Microporous Nylon Membranes Research Articles

Layer-by-layer self-assembly preparation and desalination performance of graphene oxide membrane

Abstract Unlike previous utilization of ultrafiltration membranes as supporters of graphene oxide (GO) composite membranes, this study first adopts microporous nylon membranes as substrates. The cationic polyelectrolyte/GO composite membranes are prepared by the layer-by-layer self-assembly method via electrostatic attraction. The introduction of polycations between nanochannels in the GO membranes effectively suppresses the swelling and improves the stability of the membranes. It is found that the polyelectrolytes' charge density and the surface potential of the composite membranes jointly determine the membranes' properties. The experimental results show that the novel GO membranes can obtain high flux and considerable desalination performance under low operating pressure. Typically, the salt rejection rate reaches 66.8% for 1.0 g/L MgSO4, and the flux is 39.8 L·m−2·h−1·bar−1. Benefitting from the GO composite membranes keeping similar retention for both high and low concentration salt solutions, the ideal desalination performance could be obtained through multi-stage processes on the premise of ensuring high flux, which is more suitable for industry.

Determination of the Serum Concentrations of the Monoclonal Antibodies Bevacizumab, Rituximab, and Panitumumab Using Porous Membranes Containing Immobilized Peptide Mimotopes.

Effective monoclonal antibody (mAb) therapies require a threshold mAb concentration in patient serum. Moreover, the serum concentration of the mAb Bevacizumab should reside in a specific range to avoid side effects. Methods for conveniently determining the levels of mAbs in patient sera could allow for personalized dosage schedules that lead to more successful treatments. This work utilizes microporous nylon membranes functionalized with antibody-binding peptides to capture Bevacizumab, Rituximab, or Panitumumab from diluted (25%) serum. Modification of the capture-peptide terminus is often crucial to creating the affinity necessary for effective binding. The high purity of eluted mAbs allows for their quantitation using native fluorescence, and membranes are effective in spin devices that can be used in any laboratory. The technique is effective over the therapeutic range of Bevacizumab concentrations. Future work aims at further modifications to develop rapid point-of-care devices and decrease detection limits.

Effect of moisture condensation on vapour transmission through porous membranes.

Porous membranes find natural application in various fields and industries. Water condensation on membranes can block pores, reduce vapour transmissibility, and diminish the porous membranes' performance. This research investigates the rate of water vapour transmission through microporous nylon and nanofibrous Gore-Tex membranes. Testing consisted of placing the membrane at the intersection of two chambers with varied initial humidity conditions. One compartment is initially set to a high (water vapour concentration and the other low (, with changes in humidity recorded as a function of time. The impact of pore blockage was explored by pre-wetting the membranes with water or interposing glycerine onto the membrane pores before testing. Pore blockage was measured using image analysis for the nylon membrane. The mass flow rate of water vapour (ṁv) diffusing through a porous membrane is proportional to both its area (A) and the difference in vapour concentration across its two faces (, such that where K is defined as the moisture diffusion coefficient. Correlations are presented for the variation of K as a function of . Liquid contamination on the porous membrane has been shown to reduce the moisture diffusion rate through the membrane due to pore blockage and the subsequent reduced open area available for vapour diffusion. Water evaporation from the membrane's surface was observed to add to the mass of vapour diffusing through the membrane. A model was developed to predict the effect of membrane wetting on vapour diffusion and showed good agreement with experimental data.

Ion exchange ligand design: Improving membrane adsorber efficiencies by spacer arm manipulation

Weak cation exchange membrane adsorbers were prepared by UV grafting ionic monomers from microporous nylon membranes in aqueous media using Type II photoinitiators. Protein binding was influenced by two factors: a) spacer arm length of ≥6 atoms, and b) the presence of hydrogen bonding moieties in the spacer arm. Increasing the spacer arm length reduced the steric effects associated with the grafted polymer backbone, while intra-chain hydrogen bonding interactions between near neighboring repeat units stiffened the side arm, also making the ligand more sterically accessible and hence more efficiently utilized for protein capture. Static protein binding capacities for lysozyme and IgG of >150 mg/mL were achieved, while protein binding efficiencies, as measured by the molar ratio of ligand to protein captured, are significantly enhanced when compared to those of other ligand monomers having shorter spacer arms.

