Membrane Surface Potential Research Articles

Charge characteristics of co-electrospun nanofiber membranes and their application in high-humidity environment

Enhancing the charge density and charge stability is an important approach to improve the filtration performance of electrospun nanofiber air filters. In the present study, the polymers with different electron transport capabilities were co-electrospun in pairs to prepare charge-enhanced nanofiber membranes. The results showed that the average surface potential of the interfacial regions of polyamide 6 (PA6) and polyvinyl chloride (PVC) nanofibers was 165 mV, which was substantially higher than the non-intersection area of nanofibers. The charges induced by the contact-induced electrification between nanofibers accumulated in the intersection area of the hybrid nanofibers, which contributed to the high surface potential of the nanofiber membranes. Moreover, the co-electrospinning of polymers allowed the positively charged PA 6 nanofibers and negatively charged PVC nanofibers to coexist in the nanofiber membranes. Benefiting from these charge characteristics, the co-electrospun PA 6/PVC nanofiber membranes exhibited an average filtration efficiency of 99.73 % for 50–500 nm particles at the face velocity of 5.3 cm/s, and the pressure drop was 130 Pa. A hydrophilic fiber layer was employed to mitigate the influence of humidity on the charge decay and pressure drop growth of thenanofiber membrane. The growth rate of pressure drop of the protected nanofiber membrane was as low as 0.95 Pa/min under the challenge of water droplets. In contrast, the growth rate of pressure drop for common membrane based filters was in the range of 5–120 Pa/min. Additionally, the color of the hydrophilic layer changed corresponding to the water content in the air filters, which could serve as an indicator for the filter service life visible to naked eyes. This study provides a new approach for charging nanofiber membranes and improving their filtration performance stability in practical applications.

Effect of colloidal magnetite (Fe3O4) nanoparticles on the electrical characteristics of the azolectin bilayer in a static inhomogeneous magnetic field

This work is devoted to the study of the combined effects of applied magnetic field and MNPs on the electrical characteristics of bilayer lipid membranes. We present results of the study of electrical parameters of azolectin membranes in a static inhomogeneous magnetic field at the one-sided addition of positively charged quasi-spherical superparamagnetic magnetite nanoparticles with a diameter of about 4 nm. The magnet was located at different distances from the membrane, and the magnetic field attracted the nanoparticles to the membrane surface with different strengths. We observed three pronounced effects that depended on the external magnetic field. Firstly, after addition of nanoparticles in a magnetic field, the conductance of the membranes increased. A smooth increase in conductance was accompanied in some cases by the appearance of current jumps, which can be associated with the formation of through pores with a radius of no more than 1 nm. The conductance increased with increasing magnetic field gradient. Secondly, at zero command voltage, a negative current through the membrane was observed. Although our experiments did not allow us to unambiguously determine which particles create this current, we believe that this current is associated with the penetration of particles through the membrane. This effect intensified with increasing magnetic field gradient. Thirdly, we observed a sharp change in the nonlinear dependence of capacitance on voltage associated both with the change in the surface potential of the azolectin membrane and with the effect of MNP binding to the membrane surface on the apparent membrane capacitance.

HIV-1 Gag Polyprotein Affinity to the Lipid Membrane Is Independent of Its Surface Charge.

The binding of the HIV-1 Gag polyprotein to the plasma membrane is a critical step in viral replication. The association with membranes depends on the lipid composition, but its mechanisms remain unclear. Here, we report the binding of non-myristoylated Gag to lipid membranes of different lipid compositions to dissect the influence of each component. We tested the contribution of phosphatidylserine, PI(4,5)P2, and cholesterol to membrane charge density and Gag affinity to membranes. Taking into account the influence of the membrane surface potential, we quantitatively characterized the adsorption of the protein onto model lipid membranes. The obtained Gag binding constants appeared to be the same regardless of the membrane charge. Furthermore, Gag adsorbed on uncharged membranes, suggesting a contribution of hydrophobic forces to the protein-lipid interaction. Charge-charge interactions resulted in an increase in protein concentration near the membrane surface. Lipid-specific interactions were observed in the presence of cholesterol, resulting in a two-fold increase in binding constants. The combination of cholesterol with PI(4,5)P2 showed cooperative effects on protein adsorption. Thus, we suggest that the affinity of Gag to lipid membranes results from a combination of electrostatic attraction to acidic lipids, providing different protein concentrations near the membrane surface, and specific hydrophobic interactions.

