Porous Low Density Research Articles

Influence of the anodic etching current density on the morphology of the porous SiC layer

In this report, we fabricated a porous layer in amorphous SiC thin films by using constant-current anodic etching in an electrolyte of aqueous diluted hydrofluoric acid. The morphology of the porous amorphous SiC layer changed as the anodic current density changed: At low current density, the porous layer had a low pore density and consisted of small pores that branched downward. At moderate current density, the pore size and depth increased, and the pores grew perpendicular to the surface, creating a columnar pore structure. At high current density, the porous structure remained perpendicular, the pore size increased, and the pore depth decreased. We explained the changes in pore size and depth at high current density by the growth of a silicon oxide layer during etching at the tips of the pores.

High-aspect-ratio nanoporous membranes made by reactive ion etching and e-beam and interference lithography

Nanoporous membranes engineered to mimic natural filtration systems can be used in "smart" implantable drug delivery systems, hemodialysis membranes, bio-artificial organs, and other novel nano-enabled medical devices. Conventional membranes exhibit several limitations, including broad pore size distributions and low pore densities. To overcome these problems, lithographic approaches were used to develop porous silicon, silicon nitride, ultrananocrystalline diamond (UNCD), and polymer film membranes. Here we report processing of high porosity, high-aspect-ratio membranes by two techniques: UNCD fabricated by reactive ion etching after e-beam lithography and epoxy fabricated by interference lithography.

A heparin modified polypropylene non‐woven fabric membrane adsorbent for selective removal of low density lipoprotein from plasma

In the present work, a new porous low density lipoprotein (LDL) adsorbent membrane is prepared by 60Co γ‐ray irradiation‐induced grafting copolymerization of polypropylene (PP) non‐woven fabric with acrylic acid, followed by immobilizing heparin covalently. The amount of carboxyl group and heparin on the resultant PP non‐woven fabric is determined by titration and colorimetry, respectively. The new adsorbent membrane is characterized by attenuated total reflection Fourier transform infrared spectroscopy, scanning electron microscope, and contact angle microscopy. Static adsorption and hemoperfusion tests indicate this new adsorbent can efficiently and selectively remove LDL from human plasma. Meanwhile, good adsorption of triglyceride (TG) is also obtained. The best result is achieved by the adsorbent membrane P0.45‐A15‐H, where 33.3 ± 2.9 µg of LDL‐C, 14.7 ± 1.9 µg of high density lipoprotein cholesterol (HDL‐C), 64.9 ± 4.3 µg of total cholesterol (TC), and 202.4 ± 5.7 µg of TG are removed from human plasma per square centimeter. Hemocompability and toxicity tests show this new adsorbent membrane has good blood compatibility and low toxicity. Considering the adsorbent performance, safety, low cost, and simple preparation, this new adsorbent membrane has potential clinical application for removal of LDL. Copyright © 2013 John Wiley & Sons, Ltd.

Assessing the impact of distal protection filter design characteristics on 30-day outcomes of carotid artery stenting procedures

