Effect of aging on UF membranes by a streaming potential (SP) method

Characterization Challenges of Self-Assembled Polymer-SPIONs Nanoparticles: Benefits of Orthogonal Methods

Size and zeta potential are critical physicochemical properties of nanoparticles (NPs), influencing their biological activity and safety profile. These are essential for further industrial upscale and clinical success. However, the characterization of polydisperse, non-spherical NPs is a challenge for traditional characterization techniques (ex., dynamic light scattering (DLS)). In this paper, superparamagnetic iron oxide nanoparticles (SPIONs) were coated with polyvinyl alcohol (PVAL) exhibiting different terminal groups at their surface, either hydroxyl (OH), carboxyl (COOH) or amino (NH₂) end groups. Size, zeta potential and concentration were characterized by orthogonal methods, namely, batch DLS, nanoparticle tracking analysis (NTA), tunable resistive pulse sensing (TRPS), transmission electron microscopy (TEM), asymmetric flow field flow fractionation (AF4) coupled to multi-angle light scattering (MALS), UV-Visible and online DLS. Finally, coated SPIONs were incubated with albumin, and size changes were monitored by AF4-MALS-UV-DLS. NTA showed the biggest mean sizes, even though DLS PVAL-COOH SPION graphs presented aggregates in the micrometer range. TRPS detected more NPs in suspension than NTA. Finally, AF4-MALS-UV-DLS could successfully resolve the different sizes of the coated SPION suspensions. The results highlight the importance of combining techniques with different principles for NPs characterization. The advantages and limitations of each method are discussed here.

Native RNA Purification Method for Small RNA Molecules Based on Asymmetrical Flow Field-Flow Fractionation

RNA molecules provide promising new possibilities for the prevention and treatment of viral infections and diseases. The rapid development of RNA biology and medicine requires advanced methods for the purification of RNA molecules, which allow fast and efficient RNA processing, preferably under non-denaturing conditions. Asymmetrical flow field-flow fractionation (AF4) enables gentle separation and purification of macromolecules based on their diffusion coefficients. The aim of the study was to develop an AF4 method for efficient purification of enzymatically produced antiviral small interfering (si)RNA molecules and to evaluate the overall potential of AF4 in the separation of short single-stranded (ss) and double-stranded (ds) RNA molecules. We show that AF4 separates monomeric ssRNA from dsRNA molecules of the same size and monomeric ssRNA from multimeric forms of the same ssRNA. The developed AF4 method enabled the separation of enzymatically produced 27-nt siRNAs from partially digested substrate dsRNA, which is potentially toxic for mammalian cells. The recovery of AF4-purified enzymatically produced siRNA molecules was about 70%, which is about 20% higher than obtained using anion-exchange chromatography. The AF4-purified siRNAs were not toxic for mammalian cells and fully retained their biological activity as confirmed by efficient inhibition of herpes simplex virus 1 replication in cell culture. Our work is the first to develop AF4 methods for the separation of short RNA molecules.

Sample carryover and cleaning procedures for asymmetrical flow field-flow fractionation instrument

Asymmetrical flow field-flow (AF4) fractionation aims in separation of sample components to yield elution of homogenous fractions identified as well-defined peaks in the chromatograms. Separation that occurs in matrix-free open channel potentiates high recovery that can be close to 100%. However, sample properties and separation conditions may induce carryover of sample components during AF4 analysis and in sample sequences. This compromises the quality of the data collected from the online detectors and the downstream offline analytics of the collected fractions. In this study, we followed sample carryover in AF4 using model viruses and analyzed various cleaning solutions and rinse methods to reduce carryover. We introduce an SDS-NaOH -based rinsing and decontamination protocol for the AF4 instrument enabling high-quality data collection.

Fabrication of a Novel Antifouling Polysulfone Membrane with in Situ Embedment of Mxene Nanosheets

Membrane fouling is still a critical issue for the application of ultrafiltration, which has been widely used in water treatment due to its efficiency and simplicity. In order to improve the antifouling property, a new 2D material MXene was used to fabricate composite ultrafiltration membrane with the approach of in situ embedment during the phase inversion process in this study. Scanning electron microscopy (SEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), water contact angle, bovine serum albumin rejection and porosity measurements were utilized to characterize the prepared membranes. Due to the hydrophilicity of the MXene, the composite membranes obtained higher hydrophilicity, confirmed by the decreased water contact angle. All the modified membranes had a high bovine serum albumin rejection above 90% while that of the pristine polysulfone membrane was 77.48%. The flux recovery ratio and the reversible fouling ratio of the membranes were also improved along with the increasing content of the MXene. Furthermore, the highest flux recovery ratio could also reach 76.1%. These indicated the good antifouling properties of MXene composite membranes. The enhanced water permeability and protein rejection and excellent antifouling properties make MXene a promising material for antifouling membrane modification.

Asymmetrical Flow Field-Flow Fractionation on Virus and Virus-Like Particle Applications

Asymmetrical flow field-flow fractionation (AF4) separates sample components based on their sizes in the absence of a stationary phase. It is well suited for high molecular weight samples such as virus-sized particles. The AF4 experiment can potentially separate molecules within a broad size range (~10³−10⁹ Da; particle diameter from 2 nm to 0.5−1 μm). When coupled to light scattering detectors, it enables rapid assays on the size, size distribution, degradation, and aggregation of the studied particle populations. Thus, it can be used to study the quality of purified viruses and virus-like particles. In addition to being an advanced analytical characterization technique, AF4 can be used in a semi-preparative mode. Here, we summarize and provide examples on the steps that need optimization for obtaining good separation with the focus on virus-sized particles.

