The effect of graphene oxide (GO) on biomineralization and solubility of calcium hydroxyapatite (HA)

Interaction between GO and the counterpart of the bone tissue, calcium hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (HA), is modeled in the course of synthesis of nanosize composite materials (CMs) based on graphene oxide (GO) and biocompatible HA with a GO content of 0.1, 1.0, 2.0, and 5.0 wt % GO from aqueous solutions in the system of Ca(OH)₂–H₃PO₄–GO–H₂O under native conditions (37°C). The effect of CM composition on the size and morphology of HA nanocrystals (HA NCs) is determined using the methods of physico-chemical analysis (chemical, XRD, IRS, DTA, TDG, SEM, TEM). The solubility of HA NC CMs by Ca²⁺ ions in distilled water is determined under in vitro conditions, and the possible results of interaction between GO and native calcified tissues are analyzed.     

Hot pressing of hydroxyapatite(HA)-Ti material and stability of HA

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The effect of carbon nanotubes on biomineralization and solubility of calcium hydroxyapatite Ca10(PO4)6(OH)2

Toxic characteristics of carbon nanotubes (CNTs) were estimated through the modeling of interaction between CNTs and the inorganic component of osseous tissue of mammals—calcium hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (HA)—under the conditions of biomimetic formation of HA/CNT composites containing 0.1, 1, and 5 wt % CNT. Synthesis products were identified using the methods of chemical analysis, XRD, DTG, DTA, IRS, SEM, TEM, and DE. The effect of nanotubes on crystallographic and morphological characteristics of nanocrystalline HA and solubility of HA/CNT composites was determined.     

Preparation and application of hydroxyapatite(HA) nanoparticles/NR2B-siRNA complex

Hydroxyapatite(HA) nanoparticles were prepared by coprecipitation-hydrothermal synthesis and their exosyndrome was estimated via transmission electron microscopy. Agarose gel electrophoresis and ultraviolet spectrophotometry were used to evaluate the ability of HA to bind NR2B-siRNA at different pH values and at different HA-NR2B-siRNA ratios. And the stability of the complex in saline was also evaluated. The effect of HA/NR2B-siRNA complex on chronic inflammatory pain was evaluated in vivo in mice. Transmission electron microscopy(TEM) reveals that HA nanoparticles are thin strips or short rod in shape and the one-dimensional particle size of HA nanoparticles is 40-50 nm. Under the acid or neutral condition, the Zeta potential of HA is positive; nanoparticles can completely bind NR2B-siRNA when the HA:NR2B-siRNA ratio is at or larger than 35-1; while under the alkaline condition, the affinity of HA to NR2B-siRNA is rather weak. HA/NR2B-siRNA complex is not dissociated when being resuspended in saline. The nociception of the tonic phase induced by formalin is significantly reduced in the HA/NR2B-siRNA treated mice as compared with the controls. Therefore, HA may be a new siRNA nano-vector material.     

Plasma spraying of combustion flame spheroidized hydroxyapatite (HA) powders

Tailoring powder characteristics to suit the plasma spray process can alleviate difficulties associated with the preparation of hydroxyapatite (HA) coatings. Commercial HA feedstock normally exhibit an angular morphology and a wide particle size range that present difficulties in powder transport from the powder hopper to the plasma spray gun and in nonuniform melting of the powders in the plasma flame. Hence, combustion flame spheroidized hydroxyapatite (SHA) was used as the feedstock for plasma spraying. Spherical particles within a narrow particle size range are found to be more effective for the plasma spray processes. Results show coatings generated from spheroidized HA powders have unique surface and microstructure characteristics. Scanning electron microscope (SEM) observation of the coating surface revealed well-formed splats that spread and flatten into disc configurations with no disintegration, reflecting adequate melting of the HA in the plasma and subsequent deposition consistency. The surface topography is generally flat with good overlapping of subsequent spreading droplets. Porosity in the form of macropores is substantially reduced. The cross-section microstructure reveals a dense coating comprised of randomly stacked lamellae. The tensile bond strengths of the SHA coatings, phase composition, and characteristics of the coatings generated with different particle sizes (125 to 75 μm, 45 to 75 μm, 20 to 45 μm, and 5 to 20 μm) showed that a high bond strength of ∼16 MPa can be obtained with SHA in the size range from 20 to 45 μm. This can be improved further by a postspray treatment by hot isostatic pressing (HIP). However, larger particle size ranges exhibited higher degrees of crystallinity and relatively higher HA content among the various calcium phosphate phases found in the coatings.     

