Vesicles Formed from a Poly(ethylene oxide)−Poly(propylene oxide)−Poly(ethylene oxide) Triblock Copolymer in Dilute Aqueous Solution

Role of Unimers to Polymersomes Transition in Pluronic Blends for Controlled and Designated Drug Conveyance

This study investigates the nanoscale self-assembly from mixtures of two symmetrical poly(ethylene oxide)-poly(propylene oxide)-pol(ethylene oxide) (PEO-PPO-PEO) block copolymers (BCPs) with different lengths of PEO blocks and similar PPO blocks. The blended BCPs (commercially known as Pluronic F88 and L81, with 80 and 10% PEO, respectively) exhibited rich phase behavior in an aqueous solution. The relative viscosity (ηrel) indicated significant variations in the flow behavior, ranging from fluidic to viscous, thereby suggesting a possible micellar growth or morphological transition. The tensiometric experiments provided insight into the intermolecular hydrophobic interactions at the liquid-air interface favoring the surface activity of mixed-system micellization. Dynamic light scattering (DLS) and small-angle neutron scattering (SANS) revealed the varied structural morphologies of these core-shell mixed micelles and polymersomes formed under different conditions. At a concentration of ≤5% w/v, Pluronic F88 exists as molecularly dissolved unimers or Gaussian chains. However, the addition of the very hydrophobic Pluronic L81, even at a much lower (<0.2%) concentration, induced micellization and promoted micellar growth/transition. These results were further substantiated through molecular dynamics (MD) simulations, employing a readily transferable coarse-grained (CG) molecular model grounded in the MARTINI force field with density and solvent-accessible surface area (SASA) profiles. These findings proved that F88 underwent micellar growth/transition in the presence of L81. Furthermore, the potential use of these Pluronic mixed micelles as nanocarriers for the anticancer drug quercetin (QCT) was explored. The spectral analysis provided insight into the enhanced solubility of QCT through the assessment of the standard free energy of solubilization (ΔG°), drug-loading efficiency (DL%), encapsulation efficiency (EE%), and partition coefficient (P). A detailed optimization of the drug release kinetics was presented by employing various kinetic models. The [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] MTT assay, a frequently used technique for assessing cytotoxicity in anticancer research, was used to gauge the effectiveness of these QCT-loaded mixed nanoaggregates.

Cellulose nanocrystal and Pluronic L121-based thermo-responsive composite hydrogels

Cellulose nanocrystal (CNC) is a promising sustainable material with its biocompatibility, high aspect ratio, and mechanical strength. CNC-based systems have potential applications in various fields including biosensors, packaging, coating, energy storage, and pharmaceuticals. However, turning CNC into smart systems remains a challenge due to the lack of stimuli-responsiveness, limitation in compatibility with hydrophobic matrices, and their agglomeration tendency. In this work, a thermo-responsive nanocomposite system is constructed with CNCs and polymersome forming Pluronic L121 (L121), and its phase behavior and mechanical properties are investigated in detail. Two different CNC concentration (4 % and 5 %) is studied by changing the L121 concentration (1-20 %) to understand the effect of unimers and polymersomes on the CNC network. At dilute L121 concentrations (1-5 %), the composite system becomes softer but more fragile below the transition temperature. However, it becomes much stronger at higher L121 concentrations (10-20 %), and a gel network is obtained above the transition temperature. Interestingly, the elastically reinforced CNC gels exhibit greater resistance to microstructural breakdown at large strains due to the soft and deformable nature of the large polymersomes. It is also found that the gelation temperature for hydrogels is tunable with increasing L121 concentration, and the nanocomposite hydrogels displayed thermo-reversible rheological behavior.

