Thermodynamics and kinetics of vesicles formation processes

Spontaneous nanotube formation of an asymmetric glycolipid

Over the past decades, advances in lipid nanotechnology have shown that self-assembled lipid structures providing ease of preparation, chemical stability, and biocompatibility represent a landmark on the development of multidisciplinary technologies. Lipid nanotubes (LNTs) are a unique class of lipid self-assembled structures, bearing unique properties such as high-aspect ratio, tunable diameter size, and precise molecular recognition. They can be obtained either by the action of external factors to already formed vesicles or spontaneously, the latter depending strongly on subtle molecular features. Here, we report on the spontaneous formation of supported lipid nanotubes of a particular type of glycolipid, ohmline, whose hydrophobic core displays remarkable asymmetry. The combination of bulk and surface-sensitive techniques indicates that below its main transition, ohmline displays an interdigitated gel phase, likely driven by the unique asymmetry in its hydrophobic core. Enhanced order packing by interdigitation favors the formation of ohmline nanotubes in agreement with chiral-based models of nanotube formation. The findings presented in this work call for additional studies to link lipid molecular structure-assembly relationships, whose understanding is relevant for the controlled design of lipid nanotubes networks in particular and controlled design of soft-matter nanomaterials in general.

Nanotherapeutic Heterogeneity: Sources, Effects, and Solutions

Nanomaterials have revolutionized medicine by enabling control over drugs' pharmacokinetics, biodistribution, and biocompatibility. However, most nanotherapeutic batches are highly heterogeneous, meaning they comprise nanoparticles that vary in size, shape, charge, composition, and ligand functionalization. Similarly, individual nanotherapeutics often have heterogeneously distributed components, ligands, and charges. This review discusses nanotherapeutic heterogeneity's sources and effects on experimental readouts and therapeutic efficacy. Among other topics, it demonstrates that heterogeneity exists in nearly all nanotherapeutic types, examines how nanotherapeutic heterogeneity arises, and discusses how heterogeneity impacts nanomaterials' in vitro and in vivo behavior. How nanotherapeutic heterogeneity skews experimental readouts and complicates their optimization and clinical translation is also shown. Lastly, strategies for limiting nanotherapeutic heterogeneity are reviewed and recommendations for developing more reproducible and effective nanotherapeutics provided.

Giant multilamellar and large unilamellar lecithin vesicles for the encapsulation and oral delivery of cannabinoids

The spontaneous formation of phospholipid vesicles was explored for the production of liposomal encapsulations of bioactive compounds. Low-energy processing methods were used to produce stable large unilamellar vesicles (LUVs) and giant multilamellar vesicles (GMVs) from unrefined, deoiled soybean and sunflower lecithin dispersions. The presence of these structures was confirmed by particle size analysis, bright-field and cryogenic transmission electron microscopy. Moreover, the liposomes were determined to be in a liquid crystalline state. Through molecular modelling, these liposomes were predicted to be capable of encapsulating cannabinoids within their membrane based on their structural and chemical similarity to cholesterol. The encapsulation capacities of cannabis oil in soybean and sunflower LUVs and spontaneous GMVs were then assessed based on these models. These liposomes demonstrated high thermal and oxidative stability, making them suitable for various food applications.

Kinetic control of liposome size by direct lipid transfer

Spontaneous lipid vesiculation and related size distribution are traditionally studied in the framework of equilibrium thermodynamics and continuum mechanics, overlooking the kinetic aspects of the process. In the scenario of liposomes consisting of different lipid molecules dispersed in the same medium - a non-equilibrium situation -, the system evolves driven by lipid monomer transfer among the different liposomes. This process encompasses time-dependent changes in liposome size and size distribution, thus predicting size and composition at a given time would entail the control of the size of liposomes by kinetic means, an asset in the framework of diagnostics and synthetic biology. We introduce a direct transfer model, based on the fact that monomers are highly reactive species and apply it to saturated phospholipid molecules differing in hydrophobic chain length. Considering a well-defined gamma-type liposome size distribution, we demonstrate a clear liposome size-composition correlation and are able to predict liposome size and size distribution at any time in the transfer process. The size-composition correlation opens up new prospects for the control of the self-assembling properties of lipids and thereby the control of the liposome size.

Vesicles as a Multifunctional Microenvironment for Electrochemiluminescence Signal Amplification

Vesicles as a typical interface-rich microenvironment can promote the reaction rate and the intermediate stability, which are promising for introduction in electrochemiluminescence (ECL) signal amplification. In this work, a kind of multilamellar vesicle obtained from sodium bis(2-ethylhexyl) sulfosuccinate (AOT) was used to modify the electrode surface. The AOT vesicle-modified microenvironment could significantly enhance the ECL performances for the luminol/O2 system in a neutral medium. The mechanism study demonstrated that the nanoscale multilamellar vesicles could maintain the vesicle structure on the electrode surface, which substantially improved the electron transfer and reaction rate, luminescence efficiency of the excited-state 3-aminophthalate anion, and stability of the superoxide anion radical. Alternatively, such a multifunctional microenvironment was also able to enhance the ECL signals from the tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)32+)/tripropylamine (TPrA) system. Moreover, another dodecyl dimethyl(3-sulfopropyl) ammonium hydroxide inner salt (DSB)-based vesicle was constructed to further verify the versatility of the vesicle-modified microenvironment for ECL signal amplification. Our work not only provides a versatile microenvironment for improving the efficiency of various ECL systems but also offers new insights for the microenvironment construction using the ordered assemblies in ECL fields.

