Platelet-like Structures Research Articles

Synthesis of TTCP by using inverse micelle method

Tetracalcium phosphate (TTCP, Ca4(PO4)2O) is one of the major powder components of self-setting orthopedic and dental cements. Traditionally, TTCP powders are produced by a solid-state reaction of Ca- and P-containing precursors between 1350 and 1500 °C. Such procedures require expensive high-temperature furnaces and subsequent grinding of sintered particles. Grinding not only leads to the contamination but also alters the structure of TTCP, thereby reducing its bioactivity. The present paper offers an innovative approach to the inverse micelle method of TTCP synthesis, with a subsequent thermal treatment to obtain purer TTCP phase. The obtained powder was a mixture of TTCP and octacalcium phosphate (OCP) phases for thermally untreated sample, while for the sample thermally treated at 800 °C it was a mixture of TTCP and β-TCP phases. The TTCP phase was prevailing phase in both cases. A typical shape of TTCP nanoparticles was needle-like. Somewhere, needles are joined together forming platelet-like structures. Investigations of the obtained phases were made by XRD and TEM. The mechanism of chemical synthesis and structural arrangements of the obtained phases were particularly investigated.The specific surface area and mechanical properties (compressive and flexural strength) of cements based on needle like TTCP (n-TTCP) and irregular shape TTCP (i-TTCP), as the most frequent form of TTCP appeared in literature, were compared. It was shown, by corresponding calculations, that the specific surface area of n-TTCP (determined from TEM micrographs) was much higher than in the case of i-TTCP (determined from SEM micrographs). Beside, compressive and flexural strength of n-TTCP based cement were significantly improved, because n-TTCP whiskers considerably reinforced structure of hardened cement paste.

Facile synthesis of CoAl-LDH/MnO2 hierarchical nanocomposites for high-performance supercapacitors

Abstract In this work, MnO 2 /CoAl-layered double hydroxide (CoAl-LDH) nanocomposites were prepared through a simple redox reaction between Co 2+ species and MnO 4 − . The structure and morphology of these nanocomposites were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), focused ion beam scanning electron microscopy (FIB/SEM) and high-resolution transmission electron microscopy (HRTEM). CoAl-LDH/MnO 2 nanocomposites presented their platelet-like structures with MnO 2 nanocrystals decorating the LDH host layer. Furthermore, the electrochemical properties of composites were evaluated by cycle voltammetric (CV) and galvanostatic charge–discharge measurements. Surprisingly, the hierarchical CoAl-LDH/MnO 2 composites displayed a high specific capacitance (1088 F g −1 at 1 A g −1 ), high rate capability, and excellent long-term cycling life. In principle, these findings suggested that CoAl LDHs-based nanocomposites could be promising candidates for supercapacitors electrode with enhancive electrochemical behavior.

Combinatorial exploration of rare-earth-free permanent magnets: Magnetic and microstructural properties of Fe-Co-W thin films

We have investigated the magnetic and structural properties of Fe-Co-W films using a composition spread technique. From the magnetometry measurements, large magnetization (900 emu/cm3) and enhanced perpendicular coercive fields (2–3 kOe) of low W concentration films were observed. The synchrotron diffraction results show a structural transition from a crystalline to an amorphous state and the crystallization onset increases with increasing W concentration. The SEM and TEM characterizations show that the films with low W concentrations have vertically standing platelet-like grain structures which is ascribed to the enhanced coercive fields. Magnetometry studies indicate that as the W concentration increases, microstructural change results in evolution of magnetization reversal mechanism.

Nonionic Surfactant and Interfacial Structure Impact Crystallinity and Stability of β-Carotene Loaded Lipid Nanodispersions

The stability, crystallization, and melting behavior of canola stearin (CaSt) solid lipid nanoparticle dispersions (SLN) and canola oil-in-water emulsions (COE) with 10 wt % Poloxamer 188 (P188) or Tween 20 (T20) with and without 0.1 wt % β-carotene (BC) were investigated. Particles or droplets with diameters in the range of 115 nm were formed and stable for up to 90 days at 4 or 20 °C. Polymorphism was affected by surfactant type; that is, only β versus both β' and β were observed for the P188 and T20 SLN, respectively. According to Cryo-TEM, the emulsions and SLN were spherical versus platelet-like structures, respectively, with differences observed between SLN with P188 or T20. More surfactant was interfacially adsorbed in the SLN versus COE. Incorporation of BC at 0.1 wt % had no impact on SLN or COE size, polymorphism, or melting behavior. Less BC degradation was observed for the SLN versus COE and during storage at 4 versus 20 °C (p < 0.05).

