Supramolecular dendritic polymers: from synthesis to applications

Sequence and gelation in supramolecular polymers

Supramolecular polymer networks exhibit unique and tunable thermodynamic and dynamic properties that are attractive for a wide array of applications, such as adhesives, rheology modifiers, and compatibilizers. Coherent states (CS) field theories have emerged as a powerful approach for describing the possibly infinite reaction products that result from associating polymers. Up to this point, CS theories have focused on relatively simple polymer architectures. In this work, we develop an extension of the CS framework to study polymers with reversible bonds distributed along the polymer backbone, opening a broad array of new materials that can be studied with theoretical methods. We use this framework to discern the role of reactive site placement on sol-gel phase behavior, including the prediction of a microstructured gel phase that has not been reported for neutral polymer gels. Our results highlight the subtleties of thermodynamics in supramolecular polymers and the necessity for theories that capture them.

One-Pot Synthesis, Circularly Polarized Luminescence, and Controlled Self-Assembly of Janus-Type Miktoarm Star Copolymers

With the aim of broadening the scope of Janus-type polymers with new functionalities, Janus-type miktoarm star copolymers comprising helical poly(phenyl isocyanide) (PPI) and a vinyl polymer were designed and synthesized via a combination of Pd(II)-initiated isocyanide polymerization and atom transfer radical polymerization (ATRP). A functional β-cyclodextrin bearing 7 Pd(II) complexes at one side and 14 bromine groups at the other side ((Pd(II))7-CD-(Br)14) was prepared and used as an initiator for the one-pot polymerization of phenyl isocyanide and the ATRP of vinyl monomers in a living and controlled manner. A variety of Janus-type copolymers with different structures and tunable compositions were facilely obtained by using this method. Thus, Janus-type copolymers composed of helical PPIs and tetraphenylethylene-modified vinyl polymers exhibited a significant circularly polarized luminescence performance in both soluble and aggregated states. Meanwhile, Janus-type copolymers containing PPIs and hydrophilic vinyl polymers presented amphiphilicity and self-assembled into diverse morphologies.

Abelairas A, Criado A, Gómez IJ, Mosquera J. Dendrimers: Exploring Their Wide Structural Variety and Applications

Dendrimers constitute a distinctive category of synthetic materials that bear resemblance to proteins in various aspects, such as discrete structural organization, globular morphology, and nanoscale dimensions. Remarkably, these attributes coexist with the capacity for facile large-scale production. Due to these advantages, the realm of dendrimers has undergone substantial advancement since their inception in the 1980s. Numerous reviews have been dedicated to elucidating this subject comprehensively, delving into the properties and applications of quintessential dendrimer varieties like PAMAM, PPI, and others. Nevertheless, the contemporary landscape of dendrimers transcends these early paradigms, witnessing the emergence of a diverse array of novel dendritic architectures in recent years. In this review, we aim to present a comprehensive panorama of the expansive domain of dendrimers. As such, our focus lies in discussing the key attributes and applications of the predominant types of dendrimers existing today. We will commence with the conventional variants and progressively delve into the more pioneering ones, including Janus, supramolecular, shape-persistent, and rotaxane dendrimers.

Visible Light-Guided Gene Delivery with Nonviral Supramolecular Block Copolymer Vectors

To achieve efficient gene delivery in vitro or in vivo, nonviral vectors should have excellent biostability across cellular and tissue barriers and also smart stimuli responsiveness toward controlled release of therapeutic genes into the cell nucleus. However, it remains a key challenge to effectively combine the biostability of covalent polymers with the stimuli responsiveness of noncovalent polymers into one nonviral vehicle. In this work, we report the construction of a kind of cationic supramolecular block copolymers (SBCs) through noncovalent polymerization of β-cyclodextrin/azobenzene-terminated pentaethylenehexamine (DMA-Azo-PEHA-β-CD) in aqueous media using β-CD-monosubstituted poly(ethylene glycol) (PEG-β-CD) as a supramolecular initiator. The resultant SBC exhibits superior biostability, biocompatibility, and light/pH dual-responsive characteristics, and it also demonstrates efficient plasmid DNA condensation capacity and the ability to rapidly release plasmid DNA into cells driven by visible light (450 nm). Eventually, this SBC-based delivery system demonstrates visible light-induced enhancement of gene delivery in both COS-7 and HeLa cells. We anticipate that this work provides a facile and robust strategy to enhance gene delivery in vitro or in vivo via visible light-guided manipulation of genes, further achieving safe, highly efficient, targeting gene therapy for cancer.