This study aims to review retrospectively the records of patients treated with carotid artery stenting (CAS) to investigate the potential correlations between clinical variables, distal protection filter (DPF) type and characteristics, and 30-day peri-/postprocedural outcomes. This is a multicenter, single-arm, nonrandomized retrospective study of patients who underwent filter-protected CAS in the Pittsburgh, Pennsylvania, region between July 2000 and May 2011. Analysis of peri-/postprocedural complications included myocardial infarction, transient ischemic attacks (TIA), stroke, death, and a composition of all adverse events (AEs). Filter characteristics for Accunet (Abbott Vascular, Santa Clara, Calif; n= 429 [58.8%]), Angioguard (Cordis Endovascular, Miami Lakes, Fla; n= 114 [15.6%]), FilterWire (Boston Scientific, Natick, Mass; n= 113 [15.5%]), Spider (ev3 Endovascular, Plymouth, Minn; n= 45 [6.2%]), and Emboshield (Abbott Vascular; n= 24 [3.3%]) were previously determined invitro and were used to find correlations with CAS procedural outcomes. Both univariate and multivariate analyses were performed, as well as goodness-of-fit tests to find multivariate correlations with procedural outcomes. In total, 731 CAS procedures using six different DPFs were analyzed. Peri-/postprocedural AEs included 19 TIAs (2.6%), 38 strokes (5.2%), one myocardial infarction (0.1%), 19 deaths (3.6%), and a total of 61 patients with complications (8.3%). Univariate analysis for filter design characteristics showed that the composite of AE was negatively associated withboth vascular resistance (P= .01) and eccentricity (P= .02) and was positively associated with porosity (P= .0007), number of pores (P= .005), and pore density (P= .001). Multivariate analysis and the goodness-of-fit test revealed thatpatients with a history of congestive heart failure, stroke, and TIA (each with odds ratio >1) led to a good-fit model Pvalue of .72 for peri-/postprocedural AEs. Multivariate analysis was inconclusive for all filter design characteristics. The following filter design characteristics are independently significant for minimizing peri-/postprocedural AEs: higher vascular resistance, concentric in shape, greater capture efficiency, lower porosity, lower number of pores, and lower pore density. Lower porosity and smaller wall apposition were also found to be independently significant for minimization of peri-/postprocedural TIAs. This information can be used when considering the desirable design characteristics of future DPFs.).

Permeation of Light Gases through Hexagonal Ice

Gas separation using porous solids have attracted great attention due to their energetic applications. There is an enormous economic and environmental interest in the development of improved technologies for relevant processes, such as H2 production, CO2 separation or O2 and N2 purification from air. New materials are needed for achieving major improvements. Crystalline materials, displaying unidirectional and single-sized pores, preferentially with low pore tortuosity and high pore density, are promising candidates for membrane synthesis. Herein, we study hexagonal ice crystals as an example of this class of materials. By slowly growing ice crystals inside capillary tubes we were able to measure the permeation of several gas species through ice crystals and investigate its relation with both the size of the guest molecules and temperature of the crystal.

Effect of hot rolling on the enhancement of mechanical properties of low density Cu–Cr–Nb sintered alloy

Studies have been carried out on the effect of hot rolling on the enhancement of mechanical properties of sintered low density Cu–8at.% Cr–4at.% Nb alloy made from gas-atomised powders by vacuum hot pressing using varying pressure and temperature. The pressure is varied from 10 to 30MPa whereas, 800, 900 and 1000°C are three hot-pressed temperatures. Though hot rolling of porous low density hot-pressed samples results in near theoretical density, the hot-pressed sintered material with higher initial porosity shows lower strength and ductility after rolling. Hot-pressed compacts below certain density could not be rolled and the sample has cracked during rolling. The higher density material could be easily rolled and significant improvement in mechanical properties has been noticed. This has been attributed to the conversion of porosities into microscopic cracks which could not be healed due to the presence of Cr2Nb precipitates. Finally, structure property correlation has been established.

Heat release process in three-dimensional macro-cellular SiC reactor under Diesel engine-like conditions

A specially developed macro-cellular SiC non-foam reactor has been used for investigations into Diesel–fuel injection, mixture formation and the heat release process inside a porous structure under piston-engine conditions. The heat release process has been compared to a free Diesel combustion indicating a significant influence of the reactor heat capacity on the thermodynamics of the process. Generally, the low- and high-temperature oxidation processes in a porous reactor are much faster, because of shorter delay time as compared to a free non-premixed combustion. High heat capacity of the porous reactor as compared to the gas heat capacity results in significantly reduced combustion temperature and corresponding combustion pressure peaks. Foam reactors with low and high pore density have also been compared in this investigation. The mixture formation, heat transfer and heat release processes performed in a porous reactor are very complex and depend on a number of different parameters of the combustion reactor in question: reactor structure, its heat capacity, pore size, specific surface area and wall junction geometry. Distribution of characteristic regions plotted in p–T areas indicates qualitative similarity of heat release process as performed under Diesel-like and in porous reactor conditions.

