Phase Separation and Nanodomain Formation in Hybrid Polymer/Lipid Vesicles

Poly(Sitosterol)-Based Hydrophobic Blocks in Amphiphilic Block Copolymers for the Assembly of Hybrid Vesicles

Amphiphilic block copolymer and lipids can be assembled into hybrid vesicles (HVs), which are an alternative to liposomes and polymersomes. Block copolymers that have either poly(sitostryl methacrylate) or statistical copolymers of sitosteryl methacrylate and butyl methacrylate as the hydrophobic part and a poly(carboxyethyl acrylate) hydrophilic segment are synthesized and characterized. These block copolymers assemble into small HVs with soybean L-α-phosphatidylcholine (soyPC), confirmed by electron microscopy and small-angle X-ray scattering. The membrane's hybrid nature is illustrated by fluorescence resonance energy transfer between labeled building blocks. The membrane packing, derived from spectra when using Laurdan as an environmentally sensitive fluorescent probe, is comparable between small HVs and the corresponding liposomes with molecular sitosterol, although the former show indications of transmembrane asymmetry. Giant HVs with homogenous distribution of the block copolymers and soyPC in their membranes are assembled using the electroformation method. The lateral diffusion of both building blocks is slowed down in giant HVs with higher block copolymer content, but their permeability toward (6)-carboxy-X-rhodamine is higher compared to giant vesicles made of soyPC and molecular sitosterol. This fundamental effort contributes to the rapidly expanding understanding of the integration of natural membrane constituents with designed synthetic compounds to form hybrid membranes.

Small-angle X-ray and neutron scattering applied to lipid-based nanoparticles: Recent advancements across different length scales

Lipid-based nanoparticles (LNPs), ranging from nanovesicles to non-lamellar assemblies, have gained significant attention in recent years, as versatile carriers for delivering drugs, vaccines, and nutrients. Small-angle scattering methods, employing X-rays (SAXS) or neutrons (SANS), represent unique tools to unveil structure, dynamics, and interactions of such particles on different length scales, spanning from the nano to the molecular scale. This review explores the state-of-the-art on scattering methods applied to unveil the structure of lipid-based nanoparticles and their interactions with drugs and bioactive molecules, to inform their rational design and formulation for medical applications. We will focus on complementary information accessible with X-rays or neutrons, ranging from insights on the structure and colloidal processes at a nanoscale level (SAXS) to details on the lipid organization and molecular interactions of LNPs (SANS). In addition, we will review new opportunities offered by Time-resolved (TR)-SAXS and -SANS for the investigation of dynamic processes involving LNPs. These span from real-time monitoring of LNPs structural evolution in response to endogenous or external stimuli (TR-SANS), to the investigation of the kinetics of lipid diffusion and exchange upon interaction with biomolecules (TR-SANS). Finally, we will spotlight novel combinations of SAXS and SANS with complementary on-line techniques, recently enabled at Large Scale Facilities for X-rays and neutrons. This emerging technology enables synchronized multi-method investigation, offering exciting opportunities for the simultaneous characterization of the structure and chemical or mechanical properties of LNPs.

Artificial cells for in vivo biomedical applications through red blood cell biomimicry

Recent research in artificial cell production holds promise for the development of delivery agents with therapeutic effects akin to real cells. To succeed in these applications, these systems need to survive the circulatory conditions. In this review we present strategies that, inspired by the endurance of red blood cells, have enhanced the viability of large, cell-like vehicles for in vivo therapeutic use, particularly focusing on giant unilamellar vesicles. Insights from red blood cells can guide modifications that could transform these platforms into advanced drug delivery vehicles, showcasing biomimicry's potential in shaping the future of therapeutic applications.

Glycan-Driven Formation of Raft-Like Domains with Hierarchical Periodic Nanoarrays on Dendrimersome Synthetic Cells

The accurate spatial segregation into distinct phases within cell membranes coordinates vital biochemical processes and functionalities in living organisms. One of nature's strategies to localize reactivity is the formation of dynamic raft domains. Most raft models rely on liquid-ordered L0 phases in a liquid-disordered Ld phase lacking correlation and remaining static, often necessitating external agents for phase separation. Here, we introduce a synthetic system of bicomponent glycodendrimersomes coassembled from Janus dendrimers and Janus glycodendrimers (JGDs), where lactose-lactose interactions exclusively drive lateral organization. This mechanism results in modulated phases across two length scales, yielding raft-like microdomains featuring nanoarrays at the nanoscale. By varying the density of lactose and molecular architecture of JGDs, the nanoarray type and size, shape, and spacing of the domains were controlled. Our findings offer insight into the potential primordial origins of rudimentary raft domains and highlight the crucial role of glycans within the glycocalyx.

Peptide-lipid hybrid vesicles with stimuli-responsive phase separation for controlled membrane functions

A disulfide-tethered peptide-lipid conjugate self-assembled into a homogeneously distributed peptide-lipid hybrid vesicle. Upon dithiothreitol treatment, the homogeneous peptide-lipid membrane spontaneously divided into lipid-rich and peptide-rich domains, while the vesicle retained its size and shape. Membrane phase separation enhanced temperature-dependent cargo release.

Phase separation in polymer-based biomimetic structures containing planar membranes

Phase separation in biological membranes is crucial for proper cellular functions, such as signaling and trafficking, as it mediates the interactions of condensates on membrane-bound organelles and transmembrane transport to targeted destination compartments. The separation of a lipid bilayer into phases and the formation of lipid rafts involve the restructuring of molecular localization, their immobilization, and local accumulation. By understanding the processes underlying the formation of lipid rafts in a cellular membrane, it is possible to reconstitute this phenomenon in synthetic biomimetic membranes, such as hybrids of lipids and polymers or membranes composed solely of polymers, which offer an increased physicochemical stability and unlimited possibilities of chemical modification and functionalization. In this article, we relate the main lipid bilayer phase transition phenomenon with respect to hybrid biomimetic membranes, composed of lipids mixed with polymers, and fully synthetic membranes. Following, we review the occurrence of phase separation in biomimetic hybrid membranes based on lipids and/or direct lipid analogs, amphiphilic block copolymers. We further exemplify the phase separation and the resulting properties and applications in planar membranes, free-standing and solid-supported. We briefly list methods leading to the formation of such biomimetic membranes and reflect on their improved overall stability and influence on the separation into different phases within the membranes. Due to the importance of phase separation and compartmentalization in cellular membranes, we are convinced that this compiled overview of this phenomenon will be helpful for any researcher in the biomimicry area.