Dynamic Control over Hierarchically Dendritic Architectures of Simple Heterogenous Monomers by Living Supramolecular Assembly

The successful preparation of supramolecular block copolymers (SBCPs) by living supramolecular assembly technology requires two kinetic systems in which both the seed (nucleus) and heterogenous monomer providers are in non-equilibrium. However, employing simple monomers to construct the SBCPs via this technology is almost impossible because the low spontaneous nucleation barrier of simple molecules prevents the formation of kinetic states. Here, with the help of confinement from layered double hydroxide (LDH), various simple monomers successfully form living supramolecular co-assemblies (LSCA). LDH overcomes a considerable energy barrier to obtain living seeds to support the growth of the inactivated second monomer. The ordered LDH topology is sequentially mapped to the seed, second monomer, and binding sites. Thus, the multidirectional binding sites are endowed with the ability to branch, making the branch length of dendritic LSCA reach its maximum value of 3.5 cm so far. The strategy of universality will guide exploration into the development of multi-function and multi-topology advanced supramolecular co-assemblies.

An eco-friendly photo-responsive hyaluronic acid-based supramolecular polysaccharide hybrid hydrogels for plant growth regulation and heavy metal ions adsorption

Agrochemicals are widely used in agricultural production, but they may cause agrochemicals residues and environmental pollution. Polysaccharide-based materials have emerged as a promising biopolymer carrier for agrochemicals delivery. Herein, an eco-friendly, photo-responsive supramolecular polysaccharide hybrid hydrogels (HA-AAP-Guano-CD@LP) was constructed from arylazopyrazole-modified hyaluronic acid (HA-AAP), guanidinium functionalized β-cyclodextrin (Guano-CD), and laponite clay (LP) via synergistic host-guest and electrostatic interactions, which could realize the controlled release of plant growth regulators such as naphthalene acetic acid (NAA) and gibberellin (GA) and promote the growth of Chinese cabbage and alfalfa. More interestingly, after releasing the cargo, the hydrogels could be used to capture heavy metal ions via strong complexation between the ions and carboxyl groups. This polysaccharide-based supramolecular hybrid hydrogels may provide a new strategy to realize the precision agriculture by the controlled delivery of plant growth regulators and synergetic adsorption of pollutants.

Pillararene-Based Supramolecular Polymers for Cancer Therapy

Supramolecular polymers have attracted considerable interest due to their intriguing features and functions. The dynamic reversibility of noncovalent interactions endows supramolecular polymers with tunable physicochemical properties, self-healing, and externally stimulated responses. Among them, pillararene-based supramolecular polymers show great potential for biomedical applications due to their fascinating host-guest interactions and easy modification. Herein, we summarize the state of the art of pillararene-based supramolecular polymers for cancer therapy and illustrate its developmental trend and future perspective.

Complementary, Cooperative Ditopic Halogen Bonding and Electron Donor-Acceptor π-π Complexation in the Formation of Cocrystals

This study expands and combines concepts from two of our earlier studies. One study reported the complementary halogen bonding and π-π charge transfer complexation observed between isomeric electron rich 4-N,N-dimethylaminophenylethynylpyridines and the electron poor halogen bond donor, 1-(3,5-dinitrophenylethynyl)-2,3,5,6-tetrafluoro-4-iodobenzene while the second study elaborated the ditopic halogen bonding of activated pyrimidines. Leveraging our understanding on the combination of these non-covalent interactions, we describe cocrystallization featuring ditopic halogen bonding and π-stacking. Specifically, red cocrystals are formed between the ditopic electron poor halogen bond donor 1-(3,5-dinitrophenylethynyl)-2,4,6-triflouro-3,5-diiodobenzene and each of electron rich pyrimidines 2- and 5-(4-N,N-dimethyl-aminophenylethynyl)pyrimidine. The X-ray single crystal structures of these cocrystals are described in terms of halogen bonding and electron donor-acceptor π-complexation. Computations confirm that the donor-acceptor π-stacking interactions are consistently stronger than the halogen bonding interactions and that there is cooperativity between π-stacking and halogen bonding in the crystals.

