Mimicking the cell membrane with block copolymer membranes

Large-area, self-healing block copolymer membranes for energy conversion

Membranes are widely used for separation processes in applications such as water desalination, batteries and dialysis, and are crucial in key sectors of our economy and society1. The majority of technologically exploited membranes are based on solid polymers and function as passive barriers, whose transport characteristics are governed by their chemical composition and nanostructure. Although such membranes are ubiquitous, it has proved challenging to maximize selectivity and permeability independently, leading to trade-offs between these pertinent characteristics2. Self-assembled biological membranes, in which barrier and transport functions are decoupled3,4, provide the inspiration to address this problem5,6. Here we introduce a self-assembly strategy that uses the interface of an aqueous two-phase system to template and stabilize molecularly thin (approximately 35 nm) biomimetic block copolymer bilayers of scalable area that can exceed 10 cm2 without defects. These membranes are self-healing, and their barrier function against the passage of ions (specific resistance of approximately 1 MΩ cm2) approaches that of phospholipid membranes. The fluidity of these membranes enables straightforward functionalization with molecular carriers that shuttle potassium ions down a concentration gradient with exquisite selectivity over sodium ions. This ion selectivity enables the generation of electric power from equimolar solutions of NaCl and KCl in devices that mimic the electric organ of electric rays.

Polymersomes in Drug Delivery─From Experiment to Computational Modeling

Polymersomes, composed of amphiphilic block copolymers, are self-assembled vesicles that have gained attention as potential drug delivery systems due to their good biocompatibility, stability, and versatility. Various experimental techniques have been employed to characterize the self-assembly behaviors and properties of polymersomes. However, they have limitations in revealing molecular details and underlying mechanisms. Computational modeling techniques have emerged as powerful tools to complement experimental studies and enabled researchers to examine drug delivery mechanisms at molecular resolution. This review aims to provide a comprehensive overview of the state of the art in the field of polymersome-based drug delivery systems, with an emphasis on insights gained from both experimental and computational studies. Specifically, we focus on polymersome morphologies, self-assembly kinetics, fusion and fission, behaviors in flow, as well as drug encapsulation and release mechanisms. Furthermore, we also identify existing challenges and limitations in this rapidly evolving field and suggest possible directions for future research.

Ultrasound-nanovesicles interplay for theranostics

Nanovesicles (NVs) are widely used in the treatment and diagnosis of diseases due to their excellent vascular permeability, good biocompatibility, high loading capacity, and easy functionalization. However, their yield and in vivo penetration depth limitations and their complex preparation processes still constrain their application and development. Ultrasound, as a fundamental external stimulus with deep tissue penetration, concentrated energy sources, and good safety, has been proven to be a patient-friendly and highly efficient strategy to overcome the restrictions of traditional clinical medicine. Recent research has shown that ultrasound can drive the generation of NVs, increase their yield, simplify their preparation process, and provide direct therapeutic effects and intelligent control to enhance the therapeutic effect of NVs. In addition, NVs, as excellent drug carriers, can enhance the targeting efficiency of ultrasound-based sonodynamic therapy or sonogenetic regulation and improve the accuracy of ultrasound imaging. This review provides a detailed introduction to the classification, generation, and modification strategies of NVs, emphasizing the impact of ultrasound on the formation of NVs and summarizing the enhanced treatment and diagnostic effects of NVs combined with ultrasound for various diseases.

Advanced targeted drug delivery by bioengineered white blood cell-membrane camouflaged nanoparticulate delivery nanostructures

Targeted drug delivery has emerged as a pivotal approach within precision medicine, aiming to optimize therapeutic efficacy while minimizing systemic side effects. Leukocyte membrane coated nanoparticles (NPs) have attracted a lot of interest as an effective approach for delivering targeted drugs, capitalizing on the natural attributes of leukocytes to achieve site-specific accumulation, and heightened therapeutic outcomes. An overview of the present state of the targeted medication delivery research is given in this review. Notably, Leukocyte membrane-coated NPs offer inherent advantages such as immune evasion, extended circulation half-life, and precise homing to inflamed or diseased tissues through specific interactions with adhesion molecules. leukocyte membrane-coated NPs hold significant promise in advancing targeted drug delivery for precision medicine. As research progresses, they are anticipated to contribute to improved therapeutic outcomes, enabling personalized and effective treatments for a wide range of diseases and conditions. The review covers the method of preparation, characterization, and biological applications of leucocytic membrane coated NPs. Further, patents related factors, gap of translation from laboratory to clinic, and future prospective were discussed in detail. Overall, the review covers extensive literature to establish leucocytic membrane NPs for targeted drug delivery.