Cryogenic Helium Adsorbed in Zeolite Rho: Inside Localization Controlled Self-Diffusion of Confined Quantum Particles

Applying Feynman’s treatment of quantum mechanics at finite temperatures via path integrals and the numerical analytic continuation method developed recently (Kowalczyk, P.; Gauden, P. A.; Terzyk, A. P.; Furmaniak, Sylwester, J. Chem. Theory Comput.2009, 5, 1990–1996), we study the mobility of 4He atoms adsorbed in zeolite rho at 40 K. At studied temperature, the self-diffusive motion of 4He atoms in zeolite rho is strongly concentration-dependent. At low pore concentrations, 4He atoms are adsorbed in high-energetic adsorption centers of the zeolite. Due to strong localization in the solid–fluid potential well, an average kinetic energy of 4He atoms at infinite dilution reaches ∼120 K (i.e., twice of the classical kinetic energy at 40 K, Eclass = 60 K), whereas the self-diffusion constant drops up to ∼0.001 Å2 ps–1. Increasing pore concentration of 4He leads to the rapid increase in mobility of adsorbed 4He atoms. We show that ∼8 mmol cm–3, self-diffusive motion of confined 4He atoms increases up to ∼1 Å2 ps–1. Variation of the kinetic energy, potential energy, and enthalpy of 4He adsorption with pore concentration indicates that high-energetic adsorption sites in studied zeolite sample are saturated at low pore densities. The remaining adsorption sites are characterized by weaker solid–fluid potential, which allows higher delocalization of adsorbed 4He atoms. The reported novel phenomenon of localization controlled self-diffusion of confined 4He seems to be promising for smart designing of nanoporous quantum molecular sieves and storage nanovessels. Understanding of 4He cryogenic adsorption in the smallest pores enriches our knowledge that is crucial for precise analysis of ultramicropore sizes.

Shell thickness and pore density in relation to shell colouration, female characteristics, and environmental factors in the Collared Flycatcher Ficedula albicollis

Avian eggshell structure may have important consequences for embryonic growth and development, but relatively little is known about the factors responsible for variation in eggshell characteristics of wild birds. In this paper, we explored potential causes of variation in eggshell colour and structure (shell thickness and porosity) in the Collared Flycatcher (Ficedula albicollis). We analysed if eggshell colour is affected by shell structure or pigment level, and whether female traits, laying date, local breeding density, and clutch size affect shell thickness and pore density. We found that eggshell blue-green and UV colours were unrelated to shell thickness, pore density and egg size. Eggs with higher concentration of biliverdin showed lower UV reflection and higher reflection in the blue-green part of the spectrum. We found that females in better nutritional condition, indicated by their higher mass controlled for tarsus length, laid eggs with thicker shells. It is possible that females in better condition have more time available for searching calcium-rich food, and thus could produce eggs with stronger shells. However, female physical characteristics had no significant relationships with shell porosity. In contrast to our expectation, shell thickness and pore density were unrelated to local breeding density and laying date, though very late and repeat clutches were not sampled in our study. However, we found that eggs in larger clutches had lower pore density than eggs in smaller clutches, which may be expected if the rate of water loss and nest humidity are to remain constant in clutches of different egg numbers.

HOW STINGRAYS SENSE THEIR SURROUNDINGS

![Figure][1] In some ways, stingrays are the Cinderellas of the elasmobranch world. Compared with their better-studied cousins, the sharks, little is known about the ways that stingrays sense their environment. Coupled with that, stingrays seem to have a major disadvantage relative to the

Carbonized starch microcellular foam-cellulose fiber composite structures

The production of microporous carbon foams from renewable starch microcellular foam-fiber (SMCF-Fiber) composites is described. Carbon foams are used in applications such as thermal insulation, battery electrodes, filters, fuel cells, and medical devices. SMCF-Fiber composites were created from an aquagel. The water in the aquagel was exchanged with ethanol and then dried and carbonized. Higher amylose content starches and fiber contents of up to 4% improved the processability of the foam. The SMCF structure revealed agglomerates of swollen starch granules connected by a web of starch with pores in the 50-200 nanometer range. Heating the SMCF-fiber in a nitrogen atmosphere to temperatures between 350-700˚C produced carbon foams with a three-dimensional closed cell foam structure with cell diameters around 50 microns and pore walls around 1-3 microns. The stress versus strain compression data for carbonized samples displayed a linear elastic region and a plateau indicative of brittle crushing, typical of an elastic-brittle foam. The carbon foam products from these renewable precursors are promising carbon structures with moderate strength and low density.