Influence of Process Parameters on the Kinetics of the Micelle-to-Vesicle Transition and Ripening of Polystyrene-Block-Polyacrylic Acid

Due to their ability to self-assemble into complex structures, block copolymers are of great interest for use in a wide range of future applications, such as self-healing materials. Therefore, it is important to understand the mechanisms of their structure formation. In particular, the process engineering of the formation and transition of the polymer structures is required for ensuring reproducibility and scalability, but this has received little attention in the literature. In this article, the influence of the addition rate of the selective solvent on the homogeneity of self-assembled vesicles of polystyrene-block-polyacrylic acid is demonstrated, as well as the influence of the reaction time and the mixing intensity on the morphology of the polymer structures. For example, it was demonstrated that the higher the mixing intensity, the faster the transition from micelle to vesicle. The experimental results are further supported by CFD simulations, which visually and graphically show an increase in shear rate and narrower shear rate distributions at higher stirring rates. Furthermore, it was demonstrated that the vesicle size is not only kinetically determined, since flow forces above a critical size lead to the deformation and fission of the vesicles.

Preparation of Self-Assembled Nanoparticle-Polymer Hybrids from Modified Silica Nanoparticles and Polystyrene-Block-Polyacrylic Acid Vesicles via the Co-Precipitation Method

Nanoparticle-polymer hybrids are becoming increasingly important because seemingly contrasting properties, such as mechanical stability and high elasticity, can be combined into one material. In particular, hybrids made of self-assembled polymers are of growing interest since they exhibit high structural precision and diversity and the subsequent reorganization of the nanoparticles is possible. In this work, we show, for the first time, how hybrids of silica nanoparticles and self-assembled vesicles of polystyrene-block-polyacrylic acid can be prepared using the simple and inexpensive method of co-precipitation, highlighting in particular the challenges of using silica instead of other previously well-researched materials, such as gold. The aim was to investigate the influence of the type of modification and the particle size of the silica nanoparticles on the encapsulation and structure of the polymer vesicles. For this purpose, we first needed to adjust the surface properties of the nanoparticles, which we achieved with a two-step modification procedure using APTES and carboxylic acids of different chain lengths. We found that silica nanoparticles modified only with APTES could be successfully encapsulated, while those modified with APTES and decanoic acid resulted in vesicle agglomeration and poor encapsulation due to their strong hydrophobicity. In contrast, no negative effects were observed when different particle sizes (20 nm and 45 nm) were examined.

Revealing the mechanisms of vesicle formation with multiple spectral methods

The investigation of the self-assembly of amphiphilic molecules and the formation of micelles/vesicles has attracted significant attention. However, in situ and real-time methods for such studies are rare. Here, a surface-sensitive second harmonic generation (SHG) technique was applied to study the formation of vesicles in solutions of an anti-cancer drug, doxorubicin (DOX), and a generally used surfactant (sodium bis (2-ethylhexyl) sulfosuccinate, AOT). With the aid of two-photon fluorescence (TPF), Rayleigh scattering and TEM, we revealed the structural evolution of the aggregated micelles/vesicles. It was found that AOT and DOX molecules rapidly aggregated and formed micelles in the solution. The residual DOX then acted as a "glue" that induced the aggregating/growing of the micelles and the transformation from aggregates to vesicles. The existence of lipid films, which was considered as the necessary intermediate state for vesicle formation, was excluded via the SHG observations, indicating that hollow shells may be directly transformed from solid aggregated micelles in the self-assembly formation of complex vesicles. The combined spectroscopic methods were also used to investigate the formation of vesicles from a commonly used lipid (i.e., 1,2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt, DOPG) from its stacked bilayers. The swelling, curving and sealing of the DOPG bilayers for vesicle formation was monitored and clear dynamics were revealed. This work shows that the vesicle formation mechanism varies with the initial state of the surfactant/lipid molecules. It not only demonstrates the capability of the combined spectroscopic methods in investigating the aggregated systems but also provides new insight for understanding the formation of vesicles.

Formation of Oxidation- and Acid-Sensitive Assemblies from Sterols and a Quaternary Ammonium Ferrocene Derivative: Quatsome- and Onion-like Vesicles and Extended Nanoribbons

Quatsomes are a class of nonphospholipid vesicles in which bilayers are formed from mixtures of quaternary ammonium (QA) amphiphiles and sterols. We describe the formation of oxidation and acid-sensitive quatsome-like vesicles and other bilayer assemblies from mixtures of a ferrocenylated QA amphiphile (FTDMA) and several cholesterol derivatives. The influence of the sterol and the preparation method (extrusion or probe sonication) on the stability and morphology of the resulting vesicles is explored; a variety of structures can be obtained from small (ca. 30 nm) spherical unilamellar and oligolamellar quatsome-like vesicles to large (ca. 200 nm) multilamellar onion-like vesicles to extended nanoribbons many micrometers long. FTDMA-sterol vesicles undergo drastic shifts in vesicle and membrane structure when treated with a chemical oxidant (Frémy's salt), a feature previously observed in liposomes containing FTDMA and now confirmed in nonphospholipid vesicles. Size distributions of spherical quatsome-like vesicles obtained from cryo-TEM are examined to estimate the membrane bending rigidity, and a hypothesis is presented to explain the underlying mechanism of the profound membrane alterations observed as a consequence of ferrocene oxidation.