Recent advances on next generation of polyzwitterion-based nano-vectors for targeted drug delivery

Poly (ethylene glycol) (PEG)-based nanomedicines are perplexed by the challenges of oxidation damage, immune responses after repeated injections, and limited excretion from the body. As an alternative to PEG, bioinspired zwitterions bearing an identical number of positive and negative ions, exhibit exceptional hydrophilicity, excellent biomimetic nature and chemical malleability, endowing zwitterionic nano-vectors with biocompatibility, non-fouling feature, extended blood circulation and multifunctionality. In this review, we innovatively classify zwitterionic nano-vectors into linear, hyperbranched, crosslinked, and hybrid nanoparticles according to different chemical architectures in rational design of zwitterionic nano-vectors for enhanced drug delivery with an emphasis on zwitterionic engineering innovations as alternatives of PEG-based nanomedicines. Through combination with other nanostratagies, the intelligent zwitterionic nano-vectors can orchestrate stealth and other biological functionalities together to improve the efficacy in the whole journey of drug delivery.

pH-Controlled Stereoregular Polymerization of Poly(methyl methacrylate) in Vesicle Membranes

Here, we report a pH-controlled stereoregular polymerization of methyl methacrylate (MMA) inside the membrane of H20-COOH hyperbranched polymer vesicles using a common radical polymerization process. The vesicle size decreases from 745 to 214 nm with an increase of solution pH from 2.60 to 7.26, and the isotacticity of the obtained polymethyl methacrylates (PMMAs) is accordingly elevated from 9 to 35%. The obtained isotactic-rich PMMAs show a lower glass transition temperature depending on the isotacticity than the commercial random PMMAs. A mechanism study according to the in situ Fourier transform infrared measurements indicates that the control of polymer isotacticity results from the monomer conformation confined effect inside the thin vesicle membranes. The present study provides a new method to realize the preparation of isotactic polymers with the characteristics of facile synthesis, pH controllability, and a green polymerization process in aqueous solution as well as under mild reaction conditions of ambient temperature and pressure.

Supramolecular Self-Associations of Amphiphilic Dendrons and Their Properties

This review presents precisely defined amphiphilic dendrons, their self‐association properties, and their different uses. Dendrons, also named dendritic wedges, are composed of a core having two different types of functions, of which one type is used for growing or grafting branched arms, generally multiplied by 2 at each layer by using 1→2 branching motifs. A large diversity of structures has been already synthesized. In practically all cases, their synthesis is based on the synthesis of known dendrimers, such as poly(aryl ether), poly(amidoamine) (in particular PAMAM), poly(amide) (in particular poly(L‐lysine)), 1→3 branching motifs (instead of 1→2), poly(alkyl ether) (poly(glycerol) and poly(ethylene glycol)), poly(ester), and those containing main group elements (poly(carbosilane) and poly(phosphorhydrazone)). In most cases, the hydrophilic functions are on the surface of the dendrons, whereas one or two hydrophobic tails are linked to the core. Depending on the structure of the dendrons, and on the experimental conditions used, the amphiphilic dendrons can self‐associate at the air‐water interface, or form micelles (eventually tubular, but most generally spherical), or form vesicles. These associated dendrons are suitable for the encapsulation of low‐molecular or macromolecular bioactive entities to be delivered in cells. This review is organized depending on the nature of the internal structure of the amphiphilic dendrons (aryl ether, amidoamine, amide, quaternary carbon atom, alkyl ether, ester, main group element). The properties issued from their self‐associations are described all along the review.

