Membrane Surface Potential Research Articles

Radiation Synthesis of Psyllium/Frankincense Essential Oil –Based Wound Dressing Hydrogels: Antimicrobial, Antioxidant and Wound Healing Performance

Abstract Innovative bioactive hydrogel dressings based on Psyllium (Pys) and Carbopol (Carp) supported with Frankincense essential oil (FO) were fabricated using γ- irradiation facility for crosslinking and sterilization. (Psy-Carp)/FO dressing’s characteristics, hemolytic potential, antioxidant efficiency, antimicrobial activity as well as their morphological features were evaluated. Wound healing efficacy was evaluated using a rat model. The results revealed that the gelation degrees increased by the increase of (Psy) concentration, Carbopol content, and irradiation dose. The incorporation of FO oil up to 5% improves the swelling ability as well as the dressing porosity as shown by SEM images. The incorporation of FO oil enhances the Water Vapor Transmission Rate (WVTR), increases the antioxidant activity. Antimicrobial activity and microbial barrier potency of (Psy-Carp)/FO dressing was tested against Staphylococcus aureus (S. aureus), Escherichia coli (E. coli), and Candida albicans (C. albicans), the results showed that it attenuates microbial growth of all the tested strains after 18 h. by two log cycle and cause a high rate of microbial killing. A significant increase of protein release, decrease in Exopolysaccharides (EPS) content and decrease of membrane surface potential were noticed indicating alternation of cell membrane permeability leading to cell death. In vivo wound healing evaluation using rat model confirms that the tested dressings induce faster wound healing with improvement biochemical parameters compared with that of FO free (Psy-Carp) hydrogel. Based on the above-mentioned results, it can be concluded that (Psy-Carp)/FO hydrogel dressings demonstrate a promising potential as wound care candidates.

Characterization of Ion Transport Based on Conductance Versus Concentration Curves. A Theoretical Analysis

Ion channels are regulated by voltage, various ligands, but also by membrane properties such as lipid composition and surface charge. Here, the dependence of ion transport on membrane charge and ion concentration is analyzed. The setting is that the membrane contains cation- and anion-selective channels, and the ionic strength is determined by the concentration of permeant ions. The conductance (G) is proportional to the respective ion concentration at the membrane surface, which in turn is related to the bulk concentration (c) through the Boltzmann factor: G = Acexp(-ze ψ/kT), where A is the permeability coefficient, z is the ion's charge number, including sign, e is the elementary charge, ψ is the membrane surface potential, k is the Boltzmann constant, T is the temperature.

Polyalanine peptide variations may have different mechanisms of action against multidrug-resistant bacterial pathogens.

The number of bacterial pathogens resistant to the currently available antibiotics has dramatically increased, with antimicrobial peptides (AMPs) being among the most promising potential new drugs. In this study, the applicability and mechanisms of action of Pa-MAP 2 and Pa-MAP 1.9, two AMPs synthetically designed based on a natural AMP template, were evaluated. Pa-MAP 2 and Pa-MAP 1.9 were tested against a clinically isolated multidrug-resistant (MDR) Escherichia coli strain. Biophysical approaches were used to evaluate the preference of both peptides for specific lipid membranes, and bacterial surface changes imaged by atomic force microscopy (AFM). The efficacy of both peptides was assessed both in vitro and in vivo. Experimental results showed that both peptides have antimicrobial activity against the E. coli MDR strain. Zeta potential and surface plasmon resonance assays showed that they interact extensively with negatively charged membranes, changing from a random coil structure, when free in solution, to an α-helical structure after membrane interaction. The antibacterial efficacy was evaluated in vitro, by several techniques, and in vivo, using a wound infection model, showing a concentration-dependent antibacterial effect. Different membrane properties were evaluated to understand the mechanism underlying peptide action, showing that both promote destabilization of the bacterial surface, as imaged by AFM, and change properties such as membrane surface and dipole potential. Despite their similarity, data indicate that the mechanisms of action of the peptides are different, with Pa-MAP 1.9 being more effective than Pa-MAP 2. These results highlight their potential use as antimicrobial agents against MDR bacteria.