A “like-zwitterionic” forward osmosis membranes with electrostatic deposition of aluminosilicate nanotubes for resisting positively and negatively charged protein and oil contaminant

Membrane fouling has always been a huge obstacle to the development of membrane separation technology, including forward osmosis (FO) technology. In this work, polyamide (PA) thin-film composite (TFC) membranes were simply immersed in aluminosilicate nanotubes (ANTs) dispersions to obtain thin-film nanocomposite (TFN) FO membranes. With the help of the opposite surface charge of ANTs and PA layer, and the representative “peak-valley” structure of PA TFC membrane, ANTs are stably bound to the surface of TFC membrane by electrostatic adsorption and physical confinement. The TFN membrane has greatly enhanced hydration ability due to the rich hydrophilic hydroxyl groups of ANTs, “like-zwitterionic” surface composition and rough nanostructure morphology, resulting in good underwater superoleophobicity. Combined with the water transport channel formed by its nanoporous structure, the surface anti-protein adhesion and anti-oil–water emulsion adhesion can be achieved without affecting the water flux. It is worth noting that the surface potential of TFN membrane is close to neutral due to charge neutralization. This avoids the electrostatic interaction between the membrane surface and the contaminant, and further achieves a universal anti-fouling ability that is not affected by protein or emulsion charge, and the irreversible adsorption is close to zero. In addition, the rigid ANTs coating exhibits excellent stability and reusability under long-term use, and the water flux after cleaning can be restored to nearly 99.9%. In general, this method of using ANTs deposition to improve the antifouling performance of PA based TFC membrane is simple, efficient, stable, and easy scalable. This method is not only limited to FO membrane, but also can be extended to PA based reverse osmosis and nanofiltration membranes, which has great practical application potential.

Plasma‐oxidized 2D MXenes subnanochannel membrane for high‐performance osmotic energy conversion

AbstractNanofluidic channels inspired by electric eels open a new era of efficient harvesting of clean blue osmotic energy from salinity gradients. Limited by less charge and weak ion selectivity of the raw material itself, energy conversion through nanofluidic channels is still facing considerable challenges. Here, a facile and efficient strategy to enhance osmotic energy harvesting based on drastically increasing surface charge density of MXenes subnanochannels via oxygen plasma is proposed. This plasma could break Ti–C bonds in the MXenes subnanochannels and effectively facilitate the formation of more Ti–O, C═O, O–OH, and rutile with a stronger negative charge and work function, which leads the surface potential of MXenes membrane to increase from 205 to 430 mV. This significant rise of surface charge endows the MXenes membrane with high cation selectivity, which could make the output power density of the MXenes membrane increase by 248.2%, reaching a high value of 5.92 W m−2 in the artificial sea‐river water system. Furthermore, with the assistance of low‐quality heat at 50°C, the osmotic power is enhanced to an ultrahigh value of 9.68 W m−2, which outperforms those of the state‐of‐the‐art two‐dimensional (2D) nanochannel membranes. This exciting breakthrough demonstrates the enormous potential of the facile plasma‐treated 2D membranes for osmotic energy harvesting.

