Electroformation of giant vesicles from an inverse phase precursor

Mechanisms and Factors Influencing the Production of Uniform-Sized Giant Unilamellar Vesicles by Discrete Lipid Film Arrays

In this paper, we innovatively proposed a highly uniform vesicle preparation scheme based on the intervesicle mechanical self-constraint effect of vesicle crowding. By adjusting the spacing of discrete microwell structures, we observed that during the self-assembly of phospholipid molecules in microwells to form giant unilamellar vesicles (GUVs), the scale swelling of the vesicles during the continuous growth process would lead to the crowding of vesicles in adjacent microwells, thus inducing the formation of intervesicle mechanical self-constraint effect. The results of the experiment showed that this paper obtained the optimized discretized microwell structure (micropillar side: 30 μm; pitch: 0 μm), and the corresponding lipid mass was measured and determined, yielding homogeneous giant GUVs of 37.9 ± 2.0 μm. In this paper, homogenized GUVs (∼40 μm) with different cholesterol concentrations (10, 20, and 30%) were obtained by this method, and the above vesicles were subjected to controlled electroporation experiment under external electric fields of 23, 31, and 41 kV/cm, respectively. It showed that the mechanical self-constraint effect of vesicle crowding induced by patterned microstructures during the self-assembly of phospholipid molecules significantly enhances the size homogeneity of GUVs, which would be helpful for the wide applications of GUVs in other areas such as cell-like models and controlled release of drugs.

Giant vesicles form in physiological saline and encapsulate pDNA by the modified electroformation method

Giant vesicles (GVs) are used to study the structures and functions of cells and cell membranes. Electroformation is the most commonly used method for GV preparation. However, the electroformation of GVs is hindered in highly concentrated ionic solutions, limiting their application as cell models for research under physiological conditions. In this study, giant multilayer vesicles were successfully generated in physiological saline using a modified electroformation device by adding an insulating layer between the two electrode plates. The influence of the electric frequency and strength on the electroformation of GVs in physiological saline was explored, and a possible mechanism for this improvement was assessed. It has been shown that an insulating layer between the two electrodes can improve the electroformation of GVs in physiological saline by increasing the electrical impedance, which is weakened by the saline solution, thereby restoring the reduced effective electric field strength. Furthermore, macromolecular plasmid DNA (pDNA) was successfully encapsulated in the electroformed GVs of the modified device. This modified electroformation method may be useful for generating eukaryotic cell models under physiological conditions.

Flavonoid-Labeled Biopolymer in the Structure of Lipid Membranes to Improve the Applicability of Antioxidant Nanovesicles

Nanovesicles produced with lipids and polymers are promising devices for drug and bioactive delivery and are of great interest in pharmaceutical applications. These nanovesicles can be engineered for improvement in bioavailability, patient compliance or to provide modified release or enhanced delivery. However, their applicability strongly depends on the safety and low immunogenicity of the components. Despite this, the use of unsaturated lipids in nanovesicles, which degrade following oxidation processes during storage and especially during the proper routes of administration in the human body, may yield toxic degradation products. In this study, we used a biopolymer (chitosan) labeled with flavonoid (catechin) as a component over a lipid bilayer for micro- and nanovesicles and characterized the structure of these vesicles in oxidation media. The purpose of this was to evaluate the in situ effect of the antioxidant in three different vesicular systems of medium, low and high membrane curvature. Liposomes and giant vesicles were produced with the phospholipids DOPC and POPC, and crystalline cubic phase with monoolein/DOPC. Concentrations of chitosan-catechin (CHCa) were included in all the vesicles and they were challenged in oxidant media. The cytotoxicity analysis using the MTT assay (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide) revealed that concentrations of CHCa below 6.67 µM are non-toxic to HeLa cells. The size and zeta potential of the liposomes evidenced the degradation of their structures, which was minimized by CHCa. Similarly, the membrane of the giant vesicle, which rapidly deteriorated in oxidative solution, was protected in the presence of CHCa. The production of a lipid/CHCa composite cubic phase revealed a specific cubic topology in small-angle X-ray scattering, which was preserved in strong oxidative media. This study demonstrates the specific physicochemical characteristics introduced in the vesicular systems related to the antioxidant CHCa biopolymer, representing a platform for the improvement of composite nanovesicle applicability.