Integrated Nanopore/Microchannel Devices for ac Electrokinetic Trapping of Particles

We report integrated nanopore/microfluidic devices in which the unique combination of low pore density, conical nanopore membranes with microfluidic channels created addressable, localized high-field regions for electrophoretic and dielectrophoretic trapping of particles. A poly(ethylene terephthalate) track-etched membrane containing conical pores approximately 130 nm in diameter at the tip and approximately 1 microm in diameter at the base was used as an interconnect between two perpendicular poly(dimethylsiloxane) microfluidic channels. Integration of the nanopore membrane with microfluidic channels allowed for easy coupling of the electrical potentials and for directed transport of the analyte particles, 200 nm and 1 microm polystyrene microspheres and Caulobacter crescentus bacteria, to the trapping region. Square waves applied to the device generated electric field strengths up to 1.3 x 10(5) V/cm at the tips of the nanopores in the microchannel intersection. By varying the applied potentials from +/-10 to +/-100 V and exploring frequencies from dc to 100 kHz, we determined the contributions of electrophoretic and dielectrophoretic forces to the trapping and concentration process. These results suggest that tunable filter elements can be constructed in which the nanoporous elements provide a physical barrier and the applied ac field enhanced selectivity.

Vectorial Transport of the Peptide CCK-8 by Double-Transfected MDCKII Cells Stably Expressing the Organic Anion Transporter OATP1B3 (OATP8) and the Export Pump ABCC2

CCK-8 (L-aspartyl-L-tyrosyl-L-methionylglycyl-L-tryptophyl-L-methionyl-L-aspartyl-L-phenylalaninamide hydrogen sulfate ester), a derivative of the gastrointestinal peptide hormone cholecystokinin, is specifically taken up into human hepatocytes by the organic anion transporter OATP1B3 (OATP8). So far it was unknown which transporter mediates the excretion of CCK-8 into bile. Double-transfected Madin-Darby canine kidney strain II cells, expressing recombinant human OATP1B3 in the basolateral membrane together with human ABCC2 (multidrug resistance protein 2, MRP2) in the apical membrane, represent a valuable model system to study vectorial transport. The importance of an appropriate filter support for optimized protein localization and substrate transport was demonstrated by the comparison of filter pore densities of 2 x 10(6) and 1 x 10(8) per cm(2). At the high pore density, immunofluorescence microscopy showed an intense OATP1B3 signal in the basolateral membrane of all cells, and 82 +/- 8% of cells expressed ABCC2 in the apical membrane. Uptake and efflux of radiolabeled CCK-8 in the double-transfected cells grown at high pore density was enhanced 3.5- and 5.6-fold, respectively, compared with cells grown at lower pore density. Higher transport rates were also observed with [(3)H]bromosulfophthalein. The high-affinity ATP-dependent transport of CCK-8 by ABCC2 was directly demonstrated in ABCC2-containing membrane vesicles with a K(m) value of 8.1 microM. The uptake by OATP1B3 and hence the vectorial transport of CCK-8 was inhibited by cyclosporin A (K(i) 1.2 microM) and by MK571 [(3-(3-(2-(7-chloro-2-quinolinyl)ethenyl)phenyl) ((3-dimethylamino-3-oxopropyl)thio)methyl)thiopropanoic acid] (K(i) 0.6 microM); the respective K(i) values for the ABCC2-mediated transport were 24 and 8.5 microM. Thus, using an optimized filter support, we demonstrate vectorial transport of CCK-8 by OATP1B3 and by the apical export pump ABCC2.

Synthetic single-nanopore and nanotube membranes.

