Artificial Lipid Membranes: Past, Present, and Future

DNA-Based Complexes and Composites: A Review of Fabrication Methods, Properties, and Applications

Deoxyribonucleic acid (DNA), a macromolecule that stores genetic information in organisms, has recently been gradually developed into a building block for new materials due to its stable chemical structure and excellent biocompatibility. The efficient preparation and functional integration of various molecular complexes and composite materials based on nucleic acid skeletons have been successfully achieved. These versatile materials possess excellent physical and chemical properties inherent to certain inorganic or organic molecules but are endowed with specific physiological functions by nucleic acids, demonstrating unique advantages and potential applications in materials science, nanotechnology, and biomedical engineering in recent years. However, issues such as the production cost, biological stability, and potential immunogenicity of DNA have presented some unprecedented challenges to the application of these materials in the field. This review summarizes the cutting-edge manufacturing techniques and unique properties of DNA-based complexes and composites and discusses the trends, challenges, and opportunities for the future development of nucleic acid-based materials.

Advancements in Engineering Planar Model Cell Membranes: Current Techniques, Applications, and Future Perspectives

Cell membranes are crucial elements in living organisms, serving as protective barriers and providing structural support for cells. They regulate numerous exchange and communication processes between cells and their environment, including interactions with other cells, tissues, ions, xenobiotics, and drugs. However, the complexity and heterogeneity of cell membranes-comprising two asymmetric layers with varying compositions across different cell types and states (e.g., healthy vs. diseased)-along with the challenges of manipulating real cell membranes represent significant obstacles for in vivo studies. To address these challenges, researchers have developed various methodologies to create model cell membranes or membrane fragments, including mono- or bilayers organized in planar systems. These models facilitate fundamental studies on membrane component interactions as well as the interactions of membrane components with external agents, such as drugs, nanoparticles (NPs), or biomarkers. The applications of model cell membranes have extended beyond basic research, encompassing areas such as biosensing and nanoparticle camouflage to evade immune detection. In this review, we highlight advancements in the engineering of planar model cell membranes, focusing on the nanoarchitectonic tools used for their fabrication. We also discuss approaches for incorporating challenging materials, such as proteins and enzymes, into these models. Finally, we present our view on future perspectives in the field of planar model cell membranes.

Measuring Vesicle Loading with Holographic Microscopy and Bulk Light Scattering

We report efforts to quantify the loading of cell-sized lipid vesicles using in-line digital holographic microscopy. This method does not require fluorescent reporters, fluorescent tracers, or radioactive tracers. A single-color LED light source takes the place of conventional illumination to generate holograms rather than bright field images. By modeling the vesicle's scattering in a microscope with a Lorenz-Mie light scattering model and comparing the results to data holograms, we are able to measure the vesicle's refractive index and thus loading. Performing the same comparison for bulk light scattering measurements enables the retrieval of vesicle loading for nanoscale vesicles.

Achieving Endo/Lysosomal Escape Using Smart Nanosystems for Efficient Cellular Delivery

The delivery of therapeutic agents faces significant hurdles posed by the endo-lysosomal pathway, a bottleneck that hampers clinical effectiveness. This comprehensive review addresses the urgent need to enhance cellular delivery mechanisms to overcome these obstacles. It focuses on the potential of smart nanomaterials, delving into their unique characteristics and mechanisms in detail. Special attention is given to their ability to strategically evade endosomal entrapment, thereby enhancing therapeutic efficacy. The manuscript thoroughly examines assays crucial for understanding endosomal escape and cellular uptake dynamics. By analyzing various assessment methods, we offer nuanced insights into these investigative approaches' multifaceted aspects. We meticulously analyze the use of smart nanocarriers, exploring diverse mechanisms such as pore formation, proton sponge effects, membrane destabilization, photochemical disruption, and the strategic use of endosomal escape agents. Each mechanism's effectiveness and potential application in mitigating endosomal entrapment are scrutinized. This paper provides a critical overview of the current landscape, emphasizing the need for advanced delivery systems to navigate the complexities of cellular uptake. Importantly, it underscores the transformative role of smart nanomaterials in revolutionizing cellular delivery strategies, leading to a paradigm shift towards improved therapeutic outcomes.

Plant Membrane-On-A-Chip: A Platform for Studying Plant Membrane Proteins and Lipids

The cell plasma membrane is a two-dimensional, fluid mosaic material composed of lipids and proteins that create a semipermeable barrier defining the cell from its environment. Compared with soluble proteins, the methodologies for the structural and functional characterization of membrane proteins are challenging. An emerging tool for studies of membrane proteins in mammalian systems is a "plasma membrane on a chip," also known as a supported lipid bilayer. Here, we create the "plant-membrane-on-a-chip,″ a supported bilayer made from the plant plasma membranes of Arabidopsis thaliana, Nicotiana benthamiana, or Zea mays. Membrane vesicles from protoplasts containing transgenic membrane proteins and their native lipids were incorporated into supported membranes in a defined orientation. Membrane vesicles fuse and orient systematically, where the cytoplasmic side of the membrane proteins faces the chip surface and constituents maintain mobility within the membrane plane. We use plant-membrane-on-a-chip to perform fluorescent imaging to examine protein-protein interactions and determine the protein subunit stoichiometry of FLOTILLINs. We report here that like the mammalian FLOTILLINs, FLOTILLINs expressed in Arabidopsis form a tetrameric complex in the plasma membrane. This plant-membrane-on-a-chip approach opens avenues to studies of membrane properties of plants, transport phenomena, biophysical processes, and protein-protein and protein-lipid interactions in a convenient, cell-free platform.

Bio-Inspired Functional Materials for Environmental Applications

With the global population expected to reach 9.7 billion by 2050, there is an urgent need for advanced materials that can address existing and developing environmental issues. Many current synthesis processes are environmentally unfriendly and often lack control over size, shape, and phase of resulting materials. Based on knowledge from biological synthesis and assembly processes, as well as their resulting functions (e.g., photosynthesis, self-healing, anti-fouling, etc.), researchers are now beginning to leverage these biological blueprints to advance bio-inspired pathways for functional materials for water treatment, air purification and sensing. The result has been the development of novel materials that demonstrate enhanced performance and address sustainability. Here, an overview of the progress and potential of bio-inspired methods toward functional materials for environmental applications is provided. The challenges and opportunities for this rapidly expanding field and aim to provide a valuable resource for researchers and engineers interested in developing sustainable and efficient processes and technologies is discussed.

