Controlled Self-Assembly of Multiple-Responsive Superamphiphilc Polymers Based on Host-Guest Inclusions of a Modified PEG with β-Cyclodextrin

Polymeric nanostructures based on azobenzene and their biomedical applications: synthesis, self-assembly and stimuli-responsiveness

Amphiphilic polymers can self-assemble to form nanoparticles with different structures under suitable conditions. Polymer nanoparticles functionalized with aromatic azo groups are endowed with photo-responsive properties. In recent years, a variety of photoresponsive polymers and nanoparticles have been developed based on azobenzene, using different molecular design strategies and synthetic routes. This article reviews the progress of this rapidly developing research field, focusing on the structure, synthesis, assembly and response of photo-responsive polymer assemblies. According to the molecular structure, photo-responsive polymers can be divided into linear polymers containing azobenzene in a side chain, linear polymers containing azobenzene in the main chain, linear polymers containing azobenzene in an end group, branched polymers containing azobenzene and supramolecular polymers containing azobenzene. These systems have broad biomedical application prospects in the field of drug delivery and imaging applications.

Glutathione sensitive vesicles prepared from supramolecular amphiphiles

Glutathione (GSH) sensitive vesicles were prepared by the self-assembly of amphiphilic inclusion complexes. These novel chemically sensitive supramolecular amphiphiles are anticipated to have applications in drug delivery; the nanocarriers can protect the encapsulated cargo and release it via triggered degradation in high concentrations of GSH. Additionally, the sensitivity of the vesicles to GSH indicates that the dynamic covalent disulfide bond at the vesicle surface can be used for post-modification of the nanocarrier via a thiol-disulfide exchange, a strategy that can be exploited to introduce targeting moieties to increase treatment specificity. Supramolecular amphiphiles containing a dynamic covalent disulfide bond were prepared via the host-guest inclusion complexes between alkylated β-cyclodextrin (β-CD) hosts and adamantane terminated polyethylene glycol derivatives. The significant difference between the critical micelle concentrations of the supramolecular amphiphiles and the individual host and guest components confirmed that a unique supramolecular amphiphile was formed. Fluorescence experiments and dynamic light scattering (DLS) revealed that the supramolecular amphiphiles self-assembled into vesicles of 130 nm diameter which were stable for 8 months. Degradation of the vesicles after incubation with GSH was monitored using DLS and by the release of encapsulated 5,6-carboxyfluorescein (CF), observed by an increase in fluorescence intensity. Degradation of the nanocarrier was faster at intracellular GSH concentrations than at extracellular GSH concentrations.

Force-Induced Self-Assembly of Supramolecular Modified Mica Nanosheets for Ductile and Heat-Resistant Mica Papers

Mica is a naturally abundant layered silicate mineral that has higher strength than other layered silicate minerals, but its inherent brittleness limits its application in some fields. In this work, mica was ultrasonically exfoliated into a single-layered nanomaterial after thermal activation, acidification, sodium replacement, and cetyltrimethylammonium bromide (CTAB) intercalation and then modified with ureido-pyrimidinone (UPy)-based PEG chains. Vacuum-assisted self-assembly was used to construct supramolecularly modified single-layered mica into bulk materials, in which the mica nanosheets were stacked into mica paper. The reversible quadruple hydrogen-bonded UPy moieties provided a high binding constant and significantly improved the strength and toughness of the obtained mica paper. These force-induced assembled mica papers showed significantly improved tensile strength and toughness compared with pure mica paper and simultaneously maintained the heat resistance of the mica materials, which may be good candidates for the substrates of flexible sensors working at higher temperatures.

