Polymeric Micelles Induced by Interpolymer Complexation

DPD Modelling of the Self- and Co-Assembly of Polymers and Polyelectrolytes in Aqueous Media: Impact on Polymer Science

This review article is addressed to a broad community of polymer scientists. We outline and analyse the fundamentals of the dissipative particle dynamics (DPD) simulation method from the point of view of polymer physics and review the articles on polymer systems published in approximately the last two decades, focusing on their impact on macromolecular science. Special attention is devoted to polymer and polyelectrolyte self- and co-assembly and self-organisation and to the problems connected with the implementation of explicit electrostatics in DPD numerical machinery. Critical analysis of the results of a number of successful DPD studies of complex polymer systems published recently documents the importance and suitability of this coarse-grained method for studying polymer systems.

Amphiphilic Block Copolymers Bearing Hydrophobic γ-Tocopherol Groups with Labile Acetal Bond

High concentrations of γ-tocopherol (γTCP) tend to show antioxidant, anti-inflammatory, and anticancer effects. In this study, we prepared polymer micelles under acidic conditions with a controlled release of γTCP due to the decomposition of pendant acetal bonds. First, a precursor diblock copolymer composed of poly(ethylene glycol) (PEG) and acrylic acid (AA) was prepared. This was followed by the synthesis of an amphiphilic diblock copolymer (PEG₅₄-P(AA/VE6/γTCP29)₁₄₀), incorporated into hydrophobic γTCP pendant groups attached to the main chain through an acetal bond. The prepared PEG₅₄-P(AA/VE6/γTCP29)₁₄₀ was further dispersed in water to form polymer micelles composed of hydrophobic cores that were generated from a hydrophobic block containing γTCPs and hydrophilic shells on the surface. Under acidic conditions, γTCP was then released from the core of the polymer micelles due to the decomposition of the pendant acetal bonds. In addition, polymer micelles swelled under acidic conditions due to hydration of the core.

Micellization of poly(2-vinylpyrridine)-b-poly(cyclohexyl methacrylate) (P2VP-b-PCHMA) block copolymers and their interpolymer complex formation in non-aqueous medium

HYPOTHESIS

The interpolymer complex formation between poly(vinylpyridine)-based polymers with poly(acrylic acid) (PAA), in aqueous or organic medium, is driven by the hydrogen-bonding complexation. Well-defined nanostructures, with specific practical applications, may be obtained by taking advantage of such non-covalent interactions.

EXPERIMENTS

Poly(2-vinylpyridine)-b-poly(cyclohexyl methacrylate) (P2VP-b-PCHMA) and poly(2-vinylpyridine)-b-poly(t-butyl methacrylate)-b-poly(cyclohexyl methacrylate) (P2VP-b-PtBuMA-b-PCHMA) copolymers were synthesized by sequential anionic polymerization. Their micellar characteristics were examined as a function of their molecular characteristics in methylcyclohexane and toluene respectively, as cycloaliphatic and aromatic solvents for the selective solubilization of the PCHMA sequence. The size of interpolymer complexes was determined by DLS, in 1,4 dioxane, and their structural composition was characterized by ¹H NMR.

FINDINGS

The scaling relationship between the molecular composition and the micellar characteristics, such as particle size and aggregation number, could be established for the PCHMA-based copolymers in methylcyclohexane. It was further demonstrated that controlled micellization in 1,4 dioxane, as a non-selective organic solvent, could be achieved by hydrogen bond type interpolymer complex formation between P2VP-b-PCHMA and PAA-b-PCHMA under stoichiometric P2VP/PAA conditions. Finally, the size of the PCHMA-b-PAA/P2VP block copolymer/homopolymer complexes as well as of the PCHMA-b-PAA/PCHMA-b-P2VP block copolymer/block copolymer complexes was correlated with the molecular characteristics of the copolymers.

