nanosized anatase facilitated decrease of grain sizes. Correlation was found between compressive strength and calcium phosphate precursor in the ceramic slurry.     

Sol-Gel Synthesis of Amorphous Calcium Phosphate and Sintering into Microporous Hydroxyapatite Bioceramics

A new route for preparing hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) bioceramic has been described. An amorphous, nanosized, and carbonate-containing calcium phosphate powder that had a Ca:P ratio of 1.67 was synthesized from calcium diethoxide and phosphoric acid in ethanol via a sol-gel method. The powder was pressed at 98 MPa into green specimens and then heated to a temperature range of 500°-1300°C. At 600°C, the powder crystallized to a carbonated hydroxyapatite and a trace of ß-tricalcium phosphate before converting to hydroxyapatite at 900°C. The thermal crystallization was associated with grain growth, shrinkage, and active surface diffusion. The activation energy of grain growth was 37 ± 2 kJ/mol. After sintering at 1100°C, the decomposition of carbonated hydroxyapatite generated a microporous ceramic with an average pore size of 0.2 µm and an open porosity of 15.5%. This microporous bioceramic can be used as a bone filler.     

The threonine effect on calcium phosphate preparation from a solution containing Ca/P = 1.33 molar ratio

In this study, calcium phosphate materials were prepared by a modified precipitation method using high-speed dispersing equipment. A solution with a Ca/P molar ratio of 1.33 (octacalcium phosphate stoichiometry) was transferred into the reactor vessel with different concentrations of threonine at temperature 97 °C. A white precipitant was collected after the addition of condensed ammonium solution and the samples were subsequently calcined at 900 °C. From the XRD patterns and FT-IR spectra of the uncalcined samples, three phases of octacalcium phosphate (OCP), monetite (DCP) and hydroxyapatite (HA) were obtained. Calcined samples showed two phases of β-tricalcium phosphate (β-TCP) and calcium pyrophosphate (CPP). SEM micrographs showed the different morphology of samples. The specific surface areas (ssa) were 45–53 m²/g for and 5–6 m²/g for calcined samples. From the obtained results, we found that threonine added in various amounts in the initial solution inhibits the formation of HA and consequently creates OCP and DCP.     

Mechanochemical Synthesis of Hydroxyapatite from Calcium Oxide and Brushite

Fine hydroxyapatite (HA) powders were prepared by mechanically activating a mixture of calcium oxide and brushite powders in a high-energy shaker mill. A defective HA phase was formed when the starting powder mixture was activated for ≤20 h. When the mixture was calcined at 800°C, it was converted to β-tricalcium phosphate. In contrast, a nanocrystalline HA phase was formed when the mechanical activation was extended to 30 h. The material was transformed to a HA compound (Ca₁₀(PO₄)₆(OH)₂) of high crystallinity when it was calcined at 800°C.     

Synthesis and thermal behaviour of β tricalcium phosphate precipitated from aqueous solutions

Abstract

In the present study, β tricalcium phosphate (β-TCP) was prepared by precipitation from aqueous solutions. Calcium nitrate tetrahydrate Ca(NO₃)₂.4H₂O and diammonium hydrogen phosphate (NH₄)₂HPO₄ salts with an initial Ca/P molar ratio of 1·5 were dissolved in distilled water and mixed at 20°C and pH 10. Phase evolution of the as received precipitate was studied by X-ray diffraction and infrared spectroscopy before and after calcination in a dry air atmosphere at temperatures in the range 200-1400°C for 1 h. Thermal behaviour was investigated by simultaneous thermal analysis (DTA-TG). Calcium and phosphorus contents of the as received precipitate were determined by the inductively coupled plasma technique, and a Ca/P molar ratio of 1·49 ± 0·01 was found. The densities of the as received precipitate and of powder calcined at 800°C were determined by picnometery to be 2·43 and 3·01 ± 0·05 g cm^-3 respectively. The experimental data suggest the formation of an amorphous phase corresponding to a TCP-like composition, which is calcium deficient and contains a very small amount of HPO₄^2- groups.     

磷石膏制备硫酸钙晶须的工艺研究

采用常压酸化法对磷石膏分别进行硫酸除杂和盐酸溶解,将磷石膏中的钙富集于溶解液中.再对溶液进行处理制备硫酸钙晶须,考察硫酸钙初始浓度、结晶温度及添加助晶剂种类和用量对硫酸钙晶须组成、结构和形貌的影响.实验结果表明:所制晶须均为二水硫酸钙晶须;以乙醇作为助晶剂所制备的晶须形貌最好.当乙醇的添加量为15 mL(即V乙醇∶V盐酸=1∶2)时所制备的晶须比较均一,平均直径为25 μm,平均长径比约为80.     

自硬化磷酸钙骨水泥的微结构分析

应用SEM研究了磷酸四钙(TTCP)和无水磷酸氢钙(DCPA)组成的磷酸钙骨水泥(CPC)体系水化过程中浆体的微结构.结果表明:完全硬化的CPC由纳米级针状羟基磷灰石微晶组成,微晶与人体骨有类似的低结晶度和结构特性.CPC产物结晶形态与Ca与P摩尔比有关,Ca与P摩尔比减小,CPC水化产物的轴比增大而形态较细长.     

