Polymer Vesicles Research Articles

Photochemically induced cyclic morphological dynamics via degradation of autonomously produced, self-assembled polymer vesicles

Autonomous and out-of-equilibrium vesicles synthesised from small molecules in a homogeneous aqueous medium are an emerging class of dynamically self-assembled systems with considerable potential for engineering natural life mimics. Here we report on the physico-chemical mechanism behind a dynamic morphological evolution process through which self-assembled polymeric structures autonomously booted from a homogeneous mixture, evolve from micelles to giant vesicles accompanied by periodic growth and implosion cycles when exposed to oxygen under light irradiation. The system however formed nano-objects or gelation under poor oxygen conditions or when heated. We determined the cause to be photoinduced chemical degradation within hydrated polymer cores inducing osmotic water influx and the subsequent morphological dynamics. The process also led to an increase in the population of polymeric objects through system self-replication. This study offers a new path toward the design of chemically self-assembled systems and their potential application in autonomous material artificial simulation of living systems.

Reversibly self‐assembled pH‐responsive PEG‐p(CL‐g‐TMC) polymersomes

AbstractPolymersomes have gained much interest within the biomedical field as drug delivery systems due to their ability to transport and protect cargo from the harsh environment inside the body. For an improved drug efficacy, control over cargo release is however also an important factor to take into account. An often employed method is to incorporate pH sensitive groups in the vesicle membrane, which induce disassembly and content release when the particles have reached a target site in the body with the appropriate pH, such as the acidic microenvironment of tumor tissue or the endosome. In this paper, biodegradable poly(ethylene glycol)‐poly(caprolactone‐gradient‐trimethylene carbonate)‐based polymeric vesicles have been developed with disassembly features at mild acidic conditions. Modifying the polymer backbone with imidazole moieties results in vesicle disassembly upon protonation due to the lowered pH. Furthermore, upon increasing the pH efficient re‐assembly into vesicles is observed due to the switchable amphiphilic nature of the polymer. When this re‐assembly process is conducted in presence of cargo, enhanced encapsulation is achieved. Furthermore, the potency of the polymeric system for future biomedical applications such as adjuvant delivery is demonstrated.

Design, Function and Applications of Molecular Permeable Polymer Vesicles

Vesicles are formed from the self–assembly of phospholipids, synthetic lipids, and amphiphilic polymers. Among vesicles, polymer vesicles can be introduced various functions such as stimuli–responsivity and have superior mechanical strength. Polymer vesicles also have an inner aqueous phase and can function as enzymatic reactors when enzymes are encapsulated in the inner aqueous phase. Therefore, they have been attracted attention for biomaterials such as nano/microreactors, carriers for drug delivery systems (DDS), and artificial organelle/cell models. However, the bilayers of polymer vesicles are thicker than those of phospholipid liposomes and thus have extremely low molecular permeability, making it difficult to supply molecules from the external environment. This review introduces our efforts to develop molecular permeable polymer vesicles, the functions of the vesicles, and applications for biomaterials as artificial molecular channels and biocatalytic nanoreactors.

Incorporation of nanogels within calcite single crystals for the storage, protection and controlled release of active compounds.

Nanocarriers have tremendous potential for the encapsulation, storage and delivery of active compounds. However, current formulations often employ open structures that achieve efficient loading of active agents, but that suffer undesired leakage and instability of the payloads over time. Here, a straightforward strategy that overcomes these issues is presented, in which protein nanogels are encapsulated within single crystals of calcite (CaCO3). Demonstrating our approach with bovine serum albumin (BSA) nanogels loaded with (bio)active compounds, including doxorubicin (a chemotherapeutic drug) and lysozyme (an antibacterial enzyme), we show that these nanogels can be occluded within calcite host crystals at levels of up to 45 vol%. Encapsulated within the dense mineral, the active compounds are stable against harsh conditions such as high temperature and pH, and controlled release can be triggered by a simple reduction of the pH. Comparisons with analogous systems – amorphous calcium carbonate, mesoporous vaterite (CaCO3) polycrystals, and calcite crystals containing polymer vesicles – demonstrate the superior encapsulation performance of the nanogel/calcite system. This opens the door to encapsulating a broad range of existing nanocarrier systems within single crystal hosts for the efficient storage, transport and controlled release of various active guest species.