Triggered Polymersome Fusion

The contents of biological cells are retained within compartments formed of phospholipid membranes. The movement of material within and between cells is often mediated by the fusion of phospholipid membranes, which allows mixing of contents or excretion of material into the surrounding environment. Biological membrane fusion is a highly regulated process that is catalyzed by proteins and often triggered by cellular signaling. In contrast, the controlled fusion of polymer-based membranes is largely unexplored, despite the potential application of this process in nanomedicine, smart materials, and reagent trafficking. Here, we demonstrate triggered polymersome fusion. Out-of-equilibrium polymersomes were formed by ring-opening metathesis polymerization-induced self-assembly and persist until a specific chemical signal (pH change) triggers their fusion. Characterization of polymersomes was performed by a variety of techniques, including dynamic light scattering, dry-state/cryogenic-transmission electron microscopy, and small-angle X-ray scattering (SAXS). The fusion process was followed by time-resolved SAXS analysis. Developing elementary methods of communication between polymersomes, such as fusion, will prove essential for emulating life-like behaviors in synthetic nanotechnology.

Synthetic Biology: Bottom-Up Assembly of Molecular Systems

The bottom-up assembly of biological and chemical components opens exciting opportunities to engineer artificial vesicular systems for applications with previously unmet requirements. The modular combination of scaffolds and functional building blocks enables the engineering of complex systems with biomimetic or new-to-nature functionalities. Inspired by the compartmentalized organization of cells and organelles, lipid or polymer vesicles are widely used as model membrane systems to investigate the translocation of solutes and the transduction of signals by membrane proteins. The bottom-up assembly and functionalization of such artificial compartments enables full control over their composition and can thus provide specifically optimized environments for synthetic biological processes. This review aims to inspire future endeavors by providing a diverse toolbox of molecular modules, engineering methodologies, and different approaches to assemble artificial vesicular systems. Important technical and practical aspects are addressed and selected applications are presented, highlighting particular achievements and limitations of the bottom-up approach. Complementing the cutting-edge technological achievements, fundamental aspects are also discussed to cater to the inherently diverse background of the target audience, which results from the interdisciplinary nature of synthetic biology. The engineering of proteins as functional modules and the use of lipids and block copolymers as scaffold modules for the assembly of functionalized vesicular systems are explored in detail. Particular emphasis is placed on ensuring the controlled assembly of these components into increasingly complex vesicular systems. Finally, all descriptions are presented in the greater context of engineering valuable synthetic biological systems for applications in biocatalysis, biosensing, bioremediation, or targeted drug delivery.

Spatiotemporal control of signal-driven enzymatic reaction in artificial cell-like polymersomes

Living cells can spatiotemporally control biochemical reactions to dynamically assemble membraneless organelles and remodel cytoskeleton. Herein, we present a microfluidic approach to prepare semi-permeable polymersomes comprising of amphiphilic triblock copolymer to achieve external signal-driven complex coacervation as well as biophysical reconstitution of cytoskeleton within the polymersomes. We also show that the microfluidic synthesis of polymersomes enables precise control over size, efficient encapsulation of enzymes as well as regulation of substrates without the use of biopores. Moreover, we demonstrate that the resulting triblock copolymer-based membrane in polymersomes is size-selective, allowing phosphoenol pyruvate to readily diffuse through the membrane and induce enzymatic reaction and successive coacervation or actin polymerization in the presence of pyruvate kinase and adenosine diphosphate inside the polymersomes. We envision that the Pluronic-based polymersomes presented in this work will shed light in the design of in vitro enzymatic reactions in artificial cell-like vesicles.

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.

Polymersomes: Soft Nanoparticles from Miktoarm Stars for Applications in Drug Delivery

Self-assembly of amphiphilic macromolecules has provided an advantageous platform to address significant issues in a variety of areas, including biology. Such soft nanoparticles with a hydrophobic core and hydrophilic corona, referred to as micelles, have been extensively investigated for delivering lipophilic therapeutics by physical encapsulation. Polymeric vesicles or polymersomes with similarities in morphology to liposomes continue to play an essential role in understanding the behavior of cell membranes and, in addition, have offered opportunities in designing smart nanoformulations. With the evolution in synthetic methodologies to macromolecular precursors, the construction of such assemblies can now be modulated to tailor their properties to match desired needs. This review brings into focus the current state-of-the-art in the design of polymersomes using amphiphilic miktoarm star polymers through a detailed analysis of the synthesis of miktoarm star polymers with tuned lengths of varied polymeric arms, their self-assembly, and applications in drug delivery.