Migration and deformation of polyelectrolyte vesicle through a pore in electric field

With the finite element method adopted to solve the coupling of the fluid flow, the deformation of viscoelastic membrane and the distribution of electric field, the dynamic behavior of the polyelectrolyte vesicle is investigated through a pore in the electric field. The velocity of the vesicle is reduced significantly when it approaches the pore, with the vesicle showing a bullet-like shape. Then, the velocity reaches its minimum when the vesicle approaches the center of the pore. At this time, it shows a long-strip shape with the diameter of the vesicle being no greater than the pore diameter, otherwise, it shows a slipper-like shape. After the pore is past through, a sharp increase in vesicle velocity is observed. In addition, as the lengths of pores or the diameters of vesicles increase, the minimum velocity of the vesicles along the horizontal direction declines gradually while the translocation time is extended significantly. Our results further demonstrate that the surface potential of membrane increases slowly when the vesicles approach and escape from the pore but rises sharply when they are passing through the pore. The competition of membrane surface potential, fluid resistance, and pore restriction cause the deformation of the vesicles to peak over the course of migration. Our work is believed to lay a theoretical foundation for the migration, rotation, and deformation of vesicles, thus providing valuable information for such applications as drug carrier and the experimentation on biofilm simulation.

In-situ monitoring of polyelectrolytes adsorption kinetics by electrochemical impedance spectroscopy: Application in fabricating nanofiltration membranes via layer-by-layer deposition

We herein report a novel approach based on electrochemical impedance spectroscopy (EIS) for in-situ monitoring of the adsorption kinetics in preparing polyelectrolyte multilayer nanofiltration membranes using layer-by-layer (LbL) deposition. Unlike existing methods for monitoring adsorption kinetics, this new approach is non-destructive and applicable to various substrates (as it does not use the substrate as a sensor). The model nanofiltration membrane used in this study is prepared by alternate depositions of Poly(diallyldimethylammonium chloride) and Poly(sodium 4-styrenesulfonate) on a polyacrylonitrile ultrafiltration membrane as the support. In each deposition step, the EIS measurements yield two important parameters, including the interfacial layer solution resistance and the film resistance, for probing the extent of polyelectrolyte deposition and membrane performance. The extent of polyelectrolyte deposition as probed by the EIS measurements is well corroborated by independent measurements of the membrane surface potential and the nanofiltration performance including water permeability and Na2SO4 rejection. This EIS-based approach enables the optimization of membrane fabrication using LbL deposition by conveniently identifying the minimum deposition time required to attain surface saturation.

Charge-trapping-blocking layer for enhanced triboelectric nanogenerators

Abstract The paramount parameters to determine the electrical output of triboelectric nanogenerator (TENG) are the surface triboelectric charges and the electrostatic induced transferred charges between triboelectric layer and electrode. However, diffusion of surface charge into the triboelectric layer reduces the surface charge density and thus weakens the electrostatic induction effect. In this work, we present a multifunctional layered TENG (ML-TENG) with an addition of reduced graphene oxide and Ag nanoparticles hybrid layer between a PVDF membrane triboelectric layer and bottom Al electrode to trap and block the interfacial charges. The output performance of ML-TENGs significantly yields 50 μC m−2 in charge density, which is improved by 500% compared with that of a traditional TENG. The surface potential of the PVDF membrane before triboelectrification drops with the insertion of the rGO-AgNPs hybrid layer, demonstrating the larger triboelectric potential difference and a better output performance. The trapping effect of rGO caused by sp2-hybrid structured carbon-atom coupled with the enhanced polarization effect by AgNPs to prevent interfacial charges from diffusing and drifting, providing efficient enhancements in TENG output. The output peak power from the TENG with a rGO-AgNPs hybrid layer reaches approximately 5.4 mW, which is 67.5 times that of a pristine TENG. Finally, the mechanism of the rGO-AgNPs layer working as the charge-trapping-blocking sites has been investigated and elaborated. It is anticipated to offer a new insight to the material science and device structure design for improving the performance of triboelectric devices.