3D micromixer for nanoliposome synthesis: a promising advance in high mass productivity

This paper addresses an important breakthrough in the high mass production of liposomes by microfluidics technology. We investigated the synthesis of liposomes using a high flow rate microfluidic device (HFR-MD) with a 3D-twisted cross-sectional microchannel to favor chaotic advection. A simple construction scaffold technique was used to manufacture the HFR-MD. The synthesis of liposomes combined the effects of high flow and high concentration of lipids, resulting in high mass productivity (2.27 g of lipid per h) which, to our knowledge, has never been registered by only one microdevice. We assessed the effects of the flow rate ratio (FRR), total flow rate (TFR), and lipid concentration on the liposome physicochemical properties. HFR-MD liposomes were monodisperse (0.074) with a size around 100 nm under the condition of an FRR of 1 (50% v/v ethanol) and TFR of 5 ml min^-1 (expandable to 10 ml min^-1). We demonstrated that the mixing conditions are not the only parameter controlling liposome synthesis using experimental and computational fluid dynamics analysis. A vacuum concentrator was used for ethanol removal, and there is no further modification after processing in accordance with the structural (SAXS) and morphological (cryo-TEM) analysis. Hence, the HFR-MD can be used to prepare nanoliposomes. It emerges as an innovative tool with high mass production.

Recent developments in membrane curvature sensing and induction by proteins

BACKGROUND

Membrane-bound intracellular organelles have characteristic shapes attributed to different local membrane curvatures, and these attributes are conserved across species. Over the past decade, it has been confirmed that specific proteins control the large curvatures of the membrane, whereas many others due to their specific structural features can sense the curvatures and bind to the specific geometrical cues. Elucidating the interplay between sensing and induction is indispensable to understand the mechanisms behind various biological processes such as vesicular trafficking and budding.

SCOPE OF REVIEW

We provide an overview of major classes of membrane proteins and the mechanisms of curvature sensing and induction. We then discuss the importance of membrane elastic characteristics to induce the membrane shapes similar to intracellular organelles. Finally, we survey recently available assays developed for studying the curvature sensing and induction by many proteins.

MAJOR CONCLUSIONS

Recent theoretical/computational modeling along with experimental studies have uncovered fascinating connections between lipid membrane and protein interactions. However, the phenomena of protein localization and synchronization to generate spatiotemporal dynamics in membrane morphology are yet to be fully understood.

GENERAL SIGNIFICANCE

The understanding of protein-membrane interactions is essential to shed light on various biological processes. This further enables the technological applications of many natural proteins/peptides in therapeutic treatments. The studies of membrane dynamic shapes help to understand the fundamental functions of membranes, while the medicinal roles of various macromolecules (such as proteins, peptides, etc.) are being increasingly investigated.

Microfluidic and hydrothermal preparation of vesicles using sorbitan monolaurate/polyoxyethylene (20) sorbitan monolaurate (Span 20/Tween 20)

Here, we present a method for preparing vesicles by combining hydrothermal emulsification with solvent diffusion (SD). The sorbitan monolaurate/polyoxyethylene (20) sorbitan monolaurate (Span 20/Tween 20) system was used as the target lipid because these lipids are cheap and advantageous for the production scale. The water-in-oil (W/O) emulsion stabilized with lipids was formed under hydrothermal conditions (240 °C under 10 MPa), followed by mixing with water that included lipids to obtain a W/O-in-water (W/O/W) emulsion. The SD for the W/O/W emulsion as a subsequent process yielded vesicles. The optimal preparation conditions were 50:50 wt% Span 20/Tween 20 as a mixing ratio (final lipid concentration 12 mM), octanoic acid as an organic solvent, 240 °C for 4 min during the hydrothermal treatment, and 4 °C for 24 h in the SD process. The diameter of the vesicles obtained was at most 100 nm, which was comparable to that of the W/O/W emulsion before SD. This suggested that the W/O/W emulsion acted as a template for vesicle formation. The number density, diameter, and membrane properties of vesicles depend on the mixing ratio of the water/oil/lipid system. Specifically, the number density of vesicles was low relative to that of vesicles prepared by the conventional method.

Understanding charged vesicle suspensions as Wigner glasses: dynamical aspects

Suspensions of charged vesicles in water with added salt are widespread in nature and industrial production. Here we investigate, via Brownian dynamics simulations, a model that grasps the key features of these systems, with bidisperse colloidal beads interacting via a hard-core and an electrostatic double layer potential. Our goal is to focus on a set of interaction parameters that is not generic but measured in recent experiments, and relevant for a class of consumer products, such as liquid fabric softeners. On increasing the volume fraction in a range relevant to real formulation, we show that the dynamics become progressively slower and heterogeneous, displaying the typical signatures of an approaching glass transition. On lowering the salt concentration, which corresponds to increasing the strength and range of the electrostatic repulsion, the emergence of glassy dynamics becomes significantly steeper, and, remarkably, occurs at volume fractions well below the hard-sphere glass transition. The volume fraction dependence of the structural relaxation time at different salt concentration is well described through a functional law inspired by a recently proposed model (Krausser et al 2015 Proc. Natl Acad. Sci. USA 112 13762). According to our results, the investigated system may be thought of as a Wigner glass, i.e. a low-density glassy state stabilized by long-range repulsive interactions. Overall, our study suggests that glassy dynamics plays an important role in controlling the stability of these suspensions.

