A Zwitterionic ABC Triblock Copolymer That Forms a “Trinity” of Micellar Aggregates in Aqueous Solution

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 Triblock Copolymer Prodrug for Tumor-Specific pH/Reduction Dual-Triggered Drug Delivery: Effect of Self-Assembly Behaviors

Diblock copolymer-based prodrugs have been widely designed for tumor treatment after self-assembly; however, premature drug leakage could not be ignored because their hydrophobic prodrug cores were directly exposed to the media. Here, an amphiphilic triblock copolymer prodrug with a hydrophilic PEG block, a pH-sensitive poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) block, and a hydrophobic reduction-cleavable prodrug block was synthesized for tumor-specific pH/reduction dual-triggered drug delivery, via the successive RAFT polymerization of DPA and a DOX-based monomer (MAL-DOX) with a PEG-based macro-CTA. The core-shell and core-shell-corona nanoparticles could be obtained by one-step and two-step self-assembly. With the pH-sensitive gatekeeper formed by the PDPA block, the core-shell-corona nanoparticles possessed a smaller diameter with narrow distribution and better drug release with lower drug leakage. MTT assays demonstrated the selective cytotoxicity of the core-shell-corona nanoparticles to the cancer cells was dose-dependent because of the reduction-cleavable prodrug. The negligible drug leakage and selective cytotoxicity to cancer cells endow the proposed core-shell-corona prodrug nanoparticles with promising potential for tumor treatment without toxic side effects on the normal cells.

Complex Formation of Sulfobetaine Surfactant and Ionic Polymers and Their Stimuli Responsivity

We investigated the kinds of complexes sulfobetaine surfactant and ionic polymer formed using lauramidopropyl hydroxysultane (LAPHS) as a sulfobetaine surfactant, poly(sodium styrenesulfonate) (PSSNa) as the anionic polymer and poly[3-(methacrylamido)propyl trimethylammonium chloride] (PMAPTAC) as the cationic polymer. The fundamental properties of LAPHS at various salt concentrations were estimated by various measurements, and it was confirmed that the LAPHS micelles alone did not show temperature responsiveness. The presence of large aggregates in addition to LAPHS micelles was confirmed in the aggregates prepared by adding PSSNa to LAPHS at a charge ratio of 1:0.5, 1:1, and 1:2. However, the aggregates could not be formed when the salt concentration was high or when a monomer was added instead of the polymer. This revealed that the cation part of sulfobetaine, which is the shell of LAPHS micelles, and the anion part of PSSNa electrostatically interacted with each other to form a large aggregate. On the other hand, unlike the case of LAPHS micelles alone and the aggregate consisting of LAPHS micelles and PSSNa, the aggregate of LAPHS micelles and PMAPTAC showed an unprecedented phenomenon of "clear → opaque → clear" with increasing concentration in the concentration range above CMC. The change in the transition temperature due to the change of concentration was a factor. Additionally, we confirmed that the transition temperature was lowered when the concentration was higher than CMC or the salt concentration was increased, and the transition temperature was increased when the PMAPTAC with a high degree of polymerization was added. These results suggested that the LAPHS micelles and the ionic polymer form an aggregate, and the temperature responsivity can be expressed by the interaction with the cationic polymer.

Polyzwitterions with LCST Side Chains: Tunable Self-Assembly

Manipulation of self-assembly behavior of copolymers via environmental change is attractive in the fabrication of smart polymeric materials. We present tunable self-assembly behavior of graft copolymers, poly(sulfobetaine methacrylate)-graft-poly[oligo(ethylene glycol) methyl ether methacrylate)-co-di(ethylene glycol) methyl ether methacrylate] (PSBM-g-P(OEGMA-co-DEGMA)). Upon heating the aqueous solutions, the graft copolymers undergo a transition from micelles with PSBM cores to unimers (i.e., individual macromolecules) and then to reversed micelles with P(OEGMA-co-DEGMA) cores, thus demonstrating the tunability of the self-assembling through temperature change. In the presence of salt the temperature response of PSBM is eliminated, and the structure of the micelles with the P(OEGMA-co-DEGMA) core changes. Moreover, for the graft copolymer with long side chains, micelles with aggregation number ∼ 2 were formed with a PSBM core at low temperature, which is ascribed to the steric effect of the P(OEGMA-co-DEGMA) shell.

