Flexible macromolecules attached to lipid bilayers: impact on fluidity, curvature, permeability and stability of the membranes

Structure-Based Evaluation of Hybrid Lipid-Polymer Nanoparticles: The Role of the Polymeric Guest

The combination of phospholipids and block-copolymers yields advanced hybrid nanoparticles through the self-assembly process in an aqueous environment. The physicochemical features of the lipid/polymer components, like the lipid-polymer molar ratio, the macromolecular architecture of the block copolymer, the main transition temperature of the phospholipid, as well as the formulation and preparation protocol parameters, are some of the most crucial parameters for the formation of hybrid lipid/polymer vesicles and for the differentiation of their morphology. The morphology, along with other physicochemical nanoparticle characteristics are strictly correlated with the nanoparticle's later biological behavior after being administered, affecting interactions with cells, biodistribution, uptake, toxicity, drug release, etc. In the present study, a structural evaluation of hybrid lipid-polymer nanoparticles based on cryo-TEM studies was undertaken. Different kinds of hybrid lipid-polymer nanoparticles were designed and developed using phospholipids and block copolymers with different preparation protocols. The structures obtained ranged from spherical vesicles to rod-shaped structures, worm-like micelles, and irregular morphologies. The obtained morphologies were correlated with the formulation and preparation parameters and especially the type of lipid, the polymeric guest, and their ratio.

Transmembrane Transporter Constructed from PlatinumMetal-organic Cage

A perylene diimide-based metal-organic cage (MOC4c) was found to be an efficient transmembrane transporter for ions and small molecules through the internal cavity of the cage. MOC4c could selectively transport different anions, as evidenced by vesicle-based fluorescenceassays and planar lipid bilayer-based current recordings.Furthermore, MOC4c appears tofacilitate calcein transport across the lipid bilayer membrane of a livingcell, suggesting that MOC4c could be used as a biologicaltool for small molecule drugstransmembrane transportation.

Development of Hybrid DSPC:DOPC:P(OEGMA950-DIPAEMA) Nanostructures: The Random Architecture of Polymeric Guest as a Key Design Parameter

Hybrid nanoparticles have gained a lot of attention due to their advantageous properties and versatility in pharmaceutical applications. In this perspective, the formation of novel systems and the exploration of their characteristics not only from a physicochemical but also from a biophysical perspective could promote the development of new nanoplatforms with well-defined features. In the current work, lipid/copolymer bilayers were formed in different lipid to copolymer ratios and examined via differential scanning calorimetry as a preformulation study to decipher the interactions between the biomaterials, followed by nanostructure preparation by the thin-film hydration method. Physicochemical and toxicological evaluations were conducted utilizing light scattering techniques, fluorescence spectroscopy, and MTS assay. 1,2-dioctadecanoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) in different weight ratios were the chosen lipids, while a linear random copolymer with pH- and thermoresponsive properties comprised of oligo (ethylene glycol) methyl ether methacrylate (OEGMA) and 2-(diisopropylamino) ethyl methacrylate (DIPAEMA) in different ratios was used. According to our results, non-toxic hybrid nanosystems with stimuli-responsive properties were successfully formulated, and the main parameters influencing their overall performance were the hydrophilic/hydrophobic balance, lipid to polymer ratio, and more importantly the random copolymer topology. Hopefully, this investigation can promote a better understanding of the factors affecting the behavior of hybrid systems.

SMALPs Are Not Simply Nanodiscs: The Polymer-to-Lipid Ratios of Fractionated SMALPs Underline Their Heterogeneous Nature

Amphipathic styrene-maleic acid (SMA) copolymers directly solubilize biomembranes into SMA-lipid particles, or SMALPs, that are often regarded as nanodiscs and hailed as a native membrane platform. The promising outlook of SMALPs inspires the discovery of many SMA-like copolymers that also solubilize biomembranes into putative nanodiscs, but a fundamental question remains on how much the SMALPs or SMALP analogues truly resemble the bilayer structure of nanodiscs. This unfortunate ambiguity undermines the utility of SMA or SMA-like copolymers in membrane biology because the structure and function of many membrane proteins depend critically on their surrounding matrices. Here, we report the structural heterogeneity of SMALPs revealed through fractionating SMALPs comprised of lipids and well-defined SMAs via size-exclusion chromatography followed by quantitative determination of the polymer-to-lipid (P/L) stoichiometric ratios in individual fractions. Through the lens of P/L stoichiometric ratios, different self-assembled polymer-lipid nanostructures are inferred, such as polymer-remodeled liposomes, polymer-encased nanodiscs, polymer-lipid mixed micelles, and lipid-doped polymer micellar aggregates. We attribute the structural heterogeneity of SMALPs to the microstructure variations amongst individual polymer chains that give rise to their polydisperse detergency. As an example, we demonstrate that SMAs with a similar S/MA ratio but different chain sizes participate preferentially in different polymer-lipid nanostructures. We further demonstrate that proteorhodopsin, a light-driven proton pump solubilized within the same SMALPs is distributed amongst different self-assembled nanostructures to display different photocycle kinetics. Our discovery challenges the native nanodisc notion of SMALPs or SMALP analogues and highlights the necessity to separate and identify the structurally dissimilar polymer-lipid particles in membrane biology studies.

Biophysical interactions of mixed lipid-polymer nanoparticles incorporating curcumin: Potential as antibacterial agent

The technology of lipid nanoparticles has a long history in drug delivery, which begins with the discovery of liposomes by Alec D Bangham in the 1960s. Since then, numerous studies have been conducted on these systems, and several nanomedicinal products that utilize them have entered the market, with the latest being the COVID-19 vaccines. Despite their success, many aspects of their biophysical behavior are still under investigation. At the same time, their combination with other classes of biomaterials to create more advanced platforms is a promising endeavor. Herein, we developed mixed lipid-polymer nanoparticles with incorporated curcumin as a drug delivery system for therapy, and we studied its interactions with various biosystems. Initially, the nanoparticle physicochemical properties were investigated, where their size, size distribution, surface charge, morphology, drug incorporation and stability were assessed. The incorporation of the drug molecule was approximately 99.8 % for a formulated amount of 10 % by weight of the total membrane components and stable in due time. The association of the nanoparticles with human serum albumin and the effect that this brings upon their properties was studied by several biophysical techniques, including light scattering, thermal analysis and circular dichroism. As a biocompatibility assessment, interactions with erythrocyte membranes and hemolysis induced by the nanoparticles were also studied, with empty nanoparticles being more toxic than drug-loaded ones at high concentrations. Finally, interactions with bacterial membrane proteins of Staphylococcus aureus and the antibacterial effect of the nanoparticles were evaluated, where the effect of curcumin was improved when incorporated inside the nanoparticles. Overall, the developed mixed nanoparticles are promising candidates for the delivery of curcumin to infectious and other types of diseases.