Effect of calcium deficiency on the mechanical properties of hydroxyapatite crystals

The deterioration of the mechanical properties of bone with age is related to several factors including the structure, organization and chemistry of the constituent phases; however, the relative contribution of each of these factors is not well understood. In this study, we have investigated the effect of chemistry (calcium deficiency) on the mechanical properties of single crystals of hydroxyapatite. Single crystals of stoichiometric crystals grown by the flux method and calcium-deficient platelet crystals grown using wet chemical methods were used as model systems. Using nanoindentation, we show that calcium deficiency leads to an 80% reduction in the hardness and elastic modulus and at least a 75% reduction in toughness in plate-shaped hydroxyapatite crystals. Measurement of local mechanical properties using nanoindentation and nanoscale chemistry through elemental mapping in a transmission electron microscope points to a direct correlation between the observed spatial variation in composition and the large scatter in the measured hardness and modulus values.     

The evaluation of powder processing on microstructure and mechanical properties of hydroxyapatite (HA)/yttria stabilized zirconia (YSZ) composite coatings

In clinical applications, the mechanical failure of HA-coated titanium alloy implants suffered at the interface of the HA coating and titanium alloy substrate will be a potential weakness in prosthesis. Yttria stabilized zirconia (YSZ) reinforced HA coatings have been proven to enhance the mechanical properties of the HA coating significantly and reduce the formation of calcium oxide (CaO). In this paper, HA/YSZ (30 wt.% YSZ) composite coatings were sprayed by the plasma technique. The effects of the powder processing–mechanical ball milling method and spheroidization method on the microstructure and mechanical properties of the HA/YSZ composite coatings were evaluated. The experimental results showed that the spheroidized powders melted better than the ball milled powders during plasma spraying and formed higher mechanical property coatings (1.6326±0.08 MPa m^−0.5 of fracture toughness, 58.59±2.91 GPa of elastic modulus and 43.42±2.53 MPa of tensile bond strength). HA/YSZ solid solution formed during deposition on the substrate, which played a very important role in the mechanical properties of the HA/YSZ composite coatings. Tensile bond strength tests showed that the fracture mode was cohesive and that failure occurred at the interface of HA and unmelted YSZ particles. The molten state of YSZ had a great influence on the properties of the HA/YSZ composite coatings.     

Biocompatibility and preliminary clinical application of HA/HDPE nanocomposites synthetic auditory ossicle

The biocompatibility of the hydroxyapatite/high density polyethtlene（HA/HDPE） nanocomposites synthetic auditory ossicle was evaluated, the percentage of S-period cells was detected by flow cytometry after L929 incubated with extraction of the HA/HDPE nanocomposites, titanium materials of clinical application as the control. Both of them were implanted in the animals and the histopathological evaluations were carried out, and the preliminary clinical trials about HA/HDPE nanocomposites synthetic auditory ossicles were also carried out. The statistical analysis show that there are no statistically significant differences between HA/HDPE test groups and control groups （P〉0.05）, which demonstrates that the HA/HDPE nanocomposites synthetic auditory ossicle has a good biocompatibility and clinical application outlook.     

