Incorporation Of Strontium Research Articles

Incorporation of silver and strontium in hydroxyapatite coating on titanium surface for enhanced antibacterial and biological properties

Implant-related infection in primary total joint prostheses has attracted considerable research attention. As a measure to improve the antimicrobial properties of implant materials, silver (Ag) was incorporated into calcium phosphate (CaP) coatings on Titanium (Ti) via a hydrothermal method. Further, strontium (Sr) was added as a binary dopant to reduce the cytotoxicity of Ag in the coatings. Results showed that the CaP coatings were uniformly deposited on Ti with enhanced hydrophilicity and nanoscale surface roughness. Moreover, cell adhesion, proliferation, and differentiation were improved after the CaP coating deposition. The antibacterial properties of the coatings were distinctly improved by the incorporation of Ag, but the cell proliferation and differentiation were significantly decreased. Owing to the incorporation of Sr, the Ag-CaP coatings were able to effectively counteract the negative effects of Ag while maintaining good antibacterial properties. In summary, hydrothermally deposited CaP coatings doped with Ag and Sr exhibit excellent biocompatibility and antimicrobial activity. Thus, such co-doped CaP coatings have considerable potential for orthopaedic implant modification.

The incorporation of fluoride and strontium in hydroxyapatite affects the composition, structure, and mechanical properties of human cortical bone.

Strontium ranelate and fluoride salts are therapeutic options to reduce fracture risk in osteoporosis. Incorporation of these elements in the physiological hydroxyapatite matrix of bone is accompanied by changes in bone remodeling, composition, and structure. However, a direct comparison of the effectiveness of strontium and fluoride treatment in human cortical bone with a focus on the resulting mechanical properties remains to be established. Study groups are composed of undecalcified specimens from healthy controls, treatment-naïve osteoporosis cases, and strontium ranelate or fluoride-treated osteoporosis cases. Concentrations of both elements were determined using instrumental neutron activation analysis (INAA). Backscattered electron imaging was carried out to investigate the calcium content and the cortical microstructure. In comparison to osteoporotic patients, fluoride and strontium-treated patients have a lower cortical porosity indicating an improvement in bone microstructure. Mechanical properties were assessed via reference point indentation as a measure of bone's resistance to deformation. The strontium-incorporation led to significantly lower total indentation distance values compared to osteoporotic cases; controls have the highest resistance to indentation. In conclusion, osteoporosis treatment with strontium and fluoride showed positive effects on the microstructure and the mechanical characteristics of bone in comparison to treatment-naïve osteoporotic bone. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 433-442, 2017.

Relationship between the cross-link structure and properties of peroxide and sulfur-cured magnetic composites based on NR and NBR

In the present work, rubber magnetic composites were prepared by incorporation of strontium ferrite into rubber matrices based on natural rubber (NR) and acrylonitrile butadiene rubber (NBR). The sulfur and peroxide curing systems were introduced in cross-linking of rubber matrices. The research was aimed at the evaluation of magnetic filler content and type of curing system on the cross-link density, physical–mechanical and magnetic properties of prepared composites. The relationship between the composition of elastomers and cross-link structure within the rubber matrices, formed by applying different curing systems, was under investigation through strain–stress behavior of tested materials. The achieved results showed that ferrite behaves as a reinforcing filler in peroxide-cured composites based on NR, and in both, sulfur as well as peroxide-cured composites based on NBR. The results also demonstrated that the cross-linking degree and the type of cross-link structure as well as the composition of rubber matrices, to a large extent, influence the property spectrum of tested composite systems.

Strontium-containing, carbohydrate-based polymer networks as tooth-adherent systems for the treatment of dentine hypersensitivity

This study describes the design/physicochemical properties of strontium-containing, mucoadhesive carbohydrate polymeric platforms, designed as treatments for dentine hypersensitivity. Interactive networks were composed of strontium chloride (10% w/w), one of two base polymers (sodium carboxymethylcellulose, NaCMC or hydroxyethylcellulose, HEC), polycarbophil (PC) and, when required, polyvinylpyrrolidone (PVP). The physicochemical properties were characterised using oscillatory and flow rheometry, texture profile analysis, mucoadhesion analysis and, additionally, the strontium release properties were examined. All platforms exhibited pseudoplastic flow. Increasing polymer concentrations increased network viscoelasticity, consistency, hardness, compressibility, gel strength, adhesiveness, mucoadhesion and, retarded strontium release. Principally zero-order strontium release was observed from all platforms. Incorporation of strontium reduced the network elasticity, consistency, hardness, compressibility, gel strength and mucoadhesion; HEC-based platforms being affected to a greater extent than NaCMC platforms. NaCMC-based platforms containing 10% strontium chloride, PVP (3% w/w) and PC (3% w/w) potentially displayed the correct balance of physicochemical properties for the treatment of dentine sensitivity.

