bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and Structural Transformation of Luminescent Nanostructured Gd2O3:Eu Produced by Solution Combustion Synthesis
Authors: Jacobsohn Luiz G. , Bennett Bryan L. , Sitarz Stephanie C. , Ugurlu Ozan , Sharma Ana L. Lima , Cooke D. Wayne , Muenchuasen Ross E. 
Published: April 2011

ABSTRACTIn this work we explore the uniqueness of solution combustion synthesis (SCS) technique to produce luminescent nanostructured materials with metastable phases. We synthesized Gd2O3:Eu with the high-temperature phase and induced phase transformation toward the room temperature phase to investigate the effects of structural transformation on the luminescent properties. SCS is based on exothermic redox reactions that undergo self-sustaining combustion, yielding powders composed of agglomerates of nanocrystals with typical dimensions of tens of nanometers. Synthesis of materials through SCS occurs in conditions far from thermodynamic equilibrium and, due to the high temperatures achieved during combustion, metastable crystallographic phases can be formed. Eu-doped Gd2O3 was obtained with base-centered monoclinic structure and average nanocrystal size of 35 nm as determined by Debye-Scherre analysis. Phase transformation to the cubic structure was induced by isothermal annealing at 1000 oC for up to 152 hrs and followed by x-ray diffraction (XRD). Luminescence excitation and emission spectra were obtained as a function of annealing time. The transformation from monoclinic to cubic structure was followed by the behavior of the (111) monoclinic/(222) cubic intensity ratio. The ratio value for the as-prepared material is 6, decreasing fast to 3 after 5 hrs. annealing, and reaching a value of 0.1 after 152 hrs. Concomitant to the structural transformation, nanocrystal size was followed for both crystalline phases. The average nanocrystal size for the cubic phase increases from 27 to 47 nm from 1 to 152 hrs., respectively. On the other hand, nanocrystals with the monoclinic phase remained with a constant size around 38 nm. Overall, variation in size is small due to the low connectivity among nanocrystals resulting from the low isostatic pressure employed to prepare the pellets, together with the non-uniform shape of the agglomerates. Photoluminescence excitation spectra are dominated by a broad centered near 278 nm and assigned to the O2-Eu3+ charge transfer band. Photoluminescence emission results present the 5D0-7FJ (with J = 0-4) transitions of Eu3+ ions. The behavior of these bands was investigated as a function of annealing time and subsequently related to the structural changes.
Influence of the Time-Temperatur-Profile on Powder Characteristics of Nanocrystalline Anatase (TiO2) produced by Chemical Vapor Synthesis
Authors: Djenadic Ruzica , Chowdhury Sankhanilay Roy , Spasova Marina , Gondorf Andreas , Akyildiz Erdal , Winterer Markus 
Published: April 2011

ABSTRACTChemical Vapor Synthesis (CVS) is the conversion of molecular species into nanocrystalline particles by chemical reactions in a gas flow reactor. Pure anatase nanoparticles are generated in a hot wall reactor from titanium isopropoxide using different time-temperature-profiles. The time-temperature-profile (T(t)-profile) in the gas phase of the reactor has a profound influence on the particle characteristics such as particle microstructure and surface chemistry and, therefore, on the quality of the powder consisting of nanocrystalline particles. In this study a simple reaction-coagulation-sintering model (CVSSIN) was used to predict influence of the T(t)-profile on the powder characteristics. The as-synthesized anatase powders show a very high degree of crystallinity, primary particle of about 10 nm sizes and a low degree of agglomeration.
Synthesis and Characterization of Spectroscopically Encoded Nanocomposites
Authors: Jawabrah Al-Hourani Baker , Dai Sheng , Alvarez-Puebla Ramon A. , Bravo-Vasquez Juan P. , Fenniri Hicham 
Published: April 2011

ABSTRACTThree sulfur-containing styrene monomers with different leaving groups, 4-vinylphenyl ethanethioate, 1,2-bis(4-vinylphenyl)disulfane, and butyl(4-vinylphenyl)sulfane, were synthesized through nucleophilic substitution/addition reactions and purified through column chromatography. In aqueous solution, these monomers could bind to the surface of gold nanoparticles and form self-assembled monolayers (SAMs). SAMs were analyzed by Raman spectroscopy and showed SERS activity with enhancement factors of more than 105. In addition, SAMs were also formed on the surface of gold/silver nano-island films. The bulk Raman and SERS spectra of monomers on different gold nanostructured materials were very similar. The enhancement factors and the formation of SAMs depended on monomer structure and fabrication method. Also depending on the deposition conditions, laser induced polymerization of the mercaptostyrene monomers SAMs was observed.
Development of Micro- and Nanocellular Polymers
Authors: Ruckdaeschel Holger , Gutmann Peter , Altstaedt Volker , Schmalz Holger , Mueller Axel H.E. 
Published: April 2011

