Heterogeneous Membranes Research Articles

Dehydration of Lipid Membranes Drives Redistribution of Cholesterol Between Lateral Domains.

Cholesterol-rich lipid rafts are found to facilitate membrane fusion, central to processes like viral entry, fertilization, and neurotransmitter release. While the fusion process involves local, transient membrane dehydration, the impact of reduced hydration on cholesterol's structural organization in biological membranes remains unclear. Here, we employ confocal fluorescence microscopy and atomistic molecular dynamics simulations to investigate cholesterol behavior in phase-separated lipid bilayers under controlled hydration. We unveiled that dehydration prompts cholesterol release from raft-like domains into the surrounding fluid phase. Unsaturated phospholipids undergo more significant dehydration-induced structural changes and lose more hydrogen bonds with water than sphingomyelin. The results suggest that cholesterol redistribution is driven by the equalization of biophysical properties between phases and the need to satisfy lipid hydrogen bonds. This underscores the role of cholesterol-phospholipid-water interplay in governing cholesterol affinity for a specific lipid type, providing a new perspective on the regulatory role of cell membrane heterogeneity during membrane fusion.

Three-dimensional dipole orientation mapping with high temporal-spatial resolution using polarization modulation

Fluorescence polarization microscopy is widely used in biology for molecular orientation properties. However, due to the limited temporal resolution of single-molecule orientation localization microscopy and the limited orientation dimension of polarization modulation techniques, achieving simultaneous high temporal-spatial resolution mapping of the three-dimensional (3D) orientation of fluorescent dipoles remains an outstanding problem. Here, we present a super-resolution 3D orientation mapping (3DOM) microscope that resolves 3D orientation by extracting phase information of the six polarization modulation components in reciprocal space. 3DOM achieves an azimuthal precision of 2° and a polar precision of 3° with spatial resolution of up to 128 nm in the experiments. We validate that 3DOM not only reveals the heterogeneity of the milk fat globule membrane, but also elucidates the 3D structure of biological filaments, including the 3D spatial conformation of λ-DNA and the structural disorder of actin filaments. Furthermore, 3DOM images the dipole dynamics of microtubules labeled with green fluorescent protein in live U2OS cells, reporting dynamic 3D orientation variations. Given its easy integration into existing wide-field microscopes, we expect the 3DOM microscope to provide a multi-view versatile strategy for investigating molecular structure and dynamics in biological macromolecules across multiple spatial and temporal scales.

4D Printed Soft Microactuator for Particle Manipulation via Surrounding Medium Variation.

Soft actuators have assumed vital roles in a diverse number of research and application fields, driving innovation and transformative advancements. Using 3D molding of smart materials and combining these materials through structural design strategies, a single soft actuator can achieve multiple functions. However, it is still challenging to realize soft actuators that possess high environmental adaptability while capable of different tasks. Here, the response threshold of a soft actuator is modulated by precisely tuning the ratio of stimulus-responsive groups in hydrogels. By combining a heterogeneous bilayer membrane structure and in situ multimaterial printing, the obtained soft actuator deformed in response to changes in the surrounding medium. The response medium is suitable for both biotic and abiotic environments, and the response rate is fast. By changing the surrounding medium, the precise capture, manipulation, and release of micron-sized particles of different diameters in 3D are realized. In addition, static capture of a single red blood cell is realized using biologically responsive medium changes. Finally, the experimental results are well predicted using finite element analysis. It is believed that with further optimization of the structure size and autonomous navigation platform, the proposed soft microactuator has significant potential to function as an easy-to-manipulate multifunctional robot.

Intracellular localized heterogeneous protein franking by a transmembrane domain of GP64 is sufficient to be assembled on budded virions of Bombyx mori nucleopolyhedrovirus

Baculovirus has been widely used for foreign protein expression in biomedical studies, and budded virus (BV) surface display has developed into an important research tool for heterogenous membrane protein studies. The basic strategy of surface display is to construct a recombinant virus where the target gene is fused with a complete or partial gp64 gene. In this study, we further investigate and develop this BV surface displaying strategy. We constructed stable insect cell lines to express the target protein flanking with different regions of signal peptide (SP) and GP64 transmembrane domain (TMD). Subsequently, recombinant BmNPV was used to infect the cell, and the integration of heterogeneous protein into BV was detected. The results indicated that deletion of the n-region of SP (SPΔn) decreased the incorporation rate more than that of the full-length SP. However, the incorporation rate of the protein fused with h and c-region deletion of SP (SPΔh-c) was significantly enhanced by 35–40 times compare to full-length SP. Moreover, the foreign protein without SP and TMD failed to display on the BV, while the integration of foreign proteins with GP64 TMD fusion at the c-terminal was significantly enhanced by 12–26 times compared to the control. Thus, these new strategies developed the BV surface display system further.