Polyamide/Poly(Amino Acid) Polymers for Drug Delivery

Polymers have always played a critical role in the development of novel drug delivery systems by providing the sustained, controlled and targeted release of both hydrophobic and hydrophilic drugs. Among the different polymers, polyamides or poly(amino acid)s exhibit distinct features such as good biocompatibility, slow degradability and flexible physicochemical modification. The degradation rates of poly(amino acid)s are influenced by the hydrophilicity of the amino acids that make up the polymer. Poly(amino acid)s are extensively used in the formulation of chemotherapeutics to achieve selective delivery for an appropriate duration of time in order to lessen the drug-related side effects and increase the anti-tumor efficacy. This review highlights various poly(amino acid) polymers used in drug delivery along with new developments in their utility. A thorough discussion on anticancer agents incorporated into poly(amino acid) micellar systems that are under clinical evaluation is included.

Recent advances in supramolecular block copolymers for biomedical applications

Supramolecular block copolymers (SBCs) have received considerable interest in polymer chemistry, materials science, biomedical engineering and nanotechnology owing to their unique structural and functional advantages, such as low cytotoxicity, outstanding biodegradability, smart environmental responsiveness, and so forth. SBCs comprise two or more different homopolymer subunits linked by noncovalent bonds, and these polymers, in particular, combine the dynamically reversible nature of supramolecular polymers with the hierarchical microphase-separated structures of block polymers. A rapidly increasing number of publications on the synthesis and applications of SBCs have been reported in recent years; however, a systematic summary of the design, synthesis, properties and applications of SBCs has not been published. To this end, this review provides a brief overview of the recent advances in SBCs and describes the synthesis strategies, properties and functions, and their widespread applications in drug delivery, gene delivery, protein delivery, bioimaging and so on. In this review, we aim to elucidate the general concepts and structure-property relationships of SBCs, as well as their practical bioapplications, shedding further valuable insights into this emerging research field.

The recent progress of synergistic supramolecular polymers: preparation, properties and applications

Interactions for forming supramolecular polymers were reviewed together with their unique properties and applications with detailed examples.

Flower- and Grass-like Self-Assemblies of an Oleanane-Type Triterpenoid Erythrodiol: Application in the Removal of Toxic Dye from Water

Erythrodiol (3β-olean-12-ene-3, 28-diol) (C30H50O2) 1 is a nanosized oleanane-type fused 6-6-6-6-6 pentacyclic triterpeneoid extractable from the dried leaves of olive (Olea europia). One step reduction of oleanolic acid extracted from Lantana camara also yields the same compound. The triterpenoid has one secondary -OH group attached at C3 of the "A" ring and one primary -OH group at C28 present at the junction of the "D" and "E" rings. Here, we report the spontaneous self-assembly of erythrodiol in different neat organic liquids and aqueous-organic liquid mixtures. The nanosized dihydroxy triterpenoid having an oleanane-type lipophilic rigid skeleton self-assembled in liquids, yielding nanosized fibrils, microsized flowers, and grass-like architectures via formation of densely assembled fibrils and petals or 2D sheets. The microstructures of the self-assemblies have been characterized by different techniques like optical microscopy, electron microscopy, atomic force microscopy, FTIR, and wide angle X-ray diffraction studies. The porous self-assemblies having a large surface area obtained from 1 were capable of adsorbing toxic fluorophores like rhodamine-B, rhodamine-6G, methylene blue, and crystal violet (CV). Moreover, removal of the aforementioned toxic pigments has also been demonstrated from their aqueous solutions by using UV-visible spectrophotometry and epifluorescence microscopy.

Solvent Effect on Supramolecular Self-Assembly of Chlorophylls a on Chemically Reduced Graphene Oxide

Solvent plays an important role in the surface interaction of molecules. In this study, we use "chlorophyll a", an archetypical molecule, to investigate its supramolecular self-assembly with chemically reduced graphene oxide in three different types of solvents: polar protic, polar aprotic, and non-polar. It was observed that only a polar protic solvent that can donate protons facilitates the hydrogen bonding between chlorophyll a and chemically reduced graphene oxide nanosheets in a hybrid system. The formation of hydrogen bonds further initiates the other non-covalent interactions such as π-π stacking and hydrophobic interaction, which altogether play a key driving force for supramolecular self-assembly of chlorophylls on chemically reduced graphene oxides. The experimental results are strongly supported by density functional theory calculations, which show robust electron coupling between chlorophylls and chemically reduced graphene oxide.