Near-Infrared Light-Steered Graphene Aerogel Micromotor with High Speed and Precise Navigation for Active Transport and Microassembly

Fuel-free light-driven micromotors have attracted increasing attention since the advantages of reversible, noninvasive, and remote maneuver are on demand with excellent spatial and temporal resolution. However, they suffer from a challenging bottleneck of the rather modest motion speed, which hinders their applications, needing to overcome the water flow movement in environmental water. Herein, we demonstrate a near-infrared (NIR) light-steered, precise navigation-controlled micromotor based on a reduced graphene oxide aerogel microsphere (RGOAM), which possesses an isotropic structure and is easily prepared by a one-step electrospray approach other than conventional light-propelled micromotors with the Janus structure. Benefiting from the ultralight weight of the aerogel and lesser fluid resistance on the water surface, the RGOAM motors show a higher motion speed (up to 17.60 mm/s) than that in the published literature, letting it overcome counterflow. Taking advantage of the photothermal conversion capacity of the RGOAM under an asymmetric light field, it is capable of moving both on the water driven by the Marangoni effect and under the water via light-manipulated density change. The motion direction and speed on water as well as the "start/stop" state can be precisely steered by NIR light even in a complicated maze. Due to its strong adsorption and loading capacity, the RGOAM can be applied for active loading-transport-release of dyes on demand as well as micropart assembling and shaping. Our work provides a strategy to achieve high speed, precise navigation control, and functional extensibility simultaneously for micromotors, which may offer considerable promise for the broad biomedical and environmental applications.

Host-Guest Complexation of Perethylated Pillar[6]arene toward Ferrocene Derivatives Both in Solution and Solid State: Different Binding Modes Induced by Minor Structural Changes of Guests

Herein, novel host-guest properties between perethylated pillar[6]arene and four kinds of ferrocene derivatives were fully investigated. NMR titrations, 2D NOESY NMR spectroscopy, and ESI-MS are used to confirm that they indeed formed stable inclusion complexes. Two precious single-crystal structures were obtained and showed that ferrocene derivatives with different chemical structures exhibit different binding modes with perethylated pillar[6]arenes.

Fabrication of a β-cyclodextrin-based self-assembly containing a redox-responsive ferrocene

The current research involves fabrication of a redox-responsive self-assembly system based on a ferrocene (Fc)-containing β-cyclodextrin (β-CD) derivative (βCD-EG-Fc). βCD-EG-Fc was synthesized, and its redox-sensitive self-assembly behavior was investigated using various techniques. On the basis of the intermolecular host-guest recognition between the β-CD group and the Fc moiety, βCD-EG-Fc primarily formed network-like structures and then vesicles following aging for a specified time. The formation of these structures was primarily driven by hydrogen bonding. Conversely, the oxidized molecules (βCD-EG-Fc⁺) self-assembled into cationic vesicles with the absence of host-guest complexation. Upon controlling the oxidation and reduction of Fc/Fc⁺, reversible aggregate transformation was achieved. The current study resulted in a deeper understanding of β-CD/Fc redox-responsive self-assemblies and contributed to the development of a single-component host-guest inclusion model.

Cyclodextrin-Based Multistimuli-Responsive Supramolecular Assemblies and Their Biological Functions

Cyclodextrins (CDs), which are a class of cyclic oligosaccharides extracted from the enzymatic degradation of starch, are often utilized in molecular recognition and assembly constructs, primarily via host-guest interactions in water. In this review, recent progress in CD-based supramolecular nanoassemblies that are sensitive to chemical, biological, and physical stimuli is updated and reviewed, and intriguing examples of the biological functions of these nanoassemblies are presented, including pH- and redox-responsive drug and gene delivery, enzyme-activated specific cargo release, photoswitchable morphological interconversion, microtubular aggregation, and cell-cell communication, as well as a geomagnetism-controlled nanosystem for the suppression of tumor invasion and metastasis. Moreover, future perspectives and challenges in the fabrication of intelligent CD-based biofunctional materials are also discussed at the end of this review, which is expected to promote the translational development of these nanomaterials in the biomedical field.

