Porous Polycarbonate Membrane Research Articles

Preparation and Characterization of Multilayered Polymer Nanotube Dispersions

Despite considerable efforts to synthesize nanotubes using porous alumina or polycarbonate membrane templates, few studies have addressed the resulting nanotube dispersion. We prepared dispersions of multilayered polyethylenimine/maleic anhydride alternating copolymer (PEI/MAAC) nanotubes synthesized with porous alumina templates. After mechanical polishing to remove the residual polymer surface layer from templates and subsequent template dissolution, the multilayered PEI/MAAC nanotubes were easily dispersed in water at neutral pH by polyelectrolyte adsorption, producing nanotube dispersions that were stable for at least 3 months. We characterized the dispersions using phase-contrast optical microscopy, electro-optics, electrophoresis, and viscometry to help understand their colloidal properties in the dilute and semidilute regimes. The dispersions were resistant to salt-induced aggregation up to at least 1 mM NaCl and were optically anisotropic when subjected to an electric field or flow. Interestingly, the electrophoretic mobility of polystyrene sulfonate (PSS)-stabilized nanotubes increases with increasing ionic strength, because of the high surface charge and softness of the adsorbed polyelectrolyte. Furthermore, unlike many rod-like colloid systems, the polymer nanotube dispersion has low viscosity because of weak rotary Brownian motions and strong tendency to shear thinning. At the high shear rates achieved in capillary viscometry experiments, however, we observed a slight shear thickening, which can be attributed to transient hydrocluster formation.

Selective capturing and detection of Salmonella typhi on polycarbonate membrane using bioconjugated quantum dots

Present work demonstrates the utilization of surface modified polycarbonate (PC) membrane as solid phase and antibody conjugated CdSe/ZnS quantum dots (QDs) as fluorescent label for the sensitive and selective detection of Salmonella typhi ( S. typhi) in water in a period of 2.5 h. PC membrane was surface modified with glycine and activated by EDC/NHS for immobilization of S. typhi specific IgG. Antibody immobilized porous PC membrane was incubated with bacteria contaminated water for immunocapturing of S. typhi. Antibody conjugated QDs were also prepared by using carbodiimide chemistry. Both modified PC membrane and quantum dots were characterized by using various modern analytical tools. It was estimated that 1.95 molecules of QDs were successfully bio-conjugated per unit of IgG. PC membrane with captured bacteria was incubated with prepared IgG conjugated QDs for the formation of sandwich complex. Analysis of the regions of interest (ROI) in fluorescent micrographs showed that newly developed method based on PC and fluorescent QDs has 100 times higher detection sensitivity (100 cells/mL) as compared with detection using conventional dye (FITC) based methods.

Microfiltration platform for continuous blood plasma protein extraction from whole blood during cardiac surgery

This report describes the design, fabrication, and testing of a cross-flow filtration microdevice, for the continuous extraction of blood plasma from a circulating whole blood sample in a clinically relevant environment to assist in continuous monitoring of a patient's inflammatory response during cardiac surgeries involving cardiopulmonary bypass (CPB) procedures (about 400,000 adult and 20,000 pediatric patients in the United States per year). The microfiltration system consists of a two-compartment mass exchanger with two aligned sets of PDMS microchannels, separated by a porous polycarbonate (PCTE) membrane. Using this microdevice, blood plasma has been continuously separated from blood cells in a real-time manner with no evidence of bio-fouling or cell lysis. The technology is designed to continuously extract plasma containing diagnostic plasma proteins such as complements and cytokines using a significantly smaller blood volume as compared to traditional blood collection techniques. The microfiltration device has been tested using a simulated CPB circulation loop primed with donor human blood, in a manner identical to a clinical surgical setup, to collect plasma fractions in order to study the effects of CPB system components and circulation on immune activation during extracorporeal circulatory support. The microdevice, with 200 nm membrane pore size, was connected to a simulated CPB circuit, and was able to continuously extract ~15% pure plasma volume (100% cell-free) with high sampling frequencies which could be analyzed directly following collection with no need to further centrifuge or modify the fraction. Less than 2.5 ml total plasma volume was collected over a 4 h sampling period (less than one Vacutainer blood collection tube volume). The results tracked cytokine concentrations collected from both the reservoir and filtrate samples which were comparable to those from direct blood draws, indicating very high protein recovery of the microdevice. Additionally, the cytokine concentration increased significantly compared to baseline values over the circulation time for all cytokines analyzed. The high plasma protein recovery (over 80%), no indication of hemolysis and low level of biofouling on the membrane surface during the experimental period (over 4 h) were all indications of effective and reliable device performance for future clinical applications. The simple and robust design and operation of these devices allow operation over a wide range of experimental flow conditions and blood hematocrit levels to allow surgeons and clinicians autonomous usage in a clinical environment to better understand the mechanisms of injury resulting from cardiac surgery, and allow early interventions in patients with excessive postoperative complications to improve surgical outcomes. Ultimately, monolithic integration of this microfiltration device with a continuous microimmunoassay would create an integrated microanalysis system for tracking inflammation biomarkers concentrations in patients for point-of-care diagnostics, reducing blood analysis times, costs and volume of blood samples required for repeated assays.