Terpenoids, nano-entities and molecular self-assembly

Plant metabolites being renewable in nature have tremendous significance for the development of a sustainable society. In this manuscript we show that, terpenoids having nanometric lengths, commonly having several functional groups and several centers of chirality, can be utilized as renewable Molecular Functional Nanos (MFNs). The terpenoids spontaneously self-assembled in liquids yielding different morphologies such as vesicles, tubes, flowers, petals and fibers of nano- to micro-meter dimensions and supramolecular gels. The self-assemblies were utilized for the entrapment and release of fluorophores including anticancer drug, pollutant capture, generation of hybrid materials and catalysis.

Cu(II)-Metallacryptands Self-Assembled to Vesicular Aggregates Capable of Encapsulating and Transporting an Anticancer Drug Inside Cancer Cells

Crystallographically characterized M₂ L₄ type cationic Cu(II)-metallacryptands [MC(X)] derived from a series of bis-pyridyl-bis-urea ligands (L_X ; X = O, S, C) are self-assembled to single-layered vesicular aggregates in DMSO, DMSO/water, and DMSO/DMEM (biological media). One such vesicle is MC(O)-vesicle that is demonstrated to be able to load and release (pH responsive) an anticancer drug, namely doxorubicin hydrochloride (DOX). DOX-loaded MC(O)-vesicle is also successfully transported within MDA-MB-231 cells-a highly aggressive human breast cancer cell line. Such self-assembling behavior to form vesicular aggregates by metallacryptands (MCs) is hitherto unknown.

In situ supramolecular polymerization-enhanced self-assembly of polymer vesicles for highly efficient photothermal therapy

Vesicular photothermal therapy agents (PTAs) are highly desirable in photothermal therapy (PTT) for their excellent light-harvesting ability and versatile hollow compartments. However, up to now, the reported vesicular PTAs are generally self-assembled from small molecules like liposomes, and polymer vesicles have seldom been used as PTAs due to the unsatisfactory photothermal conversion efficiency resulting from the irregular packing of chromophores in the vesicle membranes. Here we report a nano-sized polymer vesicle from hyperbranched polyporphyrins with favorable photothermal stability and extraordinarily high photothermal efficiency (44.1%), showing great potential in imaging-guided PTT for tumors through in vitro and in vivo experiments. These excellent properties are attributed to the in situ supramolecular polymerization of porphyrin units inside the vesicle membrane into well-organized 1D monofilaments driven by π–π stacking. We believe the supramolecular polymerization-enhanced self-assembly process reported here will shed a new light on the design of supramolecular materials with new structures and functions.

Photothermal therapy (PTT) has recently emerged as a promising approach for cancer therapy. Here, the authors report a hyperbranched polymer vesicle with favorable photothermal stability and high photothermal efficiency for PTT through a supramolecular polymerization-enhanced self-assembly strategy.

Design and Synthesis of ZnII -Coordination Polymers Anchored with NSAIDs: Metallovesicle Formation and Multi-drug Delivery

A series of coordination polymers synthesized from a bis-pyridyl linker, namely 4,4'-azopyridine (L), selected non-steroidal-anti-inflammatory drugs (NSAIDs), namely diclofenac (Dic), ibuprofen (Ibu), flurbiprofen (Flu), mefenamic acid (Mefe), and naproxen (Nap), and Zn(NO₃ )₂ were characterized by single crystal X-ray diffraction. One of the coordination polymers, namely CP3 derived from Flu, was able to form metallovesicles in DMSO, DMSO/H₂ O and DMSO/DMEM (biological media) as revealed by TEM, AFM and DLS. Metallovesicle formation by CP3 was further supported by loading a fluorescent dye, namely calcein, as well as an anti-cancer drug, doxorubicin hydrochloride (DOX), as revealed by UV-vis and emission spectra, and fluorescence microscopy. DOX-loaded metallovesicles of CP3 (DOX@CP3-vesicle) could be delivered in vitro to a highly aggressive human breast cancer cell line, namely MDA-MB-231, as revealed by MTT and cell migration assays, and also cell imaging performed under laser scanning confocal microscope (LSCM). Thus, a proof of concept for developing a multi-drug delivery system derived from a metallovesicle for delivering an anti-cancer drug to cancer cells is demonstrated for the first time.