Growth of platelet-structured CuAlO2 thin film on CuAl alloy by molten salt electrolysis method

Herein, we report a novel synthesis procedure of CuAlO2 thin film by applying molten salt electrolysis method on a CuAl alloy electrode. The CuAlO2 thin film was directly prepared using CuAl alloy as Cu and Al sources by electrolysis in molten potassium cryolite system (CR=1.3) at 700°C for 10h with a current density of 0.5A/cm2. The as-prepared CuAlO2 film was characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The results indicate that the rhombohedra structural CuAlO2 film has platelet-like structures with particle size of 2–10μm and the membrane thickness is ~75μm. Moreover, the reaction mechanism for the as-synthesized CuAlO2 thin film is proposed.

Alkoxy Tail Length Dependence of Gelation Ability and Supramolecular Chirality of Sugar-Appended Organogelators

A series of sugar-appended organogelators, 4-(4'-alkoxyphenyl)phenyl-β-O-D-glucoside (GBCn, where n = 1-12 denotes the number of carbon atom in the tail), are synthesized to elucidate the effect of terminal chain length on their gelation and chiral expression abilities in gels. In the mixture of H(2)O/dioxane (60/40 v/v), GBCn undergoes a phasic evolution of precipitation-solution-gel-precipitation-gel as its tail length increases from n = 1, 2, 3-6, and 7-10 to 11-12, respectively. Helical ribbons are observed in gels, but platelet-like structures are the dominant morphologies in the systems that precipitation happens. Combinatory analyses of microscopic, spectroscopic, and diffraction results reveal that the self-assembly into interdigitated bilayer structures of GBCn is driven by hydrogen bondings of sugar heads, π-π interactions of biphenyl rods, and hydrophobic interactions of alkoxy tails. The helical-morphology formation is caused by the significant steric repulsion between chiral moieties on the condition of the disordering or the size of alkoxy chains reaching the threshold of helical twisting and bending.

Fabrication and characterization of ink jet processed organic thin film transistors with poly-4-vinylphenol gate dielectric

Organic thin film transistors (OTFTs) were fabricated on polyethersulphone substrate using 6,13-bis(triisopropylsilylethynyl) (TIPS) pentacene as an active layer and cross-linked poly-4-vinylphenol (PVP) as a gate dielectric. Prior to adoption of PVP as a gate dielectric, the PVP print condition was optimized using a metal-insulator-metal structure and making a comparison with spin coated devices in terms of the leakage current, breakdown voltage, and dielectric constant. Then, OTFTs were fabricated with an optimized PVP gate dielectric and a TIPS pentacene active layer using an ink jet printer. The electrical properties such as the field effect mobility, Ion/Ioff ratio, and threshold voltage had values of 0.055 cm2/V s, 103, and −2.6 V, respectively. The smaller Ion/Ioff ratio can be attributed to the smaller coverage of the TIPS pentacene layer due to the plateletlike crystalline structures.

Involvement of ERK1/2, p38 and PI3K in megakaryocytic differentiation of K562 cells

Megakaryocytic differentiation of myelogenous leukemia cell lines induced by a number of chemical compounds mimics, in part, the physiological process that takes place in the bone marrow in response to a variety of stimuli. We have investigated the involvement of mitogen-activated protein kinases (MAPKs) [extracellular signal-regulated protein kinase (ERK1/2) and p38] and phosphoinositide 3-kinase (PI3K) signaling pathways in the differentiated phenotypes of K562 cells promoted by phorbol 12-myristate 13-acetate, staurosporine (STA), and the p38 MAPK inhibitor SB202190. In our experimental conditions, only STA-treated cells showed the phenotype of mature megakaryocytes (MKs) including GPIbalpha expression, DNA endoreduplication, and formation of platelet-like structures. We provide evidence supporting that basal activity, but not sustained activation, of ERK1/2 is required for expression of MK surface markers. Moreover, ERK1/2 signaling is not involved in cell endomitosis. The PI3K pathway exerts dual regulatory effects on K562 cell differentiation: it is intimately connected with ERK1/2 cascade to stimulate expression of surface markers and it is also necessary, but not sufficient, for polyploidization. Finally, apoptosis and megakaryocytic differentiation exhibit different sensitivity to p38 down-regulation: it is required for expression of early specific markers but is not involved in cell apoptosis. The present work with K562 cells provides new insights into the molecular mechanisms regulating MK differentiation. The results indicate that a precise orchestration of signals, including ERK1/2 and p38 MAPKs as well as PI3K pathway, is necessary for acquisition of features of mature MKs.