Novel supported liquid membranes based on deep eutectic solvents for olefin-paraffin separation via facilitated transport

Deep eutectic solvents (DESs), as a new generation of designer solvents, were firstly employed to fabricate the supported liquid membranes (SLMs) for the olefin/paraffin separation via facilitated transport. The novel CuCl/DESs-SLMs were prepared by impregnating the mixture of choline chloride-glycerol based DESs and copper (I) chloride (CuCl) into the microporous nylon membranes. The results of FTIR, 1HNMR and mass spectrometry (MS) confirmed the existence of various Cu (I)-containing anionic species and hydrogen-bond networks in the membrane liquid of CuCl/DESs. The CuCl/DESs-SLMs were characterized by scanning electron microscope (SEM), contact angle measurement and weight analysis, and their performances of CuCl/DESs-SLMs were evaluated by the C2H4/C2H6 separation experiments. The effects of DESs composition, CuCl concentration, operation pressure and temperature were investigated systemically. It was found that the activity and chemical stability of Cu (I)-containing anionic species were enhanced through the hydrogen-bond interactions between the anionic species and DESs, which significantly increased the permeability of C2H4 and selectivity of C2H4/C2H6. Compared with other studies, the CuCl/DESs-SLMs exhibited comparable permeability and higher selectivity up to 20 for C2H4/C2H6. In conclusion, the CuCl/DESs-SLMs provided a promising method for the C2H4/C2H6 separation.

Interlaminar microstructure and mechanical response of 3D robust glass fabric-polyester composites modified with carbon nanofibers

The present work explores new methodology of fabricating the polymer nanocomposite with improved interlaminar, dynamic and micro mechanical properties. Varying amount of carbon nanofibers (CNF) were filled into the glass fiber/unsaturated polyester composite using filtering membrane vacuum-assisted method. Microporous nylon membrane was used to improve the dispersion of CNF in the lamination panels. CNF reinforcement and its concentration had a significant effect on the properties of the composites. Electron microscopy studies on delamination and nanofillers dispersion showed improved interfacial adhesion with CNF filled composites. The end-notched flexure and short-beam strength tests were performed to assess the effect of filling CNF on the interlaminar fracture properties of the composites. Existence of critical concentration was observed for the reinforcement of nanofiller. The properties of the composite enhance with increase in reinforcement upto critical concentration, beyond which it decreases. Better storage modulus (∼57%) and improved interlaminar properties (∼89%) were consistently observed with 2 wt% CNF filled nanocomposite irrespective of the glass fiber loading, besides, the thermal stability and char yield which were also improved significantly. Nanoindentation study shows 39% and 26% increase in elastic modulus and hardness of the composite respectively, on reinforcement of 2 wt% CNF.

Reversible pH-independent optical potassium sensor with lipophilic solvatochromic dye transducer on surface modified microporous nylon.

A reversible and pH-independent fluorescent ion optode is introduced with an ionophore and surface confined solvatochromic dye transducer doped onto microporous nylon membranes. The resulting film responds to K+ with excellent selectivity over the range of 10-7 to 10-2 M and a response time of t95 < 60 s above 10-6 M.

A novel approach for application of nylon membranes in the biosensing domain

In this paper we report the polymer-coated microporous nylon membranes and their application as platforms for protein immobilization and subsequent detection of the dengue virus (DV) in blood serum. Protein recognition experiments were performed with enzyme-linked immunosorbent assay (ELISA). The polymers used for coatings were synthesized by free-radical polymerization reaction between methyl methacrylate (MMA) and methacrylic acid (MAA) in different concentrations. The MAA monomer has carefully been chosen to generate polymers with pendant carboxyl (–COOH) groups, which also exist on polymer surfaces. A high degree of control over surface-exposed –COOH groups has been achieved through variation of monomers concentration in polymerization reaction. The general aspect of this work relies on the dengue antibody (Ab) immobilization on surface –COOH groups via physical attachment or covalent immobilization. Prior to Ab immobilization and ELISA experiment, polymer-coated nylon samples were analyzed in detail for their physical properties by atomic force microscopy (AFM), scanning electron microscopy (SEM), and water-in-air contact angle (WCA) measurements. Membranes were further analyzed by Fourier transform infrared spectroscopy (FTIR) in order to establish the relationship between wettability, porosity, and surface roughness with chemical composition and concentration of –COOH groups on the coating's surface. Optimized coatings have shown high sensitivity towards dengue Ab molecules, revealing fundamental aspect of polymer–protein interfaces as a function of surface –COOH groups’ concentration.