ABSTRACTThe batch-foaming behavior of multiphase polymer blends and block copolymers was systematically investigated using carbon dioxide as a blowing agent. Three different polymer systems were evaluated: (i) nanostructured triblock terpolymers, (ii) microstructured polymer blends, and (iii) nanostructured polymer blends. In order to obtain nanostructured blends, immis-cible blends of poly(2,6-dimethyl-1,4-phenylene ether)/poly(styrene-co-acrylonitrile) (PPE/SAN) were melt-compatibilised via polystyrene-b-polybutadiene-b-poly(methyl methacry-late) triblock terpolymers. Due to the specific interaction between the respective components, a nanostructured interphase between PPE and SAN was observed. With regard to neat block co-polymers, the self-assembly of solvent-cast SBM triblock terpolymers was exploited in order to produce nanostructured morphologies. In each case, the resulting foam morphology was charac-terized by evaluating the foam density as well as the cell size. Combined with the multiphase structure of the non-foamed material and its thermal as well as physical behavior, relationships between the foaming characteristics and the cellular morphology were established. As an exam-ple for the foaming results, submicro-cellular structures were observed by foaming nanostruc-tured polymer blends, while the cell walls still revealed the nanostructured morphology. In con-trast, batch-foaming of neat triblock terpolymers led to the formation of microcellular foams; however, as highlighted by scanning electron microscopy, the cell walls did undergo some fur-ther expansion and formed additional nano-sized cells. In the light of these results, new routes for preparing cellular polymers are derived by systematically exploiting the multiphase charac-teristics of polymer blends and block copolymers.
Novel Planer Microwave Circuit Applications and Characterization of Ni Nanowires
Authors: Marson Ryan , Kuanr Bijoy K , Mishra Sanjay R , Camley Robert E , Celinski Zbigniew 
Published: April 2011

ABSTRACTArrays of Ni nanorods were electrodeposited into alumina oxide templates with various lengths (11-50 micro meter) and fixed pore diameter (150 nm). The magnetization behavior of these rods were investigated with ferromagnetic resonance (FMR) techniques; fixed frequency (conventional FMR) and swept frequency (Network Analyzer FMR). Both resonance spectra indicate the presence of strong dipolar interaction between the nanorods. The fundamental magnetic parameters like spontaneous magnetization, gyromagnetic ratio, and magnetic anisotropies of the nanorods were derived from the angular variation of resonance field data. Further, the use of nanorods as a tunable stop-band notch-filter in a coplanar waveguide geometry has been assessed. The stop-band frequency (fr) is observed to be tunable up to 24 GHz with an applied field (H) of up to 6 kOe. The theoretical fitting of fr(H)data to resonance relation yield values of effective field (Heff) and gyromagnetic ratio, which are a little higher than the conventional FMR results.
Electric Field Directed Growth of Molecular Wires of Charge Transfer Molecules on Prefabricated Metal Electrodes
Authors: Sai T Phanindra , Raychaudhuri A K 
Published: April 2011

ABSTRACTMolecular wires of charge transfer molecules were formed by co-evaporating the 7 7 8 8-Tetracyanoquinodimethane [TCNQ] (acceptor) and Tetrathiafulvalene [TTF] (donor) molecules across prefabricated metal electrodes. Molecular wires of TTF TCNQ were also formed by evaporating single complex of TTF:TCNQ across prefabricated metal electrodes The prefabricated metal electrodes were made using electron beam lithography on SiO2 and glass cover slip substrates. Even though TTF: TCNQ wires grown from both co-evaporation and evaporation techniques show semiconductor like behavior in temperature dependence of resistance they show different activation energies due the difference in stoichiometry of TTF and TCNQ.
Pseudo-wetting Behaviour of Nanostructures Induced by STM
Authors: Campbell Paul , Walmsley George 
Published: April 2011