Cascade-Reaction-Based Nanodrug for Combined Chemo/Starvation/Chemodynamic Therapy against Multidrug-Resistant Tumors

We report a chemo/starvation/chemodynamic trimodal combination therapy to combat multidrug-resistant (MDR) tumors by developing a ferrocene-containing nanovesicle (FcNV), which encapsulates glucose oxidase (GOx) in the hydrophilic core and coordinates cisplatin (Pt) in the hydrophobic layer (GOx&Pt@FcNV). Contrasting with other reported multimodal combination therapies, the new nanodrug (GOx&Pt@FcNV) relies on cascade reactions to drastically increase the overall effectiveness against MDR tumors. Specifically, Pt blocks deoxyribonucleic acid replication and activates hydrogen peroxide (H₂O₂) generation for chemotherapy; GOx consumes glucose to produce H₂O₂ and gluconic acid for starvation therapy; and all H₂O₂ products are catalyzed by ferrous ions decomposed from ferrocene to generate the highly toxic hydroxyl radicals (^•OH) for chemodynamic therapy. The in vitro studies reveal that GOx&Pt@FcNV exhibits a highly efficient killing effect against various MDR tumor cells. The in vivo studies of double-tumor-bearing nude mice demonstrate that the tumor inhibitory rates (TIRs) of GOx&Pt@FcNV against cisplatin-resistant A549/DDP are 8.1 times and 3.3 times higher than those of Pt and Pt@FcNV, respectively; they are also 8.6 times and 4.3 times higher than Pt and Pt@FcNV against adriamycin-resistant MCF-7/ADR, respectively. This nanodrug with endogenous stimuli-activated cascade reactions offers a reference for the design of effective trimodal combination therapies to combat MDR tumors.

Dual stimuli-responsive nano-structure transition of three-arm branched amphiphilic polymers containing ferrocene (Fc) and azobenzene (Azo) moieties in aqueous solution

Amphiphilic polymers can self-assemble into various nanostructures in solution, which can find applications in many fields such as nanotechnology, drug delivery, and template synthesis. Herein, we report the controlled self-assembly and dual stimuli-responsive nanostructure transition of a class of three-arm branched amphiphilic polymers (AzoFcPEO) containing ferrocene (Fc) and azobenzene (Azo) moieties in aqueous solution. These amphiphilic polymers were synthesized by an esterification reaction of a variety of polyethylene oxide methyl ethers (Me-PEO) with 3-(6-ferrocenyhexyloxyl)-5-(6-azobenzenehexyloxy) benzoic acid. Both the isomerization of Azo and redox of Fc moieties can respectively change the amphiphilicity of these polymers to different degrees. Consequently, these amphiphilic polymers in aqueous solution can self-assemble into various nanostructures, such as spherical micelle, worm-like micelle, spherical compound micelle, rod-like compound micelle and vesicle dependent on the PEO molecular weight, applied stimuli, and polymer concentration. This work can offer tremendous possibilities not only for the fundamental science of the controlled self-assembly but also for establishing a suitable method for regulating the nanostructures of amphiphilic polymers in aqueous solution.

Morphology-tunable and pH-responsive supramolecular self-assemblies based on AB2-type host-guest-conjugated amphiphilic molecules for controlled drug delivery

Although stimuli-responsive supramolecular self-assemblies have been constructed, the controlled drug delivery induced by morphology transitions of these supramolecular self-assemblies on the basis of host-guest-conjugated monomers (HGCMs) are few reported. In this paper, the self-assembly behaviors of AB2-type HGCMs, e.g., β-cyclodextrin-benzimidazole2 (β-CD-BM2), were investigated at neutral and acidic pH conditions, respectively. Specifically, β-CD-BM2 first self-assembled into fan-shaped supramolecular self-assemblies with a hydrodynamic diameter of 163 nm at neutral pH, whereas they were further dissociated into spherical supramolecular self-assemblies with a size of 52 nm under acidic conditions. This morphology transition process was utilized to conduct a two-stage DOX delivery under neutral and acidic pH. Basic cell experiments demonstrated that the drug-loaded β-CD-BM2-based supramolecular self-assemblies with varied morphology could inhibit cancer cell proliferation, indicating their potential application in the field of drug delivery.