Antibacterial polypeptide-bioparticle for oral administration: Powder formulation, palatability and in vivo toxicity approach

The upsurge of bacterial resistance to conventional antibiotics turned a well-recognized public health threat. The need of developing new biomaterials of effective practical use in order to tackle bacterial resistance became urgent. In this study, a submicrometric bioparticle of known antibacterial activity was produced in powder form with suitable texture and appealing characteristics for effective oral administration. Through complex coacervating a natural-source antimicrobial polypeptide with chitosan-N-arginine and alginate, the bioactive polypeptide was physically incorporated to the bioparticle whose structure positively responds to the pH variations found in gastrointestinal tract. The powder formulation presented high palatability that was evaluated using fish as in vivo animal model. A thorough survey of the fish intestinal tissues, following a systematic oral administration, revealed high penetration potential of the biomaterial through epithelial cells and deeper intestine layers. Despite, no cytotoxic effect was observed in analyzing the tissues through different histology methods. The absence of intestinal damage was corroborated by immune histochemistry, being the integrity of epithelial motor myosin Vb and related traffic proteins preserved. Hematology further endorsed absence of toxicity in blood cells whose morphology was evaluated in detail. The study evidenced the applicability potential of a new biomaterial of appealing and safe oral administration of antibacterial polypeptide.

Liposomal-Based Formulations: A Path from Basic Research to Temozolomide Delivery Inside Glioblastoma Tissue

Glioblastoma (GBM) is a lethal brain cancer with a very difficult therapeutic approach and ultimately frustrating results. Currently, therapeutic success is mainly limited by the high degree of genetic and phenotypic heterogeneity, the blood brain barrier (BBB), as well as increased drug resistance. Temozolomide (TMZ), a monofunctional alkylating agent, is the first line chemotherapeutic drug for GBM treatment. Yet, the therapeutic efficacy of TMZ suffers from its inability to cross the BBB and very short half-life (~2 h), which requires high doses of this drug for a proper therapeutic effect. Encapsulation in a (nano)carrier is a promising strategy to effectively improve the therapeutic effect of TMZ against GBM. Although research on liposomes as carriers for therapeutic agents is still at an early stage, their integration in GBM treatment has a great potential to advance understanding and treating this disease. In this review, we provide a critical discussion on the preparation methods and physico-chemical properties of liposomes, with a particular emphasis on TMZ-liposomal formulations targeting GBM developed within the last decade. Furthermore, an overview on liposome-based formulations applied to translational oncology and clinical trials formulations in GBM treatment is provided. We emphasize that despite many years of intense research, more careful investigations are still needed to solve the main issues related to the manufacture of reproducible liposomal TMZ formulations for guaranteed translation to the market.

Cubosomal lipid nanoassemblies with pH-sensitive shells created by biopolymer complexes: A synchrotron SAXS study