Highly efficient gene release in spatiotemporal precision approached by light and pH dual responsive copolymers

Triblock copolymer of poly(ethylene glycol)-b-poly(2-dimethylaminoethyl methacrylate)-b-poly(pyrenylmethyl methacrylate) (PEG-b-PDMAEMA-b-PPy) has been developed for use as an ideal gene delivery system, which showed both high stability under physiological conditions and efficient gene release in a mimetic cancer environment. The siRNA release from this system without external stimulation was 16% in 1 h and then remained steady. However, the photo-triggered siRNA release was 78% within 1 h and was higher than 91% after 24 h. The remarkable contrast between the stability and release efficiency of these siRNA-condensed micelleplexes before and after photo-irradiation has been rationalized by the light- and pH-induced structural transitions of the triblock copolymer micelles. The negligible cytotoxicity, high cellular uptake efficiency, and remarkable knockdown efficiency shown in in vitro tests further revealed the promising potential of these triblock copolymer micelleplexes for use in stimuli-responsive gene therapy.

Synthesis of One-Component Nanostructured Polyion Complexes via Polymerization-Induced Electrostatic Self-Assembly

Nanostructured polyion complexes (PICs) are expected to serve as novel platforms to stabilize and deliver drugs, proteins, and nucleic acids. Yet, traditional self-assembly suffers from lack of scale-up and reproducibility. Particularly for one-component PICs, only spheres are available to date. Here, we report an efficient and scalable strategy to prepare one-component low-dimensional PICs. It involves visible-light-mediated RAFT iterative polymerization of opposite-charge monomers at 25% w/w solids in water at 25 °C. Sphere-film-vesicle transition and charge-/medium-tunable shape selectivity are reported. One-component PIC nanowire, ultrathin film, vesicle, tube, and surface-charged vesicle are easily prepared, and vesicle-polymerization is fulfilled, using this new strategy. This strategy provides a general platform to prepare one-component low-dimensional PICs with tailorable morphologies and high reproducibility on commercially viable scale under eco-friendly conditions.

Schizophrenic poly(ε-caprolactone)s: synthesis, self-assembly and fluorescent decoration

Double hydrophilic copolymers PCCL-b-PPIL and their pyrene-modified copolymers showed pH-responsive “schizophrenic” aggregation behaviors.

Supramolecular self-assembly of a polyelectrolyte chain based on step-growth polymerization of hydrophobic and hydrophilic monomers

Polymerization of citric acid and hexamethylene diisocyanate and hydrolysis results in a polyelectrolyte PHMC. Noncovalent cross-linking of cooperative H-bonding units stabilizes the self-assembly of the PHMC chains into nanoparticles in water.

Micelle response to changes in solvent properties

The dynamics of co-polymer systems play an important role in the preparation and stability of formulations, as well as on their capability to function in drug delivery systems. Micelle inversion can occur as a result of a change in concentration when a solvent is very volatile and evaporates, or as a result of a change in solvent quality upon addition of another solvent to the original solution, or upon changes in pH. In this work, dissipative particle dynamics (DPD) is used to examine the dynamics of micelle inversion in concentrated systems of diblock and triblock amphiphiles, where interactions between neighboring aggregates are observed. Significant differences were observed in the inversion process of different amphiphilic molecules, with a large amount of co-polymer exchange between inverting aggregates made of diblock amphiphiles, and practically no exchange of molecules between aggregates during the inversion of triblock copolymer aggregates. Fundamental mechanisms of inversion are revealed that provide information which can be used to help design micelles for targeted drug release and allow understanding of history dependant formulations.

Novel dual stimuli-responsive ABC triblock copolymer: RAFT synthesis, "schizophrenic" micellization, and its performance as an anticancer drug delivery nanosystem