All Wrapped up: Stabilization of Enzymes within Single Enzyme Nanoparticles

Enzymes are extremely useful in many industrial and pharmaceutical areas due to their ability to catalyze reactions with high selectivity. In order to extend their lifetime, significant efforts have been made to increase their stability using protein- or medium engineering as well as by chemical modification. Many researchers have explored the immobilization of enzymes onto carriers, or entrapment within a matrix, framework or nanoparticle with the hope of constricting the movement of the enzyme and shielding it from aggressive environments, thus delaying the denaturation. These strategies often balance three competing interests: (i) maintaining high enzymatic activity, (ii) ensuring good long-term stability against temperature, dehydration, organic solvents, and or aggressive pH, and (iii) enabling a tuning or reversible switching of enzyme activity. In most cases, multiple enzymes will be contained within a single nanoparticle or matrix, but in recent years researchers have begun to wrap up individual enzymes within single enzyme nanoparticles (SENs). In these nanoparticles the enzyme is stabilized by a thin shell, typically a polymer, prepared either by in situ polymerization from the enzyme surface or by assembling a preformed polymer around it. Because of the increased control over the environment directly around the enzyme, and the possibility of more directly controlling substrate diffusion, many SENs show remarkable stability while retaining high initial activities even for quite fragile enzymes. Moreover, the activity of the enzyme can often be more easily fine-tuned by adjusting the layer properties. We postulate that this emerging field will offer exciting and elegant opportunities to both extend the catalytic lifetime of enzymes in aggressive solvents, temperatures and pH, and enable their activity to be switched on and off on demand by modulation of the outer material layer.

Formation of core/corona nanoparticles with interpolyelectrolyte complex cores in aqueous solution: insight into chain dynamics in the complex from fluorescence quenching

Formation of interpolyelectrolyte complexes (IPECs) of poly(methacrylic acid) (PMAA) bearing a fluorescent label (umbelliferone) at the chain end and poly[3,5-bis(trimethyl ammoniummethyl)-4-hydroxystyrene iodide]-block-poly(ethylene oxide) (QNPHOS-PEO) acting as a fluorescence quencher, was followed using a combination of scattering, calorimetry, microscopy and fluorescence spectroscopy techniques. While scattering and microscopy measurements indicated formation of spherical core/corona nanoparticles with the core of the QNPHOS/PMAA complex and the PEO corona, fluorescence measurements showed that both static and dynamic quenching efficiency were increased in the nanoparticle stability region. As the dynamic quenching rate constant remained unchanged, the quenching enhancement was caused by the increase in the local concentration of QNPHOS segments in the microenvironment of the label. This finding implies that the local dynamics of PMAA end chains affecting the interaction of the label with QNPHOS segments was independent of both PMAA and QNPHOS chain conformations.

"Grafting-from" synthesis and characterization of poly (2-ethyl-2-oxazoline)-b-poly (benzyl L-glutamate) micellar nanoparticles for potential biomedical applications

Introduction: Recent advances in the field of poly (2-oxazolines) as bio-inspired synthetic pseudopeptides have proven their potential biomedical applications such as drug delivery and tissue engineering. Methods: In order to fabricate a biodegradable micellar nanoparticle of poly (2-ethyl 2-oxazoline)-b-poly (benzyl L-glutamate) or pEOx-b-pBLG, "grafting-from" synthesis approach was used involving consecutive steps of cationic ring-opening polymerization of 2-ethyl-2-oxazoline, amine functionalization of pEOx using 1-Boc-piperazine and N-carboxyanhydride polymerization of γ-benzyl- L-glutamate. Following hydrolysis of the copolymer, the protecting γ-benzyl groups were removed yielding a double-hydrophilic block ionomer of pEOx-b-poly (L-glutamic acid). The polymers were characterized by FTIR, 1H-NMR, size exclusion chromatography and differential scanning calorimetry (DSC). Aqueous assembly of the polymers was investigated by pyrene assay, dynamic light scattering, and transmission electron microscopy. MTT cytotoxicity assay was also performed to determine the cytocompatibility in various tumor cell lines. Results: The polymeric micelles presented a uni-modal size distribution with mean hydrodynamic diameter of 149.8 ± 10.6 nm and critical aggregation concentration of 60 µg/mL. The average molecular weight of pEOx increased from ~ 14 to 20 kDa for pEOx-b-poly (L-glutamic acid) as determined by light scattering (Debye plot), indicating a successful copolymerization. MTT assay showed little to no practical cytotoxicity at concentrations below 1 mg/mL. Conclusion: Multi-step synthesis of pEOx-b-pBLG and subsequent alkaline hydrolysis were performed to obtain the block ionomer pEOx-b-poly (L-glutamic acid). Both pEOx-based copolymers can be considered for various potential applications such as loading and delivery of drugs, genes, and contrast agents either by chemical conjugation or physical loading.

