The effects of magnesium on hydroxyapatite formation in vitro from CaHPO4 and Ca4(PO4)2O at 37.4 degrees C

The effects of magnesium ion on the formation of calcium-deficient hydroxyapatite [Ca9HPO4(PO4)5OH, CDHAp] from CaHPO4 and Ca4(PO4)2O dissolution were investigated using two magnesium sources: Mg3(PO4)2 (chemical system 1) or MgCl2 . H2O (chemical system 2) solutions. Because chloroapatite does not form from aqueous solutions, the use of two magnesium sources facilitated the determination of magnesium's role during synthetic hydroxyapatite formation in vitro and possible related effects during biomineralization. Isothermal calorimetry determined the progress of reactions. Two peaks are observed as heat is evolved during the formation of CDHAp in water at 37.4 degrees C. The nucleation and growth of CDHAp are the corresponding mechanisms. Although the time for complete reaction and total heat-of-reaction DeltaHr remain constant, the height of the first peak is reduced as the concentration of magnesium ion approaches 4 mM in either chemical system. Magnesium does not substitute into CDHAp even though there are calcium vacancies available. Subsequent increases cause the remaining heat peak to broaden and the time required for complete reaction to approach 24 hours as the initial MgCl2 concentration reaches 100 mM. Supersaturation limits chemical system 1 to Mg3(PO4)2 concentrations below 10 mM. A MgCl2 concentration of 3.16 M precludes CDHAp from forming for over 3 months; rather newberyite, MgHPO4 . 3H2O, precipitates. The morphology and surface area of the CDHAp formed in 100 mM MgCl2 solution are comparable to those of CDHAp formed in water. The surface areas are approximately 80 m2/g. Magnesium concentrations below 4 mM only inhibit nucleation whereas those above 4 mM inhibit growth as well. Magnesium phosphate complexes are more inhibitory than magnesium chloride complexes. Increasing the liquid-to-solids ratio or agitation significantly increases the induction period before reaction initiates. Increasing the liquid-to-solids ratio increases the time span for growth whereas increasing agitation decreases the time span for growth. The large inhibitory effect of agitation suggests quiescent systems are more suitable for determining the kinetics of HAp formation. A magnesium inorganic chemical activity (alphaMg = gammaMg[Mg2+]) many times greater than that in biological fluids is required before inhibition of hydroxyapatite formation is realized.     

Formation of calcium-deficient hydroxyapatite from alpha-tricalcium phosphate

This study investigated the factors influencing the kinetics of Ca9HPO4(PO4)5OH (calcium deficient hydroxyapatite or CDHAp) formation from alpha-Ca3(PO4)2 (alpha-TCP). The kinetics of CDHAp formation were investigated by isothermal calorimetry at constant temperatures ranging between 30 and 75 degrees C and by changes in pH at 37.4 and 70 degrees C. The calorimetric curves were characterized by two reaction peaks. Activation energies were calculated for the events resulting in these peaks. Values obtained were 48.4 and 67.7 kJ mol(-1), respectively, indicating nucleation and growth mechanisms for both events. Temperature had a significant effect on the growth rate as indicated by a decrease in surface area (26.5-15.0 m2 g(-1)) of the CDHAp with increasing temperature (30-75 degrees C). A linear relationship between hydrolysis temperature and CDHAp surface area was observed. The morphology of the CDHAp was plate-like and the crystallites became more regular as the reaction temperature was increased. A rapid elevation in pH upon mixing with water indicated the synthesis method initially used did not entirely eliminate slight compositional variations within the alpha-Ca3(PO4)2. Rapid elevation in pH retarded subsequent reaction. This effect was eliminated by increasing the duration of high-temperature firing during alpha-TCP synthesizing.     