SEM and Raman study of thermally treated TiO 2 anatase nanopowders: Influence of calcination on photocatalytic activity

Titania (TiO 2) nanopowders called PC 500, synthesised by the sulphate process, were annealed in air at temperatures of up to 1022 K for 30 min. The X-ray Diffraction (XRD) indicates that the thermal annealing resulted in coarsening of the average crystallite size from 13 to 72 nm. However, Scanning Electron Microscopy (SEM) reveals persistence of platelet-like structures which survive up to temperatures around 900 K. This implies that the crystals at least partially grow within the plates in 2D confinement. This implies that direct usage of Scherrer equation in this case should be approached with care. Raman spectra peak positions and the Full-Width-at-Half-Maximum (FWHM) values changed considerably after calcinations crystal growth, while, material composition and oxygen content remain unchanged. The Raman peak behaviour can be cautiously attributed to the first order phonon confinement phenomena, but both, 2D and 3D models of confinement should be accounted. The highest photoactivity, as indicated by photoinduced degradation of a mono azo dye methyl-orange (C 14H 14N 3SO 3Na), was observed in material treated at 773 K.

Wet chemical synthesis and thermoelectric properties of V-VI one- and two-dimensional nanostructures

Recent advances in both theoretical and experimental studies on optimizing thermoelectric performance have proved to greatly benefit from nanostructure engineering. As a class of materials with the best thermoelectric properties near room temperature, V-VI alloy nanostructures, especially Bi(2)Te(3) and its alloy with Sb, Se and so on, have attracted a broad interest. This perspective gives an overview of the progress in the wet chemical synthesis and property study of V-VI related one- and two-dimensional nanostructures. First, we discuss the preparation of one-dimensional nanowires/tubes, axial and radial modulated heterostructures, and two-dimensional platelet-like structures through various chemical routes. Then, we attempt to give a general outlook on the thermoelectric properties of V-VI single nanowires, and nanostructured films or bulk nanocomposites made of these chemically synthesized nanostructures. On the basis of the research in the synthetic methods and thermoelectric properties, the challenging issues and future research directions are briefly discussed. By no means is this a comprehensive coverage of V-VI related nanostructures, but a selection of those studies that could benefit the advance of thermoelectric properties of this material system in the near future.

Hydrogen-Induced Passivation of Grain-Boundary Defects in Polycrystalline Silicon

The influence of the hydrogen content in the amorphous starting material on hydrogen bonding and defect passivation in laser annealed polycrystalline silicon is investigated. The samples are characterized using electron paramagnetic resonance and hydrogen effusion measurements. After laser dehydrogenation and crystallization the samples contain a residual H concentration of up to 8×1021 cm-3. During a vacuum anneal at least 1.5×1021 cm-3 are mobile of which only 3.7×1018 cm-3 H atoms passivate preexisting Si dangling bonds. It is shown that a vacuum anneal can cause the vast majority of H atoms to accumulate in platelet-like structures. Defect passivation and platelet nucleation and growth occur spatially separated requiring long range H diffusion.

In situ surface investigation of austenitic stainless steel in nitric acid medium using electrochemical atomic force microscopy

Using potentiodynamic polarization and electrochemical atomic force microscope, the surface morphology of austenitic stainless steel has been investigated with the aim of understanding the passive film property in nitric acid medium. It has been found that passive film consists of platelet-like structures with a moire pattern at lower concentrations (0.1, 0.5 M); at higher concentrations (0.6, 1 M) the platelet-like structures disappear, revealing the grain boundary structure.