Biocatalytic self-assembled synthetic vesicles and coacervates: From single compartment to artificial cells

Compartmentalization is an intrinsic feature of living cells that allows spatiotemporal control over the biochemical pathways expressed in them. Over the years, a library of compartmentalized systems has been generated, which includes nano to micrometer sized biomimetic vesicles derived from lipids, amphiphilic block copolymers, peptides, and nanoparticles. Biocatalytic vesicles have been developed using a simple bag containing enzyme design of liposomes to multienzymes immobilized multi-vesicular compartments for artificial cell generation. Additionally, enzymes were also entrapped in membrane-less coacervate droplets to mimic the cytoplasmic macromolecular crowding mechanisms. Here, we have discussed different types of single and multicompartment systems, emphasizing their recent developments as biocatalytic self-assembled structures using recent examples. Importantly, we have summarized the strategies in the development of the self-assembled structure to improvise their adaptivity and flexibility for enzyme immobilization. Finally, we have presented the use of biocatalytic assemblies in mimicking different aspects of living cells, which further carves the path for the engineering of a minimal cell.

Cell Membrane-Coated Mimics: A Methodological Approach for Fabrication, Characterization for Therapeutic Applications, and Challenges for Clinical Translation

Cell membrane-coated (CMC) mimics are micro/nanosystems that combine an isolated cell membrane and a template of choice to mimic the functions of a cell. The design exploits its physicochemical and biological properties for therapeutic applications. The mimics demonstrate excellent biological compatibility, enhanced biointerfacing capabilities, physical, chemical, and biological tunability, ability to retain cellular properties, immune escape, prolonged circulation time, and protect the encapsulated drug from degradation and active targeting. These properties and the ease of adapting them for personalized clinical medicine have generated a significant research interest over the past decade. This review presents a detailed overview of the recent advances in the development of cell membrane-coated (CMC) mimics. The primary focus is to collate and discuss components, fabrication methodologies, and the significance of physiochemical and biological characterization techniques for validating a CMC mimic. We present a critical analysis of the two main components of CMC mimics: the template and the cell membrane and mapped their use in therapeutic scenarios. In addition, we have emphasized on the challenges associated with CMC mimics in their clinical translation. Overall, this review is an up to date toolbox that researchers can benefit from while designing and characterizing CMC mimics.

A Close Look at Molecular Self-Assembly with the Transmission Electron Microscope

Molecular self-assembly is pervasive in the formation of living and synthetic materials. Knowledge gained from research into the principles of molecular self-assembly drives innovation in the biological, chemical, and materials sciences. Self-assembly processes span a wide range of temporal and spatial domains and are often unintuitive and complex. Studying such complex processes requires an arsenal of analytical and computational tools. Within this arsenal, the transmission electron microscope stands out for its unique ability to visualize and quantify self-assembly structures and processes. This review describes the contribution that the transmission electron microscope has made to the field of molecular self-assembly. An emphasis is placed on which TEM methods are applicable to different structures and processes and how TEM can be used in combination with other experimental or computational methods. Finally, we provide an outlook on the current challenges to, and opportunities for, increasing the impact that the transmission electron microscope can have on molecular self-assembly.

Early-Stage Aggregation and Crystalline Interactions of Peptoid Nanomembranes

Fully synthetic peptoid membranes are known to mimic important features of biological membranes, with several advantages over other biomimetic membranes. A fundamental understanding of how the individual peptoid amphiphiles assemble in solution to form the bilayer membrane is key to unlocking their versatility for application in a broad range of processes. In this study, in situ X-ray scattering and molecular dynamics simulations are used to understand the early stages of assembly of three different peptoids that exhibit distinctly different crystallization kinetics. The in situ measurements reveal that the peptoids aggregate first into a nascent phase that is less crystalline than the assembled peptoid membrane. Anisotropic aromatic interactions are determined to be the dominant driving force in the early stages of membrane formation. These results provide key insights into how the peptoid assembly may be manipulated during the early stages of assembly and nucleation and growth.

Nanoparticles as Drug Delivery Systems of RNAi in Cancer Therapy

RNA interference (RNAi) can mediate gene-silencing by knocking down the expression of a target gene via cellular machinery with much higher efficiency in contrast to other antisense-based approaches which represents an emerging therapeutic strategy for combating cancer. Distinct characters of nanoparticles, such as distinctive size, are fundamental for the efficient delivery of RNAi therapeutics, allowing for higher targeting and safety. In this review, we present the mechanism of RNAi and briefly describe the hurdles and concerns of RNAi as a cancer treatment approach in systemic delivery. Furthermore, the current nanovectors for effective tumor delivery of RNAi therapeutics are classified, and the characteristics of different nanocarriers are summarized.