Study of biodegradable ceramic bone graft substitute

Abstract

The aim of the present study was to obtain a biodegradable porous calcium phosphate implants as a synthetic bone graft substitute. The calcium phosphate used in the present study consisted of hydroxyapatite (HA) and dicalcium phosphate anhydrous (DCP). Porous bioceramic was fabricated by a foam casting method. By polyurethane foam and slurry containing HA/DCP (3 : 1 weight ratio) powder, water and additives a high porous structure with ～70% was created. The X-ray diffractometry revealed that the β-tricalcium phosphate (β-TCP) formation is major phase. Surface morphology analysis and porosity evaluations were performed. The variation in the compressive strength, elastic modulus and dissolution behaviour of immersed synthetic bone graft in simulated physiological solution investigated.     

阳离子交换树脂法制备L-组氨酸钙工艺

采用阳离子交换树脂法制备L-组氨酸螯合钙,测定了D151和110两种弱酸型阳离子交换树脂的钙离子交换容量及其在26℃下的交换动力学曲线,并考察了温度、NaOH与L-组氨酸摩尔比、L-组氨酸初始浓度和树脂量对2种树脂钙交换过程的影响. 结果表明,D151和110的钙交换容量分别为1.12和2.59 mmol/g;交换过程迅速,工业上交换0.5 h即可达到平衡;钙离子交换是一个放热过程,工业生产中可在室温下或低温下进行;适宜的NaOH与L-组氨酸摩尔比为(1~1.25):1;用D151树脂时适宜的L-组氨酸初始浓度和树脂量分别约为0.46 mol/L和0.125 g/mL;用110树脂时分别约为0.4 mol/L和0.15 g/mL.     

Synthesis and Photoluminescence Properties of Eu3+-Doped Calcium Phosphates

Eu³⁺-doped (1–12 mol%) calcium hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) powders were synthesized by a precipitation method and their photoluminescence (PL) properties were investigated. Eu has a limited solubility in HA and Eu₂O₃ was detected by X-ray diffraction above 3% doping, whereas a nearly single β-phase was obtained up to 6% doping in TCP but EuPO₄ appeared in the 12% Eu-doped specimen. Electron spin resonance measurement confirmed that europium ions exist as Eu³⁺ in both samples. Eu³⁺-doped HA exhibited a strong emission at 575 nm with several minor peaks at 610–640 nm and Eu³⁺-doped TCP had an intense emission at 613 nm with secondary peaks at 590–600 nm, which were consistent with the earlier reports determined at low temperatures. In Eu-doped TCP, the PL intensity increased with increasing calcination temperature without phase transformation. The more the Eu added, the higher the PL intensity obtained in both cases.     

Preparation of Apatite Thin Films through rf-Sputtering from Calcium Phosphate Glasses

Apatite thin films of calcium phosphate were successfully prepared by rf-magnetron sputtering, followed by postannealing, from calcium phosphate glass targets with Ca/P atomic ratios of 0.6 to 0.75, much lower than the stoichio-metric value of 1.67 for hydroxyapatite. Using targets with low Ca/P ratios of 0.65 to 0.25, tricalcium and pyrocalcium phosphate thin films were obtained. The formation of these calcium phosphates phases was attributed to the phosphorus oxide losses during sputtering. H₂O vapor was effective in the formation of the apatite phase at high temperatures; apatite was the exclusive phase in the ambient H₂O, even when the target with the low Ca/P ratio of 0.4 was used. Based on phase stability at high temperatures, it was assumed that various kinds of apatites, such as stoichiometric and nonstoichiometric hydroxy- and Ca-deficient hydroxy-apatites were formed, depending on the composition of the glass targets.     

Cement Formulations in the Calcium Phosphate H2O–H3PO4–H4P2O7 System

Despite numerous reports of calcium phosphate cement materials, a calcium cement that sets to form a matrix consisting of a pyrophosphate phase has not been reported. The formulation of such a material from the mixture of α-tricalcium phosphate (TCP), β-TCP, or tetracalcium phosphate with a solution containing pyro- and orthophosphoric acid is reported in this study. The effects of liquid and solid compositions on the setting times, compressive strengths and phase compositions of the resultant cements were investigated. It was found that cements could be produced that set to form up to 28 wt% dicalcium pyrophosphate, which appeared by comparison with Rietveld refinement and chemical methods to be entirely amorphous in nature. The solubilities of the different solid components were shown to have a marked effect on the composition of the cements. The strongest cement formulations exhibited compressive strengths comparable with those previously reported in the literature for brushite cements and set within clinically relevant time scales. This class of cement would appear to demonstrate potential as a bone replacement material.     

多孔双相钙磷钛合金微弧氧化膜层的制备及生物相容性

为克服钛合金生物膜层单一相的缺陷,以Ti6A14V合金为基体,用微弧氧化法制得具有双相钙磷复合陶瓷膜层(BCP)的钛合金器件.通过控制工作液成分制得由不同比例的β-磷酸三钙(β-TCP)和羟基磷灰石(HA)组成的多孔性复合膜层.研究了电源占空比对BCP膜孔隙率和孔径大小的影响.采用能谱仪和X射线衍射仪分析了BCP膜层的...