Multiplexed immunoassay biosensor for the detection of serum biomarkers — β-HCG and AFP of Down Syndrome based on photoluminescent water-soluble CdSe/ZnS quantum dots

A multiplexed immunoassay biosensor for detecting serum biomarkers was developed by using photoluminescent (PL) aqueous CdSe/ZnS quantum dots (QDs) with high efficiency and stability as fluorescence labels and carboxyl functionalized microporous nylon membrane as a matrix. Two main biomarkers of Down Syndrome (DS), β-human chorionic gonadotrophin (β-HCG) and α-fetal protein (AFP), were selected for detection in this biosensor system. For specific detection of DS, antibody-immobilized microporous nylon membrane first captured the targeted antigens from the physiological samples and formed immunocomplexes (antibody–antigen) on the membrane surface. Then the immunocomplexes continued to react with QDs conjugated antibodies (labeled antibodies), and formed triplex “sandwich” structure, which was confirmed by AFM and confocal microscopy. Quantitative detection of β-HCG and AFP was also realized, the detectable level of this new biosensor was as low as 1×10−6IU/L for β-HCG and 1ng/mL for AFP in a relatively short assay time without any enrichment.

Nylon membrane as a fluorimetric probe for the herbicide bentazone

The fluorimetric signal produced by bentazone retained in selected solid surfaces was investigated. Among the different tested supports, only a microporous nylon membrane produced the desired signal. The quantitative study was carried out by second-order calibration using parallel factor analysis, allowing the determination in a highly interfering medium. A detection limit of 0.4 ng mL(-1), a prediction relative error of 8%, and a sample frequency of ten samples per hour were obtained in spiked natural waters using green analytical chemistry principles.

Adsorption of papain with Cibacron Blue F3GA carrying chitosan-coated nylon affinity membranes

Covalent coupling of chitosan (CS) to activated nylon membrane was performed after the reaction of the microporous nylon membrane with formaldehyde. Non-specific adsorption on the CS-coated nylon membrane decreased greatly, compared with plain nylon membrane. The dye Cibacron Blue F3GA (CB F3GA) as a ligand was then covalently immobilized on the CS-coated membranes. Physical properties of the composite membrane and its applications in affinity membrane chromatography were examined. The contents of CS and CB F3GA-attached membranes were 89.6 mg/g nylon membrane and 146.1 μmol/g nylon membrane, respectively. These CB F3GA-attached composite membranes were used in the papain adsorption studies. Higher papain adsorption capacity, up to 235.3 mg/g affinity membrane, was obtained. The adsorption isotherm fitted the Freundlich model well. Significant amount of the adsorbed papain (about 94.3%) was eluted by 1.0 M NaSCN at pH 9.0. Experiments on regeneration and dynamic adsorption were also performed. It appears that CB F3GA-CS nylon membranes can be applied for papain separation without causing any denaturation.

Bilirubin removal by Cibacron Blue F3GA attached nylon-based hydrophilic affinity membrane

Covalent coupling of chitosan to the activated membrane was performed after the reaction of the microporous nylon membrane with formaldehyde. Covalent linkage of chitosan was essential to improve the hydrophilicity and consequently reduced the non-specific interactions of the membranes. Cibacron Blue F3G A (CB F3GA) was then covalently immobilized onto the composite membrane to prepare affinity membrane for bilirubin removal. Different amounts of CB F3GA were attached on the composite membranes by changing the dye-attachment conditions, i.e. initial dye concentration, addition of sodium carbonate, and sodium chloride. The maximum CB F3GA content was obtained at 142.9 μmol/g membrane. Dye release in buffers showed a tight covalent bound of CB F3GA on the composite membrane. Bilirubin molecules interacted with the absorbents directly. Non-specific adsorption on the unmodified nylon membrane remains low, and higher bilirubin adsorption capacity, of up to 63.4 mg/g was obtained after CB F3GA immobilization. The effects of the CB F3GA content, temperature, ionic strength, and pH, as well as the adsorption isotherm were investigated in this study. The adsorption capacity increased with increasing the temperature while decreased with increasing the NaCl concentration and a peak at about pH 6.0 was observed during the corresponding experiment. The adsorption isotherm fitted the Freundlich model well. Experiments on regeneration and dynamic adsorption were also performed.

