The effects of strontium on bone mineral: A review on current knowledge and microanalytical approaches

The interest in effects of strontium (Sr) on bone has greatly increased in the last decade due to the development of the promising drug strontium ranelate. This drug is used for treating osteoporosis, a major bone disease affecting hundreds of millions of people worldwide, especially postmenopausal women. The novelty of strontium ranelate compared to other treatments for osteoporosis is its unique effect on bone: it simultaneously promotes bone formation by osteoblasts and inhibits bone resorption by osteoclasts. Besides affecting bone cells, treatment with strontium ranelate also has a direct effect on the mineralized bone matrix. Due to the chemical similarities between Sr and Ca, a topic that has long been of particular interest is the incorporation of Sr into bones replacing Ca from the mineral phase, which is composed by carbonated hydroxyapatite nanocrystals. Several groups have analyzed the mineral produced during treatment; however, most analysis were done with relatively large samples containing numerous nanocrystals, resulting thus on data that represents an average of many crystalline domains. The nanoscale analysis of the bone apatite crystals containing Sr has only been described in a few studies. In this study, we review the current knowledge on the effects of Sr on bone mineral and discuss the methodological approaches that have been used in the field. In particular, we focus on the great potential that advanced microscopy and microanalytical techniques may have on the detailed analysis of the nanostructure and composition of bone apatite nanocrystals produced during treatment with strontium ranelate.     

Increased strontium uptake in trabecular bone of ovariectomized calcium‐deficient rats treated with strontium ranelate or strontium chloride

Based on clinical trials showing the efficacy to reduce vertebral and non‐vertebral fractures, strontium ranelate (SrR) has been approved in several countries for the treatment of postmenopausal osteoporosis. Hence, it is of special clinical interest to elucidate how the Sr uptake is influenced by dietary Ca deficiency as well as by the formula of Sr administration, SrR versus strontium chloride (SrCl₂). Three‐month‐old ovariectomized rats were treated for 90 days with doses of 25 mg kg^?1 d^?1 and 150 mg kg^?1 d^?1 of SrR or SrCl₂ at low (0.1% Ca) or normal (1.19% Ca) Ca diet. Vertebral bone tissue was analysed by confocal synchrotron‐radiation‐induced micro X‐ray fluorescence and by backscattered electron imaging. Principal component analysis and k‐means clustering of the acquired elemental maps of Ca and Sr revealed that the newly formed bone exhibited the highest Sr fractions and that low Ca diet increased the Sr uptake by a factor of three to four. Furthermore, Sr uptake in bone of the SrCl₂‐treated animals was generally lower compared with SrR. The study clearly shows that inadequate nutritional calcium intake significantly increases uptake of Sr in serum as well as in trabecular bone matrix. This indicates that nutritional calcium intake as well as serum Ca levels are important regulators of any Sr treatment.     

Effect of strontium ranelate on bone mineral: Analysis of nanoscale compositional changes

Strontium ranelate has been used to prevent bone loss and stimulate bone regeneration. Although strontium may integrate into the bone crystal lattice, the chemical and structural modifications of the bone when strontium interacts with the mineral phase are not completely understood. The objective of this study was to evaluate apatite from the mandibles of rats treated with strontium ranelate in the drinking water and compare its characteristics with those from untreated rats and synthetic apatites with and without strontium. Electron energy loss near edge structures from phosphorus, carbon, calcium and strontium were obtained by electron energy loss spectroscopy in a transmission electron microscope. The strontium signal was detected in the biological and synthetic samples containing strontium. The relative quantification of carbon by analyzing the C_K edge at an energy loss of ΔE = 284 eV showed an increase in the number of carbonate groups in the bone mineral of treated rats. A synthetic strontium-containing sample used as control did not exhibit a carbon signal. This study showed physicochemical modifications in the bone mineral at the nanoscale caused by the systemic administration of strontium ranelate.     