Aqueous Two-Phase Systems within Selectively Permeable Vesicles

An aqueous two-phase system (ATPS) encapsulated within a vesicle organizes the vesicle core as two coexisting phases that partition encapsulated solutes. Here, we use microfluidic technologies to produce vesicles that efficiently encapsulate mixtures of macromolecules, providing a versatile platform to determine the phase behavior of ATPSs. Moreover, we use compartmentalized vesicles to investigate how membrane permeability affects the dynamics of the encapsulated ATPS. Designing a membrane selectively permeable to one of the components of the ATPS, we show that out-of-equilibrium phase separations formed by a rapid outflow of water can be spontaneously reversed by a slower outflow of the permeating component across the vesicle membrane. This dynamics may be exploited advantageously by cells to separate and connect metabolic and signaling routes within their nucleoplasm or cytoplasm depending on external conditions.

Synthesis of block copolymers used in polymersome fabrication: Application in drug delivery

Amphiphilic block copolymers are common materials used for the fabrication of various nanostructures with biomedical applications including nanocapsules, nanospheres, micelles and polymeric vesicles. According to the literature, polymersomes have several advantages compared to other nanostructures used as drug delivery systems comprising better stability, facile synthesis, prolonged circulation time, and passive/active targeting capability. Various types of nanoparticles are formed by varying the ratio of the hydrophobic/hydrophilic blocks. Changing hydrophobic/hydrophilic ratio of amphiphilic block copolymers has an impact on the structural characteristics of polymers such as changing molecular weight and surface functionalization of the block copolymer. Thus, polymerization strategies are an important factor that influences polymersomes quality. In this review, different polymerization strategies for the synthesis of block copolymers applied in polymersomes formation, are described.

Mixing behaviour of Pluronics with gemini surfactant/plasmid DNA condensates: effect of Pluronic composition

Nanoparticles prepared from plasmid DNA (pDNA) and N,N-bis(dimethylhexadecyl)-1,3-propanediammonium bromide (16-3-16) have been mixed with various Pluronic block copolymers and investigated as binary surfactant systems in water using the previously demonstrated critical aggregation concentration of the surfactant-DNA complex. Surface tensiometry was used to determine critical micelle concentrations of mixed micelles formed within these Pluronic/16-3-16/pDNA mixtures. Use of mixed micelle theories reveals that mixed micelle composition and the interaction parameter, β, are influenced by the structure, in particular hydrophobicity, of the Pluronic component. Ethidium bromide fluorescence studies demonstrate the ability of the Pluronics to de-condense the plasmid DNA from the cationic 16-3-16 gemini surfactant complex, and show some relationship to the interaction parameter and Pluronic composition.

Small molecule-mediated self-assembly behaviors of Pluronic block copolymers in aqueous solution: impact of hydrogen bonding on the morphological transition of Pluronic micelles

The influence of hydrogen bonding on the self-assembly behaviors of Pluronic P123 micelles is experimentally and theoretically investigated by introducing three small molecules, i.e. propyl benzoate (PB), propyl paraben (PP) and propyl gallate (PG) into the aqueous solution. It is discovered that the number of phenolic hydroxyl groups and concentration of the tested small molecules exhibit a profound impact on the micellar morphology. Although all the small molecules increase the size and polydispersity of Pluronic micelles in a concentration-dependent manner, the micellar morphologies induced by them vary considerably as demonstrated by DLS and cryo-TEM measurement. PB, without phenolic hydroxyl, cannot bring about the morphological change of P123 micelles, while PP induces a series of morphological transitions from spheres to long worm-like micelles and then to unilamellar vesicles by increasing the PP content. Upon increasing the number of phenolic hydroxyls in small molecules, i.e. PG, the fusion of the intermicellar core takes place, resulting in the formation of large micelles and micellar clusters. A qualitative study by NMR reveals that the different locations of small molecules within the micelles are attributed to the balance of hydrogen bonding and hydrophobic interaction between small molecules and copolymers. In addition, molecular dynamics simulations (MDS) are performed to further confirm the experimental results and provide quantitative information on intermolecular interaction strength. It is supposed that the mechanism of micellar morphological transition mediated by small molecules is ascribed to the hydrogen bonding interactions with varying strengths between the PEO blocks and their phenolic hydroxyls, which governs their locations in micelles, affecting the free energies from different regions of micelles, and consequently leads to the varying micellar morphologies. This study deepens our understanding of the role of hydrgen bonding in the self-assembly behaviors of Pluronic micelles and provides an alternative strategy for manipulating the nanostructure of Pluronic micelles.