AZD8055 Is More Effective Than Rapamycin in Inhibiting Proliferation and Promoting Mitochondrial Clearance in Erythroid Differentiation

Background: As an important downstream effector of various signaling pathways, mTOR plays critical roles in regulating many physiological processes including erythropoiesis. It is composed of two distinct complexes, mTORC1 and mTORC2, which differ in their components and downstream signaling effects. Our previous study revealed that the inhibition of mTORC1 by rapamycin significantly repressed the erythroid progenitor expansion in the early stage but promoted enucleation and mitochondria clearance in the late stage of erythroid differentiation. However, the particular roles and differences of mTORC1 and mTORC2 in the regulation of erythropoiesis still remain largely unknown. In the present study, we investigated the comparative effects of dual mTORC1/mTORC2 mTOR kinase inhibitor AZD8055 and mTORC1 inhibitor rapamycin on erythroid differentiation in K562 cells induced by hemin and erythropoiesis in β‐thalassemia mouse model.Materials and Methods: In vitro erythroid differentiation model of hemin‐induced K562 cells and β‐thalassemia mouse model were treated with AZD8055 and rapamycin. Cell Counting Kit‐8 was used to detect cell viability. The cell proliferation, cell cycle, erythroid surface marker expression, mitochondrial content, and membrane potential were determined and analyzed by flow cytometry and laser scanning confocal microscopy. Globin gene expression during erythroid differentiation was measured by RT‐qPCR. The mTORC2/mTORC1 and autophagy pathway was evaluated using western blotting.Results: Both AZD8055 and rapamycin treatments increased the expression levels of the erythroid differentiation‐specific markers, CD235a, α‐globin, γ‐globin, and ε‐globin. Notably, AZD8055 suppressed the cell proliferation and promoted the mitochondrial clearance of hemin‐induced K562 cells more effectively than rapamycin. In a mouse model of β‐thalassemia, both rapamycin and AZD8055 remarkably improve erythroid cell maturation and anemia. Moreover, AZD8055 and rapamycin treatment inhibited the mTORC1 pathway and enhanced autophagy, whereas AZD8055 enhanced autophagy more effectively than rapamycin. Indeed, AZD8055 treatment inhibited both mTORC2 and mTORC1 pathway in hemin‐induced K562 cells.Conclusion: AZD8055 is more effective than rapamycin in inhibiting proliferation and promoting mitochondrial clearance in erythroid differentiation, which might provide us one more therapeutic option other than rapamycin for ineffective erythropoiesis treatment in the future. These findings also provide some preliminary information indicating the roles of mTORC1 and mTORC2 in erythropoiesis, and further studies are necessary to dissect the underlying mechanisms.

Sulfonated graphene oxide modified polysulfone-polyamide forward osmosis membrane and its application in fluorine-containing wastewater treatment

In view of the low water flux and fluoride ion (F−) retention rate of forward osmosis emergency water bags in coal mine emergency rescue, sulfonated graphene oxide (SGO) is selected to modify the polysulfone-polyamide forward osmosis (FO) membrane to obtain high water flux and F−retention rate in this work. The results show that the crosslinking of m-phenylenediamine (MPD) improves the sulfonated graphene oxide (SGO) dispersion of the polyamide layer in the interfacial polymerization (IP) reaction, and the polyamide active layer with more hydrophilic and more water flux is obtained, and the increase in water flux is up to 6 times. Furthermore, the negatively charged SGO reduces the surface potential of the polyamide membrane, which significantly improves the F−retention effect of the high water flux FO membrane to 83.2 %. At the same time, the existence of Donnan's law leads to differences in the retention performance of different anions. Therefore, SGO-modified polysulfone-polyamide FO membrane presents excellent permeability performance, which provides a new combination of materials and technologies for fluorine-containing wastewater environmental emergency rescue and high-fluorine wastewater treatment.

Removal of heavy metal ions from acidic wastewater by constructing positively charged hollow fiber nanofiltration separating-layer based on Fe (III)/co deposition-quaternization