Enzyme Catalysis Causes Fluid Flow, Motility, and Directional Transport on Supported Lipid Bilayers

The dynamic interplay between the composition of lipid membranes and the behavior of membrane-bound enzymes is critical to the understanding of cellular function and viability, and the design of membrane-based biosensing platforms. While there is a significant body of knowledge about how lipid composition and dynamics affect membrane-bound enzymes, little is known about how enzyme catalysis influences the motility and lateral transport on lipid membranes. Using enzyme-attached lipids in supported bilayers (SLBs), we provide direct evidence of catalysis-induced fluid flow that underlies the observed motility on SLBs. Additionally, by using active enzyme patches, we demonstrate the directional transport of tracer particles on SLBs. As expected, enhancing the membrane viscosity by incorporating cholesterol into the bilayer suppresses the overall movement. These are the first steps in understanding diffusion and transport on lipid membranes due to active, out-of-equilibrium processes that are the hallmark of living systems. In general, our study demonstrates how active enzymes can be used to control diffusion and transport in confined 2-D environments.

Membrane-Disruptive Effects of Fatty Acid and Monoglyceride Mitigants on E. coli Bacteria-Derived Tethered Lipid Bilayers

We report electrochemical impedance spectroscopy measurements to characterize the membrane-disruptive properties of medium-chain fatty acid and monoglyceride mitigants interacting with tethered bilayer lipid membrane (tBLM) platforms composed of E. coli bacterial lipid extracts. The tested mitigants included capric acid (CA) and monocaprin (MC) with 10-carbon long hydrocarbon chains, and lauric acid (LA) and glycerol monolaurate (GML) with 12-carbon long hydrocarbon chains. All four mitigants disrupted E. coli tBLM platforms above their respective critical micelle concentration (CMC) values; however, there were marked differences in the extent of membrane disruption. In general, CA and MC caused larger changes in ionic permeability and structural damage, whereas the membrane-disruptive effects of LA and GML were appreciably smaller. Importantly, the distinct magnitudes of permeability changes agreed well with the known antibacterial activity levels of the different mitigants against E. coli, whereby CA and MC are inhibitory and LA and GML are non-inhibitory. Mechanistic insights obtained from the EIS data help to rationalize why CA and MC are more effective than LA and GML at disrupting E. coli membranes, and these measurement capabilities support the potential of utilizing bacterial lipid-derived tethered lipid bilayers for predictive assessment of antibacterial drug candidates and mitigants.

Interface-mediated protein aggregation

The aggregation of proteins at interfaces has significant roles and can also lead to dysfunction of different physiological processes. The interfacial effects on the assembly and aggregation of biopolymers are not only crucial for a comprehensive understanding of protein biological functions, but also hold great potential for advancing the state-of-the-art applications of biopolymer materials. Recently, there has been remarkable progress in a collaborative context, as we strive to gain control over complex interfacial assembly structures of biopolymers. These biopolymer structures range from the nanoscale to mesoscale and even macroscale, and are attained through the rational design of interactions between biological building blocks and surfaces/interfaces. This review spotlights the recent advancements in interface-mediated assembly and properties of biopolymer materials. Initially, we introduce the solid-liquid interface (SIL)-mediated biopolymer assembly that includes the inorganic crystalline template effect and protein self-adoptive deposition through phase transition. Next, we display the advancement of biopolymer assembly instigated by the air-water interface (AWI) that acts as an energy conversion station. Lastly, we discuss succinctly the assembly of biopolymers at the liquid-liquid interface (LLI) along with their applications. It is our hope that this overview will stimulate the integration and progression of the science of interfacial assembled biopolymer materials and surfaces/interfaces.

Effects of polyethylene glycol-grafted phospholipid on the anionic magnetite nanoparticles-induced deformation and poration in giant lipid vesicles

The hydrophilic polymer polyethylene glycol-grafted phospholipid has been used extensively in the study of artificial vesicles, nanomedicine, and antimicrobial peptides/proteins. In this research, the effects of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N- [methoxy (polyethylene glycol)-2000] (abbreviated PEG-DOPE) on the deformation and poration of giant unilamellar vesicles (GUVs)-induced by anionic magnetite nanoparticles (NPs) have been investigated. For this, the size of the NPs used was 18 nm, and their concentration in the physiological solution was 2.00 μg/mL. GUVs were prepared using the natural swelling method comprising 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and PEG-DOPE. The mole% of PEG-DOPE in the membranes were 0, 2, and 5%. The degree of deformation of the GUVs was quantified by the parameter compactness (Com), which is 1.0 for the spherical-shaped GUVs. The value of Com increases with time during the interactions of NPs with GUVs for any concentration of PEG-DOPE, but the rate of increase is significantly influenced by the PEG-DOPE concentration in the membranes. The average compactness increases with the increase of PEG-DOPE%, and after 60 min of NPs interaction, the values of average compactness for 0, 2, and 5% PEG-DOPE were 1.19 ± 0.02, 1.26 ± 0.03 and 1.35 ± 0.05, respectively. The fraction of deformation (Frd) also increased with the increase of PEG-DOPE%, and at 60 min, the values of Frd for 0 and 5% PEG-DOPE were 0.47 ± 0.02 and 0.63 ± 0.02, respectively. The fraction of poration (Frp) increased with the increase of PEG-DOPE, and at 60 min, the values of Frp for 0 and 5% PEG-DOPE were 0.25 ± 0.02 and 0.48 ± 0.02, respectively. Hence, the presence of PEG-grafted phospholipid in the membranes greatly enhances the anionic magnetite NPs-induced deformation and poration of giant vesicles.

Advances in Functionalization of Bioresorbable Nanomembranes and Nanoparticles for Their Use in Biomedicine

Bioresorbable nanomembranes (NMs) and nanoparticles (NPs) are powerful polymeric materials playing an important role in biomedicine, as they can effectively reduce infections and inflammatory clinical patient conditions due to their high biocompatibility, ability to physically interact with biomolecules, large surface area, and low toxicity. In this review, the most common bioabsorbable materials such as those belonging to natural polymers and proteins for the manufacture of NMs and NPs are reviewed. In addition to biocompatibility and bioresorption, current methodology on surface functionalization is also revisited and the most recent applications are highlighted. Considering the most recent use in the field of biosensors, tethered lipid bilayers, drug delivery, wound dressing, skin regeneration, targeted chemotherapy and imaging/diagnostics, functionalized NMs and NPs have become one of the main pillars of modern biomedical applications.