Surface modifications of biodegradable polymeric nanoparticles and their characterization by advanced electron microscopy techniques

Polymeric nanoparticles have been the focus for nanocarrier preparation in numerous biomedical applications such as cancer treatment, disease diagnosis, vaccination, in the last two decades. They have been variably surface modified using copolymers, Polyethylene glycol (PEG), dextran, cyclodextrin, cytokines, small molecules to improve their efficiency and efficacy. The resulting nano-formulations include polymer-protein conjugate, polymeric micelle, polymer-small molecule conjugate, dendrimer, polymeric vesicles, nano-hybrids, hydrogels etc. These may have intrinsic immunogenicity and require accurate characterization in order to improve their pharmacological targeting, pharmacokinetic profiles and to reduce adverse reactions. Therefore, we have reviewed the polymeric nanoparticles and the electron microscopy techniques available for their characterization in the context of their surface modifications and functionalization.

Fabrication and characterization of structurally stable pH-responsive polymeric vesicles by polymerization-induced self-assembly.

Smart polymeric vesicles with both tertiary amine and epoxy functional groups were fabricated for the first time via a reversible addition–fragmentation chain transfer dispersion polymerization approach, using (2-(diisopropylamino)ethyl methacrylate (DIPEMA) and glycidyl methacrylate (GlyMA) in an ethanol–water mixture. Monitoring of the in situ polymerization revealed the low molecular weight distributions and the intermediate structures of spheres and worms, indicating an evolution in particle morphology. A phase diagram was constructed for reproducible fabrication of the vesicles, and copolymer composition was found to be more related to particle morphology. The vesicles exhibited superior structural stability for the cross-linking of the core through epoxydiamine chemistry, and intelligent pH responsibility due to the presence of the tertiary amine groups. The cross-linked vesicles showed good stability and reversibility during the swelling and shrinking cycles by switching the pH values, which endowed them with potential cell-like transmission functions. This research thus provides a method for producing structurally stable pH-responsive polymeric vesicles, and the reported vesicles are based on commercially available starting materials for possible industrial scale-up.

From spherical compartments to polymer films: exploiting vesicle fusion to generate solid supported thin polymer membranes.

Solid supported polymer membranes as scaffold for the insertion of functional biomolecules provide the basis for mimicking natural membranes. They also provide the means for unraveling biomolecule-membrane interactions and engineering platforms for biosensing. Vesicle fusion is an established procedure to obtain solid supported lipid bilayers but the more robust polymer vesicles tend to resist fusion and planar membranes rarely form. Here, we build on vesicle fusion to develop a refined and efficient way to produce solid supported membranes based on poly(dimethylsiloxane)-poly(2-methyl-2-oxazoline) (PMOXA-b-PDMS-b-PMOXA) amphiphilic triblock copolymers. We first create thiol-bearing polymer vesicles (polymersomes) and anchor them on a gold substrate. An osmotic shock then provokes polymersome rupture and drives planar film formation. Prerequisite for a uniform amphiphilic planar membrane is the proper combination of immobilized polymersomes and osmotic shock conditions. Thus, we explored the impact of the hydrophobic PDMS block length of the polymersome on the formation and the characteristics of the resulting solid supported polymer assemblies by quarz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). When the PDMS block is short enough, attached polymersomes restructure in response to osmotic shock, resulting in a uniform planar membrane. Our approach to rapidly form planar polymer membranes by vesicle fusion brings many advantages to the development of synthetic planar membranes for bio-sensing and biotechnological applications.