A surface positively charged nanofiltration (NF) membrane was successfully constructed to effectively remove heavy metal ions by co-deposition and quaternization strategy. The combination between Fe3+ and H2O2 accelerated the co-deposition of tannic acid (TA) and polyvinyl amine (PVAM) on the membrane surface. The mechanism by which metal ions accelerated co-deposition process to regulate membrane surface structure was elucidated. The convenient quaternary ammonium modification was carried out by reacting glycidyl trimethyl ammonium chloride (GTMAC), which significantly increased the potential and density of the membrane surface. The membrane had a high retention rate for heavy metal ions (1000 ppm (mg· L−1), Cr3+ (94.6 %), Fe3+ (93.7 %), Cu2+ (92.1 %), Ni2+ (90.2 %)), while maintaining an excellent water permeance (27.8 L m−2 h−1 bar−1). The membrane also presented outstanding separation performance for rare earth metal ion. In particular, the retention rate for 500 ppm (mg·L−1) Ce3+ was 95.3 %. The relationship between membrane surface potential, pore size and rejection of heavy metal revealed the removal mechanism. Furthermore, the membrane exhibited excellent acid-base resistance and long-term operation stability. This study supplies an effective surface modification method for preparing hollow fiber NF membranes used for removing heavy metal and recovering rare earth metal from wastewater.

Kinetics of Nisin-Induced Pore Formation in Giant Unilamellar Vesicles.

We have studied the kinetics of pore formation in giant unilamellar vesicles (GUV) with the antimicrobial peptide nisin. The role of charged lipid composition in the rate of pore formation by nisin in the vesicle membrane is investigated using fluorescence microscopy. We propose a model and obtain an analytical expression for the variation in the fluorescence intensity of a GUV as a function of time. We find that the analytical equation fits well to the experimental data, and the membrane surface potential can be estimated from the fit parameters. We further show that the formation of multiple pores on the vesicle membrane is affected by the charged lipid composition of the membrane.

Resting membrane state as an interplay of electrogenic transporters with various pumps.

In this study, a new idea that electrogenic transporters determine cell resting state is presented. The previous assumption was that pumps, especially the sodium one, determine it. The latter meets difficulties, because it violates the law of conservation of energy; also a significant deficit of pump activity is reported. The amount of energy carried by a single ATP molecule reflects the potential of the inner mitochondrial membrane, which is about -200 mV. If pumps enforce a resting membrane potential that is more than twice smaller, then the majority of energy stored in ATP would be dissipated by each pump turning. However, this problem could be solved if control is transferred from pumps to something else, e.g., electrogenic transporters. Then pumps would transfer the energy to the ionic gradient without losses, while the cell surface membrane potential would be associated with the reversal potential of some electrogenic transporters. A minimal scheme of this type would include a sodium-calcium exchanger as well as sodium and calcium pumps. However, note that calcium channels and pumps are positioned along both intracellular organelles and the surface membrane. Therefore, the above-mentioned scheme would involve them as well as possible intercellular communications. Such schemes where various kinds of pumps are assumed to work in parallel may explain, to a great extent, the slow turning rate of the individual members. Interaction of pumps and transporters positioned at distant biological membranes with various forms of energy transfer between them may thus result in hypoxic/reperfusion injury, different kinds of muscle fatigue, and nerve-glia interactions.

In situ activation of flexible magnetoelectric membrane enhances bone defect repair

For bone defect repair under co-morbidity conditions, the use of biomaterials that can be non-invasively regulated is highly desirable to avoid further complications and to promote osteogenesis. However, it remains a formidable challenge in clinical applications to achieve efficient osteogenesis with stimuli-responsive materials. Here, we develop polarized CoFe2O4@BaTiO3/poly(vinylidene fluoridetrifluoroethylene) [P(VDF-TrFE)] core-shell particle-incorporated composite membranes with high magnetoelectric conversion efficiency for activating bone regeneration. An external magnetic field force conduct on the CoFe2O4 core can increase charge density on the BaTiO3 shell and strengthens the β-phase transition in the P(VDF-TrFE) matrix. This energy conversion increases the membrane surface potential, which hence activates osteogenesis. Skull defect experiments on male rats showed that repeated magnetic field applications on the membranes enhanced bone defect repair, even when osteogenesis repression is elicited by dexamethasone or lipopolysaccharide-induced inflammation. This study provides a strategy of utilizing stimuli-responsive magnetoelectric membranes to efficiently activate osteogenesis in situ.

Modeling the Interaction and Uptake of Cd-As(V) Mixture to Wheat Roots Affected by Humic Acids, in Terms of root cell Membrane Surface Potential (ψ0).