A dual drug-based hyperbranched polymer with methotrexate and chlorambucil moieties for synergistic cancer chemotherapy

Dual drug-based hyperbranched polymer micelles simultaneously containing methotrexate and chlorambucil were constructed for synergistic cancer chemotherapy.

Architecture transition of supramolecular polymers through hierarchical self-assembly: from supramolecular polymers to fluorescent materials

A new supramolecular crosslinked polymer and a gel with excellent self-repairing capability were prepared by double host–guest interactions.

Synthesis and direct assembly of linear–dendritic copolymers via CuAAC click polymerization-induced self-assembly (CPISA)

A one-pot method was developed for in situ preparation of linear–dendritic copolymer assemblies via click polymerization-induced self-assembly (CPISA).

Water-soluble polyglycerol-dendronized poly(norbornene)s with functional side-chains

High molecular weight polyglycerol-dendronized poly(norbornene)s (PGD-PNBs) were prepared via ring-opening metathesis polymerization of norbornene monomers containing amine functional groups on the side-chains followed by dendron growth from the olefins of PNB backbones using iterative dihydroxylation and allylation. The fourth-generation PGD-PNB with a degree of polymerization of ca. 500 is thus functionalized with 16 peripheral hydroxyl groups as well as a single amine on each repeat unit of the PNB backbone. Furthermore, the amine functionality could be used to install hydrophobic fluorophores such as coumarin and pyrene, thereby obtaining the final PGD-PNB structures which are highly water-soluble and fluorescent.

Nanocrystal Encapsulation, Release and Application Based on pH-Sensitive Covalent Dynamic Hyperbranched Polymers

A new strategy for nanocrystal encapsulation, release and application based on pH-sensitive covalent dynamic hyperbranched polymers is described. The covalent dynamic hyperbranched polymers, with multi-arm hydrophobic chains and a hydrophilic hyperbranched poly(amidoamine) (HPAMAM) core connected with pH-sensitive imine bonds (HPAMAM–DA), could encapsulate CdTe quantum dots (QDs) and Au nanoparticles (NPs). Benefiting from its pH response property, CdTe QDs and Au NPs encapsulated by HPAMAM–DA could be released to aqueous phase after imine hydrolysis. The released CdTe/HPAMAM and Au/HPAMAM nanocomposites exhibited excellent biological imaging behavior and high catalytic activities on p-nitrophenol hydrogenation, respectively.

Fluorescent Supramolecular Assembly with Coronene Centers for Controlled DNA Condensation and Drug Delivery

A multifunctional supramolecular assembly was successfully constructed by the host-guest complexation of doubly positively charged adamantane (ADA) with β-CD-modified hexabenzocoronene and the π-stacking of coronene with mitoxantrone, which was characterized by transmission electron microscopy, scanning electron microscopy, dynamic light-scattering, and zeta potential experiments. Possessing a small size and rigid backbone coronene center, the water-soluble biocompatible supramolecular assembly has intracellular imaging abilities. Moreover, after the ester group of ADA was hydrolyzed into a carboxyl group, the positively charged quaternary amine strand converted into a zwitterion structure, which realized the controlled plasmid DNA binding and release. Besides, the cytotoxicity experiments showed that the supramolecular assembly possesses slightly lower toxicity and a slightly higher anticancer activity than free drug. We believe that this work might present a convenient method for synergetic cancer treatment.