Effect of hydroxyapatite microcrystals on macrophage activity

Hydroxyapatite (HAp) microcrystals were synthesized by a neutralization reaction of Ca(OH)2 suspension and H3PO4 solution using an ultrasonic homogenizer. The in vitro interaction of HAp microcrystals with rat peritoneal macrophages was investigated by measuring the viability, acid phosphatase (ACP) activity, lactate dehydrogenase (LDH) activity and intracellular calcium content. HAp calcined at 800 degrees C and alpha-alumina particles (alumina) were used as comparative materials. Macrophages actively phagocytosed HAp microcrystals by dissolving them. However, no damage in macrophages exposed to HAp microcrystals was observed by transmission electron microscopy. Macrophages in the presence of HAp microcrystals showed less ACP and LDH activity and higher intracellular calcium content than those in the presence of calcined HAp and alumina. HAp microcrystals had excellent biocompatibility to macrophages as well as sintered HAp.     

Preparation of high-temperature stabilized beta-tricalcium phosphate by heating deficient hydroxyapatite with Na4P2O7 x 10H2O addition

In this paper, the high-temperature stabilized beta-tricalcium phosphate (betaTCP, beta-Ca3(PO4)2) were prepared by heating the deficient HAP (d-HAP, Ca10-x(HPO4)x(PO4)6-x(OH)2-x) with tetra-sodium diphosphate decahydrate (NP, Na4P2O7 x 10H2O) addition. The betaTCP, d-HAP and d-HAP doped with 2.5, 5, 7.5 and 10 wt % NP were heated to different temperatures and were investigated by X-ray diffraction analysis (XRD) and Fourier-transformed infrared spectroscopy (FTIR). The results demonstrated that the HPO4(2-) of d-HAP condensed into P2O7(4-) occurred before 650 degrees C. The P2O7(4-) ions could be traced in the FTIR spectrum when the d-HAP was heated up to 750 degrees C. The reaction of P2O7(4-) with OH- did not occur instantly but over a wide range of temperatures. The d-HAP doped with NP would decrease the decomposition temperature of d-HAP. NP doped into d-HAP not only induced the d-HAP decomposition at lower temperature but also stabilized the betaTCP crystal structure at higher-temperature. It could also increase the conversion temperature of betaTCP to alphaTCP from 1180 degrees C up to 1300 degrees C. We could successfully prepare high-temperature (up to 1300 C) stabilized ffTCP by heating NP doped d-HAP.     

Alkoxide route for preparing hydroxyapatite and its coatings

The preparation of hydroxyapatite using n-butanol or ethanol solutions of P2O5 and Ca glycoxide as precursors of P and Ca was investigated by nuclear magnetic resonance (NMR), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Stable mixed solutions of the precursors could be obtained in the presence of acetic acid (HOAC). For the mixed solution of Ca glycoxide with the ethanol solution of P2O5, a lower HOAC/Ca ratio was needed since the ethanol solution of P2O5 contained a lower concentration of H3PO4, a species that easily forms precipitates in the presence of the Ca containing species. An amorphous powder was obtained by heating the stable solution of Ca glycoxide and PO(OH)x(OEt)3-x with an HOAC/Ca ratio of 4 in a hot plate at approximately 150 degrees C. Hydroxyapatite (HAP) was directly formed after calcining the amorphous powder at 500 degrees C. The stable mixed solutions of Ca glycoxide and the alcoholic solutions of P2O5 were used to prepare HAP coatings on alumina substrates using a dip-coating method. The resulting ceramic coatings have a rough surface and an adhesion strength of about 10 MPa. The morphology of the coatings is dependent on the preparation chemistry.     