Accurate Capture and Identification of Exosomes: Nanoarchitecture of the MXene Heterostructure/Engineered Lipid Layer

Recently, exosome detection has become an important breakthrough in clinical diagnosis. However, the effective capture and accurate identification of cancer exosomes in a complex biomatrix are still a tough task. Especially, the large size and non-conductivity of exosomes are not conducive to highly sensitive electrochemical or electrochemiluminescence (ECL) detection. Therefore, we have developed a Ti₃C₂T_x-Bi₂S_3-x heterostructure/engineered lipid layer-based nanoarchitecture to overcome the limitations. The engineered lipid layer not only specifically captured and efficiently fused CD63 positive exosomes but also showed excellent antifouling property in the biological matrix. Moreover, the MUC1 aptamer-modified Ti₃C₂T_x-Bi₂S_3-x heterostructure further identified and covered the gastric cancer exosomes that have been trapped in the engineered lipid layer. In the self-luminous Faraday cage-type sensing system, the Ti₃C₂T_x-Bi₂S_3-x heterostructure with sulfur vacancies extended the outer Helmholtz plane and amplified the ECL signal. Therefore, this sensor can be used to detect tumor exosomes in ascites of cancer patients without additional purification. It provides a new pathway to detect exosomes and other large-sized vesicles with high sensitivity.

Pore-Forming Proteins: From Pore Assembly to Structure by Quantitative Single-Molecule Imaging

Pore-forming proteins (PFPs) play a central role in many biological processes related to infection, immunity, cancer, and neurodegeneration. A common feature of PFPs is their ability to form pores that disrupt the membrane permeability barrier and ion homeostasis and generally induce cell death. Some PFPs are part of the genetically encoded machinery of eukaryotic cells that are activated against infection by pathogens or in physiological programs to carry out regulated cell death. PFPs organize into supramolecular transmembrane complexes that perforate membranes through a multistep process involving membrane insertion, protein oligomerization, and finally pore formation. However, the exact mechanism of pore formation varies from PFP to PFP, resulting in different pore structures with different functionalities. Here, we review recent insights into the molecular mechanisms by which PFPs permeabilize membranes and recent methodological advances in their characterization in artificial and cellular membranes. In particular, we focus on single-molecule imaging techniques as powerful tools to unravel the molecular mechanistic details of pore assembly that are often obscured by ensemble measurements, and to determine pore structure and functionality. Uncovering the mechanistic elements of pore formation is critical for understanding the physiological role of PFPs and developing therapeutic approaches.

Langmuir and Langmuir-Blodgett technologies as nanoarchitectonic tools for the incorporation of curcumin in membrane systems

Curcumin (CCM) is a molecule of particular interest in health applications due to its wide spectrum of benefits for humans. However, its water-insoluble character and low bioavailability have so far prevented its extended use as a therapeutic agent. Incorporation of CCM in drug delivery vehicles (liposomes, vesicles, exosomes, etc.) is expected to contribute to increasing its bioavailability. Studies of the affinity of CCM with the components of the membrane systems of such vehicles and determination of factors that may enhance curcumin entrapment in biological membranes are of fundamental importance. To that end, here we take advantage of the nanoarchitectonic capabilities of the Langmuir technique for the construction of model cell membranes and determination of thermodynamic properties in mixed films. The obtained results may serve to: (i) provide some light on the miscibility of CCM with the components in the cell membrane and (ii) determine the optimal conditions for the fabrication of membrane systems incorporating CCM. For that, binary and ternary mixed Langmuir films of CCM, DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and CHOL (cholesterol) have been prepared. Whilst binary mixtures of DPPC and CCM exhibit poor miscibility and even phase segregation, CHOL has shown itself as a key element to promote the incorporation of CCM in the phospholipidic membrane containing DPPC. Both the thermodynamic studies of the ternary Langmuir films and the Atomic Force Microscopy (AFM) images of Langmuir-Blodgett films have shown that ternary mixed films with a molar fraction composition of x_DPPC/x_CHOL/x_CCM = 0.4/0.4/0.2 exhibit good miscibility, stability, and result in monolayers with a very homogeneous topography.

Bacterial Membrane Mimetics: From Biosensing to Disease Prevention and Treatment

Plasma membrane mimetics can potentially play a vital role in drug discovery and immunotherapy owing to the versatility to assemble facilely cellular membranes on surfaces and/or nanoparticles, allowing for direct assessment of drug/membrane interactions. Recently, bacterial membranes (BMs) have found widespread applications in biomedical research as antibiotic resistance is on the rise, and bacteria-associated infections have become one of the major causes of death worldwide. Over the last decade, BM research has greatly benefited from parallel advancements in nanotechnology and bioelectronics, resulting in multifaceted systems for a variety of sensing and drug discovery applications. As such, BMs coated on electroactive surfaces are a particularly promising label-free platform to investigate interfacial phenomena, as well as interactions with drugs at the first point of contact: the bacterial membrane. Another common approach suggests the use of lipid-coated nanoparticles as a drug carrier system for therapies for infectious diseases and cancer. Herein, we discuss emerging platforms that make use of BMs for biosensing, bioimaging, drug delivery/discovery, and immunotherapy, focusing on bacterial infections and cancer. Further, we detail the synthesis and characteristics of BMs, followed by various models for utilizing them in biomedical applications. The key research areas required to augment the characteristics of bacterial membranes to facilitate wider applicability are also touched upon. Overall, this review provides an interdisciplinary approach to exploit the potential of BMs and current emerging technologies to generate novel solutions to unmet clinical needs.

Ruscogenin interacts with DPPC and DPPG model membranes and increases the membrane fluidity: FTIR and DSC studies

Ruscogenin, a kind of steroid saponin, has been shown to have significant anti-oxidant, anti-inflammatory, and anti-thrombotic characteristics. Furthermore, it has the potential to be employed as a medicinal medication to treat a variety of acute and chronic disorders. The interaction of a drug molecule with cell membranes can help to elucidate its system-wide protective and therapeutic effects, and it's also important for its pharmacological activity. The molecular mechanism by which ruscogenin affects membrane architecture is still a mystery. Ruscogenin's interaction with zwitterionic dipalmitoyl phosphatidylcholine (DPPC) and anionic dipalmitoyl phosphatidylglycerol (DPPG) multilamellar vesicles (MLVs) was studied utilizing two non-invasive approaches, including: Fourier Transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry. Ruscogenin caused considerable alterations in the phase transition profile, order, dynamics and hydration state of head groups and glycerol backbone of DPPC and DPPG MLVs at all concentrations. The DSC results indicated that the presence of ruscogenin decreased the main phase transition temperature (T_m) and enthalpy (ΔH) values of both membranes and increased half height width of the main transition (ΔT_1/2). The FTIR results demonstrated that all concentrations (1, 3, 6, 9, 15, 24 and 30 mol percent) of ruscogenin disordered the DPPC MLVs both in the gel and liquid crystalline phases while it increased the order of DPPG MLVs in the liquid crystalline phase. Moreover, ruscogenin caused an increase in the dynamics of DPPC and DPPG MLVs in both phases. Additionally, it enhanced the hydration of the head groups of lipids and the surrounding water molecules implying ruscogenin to interact strongly with both zwitterionic and charged model membranes.