Unraveling topology-induced shape transformations in dendrimersomes

The vital functions of cell membranes require their ability to quickly change shape to perform complex tasks such as motion, division, endocytosis, and apoptosis. Membrane curvature in cells is modulated by very complex processes such as changes in lipid composition, the oligomerization of curvature-scaffolding proteins, and the reversible insertion of protein regions that act like wedges in the membrane. But, could much simpler mechanisms support membrane shape transformation? In this work, we demonstrate how the change of amphiphile topology in the bilayer can drive shape transformations of cell membrane models. To tackle this, we have designed and synthesized new types of amphiphiles-Janus dendrimers-that self-assemble into uni-, multilamellar, or smectic-ordered vesicles, named dendrimersomes. We synthesized Janus dendrimers containing a photo-labile bond that upon UV-Vis irradiation cleavage lose a part of the hydrophilic dendron. This leads to a change from a cylindrically to a wedge-shaped amphiphile. The high mobility of these dendrimers allows for the concentration of the wedge-shaped amphiphiles and the generation of transmembrane asymmetries. The concentration of the wedges and their rate of segregation allowed control of the budding and generation of structures such as tubules and high genus vesicles.

A Novel, Nontoxic and Scalable Process to Produce Lipidic Vehicles

Lipidic vehicles are novel industrial products, utilized as components for pharmaceutical, cosmeceutical and nutraceutical formulations. The present study concerns a newly invented method to produce lipidic vehicles in the nanoscale that is simple, nontoxic, versatile, time-efficient, low-cost and easy to scale up. The process is a modification of the heating method (MHM) and comprises (i) providing a mixture of an amphiphilic lipid and a charged lipid and/or a fluidity regulator in a liquid medium composed of water and a liquid polyol, (ii) stirring and heating the mixture in two heating steps, wherein the temperature of the second step is higher than the temperature of the first step and (iii) allowing the mixture to cool down to room temperature. The process leads to the self-assembly of nanoparticles of small size and good homogeneity, compared with conventional approaches that require additional size reduction steps. In addition, the incorporation of bioactive molecules, such as drugs, inside the nanoparticles is possible, while lyophilization of the products provides long-term stability. Most importantly, the absence of toxic solvents and the simplicity guarantee the safety and scalability of the process, distinguishing it from most prior art processes to produce of lipidic vehicles.

Soft Nanoonions: A Dynamic Overview onto Catanionic Vesicles Temperature-Driven Transition

Catanionic vesicles are emerging interesting structures for bioapplications. They self-generate by a pairing of oppositely charged ionic surfactants that assemble into hollow structures. Specifically, the anionic-cationic surfactant pair assumes a double-tailed zwitterionic behavior. In this work, the multilamellar-to-unilamellar thermal transition of several mixed aqueous systems, with a slight excess of the anionic one, were investigated. Interestingly, it was found that the anionic counterion underwent a dissociation as a consequence of a temperature increase, leading to the mentioned thermal transition. The present work proposed the spectroscopic techniques, specifically multinuclear NMR and PGSTE (pulsed gradient stimulated echo), as a key tool to study such systems, with high accuracy and effectiveness, while requiring a small amount of the sample. The results presented herein evidence encouraging perspectives, forecasting the application of the studied vesicular nanoreservoirs, for e.g., drug delivery.

Biomimetic nanovesicle design for cardiac tissue repair

Cardiovascular disease is a major cause of mortality and morbidity worldwide. Exosome therapies are promising for cardiac repair. Exosomes transfer cargo between cells, have high uptake by native cells and are ideal natural carriers for proteins and nucleic acids. Despite their proreparative potential, exosome production is dependent on parent cell state with typically low yields and cargo variability. Therefore, there is potential value in engineering exosomes to maximize their benefits by delivering customized, potent cargo for cardiovascular disease. Here, we outline several methods of exosome engineering focusing on three important aspects: optimizing cargo, homing to target tissue and minimizing clearance. Finally, we put these methods in context of the cardiac field and discuss the future potential of vesicle design.

Preparation of nanoliposomes by microfluidic mixing in herring-bone channel and the role of membrane fluidity in liposomes formation

Introduction of microfluidic mixing technique opens a new door for preparation of the liposomes and lipid-based nanoparticles by on-chip technologies that are applicable in a laboratory and industrial scale. This study demonstrates the role of phospholipid bilayer fragment as the key intermediate in the mechanism of liposome formation by microfluidic mixing in the channel with “herring-bone” geometry used with the instrument NanoAssemblr. The fluidity of the lipid bilayer expressed as fluorescence anisotropy of the probe N,N,N-Trimethyl-4-(6-phenyl-1,3,5-hexatrien-1-yl) was found to be the basic parameter affecting the final size of formed liposomes prepared by microfluidic mixing of an ethanol solution of lipids and water phase. Both saturated and unsaturated lipids together with various content of cholesterol were used for liposome preparation and it was demonstrated, that an increase in fluidity results in a decrease of liposome size as analyzed by DLS. Gadolinium chelating lipids were used to visualize the fine structure of liposomes and bilayer fragments by CryoTEM. Experimental data and theoretical calculations are in good accordance with the theory of lipid disc micelle vesiculation.