Modeling and on-line measurement of the surface potential of electrospun membranes for the control of the fiber diameter and the pore size

Electrospinning is a widespread technology enabling the fabrication of nanofibrous materials for a wide range of applications, some of them on an industrial scale. It is shown that the online measurement of the surface potential V located over the nanofibrous membrane gives useful information on the ongoing process and on the local fibrous morphology. A model is proposed to describe the kinetics of the evolution of V during electrospinning and its decay once the production is stopped. In the case of poly(lactic acid) nanofibers, whatever the tested processing conditions, the surface potential is shown to rely on the fiber diameter and the inter-fibers pore size. A scaling law is proposed ϕf ∝τdV/dt0,21 showing that the fiber diameter ϕf is a function of the time τ, characteristic of the initial behavior of the surface potential, and the slope dV/dt measured at the steady state. In combination with the current measurement, it is an efficient and robust method for the online monitoring of the process of electrospinning. Furthermore, the method gives information on the residual charges stored in the fibrous material which is an important feature for the elaboration, by electrospinning in-situ charging, of electrets for filtering applications.

Rapid bacteria trapping and killing of metal-organic frameworks strengthened photo-responsive hydrogel for rapid tissue repair of bacterial infected wounds

During the wound healing process, it is necessary to protect the tissue from bacterial infections and other external damage in environment. Functional artificial hydrogels as suitable wound dressings to act as barriers have attracted more and more attention. In the study described herein, quaternary ammonium and double-bond modified chitosan and metal–organic framework (MOF) particles (Prussian blue nanoparticles [PBNPs]) were used to synthesize photosensitive hydrogels through free radical polymerization. The synthesized hydrogels exhibited excellent photothermal properties under 808 nm near-infrared (NIR) light irradiation due to the existence of PBNPs, which could absorb NIR light and produce light due to the charge transfer between Fe3+ and Fe2+ in the structure. The hydrogels can capture the bacteria tightly by electrostatic absorption. During this course, the normal metabolism of bacteria was inhibited due to the perturbation of the surface potential of the bacterial membrane and the subsequent inhibition of bacterial respiration, which led to the highly effective, rapid killing of bacteria together with the synergistic action of photothermal effects. The antibacterial ratio of the hydrogels could reach up to 99.97% and 99.93% against Staphylococcus aureus and Escherichia coli, respectively. Furthermore, PBNPs particles were also able to strengthen the mechanical property of the hydrogel through the interfacial interaction between the chitosan polymer and the PBNPs. The synthesized hydrogels also showed good in vitro biocompatibility and excellent in vivo antibacterial properties with no damage to the major organs. Thus, the synthesized hydrogels have great potential as a safe and efficient wound dressing.

Exosome-associated polysialic acid modulates membrane potentials, membrane thermotropic properties, and raft-dependent interactions between vesicles.

In mammals, polysialic acid (polySia) attached to a small number of transmembrane protein carriers occurs on the surface of plasma membranes of neural, cancer, immune, and placental trophoblast cells. Here, our goal was to demonstrate the presence of polySia on exosomes and its effect on membrane properties. We isolated exosomes and found that polysialylated exosomes in fetal bovine serum originate mostly from placental trophoblasts, while in calf bovine serum, they originate from immune cells. Enzymatic removal of polySia chains from the exosomal surface makes the membrane surface potential more positive, transmembrane potential more negative, and reduces the activation energy for membrane anisotropy changes. We demonstrate for the first time that exosomes could interact through polySia-raft interactions. We suggest that polysialylation of exosomal membrane can have a thermo-protecting effect and can modulate exosome-plasma membrane interactions.