Differences in solubility of two types of heterogeneous fluoridated hydroxyapatites

Two types of heterogeneous fluoridated apatites, H-F and F-H, were synthesized by supplying fluoride over the whole range of the degree of fluoridation (X = 0-1.0) during the initial or final half of the experimental period. Although X-ray diffraction patterns and scanning electron microscopy (SEM) photographs of both H-F and F-H type apatites were not significantly different, high-resolution transmission electron microscopy (HR-TEM) showed quite different features; H-F type apatites were elongated hexagons with electron beam damage in the core, while F-H type apatites were rather wider hexagons and approached the typical hexagon of fluorapatite. These results supported the previous speculations on the two different types of heterogeneous fluoridated hydroxyapatites synthesized with fluoride concentration stoichiometrically equivalent to that of fluorapatite: hydroxyapatite covered with fluorapatite and fluorapatite covered with hydroxyapatite. The apparent solubility of H-F type apatites decreased with increases in degree of fluoridation, while that of F-H type apatites decreased markedly and then remained almost constant.     

New Zincophosphite with Infinite One-dimensional [Zn(HPO3)(H2PO3)]- Chains: Synthesis, Characterizations and Spectral Properties

With dimethylamine as a template, a new one-dimensional zincophosphite (C2H8N)·[Zn(HPO3)(H2PO3)]was prepared under hydrothermal conditions and characterized by single-crystal X-ray diffraction, FTIR spectrametry, elemental analysis, powder X-ray diffraction, and thermogravimetric analysis. The compound crystallized in the Monoclinic space group P2(1)/c, with cell parameters, a=0.78410(9)nm, b=1.54744(2)nm, c=0.81418(1) nm, β=105.8150(1)°, V=0.95049(2) nm3 and Z=4. The connectivity of the ZnO4 tetrahedron and HPO3 pseudo pyramid resulted in inifinite corner-sharing 4-membered ring chains, which were further linked by the protonated amine molecules to form a 3D structure via hydrogen bonds. To the best of our knowledge, this is the first existence of a zincophosphite with the anionic framework composition of [Zn(HPO3)(H2PO3)]-. The compound exhibits intense photoluminescence at room temperature.     

Synthesis of antibiotic-loaded interporous hydroxyapatite blocks by vacuum method and in vitro drug release testing

Interporous hydroxyapatite ceramic (Ca10(PO4)6(OH)2) has excellent bio-compatibility and interlinked pore structure, antibiotics could be loaded into pores in vacuum system. To confirm penetration of the agent to the HAb (2 cm3 cubic block), the aminoglycoside antibiotic (Isepamicin Sulfate; ISP) dissolved in eosin dye at various vacuum pressures. In ISP slow release study, the blocks were placed in 5 ml of PBS at a temperature of 37 degrees C. The PBS was replaced every 48 h and samples containing released ISP were stored until assay. All were found to release the drug maintaining a mean concentration of 0.41 microg ml(-1) even after 18 days of nine exchanges. This concentration of antibiotic exceeded the minimum inhibitory concentration against the common causative organisms of osteomyelitis. The results suggest that HAb impregnated with antibiotics using a simple vacuum system may serve as a valuable new method of administering local chemotherapy, primarily when used as a strut graft for bone defects.     

A micro-Raman spectroscopic study of hydrazine-treated human dental calculus

Hydrazine has been used to remove organic components and to isolate the mineral(s) from human calculus. Micro-Raman measurements were performed on the mineral phase. After the hydrazine-treatment, not only a large reduction in fluorescence but also an increase in Raman signal was observed. The treatment was essential in minimizing thermally-induced chemical changes which could otherwise occur to the original calculus mineral due to the intense laser light. The Raman spectral features of the mineral were nearly all identical among the Raman spectra obtained at many randomly-selected sites by the micro-Raman microbe with a lateral resolution of approximately 1 micron, and were consistent with those of impure hydroxyapatite containing CO3(2-) and HPO4(2-). The spectra contained typical hydroxyapatite bands including PO4(3-)bands of the v1, v2, v3 and v4 modes and one OH- stretch band. Other minor bands due to the CO3(2-) v1 and v3 modes and bands possibly due to the HPO4(2-) v1, v2 and v4 modes were observable by the technique despite the hydrazine-treatment that could in principle remove the HPO4 and CO3 ions from the mineral. In comparison with pure synthetic hydroxyapatite, the intensity of the OH- stretch band relative to that of the PO4(3-) v1 band was approximately 70% weaker, and the bandwidth of the phosphate v1 band was 200% broader, reflecting various crystal imperfections presumably present in the calculus mineral.     