Polymeric Nanopore Membranes for Hydrophobicity-Based Separations by Conformal Initiated Chemical Vapor Deposition

High-aspect ratio hydrophobic, cylindrical nanopores having diameters as low as 5 nm are rapidly fabricated using conformal vapor deposition of fluorinated polymeric layers into porous track-etched polycarbonate membranes. The resultant selectivity of these membranes for pairs of small molecules of similar size, but of different hydrophobicity, arises from solute-pore wall interactions emphasized by confinement. Increasing selectivity was observed as pore diameter decreased and as the surface of the pore became more hydrophobic. Cylindrical pores provided higher selectivity than bottleneck-shaped pores having the same minimum diameter. A maximum selectivity of 234 was achieved between mesitylene and phloroglucinol by the best performing membrane. Membranes with small fluorinated pores exhibited an effective cutoff based on the polar surface area of the molecules, with limited correlation with solute size. This technology could lead to a new generation of membrane separations based on specific interactions.

Direct Plate-Reader Measurement of Nitric Oxide Released from Hypoxic Erythrocytes Flowing through a Microfluidic Device

The ability to perform a fluorescence-based quantitative determination of a biologically important analyte directly released from mammalian cells using a standard microtiter plate reader to measure wells integrated into a microfluidic device is reported. Specifically, the amount of nitric oxide (NO) released from flowing erythrocytes (ERYs) exposed to a hypoxic buffer is measured using a fluorescein-based probe. The ERYs are pumped through channels in one layer of the poly(dimethylsiloxane) (PDMS) device; as these cells release NO, it flows through a porous polycarbonate membrane to the probe. The device is then placed into a standard microtiter plate reader for measurement, with the entire calibration and analyte determination occurring simultaneously. Using this method, NO release from hypoxic ERYs was determined to be 6.9 +/- 1.8 microM, a significantly increased value in comparison to that from normoxic ERYs of 0.60 +/- 0.04 microM (p < 0.001, n = 4 rabbits). Furthermore, the reproducibility (reported as a %RSD) of measuring fluorescence standards was 3.5%. Detection limits, dynamic range, and optimal membrane pore diameters are also reported. This device enables the use of a standard high-throughput tool (the plate reader) to measure analytes in a microfluidic device, the ability to improve the quantitative determination of a relatively unstable molecule (NO), and the incorporation of a flow component and blood constituent into a system that can be combined with microtiter plate technology.

Effects of in vitro cultured adipose-derived stem cells of rats on the tympanic membrane fibroblasts