Dynamic Adaptive Two-Dimensional Supramolecular Assemblies for On-Demand Filtration

The construction of synthetic two-dimensional (2D) materials designates a pathway to the versatile chemical functionality by spatial control. However, current 2D materials with intelligence of stimuli-responsibility and adaptiveness have been unfledged. The approach reported here uses a supramolecular strategy to achieve the dynamic non-covalent self-assembly of a rationally designed small molecule monomer, producing large-area, ultra-thin, porous 2D supramolecular assemblies, which are solution-processable in aqueous solution. Importantly, the 2D supramolecular assemblies exhibit distinct adaptive capability to automatically regulate their network density and pore diameters in response to environmental temperature change, which could be developed into an "on-demand" filtration application for nanoparticles. Meanwhile, the 2D supramolecular assemblies can also perform reversible degradation/reformation by photo-irradiation. Our results not only show the simplicity, reliability, and effectiveness of supramolecular strategies in the construction of 2D materials with practical sizes, but also push the dynamic alterability and adaptation features from supramolecular assemblies toward 2D materials.

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2D supramolecular assemblies combine large area, nano-thickness and water solubility

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The 2D assemblies can perform reversible expansion/contraction to tune pore sizes

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The 2D material can be used for on-demand nanoparticles filtration

Multiple-Responsive Dendronized Hyperbranched Polymers

By combining topological structures of hyperbranched polymers with dendronized polymers, a series of hyperbranched poly(acylhydrazone)s pendanted with 3-fold branched dendritic oligoethylene glycol (OEG) units were efficiently prepared through A2 + B3 polycondensation. The constituents of these dendritic polymers can be mediated through dynamic covalent acylhydrazones. Owing to the dense OEG pendants, these dendronized hyperbranched polymers are biocompatible and thermoresponsive, and their cloud points (T cps) can be modulated by the branched architecture, solution pH, and addition of a third component. Cell viability in the presence of these hyperbranched poly(acylhydrazone)s can be maintained above 80%. Based on the unique dendritic architecture with rich acylhydrazine groups, dynamic hydrogels cross-linked via acylhydrazone linkages with good mechanical property were prepared, which inherit the characteristic thermoresponsive behavior of the polymer precursors and also show remarkable self-healing properties. This novel kind of topological polymers and their corresponding hydrogels with dynamic and multiple smart properties may have promising applications as biomaterials.

Self-Assembly of Spherical Organic Molecules to Form Hollow Vesicular Structures in Water for Encapsulation of an Anticancer Drug and Its Release

Developing hierarchical supramolecular structures is important for better understanding of various biological functions and possibly generating new materials for biomedical applications. Herein, we report the first examples of functional vesicles derived from cationic spherical organic molecules (C₁ -C₃ ) which were readily synthesized by reacting a C₃ -symmetric tris-benzimmidazole derivative (possessing a 1,3,5-ethyl substituted aromatic core) with 1,3,5-substituted tris-bromomethyl benzene derivatives. Vesicle formation by C₁ -C₃ was probed by high-resolution microscopy (TEM and AFM), dynamic light scattering (DLS) and fluorescence microscopic imaging of calcein-loaded vesicles. One of the vesicles [Vesicle(C₃ )] displayed the ability to load the anticancer drug doxorubicin (DOX). The drug was subsequently released from DOX@Vesicle(C₃ ) in a stimuli-responsive manner in presence of the well-known vesicle destroyer Triton X-100, as revealed by in vitro cell migration assay carried out on a highly aggressive human breast cancer cell line (MDA-MB-231).

Pillararene-based supramolecular polymers

Pillararenes, as a new type of macrocyclic hosts, possess columnar structures and electron-rich cavities. Pillararenes not only recognize suitable cations, but also bind many neutral molecules. Due to the easy modification of pillararenes, various functional groups can be conveniently attached to the rim of pillararenes to provide suitable interaction sites, and the modified pillararenes even bind anionic guests. Thus, pillararenes and their derivatives have presented intriguing and unique host-guest recognition nature in the past few years, which make them ideal building blocks for the preparation of supramolecular polymers. Pillararene-based supramolecular polymers (PSPs) not only possess many merits of traditional covalent polymers but also have many specific properties, such as self-reparability, degradability, and self-adaptation. This feature paper gives an overview of the preparation of PSPs and covers recent research advance and future trends of pillararene-based host-guest pairs, assembly methods, topological architectures, stimuli-responsiveness, and functional features. We expect that the review will be helpful to researchers working in the fields of supramolecular chemistry and polymer science.