Cinematic reflectometry using QIKR, the quite intense kinetics reflectometer

The Quite Intense Kinetics Reflectometer (QIKR) will be a general-purpose, horizontal-sample-surface neutron reflectometer. Reflectometers measure the proportion of an incident probe beam reflected from a surface as a function of wavevector (momentum) transfer to infer the distribution and composition of matter near an interface. The unique scattering properties of neutrons make this technique especially useful in the study of soft matter, biomaterials, and materials used in energy storage. Exploiting the increased brilliance of the Spallation Neutron Source Second Target Station, QIKR will collect specular and off-specular reflectivity data faster than the best existing such machines. It will often be possible to collect complete specular reflectivity curves using a single instrument setting, enabling "cinematic" operation, wherein the user turns on the instrument and "films" the sample. Samples in time-dependent environments (e.g., temperature, electrochemical, or undergoing chemical alteration) will be observed in real time, in favorable cases with frame rates as fast as 1 Hz. Cinematic data acquisition promises to make time-dependent measurements routine, with time resolution specified during post-experiment data analysis. This capability will be deployed to observe such processes as in situ polymer diffusion, battery electrode charge-discharge cycles, hysteresis loops, and membrane protein insertion into lipid layers.

Engineered Biomimetic Membranes for Organ-on-a-Chip

Organ-on-a-chip (OOC) systems are engineered nanobiosystems to mimic the physiochemical environment of a specific organ in the body. Among various components of OOC systems, biomimetic membranes have been regarded as one of the most important key components to develop controllable biomimetic bioanalysis systems. Here, we review the preparation and characterization of biomimetic membranes in comparison with the features of the extracellular matrix. After that, we review and discuss the latest applications of engineered biomimetic membranes to fabricate various organs on a chip, such as liver, kidney, intestine, lung, skin, heart, vasculature and blood vessels, brain, and multiorgans with perspectives for further biomedical applications.

Bio-Inspired Nanomembranes as Building Blocks for Nanophotonics, Plasmonics and Metamaterials

Nanomembranes are the most widespread building block of life, as they encompass cell and organelle walls. Their synthetic counterparts can be described as freestanding or free-floating structures thinner than 100 nm, down to monatomic/monomolecular thickness and with giant lateral aspect ratios. The structural confinement to quasi-2D sheets causes a multitude of unexpected and often counterintuitive properties. This has resulted in synthetic nanomembranes transiting from a mere scientific curiosity to a position where novel applications are emerging at an ever-accelerating pace. Among wide fields where their use has proven itself most fruitful are nano-optics and nanophotonics. However, the authors are unaware of a review covering the nanomembrane use in these important fields. Here, we present an attempt to survey the state of the art of nanomembranes in nanophotonics, including photonic crystals, plasmonics, metasurfaces, and nanoantennas, with an accent on some advancements that appeared within the last few years. Unlimited by the Nature toolbox, we can utilize a practically infinite number of available materials and methods and reach numerous properties not met in biological membranes. Thus, nanomembranes in nano-optics can be described as real metastructures, exceeding the known materials and opening pathways to a wide variety of novel functionalities.

A Versatile Suspended Lipid Membrane System for Probing Membrane Remodeling and Disruption

Artificial membrane systems can serve as models to investigate molecular mechanisms of different cellular processes, including transport, pore formation, and viral fusion. However, the current, such as SUVs, GUVs, and the supported lipid bilayers suffer from issues, namely high curvature, heterogeneity, and surface artefacts, respectively. Freestanding membranes provide a facile solution to these issues, but current systems developed by various groups use silicon or aluminum oxide wafers for fabrication that involves access to a dedicated nanolithography facility and high cost while conferring poor membrane stability. Here, we report the development, characterization and applications of an easy-to-fabricate suspended lipid bilayer (SULB) membrane platform leveraging commercial track-etched porous filters (PCTE) with defined microwell size. Our SULB system offers a platform to study the lipid composition-dependent structural and functional properties of membranes with exceptional stability. With dye entrapped in PCTE microwells by SULB, we show that sphingomyelin significantly augments the activity of pore-forming toxin, Cytolysin A (ClyA) and the pore formation induces lipid exchange between the bilayer leaflets. Further, we demonstrate high efficiency and rapid kinetics of membrane fusion by dengue virus in our SULB platform. Our suspended bilayer membrane mimetic offers a novel platform to investigate a large class of biomembrane interactions and processes.

Models to study basic and applied aspects of lysosomal storage disorders

The lack of available treatments and fatal outcome in most lysosomal storage disorders (LSDs) have spurred research on pathological mechanisms and novel therapies in recent years. In this effort, experimental methodology in cellular and animal models have been developed, with aims to address major challenges in many LSDs such as patient-to-patient variability and brain condition. These techniques and models have advanced knowledge not only of LSDs but also for other lysosomal disorders and have provided fundamental insights into the biological roles of lysosomes. They can also serve to assess the efficacy of classical therapies and modern drug delivery systems. Here, we summarize the techniques and models used in LSD research, which include both established and recently developed in vitro methods, with general utility or specifically addressing lysosomal features. We also review animal models of LSDs together with cutting-edge technology that may reduce the need for animals in the study of these devastating diseases.

A cell free biomembrane platform for multimodal study of influenza virus hemagglutinin and for evaluation of entry-inhibitors against hemagglutinin

Seasonal periodic pandemics and epidemics caused by Influenza A viruses (IAVs) are associated with high morbidity and mortality worldwide. They are frequent and unpredictable in severity so there is a need for biophysical platforms that can be used to provide both mechanistic insights into influenza virulence and its potential treatment by anti-IAV agents. Host membrane viral association through the glycoprotein hemagglutinin (HA) of IAVs is one of the primary steps in infection. HA is thus a potential target for drug discovery and development against influenza. Deconvolution of the multivalent interactions of HA at the interfaces of the host cell membrane can help unravel therapeutic targets. In this contribution, we reported the effect of a multivalent HA glycoprotein association on various glycosphingolipid receptors (GD1a, GM3, GM1) doped asymmetrically into an artificial host membrane spanned across an aqueous filled microcavity array. The extent of HA association and its impact on membrane resistance, capacitance, and diffusivity was measured using highly sensitive electrochemical impedance spectroscopy (EIS) and fluorescence lifetime correlation spectroscopy (FLCS). Furthermore, we investigated the inhibition of the influenza HA glycoprotein association with the host mimetic surface by natural and synthetic sialic acid-based inhibitors (sialic acid, Siaα2,3-GalOMe, FB127, 3-sialyl lactose) using electrochemical impedance spectroscopy and observe that while all inhibit, they do not prevent host binding. Overall, the work demonstrates the platform provides a label-free screening platform for the biophysical evaluation of new inhibitors in the development of potential therapeutics for IAV infection prevention and treatment.