低C、O含量氟化稀土的制备工艺研究

以氯化钇为原料,采用碳酸氢铵制备的碳酸盐,通过复合氟化剂转化生成氟化钇,经过烘干和粒子整合之后得到无水氟化钇。考察了碳酸盐晶体质量、复合氟化剂的配比和浓度、反应温度、稀土浓度、pH值等对稀土氟化物中C、O含量的影响。结果表明:在选定条件下,用复合氟化剂将碳酸钇晶体转化生成氟化稀土,可明显降低氟化稀土中C、O的含量。     

Setting reaction and hardening of an apatitic calcium phosphate cement

The combination of self-setting and biocompatibility makes calcium phosphate cements potentially useful materials for a variety of dental applications. The objective of this study was to investigate the setting and hardening mechanisms of a cement-type reaction leading to the formation of calcium-deficient hydroxyapatite at low temperature. Reactants used were alpha-tricalcium phosphate containing 17 wt% beta-tricalcium phosphate, and 2 wt% of precipitated hydroxyapatite as solid phase and an aqueous solution 2.5 wt% of disodium hydrogen phosphate as liquid phase. The transformation of the mixture was stopped at selected times by a freeze-drying techniques, so that the cement properties at various stages could be studied by means of x-ray diffraction, infrared spectroscopy, and scanning electron microscopy. Also, the compressive strength of the cement was measured as a function of time. The results showed that: (1) the cement setting was the result of the alpha-tricalcium phosphate hydrolysis, giving as a product calcium-deficient hydroxyapatite, while beta-tricalcium phosphate did not participate in the reaction; (2) the extent of conversion of alpha-TCP was nearly 80% after 24 hr; (3) both the extent of conversion and the compressive strength increased initially linearly with time, subsequently reaching a saturation level, with a strong correlation observed between them, indicating that the microstructural changes taking place as the setting reaction proceeded were responsible for the mechanical behavior of the cement; and (4) the microstructure of the set cement consisted of clusters of big plates with radial or parallel orientations in a matrix of small plate-like crystals.     

Solubility of compositions in the system CaTi(x)Zr4-(x)(PO4)6 with x = 0-4

In vitro solubility tests of granulated materials and coatings were carried out on some compositions in the system CaTi(x)Zr4-(x)(PO4)6 with x = 0-4, in order to find a biocompatible material which is less soluble than hydroxyapatite (HA) and can also be used as bone substitution material. The granulated materials were leached out by using circulating equipment in which the solvent flows in circulation. The coatings were tested under conditions where the sample containers undergo a circular movement. The results show better chemical stability of nearly all tested compounds compared with HA for both granulated materials and coatings.     

Study on Optimal Conditions for Recovery of EDTA from Soil Washing Effluents

The recovery of ethylenediaminetetraacetic acid (EDTA) from washing effluents is essential to reduce the cost of EDTA-enhanced soil washing and the production of wastewater. This study evaluated a recovery method, in which Pb or Zn was first dissociated from Pb– or Zn–EDTA complex through the replacement reaction by adding FeCl3 and then removed as phosphate precipitates through adding Na2HPO4. Finally, Fe(III) was removed as Fe(OH)3 precipitates through adding Ca(OH)2. As a result, EDTA was recovered as Ca–EDTA for further use in soil washing process. The optimal conditions for EDTA recovery, including the molar ratios of FeCl3 and Na2HPO4 to EDTA as well as the pH after adding Na2HPO4 and adding Ca(OH)2, were well investigated. Under the optimal conditions, 96% of Pb or 83% of Zn was removed from the Pb– or Zn–EDTA, respectively. The four-cycle recovery and reuse of EDTA experiments indicated the recovered EDTA from soil washing effluents did not lose much chelating capacity for Pb removal. However, there is a loss of 15% of its chelating capacity in the first cycle reuse for Zn-contaminated soil washing due to substantial Zn residual in the recovered EDTA solution.     