Transport and Structural Characteristics of Heterogeneous Ion-Exchange Membranes with Varied Dispersity of the Ion Exchanger

Transport and Structural Characteristics of Heterogeneous Ion-Exchange Membranes with Varied Dispersity of the Ion Exchanger

Effect of Surface Modification with Cerium Oxide on the Transport Properties of Heterogeneous Anion Exchange Membranes MA-41

Effect of Surface Modification with Cerium Oxide on the Transport Properties of Heterogeneous Anion Exchange Membranes MA-41

Retina‐Inspired Nanofluidic Membranes for Underwater Visual Imaging Based on Active Ion Transport

AbstractThrough evolution, biological organisms have developed ways to sense light using ion channels, which holds several advantages, such as energy efficiency and water resistance, over humanmade optoelectronic devices. Herein, a retina‐inspired nanofluidic system is presented with a Janus heterogeneous membrane (J‐HM), which can achieve underwater visual imaging through light‐driven active ion transport. The J‐HMs are obtained through sequentially assembled WS2, and a kind of metal–organic framework nanosheets via the reaction between 2,3,6,7,10,11‐hexahydroxytriphenylene hydrate (HHTP) and Cu2+ (Cu‐HHTP). Due to the formed intramembrane electric field caused by the efficient charge separation under illumination, a photovoltaic driving force is generated for active ion transport from Cu‐HHTP to WS2. Furthermore, the unidirectionally active ion transport can be enhanced by self‐diffusion under a concentration gradient. The J‐HM with a single‐pixel design shows a nearly linear response with light intensity and has enough resolution for basic object recognition as well as a long‐term memory after data processing using a defined pixelated matrix, which can pave an avenue for designing more intelligent sensing systems.

The effect of electrostatically enhanced adsorption of polylysine on a heterogeneous cation-exchange membrane

Electrostatics influences the interactions between charged biopolymers and ion-exchange membranes. When carrying a charge opposite to that bound in the membrane, the biopolymers readily adsorb on the membrane surface, altering local conditions and, thus, affecting the desalination processes that proceed. To provide a coherent description of the consequences of such adsorption, we experimentally investigate the effects of polylysine as a model cationic polymer on the behavior of a heterogenous cation-exchange membrane. We show that even short exposure to polylysine changes the membrane behavior dramatically. Such a change reflects the influence of the adsorbed polylysine on natural convection, electroconvection, and water splitting. By directly observing the membrane-electrolyte interface, we find polylysine suppresses the beneficial electrical-field-induced convective transport at the membrane-electrolyte interface. Specifically, it diminishes electroconvection dominating at the membrane surface for polylysine-free solutions and attenuates natural convection, dictating the developed flow patterns. At the same time, it provides conditions enhancing a water-splitting reaction, significantly affecting the pH of the solutions adjacent to the membrane. All these effects are dependent on the polylysine concentration. Our study emphasizes the potentially harmful impact of biomolecular adsorption mediated by electrostatic interactions.

Electrodeposition modification of heterogeneous cation exchange membrane using expanded polystyrene waste: Enhanced electrochemical properties and electrodialytic performance

In this study, surface modification of a cation exchange membrane based on polyvinyl chloride was accomplished via electrochemical deposition of post-sulfonated waste-expanded polystyrene aiming to enhance its electrochemical properties and electrodialytic performance. The membrane was synthesized by the phase inversion method, modified with different concentrations of polyelectrolyte, characterized by FTIR and SEM analyses, and applied for electrodialytic desalination of NaCl solution. Deposition of sulfonated polystyrene with polyelectrolyte concentration of 2 g/l, current of 8 mA/cm2, and period time of 30 min caused a reduction in electrical resistance up to 52 %. Furthermore, the sodium ionic flux through electrodialytic desalination was improved by 58 % as a result of the promotion of the electrochemical properties of the membrane.

Synthesis of an Imidazolium Ionic Liquid as an Additive to Enhance the Electrochemical Properties of Heterogeneous Anion Exchange Membranes

Synthesis of an Imidazolium Ionic Liquid as an Additive to Enhance the Electrochemical Properties of Heterogeneous Anion Exchange Membranes

Green Alga-Inspired Underwater Vision Based on Light-Driven Active Ion Transport across Janus Dual-Field Heterostructures.