Periodic Polymerization and the Generation of Polymer Giant Vesicles Autonomously Driven by pH Oscillatory Chemistry

Using the radicals generated during pH oscillations, a semibatch pH oscillator is used as the chemical fuel and engine to drive polymerization induced self-assembly (PISA) for the one-pot autonomous synthesis of functional giant vesicles. Vesicles with diameters ranging from sub-micron to ∼5 µm are generated. Radical formation is found to be switched ON/OFF and be autonomously controlled by the pH oscillator itself, inducing a periodic polymerization process. The mechanism underlying these complex processes is studied and compared to conventional (non-oscillatory) initiation by the same redox pair. The pH oscillations along with the continuous increase in salt concentration in the semibatch reactor make the self-assembled objects undergo morphological evolution. This process provides a self-regulated means for the synthesis of soft giant polymersomes and opens the door for new applications of pH oscillators in a variety of contexts, from the exploration of new geochemical scenarios for the origin of life and the autonomous emergence of the necessary free-energy and proton gradients, to the creation of active functional microreactors and programmable release of cargo molecules for pH-responsive materials.

Peptoid-directed assembly of CdSe nanoparticles

The high information content of proteins drives their hierarchical assembly and complex function, including the organization of inorganic nanomaterials. Peptoids offer an organic scaffold very similar to proteins, but with a wider solubility range and easily tunable side chains and functional groups to create a variety of self-assembling architectures with atomic precision. If we could harness this paradigm and understand the factors that govern how they direct nucleation and assembly of inorganic materials to design order within such materials, new dimensions of function and fundamental science would emerge. In this work, peptoid tubes and sheets were explored as platforms to assemble colloidal quantum dots (QDs) and clusters. We have successfully synthesized CdSe QDs with difunctionalized capping ligands containing both carboxylic acid and thiol groups and mixed them with maleimide containing peptoids, to create an assembly of the QDs on the peptoid surface via a covalent linkage. This conjugation was seen to be successful with peptoid tubes, sheets and CdSe QDs and clusters. The particles were seen to have a high preference for the peptoid surface but non-specific interactions with carboxylic acid groups on the peptoids limited control over QD density via maleimide conjugation. Replacing the carboxylic acid groups with methoxy ethers, however, allowed for control over QD density as a function of maleimide concentration. 1H NMR analysis demonstrated that binding of QDs to peptoids involved a subset of surface ligands bound through the carboxylate functional group, allowing the distal thiol to engage in a covalent linkage to the maleimide. Overall, we have shown the compatibility and control of CdSe-peptoid interactions via a covalent linkage with varying peptoid structures and CdSe particles to create complex hybrid structures.

Plasmonic carriers responsive to pulsed laser irradiation: a review of mechanisms, design, and applications

This review focuses on interactions which govern release from plasmonic carrier systems including liposomes, polymersomes, and nanodroplets under pulsed irradiation.

Fake It 'Till You Make It-The Pursuit of Suitable Membrane Mimetics for Membrane Protein Biophysics

Membrane proteins evolved to reside in the hydrophobic lipid bilayers of cellular membranes. Therefore, membrane proteins bridge the different aqueous compartments separated by the membrane, and furthermore, dynamically interact with their surrounding lipid environment. The latter not only stabilizes membrane proteins, but directly impacts their folding, structure and function. In order to be characterized with biophysical and structural biological methods, membrane proteins are typically extracted and subsequently purified from their native lipid environment. This approach requires that lipid membranes are replaced by suitable surrogates, which ideally closely mimic the native bilayer, in order to maintain the membrane proteins structural and functional integrity. In this review, we survey the currently available membrane mimetic environments ranging from detergent micelles to bicelles, nanodiscs, lipidic-cubic phase (LCP), liposomes, and polymersomes. We discuss their respective advantages and disadvantages as well as their suitability for downstream biophysical and structural characterization. Finally, we take a look at ongoing methodological developments, which aim for direct in-situ characterization of membrane proteins within native membranes instead of relying on membrane mimetics.

Investigating the Mechanisms of AquaporinZ Reconstitution through Polymeric Vesicle Composition for a Biomimetic Membrane

Aquaporin-Z (AqpZ) are water channel proteins with excellent water permeability and solute rejection properties. AqpZ can be reconstituted into vesicles utilizing cell-like bilayer membranes assembled from amphiphilic block copolymers, for the preparation of high-performance biomimetic membranes. However, only a few copolymers have been found suitable to act as the membrane matrix for protein reconstitution. Hence, this work analyzes the mechanism of protein reconstitution based on a composition-reconstitution relationship. The vesicle formation and AqpZ reconstitution processes in various amphiphilic block copolymers were investigated in terms of size, morphology, stability, polymeric bilayer membrane rigidity, and thermal behavior. Overall, this study contributes to the understanding of the composition-reconstitution relationship of biomimetic membranes based on AqpZ-reconstituted polymeric vesicles.

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.