We report a strategy for sustainable development of pH-responsive cubic liquid crystalline nanoparticles (cubosomes), in which the structure-defining lyotropic nonlamellar lipid and the eventually encapsulated guest molecules can be protected by pH-sensitive polyelectrolyte shells with mucoadhesive properties. Bulk non-lamellar phases as well as pH-responsive polyelectrolyte-modified nanocarriers were formed by spontaneous assembly of the nonlamellar lipid monoolein and two biopolymers tailored in nanocomplexes with pH-dependent net charge. The mesophase particles involved positively charged N-arginine-modified chitosan (CHarg) and negatively charged alginate (ALG) chains assembled at different biopolymer concentrations and charge ratios into a series of pH-responsive complexes. The roles of Pluronic F127 as a dispersing agent and a stabilizer of the nanoscale dispersions were examined. Synchrotron small-angle X-ray scattering (SAXS) investigations were performed at several N-arginine-modified chitosan/alginate ratios (CHarg/ALG with 10, 15 and 20 wt% ALG relative to CHarg) and varying pH values mimicking the pH conditions of the gastrointestinal route. The structural parameters characterizing the inner cubic liquid crystalline organizations of the nanocarriers were determined as well as the particle sizes and stability on storage. The surface charge variations, influencing the measured zeta-potentials, evidenced the inclusion of the CHarg/ALG biopolymer complexes into the lipid nanoassemblies. The polyelectrolyte shells rendered the hybrid cubosome nanocarriers pH-sensitive and influenced the swelling of their lipid-phase core as revealed by the acquired SAXS patterns. The pH-responsiveness and the mucoadhesive features of the cubosomal lipid/polyelectrolyte nanocomplexes may be of interest for in vivo drug delivery applications.

Mechanism study of how lipid vesicle electroformation is suppressed by the presence of sodium chloride

Giant lipid vesicles (GLVs) are usually adopted as models of cell membranes and electroformation is the most commonly used method for GLV formation. However, GLV electroformation are known to be suppressed by the presence of salt and the mechanism is not clear so far. In this paper, the lipid hydration and GLV electroformation were investigated as a function of the concentration of sodium chloride by depositing the lipids on the bottom substrates and top substrates. In addition, the electrohydrodynamic force generated by the electroosmotic flow (EOF) on the lipid phase was calculated with COMSOL Multiphysics. It was found that the mechanisms for the failure of GLV electroformation in salt solutions are: 1) the presence of sodium chloride decreases the membrane permeability to aqueous solution by accelerating the formation of well-packed membranes, suppressing the swelling and detachment of the lipid membranes; 2) the presence of sodium chloride decreased the electrohydrodynamic force by increasing the medium conductivity.

Polymersomes: Preparation and Characterization

Polymersomes, also called polymeric vesicles, are self-assembled by amphiphilic copolymers. Due to their unique characters, polymersomes are attracting more and more interest as an important class of vehicles for nanopharmaceuticals. In this chapter, various methods to prepare and characterize polymersomes are introduced systematically with several applicable examples. In addition, the advantages and disadvantages of each method were compared and analyzed with the aim to help readers choose the appropriate method in the process of experiments. Although some methods we introduced here are effective in preparing and characterizing polymersomes, the remaining challenge in this filed is to develop new tools. The reason is that polymersome is a kind of complex nanostructure, and some minor factors can affect the formation of polymersome. Meanwhile, more advanced technology should be developed to precisely determine the structure of some complex polymersomes such as multilayer polymersomes.

Interaction between Surface Charge-Modified Gold Nanoparticles and Phospholipid Membranes

This report clarifies the interaction of surface charge-modified gold nanoparticles (AuNPs) with phospholipid membranes, which is helpful to understand the antibacterial mechanism of positive charge-modified AuNPs to Gram-negative bacteria. Although the simulated bacterial cell membranes as a whole are negatively charged, the local electrostatic repulsive interaction between the positive charge-coated AuNPs and the small-sized flexible cationic head group of dioleyl phosphatidylethanolamine molecules induces the phase transformation of the simulated bacterial cell membranes from a lamellar to an inverted hexagonal phase. Transmembrane pores with a diameter of about 3.0 nm in the inverted hexagonal structure would result in the destruction of cell membrane function. Such an interaction of positive charge-modified AuNPs with the membrane mimics provides a promising route to develop new antibacterial agents by modifying positive charges on the surface of nanoparticles.