To explore the effects of rats adipose-derived stem cell (ASC) on the proliferation and migration of fibroblasts from the tympanic membrane, and to discuss the possibility and significance of therapy with ASC for tympanic membrane (TM) healing and regeneration. Wistar rats were sacrificed, and then the isolation, culture and identification of both ASC and the TM fibroblasts were performed respectively. To verify the effect of ASC on fibroblasts proliferation, transwell co-culture system was used. To examine the effect of ASC on fibroblasts migration, cell migration assay with transwell was also applied. All the data were analyzed under a confocal laser scan microscopy system. Immunofluorescence of cell surface markers indicated that rats ASC were positive for both of CD44 and CD29, but negative for CD34. The rat TM fibroblasts were positive for vimentin. The fibroblasts co-cultured with ASC proliferated faster than the fibroblasts of control group, and the difference of the cell counting number between the two groups was significant (t = 6.75, P = 0.003). Compared with the control group, the fibroblasts cultured with ASC conditioned culture medium migrated significantly faster, and the space between the fibroblasts and the polycarbonate membrane pore was significantly shortened at different time point (1, 2.5 and 4 h, P < 0.05). The cell number of the fibroblasts that had migrated through the polycarbonate membrane had been significantly increased 5 h after migration (P < 0.05). ASC might promote TM fibroblasts proliferation and migration by paracrine activation, and it will facilitate the regeneration of TM fibrous layer.

A novel and simple micro-irradiation technique for creating localized DNA double-strand breaks

An ataxia-telangiectasia mutated (ATM)-dependent DNA damage signal is amplified through the interaction of various factors, which are recruited to the chromatin regions with DNA double-strand breaks. Spatial and temporal regulation of such factors is analysed by fluorescence microscopy in combination with laser micro-irradiation. Here we describe a novel and simple technique for micro-irradiation that does not require a laser source. Cells were labelled with BrdU for 48–72 h, covered with porous polycarbonate membranes, and exposed to UVC. All BrdU-labelled cells showed localized foci of phosphorylated ATM, phosphorylated histone H2AX, MDC1 and 53BP1 upon irradiation, showing that these foci were induced irrespective of the cell-cycle phase. They were also detectable in nucleotide excision repair-defective XPA cells labelled with BrdU, indicating that the foci did not reflect an excision repair-related process. Furthermore, an ATM-specific inhibitor significantly attenuated the foci formation, and disappearance of the foci was significantly abrogated in non-homologous end-joining-defective cells. Thus, it can be concluded that micro-irradiation generated DNA double-strand breaks in BrdU-sensitized cells. The present technique should accelerate research in the fields of DNA damage response, DNA repair and DNA recombination, as it provides more chances to perform micro-irradiation experiments without any specific equipment.

Cell Surface of Lactococcus lactis Is Covered by a Protective Polysaccharide Pellicle

In Gram-positive bacteria, the functional role of surface polysaccharides (PS) that are not of capsular nature remains poorly understood. Here, we report the presence of a novel cell wall PS pellicle on the surface of Lactococcus lactis. Spontaneous PS-negative mutants were selected using semi-liquid growth conditions, and all mutations were mapped in a single chromosomal locus coding for PS biosynthesis. PS molecules were shown to be composed of hexasaccharide phosphate repeating units that are distinct from other bacterial PS. Using complementary atomic force and transmission electron microscopy techniques, we showed that the PS layer forms an outer pellicle surrounding the cell. Notably, we found that this cell wall layer confers a protective barrier against host phagocytosis by murine macrophages. Altogether, our results suggest that the PS pellicle could represent a new cell envelope structural component of Gram-positive bacteria.

Diffusive Flux and Magnetic Manipulation of Nanoparticles through Porous Membranes

Measurement of transport of nanometer scale particles through porous media is important to begin to understand the potential environmental impacts of nanomaterials. Using a diffusion cell with two compartments separated by either a porous alumina or polycarbonate membrane as a model system, diffusive flux through mesoporous materials is examined. Experiments are performed as a function of particle size, pore diameter, and solvent, and the particle fluxes are monitored by the change in absorbance of the solution in the receiving cell. Using the measured extinction coefficient and change in absorbance of the solution as a function of time, the fluxes of 3, 8, and 14 nm diameter CoFe(2)O(4) particles are determined as they are translocated across pores with diameters 30, 50, 100, and 200 nm in hexane and aqueous solutions. In general, flux decreases with increasing particle size and increases with pore diameter. We find that fluxes are faster in aqueous solutions than in hexane, which is attributed to the hydrophilic nature of the porous membranes and differences in wettability. The impact of an applied magnetic flux gradient, which induces magnetization and motion, on permeation is also examined. For larger membrane pore diameters, applied magnetic fluxes increase the rate of transport of 14 nm CoFe(2)O(4) particles more than that of 3 or 8 nm diameter particles, reflecting their differences in susceptibility. However, larger particles are excluded from membranes with small diameter pores, consistent with magnetic interparticle attractions that reversibly induce magnetic aggregation.