Expanding the structural diversity of peptide assemblies by coassembling dipeptides with diphenylalanine

Molecular self-assembly is a bottom-up approach to fabricate novel supramolecular structures. While the structural diversity obtained by the use of a single type of building block is limited, coassembly of different peptides has recently evolved as an extended strategy to expand the diversity of peptide nanoarchitectures. Here we systematically investigate the coassembly of diphenylalanine (FF) with each one of the 399 non-FF dipeptides by micro-second molecular dynamics simulations. Our simulations show that dipeptides, by coassembling with FF, display a greatly enhanced aggregation propensity and a significantly expanded structural diversity. Regular-shaped vesicles, single- or multi-cavity assemblies, and planar sheets are formed by coassembly of FF with different types of non-FF dipeptides, which are rarely observed in self-assemblies of non-FF dipeptides. Interaction analyses reveal that the formation of these varied structures is attributed to a delicate balance between aromatic stacking, hydrophobic, and electrostatic repulsion interactions. This study provides structural and mechanistic insights into the coassembly of FF and non-FF dipeptides, thus offering a possible way to achieve a controllable design of bionanomaterials through FF-involved dipeptide coassembly.

Macromolecular design and preparation of polymersomes

From drug delivery to nanoreactors and protocells, polymersomes have gained considerable interest from researchers due to their novel applications.

In Situ Monitoring of Membrane Protein Insertion into Block Copolymer Vesicle Membranes and Their Spreading via Potential-Assisted Approach

Synthosomes are polymer vesicles with transmembrane proteins incorporated into block copolymer membranes. They have been used for selective transport in or out of the vesicles as well as catalysis inside the compartments. However, both the insertion process of the membrane protein, forming nanopores, and the spreading of the vesicles on planar substrates to form solid-supported biomimetic membranes have been rarely studied yet. Herein, we address these two points and, first, shed light on the real-time monitoring of protein insertion via isothermal titration calorimetry. Second, the spreading process on different solid supports, namely, SiO₂, glass, and gold, via different techniques like spin- and dip-coating as well as a completely new approach of potential-assisted spreading on gold surfaces was studied. While inhomogeneous layers occur via traditional methods, our proposed potential-assisted strategy to induce adsorption of positively charged vesicles by applying negative potential on the electrode leads to remarkable vesicle spreading and their further fusion to form more homogeneous planar copolymer films on gold. The polymer vesicles in our study are formed from amphiphilic copolymers poly(2-methyl oxazoline)-block-poly(dimethylsiloxane)-block-poly(2-methyl oxazoline) (PMOXA-b-PDMS-b-PMOXA). Engineered variants of the transmembrane protein ferric hydroxamate uptake protein component A (FhuA), one of the largest β-barrel channel proteins, are used as model nanopores. The incorporation of FhuA Δ1-160 is shown to facilitate the vesicle spreading process further. Moreover, high accessibility of cysteine inside the channel was proven by linkage of a fluorescent dye inside the engineered variant FhuA ΔCVF^tev and hence preserved functionality of the channels after spreading. The porosity and functionality of the spread synthosomes on the gold plates have been examined by studying the passive ion transport response in the presence of Li⁺ and ClO₄^- ions and electrochemical impedance spectroscopy analysis. Our approach to form solid-supported biomimetic membranes via the potential-assisted strategy could be important for the development of new (bio-) sensors and membranes.

Cross-Linked Polymersomes with Reversible Deformability and Oxygen Transportability

Polymersomes are of interest as nanocarriers due to their physical and chemical robustness, which arises from the macromolecular nature of their block copolymer components. However, the physical robustness of polymersomes impairs transmembrane diffusion and responsiveness to mechanical forces. Polymer nanocarriers that can reversibly deform under stress while maintaining structural integrity and transmembrane diffusivity are desired for development of gas transport vehicles. Here, we report polymersomes composed of amphiphilic block copolymers containing polydimethylsiloxane with side-chain pendant vinyl groups. A reversibly deformable polymersome compartmentalizing membrane was obtained by cross-linkage of PEG- b-poly(dimethyl- r-methylvinyl)silane in a self-assembled bilayer via photoradical generation in aqueous media. The covalently cross-linked polymersomes exhibited superior physical robustness compared to unlinked polymersomes while maintaining deformability under stress. Transmembrane oxygen diffusion was confirmed when lumen-encapsulated Zn-porphyrin generated singlet O₂ under irradiation, and the anthracene-9,10-dipropionic acid O₂ quencher was consumed. Polymersome-encapsulated hemoglobin bound oxygen reversibly, indicating the polymersomes could be used as O₂ carriers that reversibly deform without sacrificing structural integrity or oxygen transportability.

Diblock copolymers enhance folding of a mechanosensitive membrane protein during cell-free expression

Membrane protein folding is a critical step that underlies proper cellular function as well as the design of technologies like vesicle-based biosensors and artificial cells. Membrane composition is known to play a role in membrane protein folding; however, the specific mechanical properties of membranes that govern protein folding remain unclear. Using a highly elastic nonnatural amphiphile, we highlight the importance of a membrane mechanical property, membrane elasticity, on the spontaneous insertion and folding of a model α-helical membrane protein. Through this study, we gain a deeper understanding of cellular membrane protein folding and offer a potential approach to improve the production of membrane proteins through optimizing the mechanical properties of synthetic scaffolds present in cell-free reactions.