Effect of Strontium Incorporation on the p-Type Conductivity of Cu2O Thin Films Deposited by Metal–Organic Chemical Vapor Deposition

Temperature-dependent Hall effect and resistivity measurements are performed on polycrystalline Cu2O:Sr thin films deposited on glass substrate by metal organic-chemical vapor deposition. Their electrical properties are studied as a function of the strontium content, as determined by wavelength dispersive X-ray spectrometry. These electrical transport measurements highlight a copper vacancy doping mechanism induced by strontium incorporation, leading to a large decrease of the resistivity as low as 1.2 Ω·cm and corresponding free carrier mobilities about 15 cm2·V–1·s–1 at room temperature. Moreover, in addition to the main copper vacancy acceptor level, found at EA1 = 278 ± 21 meV above the top of the valence band, a coexisting shallower acceptor level with an ionization energy of EA2 = 133 ± 15 meV occurs for a strontium content above 5% and is tentatively assigned to a large size impurity–vacancy complex.

Synthesis of magnesium- and manganese-doped hydroxyapatite structures assisted by the simultaneous incorporation of strontium

Samples of crystalline hydroxyapatite (HA) with and without the addition of individual Mg2+, Mn2+ and Sr2+ ions and samples with the addition of all three ions simultaneously were prepared using the precipitation method in an aqueous medium. Chemical, structural, spectroscopic and thermophysical analyses of the synthesized samples were conducted. The obtained results indicate that Sr2+ ions were easily incorporated into the HA crystal structure, whereas it was difficult to incorporate Mg2+ and Mn2+ ions into the HA lattice when these ions were individually introduced into the samples. The synthesis of HA with Mg2+ or Mn2+ ions is characterized by the formation of HA with a low concentration of doping elements that is outweighed by the amount of these atoms present in less biocompatible phases that formed simultaneously. However, the incorporation of Sr2+ along with Mg2+ and Mn2+ ions into the samples allowed for the synthesis of HA with considerably higher concentrations of Mg2+ and Mn2+ in the crystal lattice.

Controls on strontium and barium incorporation into freshwater bivalve shells (Corbicula fluminea)

Trace elements of bivalve shells can potentially serve as proxies of environmental change. However, to reconstruct past environments using the geochemical properties of the shells and determine the degree to which the element levels are biologically influenced, it is essential to experimentally determine the relationship between environmental variables and the element composition of the shells. To disentangle possible controls on the incorporation of strontium and barium into freshwater bivalve shells, we conducted controlled laboratory experiments using the extremely salinity and temperature tolerant Asian clam, Corbicula fluminea as a model species. Bivalves were reared for five weeks in two sets of experiments: (1) combinations of different water temperature (10, 16 and 22°C) and food levels (0.2, 2, 4 and 8×104cells/ml) with constant Sr/Cawater (2.45mmol/mol) and Ba/Cawater (367μmol/mol) levels; and (2) combinations of different water temperature (10, 16 and 22°C) and different Sr/Cawater (ca. 4, 8 and 12mmol/mol) and Ba/Cawater levels (ca. 600, 1150 and 1500μmol/mol) with constant food level (4×104cells/ml). The Sr/Cashell ratio of C. fluminea exhibited a statistically significant negative correlation with temperature and a positive correlation to Sr/Cawater, but was not affected by changing food level or shell growth rate. On the contrary, Ba/Cashell was influenced by a complexly intertwined set of variables including temperature, food level, Ba/Cawater and shell growth rate. Partition coefficients of KDSr/Ca (0.19 to 0.29) and KDBa/Ca (0.03 to 0.19) confirmed the control of vital effects over strontium and barium incorporation into the shells. As indicated by the findings, Sr/Cashell of C. fluminea from freshwater environments can serve as a reliable proxy for past water temperature if the spatiotemporal variability of strontium-to-calcium in the water is small, well-known or can be estimated from other proxies. Interpreting Ba/Cashell values, however, is much more challenging because they are controlled by a large number of environmental and physiological variables. Sr/Cashell and Ba/Cashell of C. fluminea specimens from estuarine settings in which element-to-calcium ratios are more conservative and stable can potentially function as paleoenvironmental proxies. Findings of this study can be useful to better understand the element incorporation into shells of other bivalves including marine species.