Strategies for improving the payload of small molecular drugs in polymeric micelles

In the past few years, substantial efforts have been made in the design and preparation of polymeric micelles as novel drug delivery vehicles. Typically, polymeric micelles possess a spherical core-shell structure, with a hydrophobic core and a hydrophilic shell. Consequently, poorly water-soluble drugs can be effectively solubilized within the hydrophobic core, which can significantly boost their drug loading in aqueous media. This leads to new opportunities for some bioactive compounds that have previously been abandoned due to their low aqueous solubility. Even so, the payload of small molecular drugs is still not often satisfactory due to low drug loading and premature release, which makes it difficult to meet the requirements of in vivo studies. This problem has been a major focus in recent years. Following an analysis of the published literature in this field, several strategies towards achieving polymeric micelles with high drug loading and stability are presented in this review, in order to ensure adequate drug levels reach target sites.

Exploring the construction of multicompartmental micelles by halogen bonding of complementary macromolecules

An approach to the construction of multicompartmental micelles, using halogen bonding between complementary macromolecules, is described. The design involves a sequential assembly protocol, in which the initial compartments are formed by interpolymer halogen bonding, followed by the collapse of a second, hydrophobic compartment upon transfer to aqueous solvent. Triblock terpolymers incorporating a halogen bond accepting segment have been synthesized. Transmission electron microscopy was used to characterize multicompartmental assemblies generated from these terpolymers in the presence of a halogen bond donor-functionalized polystyrene derivative.

Temperature-induced structure switch in thermo-responsive micellar interpolyelectrolyte complexes: toward core-shell-corona and worm-like morphologies

The spontaneous formation and thermo-responsiveness of a colloidally-stable interpolyelectrolyte complex (IPEC) based on a linear temperature-sensitive diblock copolymer poly(vinyl sulfonate)31-b-poly(N-isopropyl acrylamide)27 (PVS31-b-PNIPAM27) and a star-shaped quaternized miktoarm polymer poly(ethylene oxide)114-(poly(2-(dimethylamino)ethyl methacrylate)17)4 (PEO114-(qPDMAEMA17)4) was investigated in aqueous media at 0.3 M NaCl by means of dynamic light scattering (DLS), small angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryo-TEM). The micellar macromolecular co-assemblies show a temperature-dependent size and morphology, which result from the lower critical solution temperature (LCST) behavior of the PNIPAM-blocks. Hence, the micellar co-assemblies grow upon heating. At 60 °C, spherical core-shell-corona co-assemblies are proposed with a hydrophobic PNIPAM core, a water-insoluble IPEC shell, and a hydrophilic PEO corona. These constructs develop into a rod-like structure upon extended equilibration. In turn, PEO-arms and PNIPAM-blocks within a hydrophilic mixed two-component corona surround the water-insoluble IPEC domain at 20 °C, thereby forming spherical core-corona co-assemblies. Reversibility of the structural changes is suggested by the scattering data. This contribution addresses the use of a combination of oppositely charged thermo-responsive and bis-hydrophilic star-shaped polymeric components toward IPECs of diverse morphological types.

A novel approach to controlled self-assembly of pH-responsive thermosensitive homopolymer polyelectrolytes into stable nanoparticles

This review addresses the recent research progress in introducing and elaborating a novel approach to controlled polymer self-assembly into stable nanoparticles using pH-responsive thermosensitive homopolymer polyelectrolytes. Interesting aspect of this approach is that stable polymeric nanoparticles are formed from homopolymers of one type only and without any assembly-triggering additives. The process of their formation can be monitored online e.g. by light scattering and particle size can be finely custom tuned. Obtained nanoparticles have interesting properties and are very stable over long periods of time and over a broad range of salt concentrations including physiological conditions. Much effort was devoted not only to finding optimum experimental protocols and to characterizing resulting nanoparticles in detail, but also to understanding physical processes behind these successful protocols.