Pluronic®-bile salt mixed micelles

The present study was aimed to examine the interaction of two bile salts viz. sodium cholate (NaC) and sodium deoxycholate (NaDC) with three ethylene polyoxide-polypropylene polyoxide (PEO-PPO-PEO) triblock copolymers with similar PPO but varying PEO micelles with a focus on the effect of pH on mixed micelles. Mixed micelles of moderately hydrophobic Pluronic^® P123 were examined in the presence of two bile salts and compared with those from very hydrophobic L121 and very hydrophilic F127. Both the bile salts increase the cloud point (CP) of copolymer solution and decreased apparent micelle hydrodynamic diameter (D_h). SANS study revealed that P123 forms small spherical micelles showing a decrease in size on progressive addition of bile salts. The negatively charged mixed micelles contained fewer P123 molecules but progressively rich in bile salt. NaDC being more hydrophobic displays more pronounced effect than NaC. Interestingly, NaC shows micellar growth in acidic media which has been attributed to the formation of bile acids by protonation of carboxylate ion and subsequent solubilization. In contrast, NaDC showed phase separation at higher concentration. Nuclear Overhauser effect spectroscopy (NOESY) experiments provided information on interaction and location of bile salts in micelles. Results are discussed in terms of hydrophobicity of bile salts and Pluronics^® and the site of bile salt in polymer micelles. Proposed molecular interactions are useful to understand more about bile salts which play important role in physiological processes.

Effect of Vitamin E and a Long-Chain Alcohol n-Octanol on the Carbohydrate-Based Nonionic Amphiphile Sucrose Monolaurate-Formulation of Newly Developed Niosomes and Application in Cell Imaging

We have introduced new niosome formulations using sucrose monolaurate, vitamin E and n-octanol as independent additives. Detailed characterization techniques including turbidity, dynamic light scattering, transmission electron microscopy, ξ potential, and proton nuclear magnetic resonance measurements have been introduced to monitor the morphological transition of the carbohydrate-based micellar assembly into niosomal aggregates. Moreover, microheterogeneity of these niosomal aggregates has been investigated through different fluorescence spectroscopic techniques using a hydrophobic probe molecule coumarin 153 (C153). Further, it has been observed that vitamin E and octanol have an opposing effect on the rotational motion of C153 in the respective niosome assemblies. The time-resolved anisotropy studies suggest that incorporation of vitamin E and octanol into the surfactant aggregates results in slower and faster rotational motion of C153, respectively, compared to the micellar assemblies. Moreover, the ability to entrap a probe molecule by these niosomes is utilized to encapsulate and deliver the anticancer drug doxorubicin inside the mammalian cells which is monitored through fluorescence microscopic images. Interestingly, the niosome composed of vitamin E demonstrated better cytocompatibility toward primary chondrocyte cell lines compared to the octanol-forming niosome.

Vesicle to micelle transition in the ternary mixture of L121/SDS/D2O: NMR, EPR and SANS studies

Proposed model depicting vesicle to mixed micelle transformation in a ternary mixture of L121/SDS/D₂O.

Physico-Chemical Investigation of Multiple Asymmetric Amphiphilic Diblock Copolymer Morphologies in Solution

Asymmetric amphiphilic diblock copolymers are able to form self-assembled crewcut aggregates of multiple morphologies in selective solvents. Micelles are formed by the slow addition of a poor solvent, for the core-forming block, to a solution of the copolymer dissolved in a solvent suitable for both polymer segments. The morphology of the aggregates is affected by a number of factors, such as the solvent composition, the block lengths, the presence of additives, and the temperature. Some of the resulting structures are considered to be equilibrium or near-equilibrium morphologies, which can be kinetically frozen using a number of different techniques. The thermodynamics of micelle formation has been investigated, and equations for the standard Gibbs free energy, enthalpy, and entropy have been formulated. Partial phase diagrams have been constructed, giving the morphological phase boundaries. Knowledge of the location of the boundaries has paved the way for the study of the kinetics and mechanisms of the sphere to rod and rod to vesicle transitions. Both processes have two-step mechanisms, with the second step being rate determining in each case.