Charged hybrid block copolymer-lipid-cholesterol vesicles: pH, ionic environment, and composition dependence of phase transitions

The impacts of pH, salt concentration (expressed as Debye length), and composition on the phase behavior of hybrid block copolymer-lipid-cholesterol bilayers incorporating carboxyl-terminated poly(butadiene)-block-poly(ethylene oxide) copolymer (PBdPEO1800^(-)) or/and non-carboxyl-terminated PBdPEO (PBdPEO1800 or/and PBdPEO950), egg sphingomyelin (egg SM), and cholesterol were examined using fluorescence spectroscopy of laurdan. Laurdan emission spectra were decomposed into three lognormal curves as functions of energy. The ratio of the area of the mid-energy peak to the sum of the areas of all three peaks was evaluated as vesicles were cooled, yielding temperature breakpoint values (T_break) expected to be within the range of the phase transition temperature. T_break values displayed dependence on pH, Debye length, and vesicle composition consistent with an electrostatic repulsion contribution to vesicle phase behavior. Increased pH and Debye length, for which a greater dissociated fraction of PBdPEO1800^(-) and a greater energy of electrostatic repulsion would be expected, resulted in T_break values as much as 10 °C less than at low pH or short Debye lengths. Additionally, at Debye lengths comparable to those at physiologically relevant ionic strength, T_break at pH 5.9 was observed to be slightly higher than at pH 7.0 for vesicles containing 50 mol% PBdPEO1800^(-). Electrostatic effects observed for hybrid vesicles incorporating significant amounts of carboxyl-terminated polymer may have the ability to drive phase separation in response to pH drops-such as those observed after endocytosis-in physiologically relevant conditions, suggesting the utility of such materials for drug delivery.

Small-Angle Neutron Scattering for Studying Lipid Bilayer Membranes

Small-angle neutron scattering (SANS) is a powerful tool for studying biological membranes and model lipid bilayer membranes. The length scales probed by SANS, being from 1 nm to over 100 nm, are well-matched to the relevant length scales of the bilayer, particularly when it is in the form of a vesicle. However, it is the ability of SANS to differentiate between isotopes of hydrogen as well as the availability of deuterium labeled lipids that truly enable SANS to reveal details of membranes that are not accessible with the use of other techniques, such as small-angle X-ray scattering. In this work, an overview of the use of SANS for studying unilamellar lipid bilayer vesicles is presented. The technique is briefly presented, and the power of selective deuteration and contrast variation methods is discussed. Approaches to modeling SANS data from unilamellar lipid bilayer vesicles are presented. Finally, recent examples are discussed. While the emphasis is on studies of unilamellar vesicles, examples of the use of SANS to study intact cells are also presented.

Homogeneous hybrid droplet interface bilayers assembled from binary mixtures of DPhPC phospholipids and PB-b-PEO diblock copolymers

Hybrid membranes built from phospholipids and amphiphilic block copolymers seek to capitalize on the benefits of both constituents for constructing biomimetic interfaces with improved performance. However, hybrid membranes have not been formed or studied using the droplet interface bilayer (DIB) method, an approach that offers advantages for revealing nanoscale changes in membrane structure and mechanics and offers a path toward assembling higher-order tissues. We report on hybrid droplet interface bilayers (hDIBs) formed in hexadecane from binary mixtures of synthetic diphytanoyl phosphatidylcholine (DPhPC) lipids and low molecular weight 1,2 polybutadiene-b-polyethylene oxide (PBPEO) amphiphilic block copolymers and use electrophysiology measurements and imaging to assess the effects of PBPEO in the membrane. This work reveals that hDIBs containing up to 15 mol% PBPEO plus DPhPC are homogeneously mixtures of lipids and polymers, remain highly resistive to ion transport, and are stable-including under applied voltage. Moreover, they exhibit hydrophobic thicknesses similar to DPhPC-only bilayers, but also have significantly lower values of membrane tension. These characteristics coincide with reduced energy of adhesion between droplets and the formation of alamethicin ion channels at significantly lower threshold voltages, demonstrating that even moderate amounts of amphiphilic block copolymers in a lipid bilayer provide a route for tuning the physical properties of a biomimetic membrane.

Tailoring a Solvent-Assisted Method for Solid-Supported Hybrid Lipid-Polymer Membranes

Combining amphiphilic block copolymers and phospholipids opens new opportunities for the preparation of artificial membranes. The chemical versatility and mechanical robustness of polymers together with the fluidity and biocompatibility of lipids afford hybrid membranes with unique properties that are of great interest in the field of bioengineering. Owing to its straightforwardness, the solvent-assisted method (SA) is particularly attractive for obtaining solid-supported membranes. While the SA method was first developed for lipids and very recently extended to amphiphilic block copolymers, its potential to develop hybrid membranes has not yet been explored. Here, we tailor the SA method to prepare solid-supported polymer-lipid hybrid membranes by combining a small library of amphiphilic diblock copolymers poly(dimethyl siloxane)-poly(2-methyl-2-oxazoline) and poly(butylene oxide)-block-poly(glycidol) with phospholipids commonly found in cell membranes including 1,2-dihexadecanoyl-sn-glycero-3-phosphocholine, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine, sphingomyelin, and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(glutaryl). The optimization of the conditions under which the SA method was applied allowed for the formation of hybrid polymer-lipid solid-supported membranes. The real-time formation and morphology of these hybrid membranes were evaluated using a combination of quartz crystal microbalance and atomic force microscopy. Depending on the type of polymer-lipid combination, significant differences in membrane coverage, formation of domains, and quality of membranes were obtained. The use of the SA method for a rapid and controlled formation of solid-supported hybrid membranes provides the basis for developing customized artificial hybrid membranes.

Increased efficiency of charge-mediated fusion in polymer/lipid hybrid membranes

SignificanceThe discovery that amphiphilic polymers, similar to phospholipids, can self-assemble to vesicles has inspired numerous applications. For instance, these polymersomes are employed for drug delivery due to their increased chemical and mechanical stability. These polymers can be also mixed with lipids to form the so-called hybrid membranes, which provide further biocompatibility, while new properties emerge. However, the fusion of these hybrids is to date barely explored. Herein, we determined that hybrid vesicles made of poly(dimethylsiloxane)-graft-poly(ethylene oxide) and oppositely charged lipids undergo rapid fusion, surpassing the efficiency in natural membranes. We provide biophysical insights into the mechanism and demonstrate that anionic lipids are not strictly required when the process is employed for the integration of membrane proteins.