Ion concentration effect (Na+ and Cl-) on lipid vesicle formation

Lipid vesicle formation is known to be suppressed in salt solutions, but the mechanism of this phenomenon remains unclear. In order to better understand this issue, the effect of salt concentrations (0-800mM) of sodium chloride on the behavior of L-α-phosphatidylcholine (PC) in aqueous solution was investigated in this work. The results showed that fusion among vesicles, micelles and bilayers may be essential for vesicle formation. With addition of ions and an increase in ion concentration, the lipids became constrained in lateral movement and packed increasingly tightly. The resulted hard supported phospholipid bilayers (SPBs) were thus more difficult to detach from the substrate to form vesicles. These phenomena were tried to be explained at molecular level. Hydrophobic effect is the original cause of lipid vesicle formation, which in fact is absence of attraction between the involved substances. That is to say, the stronger the 3D network was bounded in the medium, the stronger the hydrophobic repulsion on the lipids would be. This might be one reason for the suppression of vesicle formation in salt solution.

Lipid membrane-assisted condensation and assembly of amphiphilic Janus particles

Amphiphilic Janus particles self-assemble into complex metastructures, but little is known about how their assembly might be modified by weak interactions with a nearby biological membrane surface. Here, we report an integrated experimental and molecular dynamics simulation study to investigate the self-assembly of amphiphilic Janus particles on a lipid membrane. We created an experimental system in which Janus particles are allowed to self-assemble in the same medium where zwitterionic lipids form giant unilamellar vesicles (GUVs). Janus particles spontaneously concentrated on the inner leaflet of the GUVs. They exhibited biased orientation and heterogeneous rotational dynamics as revealed by single particle rotational tracking. The combined experimental and simulation results show that Janus particles concentrate on the lipid membranes due to weak particle-lipid attraction, whereas the biased orientation of particles is driven predominantly by inter-particle interactions. This study demonstrates the potential of using lipid membranes to influence the self-assembly of Janus particles.

How cellular membrane properties are affected by the actin cytoskeleton

Lipid membranes define the boundaries of living cells and intracellular compartments. The dynamic remodelling of these membranes by the cytoskeleton, a very dynamic structure made of active biopolymers, is crucial in many biological processes such as motility or division. In this review, we present some aspects of cellular membranes and how they are affected by the presence of the actin cytoskeleton. We show that, in parallel with the direct study of membranes and cytoskeleton in vivo, biomimetic in vitro systems allow reconstitution of biological processes in a controlled environment. In particular, we show that liposomes, or giant unilamellar vesicles, encapsulating a reconstituted actin network polymerizing at their membrane are suitable models of living cells and can be used to decipher the relative contributions of membrane and actin on the mechanical properties of the cellular interface.

Shape control of lipid bilayer membranes by confined actin bundles

In living cells, lipid membranes and biopolymers determine each other's conformation in a delicate force balance. Cellular polymers such as actin filaments are strongly confined by the plasma membrane in cell protrusions such as lamellipodia and filopodia. Conversely, protrusion formation is facilitated by actin-driven membrane deformation and these protrusions are maintained by dense actin networks or bundles of actin filaments. Here we investigate the mechanical interplay between actin bundles and lipid bilayer membranes by reconstituting a minimal model system based on cell-sized liposomes with encapsulated actin filaments bundled by fascin. To address the competition between the deformability of the membrane and the enclosed actin bundles, we tune the bundle stiffness (through the fascin-to-actin molar ratio) and the membrane rigidity (through protein decoration). Using confocal microscopy and quantitative image analysis, we show that actin bundles deform the liposomes into a rich set of morphologies. For liposomes having a small membrane bending rigidity, the actin bundles tend to generate finger-like membrane protrusions that resemble cellular filopodia. Stiffer bundles formed at high crosslink density stay straight in the liposome body, whereas softer bundles formed at low crosslink density are bent and kinked. When the membrane has a large bending rigidity, membrane protrusions are suppressed. In this case, membrane enclosure forces the actin bundles to organize into cortical rings, to minimize the energy cost associated with filament bending. Our results highlight the importance of taking into account mechanical interactions between the actin cytoskeleton and the membrane to understand cell shape control.