The joint toxicological effects of Cd2+ and As(V) mixture on wheat root as affected by environmental factors, such as pH, coexisting cations, and humic acids etc., were investigated using hydroponic experiments. The interaction and toxicological mechanisms of co-existing Cd2+ and As(V) at the interface of solution and roots in presence of humic acid were further explored by incorporating root cell membrane surface potential ψ0 into a mechanistic model of combined biotic ligand model (BLM)-based Gouy-Chapman-Stern (GCS) model and NICA-DONNAN model. Besides, molecular dynamics (MD) simulations of lipid bilayer equilibrated with solution containing Cd2+ and H2AsO4- further revealed the molecular distribution of heavy metal(loid) ions under different membrane surface potentials. H2AsO4- and Cd2+ can be adsorbed on the surface of the membrane alone or as complexes, which consolidate the limitation of the macroscopic physical models.

Anti-fouling mechanism of ultrafiltration membranes modified by graphene oxide with different charged groups under simulated seawater conditions

There are positively charged Ca2+ and Mg2+, negatively charged colloids and lots of bacteria in seawater. The different surface potentials of ultrafiltration membranes may lead to different adsorption properties for contaminants in seawater when ultrafiltration membranes were applied to the pretreatment of Reverse Osmosis process. Herein, this work prepared modified ultrafiltration membranes with different surface potentials using three GO-based materials, and investigated the anti-fouling of Ca2+, Mg2+, humic acid, the anti-bacterial adhesion performance and mechanisms of modified ultrafiltration membranes under simulated seawater conditions. Results showed that the modified membranes exhibited enhanced hydrophilicity, anti-fouling performance, antibacterial property and permeability compared with the unmodified polyvinylidene fluoride membrane. Conspicuously, with the highest surface potential among all membranes, quaternized graphene oxide modified ultrafiltration membrane (QGO-M) presented the best anti-fouling property to Ca2+, Mg2+, humic acid and antibacterial property. In particular, the flux recovery rate against the simulated seawater solution containing humic acid and the surface bacteriostatic rate against salt-tolerant bacteria of QGO-M were 95.7% and 97.9%, respectively. The results can provide an important reference for the investigation of modified ultrafiltration membranes suitable for seawater filtration.

Facile and effectual surface modification of polyacrylonitrile (PAN)-based ultrafiltration membranes via manipulating the synergistic interaction of dopamine and enzymes

A drastic improvement in the overall permeability and antifouling performance was observed for the polyacrylonitrile (PAN) ultrafiltration (UF) membrane by the co-incorporation of dopamine (DA), protease (E1), and lipase (E2) in a facile multi-step synthetic scheme. SEM was utilized to indicate the successful formation of modifying layers on the membrane surface, whereas ATR-FTIR and zeta potential were used to provide deeper insight into the membrane surface chemistry. AFM and contact angle were used to assess the membrane's surface roughness and hydrophilicity, respectively. The optimally modified membrane surface was found to be quite hydrophilic, as indicated by the water contact angle value (39.8 ± 0.8°), and water flux across the membrane of 78.09 ± 1.6 kg/m2·h. Simultaneously, natural organic matter (NOM), including milk powder (MP), bovine serum albumin (BSA), and humic acid (HA), were efficiently removed, resulting in 99.9, 92.5, and 80.5 % removal efficiencies, respectively. Notably, the enzyme-immobilized membrane demonstrated outstanding antifouling performance as well as long-term stability. The dynamic anti-NOM fouling studies indicated that the surface modification was potentially capable of overcoming the tradeoff between membrane permeability and selectivity, resulting in FRR values of >90 %. The antibacterial properties of the surface-modified membranes against E. coli and S. aureus were also explored, and the optimal enzyme-immobilized membrane was found to be substantially antibacterial. Overall, this study aims to pave the way for the development of sustainable chemistry in designing innovative and highly efficient membranes.