Membrane stiffening in Chitosan mediated multilamellar vesicles of alkyl ether carboxylates

HYPOTHESIS

Membrane undulations are known to strongly affect the stability of uni- and multilamellar vesicles formed by surfactants or phospholipids. Herein, based on the same arguments, we hypothesise that the properties of polyelectrolyte mediated surfactant multilamellar vesicles, in particular the multiplicity - i.e. the number of layers forming the vesicle - depend on the dynamics of the membrane.

EXPERIMENTS

Small-angle neutron scattering (SANS) and neutron spin-echo (NSE) were used to probe the structure and the dynamics of the multilayered vesicles formed in mixtures of the biopolymer chitosan and oppositely charged alkyl ether carboxylates. The neutron scattering data are complemented by static and dynamic light scattering experiments. Experiments were performed in polyelectrolyte excess conditions, and at a pH close to the pKa of the surfactant.

FINDINGS

The structural investigation shows very clearly that multilayered surfactant/polyelectrolyte vesicles are formed in the investigated mixtures. Only 3 to 5 layers form, on average, one vesicle, as similarly found in mixtures of chitosan and phospholipid vesicles. NSE shows that the surfactant membrane becomes stiffer upon complexation with chitosan, and that the fluctuation of the layers is strongly coupled in time and space. Such strong coupling and the increase in overall stiffness is associated with a high entropic cost. Accordingly, the combined SANS and NSE study points out that the low multiplicity found in multilayered vesicles involving the rigid polysaccharide chitosan arises from the strongly coupled dynamics of the membrane layers.

Anionic Lipid Clustering-Mediated Bactericidal Activity and Selective Toxicity of Quaternary Ammonium-Substituted Polycationic Pullulan against the Staphylococcus aureus Bacterial Membrane

Non-amphiphilic polycations have recently been recognized to hold excellent antimicrobial potential with great mammalian cell compatibility. In a recent study, the excellent broad-spectrum bactericidal efficacy of a quaternary ammonium-substituted cationic pullulan (CP4) was demonstrated. Their selective toxicity and nominal probability to induce the acquisition of resistance among pathogens fulfill the fundamental requirements of new-generation antibacterials. However, there have been exiguous attempts in the literature to understand the antimicrobial activity of polycations against Gram-positive bacterial membranes. Here, for the first time, we have scrutinized the molecular level interactions of CP4 tetramers with a model Staphylococcus aureus membrane to understand their probable antibacterial function using molecular dynamics simulations. Our analysis reveals that the hydrophilic CP4 molecules are spontaneously adsorbed onto the membrane outer leaflet surface by virtue of strong electrostatic interactions and do not penetrate into the lipid tail hydrophobic region. This surface binding of CP4 is strengthened by the formation of anionic lipid-rich domains in their vicinity, causing lateral compositional heterogeneity. The major outcomes of the asymmetric accumulation of bulky polycationic CP4 on one leaflet are (i) anionic lipid segregation at the interaction site and (ii) a decrease in the cationic lipid acyl tail ordering and ease of water translocation across the lipid hydrophobic barrier. The membrane-CP4 interactions are strongly monitored by the ionic strength; a higher salt concentration weakens the binding of CP4 on the membrane surface. In addition, our study also substantiates the non-interacting behavior of CP4 oligomers with biomimetic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membrane, indicating their cell selectivity and specificity against pathogenic membranes.

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.

Interplay of Fusion, Leakage, and Electrostatic Lipid Clustering: Membrane Perturbations by a Hydrophobic Antimicrobial Polycation

Membrane active compounds are able to induce various types of membrane perturbations. Natural or biomimetic candidates for antimicrobial treatment or drug delivery scenarios are mostly designed and tested for their ability to induce membrane permeabilization, also termed leakage. Furthermore, the interaction of these usually cationic amphiphiles with negatively charged vesicles often causes colloidal instability leading to vesicle aggregation or/and vesicle fusion. We show the interplay of these modes of membrane perturbation in mixed phosphatidyl glycerol (PG)/phosphatidyl ethanolamine (PE) by the statistical copolymer MM:CO comprising, both, charged and hydrophobic subunits. MM:CO is a representative of partially hydrophobic, highly active, but less selective antimicrobial polycations. Cryo-electron microscopy indicates vesicle fusion rather than vesicle aggregation upon the addition of MM:CO to negatively charged PG/PE (1:1) vesicles. In a combination of fluorescence-based leakage and fusion assays, there is support for membrane permeabilization and pronounced vesicle fusion activity as distinct effects. To this end, membrane fusion and aggregation were prevented by including lipids with polyethylene glycol attached to their head groups (PEG-lipids). The leakage activity of MM:CO is very similar in the absence and presence of PEG-lipids. Vesicle aggregation and fusion however are largely suppressed. This strongly suggests that MM:CO induces leakage by asymmetric packing stress because of hydrophobically driven interactions which could lead to leakage. As a further membrane perturbation effect, MM:CO causes lipid clustering in model vesicles. We address potential artifacts and misinterpretations of experiments characterizing leakage and fusion. Additional to the leakage activity, the pronounced fusogenic activity of the polymer and potentially of many other similar compounds likely has implications for antimicrobial activity and beyond.