The expression and integration of membrane proteins into vesicle membranes is a critical step in the design of cell-mimetic biosensors, bioreactors, and artificial cells. While membrane proteins have been integrated into a variety of nonnatural membranes, the effects of the chemical and physical properties of these vesicle membranes on protein behavior remain largely unknown. Nonnatural amphiphiles, such as diblock copolymers, provide an interface that can be synthetically controlled to better investigate this relationship. Here, we focus on the initial step in a membrane protein’s life cycle: expression and folding. We observe improvements in both the folding and overall production of a model mechanosensitive channel protein, the mechanosensitive channel of large conductance, during cell-free reactions when vesicles containing diblock copolymers are present. By systematically tuning the membrane composition of vesicles through incorporation of a poly(ethylene oxide)-b-poly(butadiene) diblock copolymer, we show that membrane protein folding and production can be improved over that observed in traditional lipid vesicles. We then reproduce this effect with an alternate membrane-elasticizing molecule, C₁₂E₈. Our results suggest that global membrane physical properties, specifically available membrane surface area and the membrane area expansion modulus, significantly influence the folding and yield of a membrane protein. Furthermore, our results set the stage for explorations into how nonnatural membrane amphiphiles can be used to both study and enhance the production of biological membrane proteins.

Increasing Salt Rejection of Polybenzimidazole Nanofiltration Membranes via the Addition of Immobilized and Aligned Aquaporins

Aquaporins are water channel proteins in cell membrane, highly specific for water molecules while restricting the passage of contaminants and small molecules, such as urea and boric acid. Cysteine functional groups were installed on aquaporin Z for covalent attachment to the polymer membrane matrix so that the proteins could be immobilized to the membranes and aligned in the direction of the flow. Depth profiling using x-ray photoelectron spectrometer (XPS) analysis showed the presence of functional groups corresponding to aquaporin Z modified with cysteine (Aqp-SH). Aqp-SH modified membranes showed a higher salt rejection as compared to unmodified membranes. For 2 M NaCl and CaCl₂ solutions, the rejection obtained from Aqp-SH membranes was 49.3 ± 7.5% and 59.1 ± 5.1%. On the other hand, the rejections obtained for 2 M NaCl and CaCl₂ solutions from unmodified membranes were 0.8 ± 0.4% and 1.3 ± 0.2% respectively. Furthermore, Aqp-SH membranes did not show a significant decrease in salt rejection with increasing feed concentrations, as was observed with other membranes. Through simulation studies, it was determined that there was approximately 24% capping of membrane pores by dispersed aquaporins.

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.

Biomolecules Turn Self-Assembling Amphiphilic Block Co-polymer Platforms Into Biomimetic Interfaces

Biological membranes constitute an interface between cells and their surroundings and form distinct compartments within the cell. They also host a variety of biomolecules that carry out vital functions including selective transport, signal transduction and cell-cell communication. Due to the vast complexity and versatility of the different membranes, there is a critical need for simplified and specific model membrane platforms to explore the behaviors of individual biomolecules while preserving their intrinsic function. Information obtained from model membrane platforms should make invaluable contributions to current and emerging technologies in biotechnology, nanotechnology and medicine. Amphiphilic block co-polymers are ideal building blocks to create model membrane platforms with enhanced stability and robustness. They form various supramolecular assemblies, ranging from three-dimensional structures (e.g., micelles, nanoparticles, or vesicles) in aqueous solution to planar polymer membranes on solid supports (e.g., polymer cushioned/tethered membranes,) and membrane-like polymer brushes. Furthermore, polymer micelles and polymersomes can also be immobilized on solid supports to take advantage of a wide range of surface sensitive analytical tools. In this review article, we focus on self-assembled amphiphilic block copolymer platforms that are hosting biomolecules. We present different strategies for harnessing polymer platforms with biomolecules either by integrating proteins or peptides into assemblies or by attaching proteins or DNA to their surface. We will discuss how to obtain synthetic structures on solid supports and their characterization using different surface sensitive analytical tools. Finally, we highlight present and future perspectives of polymer micelles and polymersomes for biomedical applications and those of solid-supported polymer membranes for biosensing.

Giant polymersomes from non-assisted film hydration of phosphate-based block copolymers

Polybutadiene-block-poly(ethyl ethylene phosphate) can reproducibly self-assemble in large number into giant unilamellar vesicles (GUVs) by non-assisted film hydration, representing a stepping stone for better liposomes – substitutes towards the generation of artificial cells.