The electrostatic co-assembly in non-stoichiometric aqueous mixtures of copolymers composed of one neutral water-soluble and one polyelectrolyte (either positively or negatively charged) block: a dissipative particle dynamics study

The electrostatic co-assembly in non-stoichiometric aqueous mixtures of diblock copolymers.

Polymeric micelles stabilized by polyethylenimine–copper (C2H5N–Cu) coordination for sustained drug release

Polymeric micelles stabilized by polyethylenimine–copper (C₂H₅N–Cu) coordination were described to improve the release property of water-insoluble anticancer drug.

Giant tubular and toroidal vesicles from self-assembled triblock copolymer-polyaniline complexes in water

An ABA type amphiphilic triblock copolymer was synthesized via ATRP and sulfonation. New self-assembled morphologies such as toroidal vesicles, giant tubular vesicles, and perforated spherical vesicles were observed from triblock copolymer-polyaniline complexes in water. The mechanism of morphology transformation at different compositions was discussed.

Genipin cross-linked PEG-block-poly(l-lysine)/disulfide-based polymer complex micelles as fluorescent probes and pH-/redox-responsive drug vehicles

A simple and facile method to prepare multifunctional, cross-linked PIC micelles by properly design of constituent homopolymer/copolymer.

Controlling the morphology of glyco-nanoparticles in water using block copolymer mixtures: the effect on cellular uptake

Poly[(2-(α-d-mannosyloxy)ethyl acrylate)-block-(n-butyl acrylate)], P(ManA-b-BA), and poly[poly(ethylene glycol) methyl ether acrylate]-block-(n-butyl acrylate)], P(OEGMEA-b-BA) diblock copolymers were mixed at various ratios to generate self-assembled structures of different morphologies.

Shell and core cross-linked poly(L-lysine)/poly(acrylic acid) complex micelles

We report the versatility of polyion complex (PIC) micelles for the preparation of shell and core cross-linked (SCL and CCL) micelles with their surface properties determined by the constituent polymer composition and cross-linking agent. The negatively and positively charged PIC micelles with their molecular structure and properties depending on the mixing weight percentage and polymer molecular weight were first prepared by mixing the negatively and positively charged polyions, poly(acrylic acid) (PAA) and poly(L-lysine) (PLL). The feasibility of preparing SCL micelles was demonstrated by cross-linking the shell of the negatively and positively charged micelles using cystamine and genipin, respectively. The core of the micelles can be cross-linked by silica deposition to stabilize the assemblies. The shell and/or core cross-linked micelles exhibited excellent colloid stability upon changing solution pH. The drug release from the drug-loaded SCL micelles revealed that the controllable permeability of the SCL micelles can be achieved by tuning the cross-linking degree and the SCL micelles exhibited noticeable pH-responsive behavior with accelerated release under acidic conditions. With the versatility of cross-linking strategies, it is possible to prepare a variety of SCL and CCL micelles from PIC micelles.

Hidden structural features of multicompartment micelles revealed by cryogenic transmission electron tomography

The demand for ever more complex nanostructures in materials and soft matter nanoscience also requires sophisticated characterization tools for reliable visualization and interpretation of internal morphological features. Here, we address both aspects and present synthetic concepts for the compartmentalization of nanoparticle peripheries as well as their in situ tomographic characterization. We first form negatively charged spherical multicompartment micelles from ampholytic triblock terpolymers in aqueous media, followed by interpolyelectrolyte complex (IPEC) formation of the anionic corona with bis-hydrophilic cationic/neutral diblock copolymers. At a 1:1 stoichiometric ratio of anionic and cationic charges, the so-formed IPECs are charge neutral and thus phase separate from solution (water). The high chain density of the ionic grafts provides steric stabilization through the neutral PEO corona of the grafted diblock copolymer and suppresses collapse of the IPEC; instead, the dense grafting results in defined nanodomains oriented perpendicular to the micellar core. We analyze the 3D arrangements of the complex and purely organic compartments, in situ, by means of cryogenic transmission electron microscopy (cryo-TEM) and tomography (cryo-ET). We study the effect of block lengths of the cationic and nonionic block on IPEC morphology, and while 2D cryo-TEM projections suggest similar morphologies, cryo-ET and computational 3D reconstruction reveal otherwise hidden structural features, e.g., planar IPEC brushes emanating from the micellar core.