Nucleation of hydroxyapatite by bone sialoprotein

Bone sialoprotein (BSP) and osteopontin, the major phosphorylated proteins of mammalian bone, have been proposed to function in the initiation of mineralization. To test this hypothesis, the effects of BSP and osteopontin on hydroxyapatite crystal formation were determined by using a steady-state agarose gel system. At low calcium phosphate concentrations, no accumulation of calcium and phosphate occurred in control gels or gels containing osteopontin. Gels containing BSP at 1-5 micrograms/ml, however, exhibited a visible precipitation band and significantly elevated Ca + PO4 contents. By powder x-ray diffraction, the precipitate formed in the presence of BSP was shown to be hydroxyapatite. These findings suggest that bone sialoprotein may be involved in the nucleation of hydroxyapatite at the mineralization front of bone.     

稀土氧化物氟化反应过程的研究

本文对Ｙ２Ｏ３与无水ＨＦ气体的反应过程进行了热力学计算，并根据实验结果，计算了该反应在３００～７００℃的活化能，研究了氟化反应时间、温度等因素对氟化反应的影响，同时对氟化产物进行了Ｘ射线衍射分析，探讨了氟化反应过程的机理，为合理确定制备高质量稀土氟化物的工艺条件提供了理论依据。     

Accuracy of single-energy quantitative computed tomography in the assessment of bone mineral density of cervical vertebrae

Earlier studies have shown that single-energy quantitative computed tomography (SEQCT) is a reliable method for bone mineral density (BMD) measurements in thoracic and lumbar vertebrae. Moreover, SEQCT has proved to be a useful parameter in the selection of appropriate implants in cervical spondylodesis. The aim of this study was to determine the accuracy of SEQCT in cervical vertebrae BMD measurement. BMD with reference to calcium hydroxyapatite (Ca10[PO4]6[OH]2) was assessed by SEQCT in 100 human vertebral bodies of the cervical spine. Bone cylinders were then cut from the appropriate region of interest. The cylinder volume was determined by the liquid displacement technique. The density of the mineral component was measured following incineration at 1100 degrees C for 24 h. The calculated BMD was correlated with the SEQCT values, resulting in a coefficient of r = 0.79 (P < 0.01). Mean SEQCT values were significantly lower than those determined by direct density assessment (t-test for coupled sampling, P < 0.02). This result was in agreement with studies on thoracic and lumbar vertebrae. These data suggest that SEQCT can reliably measure BMD in the cervical spine.     

The bioactivity of titanium-cuttlefish bone-derived hydroxyapatite composites sintered at low temperature

ABSTRACT

The most limiting features of titanium as a bone substituent are lack of bioactivity and high Young’s modulus. We have prepared titanium-hydroxyapatite (Ti-HAp) composites using titanium hydride as sintering agent to provide titanium sintering at lower temperature and preserve the stability of apatite phase. After low temperature sintering, no hydroxyapatite decomposition was detected. Pure titanium samples sintered in the presence of hydride showed smooth surface indicating good densification at 800°C. Higher HAp content resulted in decreased density and higher porosity due to the formation of micro- and macro-pores caused by the integration of HAp particles into titanium matrix and titanium hydride decomposition. However, Vickers microhardness test showed increased hardness for Ti-HAp composite with 10% of HAp regarding pure Ti. The bioactivity of Ti-HAp composites evaluated in simulated body fluid significantly improved with HAp content. The presence of HAp has lowered the cytotoxic effect of Ti-based composites on Hek293 cells.     