Improvement of PVDF nanofiltration membrane potential, separation and anti-fouling performance by electret treatment

Electret treatment was a simple method to enhance the charge-electrode properties of polyvinylidene fluoride (PVDF) materials due to the increase of space charge and polarization charge of PVDF materials. The polarization charge was due to the electric dipole orientation change in loose nanofiltration PVDF membrane, which increased the electric dipole moment and improved the polarity of surface potential. Importantly, electret charges were less affected by ambient humidity. Therefore, the electret treatment could improve the surface negative potential of loose nanofiltration PVDF membrane, so as to improve its anti-fouling performance under certain conditions. Based on the above theoretical analysis, the influence and mechanism of the electret treatment on the surface potential, morphology, structure, hydrophilicity and anti-pollution performance of PVDF membrane were studied in this manuscript. When the electret time was 7.5 min and the electret voltage was 30 kV, the surface negative potential was the highest. The content of β phase crystals was 39.1%, which was 12.18% higher than that of untreated membrane. In addition, the surface morphology of PVDF membrane did not change significantly, but the water contact angle decreased slightly, and the pore size increased by 0.36–0.75 nm. Importantly, the flux and the rejection of dye and BSA increased to some extent, and the maximum rejection rate and water flux were increased by 10.34% and 20.25%, respectively. Through the cyclic filtration test and analysis, the anti-fouling performance of membrane was increased due to electrostatic repulsion.

Effects of Cation Binding to the Intracellular Vestibule of TMEM16 Ion Transport Pathways

TMEM16A and TMEM16F are prototype molecules for the two functional categories of TMEM16 family members, respectively, Ca2+-activated chloride channels and phospholipid scramblases. Upon binding of sub-µM to low µM intracellular Ca2+, TMEM16A conducts anionic currents while TMEM16F is permeable to both cations and anions. In this study, we found another divalent cation, Co2+, while unable to induce current in TMEM16A, inhibits the Ca2+-induced current via competing with Ca2+ for the high-affinity (sub-µM to low µM) channel activation sites. In addition, Co2+ also potentiates the TMEM16A current induced by Ca2+. All alkaline earth divalent cations, including Ca2+ itself, can generate this current potentiation with low affinities—at least hundreds of µM to mM concentrations are required for observing the effect. On the other hand, divalent cations at mM concentrations generate very little potentiation in TMEM16F, likely because the changes in local anion and cation concentrations caused by divalent cation bindings cancel out each other. Nonetheless, divalent cations change the cation/anion selectivity for the TMEM16F current conduction. Manipulating membrane phospholipids alters this low-affinity effect of divalent cations. Recent studies have shown that membrane phospholipids participate in various gating and permeation functions of TMEM16 molecules. Our results suggest that intracellular divalent cations bind to membrane phospholipids with a low affinity to alter the electrostatic potential near or in the ion-transport pathways of TMEM16 molecules. Monovalent cations and polyamine molecules also exert similar effects, although with different apparent affinities. The physiological significance of the TMEM16 current modulation by altering membrane surface potential will be discussed.

Electrostatics at Peptide-Lipid Interface in Nano-Bio Hybrid Systems by Spin-Labeling EPR

The ionization states of individual amino acid residues of membrane proteins are difficult to decipher or assign directly in the lipid membrane environment. The effective pK(a) values of protein groups are determined by a complex interplay between local polarity, Coulomb interactions, and a structural reorganization. The analysis is further complicated by the dearth of information about gradients in polarity, electric potentials, and hydration at the protein-membrane interface. The goal of our work is to develop spin-labeling EPR methods for assessing effects of membrane surface potential, local environment at the protein-membrane interface, and water penetration along this interface on effective pK(a) of membrane-burred ionisable groups. In this work we report on developing pH-sensitive ionizable EPR labels and related methods to 1) profile a heterogeneous dielectric environment along the α-helix of a WALP peptide integrated in a lipid bilayer; 2) asses the effect of solid support, specifically silica nanoparticles, on effective pK(a) of membrane-burred ionisable sidechains; and 3) use DEER to assess the location of spin-labeled sidechains. pH-sensitive EPR labels were attached to cysteine residues positioned at various depth within lipid bilayers at the peptide-lipid interface. We have shown that effective pK(a) of membrane-burred sidechain can be significantly shifted by varying the membrane surface charge density. The silica support exerted pronounced effects on WALP dynamics and the effective pK(a) of the ionizable probe. It was demonstrated that the silica nanoparticles shift the effective pK(a) of the ionizable nitroxide probe in a membrane depth-dependent manner. Upon protonation of the membrane-burred model ionisable sidechain the silica support caused significant changes in the membrane association of WALP peptide that is not observed when WALP is integrated into unilamellar phospholipid vesicles of similar curvature.Supported by NSF 1508607 to TIS.