A deep view in cultural heritage—confocal micro X-ray spectroscopy for depth resolved elemental analysis

Quantitative X-ray fluorescence (XRF) and particle induced X-ray emission (PIXE) techniques have been developed mostly for the elemental analysis of homogeneous bulk or very simple layered materials. Further on, the microprobe version of both techniques is applied for 2D elemental mapping of surface heterogeneities. At typical XRF/PIXE fixed geometries and exciting energies (15–25 keV and 2–3 MeV, respectively), the analytical signal (characteristic X-ray radiation) emanates from a variable but rather extended depth within the analyzed material, according to the exciting probe energy, set-up geometry, specimen matrix composition and analyte. Consequently, the in-depth resolution offered by XRF and PIXE techniques is rather limited for the characterization of materials with micrometer-scale stratigraphy or 3D heterogeneous structures. This difficulty has been over-passed to some extent in the case of an X-ray or charged particle microprobe by creating the so-called confocal geometry. The field of view of the X-ray spectrometer is spatially restricted by a polycapillary X-ray lens within a sensitive microvolume formed by the two inter-sectioned focal regions. The precise scanning of the analyzed specimen through the confocal microvolume results in depth-sensitive measurements, whereas the additional 2D scanning microprobe possibilities render to element-specific 3D spatial resolution (3D micro-XRF and 3D micro-PIXE). These developments have contributed since 2003 to a variety of fields of applications in environmental, material and life sciences. In contrast to other elemental imaging methods, no size restriction of the objects investigated and the non-destructive character of analysis have been found indispensable for cultural heritage (CH) related applications. The review presents a summary of the experimental set-up developments at synchrotron radiation beamlines, particle accelerators and desktop spectrometers that have driven methodological developments and applications of confocal X-ray microscopy including depth profiling speciation studies by means of confocal X-ray absorption near edge structure (XANES) spectroscopy. The solid mathematical formulation developed for the quantitative in-depth elemental analysis of stratified materials is exemplified and depth profile reconstruction techniques are discussed. Selected CH applications related to the characterization of painted layers from paintings and decorated artifacts (enamels, glasses and ceramics), but also from the study of corrosion and patina layers in glass and metals, respectively, are presented. The analytical capabilities, limitations and future perspectives of the two variants of the confocal micro X-ray spectroscopy, 3D micro-XRF and 3D micro-PIXE, with respect to CH applications are critically assessed and discussed.     

XRF analysis of strontium: Exploring cellulose as a soft tissue equivalent

X-ray fluorescence (XRF) is a widely used method for in vivo elemental analysis. Particularly for bone, it is a non-invasive technique that provides information on composition without significant risk to the patient. XRF contributes a capability for measuring elements beneficial to human health, such as strontium. This is a proposed supplement that has been shown in clinical trials to reduce fracture risk in people diagnosed with osteoporosis. Although XRF is a viable method for quantifying bone strontium, there are still factors that constrain its effectiveness. X-ray attenuation through overlying soft tissue decreases the signal, consequently requiring correction before estimating the true concentration of strontium in bone. A correction factor can be applied to account for the reduced signal, but an accurate measurement of overlying soft tissue thickness is required. It has been shown that using the correlation between Compton peak count rate and overlying thickness can be used as an estimation of overlying tissue. Lucite is commonly used as a soft tissue substitute; however, its mean atomic number is appreciably lower than soft tissue, somewhat limiting its applicability. This study tests the feasibility of using cellulose filter papers as a substitute for overlying soft tissue to perform XRF analysis of strontium-doped hydroxyapatite bone phantoms. Mass attenuation coefficients are shown to be closer to those of soft tissue (International Commission on Radiation Units' four-component) than Lucite, and the Compton correlation is used to estimate thickness as a correction factor to quantify true strontium concentration.     

锶热原子束二维准直的动力学过程的蒙特卡罗模拟及实验研究

在考虑随机因素的情况下, 应用蒙特卡罗方法在理论上详细研究了锶原子束二维激光准直的动力学过程. 综合考虑原子横向发散角、初始原子位置、纵向速度分布、同位素等因素, 获得了激光二维准直后的原子横向空间分布的模拟结果以及随准直光失谐、光功率等参量因素的变化. 通过与实验数据比较, 理论值和实验值很好相符, 显示蒙特卡罗方法可以精确地描述锶原子束二维准直的动力学过程. 为原子束激光二维准直的精确控制, 高精度原子钟系统的优化, 提供了一种理论分析方法. 关键词： 二维准直 蒙特卡罗方法 横向空间分布     

Electrophysical characteristics of strontium tantalate

Results are offered from a study of thin film strontium tantalate (SrTa₂O₆) obtained by vacuum hf deposition. Temperature and frequency dependences of electrical conductivity, , tan , and thermostimulted dielectric depolarization current are studied in Al-SrTa₂O₆-Al structures. Point defect parameters and their distribution over energy in the dielectric forbidden zone are determined. Polarization and electrical conductivity mechanisms are considered, and it is concluded that strontium tantalate shows promise as a dielectric material for integrated circuits.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 61–65, July, 1989.     

