Bulk Equivalence Research Articles

Nanoparticles in wound healing; from hope to promise, from promise to routine.

Chronic non-healing wounds represent a growing problem due to their high morbidity and cost. Despite recent advances in wound healing, several systemic and local factors can disrupt the weighed physiologic healing process. This paper critically reviews and discusses the role of nanotechnology in promoting the wound healing process. Nanotechnology-based materials have physicochemical, optical and biological properties unique from their bulk equivalent. These nanoparticles can be incorporated into scaffolds to create nanocomposite smart materials, which promote wound healing through their antimicrobial, as well as selective anti- and pro-inflammatory, and pro-angiogenic properties. Owed to their high surface area, nanoparticles have also been used for drug delivery as well as gene delivery vectors. In addition, nanoparticles affect wound healing by influencing collagen deposition and realignment and provide approaches for skin regeneration and wound healing.

The use of various peening methods to improve the fatigue strength of titanium alloy Ti6Al4V manufactured by electron beam melting

Additive manufacturing (AM) of metals is one of the foremost methods used for making medical implants and components for aviation. However, the fatigue strength of AM metals is weaker than that of the bulk equivalent. Mechanically treating the surface, such as by shot peening, can improve the fatigue strength, and novel peening methods without shot have also been proposed. In this paper, in order to demonstrate the improvements made in AM metals by various peening methods, specimens made of titanium alloy Ti6Al4V manufactured by electron beam melting (EBM) were treated by shot peening, laser peening and cavitation peening, then assessed by a plate bending fatigue test. In the case of shot peening, the shots were accelerated by a water jet to mitigate the incidence of dust during the process. For laser peening, the specimen was placed in water, and the effect of the impact produced at the target due to collapsing bubbles, which developed after laser ablation of the surface, was greater than the effect due to the laser ablation itself. For cavitation peening, the cavitation was generated by injecting a high speed water jet into water. In each case improvements in the fatigue strength of the Ti6Al4V were made. Improvements of 104% by laser peening, 84% by cavitation peening and 68% by shot peening compared with a non-peened specimen were achieved.

Characterisation and cytotoxic screening of metal oxide nanoparticles putative of interest to oral healthcare formulations in non-keratinised human oral mucosa cells in vitro

Nanoparticles are increasingly being utilised in the innovation of consumer product formulations to improve their characteristics; however, established links between their properties, dose and cytotoxicity are not well defined. The purpose of this study was to screen four different nanomaterials of interest to oral care product development in the absence of stabilisers, alongside their respective bulk equivalents, within a non-keratinised oral epithelial cell model (H376). Particle morphology and size were characterised using scanning electron microscopy (SEM) and dynamic light scattering (DLS). The H376 model showed that zinc oxide (ZnO) was the most cytotoxic material at concentrations exceeding 0.031% w/v, as assessed using the lactate dehydrogenase (LDH) and dimethylthiazolyl-diphenyl-tetrazolium-bromide (MTT) assays. ZnO cytotoxicity does not appear to be dependent upon size of the particle; a result supported by SEM of cell–particle interactions. Differences in cytotoxicity were observed between the bulk and nanomaterial forms of hydroxyapatite and silica (SiO2); titanium dioxide (TiO2) was well tolerated in both forms at the doses tested. Overall, nano-size effects have some impact on the cytotoxicity of a material; however, these may not be as significant as chemical composition or surface properties. Our data highlights the complexities involved at the nano-scale, in both the characterisation of materials and in relation to cytotoxic properties exerted on oral epithelial cells.

Analysis of topology transitions of swirl flames interacting with the combustor side wall

Topology transitions of swirl-stabilized flames in a cylindrical combustion chamber are analyzed for lean CH4/H2/air combustible mixtures. It is demonstrated that when the tip of a swirl flame is quenched at the combustor side wall, V to M flame topology transitions are triggered by flashback of the flame front along this wall. An analysis of the power spectral densities of the chemiluminescence luminosity reveals that these topological transitions are not consecutive to the appearance or disappearance of any axisymmetric or helical periodic flow structures interacting with the flame. It is shown that the appropriate space to analyze the stabilization regimes of these swirling flames corresponds to a diagram based on Karlovitz and Lewis numbers. Transitions from V to M flame shapes are found for a critical Karlovitz number below which the flame takes an M shape. The value of this critical Karlovitz number decreases when the Lewis number of the combustible mixture increases. The same type of law is found for M to V shape flame transitions, but this boundary does not coincide with the V to M shape transition boundary. In between these boundaries, the flame takes intermittently V or M shapes randomly. It is then shown that the critical Karlovitz number corresponding to the transition of V to M shape may be expressed by the product of a velocity gradient g calculated with the bulk injection velocity U and a characteristic scale of the outer recirculation zone, the laminar flame thickness α/SL, and the inverse of a vortex induced flame displacement speed STθ. This displacement speed is related to the maximal azimuthal velocity of the swirling jet at the injector outlet and to the laminar burning velocity. Using this definition of the Karlovitz number, V to M flame topology transitions collapse roughly on the same curve for all flow conditions explored when the swirl number (0.3 ≤ S ≤ 0.68), injection bulk velocity (7 ≤ U ≤ 25 m · s−1), equivalence ratio (0.5 ≤ ϕ ≤ 0.9), and hydrogen enrichment in the fuel blend (0≤XH2fuel≤0.37) are modified for rod stabilized and aerodynamically stabilized swirl flames. Results presented in this study might be used to ease predictions of the shape taken by swirl flames interacting with the chamber side wall when the flow operating conditions are modified.