Self-Assembly of Amphiphilic Block Copolypeptoids - Micelles, Worms and Polymersomes

Polypeptoids are an old but recently rediscovered polymer class with interesting synthetic, physico-chemical and biological characteristics. Here, we introduce new aromatic monomers, N-benzyl glycine N-carboxyanhydride and N-phenethyl glycine N-carboxyanhydride and their block copolymers with the hydrophilic polysarcosine. We compare their self-assembly in water and aqueous buffer with the self-assembly of amphiphilic block copolypeptoids with aliphatic side chains. The aggregates in water were investigated by dynamic light scattering and electron microscopy. We found a variety of morphologies, which were influenced by the polymer structure as well as by the preparation method. Overall, we found polymersomes, worm-like micelles and oligo-lamellar morphologies as well as some less defined aggregates of interconnected worms and vesicles. Such, this contribution may serve as a starting point for a more detailed investigation of the self-assembly behavior of the rich class of polypeptoids and for a better understanding between the differences in the aggregation behavior of non-uniform polypeptoids and uniform peptoids.

Nanoparticle-Templated Formation and Growth Mechanism of Curved Protein Polymer Fibrils

We investigated the growth of biosynthetic protein polymers with templated curvature on pluronic nanospheres. The protein has a central silk-like block containing glutamic residues (S(E)) and collagen-like end-blocks (C). The S(E) blocks stack into filaments when their charge is removed (pH <5). Indeed, at low pH curved and circular fibers are formed at the surface of the nanospheres, which keep their shape after removal of the pluronics. The data reveal the mechanism of the templated fibril-growth: The growth of protein assemblies is nucleated in solution; small protein fibrils adsorb on the nanospheres, presumably due to hydrogen bond formation between the silk-like blocks and the pluronic PEO blocks. The surface of the pluronic particles templates further growth. At relatively low protein/pluronic weight ratios, only a fraction of the nanospheres bears protein fibers, pointing to a limiting amount of nuclei in solution. Because the nanospheres capture fibrils at an early stage of growth, they can be used to separate growth and nucleation rates in protein fibril formation. Moreover, the nanoparticle-templated growth of stable curved fibers opens ways to build proteinaceous nanocapsules from designed protein polymers.

Microfluidic Fabrication of Pluronic Vesicles with Controlled Permeability

Block copolymers with a low hydrophilic-to-lipophilic balance form membranes that are highly permeable to hydrophilic molecules. Polymersomes with this type of membrane enable the controllable release of molecules without membrane rupture. However, these polymersomes are difficult to assemble because of their low hydrophobicity. Here, we report a microfluidic approach to the production of these polymersomes using double-emulsion drops with ultrathin shells as templates. The small thickness of the middle oil phase enables the attraction of the hydrophobic blocks of the polymers adsorbed at each of the oil/water interfaces of the double emulsions; this results in the dewetting of the oil from the surface of the innermost water drops of the double emulsions and the ultimate formation of the polymersome. This approach to polymersome fabrication enables control of the vesicle size and results in the efficient encapsulation of hydrophilic ingredients that can be released through the polymer membrane without membrane rupture. We apply our approach to the fabrication of Pluronic L121 vesicles and characterize the permeability of their membranes. Furthermore, we show that membrane permeability can be tuned by blending different Pluronic polymers. Our work thus describes a route to producing Pluronic vesicles that are useful for the controlled release of hydrophilic ingredients.

One-pot RAFT and fast polymersomes assembly: a ‘beeline’ from monomers to drug-loaded nanovectors

A ‘fast RAFT’ strategy that allows the engineering of drug-containing polymer vesicles in only a few hours, starting from functional monomers.