Application of Ethyl Cellulose and Ethyl Cellulose + Polyethylene Glycol for the Development of Polymer-Based Formulations using Spray-Drying Technology for Retinoic Acid Encapsulation

Ethyl cellulose (EC)-based microparticles, with and without the incorporation of polyethylene glycol (PEG) as a second encapsulating agent, were prepared using the spray-drying process for the encapsulation of retinoic acid (RA). The production of a suitable controlled delivery system for this retinoid will promote its antitumor efficiency against acute promyelocytic leukemia (APL) due to the possibility of increasing the bioavailability of RA. Product yield ranged from 12 to 28% in all the microparticle formulations, including unloaded microparticles and RA-loaded microparticles. Microparticles with a mean diameter between 0.090 ± 0.002 and 0.54 ± 0.02 µm (number size distribution) and with an irregular form and rough surface were obtained. Furthermore, regarding RA-loaded microparticles, both polymer-based formulations exhibited an encapsulation efficiency of around 100%. A rapid and complete RA release was reached in 40 min from EC− and EC + PEG-based microparticles.

Synthesis and Characterization of Ceramide-Containing Liposomes as Membrane Models for Different T Cell Subpopulations

A fine balance of regulatory (T_reg) and conventional CD4⁺ T cells (T_conv) is required to prevent harmful immune responses, while at the same time ensuring the development of protective immunity against pathogens. As for many cellular processes, sphingolipid metabolism also crucially modulates the T_reg/T_conv balance. However, our understanding of how sphingolipid metabolism is involved in T cell biology is still evolving and a better characterization of the tools at hand is required to advance the field. Therefore, we established a reductionist liposomal membrane model system to imitate the plasma membrane of mouse T_reg and T_conv with regards to their ceramide content. We found that the capacity of membranes to incorporate externally added azide-functionalized ceramide positively correlated with the ceramide content of the liposomes. Moreover, we studied the impact of the different liposomal preparations on primary mouse splenocytes in vitro. The addition of liposomes to resting, but not activated, splenocytes maintained viability with liposomes containing high amounts of C₁₆-ceramide being most efficient. Our data thus suggest that differences in ceramide post-incorporation into T_reg and T_conv reflect differences in the ceramide content of cellular membranes.

Encapsulated droplet interface bilayers as a platform for high-throughput membrane studies

Whilst it is highly desirable to produce artificial lipid bilayer arrays allowing for systematic high-content screening of membrane conditions, it remains a challenge due to the combined requirements of scaled membrane production, simple measurement access, and independent control over individual bilayer experimental conditions. Here, droplet bilayers encapsulated within a hydrogel shell are output individually into multi-well plates for simple, arrayed quantitative measurements. The afforded experimental throughput is used to conduct a 2D concentration screen characterising the synergistic pore-forming peptides Magainin2 and PGLa. Maximal enhanced activity is revealed at equimolar peptide concentrations via a membrane dye leakage assay, a finding consistent with models proposed from NMR data. The versatility of the platform is demonstrated by performing in situ electrophysiology, revealing low conductance pore activity (∼15 to 20 pA with 4.5 pA sub-states). In conclusion, this array platform addresses the aforementioned challenges and provides new and flexible opportunities for high-throughput membrane studies. Furthermore, the ability to engineer droplet networks within each construct paves the way for "lab-in-a-capsule" approaches accommodating multiple assays per construct and allowing for communicative reaction pathways.

Lipid nano-vesicles for thyroid hormone encapsulation: A comparison between different fabrication technologies, drug loading, and an in vitro delivery to human tendon stem/progenitor cells in 2D and 3D culture

Phosphatidylcholine (PC) vesicles loaded with Triiodothyronine (T3) were fabricated using different manufacturing methods: thin layer hydration plus sonication (TF-UF), supercritical liposome formation (SC), and microfluidic technology (MF). Vesicles obtained by MF had the lowest mean diameter (88.61 ± 44.48 nm) with a Zeta Potential of -20.1 ± 5.90 mV and loading of 10 mg/g (encapsulation efficiency: 57%). In contrast, SC vesicles showed extremely low encapsulation efficiency (<10%) probably due to T3 solubility in ethanol/carbon dioxide mixture; despite TF-UF vesicles exhibiting good size (167.7 ± 90 nm; Zp -8.50 ± 0.60 mV) and loading (10 mg/g), poor mass recovery was obtained (50% loss). MF vesicles had low cytotoxicity, and they were well enough internalized by both HeLa and human tendon stem/progenitor cells (hTSPCs). Their biological activity was also monitored in both 2D and 3D cultures of hTSPCs supplemented with therapeutical concentrations of PC/T3 nano-liposomes. 2D culture showed almost similar constitutive gene expression compared to control culture supplemented with free-T3. On the contrary, when hTPSCs 3D culture was assembled, it showed a more evident homogeneous distribution of FITC labeled vesicles within the high-density structure and a significant upregulation of cell constitutive genes, such as type I Collagen (4.8-fold; p < 0.0001) at day 7, compared to the control, suggesting that T3/PC formulation has increased T3 cytosolic concentration, thus improving cells metabolic activity. The study supported MF technology for nano-carriers fabrication and opens perspectives on the activity of PC/T3 nano-vesicles as innovative formulations for TPSCs stimulation in ECM secretion.

Membrane Protein Activity Induces Specific Molecular Changes in Nanodiscs Monitored by FTIR Difference Spectroscopy

It is well known that lipids neighboring integral membrane proteins directly influence their function. The opposite effect is true as well, as membrane proteins undergo structural changes after activation and thus perturb the lipidic environment. Here, we studied the interaction between these molecular machines and the lipid bilayer by observing changes in the lipid vibrational bands via FTIR spectroscopy. Membrane proteins with different functionalities have been reconstituted into lipid nanodiscs: Microbial rhodopsins that act as light-activated ion pumps (the proton pumps NsXeR and UmRh1, and the chloride pump NmHR) or as sensors (NpSRII), as well as the electron-driven cytochrome c oxidase RsCcO. The effects of the structural changes on the surrounding lipid phase are compared to mechanically induced lateral tension exerted by the light-activatable lipid analogue AzoPC. With the help of isotopologues, we show that the ν(C = O) ester band of the glycerol backbone reports on changes in the lipids’ collective state induced by mechanical changes in the transmembrane proteins. The perturbation of the nanodisc lipids seems to involve their phase and/or packing state. ¹³C-labeling of the scaffold protein shows that its structure also responds to the mechanical expansion of the lipid bilayer.