Luminescence Properties Of Pure CaSO4 Nanoparticles Produced By Co- Precipitation Method

Thermoluminecsence (TL) characteristics of pure CaSO4 nanoparticles produced by co-precipitation method are presented. The formation of the nanoparticles was confirmed by X-ray diffraction (XRD) and scanning electron microscope (SEM). TL glow curve of this phosphor, exposed to gamma radiation exhibits five overlapping glow peaks in the complex glow curve at 463, 470, 483, 498 and521(K) respectively, using a computerized glow curve deconvolution procedure. A photoluminescence (PL) emission band at 393 nm was observed for the synthesized nanoparticles. Different synthesis conditions were examined in order to achieve highest TL sensitivity. The produced nanoparticles exhibit superior thermoluminescent sensitivity compared to that of its bulk equivalent.

Enhanced toxicity of ‘bulk' titanium dioxide compared to ‘fresh' and ‘aged' nano-TiO2 in marine mussels (Mytilus galloprovincialis)

Marine bivalves (Mytilus galloprovincialis) were exposed to titanium dioxide (10 mg L−1) either as engineered nanoparticles (nTiO2; fresh, or aged under simulated sunlight for 7 days) or the bulk equivalent. Inductively coupled plasma-optical emission spectrometry analyses of mussel tissues showed higher Ti accumulation (>10-fold) in the digestive gland compared to gills. Nano-sized TiO2 showed greater accumulation than bulk, irrespective of ageing, particularly in digestive gland (>sixfold higher). Despite this, transcriptional expression of metallothionein genes, histology and histochemical analysis suggested that the bulk material was more toxic. Haemocytes showed significantly enhanced DNA damage, determined by the modified comet assay, for all treatments compared to the control, but no significant differences between the treatments. Our integrated study suggests that for this ecologically relevant organism photocatalytic ageing of nTiO2 does not significantly alter toxicity, and that bulk TiO2 may be less ecotoxicologically inert than previously assumed.

Effect of Gas-Jet Ignition Technique on the Extension of CNG Lean Combustion Limit

Lean combustion of CNG has the advantage of high thermal efficiency and fewer pollutants than other fossil fuels. However, problems such as ignitability, cyclic variation and high THC emission were common at combustion leaner than equivalence ratio φ=0.7. The application of gas-jet ignition method to lean combustion was able to address such problems. This paper introduces the concept of gas-jet ignition method, which ensures ignitability at lean bulk equivalence ratio. Moreover, this method is applied to a real CNG engine. Results of engine performance experiment shows that two-stage injection method combined with gas-jet ignition has successfully widen the operating range of a CNG engine from low to high load at corresponding φ=0.17 to 1.1.

Dynamic Response of Turbulent Low Emission Flames at Different Vortex Breakdown Conditions

The classic Flame Transfer Function (FTF) used in the thermoacoustic stability analysis of lean premixed combustors is linked, in a mathematically strict way, to the flow coherent structures using Large Eddy Simulation. This is based on a methodology which combines the Wiener-Hopf system identification filter—separating any field variables into a dynamic contribution driven by external forcing plus a noise contribution given by turbulent fluctuations—with the extended formulation of the Proper Orthogonal Decomposition (POD). The method is applied to partially premixed flames stabilized at two different types of Central Recirculation Zone (CRZ) due to the mechanism of vortex breakdown of the flow through a swirl burner: type A, where the CRZ appears rather narrow in the radial direction with apex located close to the burner exit and type B, where the CRZ is entirely located in the combustor and appears more flat at its apex than what observed in case of the type A vortex flow. Rather different properties are observed for the FTF. Flames stabilized at the narrow CRZ (type A), respond to inflow forcing with a time delay which depends much more on the bulk equivalence ratio than flames stabilized at the thick CRZ (type B). On the other hand the amplitude of the FTF in the case of the narrow CRZ is in general lower than in case of the thick and flat CRZ where amplification factors of the order of 4–5 are reached. By allowing a reasonable explanation of the observed trends, the methodology developed here can give an important contribution to the development of gas turbine burners.