Heterogeneity in Lateral Distribution of Polycations at the Surface of Lipid Membrane: From the Experimental Data to the Theoretical Model

Natural and synthetic polycations of different kinds attract substantial attention due to an increasing number of their applications in the biomedical industry and in pharmacology. The key characteristic determining the effectiveness of the majority of these applications is the number of macromolecules adsorbed on the surface of biological cells or their lipid models. Their study is complicated by a possible heterogeneity of polymer layer adsorbed on the membrane. Experimental methods reflecting the structure of the layer include the electrokinetic measurements in liposome suspension and the boundary potential of planar bilayer lipid membranes (BLM) and lipid monolayers with a mixed composition of lipids and the ionic media. In the review, we systematically analyze the methods of experimental registration and theoretical description of the laterally heterogeneous structures in the polymer layer published in the literature and in our previous studies. In particular, we consider a model based on classical theory of the electrical double layer, used to analyze the available data of the electrokinetic measurements in liposome suspension with polylysines of varying molecular mass. This model suggests a few parameters related to the heterogeneity of the polymer layer and allows determining the conditions for its appearance at the membrane surface. A further development of this theoretical approach is discussed.

Thermoresponsive chimeric nanocarriers as drug delivery systems

Chimeric or mixed nanosystems belong to the class of advanced therapeutics. Their distinctive characteristic compared with other types of nanoparticles is that they combine two or more different classes of biomaterials. These platforms have created a promising and versatile field of nanomedicine, incorporating materials that are biocompatible, such as lipids, but also functional, such as stimuli-responsive polymers. In the present work, thermoresponsive chimeric nanocarriers composed of l-α-phosphatidylcholine (Egg, Chicken) (EPC) phospholipids and poly(N-isopropylacrylamide)-b-poly(lauryl acrylate) (PNIPAM-b-PLA) block copolymers were designed and developed. Initially, model lipid bilayers with incorporated polymers and drug molecule TRAM-34 were built and studied for their thermodynamics, in order to assess the stability and functionality of the systems. Chimeric nanoparticles of EPC and PNIPAM-b-PLA were then developed and evaluated for their physicochemical properties in different medium conditions, as well as for their morphology. Polymer incorporation led to alterations in the properties and morphology of the nanoparticles, while interactions with serum proteins were absent. TRAM-34 was also incorporated inside the developed nanocarriers, followed by incorporation and release studies, which revealed the functionality of the system in elevated temperature conditions. Finally, in vitro studies on normal cells suggest the biocompatibility of these nanosystems. The proposed platforms are promising for further studies and applications in vitro and in vivo.

Chimeric Stimuli-Responsive Liposomes as Nanocarriers for the Delivery of the Anti-Glioma Agent TRAM-34

Nanocarriers are delivery platforms of drugs, peptides, nucleic acids and other therapeutic molecules that are indicated for severe human diseases. Gliomas are the most frequent type of brain tumor, with glioblastoma being the most common and malignant type. The current state of glioma treatment requires innovative approaches that will lead to efficient and safe therapies. Advanced nanosystems and stimuli-responsive materials are available and well-studied technologies that may contribute to this effort. The present study deals with the development of functional chimeric nanocarriers composed of a phospholipid and a diblock copolymer, for the incorporation, delivery and pH-responsive release of the antiglioma agent TRAM-34 inside glioblastoma cells. Nanocarrier analysis included light scattering, protein incubation and electron microscopy, and fluorescence anisotropy and thermal analysis techniques were also applied. Biological assays were carried out in order to evaluate the nanocarrier nanotoxicity in vitro and in vivo, as well as to evaluate antiglioma activity. The nanosystems were able to successfully manifest functional properties under pH conditions, and their biocompatibility and cellular internalization were also evident. The chimeric nanoplatforms presented herein have shown promise for biomedical applications so far and should be further studied in terms of their ability to deliver TRAM-34 and other therapeutic molecules to glioblastoma cells.

Tylopeptin B peptide antibiotic in lipid membranes at low concentrations: Self-assembling, mutual repulsion and localization

The medium-length peptide Tylopeptin B possesses activity against Gram-positive bacteria. It binds to bacterial membranes altering their mechanical properties and increasing their permeability. This action is commonly related with peptide self-assembling, resulting in the formation of membrane channels. Here, pulsed double electron-electron resonance (DEER) data for spin-labeled Tylopeptin B in palmitoyl-oleoyl-glycero-phosphocholine (POPC) model membrane reveal that peptide self-assembling starts at concentration as low as 0.1 mol%; above 0.2 mol% it attains a saturation-like dependence with a mean number of peptides in the cluster <n> = 3.3. Using the electron spin echo envelope modulation (ESEEM) technique, Tylopeptin B molecules are found to possess a planar orientation in the membrane. In the peptide concentration range between 0.1 and 0.2 mol%, DEER data show that the peptide clusters have tendency of mutual repulsion, with a circle of inaccessibility of radius around 20 nm. It may be proposed that within this radius the peptides destabilize the membrane, providing so the peptide antimicrobial activity. Exploiting spin-labeled stearic acids as a model for free fatty acids (FFA), we found that at concentrations of 0.1-0.2 mol% the peptide promotes formation of lipid-mediated FFA clusters; further increase in peptide concentration results in dissipation of these clusters.

Manipulating Phospholipid Vesicles at the Nanoscale: A Transformation from Unilamellar to Multilamellar by an n-Alkyl-poly(ethylene oxide)

We investigated the influence of an n-alkyl-PEO polymer on the structure and dynamics of phospholipid vesicles. Multilayer formation and about a 9% increase in the size in vesicles were observed by cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and small-angle neutron/X-ray scattering (SANS/SAXS). The results indicate a change in the lamellar structure of the vesicles by a partial disruption caused by polymer chains, which seems to correlate with about a 30% reduction in bending rigidity per unit bilayer, as revealed by neutron spin echo (NSE) spectroscopy. Also, a strong change in lipid tail relaxation was observed. Our results point to opportunities using synthetic polymers to control the structure and dynamics of membranes, with possible applications in technical materials and also in drug and nutraceutical delivery.