There is increasing interest in investigating transport and electrochemical phenomena in synthetic membrane samples that contain a single pore of nanoscopic diameter. Approaches used to date for preparing such single-nanopore membranes include microfabrication-based methods, the track-etch method, and a method based on the incorporation of a single fullerene nanotube within a synthetic membrane. We describe here an alternative approach that we believe is easier and more accessible than the previously described methods. This method is based on a very low pore density track-etch membrane obtained from commercial sources. Fluorescence microscopy is used to identify and isolate a single nanopore in this membrane. Membrane samples containing single nanopores with diameters as small as 30 nm have been prepared. Furthermore, we show here that an electroless plating method can be used to deposit a gold nanotube within the single nanopore, and this provides a route for further decreasing the inside diameter of the pore. A single-nanotube membrane with an electrochemically determined inside diameter of approximately 2 nm was prepared and evaluated.

Effects of some egg characteristics on the mass loss and hatchability of ostrich ( Struthio camelus ) eggs

1. This study was conducted to examine some egg characteristics and determine the effects of eggshell thickness and eggshell porosity on water loss and hatchability of eggs in ostriches. 2. Shell thickness did not correlate significantly with hatchability. However, eggs of low shell thickness lost more mass (13·03%) than those with intermediate (11·22%) and high (10·36%) shell thickness. Mass loss during incubation was higher in hatched (11·98%) than unhatched eggs (11·09%). Shell thickness was negatively correlated to egg mass loss (r = −0·65). 3. The pore density was correlated with hatchability. Hatchability was 50% lower in eggs with low pore densities (40·93%) than with high densities (80·94%). Pore density was positively correlated with egg mass loss (r = 0·63). Incubation mass losses of hatched and unhatched eggs were not significantly different. 4. Mean eggshell water vapour conductance (G) value and shell conductance constant (k) were 87·77 ± 4·21 mg H2O/d/Torr and 2·44 respectively (n = 15). 5. Because of eggshell functional properties and resulting low egg mass loss hatchability is low when ostrich eggs are artificially incubated. The mass of eggs used in the experiment was relatively high and their eggshell water vapour conductance was low. As a result, egg incubation mass loss was lower than it should be. It is concluded that incubator humidity should be low (25%) to allow enough mass loss during incubation from the eggs.

Effects of some egg characteristics on the mass loss and hatchability of ostrich (Struthio camelus) eggs

1. This study was conducted to examine some egg characteristics and determine the effects of eggshell thickness and eggshell porosity on water loss and hatchability of eggs in ostriches. 2. Shell thickness did not correlate significantly with hatchability. However, eggs of low shell thickness lost more mass (13·03%) than those with intermediate (11·22%) and high (10·36%) shell thickness. Mass loss during incubation was higher in hatched (11·98%) than unhatched eggs (11·09%). Shell thickness was negatively correlated to egg mass loss (r = −0·65). 3. The pore density was correlated with hatchability. Hatchability was 50% lower in eggs with low pore densities (40·93%) than with high densities (80·94%). Pore density was positively correlated with egg mass loss (r = 0·63). Incubation mass losses of hatched and unhatched eggs were not significantly different. 4. Mean eggshell water vapour conductance (G) value and shell conductance constant (k) were 87·77 ± 4·21 mg H2O/d/Torr and 2·44 respectively (n = 15). 5. Because of eggshell functional properties and resulting low egg mass loss hatchability is low when ostrich eggs are artificially incubated. The mass of eggs used in the experiment was relatively high and their eggshell water vapour conductance was low. As a result, egg incubation mass loss was lower than it should be. It is concluded that incubator humidity should be low (25%) to allow enough mass loss during incubation from the eggs.

Thermal performance of aluminum-foam heat sinks by forced air cooling

Experiments have been carried out to investigate the heat transfer characteristics of an aluminum-foam heat sink placed on a heat source in a channel. The thermal performance of aluminum-foam heat sinks is evaluated in terms of the Nusselt number and thermal resistance of the heat sinks. The pore density of the aluminum-foam heat sinks and the Reynolds number are varied in the range of parameters: 10, 20, 40 pores per inch (PPI) and 710/spl les/Re/spl les/2900, respectively. It is found that thermal resistance is substantially reduced by employing an aluminum-foam heat sink with low pore density due to the relatively intense airflow through the heat sink. The aluminum-foam heat sink may provide 28% or higher thermal performance than a conventional parallel-plate heat sink of the same size. Further, the aluminum-foam heat sinks can dramatically reduce the overall mass of electronics-cooling devices owing to high porosity.