CuO and ZnO nanoparticles: phytotoxicity, metal speciation, and induction of oxidative stress in sand-grown wheat

Metal oxide nanoparticles (NPs) are reported to impact plant growth in hydroponic systems. This study describes the impact of commercial CuO (<50 nm) and ZnO (<100 nm) NPs on wheat (Triticum aestivum) grown in a solid matrix, sand. The NPs contained both metallic and non-metallic impurities to different extents. Dynamic light scattering and atomic force microscopy (AFM) assessments confirmed aggregation of the NPs to submicron sizes. AFM showed transformation of ZnO NPs from initial rhomboid shapes in water to elongated rods in the aqueous phase of the sand matrix. Solubilization of metals occurred in the sand at similar rates from CuO or ZnO NPs as their bulk equivalents. Amendment of the sand with 500 mg Cu and Zn/kg sand from the NPs significantly (p = 0.05) reduced root growth, but only CuO NPs impaired shoot growth; growth reductions were less with the bulk amendments. Dissolved Cu from CuO NPs contributed to their phytotoxicity but Zn release did not account for the changes in plant growth. Bioaccumulation of Cu, mainly as CuO and Cu(I)–sulfur complexes, and Zn as Zn-phosphate was detected in the shoots of NP-challenged plants. Total Cu and Zn levels in shoot were similar whether NP or bulk materials were used. Oxidative stress in the NP-treated plants was evidenced by increased lipid peroxidation and oxidized glutathione in roots and decreased chlorophyll content in shoots; higher peroxidase and catalase activities were present in roots. These findings correlate with the NPs causing increased production of reactive oxygen species. The accumulation of Cu and Zn from NPs into edible plants has relevance to the food chain.

Effects of preferential transport and strain in bluff body stabilized lean and rich premixed CH4/air flames

The effects of preferential transport and strain on the scalar structure of turbulent premixed bluff body stabilized flames are examined using Raman–Rayleigh–LIF diagnostics. Bulk flowrate and equivalence ratio are varied parametrically. Comparisons with laminar flame calculations are used both to validate the quality of the experimental measurements and to facilitate interpretation of the measured response of the bluff body flames to changes in equivalence ratio and flow conditions. Strong effects of preferential species transport on the internal flame structure and the product composition of the recirculation zone are observed in lean, stoichiometric, and rich flames. Contrary to the standard view of differential diffusion effects in turbulent flow becoming negligible at sufficiently high Reynolds number, the preferential diffusion effects in the premixed bluff body flames reported here initially increase with the Reynolds number then saturate and persist at higher Reynolds numbers. Measurements in a rich bluff body flame are suggestive of high strain, but instantaneous profiles in the turbulent flame for this shear-flow geometry are thicker than calculated for an unstrained laminar flame.

Giant carbon solubility in Au nanoparticles

Variable temperature transmission electron microscopy of individual 5 nm Au nanoparticles shows a striking increase in the particle size on raising the temperature from room temperature to 500 °C in the presence of carbon from amorphous carbon support. Using the assembly of ordered graphene shells on the surface of individual nanoparticles at elevated temperatures—and the high pressures induced by such shells—as an experimental tool to study the origins of this swelling, we find that the volume increase is associated with the uptake of carbon to concentrations exceeding the bulk solubility by more than four orders of magnitude. The formation of stable metal–carbon nanostructures that have no bulk equivalent may have important implications on the functional properties of metal nanoparticles.

Using FlFFF and aTEM to determine trace metal–nanoparticle associations in riverbed sediment

Environmental context. Determining associations between trace metals and nanoparticles in contaminated systems is important in order to make decisions regarding remediation. This study analysed contaminated sediment from the Clark Fork River Superfund Site and discovered that in the &lt;1-μm fraction the trace metals were almost exclusively associated with nanoparticulate Fe and Ti oxides. This information is relevant because nanoparticles are often more reactive and show altered properties compared with their bulk equivalents, therefore affecting metal toxicity and bioavailability. Abstract. Analytical transmission electron microscopy (aTEM) and flow field flow fractionation (FlFFF) coupled to multi-angle laser light scattering (MALLS) and high-resolution inductively coupled plasma mass spectroscopy (HR-ICPMS) were utilised to elucidate relationships between trace metals and nanoparticles in contaminated sediment. Samples were obtained from the Clark Fork River (Montana, USA), where a large-scale dam removal project has released reservoir sediment contaminated with toxic trace metals (namely Pb, Zn, Cu and As) which had accumulated from a century of mining activities upstream. An aqueous extraction method was used to recover nanoparticles from the sediment for examination; FlFFF results indicate that the toxic metals are held in the nano-size fraction of the sediment and their peak shapes and size distributions correlate best with those for Fe and Ti. TEM data confirms this on a single nanoparticle scale; the toxic metals were found almost exclusively associated with nano-size oxide minerals, most commonly brookite, goethite and lepidocrocite.