Proteomic mechanism of decabromodiphenyl ether (BDE-209) biodegradation by Microbacterium Y2 and its potential in remediation of BDE-209 contaminated water-sediment system

The investigation of BDE-209 degradation by Microbacterium Y2 under different condition was conducted. Cell membrane permeability, cell surface hydrophobicity (CSH), membrane potential (MP) and reactive oxygen species (ROS) production were altered under BDE-209 stress. Eleven debrominated congeners were identified, suggesting that BDE-209 biodegradation by Microbacterium Y2 was dominantly a successive debromination process. Proteome analysis showed that the overexpression of haloacid dehalogenases, glutathione S-transferases (GSTs) and ATP-binding cassette (ABC) transporters might occupy important roles in BDE-209 biotransformation. Meanwhile, heat shock proteins (HSPs), ribonuclease E, oligoribonuclease (Orn) and ribosomal protein were activated to counter the BDE-209 toxicity. The up-regulated pyruvate dehydrogenase E1 component beta subunit and dihydrolipoamide dehydrogenase suggested that the pyruvate metabolism pathway was activated. Bioaugmentation of BDE-209 polluted water-sediments system with Microbacterium Y2 could efficiently improve BDE-209 removal. The detection of total 16S rRNA genes in treatment system suggested that Microbacterium (25.6 %), Luteimonas (14.3 %), Methylovorus (12.6 %), Hyphomicrobium (9.2 %) were the dominant genera and PICRUSt results further revealed that the diminution of BDE-209 was owed to cooperation between the introduced bacteria and aboriginal ones.

How Well Can You Tailor the Charge of Lipid Vesicles?

Knowledge and control of surface charge or potential is important for tailoring colloidal interactions. In this work, we compare widely used zeta potential (ζ) measurements of charged lipid vesicle surface potential to direct measurements using the surface force apparatus (SFA). Our measurements show good agreement between the two techniques. On varying the fraction of anionic lipids dimyristoylphosphatidylserine (DMPS) or dimyristoylphosphatidylglycerol (DMPG) mixed with zwitterionic dimyristoylphosphatidylcholine (DMPC) from 0 to 100 mol % we observed a near-linear increase in membrane surface charge or potential up to 20-30 mol % charged lipids beyond which charge saturation occurred in physiological (high) salt conditions. Similarly, in low salt concentrations, a linear increase in charge/potential was found but only up to ∼5-10 mol % charged lipids beyond which the surface charge or potential leveled off. While a lower degree of ionization is expected due to the lower dielectric constant (ε ∼ 4) of the lipid acyl chain environment, increasing intramembrane electrostatic repulsion between neighboring charged lipid head groups at higher charge loading contributes to charge suppression. Measured potentials in physiological salt solutions were consistent with predictions using the Gouy-Chapman-Stern-Grahame (GCSG) model of the electrical double layer with Langmuir binding of counterions, but in low salt conditions, the model significantly overestimated the surface charge/potential. The much lower ionization in low salt (maximum ∼1-2% of total lipids ionized) instead was consistent with counterion condensation at the bilayer surface which limited the charge that could be obtained. The strong interplay between membrane composition, lipid headgroup ionization, electrolyte concentration, and solution pH complicates exact prediction and tuning of membrane surface charge for applications. However, the theoretical frameworks used here can provide guidelines to understand this interplay and establish a range of achievable potentials for a system and predict the response to triggers like pH and salt concentration changes.