Electrodeposition and Characterization of Bismuth Telluride Nanowires

In this work, we report thermoelectric measurements on electroplated bismuth telluride nanowires. Porous polycarbonate membranes, obtained by ion-track irradiation lithography, were chosen as electroplating templates. Bismuth telluride nanowires were achieved in acidic media under potentiostatic conditions at −100 mV versus saturated silver chloride electrode. The filling ratio of the pores was increased to 80% by adding dimethyl sulfoxide to the electrolyte. Whatever the experimental conditions, the nanowires were polycrystalline in the rhombohedral phase of Bi2Te3. Finally, the power output of arrays of bismuth telluride nanowires was analyzed as a function of load resistance. The results were strongly dependent on the internal resistance, which can be significantly reduced by the presence of dimethyl sulfoxide during electroplating.

Chemoelectrical Energy Conversion of Adenosine Triphosphate using ATPases

Biological ion transport processes in proteins have inspired the development of bio-sensors, actuators, photoelectric, and chemoelectric energy conversion devices. These bio-inspired devices use ion transport through a protein energized by biochemical reactions in the protein’s sub-units to perform their engineering function. In an effort to advance the use of biological processes in synthetic systems, a chemoelectrical energy conversion device is demonstrated in this article that uses hydrolysis of adenosine triphosphate (ATP) in ATPase enzyme to generate electrical power. The ATPase enzyme in the device is reconstituted in a bilayer lipid membrane (BLM) and supported on a porous substrate. ATP is dissolved in pH7 buffer and added to one of the chambers in this bicameral device. The transmembrane gradient established by proton transport, resulting from hydrolysis of ATP in the enzyme, is converted into electron flow in an external circuit via silver-silver chloride electrodes placed in the buffer solution on both the sides of the membrane. The chemoelectrical energy conversion of ATP is demonstrated in this article using electrical impedance spectroscopy and load characterization experiments on BLMs supported in the pore(s) of a 25% porous polycarbonate membrane and single-pore silicon nitride chip. In electrical impedance spectroscopy, the change in conductance states of the membrane quantified by specific resistance is used to demonstrate protein activity. The mean electrical impedance of the BLM with ATPase supported on a single pore silicon nitride chip drops from 7 kΩ cm2 to 250 Ω cm2 on adding ATP to one side of the membrane. This change in ionic conductance of the BLM with ATPase in the presence of ATP demonstrates protein activity in the membrane. Impedance analysis of the membranes (BLM, BLM with ATPase) supported in multi-pore polycarbonate substrate demonstrates similar trend confirming ion transport and energy conversion in the membrane. In load characterization experiments, a resistive load of known magnitude is connected to the device and voltage across the membrane and current through the circuit are measured. The current−voltage characteristics of the device resembles a constant current power source and the slope of the response represents the internal resistance of the device. The current through the membrane supported on the single pore substrate is below the range of our data acquisition equipment and hence the device with the porous polycarbonate membrane is used in load characterization experiments. This polycarbonate membrane-based device has an open-circuit voltage of 87.5(±7.5) mV with a specific power output of 1.85 μW/cm2 and an internal resistance of 30.5k(±8.5k)Ω. The theoretical maximum specific power available from the membrane supported on the multi-pore polycarbonate membrane and the single pore silicon-nitride substrate are estimated from the current−voltage response to be 7.65 and 18 μW/cm2.

Photoelectric Properties of Electrodeposited Copper(I) Oxide Nanowires

Semiconducting copper(I) oxide nanowires were fabricated by electrochemical deposition into porous polycarbonate membranes from a copper lactate electrolyte. Nanowire composition and structure were varied by controlling the deposition potential and deposition rate, respectively. Nanowires formed at more negative potentials had increased metallic Cu content leading to composites. The nanowires were highly resistive but displayed enhanced conductivity under UV/visible light illumination. Optical spectra show both a plasmon resonance due to metallic copper and an interband absorption due to the bandgap of copper(I) oxide, calculated at .