Modifying Cell Membranes with Anionic Polymer Amphiphiles Potentiates Intracellular Delivery of Cationic Peptides

Rapid, facile, and noncovalent cell membrane modification with alkyl-grafted anionic polymers was sought as an approach to enhance intracellular delivery and bioactivity of cationic peptides. We synthesized a library of acrylic acid-based copolymers containing varying amounts of an amine-reactive pentafluorophenyl acrylate monomer followed by postpolymerization modification with a series of alkyl amines to afford precise control over the length and density of aliphatic alkyl side chains. This synthetic strategy enabled systematic investigation of the effect of the polymer structure on membrane binding, potentiation of peptide cell uptake, pH-dependent disruption of lipid bilayers for endosome escape, and intracellular bioavailability. A subset of these polymers exhibited pK_a of ∼6.8, which facilitated stable membrane association at physiological pH and rapid, pH-dependent endosomal disruption upon endocytosis as quantified in Galectin-8-YFP reporter cells. Cationic cell penetrating peptide (CPP) uptake was enhanced up to 15-fold in vascular smooth muscle cells in vitro when peptide treatment was preceded by a 30-min pretreatment with lead candidate polymers. We also designed and implemented a new and highly sensitive assay for measuring the intracellular bioavailability of CPPs based on the NanoLuciferase (NanoLuc) technology previously developed for measuring intracellular protein-protein interactions. Using this split luciferase class of assay, polymer pretreatment enhanced intracellular delivery of the CPP-modified HiBiT peptide up to 30-fold relative to CPP-HiBiT without polymer pretreatment (p < 0.05). The overall structural analyses show that polymers containing 50:50 or 70:30 molar ratios of carboxyl groups to alkyl side chains of 6-8 carbons maximized peptide uptake, pH-dependent membrane disruption, and intracellular bioavailability and that this potentiation effect was maximized by pairing with CPPs with high cationic charge density. These results demonstrate a rapid, mild method for polymer modification of cell surfaces to potentiate intracellular delivery, endosome escape, and bioactivity of cationic peptides.

Polycation-Anionic Lipid Membrane Interactions

Natural or synthetic polycations are used as biocides or as drug/gene carriers. Understanding the interactions between these macromolecules and cell membranes at the molecular level is therefore of great importance for the design of effective polymer biocides or biocompatible polycation-based delivery systems. Until now, details of the processes at the interface between polycations and biological systems have not been fully recognized. In this study, we consider the effect of strong polycations with quaternary ammonium groups on the properties of anionic lipid membranes that we use as a model system for protein-free cell membranes. For this purpose, we employed experimental measurements and atomic-scale molecular dynamics (MD) simulations. MD simulations reveal that the polycations are strongly hydrated in the aqueous phase and do not lose the water shell after adsorption at the bilayer surface. As a result of strong hydration, the polymer chains reside at the phospholipid headgroup and do not penetrate to the acyl chain region. The polycation adsorption involves the formation of anionic lipid-rich domains, and the density of anionic lipids in these domains depends on the length of the polycation chain. We observed the accumulation of anionic lipids only in the leaflet interacting with the polymer, which leads to the formation of compositionally asymmetric domains. Asymmetric adsorption of the polycation on only one leaflet of the anionic membrane strongly affects the membrane properties in the polycation-membrane contact areas: (i) anionic lipid accumulates in the region near the adsorbed polymer, (ii) acyl chain ordering and lipid packing are reduced, which results in a decrease in the thickness of the bilayer, and (iii) polycation-anionic membrane interactions are strongly influenced by the presence and concentration of salt. Our results provide an atomic-scale description of the interactions of polycations with anionic lipid bilayers and are fully supported by the experimental data. The outcomes are important for understanding the correlation of the structure of polycations with their activity on biomembranes.

How Do Amphiphilic Biopolymers Gel Blood? An Investigation Using Optical Microscopy

Amphiphilic biopolymers such as hydrophobically modified chitosan (hmC) have been shown to convert liquid blood into elastic gels. This interesting property could make hmC useful as a hemostatic agent in treating severe bleeding. The mechanism for blood gelling by hmC is believed to involve polymer-cell self-assembly, i.e., insertion of hydrophobic side chains from the polymer into the lipid bilayers of blood cells, thereby creating a network of cells bridged by hmC. Here, we probe the above mechanism by studying dilute mixtures of blood cells and hmC in situ using optical microscopy. Our results show that the presence of hydrophobic side chains on hmC induces significant clustering of blood cells. The extent of clustering is quantified from the images in terms of the area occupied by the 10 largest clusters. Clustering increases as the fraction of hydrophobic side chains increases; conversely, clustering is negligible in the case of the parent chitosan that lacks hydrophobes. Moreover, the longer the hydrophobic side chains, the greater the clustering (i.e., C₁₂ > C₁₀ > C₈ > C₆). Clustering is negligible at low hmC concentrations but becomes substantial above a certain threshold. Finally, clustering due to hmC can be reversed by adding the supramolecule α-cyclodextrin, which is known to capture hydrophobes in its binding pocket. Overall, the results from this work are broadly consistent with the earlier mechanism, albeit with a few modifications.

Protonation-induced pH increase at the triblock copolymer micelle interface for transient membrane permeability at neutral pH

Achieving controlled membrane permeability using pH-responsive block copolymers is crucial for selective intercellular uptake. We have shown that the pH at the triblock-copolymer micelle interface as compared to its bulk pH can help regulate membrane permeability. The pH-dependent acid/base equilibriums of two different interface-interacting pH probes were determined in order to measure the interfacial pH for a pH-responsive triblock copolymer (TBP) micelle under a wide range of bulk pH (4.5-9.0). According to 1H NMR studies, both pH probes provided interfacial pH at a similar interfacial depth. We revealed that the protonation of the amine moiety at the micelle interface and the subsequent formation of a positive charge caused the interface to become relatively less acidic than that of the bulk as well as an increase in the bulk-to-interfacial pH deviation (ΔpH) from ∼0.9 to 1.9 with bulk pH reducing from 8.0 to 4.5. From the ΔpH vs. interface and bulk pH plots, the apparent and intrinsic protonations or positive charge formation pKa values for the micelle were estimated to be ∼7.3 and 6.0, respectively. When the TBP micelle interacted with an anionic large unilamellar vesicle (LUV) of a binary lipid (neutral and anionic) system at the bulk pH of 7.0, fluorescence leakage studies revealed that the pH increase at the micelle interface from that of the LUV interface (pH ∼ 5.5) made the micelle interface partially protonated/cationic, thereby exhibiting transient membrane permeability. Although the increasing interface protonation causes the interface to become relatively less acidic than the bulk at any bulk pH below 6.5, the pH increase at the micelle interface may not be sufficiently large to maintain the threshold for the amine-protonated condition for effecting transient leakage and therefore, a continuous leakage was observed due to the slow disruption of the lipid bilayer.