Metalloproteinase regulation improves in vitro generation of efficacious platelets from mouse embryonic stem cells

Embryonic stem cells (ESCs) could potentially compensate for the lack of blood platelets available for use in transfusions. Here, we describe a new method for generating mouse ESC-derived platelets (ESPs) that can contribute to hemostasis in vivo. Flow cytometric sorting of cells from embryoid bodies on day 6 demonstrated that c-Kit+ integrin αIIb (αIIb)+ cells, but not CD31+ cells or vascular endothelial cadherin+ cells, are capable of megakaryopoiesis and the release of platelet-like structures by day 12. αIIbβ3-expressing ESPs exhibited ectodomain shedding of glycoprotein (GP)Ibα, GPV, and GPVI, but not αIIbβ3 or GPIbβ. ESPs showed impaired αIIbβ3 activation and integrin-mediated actin reorganization, critical events for normal platelet function. However, the administration of metalloproteinase inhibitors GM6001 or TAPI-1 during differentiation increased the expression of GPIbα, improving both thrombogenesis in vitro and posttransfusion recovery in vivo. Thus, the regulation of metalloproteinases in culture could be useful for obtaining high-quality, efficacious ESPs as an alternative platelet source for transfusions.

Microstructural evolution in H ion induced splitting of freestanding GaN

We investigated the microstructural transformations during hydrogen ion-induced splitting of GaN thin layers. Cross-sectional transmission electron microscopy and positron annihilation spectroscopy data show that the implanted region is decorated with a high density of 1–2nm bubbles resulting from vacancy clustering during implantation. These nanobubbles persist up to 450°C. Ion channeling data show a strong dechanneling enhancement in this temperature range tentatively attributed to strain-induced lattice distortion. The dechanneling level decreases following the formation of plateletlike structures at 475°C. Extended internal surfaces develop around 550°C leading to the exfoliation of GaN thin layer.

Thermo-Reversible Formation of Wormlike Micelles with a Microphase-Separated Corona from a Semicrystalline Triblock Terpolymer

The thermo-reversible formation of wormlike micelles from a polystyrene-block-polyethylene-block-poly(methyl methacrylate) (PS-b-PE-b-PMMA) triblock terpolymer with a crystallizable middle block in organic media is presented. The formation of wormlike micelles is rather unexpected, because PE containing diblock copolymers usually form platelet-like structures. Transmission electron microscopy (TEM) investigations revealed a core−corona structure for the wormlike micelles. The core is formed by crystalline PE domains, and the soluble corona exhibits a patched structure composed of microphase-separated PS and PMMA chains. Microphase separation of the coronal chains was proven by 2D 1H nuclear Overhauser effect spectroscopy (NOESY) and TEM investigations of selectively stained samples. A combination of various techniques, such as differential scanning calorimetry (DSC), dynamic light scattering (DLS), and scanning force microscopy (SFM), indicated that the wormlike micelles might be formed by crystallization-induced aggregation of spherical micelles upon cooling. The presented approach opens an alternative way to produce anisotropic polymer nanostructures with a microphase-separated corona.

Crystallization and morphology of zeolite MCM-22 influenced by various conditions in the static hydrothermal synthesis

MCM-22 zeolite was synthesized in various static hydrothermal systems with hexamethyleneimine (HMI) as the structure-directing agent. Synthesis parameters, such as silica source, alkaline source (Na +, K + or NH 4 + ), alkalinity of the reaction mixture, HMI/SiO 2 ratio and seeding, were changed to investigate their effects on the crystallization and morphology of zeolite MCM-22. The produced samples were characterized by XRD, IR, SEM, N 2 physisorption and ICP. Reaction conditions were revealed to influence the induction period and crystallization rate remarkably, and the sodium metasilicate as the silica source, the medium OH −/SiO 2 molar ratio (0.15), the high HMI/SiO 2 molar ratio and the addition of seeding could accelerate the crystallization. Moreover, by altering the reaction parameters, various morphologies of MCM-22 product with different particle sizes were achieved, such as spherical, rose-like, doughnut-like and platelet-like structures. The noteworthy observation was that with K + as the alkaline source instead of Na +, a much shorter induction period and faster crystallization rate were obtained, resulting in a higher crystallinity and a smaller crystal size. K + is more favorable to the formation of MCM-22 crystal than Na + even at very low HMI/SiO 2 ratios.