Interaction between bile salt sodium glycodeoxycholate and PEO–PPO–PEO triblock copolymers in aqueous solution

Bile salts can associate to PEO–PPO–PEO block copolymer micelles and disintegrate them depending on the relative block length and molecular weight of the copolymers and bile salt/copolymer molar ratio.

A simple method for the synthesis of porous polymeric vesicles and their application as MR contrast agents

Because of their low membrane permeability the use of polymeric vesicles in certain drug delivery and molecular imaging applications and as bioreactors is less than ideal. Here, we report a simple method to prepare porous polymeric vesicles that possess high membrane permeability. Specifically, porous vesicles were produced from the aqueous assembly of the diblock copolymer PEG-PBD, and the triblock copolymer PEG-PPO-PEG. It was found that PEG-PPO-PEG-doped polymersomes exhibited improved membrane permeability to molecules less than 5 kDa. Further, these porous vesicles retained molecules ≥10 kDa within their aqueous interiors with no significant leakage. To demonstrate its application, highly efficient magnetic resonance contrast agents were produced from porous polymersomes by encapsulating macromolecules labeled with gadolinium. Due to a fast water exchange rate with surrounding bulk water, these paramagnetic porous polymersomes exhibited higher r₁ relaxivity compared with Gd-encapsulated vesicles with no pores. Due to their simplicity, the porous polymersomes prepared with this method are expected to have additional useful applications.

Emerging methods for the fabrication of polymer capsules

Hollow polymer capsules are attracting increasing research interest due to their potential application as drug delivery vectors, sensors, biomimetic nano- or multi-compartment reactors and catalysts. Thus, significant effort has been directed toward tuning their size, composition, morphology, and functionality to further their application. In this review, we provide an overview of emerging techniques for the fabrication of polymer capsules, encompassing: self-assembly, layer-by-layer assembly, single-step polymer adsorption, bio-inspired assembly, surface polymerization, and ultrasound assembly. These techniques can be applied to prepare polymer capsules with diverse functionality and physicochemical properties, which may fulfill specific requirements in various areas. In addition, we critically evaluate the challenges associated with the application of polymer capsules in drug delivery systems.

Modeling and self-assembly behavior of PEG-PLA-PEG triblock copolymers in aqueous solution

A series of poly(ethylene glycol)-polylactide-poly(ethylene glycol) (PEG-PLA-PEG) triblock copolymers with symmetric or asymmetric chain structures were synthesized by combination of ring-opening polymerization and copper-catalyzed click chemistry. The resulting copolymers were used to prepare self-assembled aggregates by dialysis. Various architectures such as nanotubes, polymersomes and spherical micelles were observed from transmission electron microscopy (TEM), cryo-TEM and atomic force microscopy (AFM) measurements. The formation of diverse aggregates is explained by modeling from the angle of both geometry and thermodynamics. From the angle of geometry, a "blob" model based on the Daoud-Cotton model for star polymers is proposed to describe the aggregate structures and structural changes with copolymer composition and molar mass. In fact, the copolymer chains extend in aqueous medium to form single layer polymersomes to minimize the system's free energy if one of the two PEG blocks is short enough. The curvature of polymersomes is dependent on the chain structure of copolymers, especially on the length of PLA blocks. A constant branch number of aggregates (f) is thus required to preserve the morphology of polymersomes. Meanwhile, the aggregation number (N(agg)) determined from the thermodynamics of self-assembly is roughly proportional to the total length of polymer chains. Comparing f to N(agg), the aggregates take the form of polymersomes if N(agg) ≈ f, and change to nanotubes if N(agg) > f to conform to the limits from both curvature and aggregation number. The length of nanotubes is mainly determined by the difference between N(agg) and f. However, the hollow structure becomes unstable when both PEG segments are too long, and the aggregates eventually collapse to yield spherical micelles. Therefore, this work gives new insights into the self-assembly behavior of PEG-PLA-PEG triblock copolymers in aqueous solution which present great interest for biomedical and pharmaceutical applications.