Antimicrobial activities of commercial nanoparticles against an environmental soil microbe, Pseudomonas putida KT2440

BackgroundThe release of heavy metal-containing nanoparticles (NP) into the environment may be harmful to the efficacy of beneficial microbes that function in element cycling, pollutant degradation and plant growth. Nanoparticles of Ag, CuO and ZnO are of interest as antimicrobials against pathogenic bacteria. We demonstrate here their antimicrobial activity against the beneficial soil microbe, Pseudomonas putida KT2440.ResultsToxicity was detected in a KT2440 construct possessing a plasmid bearing the luxAB reporter genes. "As manufactured" preparations of nano- Ag, -CuO and -ZnO caused rapid dose-dependent loss of light output in the biosensor. Cell death accompanied loss in Lux activity with treatments by nano-Ag and -CuO, but with -ZnO the treatments were bacteriostatic rather than bactericidal. Bulk equivalents of these products showed no inhibitory activity, indicating that particle size was determinant in activity. Flow Field-Flow Fractionation (FlFFF) of an aqueous suspension of the nano-CuO and ZnO revealed a small proportion of 5 nm NP and aggregated particulates with sizes ranging between 70 nm and 300 nm; the majority portion of material was aggregated into particles larger than 300 nm in size. Thus within the commercial preparation there may be microbially active and inactive forms.ConclusionThe "as-made" NP of Ag, CuO and ZnO have toxic effects on a beneficial soil microbe, leading to bactericidal or bacteriostatic effects depending on the NP employed. The lack of toxicity from bulk materials suggests that aggregation of the NP into larger particles, possibly by factors present in the environment may reduce their nontarget antimicrobial activity.

ChemInform Abstract: Magnetic Nanoparticles Through Sonochemistry

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Effect of Biomass Gasification Tar on NO Reduction by Biogas Reburning

Reduction of NO by biogas without tar and with tar was investigated. Flow reaction experiments were performed at high-temperature (≥1000 °C), and the main parameters, such as initial oxygen concentration, bulk equivalence ratio, temperature, and initial tar content, were studied. The simulated biogas was prepared by mixing CO, CH4, H2, and CO2, and toluene was selected as a model compound as the biomass gasification tar. The moderate fuel-rich environment is favored to a high level of NO reduction by both biogas without tar and biogas with tar. The optimal bulk equivalence ratio, φ, for NO reduction by biogas with tar is larger than that of NO reduction by biogas without tar. The effect of temperature on NO reduction by biogas with model compound is stronger than that by biogas without tar. The comparison of NO reduction by biogas without tar and biogas with tar indicates that tar can either promote or limit NO reduction by biogas. The experimental results here will be helpful to the further investigation...

Emissions from the combustion of polystyrene, styrene and ethylbenzene under diverse conditions

This experimental study contrasts the products of incomplete combustion (PIC) of polystyrene, a widespread solid waste, with those from the combustion of its predominant pyrolyzate, styrene. The study also included ethylbenzene, as it has been reported to convert to styrene extensively and extremely fast in combustion conditions. Emissions were compared from: (i) steady-state combustion of vaporized ethylbenzene in premixed flames, (ii) steady-state combustion of polystyrene powders in a drop-tube furnace, (iii) batch combustion of fixed beds of polystyrene in a muffle furnace, and (iv) batch combustion of pools of liquid styrene in a muffle furnace. PICs, sampled in post-combustion zones, included unburned hydrocarbons, with emphasis to polycyclic aromatic hydrocarbons (PAH), particulates, CO2 and CO. Yields of major PIC were compared to underscore the differences in the underlying physics of premixed and non-premixed (diffusion) flames. Combustion of polystyrene and styrene in diffusion flames generated soot at any nominal global (bulk) equivalence ratio, no matter how fuel-rich or fuel-lean. On the other hand, combustion of ethylbenzene in premixed flames did not generate any soot up to its soot onset limit, which typically occurs well-within the fuel-rich domain. However, conditions that were not conducive to the formation of soot did not preclude the presence of other PIC, such as PAH.