Incorporation of PEGylated δ-decalactone into lipid bilayers: thermodynamic study and chimeric liposomes development

Liposomes have been on the market as drug delivery systems for over 25 years. Their success comes from the ability to carry toxic drug molecules to the appropriate site of action through passive accumulation, thus reducing their severe side effects. However, the need for enhanced circulation time and site and time-specific drug delivery turned research focus on other systems, such as polymers. In this context, novel composites that combine the flexibility of polymeric nanosystems with the properties of liposomes gained a lot of interest. In the present work a mixed/chimeric liposomal system, composed of phospholipids and block copolymers, was developed and evaluated in regards with its feasibility as a drug delivery system. These innovative nano-platforms combine advantages from both classes of biomaterials. Thermal analysis was performed in order to offers an insight into the interactions between these materials and consequently into their physicochemical characteristics. In addition, colloidal stability was assessed by monitoring z-potential and size distribution over time. Finally, their suitability as carriers for biomedical applications was evaluated by carrying out in vitro toxicity studies.

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.

Shaping membrane vesicles by adsorption of a semiflexible polymer

The adsorption of polymers onto fluid membranes is a problem of fundamental interest in biology and soft materials, in part because the flexibility of membranes can lead to nontrivial coupling between polymer and membrane configurations. Here, we use Monte Carlo computer simulations to study the adsorption of a semiflexible polymer onto a fluid membrane vesicle. Polymer adsorption can significantly impact both the vesicle and polymer shapes, and we identify distinct classes of configurations that emerge as a function of polymer persistence length, membrane bending rigidity, adsorption strength, and vesicle size. Large-scale deformations of the vesicle include invaginations of the membrane that internalize the polymer in a membrane bud. The buds range from disk-like shapes surrounding a collapsed polymer to tubular deformations enveloping rod-like polymers. For small vesicles, polymer adsorption also induces dumbbell-like vesicle shapes with a narrow membrane constriction circled by the polymer. Vesicles with sufficiently small or large bending rigidities adopt configurations similar to those without the polymer present. We further characterize statistical properties of the membrane and polymer configurations and identify distinct classes of polymer configurations that emerge within membrane buds. Analysis of idealized polymer-membrane configurations provides additional insight into transitions between bud shapes.

(Cryo)Transmission Electron Microscopy of Phospholipid Model Membranes Interacting with Amphiphilic and Polyphilic Molecules

Lipid membranes can incorporate amphiphilic or polyphilic molecules leading to specific functionalities and to adaptable properties of the lipid bilayer host. The insertion of guest molecules into membranes frequently induces changes in the shape of the lipid matrix that can be visualized by transmission electron microscopy (TEM) techniques. Here, we review the use of stained and vitrified specimens in (cryo)TEM to characterize the morphology of amphiphilic and polyphilic molecules upon insertion into phospholipid model membranes. Special emphasis is placed on the impact of novel synthetic amphiphilic and polyphilic bolalipids and polymers on membrane integrity and shape stability.

Effect of Polycation Structure on Interaction with Lipid Membranes

Interaction of polycations with lipid membranes is a very important issue in many biological and medical applications such as gene delivery or antibacterial usage. In this work, we address the influence of hydrophobic substitution of strong polycations containing quaternary ammonium groups on the polymer-zwitterionic membrane interactions. In particular, we focus on the polymer tendency to adsorb on or/and incorporate into the membrane. We used complementary experimental and computational methods to enhance our understanding of the mechanism of the polycation-membrane interactions. Polycation adsorption on liposomes was assessed using dynamic light scattering (DLS) and zeta potential measurements. The ability of the polymers to form hydrophilic pores in the membrane was evaluated using a calcein-release method. The polymer-membrane interaction at the molecular scale was explored by performing atomistic molecular dynamics (MD) simulations. Our results show that the length of the alkyl side groups plays an essential role in the polycation adhesion on the zwitterionic surface, while the degree of substitution affects the polycation ability to incorporate into the membrane. Both the experimental and computational results show that the membrane permeability can be dramatically affected by the amount of alkyl side groups attached to the polycation main chain.

Design and development of pH-responsive HSPC:C12H25-PAA chimeric liposomes

The application of stimuli-responsive medical practices has emerged, in which pH-sensitive liposomes figure prominently. This study investigates the impact of the incorporation of different amounts of pH-sensitive polymer, C12H25-PAA (poly(acrylic acid) with a hydrophobic end group) in l-α-phosphatidylcholine, hydrogenated (Soy) (HSPC) phospholipidic bilayers, with respect to biomimicry and functionality. PAA is a poly(carboxylic acid) molecule, classified as a pH-sensitive polymer, whose pH-sensitivity is attributed to its regulative -COOH groups, which are protonated under acidic pH (pKa ∼4.2). Our concern was to fully characterize, in a biophysical and thermodynamical manner, the mixed nanoassemblies arising from the combination of the two biomaterials. At first, we quantified the physicochemical characteristics and physical stability of the prepared chimeric nanosystems. Then, we studied their thermotropic behavior, through measurement of thermodynamical parameters, using Differential Scanning Calorimetry (DSC). Finally, the loading and release of indomethacin (IND) were evaluated, as well as the physicochemical properties and stability of the nanocarriers incorporating it. As expected, thermodynamical findings are in line with physicochemical results and also explain the loading and release profiles of IND. The novelty of this investigation is the utilization of these pH-sensitive chimeric advanced Drug Delivery nano Systems (aDDnSs) in targeted drug delivery which relies entirely on the biophysics and thermodynamics between such designs and the physiological membranes and environment of living organisms.