Lipid Phase Separation in Vesicles Enhances TRAIL-Mediated Cytotoxicity

Ligand spatial presentation and density play important roles in signaling pathways mediated by cell receptors and are critical parameters when designing protein-conjugated therapeutic nanoparticles. Here, we harness lipid phase separation to spatially control the protein presentation on lipid vesicles. We use this system to improve the cytotoxicity of TNF-related apoptosis inducing ligand (TRAIL), a therapeutic anticancer protein. Vesicles with phase-separated TRAIL presentation induce more cell death in Jurkat cancer cells than vesicles with uniformly presented TRAIL, and cytotoxicity is dependent on TRAIL density. We assess this relationship in other cancer cell lines and demonstrate that phase-separated vesicles with TRAIL only enhance cytotoxicity through one TRAIL receptor, DR5, while another TRAIL receptor, DR4, is less sensitive to TRAIL density. This work demonstrates a rapid and accessible method to control protein conjugation and density on vesicles that can be adopted to other nanoparticle systems to improve receptor signaling by nanoparticles.

Heterogeneous Synthetic Vesicles toward Artificial Cells: Engineering Structure and Composition of Membranes for Multimodal Functionalities

The desire to develop artificial cells to imitate living cells in synthetic vesicle platforms has continuously increased over the past few decades. In particular, heterogeneous synthetic vesicles made from two or more building blocks have attracted attention for artificial cell applications based on their multifunctional modules with asymmetric structures. In addition to the traditional liposomes or polymersomes, polypeptides and proteins have recently been highlighted as potential building blocks to construct artificial cells owing to their specific biological functionalities. Incorporating one or more functionally folded, globular protein into synthetic vesicles enables more cell-like functions mediated by proteins. This Review highlights the recent research about synthetic vesicles toward artificial cell models, from traditional synthetic vesicles to protein-assembled vesicles with asymmetric structures. We aim to provide fundamental and practical insights into applying knowledge on molecular self-assembly to the bottom-up construction of artificial cell platforms with heterogeneous building blocks.

Membrane mixing and dynamics in hybrid POPC/poly(1,2-butadiene-block-ethylene oxide) (PBd-b-PEO) lipid/block co-polymer giant vesicles

Lipids and block copolymers can individually self-assemble into vesicles, each with their own particular benefits and limitations. Combining polymers with lipids allows for further optimisation of the vesicle membranes for bionanotechnology applications. Here, POPC lipid is mixed with poly(1,2-butadiene-block-ethylene oxide) of two different molecular weights (PBd₂₂-PEO₁₄, Mr = 1800 g mol^-1 and PBd₁₂-PEO₁₁, Mr = 1150 g mol^-1) in order to investigate how increasing the polymer fraction affects membrane mixing, hydration and fluidity. Intensity contributions of fluorescently labelled lipid and polymer within mixed GUV membranes confirm membrane homogeneity within the hybrids. General polarisation measurements of Laurdan in GUVs showed little change in membrane hydration as polymer fraction is increased, which suggests good structural compatibility between lipids and polymers that gives rise to well-mixed vesicles. Membrane fluidity in hybrid GUVs was found to decrease non-linearly with increasing polymer fraction. However, the diffusion coefficients for the fluorescent polymer in hybrid membranes did not change significantly with increasing polymer content. While increasing the polymer fraction does reduce the movement of lipids through a polymer-rich matrix, insignificant difference in diffusion coefficients of the polymer suggests that its diffusion is minimally affected by increasing lipid composition in the range studied. These results lay further foundations for the wider development of hybrid vesicles with controlled properties for advanced biotechnologies.

Polymer-Lipid Hybrid Materials

Hierarchic self-assembly underpins much of the form and function seen in synthetic or biological soft materials. Lipids are paramount examples, building themselves in nature or synthetically in a variety of meso/nanostructures. Synthetic block copolymers capture many of lipid's structural and functional properties. Lipids are typically biocompatible and high molecular weight polymers are mechanically robust and chemically versatile. The development of new materials for applications like controlled drug/gene/protein delivery, biosensors, and artificial cells often requires the combination of lipids and polymers. The emergent composite material, a "polymer-lipid hybrid membrane", displays synergistic properties not seen in pure components. Specific examples include the observation that hybrid membranes undergo lateral phase separation that can correlate in registry across multiple layers into a three-dimensional phase-separated system with enhanced permeability of encapsulated drugs. It is timely to underpin these emergent properties in several categories of hybrid systems ranging from colloidal suspensions to supported hybrid films. In this review, we discuss the form and function of a vast number of polymer-lipid hybrid systems published to date. We rationalize the results to raise new fundamental understanding of hybrid self-assembling soft materials as well as to enable the design of new supramolecular systems and applications.

En route to dynamic life processes by SNARE-mediated fusion of polymer and hybrid membranes

A variety of artificial cells springs from the functionalization of liposomes with proteins. However, these models suffer from low durability without repair and replenishment mechanisms, which can be partly addressed by replacing the lipids with polymers. Yet natural membranes are also dynamically remodeled in multiple cellular processes. Here, we show that synthetic amphiphile membranes also undergo fusion, mediated by the protein machinery for synaptic secretion. We integrated fusogenic SNAREs in polymer and hybrid vesicles and observed efficient membrane and content mixing. We determined bending rigidity and pore edge tension as key parameters for fusion and described its plausible progression through cryo-EM snapshots. These findings demonstrate that dynamic membrane phenomena can be reconstituted in synthetic materials, thereby providing new tools for the assembly of synthetic protocells.

Large hybrid Polymer/Lipid Unilamellar vesicle (LHUV) at the nanoscale: An insight into the lipid distribution in the membrane and permeability control

Membrane structuration of Large Hybrid Unilamellar Polymer/Lipid Vesicle (LHUV) is an important parameter on the optimization of their properties and thus their valuation in various fields. However, this kind of information is hardly accessible. In this work, we will focus on the development of LHUV obtained from the self-assembly of diblock poly(dimethylsiloxane)-b-poly(ethylene oxide) (PDMS-b-PEO) of different molar masses combined with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at 15% and 25% w/w content. The hybrid character of the resulting vesicles as well as their membrane structure are characterized by the mean of different techniques such as small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM). We show that hybrid vesicles with homogeneous membrane structure are obtained whatever the molar mass of the block copolymer (from 2500 to 4000 g/mol), with of a small number of tubular structures observed with the higher molar mass. We also demonstrate that the permeability of the LHUV, evaluated through controlled release experiments of fluorescein loaded in LHUV, is essentially controlled by the lipid/polymer composition.

Hybrid lipopolymer vesicle drug delivery and release systems

Hybrid lipopolymer vesicles are membrane vesicles that can be self-assembled on both the micro- and nano-scale. On the nanoscale, they are potential novel smart materials for drug delivery systems that could combine the relative strengths of liposome and polymersome drug delivery systems without their respective weaknesses. However, little is known about their properties and how they could be tailored. Currently, most methods of investigation are limited to the microscale. Here we provide a brief review on hybrid vesicle systems with a specific focus on recent developments demonstrating that nanoscale hybrid vesicles have different properties from their macroscale counterparts.