EXPERIMENTAL AND NUMERICAL STUDY OF EMISSIONS FROM FUEL-RICH COMBUSTION OF PULVERIZED POLYSTYRENE

This is an investigation on the formation of products of incomplete combustion (PIC) of waste poly(styrene) (PS). Pulverized PS was steadily injected into an externally-heated drop-tube laboratory furnace and burned therein in fuel-rich conditions, corresponding to a bulk equivalence ratio of approximately 2.5. Iso-kinetic and iso-axial sampling with a probe was performed at five different heights along the centerline of the furnace. The goal has been to investigate the evolution of fixed product gases, unburned light volatile organic compounds (VOC) and semi-volatile organic compounds (SVOC), with emphasis to polycyclic aromatic hydrocarbons (PAH), along the reaction zone of the furnace. The magnitude of species therein and their respective trends were assessed. The centerline gas temperature was measured by suction thermometry. Moreover, the flow field and gas temperature distribution in the furnace were computed with a 3-dimensional model using the CFD code Fluent. Results showed that of the measured light VOC, acetylene exhibited the highest yields in the combustion effluent, followed by methane, ethylene and benzene. These yields were comparable to those of the most prevalent PAH species. PAH profiles varied somewhat in the sampling zone, with yields spanning the range between 13.8 mg (naphthalene) and 0.058 mg (perylene) per each gram of polystyrene burned. The results for fixed exhaust gases showed an increase in CO values with distance traveled, from 85 to 175 mg whereas CO2 stayed close to 1000 mg, per gram of PS burned. Oxygen remained somewhat steady near 85 mg/g PS burned. Copious amounts of soot were generated and collected through the probe, 0.25–0.42 g for each gram of PS burned. Computations were conducted using a detailed chemical kinetic model, allowing for the prediction of formation and depletion of major PAH and soot particles of different sizes. In this computation styrene was input as the fuel. In comparing experimental hydrocarbon species concentrations to theoretical predictions, a large number of species were found to be within a factor of 7 or less.

Pit Initiation on Partially Amorphous Alloys with Solute-Lean Nanocrystals

The good global pitting resistance of amorphous Al90Fe5Gd5 in 0.6 M NaCl solution is maintained upon partial devitrification to form solute lean crystals in an amorphous matrix. The focus of this paper is to distinguish whether this can be explained by decreased pit initiation or hindered pit growth and stabilization. The metastable pitting properties of Al90Fe5Gd5 were investigated at the nanometer (nm) and micrometer (μm) scales. The fully amorphous alloy, versions of the alloy containing a high volume fraction of isolated 5-15 nm diameter Al-rich crystals embedded within the amorphous matrix, and versions containing ~500 nm transitional phases in a remaining amorphous-nanocrystalline matrix were compared to a fully crystallized condition and pure polycrystalline Al. Nanocrystals and transitional phases embedded in an amorphous Al-Fe-Gd matrix do not promote pit initiation at the nm-scale in NaCl solution under the same electrochemical conditions where the bulk equivalent of Al-rich f.c.c. nanocrystals do initiate sub-μm sized pits. The number and size of sub-micrometer pit initiation events is similar for the fully amorphous and amorphous-nanocrystalline alloys under the same conditions.

Hydrogen storage in thin film magnesium–scandium alloys

Thorough electrochemical materials research has been performed on thin films of novel magnesium–scandium hydrogen storage alloys. It was found that palladium-capped thin films of Mg x Sc (1− x) with different compositions (ranging from x = 0.50 –0.90) show an increase in hydrogen storage capacity of more than 5–20% as compared to their bulk equivalents using even higher discharge rates. The maximum reversible hydrogen storage capacity at the optimal composition (Mg 80Sc 20) amounts to 1795 mAh/g corresponding to a hydrogen content of 2.05 H/M or 6.7 wt.%, which is close to five times that of the commonly used hydride-forming materials in commercial NiMH batteries. Galvanostatic intermittent titration technique (GITT) measurements show that the equilibrium pressure during discharge is lower than that of bulk powders by one order of magnitude (10 −7 mbar versus 10 −6 mbar, respectively).

Thermodynamic and surface properties of Ge–Ga and Ge–Sb liquid alloys

Thermodynamic and surface properties of Ge–Ga and Ge–Sb liquid alloys have been studied using statistical mechanical formulations based on complex formation and that based on the concept of layered structure near the interface. The study showed that low level of complex formation of the form Ge 2 Sb exists in Ge–Sb toward the Ge-rich end of the concentration range and the surface properties of Ge–Ga are almost equal to their corresponding bulk equivalent.