Programmable Assembly of π-Conjugated Polymers

π-Conjugated polymers have numerous applications due to their advantageous optoelectronic and mechanical properties. These properties depend intrinsically on polymer ordering, including crystallinity, orientation, morphology, domain size, and π-π interactions. Programming, or deliberately controlling the composition and ordering of π-conjugated polymers by well-defined inputs, is a key facet in the development of organic electronics. Here, π-conjugated programming is described at each stage of material development, stressing the links between each programming mode. Covalent programming is performed during polymer synthesis such that complex architectures can be constructed, which direct polymer assembly by governing polymer orientation, π-π interactions, and morphological length-scales. Solution programming is performed in a solvated state as polymers dissolve, aggregate, crystallize, or react in solution. Solid-state programming occurs in the solid state and is governed by polymer crystallization, domain segregation, or gelation. Recent progress in programming across these stages is examined, highlighting order-dependent features and assembly techniques that are unique to π-conjugated polymers. This should serve as a guide for delineating the many ways of directing π-conjugated polymer assembly to control ordering, structure, and function, enabling the further development of organic electronics.

Mitochondria-targeted vitamin E succinate delivery for reversal of multidrug resistance

Inducing mitochondrial malfunction is an appealing strategy to overcome tumor multidrug resistance (MDR). Reported here a versatile mitochondrial-damaging molecule, vitamin E succinate (VES), is creatively utilized to assist MDR reversal of doxorubicin hydrochloride (DOX·HCl) via a nanovesicle platform self-assembled from amphiphilic polyphosphazenes containing pH-sensitive 1H-benzo-[d]imidazol-2-yl) methanamine (BIMA) groups. Driven by multiple non-covalent interactions, VES is fully introduced into the hydrophobic membrane of DOX·HCl-loaded nanovesicles with loading content of 23.5%. The incorporated VES also offers robust anti-leakage property toward DOX·HCl under normal physiological conditions. More importantly, upon release within acidic tumor cells, VES can target mitochondria and result in various dysfunctions including excessive generation of reactive oxygen species (ROS), mitochondrial membrane potential (ΔΨ_m) loss, and inhibited adenosine triphosphate (ATP) synthesis, which contribute to cell apoptosis and insufficient energy supply for drug efflux pumps. Consequently, the killing-effect of DOX·HCl is significantly enhanced toward drug resistant cancer cells at the optimal mass ratio of DOX·HCl to VES. Further in vivo antitumor investigation on nude mice bearing xenograft drug-resistant human chronic myelogenous leukemia K562/ADR tumors verifies the extremely enhanced anti-tumor efficacy of the dual drug-loaded nanovesicle with the tumor inhibition rate (TIR) of 82.38%. Collectively, this study provides a s safe, facile and promising strategy for both precise drug delivery and MDR eradication to improve cancer therapy.

Amphiphilic Double-Brush Copolymers with a Polyurethane Backbone: A Bespoke Macromolecular Emulsifier for Ionic Liquid-in-Oil Emulsion

The study on ionic liquid (IL)-based emulsions is very interesting due to the "green" quality and potential wide applications of ILs, whereas the emulsifiers for the formation of IL-based emulsions are extremely limited and mainly centered on low molecular weight surfactants. In this work, synthesis of amphiphilic double-brush copolymers (DBCs) and their application as bespoke macromolecular emulsifiers for the formation of IL-containing non-aqueous emulsions are described. DBCs consisted of a polyurethane (PU) backbone and poly(N,N-dimethyl acrylamide) (PDMA) and poly(methyl methacrylate) (PMMA) chains that were grafted simultaneously at the same reactive site along the PU backbone (PU-g-PDMA/PMMA), which were synthesized through the combination of polyaddition and the reversible-deactivation radical polymerization reactions. Highly stable [Bmim][PF₆]-in-benzene emulsions could be gained by adopting PU-g-PDMA/PMMA DBCs as macromolecular emulsifiers at a low content, such as 0.025 wt %. On the basis of the stability and the size of emulsion droplets, PU-g-PDMA/PMMA DBCs exhibited much better emulsifying performances than their analogues, including PU-g-PDMA, PU-g-PMMA, and PDMA-b-PMMA copolymers. Such excellent emulsifying performances of PU-g-PDMA/PMMA DBCs were due to high interfacial activities. PU-g-PDMA/PMMA DBCs exhibited higher capabilities in lowering the interfacial tension of the [Bmim][PF₆]-benzene interface than their analogues. A large energy barrier to desorption of adsorbed PU-g-PDMA/PMMA DBCs from the interface contributed to high stability of the [Bmim][PF₆]-in-benzene emulsion.