Neuron-like tubule extension of giant polymer vesicles

Giant polymer vesicles consisting of amphiphilic diblock copolymers are helpful as artificial biomembrane models based on many similarities in their size, structure, morphological transformation, membrane permeability, etc. This paper describes the creation of neuron-like tubule extension employing the polymer vesicles. The polymerization-induced self-assembly was performed in the presence of micron-sized spherical vesicles consisting of poly(methacrylic acid)-block-poly(methyl methacrylate-random-methacrylic acid), PMAA-b-P(MMA-r-MAA), through the photo nitroxide-mediated controlled/living radical polymerization (photo-NMP) using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MTEMPO) as the mediator. The photo-NMP of methyl methacrylate (MMA) and methacrylic acid (MAA) was carried out in an aqueous methanol solution (CH3OH/H2O = 3/1 v/v) using poly(methacrylic acid) (PMAA) end-capped with MTEMPO and the spherical vesicles of PMAA141-b-P(MMA0.831-r-MAA0.169)368 with an 11.7-mm diameter. The vesicles projected many processes on their surface during the early stage of the polymerization. As the polymerization progressed, only one or two of the processes extended to thick tubules, accompanied by the slow growth of thin tubules. Further progress of the polymerization elongated the thick tubules and caused branching of the tubules. The tubules had a vesicular structure because cup-like vesicles joined in line were formed during the initial stage of the extension. The polymerization livingness supported the tubule extension based on a linear increase in the molecular weight of the component copolymer and a negligible change in the molecular weight distribution versus the monomer conversion. The spherical vesicles were similar to the neurons in the tubule extension for the initial projection, followed by the elongation and branching. This similarity implies that the neurite extension in the neurons is related to the inherent property of the bilayer membrane.

Development of Polymeric Vesicles Containing Biomacromolecules Based on Design of Polyion Complex Coupled with Control of Its Fabrication Process

Development of Polymeric Vesicles Containing Biomacromolecules Based on Design of Polyion Complex Coupled with Control of Its Fabrication Process

Encapsulation of inorganic nanoparticles in a block copolymer vesicle wall driven by the interfacial instability of emulsion droplets

We proposed an effective route, i.e., three-dimensional confined co-assembly of block copolymers and inorganic nanoparticles, to efficiently encapsulate high-density and large-size nanoparticles into the wall of polymeric vesicles.

Formation of giant polymer vesicles by simple double emulsification using block copolymers as the sole surfactant

Polymer vesicles that mimic the function of cell membranes can be obtained through the self-assembly of amphiphilic block copolymers. The cell-like characteristics of polymer vesicles, such as the core-shell structure, semi-permeability and tunable surface chemistry make them excellent building blocks for artificial cells. However, the standard preparation methods for polymer vesicles can be time consuming, require special equipment, or have low encapsulation efficiency for large components, such as nanomaterials and proteins. Here, we introduce a new encapsulation strategy based on a simple double emulsification (SDE) approach which allows giant polymer vesicles to be formed in a short time and with basic laboratory equipment. The SDE method requires a single low molecular weight block copolymer that has the dual role of macromolecular surfactant and membrane building block. Giant polymer vesicles with diameters between 20-50 μm were produced, which allowed proteins and nanoparticles to be encapsulated. To demonstrate its practical application, we used the SDE method to assemble a simple artificial cell that mimics a two-step enzymatic cascade reaction. The SDE method described here introduces a new tool for simple and rapid fabrication of synthetic compartments.

Using reactive dissipative particle dynamics to understand local shape manipulation of polymer vesicles.

Biological cells have long been of interest to researchers due to their capacity to actively control their shape. Accordingly, there is significant interest in generating simplified synthetic protocells that can alter their shape based on an externally or internally generated stimulus. To date, most progress has been made towards controlling the global shape of a protocell, whereas less is known about generating a local shape change. Here, we seek to better understand the possible mechanisms for producing local morphological changes in a popular protocell system, the block copolymer vesicle. Accordingly, we have combined Dissipative Particle Dynamics (DPD) and the Split Reactive Brownian Dynamics algorithm (SRBD) to produce a simulation tool that is capable of modeling the dynamics of self-assembled polymer structures as they undergo chemical reactions. Using this Reactive DPD or RDPD method, we investigate local morphological change driven by either the microinjection of a stimulus or an enzymatically-produced stimulus. We find that sub-vesicle-scale morphological change can be induced by either a solvent stimulus that swells the vesicle membrane, or by a reactant stimulus that alters the chemistry of the block polymer in the membrane corona. Notably, the latter method results in a more persistent local deformation than the former, which we attribute to the slower diffusion of polymer chains relative to the solvent. We quantify this deformation and show that it can be modulated by altering the interaction parameter of the parts of the polymer chain that are affected by the stimulus.