The effect of temperature and ionic strength on iron carbonate (FeCO3) solubility limit

In CO₂ corrosion, precipitation of iron carbonate can significantly reduce the corrosion rate of the underlying steel. Precipitation rate depends on a reliable calculation of the iron carbonate solubility limit. The open literature does not provide an expression for iron carbonate solubility that covers a wide enough range of parameters. In this study a unified iron carbonate solubility (K_sp in mol²/L²) expression is developed based on the literature data:

     

晶化处理对HA/(HA+TiO2)涂层组织结构的影响

用X射线衍射仪（XRD）、电子探针（EPMA）等检测手段，以晶化处理对大气等离子喷涂法在纯钛表面制备的HA／（HA＋TiO2）复合涂层为研究对象，探讨了晶化处理对HA／（HA＋TiO2）涂层组织结构和成分分布的影响。结果表明：晶化处理后HA／（HA＋TiO2）涂层结晶度明显提高；（HA＋TiO2）过渡层中交替分布的HA和TiO2结合致密；涂层表面裂纹比对应纯HA涂层细小，涂层内部结合致密，证实TiO2的加入具有缓和应力的作用。     

Influence of Ca/P ratios of starting solutions on the crystallization of amorphous calcium phosphate to hydroxyapatite

Amorphous calcium phosphate was precipitated at 20°C from highly supersaturated solutions having compositions of 1.5≤Ca/P≤2.0 at a pH=11. The phase evolution and morphological changes in precipitates as a function of aging time were investigated using XRD and TEM analyses. Higher Ca/P molar ratio of the starting solution resulted in faster crystallization to hydroxyapatite. Shorter induction times for crystallization were attributed to smaller particle sizes of the initially precipitated ACP as well as to the Ca-rich environment. Nucleation of the hydroxyapatite phase was suggested to be a major mechanism of crystallization, which was supported by the observation that no considerable growth of hydroxyapatite occurred during further aging. The increase in the number of HAp nuclei was accompanied by a size reduction of particles of amorphous phase.     

Chemically synthesizing exchange-coupled SmCo_5/Sm_2Co_(17)nanocomposites

A new strategy to chemically synthesize exchange-coupled SmCo_5/Sm_2 Co_(17) nanocomposites by in situ decomposition of SmCox(5 x 8.5) is reported in this work.Our synthesis starts with the fabrication of Co/Sm_2 O_3(Sm to Co atomic ratio of Sn/Co=1:4.2),which can be reduced into 40-nm SmCo_5 single crystal nanoparticles by Ca under the protection of CaO,showing a high coercivity of 2.85 T and saturation magnetization(M_s) of 0.0671 A·m~2·g~(-1).By changing the Sm/Co to 1:4.5,1:4.8 and 1:5.2,SmCo_5/Sm_2 Co_(17) nanocomposites with different proportions were acquired using the same process.Owing to the in situ decomposition of SmCo_x intermediate,the small size(both of their size less than 10 nm) and uniform phase distribution were achieved in our nanocomposites.Thus,the as-prepared nanocomposites display a strong exchange-coupling interaction.As a consequence,SMCo_5/Sm_2 Co_(17)(Sm/Co=1:5.2) exhibits a coercivity of 1.23 T and enhanced M_(7 T)(magnetization at 7 T) of 0.0812 A·m~2·g~(-1),increasing by 21% than pure SmCo~5.Our synthesis provides a new protocol to prepare exchange-coupled high-performance nanocomposites.     

The characterization of high-density polyethylene/organoclay nanocomposites

Polymeric nanocomposites, which are hybrids of polymers and modified inorganic clay with organic surfactants, are extremely attractive in both science and industry. These materials present improvements in such polymer properties as modulus, heat capacity, thermal stability, flame resistance, and so on. Research has been conducted in recent decades to obtain high-quality materials that can be used in applications like food packing, car components, and combustible cells. Polymeric nanocomposites present many advantages in relation to composites due to the quantity of filler added to the polymer and also to the improved properties. In a composite, the quantity of filler must be as high as possible (i.e., over 30%). In the polymeric nanocomposite the quantity of filler varies from 1% to 5% because of the nanosize of the particles. These nanoparticles often have a large surface area that results in improved polymer-matrix properties.     