Vesicle formation mechanisms: an overview

Vesicle structures primarily embody spherical capsules composed of a single or multiple bilayers, entrapping a pool of aqueous solution in their interior. The bilayers can be synthesised by phospholipids or other amphiphiles (surfactants, block copolymers, etc.). Vesicles with broad-spectrum applications in numerous scientific disciplines, including biochemistry, biophysics, biology, and various pharmaceutical industries, have attracted widespread attention. Consequently, a multitude of protocols have been devised and proposed for their fabrication. In this review, with a motivation to derive the basic conditions for the formation of vesicles, the associated thermodynamic and kinetic aspects are comprehensively appraised. Contextually, an all-purpose overview of the underlying thermodynamics of bilayer/membrane generation and deformation, including the chemical potential of aggregates, geometric packing and the concept of elastic properties, is presented. Additionally, the current review highlights the probable, inherent mechanisms of vesicle formation under distinct modes of manufacturing. We lay focus on vesicle formation from pre-existing bilayers, as well as from bilayers, which form when lipids from an organic solvent are transferred into an aqueous medium. Furthermore, we outline the kinetic effects on vesicle formation from the lamellar phase, with and without the presence of shearing force. Wherever required, the experimental and/or theoretical outcomes, the driving forces for vesicle size selection, and various scaling laws are also reviewed, all of which facilitate an overall improved understanding of the vesicle formation mechanisms.

Electrostatic interaction effects on the size distribution of self-assembled giant unilamellar vesicles

The influence of electrostatic conditions (salt concentration of the solution and vesicle surface charge density) on the size distribution of self-assembled giant unilamellar vesicles (GUVs) is considered. The membranes of GUVs are synthesized by a mixture of dioleoylphosphatidylglycerol and dioleoylphosphatidylcholine in a physiological buffer using the natural swelling method. The experimental results are presented in the form of a set of histograms. The log-normal distribution is used for statistical treatment of results. It is obtained that the decrease of salt concentration and the increase of vesicle surface charge density of the membranes increase the average size of the GUV population. To explain the experimental results, a theory using the Helmholtz free energy of the system describing the GUV vesiculation is developed. The size distribution histograms and average size of GUVs under various conditions are fitted with the proposed theory. It is shown that the variation of the bending modulus due to changing of electrostatic parameters of the system is the main factor causing a change in the average size of GUVs.

Polymersome formation induced by encapsulation of water-insoluble molecules within ABC triblock terpolymers

We found a morphological transition from spherical micelles to polymersomes induced by encapsulation of hydrophobic guest molecules.

Electrostatically Driven Encapsulation of Hydrophilic, Non-Conformational Peptide Epitopes into Liposomes

Since the first use of liposomes as carriers for antigens, much work has been done to elucidate the mechanisms involved in the encapsulation of vaccine-relevant biomolecules. However, only a few studies have specifically investigated the encapsulation of hydrophilic, non-conformational peptide epitopes. We performed comprehensive and systematic screening studies, in order to identify conditions that favor the electrostatic interaction of such peptides with lipid membranes. Moreover, we have explored bi-terminal sequence extension as an approach to modify the isoelectric point of peptides, in order to modulate their membrane binding behavior and eventually shift/expand the working range under which they can be efficiently encapsulated in an electrostatically driven manner. The findings of our membrane interaction studies were then applied to preparing peptide-loaded liposomes. Our results show that the magnitude of membrane binding observed in our exploratory in situ setup translates to corresponding levels of encapsulation efficiency in both of the two most commonly employed methods for the preparation of liposomes, i.e., thin-film hydration and microfluidic mixing. We believe that the methods and findings described in the present studies will be of use to a wide audience and can be applied to address the ongoing relevant issue of the efficient encapsulation of hydrophilic biomolecules.

Neutralisation rate controls the self-assembly of pH-sensitive surfactants

The degree of ionisation of a weakly acidic surfactant can be continuously modified from nonionic to ionic by adjusting the pH. This property can be used to control the curvature and therefore the morphology of the self-assembled aggregates it forms in solution. Herein, we report the surprising phenomenon, observed in the alkyl ether oligo(ethylene oxide) carboxylate (CH3(CH2)11/13OEO4.5CH2COOH), whereby it is not only the pH but also the neutralisation rate that affects the aggregate morphology. Specifically, when the pH is increased slowly, up to 40 wt% of the surfactant remains in a long-lived vesicle state at high pH. This phenomenon was characterised in detail by small-angle neutron scattering and light scattering techniques. The cause of this phenomenon is thought to be related to a combination of polydispersity and the formation of acid-carboxylate dimers close to the pKa. The transition of these vesicles to the thermodynamically favoured micelles at high pH is inhibited by a high activation energy barrier and therefore only occurs very slowly. Increasing the NaCl concentration eliminates the presence of vesicles at high pH, demonstrating that the activation energy for the vesicle-to-micelle transition depends strongly on electrostatic interactions. These experiments show that the preparation pathway can be used to obtain different self-assembled structures at identical conditions via kinetic control. This phenomenon provides a useful tool for devising formulations where the properties of the system can be altered without changing the composition.