ABSTRACTThe behavior of nano-scale liquid metal droplets has recently received renewed research interest following the exciting new observations of Sutter and Sutter [1]. In the present paper, we consider whether similar conditions can be generated for observing liquid metal droplet phenomena in a scanning probe architecture. Strong interactions between tip and sample in tunnelling microscopies can be deliberately invoked by lowering the tunnel gap impedance. Indeed, nanoscale features may be created this may, often exhibiting temporal stability suggestive of applications for ultra high density data storage. Alternatively, unstable features may form, and their decay characteristics can be related to local dynamics and kinetics. In real liquids, one such evolutionary mode involves the phenomenon of wetting, and the formation of thin precursor films. Here, it is demonstrated that a similar process may occur for the decay of a nanoscale mound of [presumed] Au atoms onto an Au(111) substrate. The mound is thought to be created by a ‘jump-to-contact’ process when the gap impedance, Zg, is deliberately lowered by reducing the tip-surface displacement. Resultant features have a diameter of circa 30nm, and heights of up to l0nm. They appear stable when scanned repeatedly at gap impedances higher than 10MΩ, however if Zg is lowered below 500kΩ, then morphology can alter dynamically, and a thin layer of material, only two atomic widths thick, is seen to emanate from the periphery. Relaxation in the nanostructure is observed. Interestingly, the observations agree qualitatively with wetting phenomena observed on microscale droplets of involatile liquids on solid surfaces. Favourable comparisons may also be drawn in the light of recent results using molecular-dynamics simulations and Monte-Carlo methods.
Elasticity Models for the Spherical Indentation of Gels and Soft Biological Tissues
Authors: Lin David C. , Dimitriadis Emilios K. , Horkay Ferenc 
Published: April 2011

ABSTRACTAFM micro- or nanoindentation is a powerful technique for mapping the elasticity of materials at high resolution. When applied to soft matter, however, its accuracy is equivocal. The sources of the uncertainty can be methodological or analytical in nature. In this paper, we address the lack of practicable nonlinear elastic contact models, which frequently compels the use of Hertzian models in analyzing force curves. We derive and compare approximate force-indentation relations based on a number of hyperelastic general strain energy functions. These models were applied to existing data from the spherical indentation of native mouse cartilage tissue as well as chemically crosslinked poly(vinyl alcohol) gels. For the biological tissue, the Fung and single-term Ogden models were found to provide the best fit of the data while the Mooney-Rivlin and van der Waals models were most suitable for the synthetic gels. The other models (neo-Hookean, two-term reduced polynomial, Fung, van der Waals, and Hertz) were effective to varying degrees. The Hertz model proved to be acceptable for the synthetic gels at small strains (<20% for the samples tested). Although this finding supports the generally accepted view that many soft elastic materials can be assumed to be linear elastic at small strains, we propose the use of the nonlinear models when evaluating the large-strain indentation response of gels and tissues.
Highly Efficient Silver Nanoparticle Formation on Dialdehyde-Modified DNA
Authors: Wirges Christian Thomas , Timper Jan , Simon Ulrich , Carell Thomas 
Published: April 2011

ABSTRACTWe investigated the efficient nucleation of silver nanoparticles on aldehyde-modified DNA strands. The aldehyde-bearing DNA was prepared by PCR incorporation of diol-modified synthetic deoxyuridine derivatives and subsequent cleavage of the diol groups to aldehyde functions using sodium periodate. Formerly unavailable dialdehyde-bearing DNA could be prepared by this mild and selective method. Both dialdehyde-DNA and monoaldehyde-DNA are capable of inducing silver nanoparticle formation without the addition of any external reductant. Interestingly, dialdehyde-DNA shows a different kinetic behavior and is about four times as efficient in silver nanoparticle formation as monoaldehyde-DNA. These data suggest a potentially unique mechanism of silver nanocluster formation induced by the dialdehyde groups. SEM measurements of fully metallized DNA strands show homogeneous metal coverage and selective metal deposition exclusively on the DNA template.
Failure Characteristics of Bilayer Lipid Membranes (BLMs) Formed over a Single Pore
Authors: Hopkinson David , Leo Donald J. 
Published: April 2011