Design of Hybrid Gels Based on Gellan-Cholesterol Derivative and P90G Liposomes for Drug Depot Applications

Gels are extensively studied in the drug delivery field because of their potential benefits in therapeutics. Depot gel systems fall in this area, and the interest in their development has been focused on long-lasting, biocompatible, and resorbable delivery devices. The present work describes a new class of hybrid gels that stem from the interaction between liposomes based on P90G phospholipid and the cholesterol derivative of the polysaccharide gellan. The mechanical properties of these gels and the delivery profiles of the anti-inflammatory model drug diclofenac embedded in such systems confirmed the suitability of these hybrid gels as a good candidate for drug depot applications.

Membrane-Anchoring, Comb-Like Pseudopeptides for Efficient, pH-Mediated Membrane Destabilization and Intracellular Delivery

Endosomal release has been identified as a rate-limiting step for intracellular delivery of therapeutic agents, in particular macromolecular drugs. Herein, we report a series of synthetic pH-responsive, membrane-anchoring polymers exhibiting dramatic endosomolytic activity for efficient intracellular delivery. The comb-like pseudopeptidic polymers were synthesized by grafting different amounts of decylamine (NDA), which act as hydrophobic membrane anchors, onto the pendant carboxylic acid groups of a pseudopeptide, poly(l-lysine iso-phthalamide). The effects of the hydrophobic relatively long alkyl side chains on aqueous solution properties, cell membrane destabilization activity, and in-vitro cytotoxicity were investigated. The optimal polymer containing 18 mol % NDA exhibited limited hemolysis at pH 7.4 but induced nearly complete membrane destabilization at endosomal pH within only 20 min. The mechanistic investigation of membrane destabilization suggests the polymer-mediated pore formation. It has been demonstrated that the polymer with hydrophobic side chains displayed a considerable endosomolytic ability to release endocytosed materials into the cytoplasm of various cell lines, which is of critical importance for intracellular drug delivery applications.

A Virus-Mimicking, Endosomolytic Liposomal System for Efficient, pH-Triggered Intracellular Drug Delivery

A novel multifunctional liposomal delivery platform has been developed to resemble the structural and functional traits of an influenza virus. Novel pseudopeptides were prepared to mimic the pH-responsive endosomolytic behavior of influenza viral peptides through grafting a hydrophobic amino acid, l-phenylalanine, onto the backbone of a polyamide, poly(l-lysine isophthalamide), at various degrees of substitution. These pseudopeptidic polymers were employed to functionalize the surface of cholesterol-containing liposomes that mimic the viral envelope. By controlling the cholesterol proportion as well as the concentration and amphiphilicity of the pseudopeptides, the entire payload was rapidly released at endosomal pHs, while there was no release at pH 7.4. A pH-triggered, reversible change in liposomal size was observed, and the release mechanism was elucidated. In addition, the virus-mimicking nanostructures efficiently disrupted the erythrocyte membrane at pH 6.5 characteristic of early endosomes, while they showed negligible cytotoxic effects at physiological pH. The efficient intracellular delivery of the widely used anticancer drug doxorubicin (DOX) by the multifunctional liposomes was demonstrated, leading to significantly increased potency against HeLa cancer cells over the DOX-loaded bare liposomes. This novel virus-mimicking liposomal system, with the incorporated synergy of efficient liposomal drug release and efficient endosomal escape, is favorable for efficient intracellular drug delivery.

Interactions of Polyethylenimines with Zwitterionic and Anionic Lipid Membranes

Interactions between polyethylenimines (PEIs) and phospholipid membranes are of fundamental importance for various biophysical applications of these polymers such as gene delivery. Despite investigations into the nature of these interactions, their molecular basis remains poorly understood. In this article, we combined experimental methods and atomistic molecular dynamics (MD) simulations to obtain comprehensive insight into the effect of linear and branched PEIs on zwitterionic and anionic bilayers used as simple models of mammalian cellular membranes. Our results show that PEIs adsorb only partially on the surface of zwitterionic membranes by forming hydrogen bonds to the lipid headgroups, whereas a large part of the polymer chains dangles freely in the aqueous phase. In contrast, PEIs readily adhere to and insert into the anionic membrane. The attraction of the polymer chains to the membrane is due to electrostatic interactions as well as hydrogen bonding between the amine groups of PEI and the phosphate groups of lipids. These interactions were found to induce a substantial reorganization of the bilayer in the polymer vicinity due to the reorientation of lipid molecules. The lipid headgroups were pulled toward the center of the membrane, which can facilitate transmembrane translocations of anionic lipids. Furthermore, the PEI-lipid interactions affect the stability of liposomal dispersions, but we did not see any evidence of disruption of the vesicular structures into small fragments at polymer concentrations typically used in gene therapy. Our results provide a detailed molecular-level description of the lipid organization in the membrane in the presence of polycations that can be useful in understanding their mechanisms of in vitro and in vivo cytotoxicity.

Soft landing of cell-sized vesicles on solid surfaces for robust vehicle capture/release

Based on a concept of a smooth and steady landing of fragile objects without destruction via a soft cushion, we have developed a model for the soft landing of deformable lipid giant unilamellar vesicles (GUVs) on solid surfaces. The foundation for a successful soft landing is a solid substrate with a two-layer coating, including a bottom layer of positively charged lysozymes and an upper lipid membrane layer. We came to a clear conclusion that anionic GUVs when sedimented on a surface, the vesicle rupture occurs upon the direct contact with the positively charged lysozyme layer due to the strong coulombic interactions. In contrast, certain separation distances was achieved by the insertion of a soft lipid membrane cushion between the charged GUVs and the lysozyme layer, which attenuated the coulombic force and created a mild buffer zone, ensuring the robust capture of GUVs on the substrate without their rupture. The non-covalent bonding facilitated a fully reversible stimuli-responsive capture/release of GUVs from the biomimetic solid surface, which has never been demonstrated before due to the extreme fragility of GUVs. Moreover, the controllable capture/release of cells has been proven to be of vital importance in biotechnology, and similarity the present approach to capture/release cells is expected to open the previously inaccessible avenues of research.