Accumulation of styrene oligomers alters lipid membrane phase order and miscibility

Growth of plastic waste in the natural environment, and in particular in the oceans, has raised the accumulation of polystyrene and other polymeric species in eukyarotic cells to the level of a credible and systemic threat. Oligomers, the smallest products of polymer degradation or incomplete polymerization reactions, are the first species to leach out of macroscopic or nanoscopic plastic materials. However, the fundamental mechanisms of interaction between oligomers and polymers with the different cell components are yet to be elucidated. Simulations performed on lipid bilayers showed changes in membrane mechanical properties induced by polystyrene, but experimental results performed on cell membranes or on cell membrane models are still missing. We focus here on understanding how embedded styrene oligomers affect the phase behavior of model membranes using a combination of scattering, fluorescence, and calorimetric techniques. Our results show that styrene oligomers disrupt the phase behavior of lipid membranes, modifying the thermodynamics of the transition through a spatial modulation of lipid composition.

Hybrid lipid/block copolymer vesicles display broad phase coexistence region

The fluidity and polar environment of ~100 nm hybrid vesicles combining dipalmitoylphosphatidylcholine (DPPC) and poly(1,2-butadiene)-block-polyethylene oxide (PBd-PEO, average molecular weight 950 g/mol) were studied upon vesicle heating using the fluorescence spectroscopy techniques of DPH anisotropy and laurdan generalized polarization (GP). These techniques indicated PBd-PEO membranes are less ordered than solid DPPC, but slightly more ordered than fluid DPPC or dioleoylphosphatidylcholine (DOPC) membranes. We find the DPH anisotropy values are less than expected from additivity of the components' anisotropies in the fluid phase mixture of DPPC and PBd-PEO, inferring that DPPC strongly fluidizes the PBd-PEO. We use transitions in DPH anisotropy and laurdan GP to create a temperature/composition phase diagram for DPPC/PBd-PEO which we find displays a significantly broader solid/fluid phase coexistence region than DPPC/DOPC, showing that DPPC partitions less readily into fluid PBd-PEO than into fluid DOPC. The existence of a broad solid/fluid phase coexistence region in DPPC/PBd-PEO vesicles is verified by Förster resonance energy transfer results and the visualization of phase separation in giant unilamellar vesicles containing up to 95% PBd-PEO and a single phase in 100% PBd-PEO vesicles at room temperature. These results add to the limited knowledge of phase behavior and phase diagrams of hybrid vesicles, and should be useful in understanding and tailoring membrane surface architecture toward biomedical applications such as drug delivery or membrane protein reconstitution.

Interface Engineering in Multiphase Systems toward Synthetic Cells and Organelles: From Soft Matter Fundamentals to Biomedical Applications

Synthetic cells have a major role in gaining insight into the complex biological processes of living cells; they also give rise to a range of emerging applications from gene delivery to enzymatic nanoreactors. Living cells rely on compartmentalization to orchestrate reaction networks for specialized and coordinated functions. Principally, the compartmentalization has been an essential engineering theme in constructing cell-mimicking systems. Here, efforts to engineer liquid-liquid interfaces of multiphase systems into membrane-bounded and membraneless compartments, which include lipid vesicles, polymer vesicles, colloidosomes, hybrids, and coacervate droplets, are summarized. Examples are provided of how these compartments are designed to imitate biological behaviors or machinery, including molecule trafficking, growth, fusion, energy conversion, intercellular communication, and adaptivity. Subsequently, the state-of-art applications of these cell-inspired synthetic compartments are discussed. Apart from being simplified and cell models for bridging the gap between nonliving matter and cellular life, synthetic compartments also are utilized as intracellular delivery vehicles for nuclei acids and nanoreactors for biochemical synthesis. Finally, key challenges and future directions for achieving the full potential of synthetic cells are highlighted.

Organized Hybrid Molecular Films from Natural Phospholipids and Synthetic Block Copolymers: A Physicochemical Investigation

In the last few years, hybrid lipid-copolymer assemblies have attracted increasing attention as possible two-dimensional (2D) membrane platforms, combining the biorelevance of the lipid building blocks with the stability and chemical tunability of copolymers. The relevance of these systems varies from fundamental studies on biological membrane-related phenomena to the construction of 2D complex devices for material science and biosensor technology. Both the fundamental understanding and the application of hybrid lipid-copolymer-supported bilayers require thorough physicochemical comprehension and structural control. Herein, we report a comprehensive physicochemical and structural characterization of hybrid monolayers at the air/water interface and of solid-supported hybrid membranes constituted by 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and the block copolymer poly(butadiene-b-ethyleneoxide) (PBD-b-PEO). Hybrid lipid-copolymer supported bilayers (HSLBs) with variable copolymer contents were prepared through spontaneous rupture and fusion of hybrid vesicles onto a hydrophilic substrate. The properties of the thin films and the parent vesicles were probed through dynamic light scattering (DLS), differential scanning calorimetry (DSC), optical ellipsometry, quartz crystal microbalance with dissipation monitoring (QCM-D), and confocal scanning laser microscopy (CSLM). Stable, hybrid lipid/copolymer systems were obtained for a copolymer content of 10-65 mol %. In particular, DSC and CSLM show lateral phase separation in these hybrid systems. These results improve our fundamental understanding of HSLBs, which is necessary for future applications of hybrid systems as biomimetic membranes or as drug delivery systems, with additional properties with respect to phospholipid liposomes.

Supported polymer/lipid hybrid bilayers formation resembles a lipid-like dynamic by reducing the molecular weight of the polymer

Amphiphilic block copolymers form self-assembled bilayers even in combination with phospholipids. They represent an attractive alternative to native lipid-based membrane systems for supported bilayer formation with applications in biomedical research, sensoring and drug delivery. Their enhanced stability and excellent mechanical properties are linked to their higher molecular weight which generates thicker bilayers. Hypothesis: It is hypothesized that reducing the molecular weight of the polymer facilitates the formation of a thinner, more homogeneous polymer/lipid hybrid bilayer which would benefit the formation of supported bilayers on silicon oxide. Experiment: We investigated hybrid bilayers composed of mixtures of 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine and increasing amounts of a low molecular weight polybutadiene-b-polyethylene oxide copolymer (1050 g/mol). By assessing the bilayer thickness and the molecular packing behavior we sought to demonstrate how reducing the polymer molecular weight increases the tendency to form supported hybrid bilayers in a lipid-like manner. Findings: The formation of a supported hybrid bilayers occurs at polymer contents <70 mol% in a lipid-like fashion and is proportional to the cohesive forces between the bilayer components and inversely related to the bilayer hydrophobic core thickness and the extended brush regime of the PEGylated polymeric headgroup.