Plant-Derived Exosomes as A Drug-Delivery Approach for the Treatment of Inflammatory Bowel Disease and Colitis-Associated Cancer

Inflammatory bowel disease (IBD) is a chronic recurrent intestinal disease and includes Crohn’s disease (CD) and ulcerative colitis (UC). Due to the complex etiology of colitis, the current treatments of IBD are quite limited and are mainly concentrated on the remission of the disease. In addition, the side effects of conventional drugs on the body cannot be ignored. IBD also has a certain relationship with colitis-associated cancer (CAC), and inflammatory cells can produce a large number of tumor-promoting cytokines to promote tumor progression. In recent years, exosomes from plants have been found to have the ability to load drugs to target the intestine and have great potential for the treatment of intestinal diseases. This plant-derived exosome-targeting delivery system can load chemical or nucleic acid drugs and deliver them to intestinal inflammatory sites stably and efficiently. This review summarizes the pathophysiological characteristics of IBD and CAC as well as the application and prospect of plant exosomes in the treatment of IBD and CAC.

Model architectures for bacterial membranes

The complex composition of bacterial membranes has a significant impact on the understanding of pathogen function and their development towards antibiotic resistance. In addition to the inherent complexity and biosafety risks of studying biological pathogen membranes, the continual rise of antibiotic resistance and its significant economical and clinical consequences has motivated the development of numerous in vitro model membrane systems with tuneable compositions, geometries, and sizes. Approaches discussed in this review include liposomes, solid-supported bilayers, and computational simulations which have been used to explore various processes including drug-membrane interactions, lipid-protein interactions, host-pathogen interactions, and structure-induced bacterial pathogenesis. The advantages, limitations, and applicable analytical tools of all architectures are summarised with a perspective for future research efforts in architectural improvement and elucidation of resistance development strategies and membrane-targeting antibiotic mechanisms.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12551-021-00913-7.

Thermodynamic Modeling of Solvent-Assisted Lipid Bilayer Formation Process

The solvent-assisted lipid bilayer (SALB) formation method provides a simple and efficient, microfluidic-based strategy to fabricate supported lipid bilayers (SLBs) with rich compositional diversity on a wide range of solid supports. While various studies have been performed to characterize SLBs formed using the SALB method, relatively limited work has been carried out to understand the underlying mechanisms of SALB formation under various experimental conditions. Through thermodynamic modeling, we studied the experimental parameters that affect the SALB formation process, including substrate surface properties, initial lipid concentration, and temperature. It was found that all the parameters are critically important to successfully form high-quality SLBs. The model also helps to identify the range of parameter space within which conformal, homogeneous SLBs can be fabricated, and provides mechanistic guidance to optimize experimental conditions for lipid membrane-related applications.

Lateral voltage as a new input for artificial lipid bilayer systems

In this work, we propose lateral voltage as a new input for use in artificial lipid bilayer systems in addition to the commonly used transmembrane voltage. To apply a lateral voltage to bilayer lipid membranes, we fabricated electrode-equipped silicon and Teflon chips. The Si chips could be used for photodetector devices based on fullerene-doped lipid bilayers, and the Teflon chips were used in a study of the ion channel functions in the lipid bilayer. The findings indicate that the lateral voltage effectively regulates the transmembrane current, in both ion-channel-incorporated and fullerene-incorporated lipid bilayer systems, suggesting that the lateral voltage is a practicable and useful additional input for use in lipid bilayer systems.

Demolish and Rebuild: Controlling Lipid Self-Assembly toward Triggered Release and Artificial Cells

The ability to modulate the structures of lipid membranes, predicated on our nuanced understanding of the properties that drive and alter lipid self-assembly, has opened up many exciting biological applications. In this Perspective, we focus on two endeavors in which the same principles are invoked to achieve completely opposite results. On one hand, controlled liposome decomposition enables triggered release of encapsulated cargo through the development of synthetic lipid switches that perturb lipid packing in the presence of disease-associated stimuli. In particular, recent approaches have utilized artificial lipid switches designed to undergo major conformational changes in response to a range of target conditions. On the other end of the spectrum, the ability to drive the in situ formation of lipid bilayer membranes from soluble precursors is an important component in the establishment of artificial cells. This work has culminated in chemoenzymatic strategies that enable lipid manufacturing from simple components. Herein, we describe recent advancements in these two unique undertakings that are linked by their reliance on common principles of lipid self-assembly.

The interaction of a β2 adrenoceptor agonist drug with biomimetic cell membrane models: The case of terbutaline sulphate

Terbutaline sulphate (TS) is a selective short-acting β₂ adrenoceptor agonist used for asthma treatment. The pharmacological activity of TS depends on its binding to the transmembrane protein, β₂ adrenoceptor. Thus, the interactions of this drug with biological membranes are expected, affecting its pharmacological activity. Using in vitro models to study the interaction of TS with biological membranes can provide important information about the activity of the drug. Here, liposomes with different lipid compositions were used as biomimetic models of cell membranes to evaluate the effect of composition, complexity, and physical state of membranes on TS-membrane interactions. For that, liposomes containing dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and liposomes containing DMPC and cholesterol (CHOL) were prepared. For the study of TS-membrane interactions, the TS lipophilicity was evaluated in terms of i) partition coefficient; ii) the preferential location of the drug within the membrane; iii) and the effect of TS on the membrane fluidity. The obtained data suggest that TS has an affinity for the lipid membrane, partitioning from the aqueous to the lipid phase. The affinity was dependent on the liposomes' compositions, showing a greater affinity for DMPC membranes than for DMPC:CHOL model. Dynamic light scattering (DLS) results revealed that this is due to the rigidizing effect caused by CHOL molecules. These findings provide valuable insights in the understanding of the complex interaction of TS with biomembrane models as well as the relevance of lipid compositions and membrane structure in such interactions, which may be related to its pharmacological activity and side effects.

Direct-Write Patterning of Biomimetic Lipid Membranes In Situ with FluidFM

The creation of biologically inspired artificial membranes on substrates with custom size and in close proximity to each other not only provides a platform to study biological processes in a simplified manner, but they also constitute building blocks for chemical or biological sensors integrated in microfluidic devices. Scanning probe lithography tools such as dip-pen nanolithography (DPN) have opened a new paradigm in this regard, although they possess some inherent drawbacks like the need to operate in air environment or the limited choice of lipids that can be patterned. In this work, we propose the use of the fluid force microscopy (FluidFM) technology to fabricate biomimetic membranes without losing the multiplexing capability of DPN but gaining flexibility in lipid inks and patterning environment. We shed light on the driving mechanisms of the FluidFM-mediated lithography processes in air and liquid. The obtained results should prompt the creation of more realistic biomimetic membranes with arbitrary complex phospholipid mixtures, cholesterol, and potential functional membrane proteins directly patterned in physiological environment.