Temperature-dependent in-plane structure formation of an X-shaped bolapolyphile within lipid bilayers

Polyphilic compound B12 is an X-shaped molecule with a stiff aromatic core, flexible aliphatic side chains, and hydrophilic end groups. Forming a thermotropic triangular honeycomb phase in the bulk between 177 and 182 °C but no lyotropic phases, it is designed to fit into DPPC or DMPC lipid bilayers, in which it phase separates at room temperature, as observed in giant unilamellar vesicles (GUVs) by fluorescence microscopy. TEM investigations of bilayer aggregates support the incorporation of B12 into intact membranes. The temperature-dependent behavior of the mixed samples was followed by differential scanning calorimetry (DSC), FT-IR spectroscopy, fluorescence spectroscopy, and X-ray scattering. DSC results support in-membrane phase separation, where a reduced main transition and new B12-related transitions indicate the incorporation of lipids into the B12-rich phase. The phase separation was confirmed by X-ray scattering, where two different lamellar repeat distances are visible over a wide temperature range. Polarized ATR-FTIR and fluorescence anisotropy experiments support the transmembrane orientation of B12, and FT-IR spectra further prove a stepwise "melting" of the lipid chains. The data suggest that in the B12-rich domains the DPPC chains are still rigid and the B12 molecules interact with each other via π-π interactions. All results obtained at temperatures above 75 °C confirm the formation of a single, homogeneously mixed phase with freely mobile B12 molecules.

The lantibiotic nisin induces lipid II aggregation, causing membrane instability and vesicle budding

The antimicrobial peptide nisin exerts its activity by a unique dual mechanism. It permeates the cell membranes of Gram-positive bacteria by binding to the cell wall precursor Lipid II and inhibits cell wall synthesis. Binding of nisin to Lipid II induces the formation of large nisin-Lipid II aggregates in the membrane of bacteria as well as in Lipid II-doped model membranes. Mechanistic details of the aggregation process and its impact on membrane permeation are still unresolved. In our experiments, we found that fluorescently labeled nisin bound very inhomogeneously to bacterial membranes as a consequence of the strong aggregation due to Lipid II binding. A correlation between cell membrane damage and nisin aggregation was observed in vivo. To further investigate the aggregation process of Lipid II and nisin, we assessed its dynamics by single-molecule microscopy of fluorescently labeled Lipid II molecules in giant unilamellar vesicles using light-sheet illumination. We observed a continuous reduction of Lipid II mobility due to a steady growth of nisin-Lipid II aggregates as a function of time and nisin concentration. From the measured diffusion constants of Lipid II, we estimated that the largest aggregates contained tens of thousands of Lipid II molecules. Furthermore, we observed that the formation of large nisin-Lipid II aggregates induced vesicle budding in giant unilamellar vesicles. Thus, we propose a membrane permeation mechanism that is dependent on the continuous growth of nisin-Lipid II aggregation and probably involves curvature effects on the membrane.

Modeling the effect of nano-sized polymer particles on the properties of lipid membranes

The interaction between polymers and biological membranes has recently gained significant interest in several research areas. On the biomedical side, dendrimers, linear polyelectrolytes, and neutral copolymers find application as drug and gene delivery agents, as biocidal agents, and as platforms for biological sensors. On the environmental side, plastic debris is often disposed of in the oceans and gets degraded into small particles; therefore concern is raising about the interaction of small plastic particles with living organisms. From both perspectives, it is crucial to understand the processes driving the interaction between polymers and cell membranes. In recent times progress in computer technology and simulation methods has allowed computational predictions on the molecular mechanism of interaction between polymeric materials and lipid membranes. Here we review the computational studies on the interaction between lipid membranes and different classes of polymers: dendrimers, linear charged polymers, polyethylene glycol (PEG) and its derivatives, polystyrene, and some generic models of polymer chains. We conclude by discussing some of the technical challenges in this area and future developments.

Amphipols for each season

Amphipols (APols) are short amphipathic polymers that can substitute for detergents at the transmembrane surface of membrane proteins (MPs) and, thereby, keep them soluble in detergent free aqueous solutions. APol-trapped MPs are, as a rule, more stable biochemically than their detergent-solubilized counterparts. APols have proven useful to produce MPs, most noticeably by assisting their folding from the denatured state obtained after solubilizing MP inclusion bodies in either SDS or urea. They facilitate the handling in aqueous solution of fragile MPs for the purpose of proteomics, structural and functional studies, and therapeutics. Because APols can be chemically labeled or functionalized, and they form very stable complexes with MPs, they can also be used to functionalize those indirectly, which opens onto many novel applications. Following a brief recall of the properties of APols and MP/APol complexes, an update is provided of recent progress in these various fields.

Conditions for liposome adsorption and bilayer formation on BSA passivated solid supports

Planar solid supported lipid membranes that include an intervening bovine serum albumen (BSA) cushion can greatly reduce undesirable interactions between reconstituted membrane proteins and the underlying substrate. These hetero-self-assemblies reduce frictional coupling by shielding reconstituted membrane proteins from the strong surface charge of the underlying substrate, thereby preventing them from strongly sticking to the substrate themselves. The motivation for this work is to describe the conditions necessary for liposome adsorption and bilayer formation on these hetero-self-assemblies. Described here are experiments that show that the state of BSA is critically important to whether a lipid bilayer is formed or intact liposomes are adsorbed to the BSA passivated surface. It is shown that a smooth layer of native BSA will readily promote lipid bilayer formation while BSA that has been denatured either chemically or by heat will not. Atomic force microscopy (AFM) and fluorescence microscopy was used to characterize the surfaces of native, heat denatured, and chemically reduced BSA. The mobility of several zwitterionic and negatively charged lipid combinations has been measured using fluorescence recovery after photobleaching (FRAP). From these measurements diffusion constants and percent recoveries have been determined and tabulated. The effect of high concentrations of beta-mercaptoethanol (β-ME) on liposome formation as well as bilayer formation was also explored.