Magnetic composites prepared by incorporation of strontium ferrite into polar and non‐polar rubber matrices

Strontium ferrite was incorporated into different rubber matrices to prepare rubber magnetic composites. Three types of elastomers, butadiene rubber BR as non‐polar elastomer, acrylonitrile butadiene rubber NBR and blend acrylonitrile butadiene rubber–polyvinyl chloride NBR/PVC as polar elastomers were chosen as rubber matrices. Surface modified strontium ferrite as magnetic filler was applied in concentration scale ranging from 0 to 100 phr. Besides the rubber and the filler, the rubber compounds contained only the ingredients of sulfur curing system. The results revealed that thermo‐physical and magnetic properties of composites increased with doping content of ferrite. Moreover, the improvement of mechanical properties in dependence on strontium ferrite content was also recorded. It can be stated that the improvement of composite properties is in close correlation with the increase of polarity of the rubber matrix. POLYM. COMPOS., 38:2480–2487, 2017. © 2015 Society of Plastics Engineers

Strontium incorporation to optimize the antibacterial and biological characteristics of silver-substituted hydroxyapatite coating.

Infection in primary total joint prostheses is attracting considerable attention. In this study, silver (Ag) was incorporated into hydroxyapatite (HA) using a hydrothermal method in order to improve its antimicrobial properties. Strontium (Sr) was added as a second binary element to improve the biocompatibility. The substituted HA samples were fixed on titanium (Ti) substrates by dopamine-assisted immobilization in order to evaluate their antibacterial and biological properties. The results showed that Ag and Sr were successfully incorporated into HA without affecting their crystallinity. Further, the antibacterial tests showed that all the Ag-substituted samples had good anti-bacterial properties against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Despite their good antibacterial ability, the Ag-substituted samples showed evidence of cytotoxicity on MG63 cells, characterized by low cell density and poor spreadability. The addition of Sr to the Ag-substituted samples considerably reduced the cytotoxicity of Ag. Although the viability of the cells grown on the surfaces of co-substituted HA was not as high as that of the cells grown on the HA surfaces, it is believed that excellent antibacterial properties and good biological activity can be achieved by balancing the dosage of Sr and Ag.

Electrical properties of zinc-oxide-based thin-film transistors using strontium-oxide-doped semiconductors**Project supported by the National Natural Science Foundation of China (Grant No. 6140031454) and the Innovation Program of Chinese Academy of Sciences and State Key Laboratory of Luminescence and Applications.

Strontium-zinc-oxide (SrZnO) films forming the semiconductor layers of thin-film transistors (TFTs) are deposited by using ion-assisted electron beam evaporation. Using strontium-oxide-doped semiconductors, the off-state current can be dramatically reduced by three orders of magnitude. This dramatic improvement is attributed to the incorporation of strontium, which suppresses carrier generation, thereby improving the TFT. Additionally, the presence of strontium inhibits the formation of zinc oxide (ZnO) with the hexagonal wurtzite phase and permits the formation of an unusual phase of ZnO, thus significantly changing the surface morphology of ZnO and effectively reducing the trap density of the channel.

Strontium incorporation during calcite growth: Implications for chemical mapping using friction force microscopy

Sr partitioning on calcite crystals growing from Ca2+–Sr2+–CO32− solutions was studied by means of friction force microscopy (FFM). Experiments were performed with various Sr2+(aq)/Ca2+(aq) concentration ratios and total Sr2+(aq) concentration in order to examine conditions under which Sr-calcite growth is self-limiting (e.g., the so-called “template effect”) and also to investigate continuous Sr-calcite growth, where spiral growth predominates and Sr incorporation is sector-dependent. In these latter experiments, the goal was to evaluate the utility of friction force microscopy to discriminate sector zoning. Results from the experiments show that friction increases with the incorporation of Sr into the growing calcite layers. The maximum increase in friction was measured at high Sr2+(aq)/Ca2+(aq), although a quantitative link between a specific amount of increase in friction to a specific amount of Sr incorporation was not possible to determine due to experimental uncertainties. Nevertheless, it was possible to establish that no change in friction is detectable when Sr incorporation yields a solid composition of Sr0.05Ca0.95CO3. Friction was found to increase during growth of several layers in an incremental fashion. The increase can be linked either to an incremental increase in Sr content in the newly formed calcite, controlled by the thermodynamics of the strained layers necessitated by the substitution of larger Sr cations into the calcite, or to the incremental increase in layer thickness which in turn leads to increases in the probe-surface contact area. No difference in friction could be observed between acute and obtuse sectors under any of the experimental conditions, which was primarily due to the limits of the friction measurement sensitivity.