Increasing the Resistance of Living Cells against Oxidative Stress by Nonnatural Surfactants as Membrane Guards

The importation of construction principles or even constituents from biology into materials science is a prevailing concept. Vice versa, the cellular level modification of living systems with nonnatural components is much more difficult to achieve. It has been done for analytical purposes, for example, imaging, to learn something about intracellular processes. Cases describing the improvement of a biological function by the integration of a nonnatural (nano)constituent are extremely rare. Because biological membranes contain some kind of a surfactant, for example, phospholipids, our idea is to modify cells with a newly synthesized surfactant. However, this surfactant is intended to possess an additional functionality, which is the reduction of oxidative stress. We report the synthesis of a surfactant with Janus-type head group architecture, a fullerene C₆₀ modified by five alkyl chains on one side and an average of 20 oxygen species on the other hemisphere. It is demonstrated that the amphiphilic properties of the fullerenol surfactant are similar to that of lipids. Not only quenching of reactive oxygen species (superoxide, hydroxyl radicals, peroxynitrite, and hydrogen peroxide) was successful, but also the fullerenol surfactant exceeds benchmark antioxidant agents such as quercetin. The surfactant was then brought into contact with different cell types, and the viability even of delicate cells such as human liver cells (HepG2) and human dopaminergic neurons (LUHMES) has proven to be extraordinarily high. We could show further that the cells take up the fullerenol surfactant, and as a consequence, they are protected much better against oxidative stress.

Mixed micellar system stabilized with saponins for oral delivery of vitamin K

Poorly soluble vitamin K cannot be absorbed by patients suffering from cholestasis due to extremely low level of bile salts in the intestine. A formulation of vitamin K including glycocholic acid (i.e. Konakion® MM), does not increase bioavailability because it is unstable due to protonation of glycocholic acid at gastric pH. To develop a stable formulation, saponins were introduced as neutral surfactants to (partly) replace glycocholic acid. Experimental design was made to investigate the effect of the composition on particle size at neutral pH and upon acidification at pH 1.5. Two formulations that were within the optimized composition window were loaded with vitamin K and those showed superior stability at low pH as compared to Konakion® MM: sizes were between 43 and 46 nm at pH 7.3 and between 46 and 58 nm after 1 h incubation at pH 1.5, respectively, but large aggregates were formed at pH 1.5 in presence of Konakion® MM. Micelles were cytocompatible with Caco-2 cells at concentration of surfactants (saponins and glycocholic acid) up to 0.15 mg/ml. Uptake of vitamin K by Caco-2 cells was 4.2-4.9 nmol/mg protein for saponins-containing formulations and 7.1 nmol/mg protein for Konakion® MM. This, together with the superior stability at low pH, makes saponins-containing mixed micelles promising oral formulations for vitamin K.

Recent advances in smart biotechnology: Hydrogels and nanocarriers for tailored bioactive molecules depot

Over the past ten years, the global biopharmaceutical market has remarkably grown, with ten over the top twenty worldwide high performance medical treatment sales being biologics. Thus, biotech R&D (research and development) sector is becoming a key leading branch, with expanding revenues. Biotechnology offers considerable advantages compared to traditional therapeutic approaches, such as reducing side effects, specific treatments, higher patient compliance and therefore more effective treatments leading to lower healthcare costs. Within this sector, smart nanotechnology and colloidal self-assembling systems represent pivotal tools able to modulate the delivery of therapeutics. A comprehensive understanding of the processes involved in the self-assembly of the colloidal structures discussed therein is essential for the development of relevant biomedical applications. In this review we report the most promising and best performing platforms for specific classes of bioactive molecules and related target, spanning from siRNAs, gene/plasmids, proteins/growth factors, small synthetic therapeutics and bioimaging probes.

Dynamic behaviour of multilamellar vesicles under Poiseuille flow

Surfactant solutions exhibit multilamellar surfactant vesicles (MLVs) under flow conditions and in concentration ranges which are found in a large number of industrial applications. MLVs are typically formed from a lamellar phase and play an important role in determining the rheological properties of surfactant solutions. Despite the wide literature on the collective dynamics of flowing MLVs, investigations into the flow behavior of single MLVs are scarce. In this work, we investigate a concentrated aqueous solution of linear alkylbenzene sulfonic acid (HLAS), characterized by MLVs dispersed in an isotropic micellar phase. Rheological tests show that the HLAS solution is a shear-thinning fluid with a power law index dependent on the shear rate. Pressure-driven shear flow of the HLAS solution in glass capillaries is investigated using high-speed video microscopy and image analysis. The so obtained velocity profiles provide evidence for a power-law fluid behaviour of the HLAS solution and images show a flow-focusing effect of the lamellar phase in the central core of the capillary. The flow behavior of individual MLVs shows analogies with that of unilamellar vesicles and emulsion droplets. Deformed MLVs exhibit typical shapes of unilamellar vesicles, such as parachute and bullet-like. Furthermore, MLV velocity follows the classical Hetsroni theory for droplets provided that the power law shear dependent viscosity of the HLAS solution is taken into account. The results of this work are relevant for the processing of surfactant-based systems in which the final properties depend on the flow-induced morphology, such as cosmetic formulations and food products.

Formation and size distribution of self-assembled vesicles

When detergents and phospholipid membranes are dispersed in aqueous solutions, they tend to self-assemble into vesicles of various shapes and sizes by virtue of their hydrophobic and hydrophilic segments. A clearer understanding of such vesiculation processes holds promise for better elucidation of human physiology and disease, and paves the way to improved diagnostics, drug development, and drug delivery. Here we present a detailed analysis of the energetics and thermodynamics of vesiculation by recourse to nonlinear elasticity, taking into account large deformation that may arise during the vesiculation process. The effects of membrane size, spontaneous curvature, and membrane stiffness on vesiculation and vesicle size distribution were investigated, and the critical size for vesicle formation was determined and found to compare favorably with available experimental evidence. Our analysis also showed that the critical membrane size for spontaneous vesiculation was correlated with membrane thickness, and further illustrated how the combined effects of membrane thickness and physical properties influenced the size, shape, and distribution of vesicles. These findings shed light on the formation of physiological extracellular vesicles, such as exosomes. The findings also suggest pathways for manipulating the size, shape, distribution, and physical properties of synthetic vesicles, with potential applications in vesicle physiology, the pathobiology of cancer and other diseases, diagnostics using in vivo liquid biopsy, and drug delivery methods.