Comparison of platelet formation in hydrogen and helium-implanted silicon

A comparative transmission electron microscopy study of the extended defects formed in (0 0 1) Si after hydrogen or helium implantation was performed. Quantitative data on the size and density of the defects with different crystallographic variants have been obtained. Common defects observed after implants with a dose of 1 × 10 16 cm −2 and isothermal anneals at 350 °C in the presence of a stiffener were platelet-like structures lying on {1 0 0} habit planes parallel and perpendicular to the wafer surface. The differences in the defect morphology and in the variant platelet population are correspondingly related to the different chemical reactivity of H and He and the different compressive biaxial stresses generated by the H and He implants.

Translational regulation of PGHS-1 mRNA: 5′ untranslated region and first two exons conferring negative regulation

Prostaglandin endoperoxide H synthase-1 gene expression is described as inducible in a few contexts such as differentiation of megakaryoblastic MEG-01 cells into platelet-like structures. In the MEG-01 cells model of PGHS-1 gene induction, we previously reported a delay in protein synthesis and identified the translational step of gene expression as being regulated. In the current study, we mapped PGHS-1 mRNA sequences regulating translational efficiency and identified an RNA binding protein. The 5′UTR and first two exons of the PGHS-1 5′ mRNA decreased the synthesis of Luciferase protein by approximately 80% without significant changes in mRNA levels when compared to controls. Both the PGHS-1 5′-UTR and the first two exons were required for activity. Sucrose density gradient fractionations of cytoplasmic extracts from MEG-01 cells infected with reporter constructs, either controls or containing PGHS-1 sequence, presented a similar profile of distribution of reporter transcripts between polysomal and non-polysomal fractions. RNA/protein interaction studies revealed nucleolin binding to the 135 nt PGHS-1 sequence. Mutation of the two NRE elements located in the 5′end of PGHS-1 mRNA sequence partially reduced the negative activity of the 135 nt sequence. Stable secondary structures predicted at the 5′ end of the transcript are potentially involved in translational regulation. We propose that the 5′end of PGHS-1 mRNA represses translation and could delay the synthesis of PGHS-1 enzyme.

Nanoscale modeling of the structure of perfluorosulfonated ionomer membranes at varying degrees of swelling

We present a comprehensive model for the structure of swollen ionic membranes using a stochastic simulation process at the nanoscale level. In our model, the membrane is viewed as an entangled network of chains interacting at their backbone and ionic groups. Equilibration of the network is obtained through local moves of the groups according to the Boltzmann exponents of the corresponding changes in internal energy. The approach allows one to consider in detail the importance of equivalent weight, polymer molecular weight, length of pendant ionic groups as well as crosslinks and non-ionic polymer additives. At infinite dilution, our simulation results reveal that the ionic chains segregate into platelet-like structures with the ionic sites exposed on each surface and a core (∼2 nm thick) made of two layers of the hydrophobic polytetrafluoro-backbone units. As concentration is increased above the critical value for network formation, the platelets are stretched into narrow ribbons connected at entanglement points. Our description is in line with recent experimental evidence suggesting that ionic membranes can be considered as a connected network of rods. Finally, model predictions of X-ray scattering data are found to be in good agreement with experimental values obtained over a wide range of water content spanning two orders of magnitude.

Multiscale Analysis of Surface Thrombosis In Vivo in a Left Ventricular Assist System

Thrombosis limits the success of ventricular assist devices as the demand for alternatives to heart transplants is increasing. This study mapped the occurrence of thrombosis in a left ventricular assist system (LVAS) to better understand the biologic response to these devices. Nine calves divided into two groups were implanted with LVAS for 28 to 30 days. One group was anticoagulated, whereas the second group received no long-term anticoagulation. The blood-contacting poly(urethane urea) surfaces of blood sacs in the LVAS were examined for macroscopic thrombi upon retrieval. The sac was partitioned into eight sections and imaged for thrombi by scanning electron microscopy. No difference in thrombosis was observed macroscopically between the groups. Anticoagulation appeared to result in reduction of platelet-like structures, but the presence of fibrin-like structures remained similar between groups. Regional differences correlating with high and low shear stress regions were observed. At the macroscale, fewer thrombi were recorded in the high shear stress ports. At the microscale, features resembling fibrin were observed primarily in the ports and platelet-like features were common in lower shear stress regions. These variations in thrombosis with anticoagulation and location are likely due to varied fluid dynamics within the LVAS blood sac.