Antifouling forward osmosis membranes by ε-polylysine mediated molecular grafting for printing and dyeing wastewater: Preparation, characterization, and performance

Membrane fouling during forward osmosis (FO) seriously affects the service life of the membrane and increases the treatment cost. A facile strategy was developed to mitigate membrane surface fouling and simultaneously achieve high pollutants rejection. The amino group on ε-Polylysine (PL) reacted covalently with the active sites (acyl chloride and carboxyl group) on the polyamide (PA), thereby grafting the ε-PL onto the PA active layer of PAN/LiCl supported membrane. Effects of membrane orientation, concentration of draw solution (DS), and pH of feed solution (FS) on pollutants rejection were investigated. Results showed that rejection efficiencies of TOC, Ca, Mg, Sb, Cr, and aniline in wastewater by the 0.5 wt% PL-grafted PAN-1.5LiCl TFC-FO membrane (FO-0.5 PL) attained 93.3%, 96.7%, 99.3%, 98.3%, 99.9%, and 99.8%, respectively. The high rejection efficiencies were mainly attributed to the improvement of the surface hydrophilicity of the grafted membrane, the reduction of the roughness, and the improvement of membrane surface potential. The microbubble-assisted cleaning experiment showed that the flux recovery efficiency of the FO-0.5 PL membrane could reach 98.8%, which is 6% higher than that of the FO-P membrane. The PL-grafted FO membrane simultaneously improves the stability of permeation flux (15.2 L m−2 h−1) and fouling resistance performance of the membrane. This study revealed that the PL grafted method can improve the antifouling performance of the membrane and can be used as a feasible treatment method for printing and dyeing wastewater. The research results provided a new idea for facile preparation and application of FO membranes and had a certain reference value for the development of antifouling FO membrane.

Ion Current Rectification and Long-Range Interference in Conical Silicon Micropores.

Fluidic devices exhibiting ion current rectification (ICR), or ionic diodes, are of broad interest for applications including desalination, energy harvesting, and sensing, among others. For such applications a large conductance is desirable, which can be achieved by simultaneously using thin membranes and wide pores. In this paper we demonstrate ICR in micrometer sized conical channels in a thin silicon membrane with pore diameters comparable to the membrane thickness but both much larger than the electrolyte screening length. We show that for these pores the entrance resistance is key not only to Ohmic conductance around 0 V but also for understanding ICR, both of which we measure experimentally and capture within a single analytic theoretical framework. The only fit parameter in this theory is the membrane surface potential, for which we find that it is voltage dependent and its value is excessively large compared to the literature. From this we infer that surface charge outside the pore strongly contributes to the observed Ohmic conductance and rectification by a different extent. We experimentally verify this hypothesis in a small array of pores and find that ICR vanishes due to pore-pore interactions mediated through the membrane surface, while Ohmic conductance around 0 V remains unaffected. We find that the pore-pore interaction for ICR is set by a long-ranged decay of the concentration which explains the surprising finding that the ICR vanishes for even a sparsely populated array with a pore-pore spacing as large as 7 μm.

Rapid Determination of Mercury Ions in Environmental Water Based on an N-Rich Covalent Organic Framework Potential Sensor

In this article, an N-rich covalent organic framework (COFTFPB-TZT) was successfully synthesized using 4,4′,4′-(1,3,5-triazine-2,4,6-triyl) trianiline (TZT), and 4-[3,5-bis (4-formyl-phenyl) phenyl] benzaldehyde (TFPB). The as-prepared COFTFPB-TZT possesses irregular cotton wool patches with a large specific surface area. A novel selective electrode based on COFTFPB-TZT was used for the determination of Mercury ions. The abundance of N atoms in COFTFPB-TZT provides more coordination sites for Hg2+ adsorption, resulting in a change in the surface membrane potential of the electrode to selectively recognize Hg2+. Under optimal experimental conditions, the ion-selective electrode shows a good potential response to Hg2+, with a linear range of 1.0 × 10−9∼1.0 × 10−4, a Nernst response slope of 30.32 ± 0.2 mV/-PC at 25°C and a detection limit of 4.5 pM. At the same time, the mercury-ion electrode shows a fast response time of 10 s and good reproducibility and stability. The selectivity coefficients for Fe2+, Zn2+, As3+, Cr6+, Cu2+, Cr3+, Al3+, Pb2+, NH4+, Ag+, Ba2+, Mg2+, Na+, and K+ are found to be small, indicating no interference in the detection system. The proposed method can be successfully applied to the determination of Hg2+ in 3 typical environmental water samples, with a recovery rate of 98.6–101.8%. In comparison with the spectrophotometric method utilizing dithizone, the proposed method is simple and fast and holds great potential application prospects in environmental water quality monitoring and other fields.