Simulation of self-assembly of polyzwitterions into vesicles

Using the Langevin dynamics method and a coarse-grained model, we have studied the formation of vesicles by hydrophobic polymers consisting of periodically placed zwitterion side groups in dilute salt-free aqueous solutions. The zwitterions, being permanent charge dipoles, provide long-range electrostatic correlations which are interfered by the conformational entropy of the polymer. Our simulations are geared towards gaining conceptual understanding in these correlated dipolar systems, where theoretical calculations are at present formidable. A competition between hydrophobic interactions and dipole-dipole interactions leads to a series of self-assembled structures. As the spacing d between the successive zwitterion side groups decreases, single chains undergo globule → disk → worm-like structures. We have calculated the Flory-Huggins χ parameter for these systems in terms of d and monitored the radius of gyration, hydrodynamic radius, spatial correlations among hydrophobic and dipole monomers, and dipole-dipole orientational correlation functions. During the subsequent stages of self-assembly, these structures lead to larger globules and vesicles as d is decreased up to a threshold value, below which no large scale morphology forms. The vesicles form via a polynucleation mechanism whereby disk-like structures form first, followed by their subsequent merger.

Polymeric vesicle formation via temperature-assisted nanoprecipitation

We here report an easy and efficient strategy to prepare submicron-sized polymeric vesicles with tetrahydrofuran (THF) as a good solvent through temperature-assisted nanoprecipitation (TAN).

Efficient Ugi reactions in an aqueous vesicle system

A new, alternative route for the synthesis of a variety of α-aminoacyl amides via the four-component Ugi reaction in the presence of different surfactants in aqueous solution was investigated. High reaction yields were obtained in many cases with vesicles formed from DDAB.

Self-Assembly Mechanism of pH-Responsive Glycolipids: Micelles, Fibers, Vesicles, and Bilayers

A set of four structurally related glycolipids are described: two of them have one glucose unit connected to either stearic or oleic acid, and two other ones have a diglucose headgroup (sophorose) similarly connected to either stearic or oleic acid. The self-assembly properties of these compounds, poorly known, are important to know due to their use in various fields of application from cleaning to cosmetics to medical. At basic pH, they all form mainly small micellar aggregates. At acidic pH, the oleic and stearic derivatives of the monoglucose form, respectively, vesicles and bilayer, while the same derivatives of the sophorose headgroup form micelles and twisted ribbons. We use pH-resolved in situ small angle X-ray scattering (SAXS) under synchrotron radiation to characterize the pH-dependent mechanism of evolution from micelles to the more complex aggregates at acidic pH. By pointing out the importance of the COO^-/COOH ratio, the melting temperature, T_m, of the lipid moieties, hydration of the glycosidic headgroup, the packing parameter, membrane rigidity, and edge stabilization, we are now able to draw a precise picture of the full self-assembly mechanism. This work is a didactical illustration of the complexity of the self-assembly process of a stimuli-responsive amphiphile during which many concomitant parameters play a key role at different stages of the process.

Interaction between a cationic bolaamphiphile and DNA: The route towards nanovectors for oligonucleotide antimicrobials

Bacterial resistance to antimicrobials is a global threat that requires development of innovative therapeutics that circumvent its onset. The use of Transcription Factor Decoys (TFDs), DNA fragments that act by blocking essential transcription factors in microbes, represents a very promising approach. TFDs require appropriate carriers to protect them from degradation in biological fluids and transfect them through the bacterial cell wall into the cytoplasm, their site of action. Here we report on a bolaform cationic surfactant, [12-bis-THA]Cl2, with proven transfection activity in vivo. By studying the physical-chemical properties of its aqueous solutions with light scattering, cryo-TEM, ζ-potential, absorption and fluorescence spectroscopies, we prove that the bolaamphiphiles associate into transient vesicles which convert into one-dimensional elongated structures over time. These surfactant assemblies complex TFDs with extremely high efficiency, if compared to common cationic amphiphiles. At Z+/-=11, the nanoplexes are stable and have a size of 120nm, and they form independently of the original morphology of the [12-bis-THA]Cl2 aggregate. DNA is compacted in the nanoplexes, as shown through CD spectroscopy and fluorescence, but is readily released in its native form if sodium taurocholate is added.

Sea Spray Aerosol Structure and Composition Using Cryogenic Transmission Electron Microscopy

The composition and surface properties of atmospheric aerosol particles largely control their impact on climate by affecting their ability to uptake water, react heterogeneously, and nucleate ice in clouds. However, in the vacuum of a conventional electron microscope, the native surface and internal structure often undergo physicochemical rearrangement resulting in surfaces that are quite different from their atmospheric configurations. Herein, we report the development of cryogenic transmission electron microscopy where laboratory generated sea spray aerosol particles are flash frozen in their native state with iterative and controlled thermal and/or pressure exposures and then probed by electron microscopy. This unique approach allows for the detection of not only mixed salts, but also soft materials including whole hydrated bacteria, diatoms, virus particles, marine vesicles, as well as gel networks within hydrated salt droplets-all of which will have distinct biological, chemical, and physical processes. We anticipate this method will open up a new avenue of analysis for aerosol particles, not only for ocean-derived aerosols, but for those produced from other sources where there is interest in the transfer of organic or biological species from the biosphere to the atmosphere.