Polymer-Lipid Hybrid Vesicles and Their Interaction with HepG2 Cells

Polymer-lipid hybrid vesicles are an emerging type of nano-assemblies that show potential as artificial organelles among others. Phospholipids and poly(cholesteryl methacrylate)-block-poly(methionine methacryloyloxyethyl ester (METMA)-random-2-carboxyethyl acrylate (CEA)) labeled with a Förster resonance energy transfer (FRET) reporter pair are used for the assembly of small and giant hybrid vesicles with homogenous distribution of both building blocks in the membrane as confirmed by the FRET effect. These hybrid vesicles have no inherent cytotoxicity when incubated with HepG2 cells up to 1.1 × 10¹¹ hybrid vesicles per mL, and they are internalized by the cells. In contrast to the fluorescent signal originating from the block copolymer, the fluorescent signal coming from the lipids is barely detectable in cells incubated with hybrid vesicles for 6 h followed by 24 h in cell media, suggesting that the two building blocks have a different intracellular fate. These findings provide important insight into the design criteria of artificial organelles with potential structural integrity.

Membrane Engineering: Phase Separation in Polymeric Giant Vesicles

Cell membranes exhibit elaborate lipidic patterning to carry out a myriad of functions such as signaling and trafficking. Domain formation in giant unilamellar vesicles (GUVs) is thus of interest for understanding fundamental biological processes and to provide new prospects for biocompatible soft materials. Lipid rearrangements in lipidic GUVs and lipid/polymer GUVs are extensively studied whereas polymer/polymer hybrid GUVs remain evasive. Here, the focus is on the thermodynamically driven phase separation of amphiphilic polymers in GUVs. It is demonstrated that polymer phase separation is entropically dictated by hydrophobic block incompatibilities and that films topology can help to determine the outcome of polymeric phase separation in GUVs. Lastly, Janus-GUVs are obtained and GUVs exhibit a single large domain by using a compatibilizing hydrophobic block copolymer.

Constructing artificial respiratory chain in polymer compartments: Insights into the interplay between bo3 oxidase and the membrane

Cytochrome bo3 ubiquinol oxidase is a transmembrane protein, which oxidizes ubiquinone and reduces oxygen, while pumping protons. Apart from its combination with F1Fo-ATPase to assemble a minimal ATP regeneration module, the utility of the proton pump can be extended to other applications in the context of synthetic cells such as transport, signaling, and control of enzymatic reactions. In parallel, polymers have been speculated to be phospholipid mimics with respect to their ability to self-assemble in compartments with increased stability. However, their usability as interfaces for complex membrane proteins has remained questionable. In the present work, we optimized a fusion/electroformation approach to reconstitute bo3 oxidase in giant unilamellar vesicles made of PDMS-g-PEO and/or phosphatidylcholine (PC). This enabled optical access, while microfluidic trapping allowed for online analysis of individual vesicles. The tight polymer membranes and the inward oriented enzyme caused 1 pH unit difference in 30 min, with an initial rate of 0.35 pH·min-1 To understand the interplay in these composite systems, we studied the relevant mechanical and rheological membrane properties. Remarkably, the proton permeability of polymer/lipid hybrids decreased after protein insertion, while the latter also led to a 20% increase of the polymer diffusion coefficient in polymersomes. In addition, PDMS-g-PEO increased the activity lifetime and the resistance to free radicals. These advantageous properties may open diverse applications, ranging from cell-free biotechnology to biomedicine. Furthermore, the presented study serves as a comprehensive road map for studying the interactions between membrane proteins and synthetic membranes, which will be fundamental for the successful engineering of such hybrid systems.

Hybrid Unilamellar Vesicles of Phospholipids and Block Copolymers with Crystalline Domains

Phospholipid (PL) membranes are ubiquitous in nature and their phase behavior has been extensively studied. Lipids assemble in a variety of structures and external stimuli can activate a quick switch between them. Amphiphilic block copolymers (BCPs) can self-organize in analogous structures but are mechanically more robust and transformations are considerably slower. The combination of PL dynamical behavior with BCP chemical richness could lead to new materials for applications in bioinspired separation membranes and drug delivery. It is timely to underpin the phase behavior of these hybrid systems and a few recent studies have revealed that PL-BCP membranes display synergistic structural, phase-separation, and dynamical properties not seen in pure components. One example is phase-separation in the membrane plane, which seems to be strongly affected by the ability of the PL to form lamellar phases with ordered alkyl chains. In this paper we focus on a rather less explored design handle which is the crystalline properties of the BCP component. Using a combination of confocal laser scanning microscopy and X-ray scattering we show that hybrid membranes of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and methoxy-poly(ethylene glycol)-b-poly(ε-caprolactone) (mPEG-b-PCL) display BCP-rich and PL-rich domains when the BCP comprises crystalline moieties. The packing of the hydrophilic part of the BCP (PEG) favors mixing of DPPC at the molecular level or into nanoscale domains while semi-crystalline and hydrophobic PCL moieties bolster microscopic domain formation in the hybrid membrane plane.

Facile Mixing of Phospholipids Promotes Self-Assembly of Low-Molecular-Weight Biodegradable Block Co-Polymers into Functional Vesicular Architectures

In this work, we have used low-molecular-weight (PEG12-b-PCL6, PEG12-b-PCL9 or PEG16-b-PLA38; MW, 1.25-3.45 kDa) biodegradable block co-polymers to construct nano- and micron-scaled hybrid (polymer/lipid) vesicles, by solvent dispersion and electroformation methods, respectively. The hybrid vesicles exhibit physical properties (size, bilayer thickness and small molecule encapsulation) of a vesicular boundary, confirmed by cryogenic transmission electron microscopy, calcein leakage assay and dynamic light scattering. Importantly, we find that these low MW polymers, on their own, do not self-assemble into polymersomes at nano and micron scales. Using giant unilamellar vesicles (GUVs) model, their surface topographies are homogeneous, independent of cholesterol, suggesting more energetically favorable mixing of lipid and polymer. Despite this mixed topography with a bilayer thickness similar to that of a lipid bilayer, variation in surface topology is demonstrated using the interfacial sensitive phospholipase A2 (sPLA2). The biodegradable hybrid vesicles are less sensitive to the phospholipase digestion, reminiscent of PEGylated vesicles, and the degree of sensitivity is polymer-dependent, implying that the nano-scale surface topology can further be tuned by its chemical composition. Our results reveal and emphasize the role of phospholipids in promoting low MW polymers for spontaneous vesicular self-assembly, generating a functional hybrid lipid-polymer interface.