ABSTRACTA new methodology has been developed to measure the maximum pressure that can be withstood by a bilayer lipid membrane (BLM) formed over porous substrates. A custom test fixture was fabricated to pressurize BLMs in very fine increasing increments until they fail. This experiment was performed on 1-Stearoyl-2-Oleoyl-sn-Glycero-3-Phosphatidylocholine (SOPC) BLMs formed over polycarbonate substrates with a single pore ranging from 5 to 20 microns in diameter. Failure pressure was found to be inversely proportional to pore diameter. The same set of experiments was repeated for BLMs that were formed from a mixture of SOPC and 50 mol% cholesterol (CHOL). The presence of cholesterol was found to increase the failure pressure of the BLMs by 56% on average. A model of the characteristic pressure curve from this experiment was developed based on the pressurization and flow of fluid through a porous substrate. The model was found to accurately fit the experimental pressure curves.
Toxicity of BSA-stabilized Silver Nanoparticles on Immune Circulating Cells
Authors: Hayman Imani , Mehl Patrick , Kapoor Veena , Wilson Otto 
Published: April 2011

ABSTRACTSilver nanoparticles have shown immense potential in many biomedical applications, specifically wound healing. These nanoparticles reduce the degree of inflammation in wounds and increase the rate of wound healing overall in a dose-dependent manner. Moreover, silver nanoparticles exhibit antibacterial and antimicrobial properties. While the mechanism of action for silver nanoparticles is not clear, current studies focus on the effect of silver nanoparticles on recipient cells and tissues. It is shown that silver nanoparticles are more toxic to these recipient cells in comparison to other metal nanoparticles. This suggests that the bactericidal properties of the silver nanoparticles are size dependent. Our present work investigates the toxicity level of silver nanoparticles on specific immune circulating cells. The approach is to report the LD50 level as a function of the ratio of the nanoparticles concentration (ppm) to the cell concentration (cell number/ml) used in the assays. This method allows a normalization of the LD50 capable to compare the toxicity of the nanoparticle on different types of cells. Next, the localization of the silver nanoparticles within the cells will be determined, and the toxic mode of action of the nanoparticles will be modulated by the modification of the synthesis method.
Cell-Adaptable Protein Scaffolds for Spinal Cord Nerve Regeneration
Authors: Straley Karin , Po Foo Cheryl Wong , Heilshorn Sarah 
Published: April 2011

ABSTRACTA key attribute missing from current state-of-the-art biomaterials is the ability to be remodeled by the host after implantation. In contrast, the natural extracellular matrix (ECM) is constantly being remodeled by proteases secreted from cells in response to local environmental changes. Mimicking this strategy, we have designed a new protein-based scaffold that can be degraded and remodeled on demand by the growth cones of regenerating neurites. Using recombinant protein techniques, we synthesized a family of biodegradable and biologically active scaffold materials. The scaffolds include peptide sequences derived from natural ECM proteins. Interspersed with these ECM domains are proteolytic sequences readily degraded by tissue plasminogen activator (tPA) and urokinase plasminogen activator (uPA), two proteases secreted by the growth cones of extending neurites. By altering the primary amino acid sequences of the protease cleavage domains, we can tune the degradation rates of otherwise identical engineered proteins in a controlled and predictable manner over approximately two orders of magnitude. These recombinant proteins are crosslinked to form bulk, protein-based scaffolds with mechanical properties that can be tuned to match that of the spinal cord. Initial cell experiments have shown that the proteins support growth and differentiation of the model PC-12 neuronal-like cell line. By tailoring the scaffold degradation rate to the tPA and uPA secretion levels of specific neuronal populations, we aim to fabricate a scaffold that will promote neurite extension through the matrix by allowing local degradation to occur specifically around the neuronal growth cone while maintaining the bulk integrity of the overall scaffold.
Buckling of Microtubules in Living Cells Modulated by Surrounding Cytoplasm and Filament Network
Authors: Li Teng 
Published: April 2011

ABSTRACTThe mechanics of living cells is largely determined by their cytoskeleton, a dynamic network of microtubules and protein filaments in the cytoplasm. Microtubules are the most rigid cytoskeletal filaments and bear compressive forces in cells. Microtubules in vivo often severely buckle into short wavelengths. By contrast, isolated microtubules in vitro buckle into single long-wavelength arcs. To explain this discrepancy, we describe a mechanics model of microtubule buckling in living cells. The model shows that, while the buckling wavelength is set by the interplay between the microtubules and the elastic surrounding filament network, the buckling growth rate is set by the viscous cytoplasm. The quantitative results from the model shed light on developing new and robust methods to measure various in vivo mechanical properties of subcellular structures, e.g., bending rigidity of microtubules, elastic modulus of filament network, and viscosity of cytoplasm. The model can also be readily generalized to study the deformation of hard engineering materials at soft bio-interfaces.
Mechanical Properties of Nanoparticle Hydroxyapatite/gelatin Constructs
Authors: Fox Steven , Stanishevskaya Inessa , Chowdhury Shafiul , Catledge Shane , Stanishevsky Andrei 
Published: April 2011