Brain targeting of olanzapine via intranasal delivery of core-shell difunctional block copolymer mixed nanomicellar carriers: in vitro characterization, ex vivo estimation of nasal toxicity and in vivo biodistribution studies

Olanzapine (OZ) is atypical antipsychotic drug that suffers from low brain permeability due to efflux by P-glycoproteins and hepatic first-pass metabolism. The current work aimed to develop OZ-loaded micellar nanocarriers and investigate their nose-to-brain targeting potential. OZ-loaded (5mg/ml) micelles (F1-F12) were prepared, using a Pluronic(®) mixture of L121 and P123, adopting thin-film hydration method. The micelles were evaluated for turbidity, particle size, morphology, drug-entrapment efficiency (EE%), drug-loading characteristics, in vitro drug release and ex vivo nasal toxicity in sheep. The in vivo biodistribution and pharmacokinetic studies in the brain/blood following intravenous (i.v.) and intranasal (i.n.) administrations of technetium-labeled OZ-loaded micelles and OZ-solution were evaluated in rats. Spherical micelles ranging in size from 18.97 to 380.70 nm were successfully developed. (1)H NMR studies confirmed OZ incorporation into micelle core. At a drug:Pluronic(®) L121:Pluronic(®) P123 ratio of 1:8:32 (F11), the micelles achieved a conciliation between kinetic and thermodynamic stability, high drug-EE%, controlled drug-release characteristics and evoked minor histopathological changes in sheep nasal mucosa. The significantly (P<0.05) higher values for F11 micelles (i.n.); brain/blood ratio (0.92), drug targeting index (5.20), drug targeting efficiency (520.26%) and direct transport percentage (80.76%) confirm the development of a promising non-invasive OZ-loaded nose-to-brain delivery system.

Well-defined amphiphilic poly(2-oxazoline) ABA-triblock copolymers and their aggregation behavior in aqueous solution

Self-organization of block copolymers in solution is a way to obtain advanced functional superstructures. The synthesis of well-defined polymethyloxazoline-block-polyphenyloxazoline-block-polymethyloxazoline triblock copolymers is described and proven by (1) H NMR spectroscopy, SEC, and ESI-MS. The surprisingly water- soluble block copolymers do self-organize in aqueous solutions uniquely forming three coexisting well-defined structures: unimolecular micelles, micellar aggregates, and very form-stable polymersomes. This is the first example of a polymersome forming ABA-triblock copolymer with a glassy middle block. The spherical vesicles are analysed by scanning electron microscopy and transmission electron microscopy. It could be shown that these vesicles are indeed hollow spheres.

The effects of polymeric nanostructure shape on drug delivery

Amphiphilic polymeric nanostructures have long been well-recognized as an excellent candidate for drug delivery applications. With the recent advances in the "top-down" and "bottom-up" approaches, development of well-defined polymeric nanostructures of different shapes has been possible. Such a possibility of tailoring the shape of the nanostructures has allowed for the fabrication of model systems with chemically equivalent but topologically different carriers. With these model nanostructures, evaluation of the importance of particle shape in the context of biodistribution, cellular uptake and toxicity has become a major thrust area. Since most of the current polymeric delivery systems are based upon spherical nanostructures, understanding the implications of other shapes will allow for the development of next generation drug delivery vehicles. Herein we will review different approaches to fabricate polymeric nanostructures of various shapes, provide a comprehensive summary on the current understandings of the influence of nanostructures with different shapes on important biological processes in drug delivery, and discuss future perspectives for the development of nanostructures with well-defined shapes for drug delivery.