电磁铸造对Al-Zn-Mg-Cu-Zr合金微观组织及晶内固溶度的影响

分别采用电磁铸造和普通连铸技术制备Al-Zn-Mg-Cu-Zr合金,研究电磁场对合金显微组织、合金元素晶内固溶度的影响.结果表明:采用电磁铸造技术制备的Al-Zn-Mg-Cu-Zr合金具有良好的表面质量和内部组织;电磁场显著提高合金元素在晶内的固溶度,减小了微观偏析程度.相对于普通连铸,电磁铸造法制备的Al-Zn-Mg-Cu-Zr合金的晶粒平均尺寸从68μm减小到53μm,Zn、Mg和Cu元素的晶内相对溶质固溶度分别由56%、62%和25%提高到79%、74%和44%.     

Semi-solid casting (SSC) of zinc alloy nanocomposites

An innovative casting method that combines semi-solid casting (SSC) and metal matrix nanocomposite (MMNC) technology was successfully demonstrated. The method uses the grain refining properties of the nanoparticles in the MMNC to produce slurry with the appropriate globular structure for semi-solid casting. In this way no additional material processing or mechanical agitation is necessary to achieve the desirable slurry microstructure. The grain refining attributes of the nanoparticles were shown to stem from the promotion of nucleation in the solidifying matrix alloy. Differential scanning calorimetry (DSC) showed a reduced undercooling necessary for nucleation owing to the nucleation catalytic potency of the nanoparticles. Using this method zinc alloy AC43A nanocomposite with 0.5 wt.% SiC β nanoparticle additions were cast at a 30% solid fraction. The resulting castings showed increased ductility, reduced shrinkage, and increased strength compared to their monolithic liquid cast counterparts.     

The influence of silicate on the development of acidity in corrosion product deposits on SIMFUEL (UO2)

The influence of silicate on the formation of corrosion products and secondary phase deposits on corroding/dissolving nuclear fuel surfaces under waste disposal conditions were investigated. SIMFUEL (doped uranium dioxide) has been characterized over the potential range 100-500 mV (vs. SCE). Through the use of X-ray photoelectron spectroscopy (XPS) the surface composition over this potential range has been determined. The presence of silicate was found to have little influence on the oxidation of UO₂ to produce the oxidized surface layer . However, depending on its concentration it could suppress the conversion reaction for potentials ?250 mV (vs. SCE). This suppression appears due to the adsorption of silicate on the fuel surface. The accumulation of a hydrated U^VI silicate on the fuel surface occurs when U^VI is formed at higher anodic potentials, leading to a suppression of anodic dissolution. The formed in, and subsequently transported out of, the acidified sites accumulates on the outer fuel surface as a hydrated U^VI silicate.     

Characteristics of the nanostructures in thermal sprayed hydroxyapatite coatings and their influence on coating properties

There are generally two methods for depositing nanostructured coatings, retaining the nanostructures from starting feedstock and forming novel nanostructures through quenching. The present study utilized spray-dried nanostructured hydroxyapatite (nSD-HA) feedstock for coating/splat deposition. The nanostructures were characterized by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). Results revealed that the rod-shaped nano-grains in the starting HA particles (< 500 nm in length and 40-70 nm in diameter) encountered two major experiences: enlargement due to unmelt state and reorganization due to melting-solidification. The molten part of the particles results in formation of spherical nanosized particles with grain sizes of 30-110 nm. TEM observation of the HA splats demonstrates consistent nanostructures. The unmelted part of individual nSD-HA particles showed significantly enlarged grains along radial direction (< 550 nm in length and < 400 nm in diameter). In addition, individual hexagonal grains were observed in the HVOF coating made from 30 ± 10 μm powder. The grains have the size of < 250 nm in height and < 50 nm in side length and are perpendicular to the coating/substrate interface. The nanostructures within the coatings contribute to an increased Young's modulus with up to 60.11 GPa, however, they showed detrimental effect on adhesion of the coatings. In vitro cell culturing revealed marked attachment and proliferation of the osteoblast cells on the nanostructured coatings. However, the results suggest that the nanostructures possess less importance than the phases (preferably high content of crystalline HA) on enhancing the cell proliferation.     

数控加工中心工件坐标系的建立

工件坐标系的建立，是数控加工中一个非常重要的环节，它对数控编程、加工质量都会产生重大影响。文章对工件坐标系的建立及零点偏置值的测量，进行了较为全面的介绍，对数控加工有一定的指导意义。