Influence of peroxide curing systems on the performance of natural rubber-based magnetic composites

Rubber magnetic composites were prepared by incorporation of strontium ferrite into natural rubber-based continuous matrix. The prepared rubber compounds have model character and besides the rubber and the filler, they contained only ingredients of peroxide curing system, dicumyl peroxide as curing agent, and ethylene glycol dimethacrylate as co-agent. The work was focused on the evaluation of curing system composition and magnetic filler content on curing process, cross-link density, physical–mechanical and magnetic properties of tested materials. The achieved results revealed that the evaluated properties are dependent on the composition of curing system and on the content of ferrite too. Ferrite incorporated in the rubber matrix imparts magnetic properties to the composites considerably. In addition, the improvement of physical–mechanical properties with doping content of ferrite was observed.

Incorporation of strontium into hydroxyapatite via biomineralization of collagen fibrils

Mineralized collagen fibrils (nHAC) are the main extracellular matrix composites of hard tissues, such as bone and teeth. nHAC formed in vivo contains trace of foreign ions, such as HPO42−, Cl−, Na+, and Sr2+. The role of Sr2+ on the composition and microstructure of nHAC is still unknown. In this study, we prepared Sr2+ incorporated nHAC via biomineralization of collagen fibrils. We evaluated the effects of Sr2+ on mineralization of collagen by using FTIR, XRD, SEM and TEM. The FTIR results revealed that HPO42−, CO32−, and OH− functional groups were all incorporated into nHAC. The FTIR, XRD, SEM and TEM results revealed that the incorporation of Sr2+ into nHAC did not influence the organization of apatite crystals and collagen fibrils. The inorganic phase was determined as apatite and the variation of lattice constants of apatite crystals gave evidence that the incorporation of Sr2+ produced distortions in the apatite crystal structure at PO43− sites. More CO32− ions were incorporated in the Sr-doped nHAC. Thus, the incorporation of Sr2+ into nHAC changed the composition and crystal structure of apatite crystals which grew on the surface of collagen fibrils.

Activin receptor-like kinase ALK5 and ALK1 are both required for TGFβ-initiated chondrogenic differentiation of mesenchymal stem cells

Activin receptor-like kinase ALK5 and ALK1 are both required for TGFβ-initiated chondrogenic differentiation of mesenchymal stem cells

The osteogenic response of mesenchymal stromal cells to strontium-substituted bioactive glasses.

Bioactive glasses are known to stimulate bone healing, and the incorporation of strontium has the potential to increase their potency. In this study, calcium oxide in the 45S5 bioactive glass composition was partially (50%, Sr50) or fully (100%, Sr100) substituted with strontium oxide on a molar basis. The effects of the substitution on bioactive glass properties were studied, including density, solubility, and in vitro cytotoxicity. Stimulation of osteogenic differentiation was investigated using mesenchymal stromal cells obtained from rat bone marrow. Strontium substitution resulted in altered physical properties including increased solubility. Statistically significant reductions in cell viability were observed with the addition of bioactive glass powders to culture medium. Specifically, addition of ≥ 13.3 mg/ml of 45S5 bioactive glass or Sr50, or ≥ 6.7 mg/ml of Sr100, resulted in significant inhibition. Real‐time PCR analyses detected the upregulation of genes associated with osteoblastic differentiation in the presence of all bioactive glass compositions. Some genes, including Alpl and Bglap, were further stimulated in the presence of Sr50 and Sr100. It was concluded that strontium‐substituted bioactive glasses promoted osteogenesis in a differentiating bone cell culture model and, therefore, have considerable potential for use as improved bioactive glasses for bone tissue regeneration. © 2015 The Authors. Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons Ltd.

Influence of carbonate ion in the crystallization medium on the formation and chemical composition of CaHA–SrHA solid solutions

The study of the influence of carbonate ions in a solution to Sr-distribution in system «solution–crystal» and to ion substitutions and the non-stoichiometry of formed CaHA–SrHA solid solutions was carried out. The CaHA–SrHA solid solutions were synthesized by precipitation from aqueous solutions with the atomic C/P ratio equal to 0, 0.05 and 0.1 at T=90°C. Resulting precipitates were studied using various methods including X-ray powder diffraction, infrared spectroscopy and different chemical analyses.The results of the study have shown that in the range of values of (Ca+Sr)/P in the water solution from 40% to 85%, the presence of carbonate ions (C/P=0.05–0.1) promotes the incorporation of strontium in the apatite. Crystalline apatite solid solutions formed from water solutions of such composition are more defective compared to apatites that are mainly calcium or strontium. They are characterized by a smaller size coherence scattering domain length along [001] direction and a greater number of carbonate ions, water molecules and vacancies at the Ca-sites.