Newly Designed Compliant Hierarchic Hybrid Vascular Graft Wrapped with Microprocessed Elastomeric Film—II: Morphogenesis and Compliance Change upon Implantation

Hierarchic structured hybrid tubular vascular media composed of endothelial cells (ECs), which covered the luminal surface, and smooth muscle cells (SMCs), which resided in the tubular collagen gel, were wrapped with thin segmented polyurethane elastomeric films designed to provide compliance matching with native arteries and transmural tissue permeability using a laser-directed ablation technique to provide different pore densities. Two hybrid grafts with high and low pore densities (inner diameter: 150 microm and length: 4 cm), and exhibiting pressure-dependent distensibility in response to pulsatile pressure, were bilaterally implanted into canine common arteries for up to 6 months. Irrespective of the pore density, high patency was achieved and no dilation and bursting occurred. Maintenance of full endothelialization during the entire course of implantation period was observed for the graft wrapped with the film with higher pore density. On the other hand, the graft wrapped with the film with lower pore density exhibited markedly reduced endothelialization at a later period of implantation, probably due to delamination of neoarterial tissue from the segmented polyurethane (SPU) surface. There were some differences in transmural tissue ingrowth between the two grafts. At anastomotic sites, neoarterial thickness for type A graft was smaller than that for type B graft regardless of the implantation period. Slightly reduced compliance was observed for both types of grafts at the sixth month of the implantation period. This study indicates that a hybrid vascular graft minimally supported with a thin elastomeric film can be used to replace diseased arteries if micropores are well designed for tissue permeability and anchoring.

Barrier function of porcine choroid plexus epithelial cells is modulated by cAMP-dependent pathways in vitro

In the present paper, we demonstrate that the barrier properties of primary cultured epithelial cells isolated from porcine choroid plexus are regulated by cAMP-dependent signal transduction pathways in vitro. Triggering cAMP-connected cascades in cell layers grown on permeable filters with cAMP-analogues or forskolin led to a significant increase of transepithelial electrical resistances and a pronounced reduction in the permeation rate of a 4 kDa-dextran probe. In dose–response experiments using the cAMP-analogue 8-(4-chlorophenylthio)-cAMP transepithelial electrical resistances were observed to increase above a threshold concentration ranging between 10 −5.5 and 10 −5 M. Additional impedance studies performed with confluent cell layers grown on gold-film electrodes revealed that the observed changes in transepithelial resistances and presumably also in macromolecular permeation rates were not entirely caused by a reinforcement of intercellular junctions but also contained contributions from changes in the cell-substrate adhesion pattern. These inherent contributions to the electrical resistance and macromolecular permeability are caused by a restricted diffusion pathway between basal plasma membrane and culture substrate that have to be considered in data analysis, especially when leaky cell layers on filter substrates with low pore densities are used.

シナジー磁石と磁性材料 ＭｇＺｎ系フェライトの磁気損失について

The effects of substitution of Mn2O3 for Fe2O3 Or CuO for MgO in MgZn ferrite have been studied in order to achieve low core loss, focusing on the microstructure, the initial permeability and the resistivity of MnZn, MnMgZn, and MnMgCuZn ferrites.Initial permeability and resistivity of both MnMgZn and MnMgCuZn ferrites are higher than those of MgZn ferrite. Intragrain pores were observed in all of these ferrites. The pore density increases with grain growth.The core loss of these ferrites consists of hysteresis loss and eddy current loss at frequencies lower than 120kHz. Hysteresis loss clearly depends on initial permeability because of magnetic anisotropy, grain size and pore density. It has been found that eddy current loss is related to the microstructure and not to the resistivity. It is suggested that the decrease in the amount of pores inside the grains is effective to lower hysteresis and eddy current losses.Substitution of Cu enables MgZn ferrite to be sintered at lower temperatures, and it leads to the reduction of the core loss because of the formation of fine microstructure having small grain and low pore density. The lowest core loss (320kW/m3 at 100°C, 100mT and 100kHz) was achieved in the case of 11mol% CuO material sintered at 1120°C.