Immunoaffinity removal of xenoreactive antibodies using modified dialysis or microfiltration membranes.

Hyperacute rejection following xenogeneic transplantation in primates is mediated by naturally occurring IgM antibodies, which are specifically directed to alpha-Galactosyl residues on many nonprimate mammalian cells. Current approaches to remove these anti-alphaGal IgM include plasmapheresis followed by immunoaffinity adsorption on bead columns using synthetic Gal epitopes, which requires two pieces of complex equipment. In this study, we explored the use of immunoaffinity adsorption with hollow fiber microporous or dialysis membranes to which a synthetic alphaGal trisaccharide ligand is bound. Covalent attachment of ligand directly to the surface produced negligible binding, but use of long-chain polyamines as reactive spacers yielded binding densities for anti-alphaGal IgM as high as 89 mg/mL membrane volume in breakthrough curve experiments with microporous nylon membranes having an internal surface area of 4.2 m(2)/mL membrane volume. A crossflow microfilter fabricated from the membranes described in this study and having about 0.4 m(2) luminal surface area would be able to carry out plasma separation and immunoadsorption in a single device with a large excess of binding capacity to ensure that all plasma that filters across the device and is returned to a human patient is essentially free of anti-alphaGal IgM. We conclude that immunoaffinity removal of xenoreactive antibodies using microfiltration hollow fiber membranes is feasible and has potential advantages of efficiency and simplicity for clinical application.

Immobilisation of pig liver esterase in hollow fibre membranes

Different methods were evaluated to immobilise Pig Liver Esterase (PLE) in hollow fibre membranes. Four covalent bonding techniques (using epoxy, imidazol, amino and carboxylic acid terminal groups) were tested to link the enzyme to microporous nylon membranes. Physical immobilisation was also studied, by entrapment of the enzyme inside the microporous structure of a polysulfone asymmetric ultrafiltration membrane. The entrapment method lead to a higher retention of enzymatic activity for a longer period of time. This technique was selected to be used in a biphasic membrane bioreactor where the microporous hydrophilic membrane, containing the enzyme, is used to separate an aqueous from an organic phase, in which the substrate is dissolved. Different enzyme loading procedures were studied in the biphasic reactor and the resulting axial and radial enzyme distribution in the hollow fibre module were related to the global enzymatic activity.

A facile route to thin-film solid state lithium microelectronic batteries

We describe the synthesis and characterization of a thin-film solid state lithium rechargeable battery. This battery was designed for integration into a multi-chip module (MCM). The battery consists of a spin-on Ag 2WO 4 — polymer cathode, a lithium hexaflurophosphate — polymer-impregnated microporous nylon membrane electrolytic separator, and a lithium foil anode. Kapton™ was used as the substrate and encapsulating top layer of the battery. The battery had a total area of approximately 4.0 cm 2 , thickness of 0.6 mm, and weighed 0.4 g. The battery had an open circuit voltage of 3.5 V and was able to deliver a current density of 0.05 mA/cm 2 for 1.5 h while maintaining a voltage above 2.0 V. The battery was cycled over 12,000 times between 3.5 and 2.0 V using a constant discharging current density of 0.1 mA/cm 2 and charging current density of 0.05 mA/cm 2. The battery was designed for integration into a standard 96 pin Kovar/Glass Bead quad-flatpack programmable MCM (1.42×1.42×0.16 in.). The charging and discharging characteristics of this battery are presented and discussed in terms of its intended application.

Nature of immobilized antibody layers linked to thioctic acid treated gold surfaces

Utilization of 125I-labeled IgG enables an investigation of protein immobilized to gold electrodes sputter deposited on microporous nylon membranes, including the precise nature of the surface–protein bond (i.e. covalent or non-specific adsorption), physical location of the immobilized protein (i.e. on the surface of the gold electrode or within the pores of the membrane), and the amount of protein immobilized. This is accomplished by comparing the mass of protein immobilized to gold surfaces that have been treated in several different fashions, as well as, deposition of the gold on nylon membranes that have been treated differently. It is shown that these microporous gold electrodes, proposed previously for conducting novel non-separation electrochemical enzyme immunoassays, consist of multiple protein layers non-specifically adsorbed. Approximately, half of the total adsorbed protein is immobilized to the gold surface with the remaining protein bound within the pores on the nylon membrane.