Chemical signature of magnetotactic bacteria

There are longstanding and ongoing controversies about the abiotic or biological origin of nanocrystals of magnetite. On Earth, magnetotactic bacteria perform biomineralization of intracellular magnetite nanoparticles under a controlled pathway. These bacteria are ubiquitous in modern natural environments. However, their identification in ancient geological material remains challenging. Together with physical and mineralogical properties, the chemical composition of magnetite was proposed as a promising tracer for bacterial magnetofossil identification, but this had never been explored quantitatively and systematically for many trace elements. Here, we determine the incorporation of 34 trace elements in magnetite in both cases of abiotic aqueous precipitation and of production by the magnetotactic bacterium Magnetospirillum magneticum strain AMB-1. We show that, in biomagnetite, most elements are at least 100 times less concentrated than in abiotic magnetite and we provide a quantitative pattern of this depletion. Furthermore, we propose a previously unidentified method based on strontium and calcium incorporation to identify magnetite produced by magnetotactic bacteria in the geological record.

Abrupt change of dielectric properties in mullite due to titanium and strontium incorporation by sol-gel method

Highly crystallized mullite has been achieved at temperatures of 1100 ℃ and 1400 ℃ by sol-gel technique in presence of titanium and strontium ions of different concentrations: G0 = 0 M, G1 = 0.002 M, G2 = 0.01 M, G3 = 0.02 M, G4 = 0.1 M, G5 = 0.2 M and G6 = 0.5 M. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), LCR meter characterized the samples. Mullite formation was found to depend on the concentration of the ions. The dielectric properties (dielectric constant, loss tangent and AC conductivity) of the composites have been measured, and their variation with increasing frequency and concentration of the doped metals was investigated. All the experiments were performed at room temperature. The composites showed maximum dielectric constants of 24.42 and 37.6 at 1400 ℃ of 0.01 M concentration for titanium and strontium ions at 2 MHz, respectively. Due to the perfect nature of the doped mullite, it can be used for the fabrication of high charge storing capacitors and also as ceramic capacitors in the pico range.

Rubber composites with incorporated magnetic filler

In this study, rubber magnetic composites were prepared by incorporation of strontium ferrite into non-polar and polar rubber matrices. The aim was to investigate the influence of magnetic filler content on the cross-linking and properties of the tested materials. The results demonstrate that the presence of strontium ferrite in rubber matrices leads to a significant increase in the magnetic characteristics of composites. The physical properties of the tested systems seem to be less dependent on magnetic filler content although the improvement of evaluated characteristics with increasing content of ferrite was achieved.

Strontium exerts dual effects on calcium phosphate cement: Accelerating the degradation and enhancing the osteoconductivity both in vitro and in vivo.

Calcium phosphate cements (CPCs) have long been used as osteoconductive bone substitutes in the treatment of bone defects. However, the degradation rate of CPC is typically too slow to match the new bone growth rate. It is known that strontium increases the solubility of hydroxyapatite as well as exerts both anabolic and anticatabolic effects on bone. Therefore, we hypothesized that the incorporation of strontium would accelerate the degradation rate and enhance the osteoconductivity of CPC. In this study, Three groups, CPC (0% Sr-CPC), 5% Sr-CPC, and 10% Sr-CPC, were prepared, with the total molar ratio for Sr/(Sr+Ca) in the cement powder phase being 0, 5, and 10%, respectively. In the immersion test, less residual weight was observed in both 5% Sr-CPC and 10% Sr-CPC groups than CPC group. In addition, a higher osteoblastic cell proliferation rate and alkaline phosphatase activity were obtained in the strontium groups. In a rat femur bone defect model comparing CPC with 10% Sr-CPC, at 2 weeks postoperation, early endochondral ossification was found in the 10% Sr-CPC group, whereas only fibrous tissue was observed in control group; at 4-16 weeks postoperation, progressive osteoconduction toward the cement was observed in both groups. At 32 weeks, a higher peri-cement bone area and reduced cement area were noted in the 10% Sr-CPC group. In conclusion, in the 10% Sr-CPC group, strontium exerts dual effects on CPC: accelerating degradation rate and enhancing osteoconductivity, as shown here both in vitro and in vivo.