Life-Inspired Endogenous Dynamic Behavior of Lipid Droplet-like Microcompartments in Artificial Adipocyte-like Structures

Chemical systems that can replicate cellular behaviors are gaining increasing attention and are being used to study various biological processes. Here, a protein- or amylose-based assembly at an oi...

Probing Thermoresponsive Polymerization-Induced Self-Assembly with Variable-Temperature Liquid-Cell Transmission Electron Microscopy

Summary We directly initiate and visualize the formation of polymeric nanomaterials via variable-temperature liquid-cell transmission electron microscopy (VT-LCTEM). With temperature control in the liquid cell, reversible addition-fragmentation chain transfer polymerization was thermally initiated, leading to the formation of amphiphilic block copolymers that assemble upon dispersion polymerization-induced self-assembly (PISA). In combination with traditional ex situ analyses, VT-LCTEM enabled not only the characterization of the nanoparticles in situ but also the observation of a thermal phase transition. Critically, because these assemblies form from thermoresponsive components, any temperature changes during sample preparation and analysis can alter morphologies, necessitating direct in situ characterization of reaction progression. We believe that the findings and the technique described herein will lead to unprecedented possibilities for the development and characterization of self-organizing soft matter.

Porphyrin Alternating Copolymer Vesicles for Photothermal Drug-Resistant Bacterial Ablation and Wound Disinfection.

In the past two decades, polymer vesicles have aroused widespread interest and made significant developments. However, the applications of polymer vesicles in anti-infective therapy are still limited. Here, we construct a polymer vesicle (TPPBV) from a porphyrin alternating copolymer P(TPP-a-BDE) with a high photothermal conversion efficiency (54.1%), which is attributed to the unique chain-folding mechanisms of the alternating copolymer. In particular, TPPBVs exhibit great photothermal antibacterial activity against both Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative extended-spectrum β-lactamases Escherichia coli (ESBL E. coli). Moreover, TPPBVs present a specific antibiofilm effect, and they also have remarkable therapeutic effects in vivo on an MRSA-infected mice model. We believe that the porphyrin alternating copolymer vesicles for photothermal bacterial ablation reported here will extend the applications of polymer vesicles.

Enzyme Degradable Polymersomes from Chitosan-g-[poly-l-lysine-block-ε-caprolactone] Copolymer.

The scope of this study includes the synthesis of chitosan-g-[peptide-poly-ε-caprolactone] and its self-assembly into polymeric vesicles employing the solvent shift method. In this way, well-defined core-shell structures suitable for encapsulation of drugs are generated. The hydrophobic polycaprolactone side-chain and the hydrophilic chitosan backbone are linked via an enzyme-cleavable peptide. The synthetic route involves the functionalization of chitosan with maleimide groups and the preparation of polycaprolactone with alkyne end-groups. A peptide functionalized with a thiol group on one side and an azide group on the other side is prepared. Thiol-ene click-chemistry and azide-alkyne Huisgen cycloaddition are then used to link the chitosan and poly-ε-caprolactone chains, respectively, with this peptide. For a preliminary study, poly-l-lysin is a readily available and cleavable peptide that is introduced to investigate the feasibility of the system. The size and shape of the polymersomes are studied by dynamic light scattering and cryo-scanning electron microscopy. Furthermore, degradability is studied by incubating the polymersomes with two enzymes, trypsin and chitosanase. A dispersion of polymersomes is used to coat titanium plates and to further test the stability against enzymatic degradation.