Decoupling copolymer, lipid and carbon nanotube interactions in hybrid, biomimetic vesicles

Bilayer vesicles that mimic a real biological cell can be tailored to carry out a specific function by manipulating the molecular composition of the amphiphiles. These bio-inspired and bio-mimetic structures are increasingly being employed for a number of applications from drug delivery to water purification and beyond. Complex hybrid bilayers are the key building blocks for fully synthetic vesicles that can mimic biological cell membranes, which often contain a wide variety of molecular species. While the assembly and morpholgy of pure phospholid bilayer vesicles is well understood, the functionality and structure dramaticlly changes when copolymer and/or carbon nanotube porins (CNTP) are added. The aim of this study is to understand how the collective molecular interactions within hybrid vesicles affect their nanoscale structure and properties. In situ small and wide angle X-ray scattering (SAXS/WAXS) and molecular dynamics simulations (MD) are used to investigate the morphological effect of molecular interactions between polybutadiene polyethylene oxide, lipids and carbon nanotubes (CNT) within the hybrid vesicle bilayer. Within the lipid/copolymer system, the hybrid bilayer morphology transitions from phase separated lipid and compressed copolymer at low copolymer loadings to a mixed bilayer where opposing lipids are mostly separated from the inner region. This transition begins between 60 wt% and 70 wt%, with full homogenization observed by 80 wt% copolymer. The incorporation of CNT into the hybrid vesicles increases the bilayer thickness and enhances the bilayer symmetry. Analysis of the WAXS and MD indicate that the CNT-dioleoyl interactions are much stronger than the CNT-polybutadiene.

Formation and characteristics of mixed lipid/polymer membranes on a crystalline surface-layer protein lattice

The implementation of self-assembled biomolecules on solid materials, in particular, sensor and electrode surfaces, gains increasing importance for the design of stable functional platforms, bioinspired materials, and biosensors. The present study reports on the formation of a planar hybrid lipid/polymer membrane on a crystalline surface layer protein (SLP) lattice. The latter acts as a connecting layer linking the biomolecules to the inorganic base plate. In this approach, chemically bound lipids provided hydrophobic anchoring moieties for the hybrid lipid/polymer membrane on the recrystallized SLP lattice. The rapid solvent exchange technique was the method of choice to generate the planar hybrid lipid/polymer membrane on the SLP lattice. The formation process and completeness of the latter were investigated by quartz crystal microbalance with dissipation monitoring and by an enzymatic assay using the protease subtilisin A, respectively. The present data provide evidence for the formation of a hybrid lipid/polymer membrane on an S-layer lattice with a diblock copolymer content of 30%. The hybrid lipid/polymer showed a higher stiffness compared to the pure lipid bilayer. Most interestingly, both the pure and hybrid membrane prevented the proteolytic degradation of the underlying S-layer protein by the action of subtilisin A. Hence, these results provide evidence for the formation of defect-free membranes anchored to the S-layer lattice.

Novel chitosan-based pH-responsive lipid-polymer hybrid nanovesicles (OLA-LPHVs) for delivery of vancomycin against methicillin-resistant Staphylococcus aureus infections

The development of novel materials is necessary for adequate delivery of drugs to combat the Methicillin-resistant Staphylococcus aureus (MRSA) burden due to the limitations of conventional methods and challenges associated with antimicrobial resistance. Hence, this study aimed to synthesise a novel oleylamine based zwitterionic lipid (OLA) and explore its potential to formulate chitosan-based pH-responsive lipid-polymer hybrid nanovesicles (VM-OLA-LPHVs1) to deliver VM against MRSA. The OLA was synthesised, and the structure characterised by ¹H NMR, ¹³C NMR, FT-IR and HR-MS. The preliminary biocompatibility of OLA and VM-OLA-LPHVs1 was evaluated on HEK-293, A-549, MCF-7 and HepG-2 cell lines using in vitro cytotoxicity assay. The VM-OLA-LPHVs1 were formulated by ionic gelation method and characterised in order to determine the hydrodynamic diameter (D_H), morphology in vitro and in vivo antibacterial efficacy. The result of the in vitro cytotoxicity study revealed cell viability of above 75% in all cell lines when exposed to OLA and VM-OLA-LPHVs1, thus indicating their biosafety. The VM-OLA-LPHVs1 had a D_H, polydispersity index (PDI), and EE% of 198.0 ± 14.04 nm, 0.137 ± 0.02, and 45.61 ± 0.54% respectively at physiological pH, with surface-charge (ζ) switching from negative at pH 7.4 to positive at pH 6.0. The VM release from the VM-OLA-LPHVs1 was faster at pH 6.0 compared to physiological pH, with 97% release after 72-h. The VM-OLA-LPHVs1 had a lower minimum inhibitory concentration (MIC) value of 0.59 μg/mL at pH 6.0 compared to 2.39 μg/mL at pH 7.4, against MRSA with 52.9-fold antibacterial enhancement. The flow cytometry study revealed that VM-OLA-LPHVs1 had similar bactericidal efficacy on MRSA compared to bare VM, despite an 8-fold lower VM concentration in the nanovesicles. Additionally, fluorescence microscopy study showed the ability of the VM-OLA-LPHVs1 to eliminate biofilms. The electrical conductivity, and protein/DNA concentration, increased and decreased respectively, as compared to bare VM which indicated greater MRSA membrane damage. The in vivo studies in a BALB/c mouse-infected skin model treated with VM-OLA-LPHVs1 revealed 95-fold lower MRSA burden compared to the group treated with bare VM. These findings suggest that OLA can be used as an effective novel material for complexation with biodegradable polymer chitosan (CHs) to form pH-responsive VM-OLA-LPHVs1 nanovesicles which show greater potential for enhancement and improvement of treatment of bacterial infections.

Barcoding Biological Reactions with DNA-Functionalized Vesicles

Targeted vesicle fusion is a promising approach to selectively control interactions between vesicle compartments and would enable the initiation of biological reactions in complex aqueous environments. Here, we explore how two features of vesicle membranes, DNA tethers and phase-segregated membranes, promote fusion between specific vesicle populations. Membrane phase-segregation provides an energetic driver for membrane fusion that increases the efficiency of DNA-mediated fusion events. The orthogonality provided by DNA tethers allows us to direct fusion and delivery of DNA cargo to specific vesicle populations. Vesicle fusion between DNA-tethered vesicles can be used to initiate in vitro protein expression to produce model soluble and membrane proteins. Engineering orthogonal fusion events between DNA-tethered vesicles provides a new strategy to control the spatiotemporal dynamics of cell-free reactions, expanding opportunities to engineer artificial cellular systems.