Polymeric vesicles: from drug carriers to nanoreactors and artificial organelles

One strategy in modern medicine is the development of new platforms that combine multifunctional compounds with stable, safe carriers in patient-oriented therapeutic strategies. The simultaneous detection and treatment of pathological events through interactions manipulated at the molecular level offer treatment strategies that can decrease side effects resulting from conventional therapeutic approaches. Several types of nanocarriers have been proposed for biomedical purposes, including inorganic nanoparticles, lipid aggregates, including liposomes, and synthetic polymeric systems, such as vesicles, micelles, or nanotubes. Polymeric vesicles--structures similar to lipid vesicles but created using synthetic block copolymers--represent an excellent candidate for new nanocarriers for medical applications. These structures are more stable than liposomes but retain their low immunogenicity. Significant efforts have been made to improve the size, membrane flexibility, and permeability of polymeric vesicles and to enhance their target specificity. The optimization of these properties will allow researchers to design smart compartments that can co-encapsulate sensitive molecules, such as RNA, enzymes, and proteins, and their membranes allow insertion of membrane proteins rather than simply serving as passive carriers. In this Account, we illustrate the advances that are shifting these molecular systems from simple polymeric carriers to smart-complex protein-polymer assemblies, such as nanoreactors or synthetic organelles. Polymeric vesicles generated by the self-assembly of amphiphilic copolymers (polymersomes) offer the advantage of simultaneous encapsulation of hydrophilic compounds in their aqueous cavities and the insertion of fragile, hydrophobic compounds in their membranes. This strategy has permitted us and others to design and develop new systems such as nanoreactors and artificial organelles in which active compounds are simultaneously protected and allowed to act in situ. In recent years, we have created a variety of multifunctional, proteinpolymersomes combinations for biomedical applications. The insertion of membrane proteins or biopores into the polymer membrane supported the activity of co-encapsulated enzymes that act in tandem inside the cavity or of combinations of drugs and imaging agents. Surface functionalization of these nanocarriers permitted specific targeting of the desired biological compartments. Polymeric vesicles alone are relatively easy to prepare and functionalize. Those features, along with their stability and multifunctionality, promote their use in the development of new theranostic strategies. The combination of polymer vesicles and biological entities will serve as tools to improve the observation and treatment of pathological events and the overall condition of the patient.

Recent trends in the tuning of polymersomes' membrane properties

"Polymersomes" are vesicular structures made from the self-assembly of block copolymers. Such structures present outstanding interest for different applications such as micro- or nano-reactor, drug release or can simply be used as tool for understanding basic biological mechanisms. The use of polymersomes in such applications is strongly related to the way their membrane properties are controlled and tuned either by a precise molecular design of the constituting block or by addition of specific components inside the membrane (formulation approaches). Typical membrane properties of polymersomes obtained from the self-assembly of "coil coil" block copolymer since the end of the nineties will be first briefly reviewed and compared to those of their lipidic analogues, named liposomes. Therefore the different approaches able to modulate their permeability, mechanical properties or ability to release loaded drugs, using macromolecular engineering or formulations, are detailed. To conclude, the most recent advances to modulate the polymersomes' properties and systems that appear very promising especially for biomedical application or for the development of complex and bio-mimetic structures are presented.

Dynamic assembly of block-copolymers

Block copolymers (BCs) are well-known building blocks for the creation of a large variety of nanostructured materials or objects through a dynamic assembly stage which can be either autonomous or guided by an external force. Today's nanotechnologies require sharp control of the overall architecture from the nanoscale to the macroscale. BCs enable this dynamic assembly through all the scales, from few aggregated polymer chains to large bulk polymer materials. Since the discovery of controlled methods to polymerize monomers with different functionalities, a broad diversity of BCs exists, giving rise to many different nanoobjects and nanostructured materials. This chapter will explore the potentialities of block copolymer chains to be assembled through dynamic interactions either in solution or in bulk.

Binary mixing of micelles using Pluronics for a nano-sized drug delivery system

Pluronics with different structural compositions and properties are used for several applications, including drug delivery systems. We developed a binary mixing system with two Pluronics, L121/P123, as a nano-sized drug delivery carrier. The lamellar-forming Pluronic L121 (0.1 wt%) was incorporated with Pluronic P123 to produce nano-sized dispersions (in case of 0.1 and 0.5 wt% P123) with high stability due to Pluronic P123 and high solubilization capacity due to Pluronic L121. The binary systems were spherical and less than 200-nm diameter, with high thermodynamic stability (at least 2 weeks) in aqueous solution. The CMC of the binary system was located in the middle of the CMC of each polymer. In particular, the solubilization capacity of the binary system (0.1/0.1 wt%) was higher than mono-systems of P123. The main advantage of binary systems is overcoming limitations of mono systems to allow tailored mixing of block copolymers with different physicochemical characteristics. These nano-sized systems may have potential as anticancer drug delivery systems with simple preparation method, high stability, and high loading capacity.