Capture of anti-(Galalpha1-3Gal) antibodies by immobilized Galalpha1-3Gal oligomers derived from carrageenan.

An immobilized Galalpha1-3Gal-bearing affinity ligand was prepared as a possible prophylactic binding site of human anti-(Galalpha1-3Gal) antibodies for the prevention of hyperacute rejection of pig xenografts. lambda-Carrageenan, a natural polysaccharide known to possess alternately alpha1-3 and beta1-4-linked D-galactopyranose sulphate residues, was selectively degraded by acetolysis and subsequently deacetylated to obtain lambda-carrageenan oligosaccharides. The resulting syrup was ultrafiltered to remove higher polymers and chromatographed on Sephadex G-15 to produce a series of sized oligosaccharide fractions. An immuno-dot-blot method was established on the basis of the competition between the lambda-carrageenan oligosaccharides in solution and bovine thyroglobulin (BTG), a glycoprotein known to express the Galalpha1-3Gal marker, as the solid-phase antigen. Increasing amounts of lambda-carrageenan fractions added to normal human plasma resulted in a progressive decrease in Galalpha1-3Gal-specific human IgM and IgG binding to BTG. Complete inhibition of Galalpha1-3Gal-specific human immunoglobulin was attained at concentrations less than 0.6 mg of carbohydrate/ml of human plasma with the more active fractions. These bioactive lambda-carrageenan oligosaccharides were immobilized on hydrazide-modified microporous nylon membranes, yielding capacities between 2.18 and 2.86 mg/ml of membrane. A subsequent decrease in the human anti-(Galalpha1-3Gal) antibody level in normal human plasma was demonstrated and proved with the established immuno-dot-blot procedure.

High specific activity of whole cells in an aqueous-organic two-phase membrane bioreactor

Whole Bacillus subtilis cells can catalyze stereoselective hydrolysis of menthyl acetate in a small-scale two-phase membrane bioreactor. A layer of cells was deposited on one side of a 0.2 μm microporous nylon membrane and then neat liquid racemic menthyl acetate was circulated past the same side. This organic phase was pressurized slightly relative to the aqueous buffer which flowed past the other face of the membrane. No breakthrough or cell detachment was observed over 24 h operation. The total reaction rate reached a maximum with a cell layer of about 40 μm, then declined for thicker layers. The specific activity (per unit biomass) at the maximum was about five times higher than with the same cells in an emulsion reactor. This probably reflects continuous good contact with both phases.

Immobilization of proteins on gold coated porous membranes via an activated self-assembled monolayer of thioctic acid

A new methodology for efficient protein (e.g., antibodies, enzymes, etc.) immobilization on microporous nylon membranes for use in a variety of bioanalytical systems is introduced. The method utilizes an activated self-assembled monolayer (SAM) of thioctic acid on gold coated forms of the membranes. Via a carbodiimide mediated reaction, the protein is anchored to the gold surface through an amide bond with the terminal carboxyl group of the adsorbed thioctic acid. The immobilization efficiency is high (∼95% for a monoclonal immunoglobulin G(IgG) and the surface bound protein appears to be stable enough to resist any displacement by other proteins in a matrix as complex as serum. Immunological activity of immobilized antibody is retained as demonstrated via use of such membrances in colorimetric ELISA for human chorionic gonadatropin (hCG). The high protein immobilization efficiency, the high tensile strength of microporous nylon membranes, and the excellent electrochemical characteristics of gold make this approach very attractive for preparing biomembranes that should be useful in affinity chromatography, electrochemical immunosensing systems, flow-through enzyme reactors, etc.

Comparative study of reaction kinetics in membrane and agarose bead affinity systems

Compared to conventional agarose bead affinity supports, a microporous nylon membrane exhibits greatly improved reaction kinetics as quantified in the reaction between γ-globulin and immobilised protein A. The improvement is only observed when the solution of γ-globulin is forced through the membrane pores. In the absence of flow in the pores, it is possible to relate approximately the rate of uptake onto either type of affinity support to independently determined diffusion coefficients. In the presence of flow, the reaction rate is similar for membranes having 0.45 and 3.0 μm diameter pores, and considerably smaller than predicted by the Smoluchowski formula.