Large and Giant Unilamellar Vesicle(s) Obtained by Self-Assembly of Poly(dimethylsiloxane)-b-poly(ethylene oxide) Diblock Copolymers, Membrane Properties and Preliminary Investigation of their Ability to Form Hybrid Polymer/Lipid Vesicles

In the emerging field of hybrid polymer/lipid vesicles, relatively few copolymers have been evaluated regarding their ability to form these structures and the resulting membrane properties have been scarcely studied. Here, we present the synthesis and self-assembly in solution of poly(dimethylsiloxane)-block-poly(ethylene oxide) diblock copolymers (PDMS-b-PEO). A library of different PDMS-b-PEO diblock copolymers was synthesized using ring-opening polymerization of hexamethylcyclotrisiloxane (D3) and further coupling with PEO chains via click chemistry. Self-assembly of the copolymers in water was studied using Dynamic Light Scattering (DLS), Static Light Scattering (SLS), Small Angle Neutron Scattering (SANS), and Cryo-Transmission Electron Microscopy (Cryo-TEM). Giant polymersomes obtained by electroformation present high toughness compared to those obtained from triblock copolymer in previous studies, for similar membrane thickness. Interestingly, these copolymers can be associated to phospholipids to form Giant Hybrid Unilamellar Vesicles (GHUV); preliminary investigations of their mechanical properties show that tough hybrid vesicles can be obtained.

Physicochemical considerations for bottom-up synthetic biology

The bottom-up construction of synthetic cells from molecular components is arguably one of the most challenging areas of research in the life sciences. We review the impact of confining biological systems in synthetic vesicles. Complex cell-like systems require control of the internal pH, ionic strength, (macro)molecular crowding, redox state and metabolic energy conservation. These physicochemical parameters influence protein activity and need to be maintained within limits to ensure the system remains in steady-state. We present the physicochemical considerations for building synthetic cells with dimensions ranging from the smallest prokaryotes to eukaryotic cells.

Ultrasound-Assisted Facile Synthesis of Nanostructured Hybrid Vesicle for the Nasal Delivery of Indomethacin: Response Surface Optimization, Microstructure, and Stability

This work is devoted to design a novel nanostructured hybrid vesicle (NHV) made of lecithin and an acrylate/C10-C30 alkyl acrylate for the nasal delivery of a model active indomethacin (IND), and further to probe its microstructure, intermolecular interactions, drug release behavior, ex vivo permeation, and stability. NHVs were prepared by cavitation technology employing RSM-based central composite design (CCD). Amount of lecithin (X₁), power of ultrasound (X₂), and sonication time (X₃) were selected as three independent variables while the studied response included Z-Avg (nm), polydispersity index (PDI), and zeta potential (mV). The designed system (NHV) was investigated through dynamic (DLS) and electrophoretic light scattering (ELS), attenuated total reflectance (ATR-FTIR), oscillatory measurement (stress and frequency sweep), and transmission electron microscopy (TEM). CCD was found useful in optimizing NHV. An optimized formulation (S6) had Z-Avg 80 nm, PDI 0.2, and zeta potential of - 43.26 mV. Morphology investigation revealed spherical vesicles with smaller TEM diameters (the largest particle being 52.26 nm). ATR analysis demonstrated significant intermolecular interactions among the drug (IND) and the components of vesicles. The designed vesicles had an elastic predominance and displayed supercase II (n > 1) type of drug release. Besides, the vesicles possessed potential to transport IND across the nasal mucosa with the steady-state flux (μg/cm²/h) and permeability coefficient (cm/h) of 26.61 and 13.30 × 10^-3, respectively. NHV exhibited an exceptional stability involving a combination of electrostatic and steric interactions while the histopathology investigation confirmed their safety for nasal administration.

PEO-b-PCL grafted niosomes: The cooperativilty of amphiphilic components and their properties in vitro and in vivo

Niosomes belong to drug delivery systems and consist mainly of non-ionic surfactants and cholesterol. In this study, we designed and developed systems composed of non-ionic surfactants i.e. Tween 80, Span 80 and cholesterol with and without poly(ethylene oxide)-b-poly(ε-caprolactone) (PEO-b-PCL) block copolymer, using different molar ratios of the above components. The nanosystems were formed by the thin-film hydration method with purified water as dispersion medium. Several physicochemical techniques were utilized in order to study the physicochemical and morphological characteristics of the prepared assemblies. The results showed that the presence of the block copolymer alters significantly the size and morphology of neat surfactant/cholesterol niosomes. The ageing studies also revealed that the stability is strongly dependent on the nature and the molar ratios of the components. Moreover, neither of the studied nanosystems exhibited elevated signs of cellular toxicity in vitro nor acute systemic toxicity in vivo short-term experiments. This investigation covers a new field of drug delivery platforms those of niosomes composed by different biomaterials i.e. surfactants and block copolymers.

Formation and Characteristics of Lipid-Blended Block Copolymer Bilayers on a Solid Support Investigated by Quartz Crystal Microbalance and Atomic Force Microscopy

Liposomes grafted with polymer have long been used in drug delivery applications, and block copolymersomes have emerged as attractive and more robust alternatives for both drug delivery and artificial organelle applications. Hybrid membranes that could combine the respective advantages of fluid lipid and robust polymer bilayers are an attractive and enticing alternative. The properties of membranes in amphiphile vesicles are challenging to study and many applications benefit from surface-based access to the membrane. We therefore explore the self-assembly and mechanical properties of supported hybrid bilayers (SHBs) composed of polybutadiene- block-poly(ethylene oxide) block copolymers and zwitterionic phosphatidylcholine lipids on SiO₂ supports. Quartz crystal microbalance with dissipation monitoring (QCM-D) measurements show that formation of SHB on SiO₂ by vesicle fusion depends on the mass fractions of lipids and block copolymers. Atomic force microscopy was used to study the microscopic mixing of lipids in the SHB to reveal that lipid-phase separation is not observed in SHBs. Force spectroscopy was performed to extract information about thickness and mechanical properties of the hybrid membranes. SHBs are shown to combine the properties of lipid membranes and polymer brushes, and the tip force required to rupture the membrane decreases and the bilayer thickness increases as the block copolymer fraction is increased.

Nanoparticle heterogeneity: an emerging structural parameter influencing particle fate in biological media?

Drug nanocarriers' surface chemistry is often presumed to be uniform. For instance, the polymer surface coverage and distribution of ligands on nanoparticles are described with averaged values obtained from quantification techniques based on particle populations. However, these averaged values may conceal heterogeneities at different levels, either because of the presence of particle sub-populations or because of surface inhomogeneities, such as patchy surfaces on individual particles. The characterization and quantification of chemical surface heterogeneities are tedious tasks, which are rather limited by the currently available instruments and research protocols. However, heterogeneities may contribute to some non-linear effects observed during the nanoformulation optimization process, cause problems related to nanocarrier production scale-up and correlate with unexpected biological outcomes. On the other hand, heterogeneities, while usually unintended and detrimental to nanocarrier performance, may, in some cases, be sought as adjustable properties that provide NPs with unique functionality. In this review, results and processes related to this issue are compiled, and perspectives and possible analytical developments are discussed.