Rapid ejection of giant Pluronic L121 vesicles from spreading double emulsion droplets

We report the formation of giant Pluronic L121 vesicles with diameters of the order of 200 microm obtained by a previously unreported mechanism that occurs during the solvent evaporation method of vesicle formation. We begin with a water-oil-water double emulsion that is stabilized by dissolving the commercially available triblock copolymer Pluronic L121 in the volatile oil-phase. During the evaporation, the oil phase spreads on the surface of the continuous aqueous phase, leaving behind the aqueous inner droplet of the double emulsion droplet that eventually yields the vesicle. The spreading of the solvent mixture of the oil phase is induced either by the rapid ejection of the inner droplet out of the double emulsion droplet, or by the spreading of the oil phase of a neighboring emulsion droplet.

Aggregation behavior of poly(ethylene glycol-bl-propylene sulfide) di- and triblock copolymers in aqueous solution

Block copolymers of poly(ethylene glycol)-bl-poly(propylene sulfide) (PEG-PPS) have recently emerged as a new macromolecular amphiphile capable of forming a wide range of morphologies when dispersed in water. To understand better the relationship between stability and morphology in terms of the relative and absolute block compositions, we have synthesized a collection of PEG-PPS block copolymers and quantified their critical aggregation concentration and observed their morphology using cryogenic transmission electron microscopy after thin film hydration with extrusion and after solvent dispersion from tetrahydrofuran, a solvent for both blocks. By understanding the relationship between aggregate character and block copolymer architecture, we have observed that whereas the relative block lengths control morphology, the stability of the aggregates upon dilution is determined by the absolute block length of the hydrophobic PPS block. We have compared results obtained with PEG-PPS to those obtained with poly(ethylene glycol)-bl-poly(propylene oxide)-bl-poly(ethylene glycol) block copolymers (Pluronics). The results reveal that the PEG-PPS aggregates are substantially more stable than Pluronic aggregates, by more than an order of magnitude. PEG-PPS can form a wide variety of stable or metastable morphologies in dilute solution within normal time and temperature ranges, whereas Pluronics can generally form only spherical micelles under the same conditions. On the basis of these results, block copolymers of PEG with poly(propylene sulfide) may present distinct advantages over those with poly(propylene glycol) for a number of applications.

Supramolecular assemblies of amphiphilic homopolymers

Amphiphilic molecules self-assemble in solvents because of the differential solvation of the hydrophilic and lipophilic functionalities. Small-molecule surfactants have long been known to form micelles in water that can solubilize lipophilic guest molecules in their water-excluded interior. Polymeric surfactants based on block copolymers are also known to form several types of aggregates in water owing either to the mutual incompatibility of the blocks or better solvation of one of the blocks by the solvent. Incorporating amphiphilicity at smaller length scales in polymers would provide an avenue to capture the interesting properties of macromolecules and fine tune their supramolecular assemblies. To address this issue, we designed and synthesized amphiphilic homopolymers containing hydrophilic and lipophilic functionalities in the monomer. Such a polymer can be imagined to be a string of small-molecule surfactants tethered together such that the hydrophilic and lipophilic functionalities are located on opposite faces, rendering the assemblies facially amphiphilic. This feature article describes the self-assembly of our amphiphilic homopolymers in polar and apolar solvents. These homopolymers not only form micelles in water but also form inverse micelles in organic solvents. Subtle changes to the molecular structure have been demonstrated to yield vesicles in water and inverted micelles in organic solvents. The characterization of these assemblies and their applications in separations, catalysis, and sensing are described here.