“Linking microstructure of membranes and performance”

This work addresses the important link between the microstructure of a membrane and its filtration performance. 2D computational fluid and particle drag mechanics are combined with particle and membrane force measurements in aqueous solutions containing inorganic ions to study particle intrusion and capture in microporous commercial polymer and computer-generated teardrop membranes. Fits of the DLVO theory to force-distance profiles obtained membrane surface potentials needed for the computations. In silico predictions of particle intrusion for a commercial membrane qualitatively agree with experimental filtration measurements using scanning electron microscopy with particle tracking via energy dispersive X-ray spectroscopy. Highlighting the poor flow field, several dominant inhomogeneous 2D flow conduits with large unused regions of the internal pore structure are discovered. To guide improved design, new computer-generated microporous teardrop structures that can equalize the flow field, adjust the tortuosity of the flow path and vary the reactivity of the surface were tested in silico. The main assumptions of the computational model were that 2D flows are a valid description of 3D flows, all forces were applied at the particle center of mass, forces were calculated based on the physical diameter of the spherical particles. Relatively large pores (~5 μm) and large particles (~1 μm) were selected for easy detection and analysis. However, the computational fluid and particle flow analysis and the inter-surface forces scale independently with size and should apply at all classical dimensions (i.e. for nano, ultra and microfiltration). Assumptions for the intermolecular force measurements were that electrostatic and van der Waal's forces dominated and hence that the DLVO theory was valid and that the zeta potential values were close to those at the wall (i.e. surface potential). In particular the DLVO was applied to ideal geometries: a sphere (i.e. AFM probe) near to a flat surface (i.e. either a silica wafer or a hot pressed PES membrane). To our knowledge, this is the first attempt combining particle drag mechanics with intermolecular force measurements to help explain particle dynamics in synthetic membranes. This computational fluid mechanics-based tool can be used to characterize membranes for separation performance and guide improved design, synthesis and testing of new microporous membranes.

CDs@ZIF-8 Modified Thin Film Polyamide Nanocomposite Membrane for Simultaneous Enhancement of Chlorine-Resistance and Disinfection Byproducts Removal in Drinking Water.

Reverse osmosis (RO) is an emerging membrane technology for disinfection byproducts (DBPs) removal. However, the chlorine-resistance and DBPs removal performance of thin film composite (TFC) polyamide membranes should be simultaneously improved when used in chlorinated drinking water. This study was dedicated to synthesize a novel nanoparticle of ZIF-8 with carbon dots (CDs@ZIF-8) and then modify thin film nanocomposite (TFN) membranes to enhance their performance in removing four trihalomethanes (THMs), four haloacetonitriles (HANs), and two haloketones (HKs) in chlorinated drinking water. The fabricated CDs@ZIF-8 nanoparticles and TFN membranes were characterized by FESEM, AFM, XPS, water contact angle, membrane surface potential, and a three-dimensional excitation-emission matrix (EEM) to investigate the influences of CDs@ZIF-8 on TFN membranes. After chlorination, percentage reduction in salt rejection of the CDs@ZIF-8 TFN membranes was lower than that of the TFC membranes due to hydrogen bonding between CDs and polyamide, replacing amidic hydrogen with chlorine, rendering the membrane less susceptible to chlorine attack and enhancing chlorine-resistance. Results also showed that the rejection of DBPs in chlorinated drinking water by CDs@ZIF-8 TFN membranes was more than 95%. The large surface area and abundant oxygen-containing groups of CDs@ZIF-8 made the nanoparticle act as a nanocarbon filler with high adsorption capacity of DBPs. The enhanced performances of chlorine-resistance and DBPs removal by CDs@ZIF-8 TFN membranes determined in this study provided valuable insights on the DBPs control in chlorinated drinking water by RO membranes.