Spontaneous Formation of Gating Lipid Domain in Uniform-Size Peptide Vesicles for Controlled Release

Hybrid assemblies composed of phospholipids and amphiphilic polymers have been investigated previously as a biomimetic model of biological cells. However, these studies focused on the functions of polymers in a sea of membrane lipids. Here, we prepared a highly stable peptide-lipid hybrid vesicle from a combination of an amphiphilic polypeptide and the phospholipid, 1,2-dimyristoyl- sn-glycero-3-phosphocholine, with a mixing molar ratio of 1:1. The phase-separated structure of the hybrid vesicle was demonstrated by fluorescence resonance energy transfer analysis. The lipid domain of the hybrid vesicle had a phase-transition temperature of 38 °C and allowed the permeation of a hydrophilic molecule, fluorescein isothiocyanate-labeled polyethylene glycol ( M_w: 2000), above 38 °C. The designed peptide-lipid hybrid vesicle and a "lipidic gate" are a promising tool for smart drug delivery.

Development and Evaluation of Stimuli-Responsive Chimeric Nanostructures

Chimeric/mixed stimuli-responsive nanocarriers are promising agents for therapeutic and diagnostic applications, as well as in the combinatorial field of theranostics. Herein, we designed chimeric nanosystems, composed of natural phospholipid and pH-sensitive amphiphilic diblock copolymer, in different molar ratios and assessed the polymer lyotropic effect on their properties. Initially, polymer-grafted bilayers were evaluated for their thermotropic behavior by thermal analysis. Chimeric liposomes were prepared through thin-film hydration and the obtained vesicles were studied by light scattering techniques, to measure their physicochemical characteristics and colloidal stability, as well as by imaging techniques, to elucidate their global and membrane morphology. Finally, in vitro screening of the systems' toxicity was held. The copolymer effect on the membrane phase transition strongly depended on the pH of the surrounding environment. Chimeric nanoparticles were around and above 100 nm, while electron microscopy revealed occasional morphology diversity, probably affecting the toxicity of the systems. The latter was assessed to be tolerable, while dependent on the nanosystems' material concentration, polymer concentration, and polymer composition. All experiments suggested that the thermodynamic and biophysical properties of the nanosystems are copolymer-composition- and concentration-dependent, since different amounts of incorporated polymer would produce divergent effects on the lyotropic liquid crystal membrane. Certain chimeric systems can be exploited as advanced drug delivery nanosystems, based on their overall promising profiles.

The combination of block copolymers and phospholipids to form giant hybrid unilamellar vesicles (GHUVs) does not systematically lead to "intermediate" membrane properties

In this work, the elasticity under stretching as well as the fluidity of Giant Hybrid Unilamellar Vesicles (GHUV) has been studied. The membrane structuration of these GHUVs has already been studied at the micro and nanoscale in a previous study of the team. These GHUVs were obtained by the association of a fluid phospholipid (POPC) and a triblock copolymer, poly(ethyleneoxide)-b-poly(dimethylsiloxane)-b-poly(ethyleneoxide). Although the architecture of triblock copolymers can facilitate vesicle formation, they have been scarcely used to generate GHUVs. We show, through micropipette aspiration and FRAP experiments, that the incorporation of a low amount of lipids in the polymer membrane leads to a significant loss of the toughness of the vesicle and subtle modification of the lateral diffusion of polymer chains. We discuss the results within the framework of the conformation of the triblock copolymer chain in the membrane and in the presence of lipid nanodomains.

Small Angle Scattering for Pharmaceutical Applications: From Drugs to Drug Delivery Systems

The sub-nanometer scale provided by small angle neutron and X-ray scattering is of special importance to pharmaceutical and biomedical investigators. As drug delivery devices become more functionalized and continue decreasing in size, the ability to elucidate details on size scales smaller than those available from optical techniques becomes extremely pertinent. Information gathered from small angle scattering therefore aids the endeavor of optimizing pharmaceutical efficacy at its most fundamental level. This chapter will provide some relevant examples of drug carrier technology and how small angle scattering (SAS) can be used to solve their mysteries. An emphasis on common first-step data treatments is provided which should help clarify the contents of scattering data to new researchers. Specific examples of pharmaceutically relevant research on novel systems and the role SAS plays in these studies will be discussed. This chapter provides an overview of the current applications of SAS in drug research and some practical considerations for selecting scattering techniques.

Fabrication and Characterization of Hybrid Stealth Liposomes

Next-generation liposome systems for anticancer and therapeutic delivery require the precise insertion of stabilizing polymers and targeting ligands. Many of these functional macromolecules may be lost to micellization as a competing self-assembly landscape. Here, hybrid stealth liposomes, which utilize novel cholesteryl-functionalized block copolymers as the molecular stabilizer, are explored as a scalable platform to address this limitation. The employed block copolymers offer resistance to micellization through multiple liposome insertion moieties per molecule. A combination of thermodynamic and structural investigations for a series of hybrid stealth liposome systems suggests that a critical number of cholesteryl moieties per molecule defines whether the copolymer will or will not insert into the liposome bilayer. Colloidal stability of formed hybrid stealth liposomes further corroborates the critical copolymer architecture value.

Phospholipase A2-Induced Degradation and Release from Lipid-Containing Polymersomes

Hybrid vesicles, comprising blends of amphiphilic block copolymers and phospholipids, have attracted significant attention recently because of their unique combination of chemical and physical properties. We report a method to make unilamellar hybrid vesicles with diameters of 100 nm by mixing polybutadiene-block-poly(ethylene oxide) and phosphocholine lipids using a combination of solvent inversion and sonication. We show that homogeneous hybrid vesicles are formed when one component is a minor fraction. At compositions with balanced mass fractions, separate populations of similarly sized pure liposomes and hybrid vesicles are indicated. We investigate the release kinetics of calcein encapsulated in the lumen as hybrid large and giant unilamellar vesicles (LUVs and GUVs) of different compositions are exposed to phospholipase A₂ (PLA₂). PLA₂ hydrolyzes lipids, which leads to dissolution of lipid domains and provides a trigger for the release of calcein as pores are formed. We demonstrate that depending on the polymer mole fraction, block copolymers can either protect or boost the rate of lipid degradation and thereby the release rate from nanoscale hybrid vesicles. Strong indications of lipid phase separation into nanoscale domains in LUVs are observed. Most importantly, hybrid GUV with lipids in the fluid phase release calcein slowly as lipids in the liquid-disordered phase do not phase-separate, but they show the fastest release of all blends as LUVs. This indicates phase separation on the nanoscale in contrast to on the microscale, but it also indicates retained high mobility of lipids between the nanoscale domains, which is absent for lipids in the gel phase. Our results demonstrate several ways in which nanoscale hybrid vesicles can and should be optimized for PLA₂-triggered release of water-soluble compounds.