Natural organisms have evolved various biological ion channels to make timely responses toward different physical and/or chemical stimuli, giving guidance to construct artificial counterparts and expand the corresponding applications. They have also shown promising potential to overcome disadvantages of traditional electronic devices (e.g., energy-consuming operation and adverse humidity interference). Herein, we constructed a green alga-inspired nanofluidic system based on a Janus dual-field heterogeneous membrane (i.e., J-HM), which can function underwater as an artificial visual platform for light perception through enhanced active ion transport. The J-HM was obtained through sequentially assembled MXene and Cu-HHTP (i.e., a metal-organic framework based on the reaction between 2,3,6,7,10,11-hexahydroxytriphenylene hydrate (HHTP) and Cu2+) building units. Due to the formed temperature gradient and intramembrane electric field caused by the localized thermal excitation and efficient charge separation of J-HM under illumination, thermo-osmotic and photo-driven forces are generated for preferential cation transport from Cu-HHTP to MXene. Furthermore, unidirectional active transport can be enhanced by self-diffusion under a concentration gradient. Then, the corresponding underwater light perceptions at various light illumination conditions are explored, showing nearly a linear correlation with the light intensity. Finally, it is demonstrated that the visual platform can achieve object shape, definition, and distance recognition using a defined pixelated matrix, giving impetus to develop ionic signal transmission based sensing systems.

Superstructured Optoionic Heterojunctions for Promoting Ion Pumping Inspired by Photoreceptor Cells.

Photoreceptor cells of vertebrates feature ultrastructural membranes interspersed with abundant photosensitive ion pumps to boost signal generation and realize high gain in dim light. In light of this, superstructured optoionic heterojunctions (SSOHs) with cation-selective nanochannels are developed for manipulating photo-driven ion pumping. A template-directed bottom-up strategy is adopted to sequentially assemble graphene oxide (GO) and PEDOT:PSS into heterogeneous membranes with sculptured superstructures, which feature programmable variation in membrane topography and contain a donor-acceptor interface capable of maintaining electron-hole separation upon photoillumination. Such elaborate design endows SSOHs with a much higher magnitude of photo-driven ion flux against a concentration gradient in contrast to conventional optoionic membranes with planar configuration. This can be ascribed to the buildup of an enhanced transmembrane potential owing to the effective separation of photogenerated carriers at the heterojunction interface and the increase of energy input from photoillumination due to a synergistic effect of reflection reduction, broad-angle absorption, and wide-waveband absorption. This work unlocks the significance of membrane topographies in photo-driven transmembrane transportation and proposes such a universal prototype that could be extended to other optoionic membranes to develop high-performance artificial ion pumps for energy conversion and sensing.

PET-hydrogel heterogeneous membranes that eliminate concentration polarization for salinity gradient power generation

Salinity gradient (blue) energy has been identified as a promising power source and many technologies have been proposed for its recovery, one of which is nanopore power generators. The single-pore/channel membranes selectively transport ions to achieve efficient salinity gradient power generation. However, porous membranes fail due to concentration polarization. Here, we constructed a heterogeneous membrane by covering ion-selective hydrogel on a polyethylene terephthalate (PET) cylindrical nanochannel porous membrane for the first time to eliminate concentration polarization. The gel layer enhances the ion selectivity of cylindrical nanochannels, making heterogeneous membrane present the ion current rectification effect. The gel layer also avoids the negative impact of concentration polarization on the power generation of porous membranes. The results show that PET porous membrane can hardly generate electricity, but the power density of PET-hydrogel heterogeneous membrane can reach 1.92 W/m2 under 50 times salinity gradient, which is superior to commercial ion exchange membranes. Our work provides a strategy (ion-selective hydrogel covering) to eliminate concentration polarization of porous membranes, and shows the prospect of cylindrical nanochannels for salinity gradient power generation.

Tempospatially Confined Catalytic Membranes for Advanced Water Remediation.

The application of homogeneous catalysts in water remediation is limited by their excessive chemical and energy input, weak regenerability, and potential leaching. Heterogeneous catalytic membranes (CMs) offer a new approach to facilitate efficient, selective, and continuous pollutant degradation. Thus, integrating membranes and continuous filtration with heterogeneous advanced oxidation processes (AOPs) can promote thermodynamic and kinetic mass transfers in spatially confined intrapores and facilitate diffusion-reaction processes. Despite the remarkable advantages of heterogeneous CMs, their engineering application is practically restricted due to the fuzzy design criteria for specific applications. Herein, the recent advances in CMs for advanced water remediation are critically reviewed and the design flow for tempospatially confined CMs is proposed. Further, state-of-the-art CM materials and their catalytic mechanisms are reviewed, after which the tempospatial confinement mechanisms comprising the nanoconfinement effect, interface effect, and kinetic mass transfer are emphasized, thus clarifying their roles in the construction and performance optimization of CMs. Additionally, the fabrication methods for CMs based on their catalysts and pore sizes are summarized and an overview of their application and performance evaluations is presented. Finally, future directions for CMs in materials research and water treatment, are presented.

Charge-Gradient Sulfonated Poly(ether ether ketone) Membrane with Enhanced Ion Selectivity for Osmotic Energy Conversion.