An Electrophysiological Approach to Measure Changes in the Membrane Surface Potential in Real Time

Biological membranes carry fixed charges at their surfaces. These arise primarily from phospholipid headgroups. In addition, membrane proteins contribute to the surface potential with their charged residues. Membrane lipids are asymmetrically distributed. Because of this asymmetry, the net-negative charge at the inner leaflet exceeds that at the outer leaflet. Changes in surface potential are predicted to give rise to apparent changes in membrane capacitance. Here, we show that it is possible to detect changes in surface potential by an electrophysiological approach; the analysis of cellular currents relies on assuming that the electrical properties of a cell are faithfully described by a three-element circuit (i.e., the minimal equivalent circuit) comprised of two resistors and one capacitor. However, to account for changes in surface potential, it is necessary to add a battery to this circuit connected in series with the capacitor. This extended circuit model predicts that the current response to a square-wave voltage pulse harbors information, which allows for separating the changes in surface potential from a true capacitance change. We interrogated our model by investigating changes in the capacitance induced by ligand binding to the serotonin transporter and to the glycine transporters (GlyT1 and GlyT2). The experimental observations were consistent with the predictions of the extended circuit. We conclude that ligand-induced changes in surface potential (reflecting the binding event) and in true membrane capacitance (reflecting the concomitant conformational change) can be detected in real time even in instances in which they occur simultaneously.

Electrochemical characterization of mixed matrix electrodialysis cation exchange membrane incorporated with carbon nanofibers for desalination

A new type of electrodialysis mixed matrix (MM) cation exchange membrane was prepared by incorporating carbon nanofibers (CNFs) into membrane matrix. The microscopy images showed uniform surface for the membrane relatively. The use of CNFs into membrane body enhanced membrane surface hydrophilicity, potential, transport number, permselectivity, and ionic conductivity obviously, while water uptake decreased. The sodium flux was also enhanced by incorporation of CNFs into membrane matrix from 0 to 0.5%wt and 2 to 8%wt, while declined for the samples in the range of 0.5 to 2%wt CNF ratios. Compared to pristine membrane, a smoother surface was observed for PVC-CNF membrane. Electrodialysis showed the (K+/Na+) flux ratio about 2.14. The transport mechanism of K+ and Na+ ions through the membranes discussed by considering ionic and hydrated radius, hydration potential, hydration free energy, entropy of hydration, and the Jones-Dole coefficient. Optimal performance was achieved for PVC-0.5%wt CNF membrane.

Characterization of Mitochondrial Bioenergetics of Adipose‐Derived Stem Cells from Burned and Non‐burned Patients