Effective protection of biological membranes against photo-oxidative damage: Polymeric antioxidant forming a protecting shield over the membrane

We have prepared a chitosan polymer modified with gallic acid in order to develop an efficient protection strategy biological membranes against photodamage. Lipid bilayers were challenged with photoinduced damage by photosensitization with methylene blue, which usually causes formation of hydroperoxides, increasing area per lipid, and afterwards allowing leakage of internal materials. The damage was delayed by a solution of gallic acid in a concentration dependent manner, but further suppressed by the polymer at very low concentrations. The membrane of giant unilamellar vesicles was covered with this modified macromolecule leading to a powerful shield against singlet oxygen and thus effectively protecting the lipid membrane from oxidative stress. The results have proven the discovery of a promising strategy for photo protection of biological membranes.

Gel-assisted formation of giant unilamellar vesicles

Giant unilamellar vesicles or GUVs are systems of choice as biomimetic models of cellular membranes. Although a variety of procedures exist for making single walled vesicles of tens of microns in size, the range of lipid compositions that can be used to grow GUVs by the conventional methods is quite limited, and many of the available methods involve energy input that can damage the lipids or other molecules present in the growing solution for embedment in the membrane or in the vesicle interior. Here, we show that a wide variety of lipids or lipid mixtures can grow into GUVs by swelling lipid precursor films on top of a dried polyvinyl alcohol gel surface in a swelling buffer that can contain diverse biorelevant molecules. Moreover, we show that the encapsulation potential of this method can be enhanced by combining polyvinyl alcohol-mediated growth with inverse-phase methods, which allow (bio)molecule complexation with the lipids.

Tunable adsorption of soft colloids on model biomembranes

A simple procedure is developed to probe in situ the association between lipid bilayers and colloidal particles. Here, a one-step method is applied to generate giant unilamellar 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) vesicles (GUVs) by application of an alternating electric field directly in the presence of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microgels. We demonstrate that the soft PNIPAM microgel particles act as switchable stabilizers for lipid membranes. The change of the particle conformation from the swollen to the collapsed state enables the reversible control of the microgel adsorption as a function of temperature. At 20 °C, the swollen and hydrophilic soft microgel particles adsorb evenly and densely pack in 2D hexagonal arrays at the DOPC GUV surfaces. In contrast, at 40 °C, that is, above the volume phase transition temperature (TVPT = 32 °C) of the PNIPAM microgels, the collapsed and more hydrophobic particles partially desorb and self-organize into domains at the GUV/GUV interfaces. This study shows that thermoresponsive PNIPAM microgels can be used to increase and control the stability of lipid vesicles where the softness and deformability of these types of particles play a major role. The observed self-assembly, where the organization and position of the particles on the GUV surface can be controlled "on demand", opens new routes for the design of nanostructured materials.

Insights on the interactions of chitosan with phospholipid vesicles. Part I: Effect of polymer deprotonation

Interactions between the polysaccharide chitosan and negatively charged phospholipid liposomes were studied as a function of compositional and environmental conditions. Using isothermal titration calorimetry, different levels of deprotonation of chitosan in acidic solutions were attained with titration of the fully protonated polymer at pH 4.48 into solutions with increasing pH. The process was found to be highly endothermic. We then examined the interaction of the polymer with vesicles in solutions of different pH. Even when partially deprotonated, the chitosan chains retain their affinity to the negatively charged liposomes. However, the stronger adsorption results in lower organization of the chains over the membrane.

Insights on the interactions of chitosan with phospholipid vesicles. Part II: Membrane stiffening and pore formation

The interactions between the polysaccharide chitosan and phospholipids are studied using giant unilamellar vesicles (GUVs). We explore both bare GUVs incubated in chitosan solution post vesicle formation and GUVs prepared using a reverse-phase method where the polymer is adsorbed on both sides of the membrane leaflet. The fluctuations of the vesicle membrane are significantly reduced in the presence of chitosan as characterized by the bending rigidity, which increases with chitosan concentration denoting physical restrictions imposed to the bilayer as a consequence of the interaction with the polysaccharide. In the absence of chitosan, the rigidity of the bare phosphatidylcholine vesicles is also observed to increase (about 3-fold) upon the incorporation of a small fraction (10 mol %) of phosphatidylglycerol. Pore formation caused by chitosan is evidenced by loss of optical contrast of the giant vesicles denoting exchange between internal and external solutions through the pores. Our study provides evidence for the potential of chitosan to affect the bilayer permeability and to disrupt negatively charged membranes as well as to promote adhesiveness of vesicles on glass surfaces.