Effect of strontium substitution on superconductivity in YBa 2 Cu 4 O 8

Superconducting powders with the composition Y(Ba 1 mx Sr x ) 2 Cu 4 O 8 ( x = 0.00-0.50) have been prepared by an aqueous sol-gel method. The effects of strontium substitution on the properties of compounds were studied by resistivity measurements, X-ray powder diffraction, thermogravimetric analysis, electron microscopy and elemental analysis. The data indicate that single-phase Y(Ba 1 mx Sr x ) 2 Cu 4 O 8 superconducting samples were obtained. They also show that doping with strontium has a strong effect on the superconducting properties of the YBa 2 Cu 4 O 8 phase. The critical temperature is enhanced from 78 K (for a non-substituted sample) to 88 K (for Y(Ba 1 mx Sr x ) 2 Cu 4 O 8 ). Elemental analysis data clearly indicate that small amounts of strontium enter the copper sites in the Y(Ba 1 mx Sr x ) 2 Cu 4 O 8 compounds. A point-defect chemistry approach, which explains the enhancement of T c by substituting strontium for barium, is presented.     

Structural and electromagnetic characteristics of substituted strontium hexaferrite nanoparticles

Substituted strontium ferrite SrFe₉(Mn_0.5Co_0.5Zr)_3/2O₁₉ has been prepared from sol–gel method. X-ray diffraction (XRD), transmission electron microscope (TEM) and vector network analyzer, were used to analyze the structure and dynamic magnetic properties. Powders of sample show a hexagonal fine platelet structure and narrow particle size distribution. Based on microwave measurement on reflectivity, SrFe₉(Mn_0.5Co_0.5Zr)_3/2O₁₉ may be a good candidate for electromagnetic compatibility and other practical applications at high frequency.     

基于软X射线谱学显微双能衬度图像的元素空间分布研究

上海光源软X射线谱学显微实验站(BL08U)可实现30nm空间分辨的元素探测功能.实验中,对样品内要标识元素的吸收边附近两个能量(E1和E2,且E1E2)分别进行扫描成像,然后将这两幅吸收图上对应像素点的光密度相比,得到的相比双能衬度图像可有效地显示该元素的空间分布信息.相对于另一种常用的相减双能衬度图像分析法,这种方法对元素空间分布的显示更为灵敏、精确,判断空间点是否含有要标识元素的阈值的定义更为简单,物理意义更为清晰.通过对聚丙烯腈预氧化纤维截面氧元素分布的测量结果的分析计算,比较了这两种分析方法的差异,验证了相比双能衬度法的有效性.该方法为快速标识样品中的微量元素提供了一种很好的新型分析手段.     

High-field QCPMG NMR of strontium nuclei in natural minerals

The only stable NMR-active isotope of strontium, (87)Sr, is a spin-9/2 quadrupolar nucleus that has a low gyromagnetic ratio, a low natural abundance, and a large nuclear electric quadrupole moment. In this work, we utilize the quadrupolar Carr-Purcell-Meiboom-Gill (QCPMG) pulse sequence and a 21.14 T NMR spectrometer at the Pacific Northwest National Laboratory to characterize the strontium sites in the natural minerals strontianite (SrCO(3)) and celestine (SrSO(4)). QCPMG at 21.14 T was found to provide sensitivity enhancements of roughly two orders of magnitude over Hahn-echo experiments at an 11.74 T magnetic field. We extracted the quadrupolar parameters for the strontium nuclei through iterative simulations of the experimental spectra with the SIMPSON program by Bak, Rasmussen, and Nielsen. The data show that the quadrupolar parameters of (87)Sr appear to be highly sensitive to the symmetry of the strontium coordination environment and can thus provide information about the strontium binding environment in complex systems.     