Low calcium diet and 1,25-dihydroxyvitamin D(3) infusion modulate immune responses during Mycobacterium paratuberculosis infection in beige mice

A 12-month study was conducted to evaluate the effects of feeding a low calcium (Ca) diet or 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3) infusion on the persistence of Mycobacterium paratuberculosis infection using a mouse model. Male beige mice 6-8 weeks of age were assigned to one of the following treatments: (1) non-infected, (2) infected,(3) non-infected/1,25(OH)(2)D(3), (4) infected/1,25(OH)(2)D(3), and (5) infected/low Ca (0.15 percent) diet. Infected mice were inoculated intravenously with live M. paratuberculosis. At 1, 6 and 12 months postinfection, mice in Treatments 3 and 4 were implanted subcutaneously with mini-osmotic pumps to deliver 1,25(OH)(2)D(3). Infusion with 1,25(OH)(2)D(3) exacerbated M. paratuberculosis infection in most tissues at all time points. Mice infused with 1,25(OH)(2)D(3) had higher bacterial counts in spleen, liver, and ileum compared with control infected mice after 1 month of infection. In contrast, feeding a low Ca diet reduced the number of viable organisms cultured from the liver and ileum of infected mice. Plasma Ca and 1,25(OH)(2)D(3) were increased in mice infused with 1,25(OH)(2)D(3) at all time points but values for low Ca mice were not different than for non-infused mice. Splenocyte production of TNF, IL-1 and IL-6 was higher for mice fed the low Ca diet compared with control infected mice after 1 month of infection. Inducible IL-6 activity remained higher for this treatment at 6 months postinfection. These results suggest that feeding a low Ca diet to mice chronically infected with M. paratuberculosis appears to enhance their ability to clear the infection in a manner distinct from any effect of 1,25(OH)2D3.     

水热法合成不同形貌羟基磷灰石

羟基磷灰石由于具有良好的生物相容性和生物活性而应用广泛,形貌控制对其应用至关重要。本文分别以Ca(NO3)2.4H2O、KH2PO4.3H2O为Ca源和P源,采用水热法制备不同形貌的羟基磷灰石。用X射线衍射(XRD)和扫描电镜(SEM)对反应产物进行表征,研究水热反应温度、水热反应时间和反应物浓度对羟基磷灰石形貌的影响。结果表明,不同条件下,产物为长径比不同的片状、带状及花状羟基磷灰石(HA),其长度为1~100μm、宽1~5μm、厚约100 nm、长径比为1~100,并从晶体生长动力学方面探讨不同合成条件对羟基磷灰石形貌的影响机理。     

Hydrolysis of CaHPO4 in sodium fluoride solutions at 37.4 degrees C

A possible chemical process occurring during caries reversal is conversion of acidic calcium phosphates to apatite. The role of fluoride in this process is of particular interest. The effects of fluoride on the rate of CaHPO4 hydrolysis at 37.4 degrees C were studied by a multimethod analysis involving X-ray diffraction, analyses of variations in solution chemistry, and observation of microstructural evolution. Hydrolysis in low NaF concentrations results in the formation of discrete fluorapatite crystals on the surfaces of the CaHPO4 crystallites. At CaHPO4/NaF molar ratios from approximately 9:1 to 10:2, fluorapatite formed in approximately 3 h as the only crystalline product and complete hydrolysis of CaHPO4 occurred; a pH value as low as 2.4 was attained with solution species being predominantly sodium phosphate. At NaF concentrations beyond those which result in pH minima, fluorapatite and CaF2 are the crystalline products. At 0.6 M NaF, pseudomorphs composed of fluorapatite and CaF2 crystals form without developing morphologies characteristic of individual fluorapatite and CaF2 crystals. CaHPO2 can hydrolyze completely to fluorapatite and CaF2 within a few hours depending on NaF concentration and liquid-to-solids ratio.