Cell-sized liposomes reveal how actomyosin cortical tension drives shape change

Animal cells actively generate contractile stress in the actin cortex, a thin actin network beneath the cell membrane, to facilitate shape changes during processes like cytokinesis and motility. On the microscopic scale, this stress is generated by myosin molecular motors, which bind to actin cytoskeletal filaments and use chemical energy to exert pulling forces. To decipher the physical basis for the regulation of cell shape changes, here, we use a cell-like system with a cortex anchored to the outside or inside of a liposome membrane. This system enables us to dissect the interplay between motor pulling forces, cortex-membrane anchoring, and network connectivity. We show that cortices on the outside of liposomes either spontaneously rupture and relax built-up mechanical stress by peeling away around the liposome or actively compress and crush the liposome. The decision between peeling and crushing depends on the cortical tension determined by the amount of motors and also on the connectivity of the cortex and its attachment to the membrane. Membrane anchoring strongly affects the morphology of cortex contraction inside liposomes: cortices contract inward when weakly attached, whereas they contract toward the membrane when strongly attached. We propose a physical model based on a balance of active tension and mechanical resistance to rupture. Our findings show how membrane attachment and network connectivity are able to regulate actin cortex remodeling and membrane-shape changes for cell polarization.

Dual effects of chitosan decoration on the liposomal membrane physicochemical properties as affected by chitosan concentration and molecular conformation

This study was devoted to a further understanding of the dependence of liposomal membrane properties on chitosan conformation and proved the dual effects of chitosan. The concentration dependence of chitosan conformation in aqueous solution was illustrated by surface tension and fluorescence probe techniques. Fluorescence and Raman spectra were subsequently employed to investigate the dynamic and structural changes of the liposomal membrane resulting from chitosan decoration. Results showed that the unfolded and crimped chains of chitosan flatly adsorbed onto the membrane surface via electrostatic attraction and favored liposome stability. Furthermore, the adsorption of crimped chains seemed stronger due to the embedding of their hydrophobic moieties. However, the presence of chitosan coils induced the increase in membrane fluidity, the intrachain disorder in lipid molecules, and the gauche conformation change of choline group. Dynamic light scattering and lipid oxidation measurements demonstrated that this perturbation was correlated with the permeation of coils into the lipid bilayer.

Binding of chitosan to phospholipid vesicles studied with isothermal titration calorimetry

We thermodynamically characterize the interaction of chitosan with small liposomes and the binding and organization of the polysaccharide on the membrane of the vesicles. By means of isothermal titration calorimetry (ITC), we obtain the enthalpy variations arising from binding of the positively ionized chitosan to neutral and negatively charged liposomes. The strong electrostatic interaction of the polysaccharide with the negative charges at the membrane gives rise to highly exothermic signal until charge compensation is reached. The equilibrium constant, the interaction stoichiometry, and the molar enthalpy of binding chitosan monomers to phospholipids from the external leaflet of the vesicle membrane are obtained from the isotherm curve fitting assuming independent binding sites. The strong exothermic signal indicates that the electrostatically driven binding of chitosan to the membrane is energetically favored, leading to further stabilization of the vesicle suspension. The higher the net negative charge of the vesicles, the more pronounced the adsorption of chitosan is, leading to weaker chain organization of the adsorbed chitosan at the membrane. At the point of charge saturation, vesicle aggregation takes place and we show that this behavior does not always lead to charge reversal at the membrane. Models for the binding behavior and structural organization of chitosan are proposed based on the experimental results from ITC, ζ-potential, and dynamic light scattering.