A novel pH- and thermo-responsive ABC triblock copolymer {poly[(2-succinyloxyethyl methacrylate)-b-(N-isopropylacrylamide)-b-[(N-4-vinylbenzyl),N,N-diethylamine]]} [P(SEMA-b-NIPAAm-b-VEA)] was successfully synthesized via reversible addition of fragmentation chain transfer (RAFT) polymerization technique. The molecular weights of PHEMA, PNIPAAm, and PVEA segments in the synthesized triblock copolymer were calculated to be 10,670, 6140, and 9060gmol^-1, respectively, from proton nuclear magnetic resonance (¹H NMR) spectroscopy. The "schizophrenic" self-assembly behavior of the synthesized P(SEMA-b-NIPAAm-b-VEA) triblock copolymer under pH and thermal stimulus were investigated by means of ¹H NMR and ultraviolet-visible (UV-vis) spectroscopies as well as dynamic light scattering (DLS) and zeta potential (ξ) measurements. The doxorubicin hydrochloride (DOX)-loading capacity, and stimuli-responsive drug release ability of the synthesized triblock copolymer were also investigated. The biocompatibility of the synthesized triblock copolymer was confirmed through the assessing survival rate of breast cancer cell line (MCF7) using MTT assay. In contrast, DOX-loaded triblock copolymer exhibited an efficient anticancer performance in comparison with free DOX verified by MTT and DAPI staining assays. As the results, we envision that the synthesized P(SEMA-b-NIPAAm-b-VEA) triblock copolymer can be applied as an enhanced anticancer drug delivery nanosystem, mainly due to its smart physicochemical and biocompatibility properties.

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.

Poly(ethylene oxide) (PEO)-based ABC triblock terpolymers – synthetic complexity vs. application benefits

This review presents a short summary of possible synthetic routes for the synthesis of poly(ethylene oxide) (PEO) containing triblock terpolymers, as well as different applications in the bulk or in solution – including the preparation of porous materials, hybrid systems, and carriers for controlled drug delivery.

Switchable vesicles formed by diblock random copolymers with tunable pH- and thermo-responsiveness

The thermo-responsiveness of polymers in aqueous media can be tuned by the choice of comonomers used in the synthesis of block copolymers made of random sequences of the same comonomers but of different molar ratios. The same synthetic approach may be applied to other stimuli and we have made diblock random copolymers with both pH- and thermo-responsiveness and studied the formation of vesicles whose membrane core and coronas may be inverted in aqueous media. Sequential reversible addition-fragmentation chain transfer (RAFT) polymerization was used to prepare well-defined block copolymers in the form of AnBm-b-ApCq, where A, B, and C are N-n-propylacrylamide (nPA), 2-(diethylamino)ethyl methacrylate (DEAEMA), and N-ethylacrylamide (EA), respectively. This polymer shows interesting "schizophrenic" behavior in aqueous solutions. Both blocks are thermo-responsive, and one block is pH-responsive in which the tertiary amine group of DEAEMA may be protonated at a lower pH. A molecularly dissolved polymer is obtained at neutral pH and ambient temperature. At pH 7 and 37 °C, the polymer self-assembles into vesicles with the poly(nPA0.8-co-EA0.2) block as the membrane core (mean hydrodynamic diameter of the vesicles Dh = 148 nm). In an alkaline medium (pH 10) at 25 °C, the membrane core and the coronas of the vesicles are inverted with poly(nPA0.8-co-DEAEMA0.2) block forming the core (Dh = 60 nm). In addition, two-step phase transitions are observed in both alkaline and neutral solutions corresponding to the cloud points of the individual blocks. Here, the random nature of the blocks allows fine-tuning the thermo-responsiveness based solely on lower critical solution temperatures and its combination with pH-sensitivity provides vesicles with switchable membrane core and corona in aqueous solution.

Biological stimuli and biomolecules in the assembly and manipulation of nanoscale polymeric particles

Living systems are replete with complex, stimuli-responsive nanoscale materials and molecular self-assemblies. There is an ever increasing and intense interest within the chemical sciences to understand, mimic and interface with these biological systems utilizing synthetic and/or semi-synthetic tools. Our aim in this review is to give perspective on this emerging field of research by highlighting examples of polymeric nanoparticles and micelles that are prepared utilizing biopolymers together with synthetic polymers for the purpose of developing nanomaterials capable of interacting and responding to biologically relevant stimuli. It is expected that with the merging of evolved biological molecules with synthetic materials, will come the ability to prepare complex, functional devices. A variety of applications will become accessible including self-healing materials, self-replicating systems, biodiagnostic tools, drug targeting materials and autonomous, adaptive sensors. Most importantly, the success of this type of strategy will impact how biomolecules are stabilized and incorporated into synthetic devices and at the same time, will influence how synthetic materials are utilized within biomedical applications.