Structural and magnetic properties of electrodeposited Cobalt nanowire arrays

Ordered magnetic nanowires have tremendous potential in future magnetic storage and high frequency magnetic logic devices. Here, we present the fabrication of ordered arrays of Cobalt nanowires by electrodeposition through porous polycarbonate membranes. Vertically and horizontally aligned nanowires were produced in presence of an external bias field during post deposition etching of the polycarbonate membrane. Structural and compositional analyses have been carried out to establish the material and structural purity. The magneto-optical Kerr effect was employed to measure the magnetic hysteresis loops for the nanowires assembled in the substrate plane. A good magneto-optical signal to noise ratio is observed with clean ferromagnetic hysteresis loops. The loops measured with external magnetic field applied parallel and perpendicular to the axis of the nanowires show a clear difference in the shape and the coercive field, indicating the effect of shape anisotropy in these samples. Micromagnetic simulations were performed to understand the experimental results and to obtain insight to the magnetization reversal mechanism in magnetic nanowires.

Synthesis and characterization of cobaltite nanotubes for solid-oxide fuel cell cathodes

La1-xSrxCo1-yFeyO3-δ oxides are good candidates for solid oxide fuel cell (SOFC) cathodes because these materials present high ionic and electronic conductivity, and compatibility with Cerium Gadolinium Oxide (CGO) electrolytes allowing a lower operation temperature. In this work, we report the synthesis of La0.4Sr0.6Co0.8Fe0.2O3-δ (LSCF) nanotubes prepared by a porous polycarbonate membrane approach, obtaining different microstructures depending on sintering conditions. The structure and morphology of the nanotubes and deposited films were characterized by X-ray diffraction, transmission and scanning microscopy. Finally, we obtained nanostructured films of vertically aligned LSCF tubes deposited over the whole surface of CGO pellets with diameter up to 2.5cm in a direct and single step process.

Evaluation of a bioreactor with stacked sheet shaped organoids of primary hepatocytes

Hepatocyte organoids have an in vivo-like cell morphology and maintain cell viability and function in vitro. On the other hand, the oxygen supply to hepatocytes is sometimes limited in the core of organoids that are more than 100 mum in thickness. In this study, we designed and examined a new bioreactor using sheet-shaped organoids (organoid-sheets) in which the thickness was controlled to prevent hepatocyte death in the core of organoid due to limitation of oxygen supply. The cell culture space consisted of stacked organoid formation spaces and medium flow channels. Each space was separated by flat porous polycarbonate membranes, and the organoid thickness was controlled at 100 microm with a stainless steel spacer. Freshly isolated hepatocytes (7.0 x 10(7)) were immobilized in the bioreactor, yielding a cell density of 4.5 x 10(7) cells/cm(3)-bioreactor. Of the five flow rates tested (1.0, 5.0, 10, 20, and 50 mL/min), the bioreactor with the 10 mL/min had the highest ammonia removal and albumin secretion activities for at least 14 days. In conclusion, a new bioreactor controlling organoid thickness is useful for achieving high cell density culture and the maintenance of hepatocyte function to avoid cell death in the core of the organoids due to limitation of oxygen supply. The bioreactor may be useful for the development of various applications using cultured hepatocytes.

Direct Determination of Uric Acid in Human Serum Samples Using Polypyrrole Nanoelectrode Ensembles

Polypyrrole (PPy) nanotubes have been synthesized by chemical oxidative polymerization of pyrrole within the pores of polycarbonate membrane using the technology of diffusion of solutes. The nanotubes array prepared by the proposed method can be considered as nanoelectrode ensembles (NEEs). An amperometric uric acid sensor based on PPy NEEs has been developed and used for determination of uric acid in human serum samples. The electrode can direct response to uric acid at potential of 0.60V vs. SCE with wide linear range of <TEX>$1.52{\times}10^{-6}\;to\;1.54{\times}10^{-3}\;M.\;The\;detection\;limit\;is \;3.02{\times}10^{-7}$</TEX> M. This sensor has been used to determine uric acid in real serum samples. PPy NEEs is thought of as a good application in the foreground.