Nanocrystals formation on Ho doped strontium barium niobate glass

The study of two different methods to obtain strontium barium niobate nanocrystals immersed in a glass matrix has been carried out. Ho₂O₃-doped SrO-BaO-Nb₂O₅-B₂O₃ glasses were fabricated using the melt quenching method. Glass ceramic samples were obtained from the precursor glass by thermal treatment in a furnace and by laser irradiation. These glass ceramic samples are formed by a glassy phase and a crystalline phase of strontium barium niobate nanocrystals. This structure was confirmed by X-ray diffraction and Atomic Force Microscope images. The incorporation of Ho³⁺ ions in the strontium barium niobate nanocrystals were corroborated by optical measurements, which produced an increment in the luminescence intensity compared to the precursor glass.     

Monte Carlo simulation code for confocal 3D micro‐beam X‐ray fluorescence analysis of stratified materials

Stratified materials are of great importance for many branches of modern industry, e.g. electronics or optics and for biomedical applications. Examination of chemical composition of individual layers and determination of their thickness helps to get information on their properties and function. A confocal 3D micro X‐ray fluorescence (3D µXRF) spectroscopy is an analytical method giving the possibility to investigate 3D distribution of chemical elements in a sample with spatial resolution in the micrometer regime in a non‐destructive way. Thin foils of Ti, Cu and Au, a bulk sample of Cu and a three‐layered sandwich sample, made of two thin Fe/Ni alloy foils, separated by polypropylene, were used as test samples. A Monte Carlo (MC) simulation code for the determination of elemental concentrations and thickness of individual layers in stratified materials with the use of confocal 3D µXRF spectroscopy was developed. The X‐ray intensity profiles versus the depth below surface, obtained from 3D µXRF experiments, MC simulation and an analytical approach were compared. Correlation coefficients between experimental versus simulated, and experimental versus analytical model X‐ray profiles were calculated. The correlation coefficients were comparable for both methods and exceeded 99%. The experimental X‐ray intensity profiles were deconvoluted with iterative MC simulation and by using analytical expression. The MC method produced slightly more accurate elemental concentrations and thickness of successive layers as compared to the results of the analytical approach. This MC code is a robust tool for simulation of scanning confocal 3D µXRF experiments on stratified materials and for quantitative interpretation of experimental results. Copyright © 2011 John Wiley & Sons, Ltd.     

Stark broadening of singly ionized strontium and calcium lines

Profiles of five calcium II and six strontium II lines have been measured in an argon plasma behind the reflected shock wave. The plasma was produced in an electromagnetically drivenT tube and calcium and strontium were present as an impurities. Electron densities were in the range 1.91–3.40·10¹⁷ cm^?3 and the electron temperatures between 10300 and 14200 °K. The half halfwidths of the measured profiles of some Ca II and Sr II multiplets show large discrepancies with theoretical predictions.     

Fabrication of barium/strontium carbonate coated amorphous carbon nanotubes as an improved field emitter

Amorphous carbon nanotubes (aCNTs) were synthesized by a chemical reaction between ferrocene and ammonium chloride at a temperature ～250 ^°C in an air furnace. As-synthesized aCNTs were coated with the barium/strontium carbonate through a simple chemical process. The coating of barium/strontium carbonate was confirmed by a high resolution transmission electron microscopy, X-ray diffraction, and Fourier transformed infrared spectroscopy. Morphology of the as-prepared samples was studied by field emission scanning electron microscopy. Thermal gravimetric analysis showed that barium/strontium carbonate coated aCNTs are more stable than the pristine aCNTs. As-prepared barium/strontium carbonate coated aCNTs showed significantly improved field emission properties with a turn-on field as low as 2.5 V/μm. The variation of field emission characteristics of the barium/strontium carbonate coated aCNTs with interelectrode distances was also studied.     

Europium doped strontium borate glasses and their optical properties

Optical absorption and luminescence spectra of europium doped strontium borate glasses prepared in different conditions are studied. It is found that the percentage of Eu³⁺ ions varies from 100 to 30% being controlled by the conditions of preparation. The mechanism, favoring reduction of europium to Eu²⁺ state in polycrystalline strontium tetraborate, is much weaker in glasses of the same composition. In samples containing mixed valence europium at densities of 8×10²⁰ cm⁻³, the efficient transfer of optical excitation from Eu³⁺ to Eu²⁺, suppressing the Eu³⁺ luminescence, has been found. The most reliable way of monitoring the percentage of europium ions in different valences for strontium borate glasses is the measuring of absorption at f-f transition ⁷F₀→⁵D₂ of Eu³⁺.     