Design of pH-Sensitive Nanovesicles via Cholesterol Analogue Incorporation for Improving in Vivo Delivery of Chemotherapeutics

pH-responsive polymersomes have emerged as promising nanocarriers for antitumor drugs to realize their fast release and action in a weakly acidic microenvironment of tumor cells. Herein, however, we designed a remarkably pH-responsive polymersome self-assembled from amphiphilic benzimidazole-based polyphosphazenes via the incorporation of cholesteryl hemisuccinate (CholHS), a type of cholesteric molecule, into the polymersome bilayers to inhibit the drug release during blood circulation. Actually, unwanted premature drug leakage before arriving at the acidic tumor site has become a serious problem for polymersomes encapsulating water-soluble drugs, especially when the drug loading is at a high level, thus limiting the therapeutic efficacy. In this study, polymersomes displayed high loading capability of doxorubicin hydrochloride as 12.83%. More importantly, CholHS incorporation decreased the membrane permeability of the polymersome and effectively retarded the cargo release under physiological conditions but induced the fast drug-release rate at pH 5.5, demonstrating a more remarkably acid-responsive release behavior when compared to that of the CholHS-free polymersomes. Further in vivo investigations including pharmacokinetic and antitumor activity studies verified the extended circulation time and enhanced antitumor efficacy of the drug-loaded CholHS-incorporated polymersomes.

Concentration-Driven Fascinating Vesicle-Fibril Transition Employing Merocyanine 540 and 1-Octyl-3-methylimidazolium Chloride

In this article, anionic lipophilic dye merocyanine 540(MC540) and cationic surface-active ionic liquid (SAIL) 1-octyl-3-methylimidazolium chloride (C₈mimCl) are employed to construct highly ordered fibrillar and vesicular aggregates exploiting an ionic self-assembly (ISA) strategy. It is noteworthy that the concentration of the counterions has exquisite control over the morphology, in which lowering the concentration of both the building blocks in a stoichiometric ratio of 1:1 provides a vesicle to fibril transition. Here, we have reported the concentration-controlled fibril-vesicle transition utilizing the emerging fluorescence lifetime imaging microscopy (FLIM) technique. Furthermore, we have detected this morphological transformation by means of other microscopic techniques such as field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and cryogenic-transmission electron microscopy (cryo-TEM) to gain additional support. Besides, multiwavelength FLIM (MW-FLIM) and atomic force microscopy (AFM) techniques assist us in knowing the microheterogeneity and the height profile of the vesicles, respectively. We have replaced the SAIL, C₈mimCl, by an analogous traditional surfactant, n-octyltrimethylammonium bromide (OTAB), and it provides a discernible change in morphology similar to that of C₈mimCl, whereas 1-octanol is unable to exhibit any structural aggregation and thus reveals the importance of electrostatic interaction in supramolecular aggregate formation. However, the SAILs having the same imidazolium headgroup with different chain lengths other than C₈mimCl are unable to display any structural transition and determine the importance of the correct chain length for efficient packing of the counterions to form a specific self-assembly. Therefore, this study reveals the synergistic interplay of electrostatic, hydrophobic, and π-π stacking interactions to construct the self-assembly and their concentration-dependent morphological transition.

Ionic Self-Assembly of a Giant Vesicle as a Smart Microcarrier and Microreactor

Giant vesicles (1-10 μm) were constructed via a facile ionic self-assembly (ISA) strategy using an anionic dye Acid Orange II (AO) and an oppositely charged ionic-liquid-type cationic surfactant 1-tetradecyl-3-methylimidazolium bromide (C14mimBr). This is the first report about preparing giant vesicles through ISA strategy. Interestingly, the giant vesicle could keep the original morphology during the evaporation of solvent and displayed solid-like properties at low concentration. Moreover, giant vesicles with large internal capacity volume and good stability in solution could also be achieved by increasing the concentrations of AO and C14mimBr which contributed to the increase of the other noncovalent cooperative interactions. In order to facilitate comparison, a series of parallel experiments with similar materials were carried out to investigate and verify the driving forces for the formation of these kinds of giant vesicles by changing the hydrophobic moieties or the head groups of the surfactants. It is concluded that the electrostatic interaction, hydrophobic effect and π-π stacking interaction play key roles in this self-assembly process. Importantly, the giant vesicles can act as a smart microcarrier to load and release carbon quantum dot (CQD) under control. Besides, the giant vesicles could also be applied as a microrector to synthesize monodispersed Ag nanoparticles with diameter of about 5-10 nm which exhibited the ability to catalyze reduction of 4-nitroaniline. Therefore, it is indicated that our AO/C14mimBr assemblies hold promising applications in the areas of microencapsulation, catalyst support, and lightweight composites owing to their huge sizes and large microcavities.