Electreted Sandwich Membranes with Persistent Electrical Stimulation for Enhanced Bone Regeneration.

Physiologically relevant electrical microenvironments play an indispensable role in manipulating bone metabolism. Although implanted biomaterials that simulate the electrical properties of natural tissues using conductive or piezoelectric materials have been introduced in the field of bone regeneration, the application of electret materials to provide stable and persistent electrical stimulation has rarely been studied in biomaterial design. In this study, a silicon dioxide electret-incorporated poly(dimethylsiloxane) (SiO2/PDMS) composite electroactive membrane was designed and fabricated to explore its bone regeneration efficacy. SiO2 electrets were homogeneously dispersed in the PDMS matrix, and sandwich-like composite membranes were fabricated using a facile layer-by-layer blade-coating method. Following the encapsulation, electret polarization was conducted to obtain the electreted composite membranes. The surface potential of the composite membrane could be adjusted to a bone-promotive biopotential by tuning the electret concentration, and the prepared membranes exhibited favorable electrical stability during an observation period of up to 42 days. In vitro biological experiments indicated that the electreted SiO2/PDMS membrane promoted cellular activity and osteogenic differentiation of mesenchymal stem cells. In vivo, the electreted composite membrane remarkably facilitated bone regeneration through persistent endogenous electrical stimulation. These findings suggest that the electreted sandwich-like membranes, which maintain a stable and physiological electrical microenvironment, are promising candidates for enhancing bone regeneration.

Protonation of model ionizable sidechains in transmembrane protein domains

The ionization states of individual amino acid residues of membrane proteins in lipid membrane environment are difficult to decipher or assign directly. The effective pK(a) values of protein groups are determined by a complex interplay between local polarity, Coulomb interactions, and structural reorganizations. The analysis is further complicated by the dearth of information about gradients in polarity, electric potentials, and hydration at the protein-membrane interface. In this work we report on a spin-labeling EPR method 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-buried ionizable groups.

Ultralight ethyl cellulose-based electret fiber membrane for low-resistance and high-efficient capture of PM2.5

Atmospheric particulate matter (PM) pollution is a serious threat to human health, so the preparation of electret films with high efficiency and low resistance capturing particulate has attracted wide attention. Herein, a strategy for the fabrication of all-polymer hybrid electret fiber membranes by electrospinning is reported based on the ethyl cellulose (EC) and polystyrene (PS). The preparation conditions of electret fiber membrane were optimized by focusing on the effect of the mass ratio of EC/PS and the spinning time on the structure, surface potential and purification performance of fiber membrane. The result showed that the fiber membrane has a low fiber diameter of 572 ± 113 nm and porosity of 82.4%, and a better potential stability when the EC/PS mass ratio was 2.5/1 and the spinning time was 10 min. As a result of the enhanced effect of electrostatic attraction on particle capture, the EC/PS composite electret membrane could make the purification efficiency of PM2.5 reach to100% within 11 min. Moreover, the EC/PS composite electret membrane has the properties of ultra-light base weight of 1.08 g·m −2 , low air resistance of 28 Pa and long service life. Therefore, the all-polymer EC/PS electret nanofiber membranes have broad application prospects in the field of air purification. • All-polymer electret EC/PS fibers without nanotoxicity are prepared. • Biomass-based electret based on ethyl cellulose as the main raw material increases the environmental friendliness of the material. • the fabricated electret fiber has an ultralight base weight. • the resultant electret fibers with high efficiency and low resistance can be compared with high efficiency air purification membrane.