Asymmetric flow field flow fractionation methods for virus purification

Detailed biochemical and biophysical characterization of viruses requires viral preparations of high quantity and purity. The optimization of virus production and purification is an essential, but laborious and time-consuming process. Asymmetric flow field flow fractionation (AF4) is an attractive alternative method for virus purification because it is a rapid and gentle separation method that should preserve viral infectivity. Here we optimized the AF4 conditions to be used for purification of a model virus, bacteriophage PRD1, from various types of starting materials. Our results show that AF4 is well suited for PRD1 purification as monitored by virus recovery and specific infectivity. Short analysis time and high sample loads enabled us to use AF4 for preparative scale purification of PRD1. Furthermore, we show that AF4 enables the rapid real-time analysis of progeny virus production in infected cells.

Influence of steric, electric, and dielectric effects on membrane potential

The membrane potential arising through nanofiltration membranes separating two aqueous solutions of the same electrolyte at identical hydrostatic pressures but different concentrations is investigated within the scope of the steric, electric, and dielectric exclusion model. The influence of the ion size and the so-called dielectric exclusion on the membrane potential arising through both neutral and electrically charged membranes is investigated. Dielectric phenomena have no influence on the membrane potential through neutral membranes, unlike ion size effects which increase the membrane potential value. For charged membranes, both steric and dielectric effects increase the membrane potential at a given concentration but the diffusion potential (that is the high-concentration limit of the membrane potential) is affected only by steric effects. It is therefore proposed that membrane potential measurements carried out at high salt concentrations could be used to determine the mean pore size of nanofiltration membranes. In practical cases, the membrane volume charge density and the dielectric constant inside pores depend on the physicochemical properties of both the membrane and the surrounding solutions (pH, concentration, and chemical nature of ions). It is shown that the Donnan and dielectric exclusions affect the membrane potential of charged membranes similarly; namely, a higher salt concentration is needed to screen the membrane fixed charge. The membrane volume charge density and the pore dielectric constant cannot then be determined unambiguously by means of membrane potential experiments, and additional independent measurements are in need. It is suggested to carry out rejection rate measurements (together with membrane potential measurements).

Modification of active and porous sublayers of aged polyamide/polysulfone composite membranes due to HNO3 treatment: Effect of treatment time

Changes in electrical and transport parameters for aged composite polyamide/polysulfone membrane samples (PAC) and their porous support layers (PSU) as a result of chemical treatment (immersion in 1 M HNO3 solution) at four different times (12 h < or = t < or = 72 h) have been obtained. Salt permeability, ion transport number, and membrane electrical resistance for the treated samples were determined from salt diffusion, membrane potential, and impedance spectroscopy measurements, which were carried out with the membranes in contact with NaCl solutions at different concentrations and compared with those determined for fresh and aged nontreated samples. Results show the strong effect of aging on membrane parameters, particularly the decrease in salt permeability (P(s)) and the increase in membrane electrical resistance (R(m)), while ion transport number is hardly affected by aging, chemical treatment, or treatment time. Results show how the compaction of the porous structure causes by aging (dried membrane matrix structure) can be partially reduced by HNO3 treatment, and they also allow the estimation of 24-h treatment as the optimum time (higher salt permeability and lower membrane electrical resistance), mainly for the polysulfone support layer. The use of equivalent circuits in the analysis of impedance spectroscopy data allows separate estimation of the electrical resistance associated with each sublayer of the composite PAC membrane samples. On the other hand, chemical changes in the active top layer of the PAC membrane (polyamide active layer) were obtained from XPS analysis, which show some modifications in the atomic concentration percentages of the polyamide characteristic elements as a result of acidic treatment time, which are more significant after 72-h acidic immersion.

Effect of age and chemical treatments on characteristic parameters for active and porous sublayers of polymeric composite membranes

Changes in the transport parameters and the chemical nature of the surface of composite polyamide/polysulfone membranes due to both aging and treatment with chemical products (HCl, H(3)NO, and NaOH) have been considered. Hydraulic and salt permeability were obtained from water flow and salt diffusion measurements, respectively, and their values seem to indicate a modification in the structural parameters (porosity/thickness) of aging samples, while HCl and HNO(3) treatments will act in the opposite way. Chemical modifications in the membrane surfaces were studied by X-ray photoelectron spectroscopy (XPS), which mainly show the effect of H(3)NO and HCl on the polyamide active layer of the membranes (polyamide oxidation), but no chemical damage for that sublayer. Electrical characterization of both sublayers of the composite membranes were determined from impedance spectroscopy (IS) measurements using equivalent circuits as models, and these results indicate: (i) a strong increase of the membrane electrical resistance as a consequence of aging, mainly that associated with the active sublayer (30 times higher for an old sample than for a fresh one) and treatment with NaOH; (ii) the reduction of this effect when the samples were treated with HCl and HNO(3) solutions. Changes in the values of the electrical resistance of the composite membranes are in agreement with those obtained for permeabilities, but the electrical parameter also allows the determination of the contribution of each sublayer.