Large compound vesicles from amphiphilic block copolymer/rigid-rod conjugated polymer complexes

Morphology evolution in complexes of amphiphilic block copolymers poly(styrene)-b-poly(acrylic acid) (PS-b-PAA) and poly(styrene)-b-poly(ethylene oxide) (PS-b-PEO) in the presence of polyaniline (PANI) in aqueous solution is reported. Transmission electron microscopy, atomic force microscopy, and dynamic light scattering techniques were used to study the morphologies at various PANI contents [aniline]/[acrylic acid] ([ANI]/[AA]) ranging from 0.1 to 0.7. The interpolyelectrolyte complex formed between PAA and PANI plays a key role in the morphology transformation. Spherical micelles formed from pure block copolymers were transformed into large compound vesicles upon increasing PANI concentration due to internal block copolymer segregation. In addition to varying PANI content, the kinetic pathway of nanoparticle formation was controlled through different water addition methods and was critical in the formation of multigeometry nanoparticles.

Self-assembled multimicellar vesicles via complexation of a rigid conjugated polymer with an amphiphilic block copolymer

We report here a facile method for fabrication of multimicellar vesicles from self-assembled complexes of a flexible coil-like block copolymer and a rigid rod conjugated homopolymer.

Thermo, pH and reduction responsive coaggregates comprising AB2C2 star terpolymers for multi-triggered release of doxorubicin

Novel disulfide-linked PEG(PCL)₂(PNIPAM)₂ and PEG(PCL)₂(PAA)₂ star terpolymers were synthesized and coassembled into mixed micelles or vesicles for multi-triggered drug release.

Progressive macromolecular self-assembly: from biomimetic chemistry to bio-inspired materials

Macromolecular self-assembly (MSA) has been an active and fruitful research field since the 1980s, especially in this new century, which is promoted by the remarkable developments in controlled radical polymerization in polymer chemistry, etc. and driven by the demands in bio-related investigations and applications. In this review, we try to summarize the trends and recent progress in MSA in relation to biomimetic chemistry and bio-inspired materials. Our paper covers representative achievements in the fabrication of artificial building blocks for life, cell-inspired biomimetic materials, and macromolecular assemblies mimicking the functions of natural materials and their applications. It is true that the current status of the deliberately designed and obtained nano-objects based on MSA including a variety of micelles, multicompartment vesicles, and some hybrid and complex nano-objects is at their very first stage to mimic nature, but significant and encouraging progress has been made in achieving a certain similarity in morphologies or properties to that of natural ones. Such achievements also demonstrate that MSA has played an important and irreplaceable role in the grand and long-standing research of biomimetic and bio-inspired materials, the future success of which depends on mutual and persistent efforts in polymer science, material science, supramolecular chemistry, and biology.

Self-assembly and chemical processing of block copolymers: a roadmap towards a diverse array of block copolymer nanostructures

Block copolymers can yield a diverse array of nanostructures. Their assembly structures are influenced by their inherent structures, and the wide variety of structures that can be prepared especially becomes apparent when one considers the number of routes available to prepare block copolymer assemblies. Some examples include self-assembly, directed assembly, coupling, as well as hierarchical assembly, which can yield assemblies having even higher structural order. These assembly routes can also be complemented by processing techniques such as selective crosslinking and etching, the former technique leading to permanent structures, the latter towards sculpted and the combination of the two towards permanent sculpted structures. The combination of these pathways provides extremely versatile routes towards an exciting variety of architectures. This review will attempt to highlight destinations reached by LIU Guojun and coworkers following these pathways.