Engineered asymmetric heterogeneous ion-selective membranes have become a focal point for their improved efficiency in harnessing osmotic energy from ionic solutions with varying salinity. However, achieving both energy conversion efficiency and excellent chemical stability necessitates effectively mitigating the formation of detrimental interface cracks between two different layers. We develop a charge-gradient sulfonated poly(ether ether ketone) (SPEEK) membrane (CG-SPEEK) on a large-scale using a straightforward coating method. As an osmotic energy generator, CG-SPEEK membrane achieves an impressive output power density of 9.2 W m-2 and exhibits ultrahigh cation selectivity (0.99), with an energy conversion efficiency of 48% at a 50-fold NaCl concentration gradient. The results highlight the ion diode effects of CG-SPEEK, driven by a charge density gradient that accelerates cation transport while suppressing ion concentration polarization. Density functional theory simulations provide further insights, revealing that the energy barrier for Na+ ion transport through CG-SPEEK membrane is lower than that through a homogeneous SPEEK membrane. This work not only enhances our understanding of ion transport dynamics but also establishes the CG-SPEEK membrane as a promising candidate for efficient osmotic energy conversion applications.

Pre-fusion motion state determines the heterogeneity of membrane fusion dynamics for large dense-core vesicles.

In neuroendocrine cells, large dense-core vesicles (LDCVs) undergo highly regulated pre-fusion processes before releasing hormones via membrane fusion. Significant heterogeneity has been found for LDCV population based on the dynamics of membrane fusion. However, how the pre-fusion status impacts the heterogeneity of LDCVs still remains unclear. Hence, we explored pre-fusion determinants of heterogeneous membrane fusion procedure of LDCV subpopulations. We assessed the pre-fusion motion of two LDCV subpopulations with distinct membrane fusion dynamics individually, using total internal reflection fluorescence microscopy. These two subpopulations were isolated by blocking Rho GTPase-dependent actin reorganization using Clostridium difficile toxin B (ToxB), which selectively targets the fast fusion vesicle pool. We found that the fast fusion subpopulation was in an active motion mode prior to release, termed "active" LDCV pool, while vesicles from the slow fusion subpopulation were also moving but in a significantly more confined status, forming an "inert" pool. The depletion of the active pool by ToxB also eliminated fast fusion vesicles and was not rescued by pre-treatment with phorbol ester. A mild actin reorganization blocker, latrunculin A, that partially disrupted the active pool, only slightly attenuated the fast fusion subpopulation. The pre-fusion motion state of LDCVs also exhibits heterogeneity and dictates the heterogeneous fusion pore dynamics. Rearrangement of F-actin network mediates vesicle pre-fusion motion and subsequently determines the membrane fusion kinetics.

Engineered Heterogenous Subnanochannel Membranes with a Tri‐Continuous Pore Structure of Large Geometry Gradient for Massively Enhanced Osmotic Power Conversion from Organic Solutions (Adv. Funct. Mater. 7/2024)

Engineered Heterogenous Subnanochannel Membranes with a Tri‐Continuous Pore Structure of Large Geometry Gradient for Massively Enhanced Osmotic Power Conversion from Organic Solutions (Adv. Funct. Mater. 7/2024)

FLImP-assisted MINFLUX overcomes molecular localization errors to reveal the structure of heterogeneous membrane protein systems

FLImP-assisted MINFLUX overcomes molecular localization errors to reveal the structure of heterogeneous membrane protein systems

Reconciling modern observations of membrane heterogeneity with the lipid raft hypothesis

Reconciling modern observations of membrane heterogeneity with the lipid raft hypothesis

Polyamide Nanofilms through a Non‐Isothermal‐Controlled Interfacial Polymerization

AbstractEfficient thin film composite polyamide (PA) membranes require optimization of interfacial polymerization (IP) process. However, it is challengeable owing to its ultrafast reaction rate coupled with mass and heat transfer, yielding heterogeneous PA membranes with low performance. Herein, a non‐isothermal‐controlled IP (NIIP) method is proposed to fabricate a highly permeable and selective PA membrane by engineering IP at the cryogenic aqueous phase (CAP) to achieve synchronous control of heat and mass transfer in the interfacial region. The CAP also enables the phase transition of the aqueous solution from the liquid to solid state, providing a more comprehensive understanding of the fundamental mechanisms involved in different phase states in the IP process. Consequently, the PA membrane exhibits excellent separation performance with ultrahigh water permeance (42.9 L m−2 h−1 bar−1) and antibiotic desalination efficiency (antibiotic/NaCl selectivity of 159.3). This study provides new insights for the in‐depth understanding of the precise mechanism linking IP to the performance of the targeting membrane.