Effecting factors of the emission spectral characteristics of rare-earth strontium aluminate for anti-counterfeiting application

The rare-earth strontium aluminate phosphor with stable physical and luminescent performances is a suitable rare-earth luminescent material for spectrum-fingerprint anti-counterfeiting fiber. In order to promote further the development of variety and the improvement of anti-counterfeiting effects of spectrum-fingerprint fiber, in this research, several kinds of rare-earth strontium aluminates and spectrum-fingerprint anti-counterfeiting fiber were prepared by solid-state reaction and special spinning technique, respectively. The effects upon manufacturing elements of strontium aluminate including calcining temperature, Al/Sr ratios, the addition of H₃BO₃, Eu²⁺ and Dy³⁺ and external environmental factors of applications such as fiber-forming polymer on emission spectral characteristics were investigated systematically in the anti-counterfeiting application. The results showed that with the increase in the calcining temperature, the amounts of H₃BO₃ doping and the concentration of Eu²⁺ and Dy³⁺, the emission intensity of rare-earth strontium aluminate increased and reached to the peak at a certain point at start, and then decreased gradually beyond this point. Al/Sr molar ratios influenced not only the intensity but also the wavelength of emission. Fiber-forming polymer had little effect on the emission wavelength and the shape in the luminescence, but greatly lowered the intensity of emission.     

基于电子顺磁共振的锶铁氧体磁特性研究

为了研究配料、温度、氧环境和掺杂等条件对锶铁氧体的磁性能的影响问题, 利用溶胶-凝胶法制备了锶铁氧体粉末, 建立了一种基于电子顺磁共振技术研究锶铁氧体粉末的磁特性的方法. 用电子顺磁共振波谱仪对烧结后的产物进行测试发现: 400 ℃预烧下, 锶铁摩尔比为1:9时, 中间产物顺磁相α-Fe₂O₃含量最多, 高于400 ℃时其含量减少, 亚铁磁相增加, 并确定最佳煅烧温度介于800-900 ℃. 这是由于外磁场和其他磁场综合作用产生亚铁磁相, 进而产生较强的磁矩相互作用所致. 结合工业实际应用, 发现缺氧退火环境下, 顺磁相α-Fe₂O₃含量较大, 不利于亚铁磁相生成; X-射线衍射(XRD)表征结果表明: 除了少量杂相, 其余均为顺磁相和亚铁磁相; 电子顺磁共振谱和XRD 谱检测结果综合表明, 锶铁摩尔比为1:9时, 最终产物的顺磁相含量最少, 亚铁磁相含量最多, 磁性最强; 毫特斯拉计的剩磁检测结果也证实了上述结果. 掺杂实验发现镧离子占锶镧总摩尔数的20% 至30% 时, 能够有效降低顺磁相的产生, 增强最终产物的亚铁磁性.     

Three-dimensional polarimetric integral imaging

A three-dimensional (3D) polarimetric image sensing and display technique based on integral imaging is proposed. Three-dimensional polarization distribution of reflected light from a 3D object can be measured as elemental image arrays by a rotating linear polarizer. After the measurement of the polarization of the 3D object, the 3D polarimetric object can be reconstructed optically by displaying the polarization-selected elemental images in spatial light modulators with two quarter-wave plates. Experimental demonstration of 3D polarimetric imaging of a 3D object attached to two orthogonal linear polarizers is presented. To the best of our knowledge, this is the first report on 3D polarimetric sensing imaging and 3D optical reconstruction by integral imaging.     

Properties of strontium titanate in the SrTiO3/CeO2/Al2O3 multilayered structure

Studies of the crystal structure, elemental composition, and dielectric properties of strontium titanate films in SrTiO₃/CeO₂/Al₂O₃ multilayered structures are reported. Data on the crystal lattice and impurity contents have been obtained, and temperature and electric field dependences of the dielectric properties of SrTiO₃ films in the microwave range have been measured. An analysis of the results is made to establish the reason for the nonmonotonic dependence of the small-signal dielectric permittivity of SrTiO₃ films on temperature. Fiz. Tverd. Tela (St. Petersburg) 39, 1024–1029 (June 1997)