ABSTRACTBone consists of up to 70% mostly nanocrystalline hydroxyapatite (HA), and the rest is mostly collagen. One can suggest that synthetic nanoHA/collagen composites could potentially be the closest materials to resemble the bone microarchitecture and prepare resorbable bone substitutes and scaffolds. However, the data on the mechanical properties and property/structure relationships of HA/collagen composites are still scarce. It can be explained, in part, by the high cost of collagen and substantial amounts of materials needed for many tests. However, gelatin is cheap, has many properties similar to collagen, and can be used as a model material for the mechanical testing of HA-based composites. In this study, we report the results of an investigation of some mechanical properties of HA/gelatin composites with 0 to 80% HA nanoparticle (size 15-60 nm) loading by weight. The HA nanoparticle dispersions were mixed with gelatin in trifluoroethanol or in water in different ratios and placed in Teflon molds to produce the sheets with the thickness in the range of 0.4 – 1.0 mm. Nanoindentation technique was used to determine the Young's modulus and hardness. Bending tests were performed using dynamic mechanical analysis with the amplitudes in the 1 – 50 micron range at 1 Hz. The values of Young's modulus (1 – 20 GPa), hardness (70 – 500 MPa) and bending modulus (0.3 – 2.4 GPa) were obtained. The highest values of the Young's modulus and hardness of these composite materials were achieved for 40% – 60% HA content by weight, which was close to the values for similar HA/collagen composites. However, the maximum bending strength was observed for 20 – 35% HA content. We discuss further the observed trends of the mechanical properties and their dependence on other factors such as the test conditions, sample geometry, and HA particle size.
Drug Delivery Systems Based on Hydroxyapaptite-coated Poly(lactic-co-glycolic acid) Microspheres
Authors: Xu Qingguo , Czernuszka Jan T 
Published: April 2011

ABSTRACTNegatively charged poly(lactic-co-glycolic acid) (PLGA) microspheres were prepared by the solid-in-oil-in-water (s/o/w) method using the anionic surfactant, sodium dodecyl sulfate (SDS), and a hydrophilic antibiotic (amoxicillin) was encapsulated with an encapsulation efficiency of 40.6%. A layer of hydroxyapatite (HA) was coated on these negatively charged PLGA microspheres by a dual constant composition method in 3 - 6 hours. The HA-coated PLGA microspheres (HPLG) had a core-shell structure and were characterised by scanning electron microscopy, focused ion beam microscopy, energy-dispersive X-ray spectrometry, X-ray diffraction and Fourier transform infrared spectroscopy. Sustained release of amoxicillin from HPLG for at least 31 days was shown from in-vitro drug release experiments. A typical triphasic drug release profile had been observed for PLGA and HPLG microspheres. This device exhibited two desirable properties: the sustained release from PLGA and osteoconductivity from HA. Hence, it could have potential applications in delivering drugs to treat bone disorders or infections.
The Effects of Chemical Functionalization vs. Biological Functionalization on Nanoparticle Binding Affinity
Authors: Benkoski Jason J , Patrone Julia J , Crookston James , Le Huong , Sample Jennifer 
Published: April 2011

ABSTRACTDue to their small size, high diffusivity, and chemically active surfaces, nanoparticles share much in common with water-soluble proteins. These similarities have generated great interest in using biofunctional nanoparticles as a route to deliver targeted therapeutics. Already nanoparticles have found applications in the hyperthermia of tumors, personal care lotions, and tissue scaffolding. Our study focuses on the targeting of such nanoparticles to specific biological sites. It therefore seeks to identify the factors that control the migration and capture of nanoparticles within living systems. In particular, we examine the affinity of anti-collagen coated magnetite nanoparticles for collagen IV-coated surfaces under flow stress. The studies are performed within microfluidic devices that are designed to mimic various fluid flow patterns within the body. We find, in this case, a large background signal due to nonspecific binding. Further examination shows a correlation between chemical functionality (e.g., surface charge, hydrophilicity) that suggests that a balanced approach between biological functionality and chemical functionality may reduce the background from nonspecific binding to acceptable levels.