Amphiphilic macromolecules on cell membranes: from protective layers to controlled permeabilization

Antimicrobial and cell-penetrating peptides have inspired developments of abiotic membrane-active polymers that can coat, penetrate, or break lipid bilayers in model systems. Application to cell cultures is more recent, but remarkable bioactivities are already reported. Synthetic polymer chains were tailored to achieve (i) high biocide efficiencies, and selectivity for bacteria (Gram-positive/Gram-negative or bacterial/mammalian membranes), (ii) stable and mild encapsulation of viable isolated cells to escape immune systems, (iii) pH-, temperature-, or light-triggered interaction with cells. This review illustrates these recent achievements highlighting the use of abiotic polymers, and compares the major structural determinants that control efficiency of polymers and peptides. Charge density, sp. of cationic and guanidinium side groups, and hydrophobicity (including polarity of stimuli-responsive moieties) guide the design of new copolymers for the handling of cell membranes. While polycationic chains are generally used as biocidal or hemolytic agents, anionic amphiphilic polymers, including Amphipols, are particularly prone to mild permeabilization and/or intracell delivery.

Lateral surface engineering of hybrid lipid-BCP vesicles and selective nanoparticle embedding

Bio-inspired recognition between macromolecules and antibodies can be used to reveal the location of amphiphilic block copolymers (BCPs) in model biomembranes and their subsequent scaffolding with nanoparticles (NPs). Potential applications of this novel class of lipid-BCP membranes require an understanding of their compositional heterogeneities with a variety of different molecules including natural proteins or synthetic NPs, whose selective incorporation into a specific part of phase separated membranes can serve as a model system for the targeted delivery of therapeutics. We demonstrate the selective incorporation of polymer-functionalized CdSe NPs into the polymer-rich domains in vesicular hybrid membranes using 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC, Tm = 41 °C) or 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC, Tm = -20 °C) as the lipid component. Furthermore, we demonstrate a method to detect PIB-PEO based amphiphilic BCPs on liposomal surfaces by a PEO binding antibody (anti-PEO). As a result, hybrid membrane morphologies, which depend on the lipid/BCP composition, are selectively monitored and engineered.

Near-infrared-fluorescence imaging of lymph nodes by using liposomally formulated indocyanine green derivatives

Liposomally formulated indocyanine green (LP-ICG) has drawn much attention as a highly sensitive near-infrared (NIR)-fluorescence probe for tumors or lymph nodes in vivo. We synthesized ICG derivatives tagged with alkyl chains (ICG-Cn), and we examined NIR-fluorescence imaging for lymph nodes in the lower extremities of mice by using liposomally formulated ICG-Cn (LP-ICG-Cn) as well as conventional liposomally formulated ICG (LP-ICG) and ICG. Analysis with a noninvasive preclinical NIR-fluorescence imaging system revealed that LP-ICG-Cn accumulates in only the popliteal lymph node 1h after injection into the footpad, whereas LP-ICG and ICG accumulate in the popliteal lymph node and other organs like the liver. This result indicates that LP-ICG-Cn is a useful NIR-fluorescence probe for noninvasive in vivo bioimaging, especially for the sentinel lymph node.

Critical role of the degree of substitution in the interaction of biocompatible cholic acid-modified dextrans with phosphatidylcholine liposomes

The interaction between biocompatible cholic acid-modified dextrans with different pendent cholic acid groups' content and phosphatidylcholine liposomes was studied by a variety of techniques including isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), turbidity measurements, microscopy imaging (transmission electron microscopy (TEM), and cryo-scanning electron microscopy (cryo-SEM)). The variation of the interaction enthalpy with polymer concentration, as obtained by ITC, highlighted the formation of different aggregates. Complete phase modification, from vesicles covered with a few polymer chains to vesicle disintegration, was observed by turbidity measurements. DSC showed the effect of polymer addition to the liposome gel to liquid-crystalline phase transition, and microscopy images gave information about the size and morphology of the aggregates. The composition, structure, and morphology of polymer/liposome aggregates were found to be strongly influenced by the cholic acid content in the polymer (degree of substitution, DS). Along with a rather monotonous change in the polymer/liposome system's properties with increasing DS, a discontinuity in behavior could also be observed at DS = 4 mol %. For DS ≤ 4 mol %, the polymer/liposome interaction takes place mainly between individual components, and liposome disintegration occurs in a narrow concentration range, whereas for DS > 4 mol % extended physical networks are formed, which last over a wide concentration range. A mechanism of interaction, as a function of DS, is proposed and discussed in detail.

Lipid membrane domains for the selective adsorption and surface patterning of conjugated polyelectrolytes

Conjugated polyelectrolytes (CPEs) are promising materials for generating optoelectronics devices under environmentally friendly processing conditions, but challenges remain to develop methods to define lateral features for improved junction interfaces and direct optoelectronic pathways. We describe here the potential to use a bottom-up approach that employs self-assembly in lipid membranes to form structures to template the selective adsorption of CPEs. Phase separation of gel phase anionic lipids and fluid phase phosphocholine lipids allowed the formation of negatively charged domain assemblies that selectively adsorb a cationic conjugated polyelectrolyte (P2). Spectroscopic studies found the adsorption of P2 to negatively charged membranes resulted in minimal structural change of the solution phase polymer but yielded an enhancement in fluorescence intensity (~50%) due to loss of quenching pathways. Fluorescence microscopy, dynamic light scattering, and AFM imaging were used to characterize the polymer-membrane interaction and the polymer-bound domain structures of the biphasic membranes. In addition to randomly formed circular gel phase domains, we also show that predefined features, such as straight lines, can be directed to form upon etched patterns on the substrate, thus providing potential routes toward the self-organization of optoelectronic architectures.