Liposomes and polymersomes: a comparative review towards cell mimicking

Minimal cells: we compare and contrast liposomes and polymersomes for a bettera priorichoice and design of vesicles and try to understand the advantages and shortcomings associated with using one or the other in many different aspects (properties, synthesis, self-assembly, applications).

Layer-by-layer Assembled Membranes with Immobilized Porins

With the synthesis and functionalization of membranes for selective separations, reactivity, and stimuli responsive behavior arises new and advanced opportunities. The integration of bio-based channels is one of these advancements in membrane technologies. By a layer-by-layer (LbL) assembly of polyelectrolytes, outer membrane protein F trimers (OmpF) or "porins" from Escherichia coli with a central pore of ~2 nm diameter at its opening and ~0.7 × 1.1 nm at its constricted region are immobilized within the pores of poly(vinylidene fluoride) microfiltration membranes, as opposed to traditional ruptured lipid bilayer or vesicles processes. These OmpF-membranes demonstrate selective rejections of non-charged organics over ionic solutes, allowing the passage of salts up to 2 times higher than traditional nanofiltration membranes starting with rejections of 84% for 0.4-1.0 kDa organics. The presence of charged groups in OmpF membranes also leads to pH-dependent salt rejection through Donnan exclusion. These OmpF-membranes also show exceptional durability and stability, delivering consistent and constant permeability and recovery for over 160 h of operation. Characterization of solutions containing OmpF, and membranes were conducted during each stage of the process, including detection by fluorescence labelling (FITC), zeta potential, pH responsiveness, flux changes, and rejections of organic-inorganic solutions.

Morphology Under Control: Engineering Biodegradable Stomatocytes

Biodegradable nanoarchitectures, with well-defined morphological features, are of great importance for nanomedical research; however, understanding (and thereby engineering) their formation is a substantial challenge. Herein, we uncover the supramolecular potential of PEG-PDLLA copolymers by exploring the physicochemical determinants that result in the transformation of spherical polymersomes into stomatocytes. To this end, we have engineered blended polymersomes (comprising copolymers with varying lengths of PEG), which undergo solvent-dependent reorganization inducing negative spontaneous membrane curvature. Under conditions of anisotropic solvent composition across the PDLLA membrane, facilitated by the dialysis methodology, we demonstrate osmotically induced stomatocyte formation as a consequence of changes in PEG solvation, inducing negative spontaneous membrane curvature. Controlled formation of unprecedented, biodegradable stomatocytes represents the unification of supramolecular engineering with the theoretical understanding of shape transformation phenomena.

Controlling the generation of bilayer and multilayer vesicles in block copolymer/epoxy blends by a slow photopolymerization process

Vesicles are a highly attractive morphology to achieve in micellar dispersions of block copolymers (BCP) in epoxy thermosets due to the fact that small amounts can affect a large volume fraction of the matrix, a fact that is important for toughening purposes. However, generating vesicles in epoxy matrices requires operating in a narrow range of formulations and processing conditions. In this report, we show that block-copolymer vesicles dispersed in an epoxy matrix could be obtained through a sphere-to-cylinder-to-vesicle micellar transition induced by visible-light photopolymerization at room temperature. A 10 wt% colloidal solution of poly(ethylene-co-butene)-block-poly(ethylene oxide) (PEB-b-PEO) block copolymer (BCP) in an epoxy monomer (DGEBA) self-assembled into spherical micelles as shown by small-angle X-ray scattering (SAXS). During a slow photopolymerization of the epoxy monomer carried out at room temperature, a sphere-to-cylinder-to-vesicle transition took place as revealed by in situ SAXS and TEM images. This was driven by the tendency of the system to reduce the local interfacial curvature as a response to a decrease in the miscibility of PEO blocks in the polymerizing epoxy matrix. When the BCP concentration was increased from 10 to 20 and 40 wt%, the final structure evolved from bilayer vesicles to multilayer vesicles and to lamellae, respectively. In particular, for 20 wt% PEB-b-PEO, transient structures such as partially fused multilayered vesicles were observed by TEM, giving insight into the growth mechanism of multilayer vesicles. On the contrary, when a relatively fast thermal polymerization was performed at 80 °C, the final morphology consisted of kinetically trapped spherical and cylindrical micelles. Hopefully, this study will lead to new protocols for the preparation of vesicles dispersed in epoxy matrices in a controlled way.