Liposomal nanoparticles based on steroids and isoprenoids for nonviral gene delivery

Natural lipid molecules are an essential part of life as they constitute the membrane of cells and organelle. In most of these cases, the hydrophobicity of natural lipids is contributed by alkyl chains. Although natural lipids with a nonfatty acid hydrophobic backbone are quite rare, steroids and isoprenoids have been strong candidates as part of a lipid. Over the years, these natural molecules (steroid and isoprenoids) have been used to make either lipid-based nanoparticle or functionalize in such a way that it could form nano assembly alone for therapeutic delivery. Here we mainly focus on the synthetic functionalized version of these natural molecules which forms cationic liposomal nanoparticles (LipoNPs). These cationic LipoNPs were further used to deliver various negatively charged genetic materials in the form of pDNA, siRNA, mRNA (nucleic acids), and so on. This article is categorized under: Biology-Inspired Nanomaterials > Lipid-Based Structures.

Caffeic acid for the prevention and treatment of Alzheimer's disease: The effect of lipid membranes on the inhibition of aggregation and disruption of Aβ fibrils

The onset of Alzheimer's disease (AD) is triggered by the aggregation of amyloid β (Aβ) peptides which leads to the formation of fibrils. Molecules that are able to inhibit fibrillation and/or disrupt fibrils have aroused interest for AD therapy. Fibrillation is a complex process highly dependent on the surrounding environment. One of the most relevant factors affecting Aβ aggregation is the presence of cellular membranes. Here, the ability of caffeic acid (CA) in preventing the Aβ_1-42 aggregation and disaggregating mature fibrils was evaluated in a membrane-like environment and in a bulk solution for comparison. To this end, liposomes were used as in vitro models of neuronal membranes. CA exhibited strong activity in inhibiting the fibrillation of Aβ_1-42 in the aqueous medium, which remained in the presence of liposomes. Furthermore, CA disrupted instantly preformed fibrils in the aqueous medium. However, the CA's disaggregating activity was disturbed by the presence of lipid membranes. Instead of being immediate, the CA's disaggregating activity increased over time. The moderate affinity of CA for the lipid bilayer may explain the distinct fibrils disaggregation profiles. These findings emphasize the therapeutic potential of CA in preventing and treating AD, thus justifying further investigations in animal models.

Influence of in vitro neuronal membranes on the anti-amyloidogenic activity of gallic acid: Implication for the therapy of Alzheimer's disease

Molecules inhibiting the amyloid beta (Aβ) peptide aggregation and/or disaggregating mature fibrils are a promising approach for the Alzheimer's disease (AD) therapy, as the Aβ fibrillation is one of the key triggers of the disease. Gallic acid (GA) is a phenolic acid with anti-amyloidogenic activity against Aβ in buffered solutions. However, there is still no evidence of these properties in vivo. Given the rate of failures of AD drug development, there is a huge demand of replicating the in vivo environment in in vitro studies, thus allowing to stop earlier the study of molecules with no effect in vivo. Thus, this study aims to evaluate the effect of in vitro neuronal membranes on the GA's ability in preventing Aβ_1-42 aggregation and disrupting preformed fibrils. To this end, liposomes were employed to mimic the cell membrane environment. The results reveal that the lipid membranes did not affect the GA's ability in inhibiting Aβ_1-42 fibrillation. However, in vitro neuronal membranes modulate the GA-induced Aβ fibrils disaggregation, which may be related with the moderate affinity of the compound for the lipid membrane. Even so, GA presented strong anti-amyloidogenic properties in the cell membrane-like environment. This work highlights the promising value of GA on preventing and treating AD, thus justifying its study in animal models.

Rapid Capture of Cancer Extracellular Vesicles by Lipid Patch Microarrays

Extracellular vesicles (EVs) contain various bioactive molecules such as DNA, RNA, and proteins, and play a key role in the regulation of cancer progression. Furthermore, cancer-associated EVs carry specific biomarkers and can be used in liquid biopsy for cancer detection. However, it is still technically challenging and time consuming to detect or isolate cancer-associated EVs from complex biofluids (e.g., blood). Here, a novel EV-capture strategy based on dip-pen nanolithography generated microarrays of supported lipid membranes is presented. These arrays carry specific antibodies recognizing EV- and cancer-specific surface biomarkers, enabling highly selective and efficient capture. Importantly, it is shown that the nucleic acid cargo of captured EVs is retained on the lipid array, providing the potential for downstream analysis. Finally, the feasibility of EV capture from patient sera is demonstrated. The demonstrated platform offers rapid capture, high specificity, and sensitivity, with only a small need in analyte volume and without additional purification steps. The platform is applied in context of cancer-associated EVs, but it can easily be adapted to other diagnostic EV targets by use of corresponding antibodies.

Effects of ethanol and n-butanol on the fluidity of supported lipid bilayers

The interactions of molecules such as short-chain alcohols with the mammalian plasma membrane are thought to play a role in anesthetic effects. We have examined the concentration-dependent effects of ethanol and n-butanol on the fluidity of planar model lipid bilayer structures supported on mica. The supported model bilayer was composed of 1,2-dioleoyl-sn-phosphatidylcholine (DOPC), cholesterol, and sphingomyelin, and the bilayers were formed by vesicle fusion from extruded unilamellar vesicles (133 nm diameter, polydispersity index of 0.17). Controlled amounts of ethanol and n-butanol were added during vesicle deposition. Translational diffusion constants were obtained utilizing fluorescence recovery after photobleaching (FRAP) measurements on the micrometer scale with perylene as the fluorophore. The translational diffusion constants increased and then decreased with increasing ethanol concentration, with the bilayer structure degrading at ca. 0.8 M ethanol. A similar trend was observed for n-butanol at lower alcohol concentrations owing to greater interactions with phospholipid bilayer constituents. For n-butanol, the integrity of the planar bilayer structure deteriorated at ca. 0.4 M n-butanol. The results are consistent with bilayer interdigitation.

The Elucidation of the Molecular Mechanism of the Extrusion Process

Extrusion is a popular method for producing homogenous population of unilamellar liposomes. The technique relies on forcing a lipid suspension through cylindrical pores in a polycarbonate membrane. The quantification of the extrusion and/or recalibration processes make possible the acquisition of experimental data, which can be correlated with the mechanical properties of the lipid bilayer. In this work, the force needed for the extrusion process was correlated with the mechanical properties of a lipid bilayer derived from other experiments. Measurements were performed using a home-made dedicated device capable of maintaining a stable volumetric flux of a liposome suspension through well-defined pores and to continuously measure the extrusion force. Based on the obtained results, the correlation between the lipid bilayer bending rigidity and extrusion force was derived. Specifically, it was found that the bending rigidity of liposomes formed from well-defined lipid mixtures agrees with data obtained by others using flicker-noise spectroscopy or micromanipulation. The other issue addressed in the presented studies was the identification of molecular mechanisms leading to the formation of unilamellar vesicles in the extrusion process. Finally, it was demonstrated that during the extrusion, lipids are not exchanged between vesicles, i.e., vesicles can divide but no membrane fusion or lipid exchange between bilayers was detected.