Structural evolution of multicompartment micelles self-assembled from linear ABC triblock copolymer in selective solvents

Using dissipative particle dynamics simulation, structural evolution from concentric multicompartment micelles to raspberry-like multicompartment micelles self-assembled from linear ABC triblock copolymers in selective solvents was investigated. The structural transformation from concentric micelles to raspberry-like micelles can be controlled by changing either the length of B blocks or the solubility of B block. It was found that the structures with B bumps on C surface (B-bump-C) are formed at shorter B block length and the structures with C bumps on B surface (C-bump-B) are formed at relative lower solubility of B blocks. The formation of B-bump-C is entropy-driven, while the formation of C-bump-B is enthalpy-dominated. Furthermore, when the length of C blocks is much lower than that of B blocks, an inner-penetrating vesicle was discovered. The results gained through the simulations provide an insight into the mechanism behind the formation of raspberry-like micelles.

Microphase separation in mixed monolayers of DPPG with a double hydrophilic block copolymer at the air-water interface: a BAM, LSCFM, and AFM study

Phase separation and interactions in mixed monolayers of dipalmitoylphosphatidylglycerol (DPPG) with the rhodamine B end-labeled double-hydrophilic block copolymer (DHBC), poly(N,N-dimethylacrylamide)-block-poly(N,N-diethylacrylamide) (RhB-PDMA(207)-b-PDEA(177)), was studied at the air-water interface. Surface pressure versus area isotherms indicate that both components behave almost independently. Brewster angle microscopy (BAM) images show a random distribution of liquid condensed (LC) domains of DPPG in an apparent homogeneous matrix of DHBC, excluding the macroscopic phase separation. The laser scanning confocal fluorescence microscopy (LSCFM) of the rhodamine dye at the end of the PDMA chain showed how the DHBC is distributed in Langmuir-Blodgett (LB) mixed monolayers. The high spatial resolution of atomic force microscopy (AFM) combined with the LCSFM images indicates that DHBC incorporates in the expanded phase of DPPG to form mixed domains, being excluded from the condensed regions. Upon compression, nanosized LC domains of DPPG nucleate inside the mixed domains corralled in the nanopatterning of pure DHBC. The negatively charged polar group of DPPG inhibits rhodamine aggregation, while the long polymer chains promote the formation of corralled nanodomains of DPPG in two dimensions.

Dissipative particle dynamics simulations on inversion dynamics of spherical micelles

We simulate the inversion process of a spherical micelle composed of symmetric diblock copolymers by means of dissipative particle dynamics. The evolution of micelle morphology reveals that the inversion is a two-staged process, in which a rapid agglomeration of outer lyophobic blocks occurs first, followed by a slow penetration of inner lyophilic blocks through the porous lyophobic layer. Calculation of the radius of gyration and hydrodynamic radius indicates that an intermediate with a dilute core and a dense shell emerges in the inversion. The characteristic time of inversion scales with the block copolymer chain length with the scaling exponent ranging from 1.67 to 1.89, which can be well described by a simplified chemical-potential-driven flow model. Further simulations incorporating different denaturation times for the two types of blocks indicate the inversions do not experience molecularly scattered states, but form either collapsed intermediates or loosely associated clusters of small sizes. Possible connections of the simulations to the light scattering experiments are discussed.

Nanosized diblock copolymer micelles as a scaffold for constructing a ratiometric fluorescent sensor for metal ion detection in aqueous media

A facile strategy was employed to create a fluorescence resonance energy transfer (FRET) based ratiometric sensing system for ferric ions in all-aqueous media by using nanosized poly(ethylene oxide)-b-polystyrene micelles as the scaffold. A hydrophobic fluorescent dye nitrobenzoxadiazolyl derivative (NBD), which served as the energy transfer donor, was incorporated into the micelle core during the micelle formation; a spirolactam rhodamine derivative (SRhB-OH) was chosen as a sensitive and selective sensor for Fe(III) ions and was then 'adsorbed' into the micelle core/corona interface. A highly efficient ring-opening reaction of SRhB-OH induced by Fe(III) generates the long-wavelength rhodamine B fluorophore which can act as the energy acceptor; thus, the micelle nanoparticles can serve as a FRET-based ratiometric detection system for ferric ions. The effects of PS block length on the ion sensing performance of the micelles were investigated, and it has been found that the micelles formed by the copolymer with moderate block length (PEO(113)-b-PS(115)) were preferable as the scaffold for the FRET system and exhibited a sensitive and selective sensing capacity for Fe(III) with a detection limit of 1 microM. This nanoparticle-based sensing strategy may be utilized to construct other ratiometric chemosensors by replacing the current dyes with other suitable ones.