Photo-Cross-Linked Dual-Responsive Hollow Capsules Mimicking Cell Membrane for Controllable Cargo Post-Encapsulation and Release

Multifunctional and responsive hollow capsules are ideal candidates to establish highly sophisticated compartments mimicking cell membranes for controllable bio-inspired functions. For this purpose pH and temperature dual-responsive and photo-cross-linked hollow capsules, based on silica-templated layer-by-layer approach by using poly(N-isopropyl acrylamide)-block-polymethacrylate) and polyallylamine, have been prepared to use them for the subsequent and easily available post-encapsulation process of protein-like macromolecules at room temperature and pH 7.4 and their controllable release triggered by stimuli. The uptake and release properties of the hollow capsules for cargos are highly affected by changes in the external stimuli temperature (25, 37, or 45 °C) and internal stimuli pH of the phosphate-containing buffer solution (5.5 or 7.4), by the degree of photo-cross-linking, and the size of cargo. The photo-cross-linked and dual stimuli-responsive hollow capsules with different membrane permeability can be considered as attractive material for mimicking cell functions triggered by controllable uptake and release of different up to 11 nm sized biomolecules.

Highly stable and self-repairing membrane-mimetic 2D nanomaterials assembled from lipid-like peptoids

An ability to develop sequence-defined synthetic polymers that both mimic lipid amphiphilicity for self-assembly of highly stable membrane-mimetic 2D nanomaterials and exhibit protein-like functionality would revolutionize the development of biomimetic membranes. Here we report the assembly of lipid-like peptoids into highly stable, crystalline, free-standing and self-repairing membrane-mimetic 2D nanomaterials through a facile crystallization process. Both experimental and molecular dynamics simulation results show that peptoids assemble into membranes through an anisotropic formation process. We further demonstrated the use of peptoid membranes as a robust platform to incorporate and pattern functional objects through large side-chain diversity and/or co-crystallization approaches. Similar to lipid membranes, peptoid membranes exhibit changes in thickness upon exposure to external stimuli; they can coat surfaces in single layers and self-repair. We anticipate that this new class of membrane-mimetic 2D nanomaterials will provide a robust matrix for development of biomimetic membranes tailored to specific applications.

Biomimetic membranes can be used for various applications such as sensors and separations. Here, Chen et al. report the assembly of lipid-like peptoids into stable and self-repairing 2D membrane nanomaterials that change in thickness when under external stimuli.

Multifunctional Surface Manipulation Using Orthogonal Click Chemistry

Polymer brushes are excellent substrates for the covalent immobilization of a wide variety of molecules due to their unique physicochemical properties and high functional group density. By using reactive microcapillary printing, poly(pentafluorophenyl acrylate) brushes with rapid kinetic rates toward aminolysis can be partially patterned with other click functionalities such as strained cyclooctyne derivatives and sulfonyl fluorides. This trireactive surface can then react locally and selectively in a one pot reaction via three orthogonal chemistries at room temperature: activated ester aminolysis, strain promoted azide-alkyne cycloaddition, and sulfur(VI) fluoride exchange, all of which are tolerant of ambient moisture and oxygen. Furthermore, we demonstrate that these reactions can also be used to create areas of morphologically distinct surface features on the nanoscale, by inducing buckling instabilities in the films and the grafting of nanoparticles. This approach is modular, and allows for the development of highly complex surface motifs patterned with different chemistry and morphology.

Immobilized Multifunctional Polymersomes on Solid Surfaces: Infrared Light-Induced Selective Photochemical Reactions, pH Responsive Behavior, and Probing Mechanical Properties under Liquid Phase

Fixing polymersomes onto surfaces is in high demand not only for the characterization with advanced microscopy techniques but also for designing specific compartments in microsystem devices in the scope of nanobiotechnology. For this purpose, this study reports the immobilization of multifunctional, responsive, and photo-cross-linked polymersomes on solid substrates by utilizing strong adamantane-β-cyclodextrin host-guest interactions. To reduce nonspecific binding and retain better spherical shape, the level of attractive forces acting on the immobilized polymersomes was tuned through poly(ethylene glycol) passivation as well as decreased β-cyclodextrin content on the corresponding substrates. One significant feature of this system is the pH responsivity of the polymersomes which has been demonstrated by swelling of the immobilized vesicles at acidic condition through in situ AFM measurements. Also, light responsivity has been provided by introducing nitroveratryloxycarbonyl (NVOC) protected amine molecules as photocleavable groups to the polymersome surface before immobilization. The subsequent low-energy femtosecond pulsed laser irradiation resulted in the cleavage of NVOC groups on immobilized polymersomes which in turn led to free amino groups as an additional functionality. The freed amines were further conjugated with a fluorescent dye having an activated ester that illustrates the concept of bio/chemo recognition for a potential binding of biological compounds. In addition to the responsive nature, the mechanical stability of the analyzed polymersomes was supported by computing Young's modulus and bending modulus of the membrane through force curves obtained by atomic force microscopy measurements. Overall, polymersomes with a robust and pH-swellable membrane combined with effective light responsive behavior are promising tools to design smart and stable compartments on surfaces for the development of microsystem devices such as chemo/biosensors.