The dynamic face of lipid membranes

Cell membranes - primarily composed of lipids, sterols, and proteins - form a dynamic interface between living cells and their environment. They act as a mechanical barrier around the cell while selectively facilitating material transport, signal transduction, and various other functions necessary for the cell viability. The complex functionality of cell membranes and the hierarchical motions and responses they exhibit demand a thorough understanding of the origin of different membrane dynamics and how they are influenced by molecular additives and environmental cues. These dynamic modes include single-molecule diffusion, thermal fluctuations, and large-scale membrane deformations, to name a few. This review highlights advances in investigating structure-driven dynamics associated with model cell membranes, with a particular focus on insights gained from neutron scattering and spectroscopy experiments. We discuss the uniqueness of neutron contrast variation and its remarkable potential in probing selective membrane structure and dynamics on spatial and temporal scales over which key biological functions occur. We also present a summary of current and future opportunities in synergistic combinations of neutron scattering with molecular dynamics (MD) simulations to gain further understanding of the molecular mechanisms underlying complex membrane functions.

Reconstitution of Functional Integrin αIIbβ3 and Its Activation in Plasma Membrane-Mimetic Lipid Environments

The study of the platelet receptor integrin αIIbβ3 in a membrane-mimetic environment without interfering signalling pathways is crucial to understand protein structure and dynamics. Our understanding of this receptor and its sequential activation steps has been tremendously progressing using structural and reconstitution approaches in model membranes, such as liposomes or supported-lipid bilayers. For most αIIbβ3 reconstitution approaches, saturated short-chain lipids have been used, which is not reflecting the native platelet cell membrane composition. We report here on the reconstitution of label-free full-length αIIbβ3 in liposomes containing cholesterol, sphingomyelin, and unsaturated phosphatidylcholine mimicking the plasma membrane that formed supported-lipid bilayers for quartz-crystal microbalance with dissipation (QCM-D) experiments. We demonstrate the relevance of the lipid environment and its resulting physicochemical properties on integrin reconstitution efficiency and its conformational dynamics. We present here an approach to investigate αIIbβ3 in a biomimetic membrane system as a useful platform do dissect disease-relevant integrin mutations and effects on ligand binding in a lipid-specific context, which might be applicable for drug screening.

Basic Methods for Preparation of Liposomes and Studying Their Interactions with Different Compounds, with the Emphasis on Polyphenols

Studying the interactions between lipid membranes and various bioactive molecules (e.g., polyphenols) is important for determining the effects they can have on the functionality of lipid bilayers. This knowledge allows us to use the chosen compounds as potential inhibitors of bacterial and cancer cells, for elimination of viruses, or simply for keeping our healthy cells in good condition. As studying those effect can be exceedingly difficult on living cells, model lipid membranes, such as liposomes, can be used instead. Liposomal bilayer systems represent the most basic platform for studying those interactions, as they are simple, quite easy to prepare and relatively stable. They are especially useful for investigating the effects of bioactive compounds on the structure and kinetics of simple lipid membranes. In this review, we have described the most basic methods available for preparation of liposomes, as well as the essential techniques for studying the effects of bioactive compounds on those liposomes. Additionally, we have provided details for an easy laboratory implementation of some of the described methods, which should prove useful especially to those relatively new on this research field.

Pore-Spanning Plasma Membranes Derived from Giant Plasma Membrane Vesicles

Giant plasma membrane vesicles (GPMVs) are a highly promising model system for the eukaryotic plasma membrane. The unresolved challenge, however, is a path to surface-based structures that allows accessibility to both sides of the plasma membrane through high-resolution techniques. Such an approach would pave the way to advanced chip-based technologies for the analysis of complex cell surfaces to study the roles of membrane proteins, host-pathogen interactions, and many other bioanalytical and sensing applications. This study reports the generation of planar supported plasma membranes and for the first-time pore-spanning plasma membranes (PSPMs) derived from pure GPMVs that are spread on activated solid and highly ordered porous silicon substrates. GPMVs were produced by two different vesiculation agents and were first investigated with respect to their growth behavior and phase separation. Second, these GPMVs were spread onto silicon substrates to form planar supported plasma membrane patches. PSPMs were obtained by spreading of pure GPMVs on oxygen-plasma activated porous substrates with pore diameters of 3.5 μm. Fluorescence micrographs unambiguously showed that the PSPMs partially phase separate in a mobile ordered phase surrounded by a disordered phase, which was supported by cholesterol extraction using methyl-β-cyclodextrin.

Investigating the structural properties of hydrophobic solvent-rich lipid bilayers

In vitro reconstitutions of lipid membranes have proven to be an indispensable tool to rationalize their molecular complexity and to understand their role in countless cellular processes. However, amongst the various techniques used to reconstitute lipid bilayers in vitro, several approaches are not solvent-free, but rather contain residual hydrophobic solvents in between the two bilayer leaflets, generally as a consequence of the procedure used to generate the bilayer. To what extent the presence of these hydrophobic solvents modifies bilayer properties with respect to native, solvent-free, conditions remains an open question that has important implications for the appropriate interpretation of numerous experimental observations. Here, we thorouhgly characterize hydrophobic solvent-rich lipid bilayers using atomistic molecular dynamics simulations. Our data indicate that while the presence of hydrophobic solvents at high concentrations, such as hexadecane, has a significant effect on membrane thickness, their effects on surface properties, membrane order and lateral stress are quite moderate. Our results corroborate the validity of in vitro approaches as model systems for the investigations of biological membranes but raise a few cautionary aspects that must be considered when investigating specific membrane properties.

Antibacterial green tea catechins from a molecular perspective: mechanisms of action and structure-activity relationships

This review summarizes the mechanisms of antibacterial action of green tea catechins, discussing the structure-activity relationship (SAR) studies for each mechanism. The antibacterial activity of green tea catechins results from a variety of mechanisms that can be broadly classified into the following groups: (1) inhibition of virulence factors (toxins and extracellular matrix); (2) cell wall and cell membrane disruption; (3) inhibition of intracellular enzymes; (4) oxidative stress; (5) DNA damage; and (6) iron chelation. These mechanisms operate simultaneously with relative importance differing among bacterial strains. In all SAR studies, the highest antibacterial activity is observed for galloylated compounds (EGCG, ECG, and theaflavin digallate). This observation, combined with numerous experimental and theoretical evidence, suggests that catechins share a common binding mode, characterized by the formation of hydrogen bonds and hydrophobic interactions with their target.