Emergent properties arising from the assembly of amphiphiles. Artificial vesicle membranes as reaction promoters and regulators

This article deals with artificial vesicles and their membranes as reaction promoters and regulators. Among the various molecular assemblies which can form in an aqueous medium from amphiphilic molecules, vesicle systems are unique. Vesicles compartmentalize the aqueous solution in which they exist, independent on whether the vesicles are biological vesicles (existing in living systems) or whether they are artificial vesicles (formed in vitro from natural or synthetic amphiphiles). After the formation of artificial vesicles, their aqueous interior (the endovesicular volume) may become - or may be made - chemically different from the external medium (the exovesicular solution), depending on how the vesicles are prepared. The existence of differences between endo- and exovesicular composition is one of the features on the basis of which biological vesicles contribute to the complex functioning of living organisms. Furthermore, artificial vesicles can be formed from mixtures of amphiphiles in such a way that the vesicle membranes become molecularly, compositionally and organizationally highly complex, similarly to the lipidic matrix of biological membranes. All the various properties of artificial vesicles as membranous compartment systems emerge from molecular assembly as these properties are not present in the individual molecules the system is composed of. One particular emergent property of vesicle membranes is their possible functioning as promoters and regulators of chemical reactions caused by the localization of reaction components, and possibly catalysts, within or on the surface of the membranes. This specific feature is reviewed and highlighted with a few selected examples which range from the promotion of decarboxylation reactions, the selective binding of DNA or RNA to suitable vesicle membranes, and the reactivation of fragmented enzymes to the regulation of the enzymatic synthesis of polymers. Such type of emergent properties of vesicle membranes may have been important for the prebiological evolution of protocells, the hypothetical compartment systems preceding the first cells in those chemical and physico-chemical processes that led to the origin of life.

Photodynamic therapy: one step ahead with self-assembled nanoparticles

Photodynamic therapy (PDT) is a promising treatment modality for cancer with possible advantages over current treatment alternatives. It involves combination of light and a photosensitizer (PS), which is activated by absorption of specific wavelength light and creates local tissue damage through generation of reactive oxygen species (ROS) that induce a cascade of cellular and molecular events. However, as of today, PDT is still in need of improvement and nanotechnology may play a role. PDT frequently employs PS with molecular structures that are highly hydrophobic, water insoluble and prone to aggregation. Aggregation of PS leads to reduced ROS generation and thus lowers the PDT activity. Some PS such as 5-aminolevulinic acid (ALA) cannot penetrate through the stratum corneum of the skin and systemic administration is not an option due to frequently encountered side effects. Therefore PS are often encapsulated or conjugated in/on nano-drug delivery vehicles to allow them to be better taken up by cells and to more selectively deliver them to tumors or other target tissues. Several nano-drug delivery vehicles including liposomes, fullerosomes and nanocells have been tested and reviewed. Here we cover non-liposomal self-assembled nanoparticles consisting of polymeric micelles including block co-polymers, polymeric micelles, dendrimers and porphysomes.

Supramolecular systems chemistry

The field of supramolecular chemistry focuses on the non-covalent interactions between molecules that give rise to molecular recognition and self-assembly processes. Since most non-covalent interactions are relatively weak and form and break without significant activation barriers, many supramolecular systems are under thermodynamic control. Hence, traditionally, supramolecular chemistry has focused predominantly on systems at equilibrium. However, more recently, self-assembly processes that are governed by kinetics, where the outcome of the assembly process is dictated by the assembly pathway rather than the free energy of the final assembled state, are becoming topical. Within the kinetic regime it is possible to distinguish between systems that reside in a kinetic trap and systems that are far from equilibrium and require a continuous supply of energy to maintain a stationary state. In particular, the latter systems have vast functional potential, as they allow, in principle, for more elaborate structural and functional diversity of self-assembled systems - indeed, life is a prime example of a far-from-equilibrium system. In this Review, we compare the different thermodynamic regimes using some selected examples and discuss some of the challenges that need to be addressed when developing new functional supramolecular systems.

Vesicle formation by L-cysteine-derived unconventional single-tailed amphiphiles in water: a fluorescence, microscopy, and calorimetric investigation

Two new L-cysteine-derived zwitterionic amphiphiles with poly(ethylene glycol) methyl ether (mPEG) tail of different chain lengths were synthesized and their surface activity and self-assembly properties were investigated. In aqueous phosphate buffered solution of pH 7.0, the amphiphiles were observed to form stable unilamellar vesicles, the bilayer membrane of which is constituted by the mPEG chains. The vesicle phase was characterized by a number of methods including fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. The thermodynamics of self-assembly was also studied by isothermal titration calorimetry through measurements of the standard Gibbs free energy change (ΔG°m), standard enthalpy change (ΔH°m) and standard entropy change (ΔS°m) of micellization. The self-assembly process was found to be entropy-driven, which implies that the mPEG chain behaves like a hydrocarbon tail of conventional surfactants. The effects of pH, temperature, salt, and aging time on the bilayer stability were also investigated. Encapsulation and pH-triggered release of model hydrophobic and hydrophilic drugs is demonstrated.

Self-assembled structures of amphiphiles regulated via implanting external stimuli

This review article has summarized recent achievements of manipulating amphiphilic molecules and their self-assembled structures via different external stimuli.