Prolonged hypermetabolism is a hallmark of severe burn injury (over 20% of the total body surface area) that produces cachexia and hinders the wound healing process. Topical treatment with adipose‐derived stem cells (ASCs) have been proposed as an attractive solution to hasten the recovery of burn wounds. A potentially viable source of ASC is from the subcutaneous adipose tissue of severely burned patients, which would normally be discarded during surgical debridement. While previous studies found that severe burn injury alters the metabolic profile of subcutaneous adipocytes, the effect of severe burns on ASCs from burned victims is largely unknown. The purpose of this study is to compare the metabolic activity of ASCs from burned patients to those from non‐burned abdominoplasty patients by analyzing mitochondrial respiration and glycolysis. ASCs were isolated from adipose tissues from severely burned patients (BP, n=6) and abdominoplasty patients (AP, n=6). Cells were cultured to 80% confluence and harvested at at passage 2, 4, and 6 for analysis. Flow cytometry was used to determine ASC cell surface markers CD90, CD105, and CD73 and negative for CD34, CD11, CD19 and CD45. Mitochondrial abundance and reactive oxygen species (ROS) production were determined with MitoTracker Green and MitoSOX Red, respectively. JC‐10 Mitochondrial Membrane Potential Assays were used to determine mitochondrial membrane integrity. Mitochondrial respiration and glycolysis were analyzed in technical quadruplicates by a Seahorse XFe24 Analyzer. No significant differences were found in ASC surface markers, mitochondrial abundance or membrane potential among passages or between groups. A two‐way ANOVA showed that there was a significant effect (p<0.01) of passage number on mitochondrial ROS production. Mitochondrial respiratory states Basal, Leak (uncoupled), and Non‐mitochondrial respiration was significantly higher (p<0.05) at passage 6 than passage 2 for BP, but not AP. Additionally, Basal respiration was significantly higher at passage 6 in BP than AP (63.5±3.49 vs 45.7±4.26 pmol O2/min, p<0.001). Glycolysis significantly decreased (p<0.05) from passage 4 to 6 in AP but not BP ASCs. In summary, BP ASCs showed increased mitochondrial respiration with increasing passages and basal respiration was higher than AP ASCs patients at passage 6. While all ASCs retained their stem cell properties, they also showed increased ROS production through multiple passages which may cause oxidative stress that could limit the expansion of these cells ex vivo. The elevated mitochondrial activity from ASCs of burned patients may suggest these cells are more metabolically primed than those from abdominoplasty patients, but whether this thwarts their therapeutic potential requires additional investigation. Adipose‐derived stem cells from burned injured patients remain a potential viable source for burn wound therapies. While other studies have demonstrated efficacy in healing burn wounds, this study uncovers potential limitations in expansion of these cells ex vivo to use as coverage options for burned victims.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A bipolar electret-based micro-vibration-driven energy harvester with multi-air-gap structure

Micro mechanical energy harvester as a kind of micro power source for micro electro mechanical systems (MEMS) has been paid considerable attention. Electret-based vibration energy harvester (E-MVEH) has been a research highlight due to its high sensitivity, simplicity and compatibility to the fabrication process of MEMS. In this manuscript, a novel E-MVEH with multiple-air-gap structure based on bipolar electrets is comparatively investigated. The E-MVEH with single-air-gap structure consists of an electret membrane (EM) with an electrode on one surface and a counter-electrode supported by means of micro-springs. The E-MVEH with double air gaps is made of a bipolar electret membrane put in the middle of two counter-electrodes that are supported by means of micro-springs. It is essentially equivalent to two variable capacitors in series. The E-MVEH with four air gaps consists of two double-air-gaps E-MVEH in parallel connection. When an external vibration causes a relative displacement between the electret membrane (EM) and the counter-electrode, the capacitance varies, leading to re-organization of the charges on the counter-electrode. Thus, an alternating current is generated and the vibration energy is converted into electric energy. This alternating current can be changed into direct current through a full bridge rectifier. The bipolar EM used in this study is a sandwich FEP/THV/FEP perfluoropolymer EM reported previously by our group. It can display persistent and strong electrostatic field with both polarities on the top and bottom surface, respectively. The experimental results of the output characteristic for the proposed E-MVEH show that there exists a resonant frequency in the vibration frequency range of 30−180 Hz, at which the open-circuit voltage and short-circuit current and hence the output power reach their respective maximum. The resonant frequency moves towards the low frequency with increasing vibration intensity, whereas the effect of air-gap number on the resonant frequency is rather small. On the basis of experimental results and theoretical analysis, the maximum output power is positively correlated to the vibration driving force, the surface potential and the area of the electret membrane, and the air-gap number. When the surface potential of the electret membrane is 1200±50 V, the maximum output power is only 0.19 μW for single-air-gap structure and reaches 27.02 μW for the four-air-gap structures under a vibration driving force of 0.5 N and a load resistance of 55 MΩ. For the four-air-gap structures, the maximum output power increases to 59.12 μW when the surface potential of the electret membrane increases to 2150 V. The multi-air-gap energy harvester fabricated with bipolar electret membrane can produce larger variable capacitance; therefore, the output power is significantly enhanced. This novel E-MVEH provides an up-to-date strategy for the design of self-powered sensor systems.