Protein Nanotubes Comprised of an Alternate Layer‐by‐Layer Assembly Using a Polycation as an Electrostatic Glue

We present the synthesis and structure of various protein nanotubes comprised of an alternate layer-by-layer (LbL) assembly using a polycation as an electrostatic glue. The nanotubes were fabricated by sequential LbL depositions of positively charged polycations and negatively charged proteins into a porous polycarbonate (PC) membrane, followed by release of the cylindrical core by quick dissolution of the template with CH(2)Cl(2). This procedure provides a variety of protein nanotubes without interlayer cross-linking. The three-cycle depositions of poly-L-arginine (PLA) and human serum albumin (HSA, M(w)=66.5 kDa) into the porous PC template (pore diameter, D(p)=400 nm) yielded well-defined (PLA/HSA)(3) nanotubes with an outer diameter of 419+/-29 nm and a wall thickness of 46+/-8 nm, revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. The outer diameter of the tubules can be controlled by the pore size of the template (200-800 nm), whereas the wall thickness is always constant, independent of the D(p) value. The (PEI/HSA)(3) (PEI: polyethylenimine) nanotubes showed a slightly thin wall of 39+/-5 nm. CD spectra of the multilayered (PEI/HSA)(n) film on a flat quartz plate suggested that the secondary structure of HSA between the polycations was almost the same as that in aqueous solution. The three-cycle LbL depositions of PLA and ferritin (M(w)=460 kDa) or myoglobin (Mb, M(w)=1.7 kDa) into the porous PC membrane also gave cylindrical hollow structures. The wall thickness of the (PLA/ferritin)(3) and (PLA/Mb)(3) nanotubes were 55+/-5 nm and 31+/-4 nm; it depends on the globular size of the protein (ferritin>HSA>Mb). The individual ferritin molecule was clearly seen in the tubular walls by SEM and TEM measurements.

Enhanced Sensitivity of a Glucose Sensor Adopting Polymer Microtubule

Sensitivity of a glucose biosensor based on conducting polymer micro-tubule was enhanced by introducing a Pt transducer layer. Electrochemical template synthesis using polycarbonate membrane was used to fabricate the micro tubule. Glucose oxidase from Aspergillus Niger was caged into the micro tubule structure by capping the mouth of the tubule with a nano porous polycarbonate membrane. This capped tubule structure worked as a cell-array retaining enzyme inside and as a sensing current collector for the electrochemical reaction of the species retained inside simultaneously. The nano pores of the capping membrane were filled with poly (1,3-phenylenediamine) by using electrochemical polymerization. Introducing a Pt transducer layer at the bottom side of the template enhanced the sensitivity of the sensor about sixty times compared to the one having Au layer. The larger the pore size of the template was, the faster was the response and the higher was the detection current because of the faster material transport into and out of the cells.

Dipolar interactions in multilayered Co0.96Cu0.04/Cu nanowire arrays

AbstractArrays of electrodeposited Co0.96Cu0.04/Cu nanowires into porous polycarbonate membranes have been characterized by ferromagnetic resonance measurements in order to study the effect of the dipolar interactions on the effective anisotropy field as a function of the magnetic and non magnetic layer thickness. It is found that breaking the infinite cylinder geometry reduces their shape anisotropy field, which can be modified to a large extent from 6.5 kOe for non layered nanowires down to nearly zero for layered nanowires with the thinnest magnetic layers. An analytical model is proposed to describe the magnetostatic interactions between magnetic layers and their effect on the total anisotropy field which shows a good agreement with the experiment. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Investigation of superconductivity in electrochemically fabricated AuSn nanowires

We have fabricated intermetallic AuSn nanowires by electrochemical deposition in porouspolycarbonate membranes. By controlling the deposition parameters, nanowires ofa single intermetallic phase, namely AuSn, can be fabricated. AuSn nanowiresare found to be crystalline and fairly resistant to oxidation. Electrical transportmeasurements on arrays of nanowires showed a superconducting transition temperature,Tc∼1.5 K. In addition, four-probe measurements were made on individual freestanding nanowireswith electrodes formed by a focused ion beam (FIB). Results from the two sets ofmeasurements are found to be in close agreement.