Promotion of morphology transition of di-block copolymer nano-objects via RAFT dispersion copolymerization

Promotion of morphology transition of di-block copolymer nano-objects was achieved via RAFT dispersion copolymerization because of the enhancement of the mobility of the solvophobic block.

Spontaneous formation of giant vesicles with tunable sizes based on jellyfish-like graft copolymers

For self-assembly studies, a series of “jellyfish-like” graft copolymers with short hydrophilic backbones and long hydrophobic branch chains was adopted. It was found that these special graft copolymers in 1,4-dioxane–water mixtures could self-assemble into giant vesicles with diameter in the range of 0.5–54 μm.

Biomimetic polymersomes as carriers for hydrophilic quantum dots

For polymersomes to achieve their potential as effective delivery vehicles, they must efficiently encapsulate therapeutic agents into either the aqueous interior or the hydrophobic membrane. In this study, cell membrane-mimetic polymersomes were prepared from amphiphilic poly(D,L-lactide)-b-poly(2-methacryloyloxyethylphosphorylcholine) (PLA-b-PMPC) diblock copolymers and were used as encapsulation devices for water-soluble molecules. Thioalkylated zwitterionic phosphorylcholine protected quantum dots (PC@QDs) were chosen as hydrophilic model substrates and successfully encapsulated into the aqueous polymersome interior, as evidenced by transmission electron microscopy (TEM) and flow cytometry. In addition, we also found a fraction of the PC@QDs were bound to both the external and internal surfaces of the polymersome. This interesting immobilization might be due to the ion-pair interactions between the phosphorylcholine groups on the PC@QDs and polymersomes. The experimental encapsulation results support a mechanism of PLA-b-PMPC polymersome formation in which PLA-b-PMPC copolymer chains first form spherical micelles, then worm-like micelles, and finally disk-like micelles which close up to form polymersomes.

Self-assembly and morphology control of new L-glutamic acid-based amphiphilic random copolymers: giant vesicles, vesicles, spheres, and honeycomb film

New amphiphilic random copolymers containing hydrophobic dodecyl (C12) chain and hydrophilic L-glutamic acid were synthesized, and their self-assembly in solution as well as on the solid surfaces was investigated. The self-assembly behavior of these polymers are largely dependent on their hydrophilic and hydrophobic balances. The copolymer with a more hydrophobic alkyl chain (∼90%) self-assembled into giant vesicles with a diameter of several micrometers in a mixed solvent of ethanol and water. When the hydrophobic ratio decreased to ca. 76%, the polymer self-assembled into conventional vesicles with several hundred nanometers. The giant vesicles could be fused in certain conditions, while the conventional vesicles were stable. When the content of the hydrophilic part was further increased, no organized structures were formed. On the other hand, when the copolymer solutions were directly cast on solid substrates such as silicon plates, films with organized nanostructures could also be obtained, the morphology of which depended on solvent selection. When ethanol or methanol was used, spheres were obtained. When dichloromethane was used as the solvent, honeycomb-like morphologies were obtained. These results showed that through appropriate molecular design, random copolymer could self-assemble into various organized structures, which could be regulated through the hydrophobic/hydrophilic balance and the solvents.

Vesicular assembly and thermo-responsive vesicle-to-micelle transition from an amphiphilic random copolymer

Vesicular assembly from a thermo-responsive amphiphilic random copolymer is reported. Vesicle-to-micelle transition above a critical morphology transition temperature (CMTT) resulted in selective triggered release of encapsulated hydrophilic guests over hydrophobic ones. The aggregation pattern of a control polymer indicated a defined role of the methacrylamide groups in the polymer backbone for such unprecedented self-assembly from a simple polymer.