Fast and effective chromatographic separation of polymersomes from proteins by multimodal chromatography

Artificial vesicles made of block copolymers, so-called polymersomes, represent a versatile chassis for the creation of functionalized nanocompartments with a wide range of biotechnological applications. The specific application depends on the biomolecules – usually proteins – that are positioned in the interior, in the membrane or on the surface of the vesicles. However, not all added proteins are integrated into the vesicles during the usual manufacturing processes of polymersomes. Excess proteins must therefore be removed. The separation techniques currently used for this, however, are associated with decisive disadvantages, such as damaged vesicles, long process times, or small sample volumes that can be processed. To overcome these drawbacks, we investigated the applicability of Capto™ Core 700 resin for polymersome purification. Polymersomes were not damaged or otherwise affected by passage through the column verified by hollow fiber flow field flow fractionation technique. Using three proteins with divergent physico-chemical properties as examples, it was demonstrated that different types of unentrapped proteins were efficiently removed from polymersome dispersions. The dynamic binding capacities in the presence of polymersomes varied between 9.5 and 16.5 mg per mL resin for the proteins applied. The technique can be used for small and large sample volumes alike. In addition, it can be used without special laboratory equipment. This adds a new and easy-to-use purification method for polymer vesicles to the repertoire that will also facilitate the large-scale production of functionalized polymersomes.

Microfluidic Tracking of the Growth of Polymeric Vesicles in Hydrodynamic Flow

Polymeric vesicles (PVs) have proven to be a promising container for various agents because of the benefit of core–shell structures. The formation mechanism of PVs has been investigated in the hydr...

Fabrication of the Polymersomes with Unique and Even Nonequilibrium Morphologies.

Herein, efficient fabrication of polymersomes that have unique and nonequilibrium morphologies is reported. Starting from preparing big polymeric vesicles sized around 2µm with a flexible but crosslinkable structure, a controllable morphological transformation process from the vesicles via prolate vesicles and the pearl-chain-like structure, which are the two intermediate structures, to vesicle-end-capped tubes is conducted. Significantly, each of the intermediates is a regular polymersome and occupies a distinct phase space in the transformation process and thus can be separately processed and prepared. By crosslinking the structures, respectively, regular polymersomes with unique but stable morphologies are fabricated. Furthermore, the 1D polymersomes contain narrow necks. These narrow necks are sensitive to ultrasound vibration and broken by gentle ultrasound treatment to form regular open-ended tubes and open-ended vesicles, which are nonequilibrium but stable morphologies and difficult to prepare by existing methods.

Tailored functional polymeric vesicles as smart nanostructured materials for aqueous monitoring of transition metal cations

In this study, we report the newly engineered functional polymeric vesicles as the robust nanostructured materials for the recognition and quantification of transition metal cations i.e. Hg(II) and Cr(III) as the naked eye recognition architectures in aqueous solution. The as prepared visual detector was synthesized by the combination of a hyperbranched poly(3-ethyl-3-oxetanemethanol)-star-poly(ethylene oxide) (HBPO-star-PEO, HSP) functionalized with rhodamine-2-amino-5-bromopyrimidine based chemosensor (RBP). The nanostructured vesicular sensor was regarded as HSP-RBP sensor. The naked eye detection owes from the spriolactam ring opening of the rhodamine based sensor (RBP) which was grafted onto the multiarm hyperbranched amphiphilic polymer. This newly synthesized sensor can facilely self-assemble into vesicles with enriched RBP groups on the outer surface of amphiphilic polymer. As a result of the introduction of these analytes (Hg2+/Cr3+) the structural changes of RBP takes place and a transition in color change from colorless solution to pink colored solution takes place. This transition of color can clearly be seen with bare eye. Therefore, the term visual detection can be coined for the vesicular sensor. Furthermore, the limit of detection for Hg2+ and Cr3+ was calculated as low as 1.2 and 2.9 μM respectively. The striking feature of the newly prepared sensor, is its extraordinary ability for the recognition and quantification of Hg2+/Cr3+ with outstanding selectivity in raw water samples.