Sensitive Detection of Serum Creatinine Based on β-Cyclodextrin-Ferrocenylmethanol Modified Screen-printed Electrode

Ferrocenylmethanol (Fc-OH) is included in β-cyclodextrin (β-CD) to form the β-CD-Fc-OH complex by host-guest supramolecular interaction. β-CD dissociates from the β-CD-Fc-OH complex due to the conversion of Fc-OH to Fc⁺-OH under a stimulus of oxidant. In our study, Fc-OH is oxidized after a series of enzymatic reactions of creatinine, which blocks the other means for oxidation of Fc-OH. And the background noise is reduced for testing for serum creatinine (sCr). The chronoamperometry signal for creatinine (with a constant potential -0.3 V vs. Ag/AgCl) increases linearly in the 1 - 1000 μM range, with a limit of detection as low as 0.5 μM. The amperometric potential of -0.3 V greatly prevents the interference of various redox substances in serum. The biosensor was used to test 120 clinical specimens and the results showed a linear correlation with the biochemical analyzer (R² = 0.9885). The biosensor could be applied to clinical trials and offers good prospects for clinical sCr detection.

Complex systems that incorporate cyclodextrins to get materials for some specific applications

Cyclodextrins (CDs) are a family of biodegradable cyclic hydrocarbons composed of α-(1,4) linked glucopyranose subunits, the more common containing 6, 7 or 8 glucose units are named α, β and γ-cyclodextrins respectively. Since the discovery of CDs, they have attracted interest among scientists and the first studies were about the properties of the native compounds and in particular their use as catalysts of organic reactions. Characteristics features of different types of cyclodextrins stimulated investigation in different areas of research, due to its non-toxic and non-inmunogenic properties and also to the development of an improved industrial production. In this way, many materials with important properties have been developed. This mini-review will focus on chemical systems that use cyclodextrins, whatever linked covalently or mediated by the non covalent interactions, to build complex systems developed mainly during the last five years.

Self-Assembly of Aggregation-Induced-Emission Molecules

The last decade has witnessed rapid developments in aggregation-induced emission (AIE). In contrast to traditional aggregation, which causes luminescence quenching (ACQ), AIE is a reverse phenomenon that allows robust luminescence to be retained in aggregated and solid states. This makes it possible to fabricate various highly efficient luminescent materials, which opens new paradigms in a number of fields, such as imaging, sensing, medical therapy, light harvesting, light-emitting devices, and organic electronic devices. Of the various important features of AIE molecules, their self-assembly behavior is very attractive because the formation of a well-defined emissive nanostructure may lead to advanced applications in diverse fields. However, due to the nonplanar topology of AIEgens, it is not easy for them to self-assemble into well-defined structures. To date, some strategies have been proposed to achieve the self-assembly of AIEgens. Herein, we summarize the most recent approaches for the self-assembly of AIE molecules. These approaches can be sorted into two classes: 1) covalent molecular design and 2) noncovalent supramolecular interactions. We hope this will inspire more excellent work in the field of AIE.

Construction of Crowning β-cyclodextrin with Temperature Response and Efficient Properties of Host-Guest Inclusion

Promoting a drug inclusion proportion in hydrophobic cavity of β-cyclodextrin using simple methods is a highly ambitious task. Herein, we report the crowning β-cyclodextrins formed by intramolecular hydrogen bonding interaction, which has greatly prolonged the cavity depth of β-cyclodextrin, and therefore further efficiently improved the inclusion proportion to complex drug molecule (vitamin E). Furthermore, the self-assembly behaviors, controllable release, and antioxidant properties of vitamin E embedded into the cavity of crowning β-cyclodextrins was investigated, and host-guest inclusions exhibited temperature-responsive controlled release, excellent antioxidant activity, and photostability.

A Translucent Nanocomposite with Liquid Inclusions of a Responsive Nanoparticle Dispersion

Active nanocomposites are created with liquid inclusions that contain plasmonic gold nanoparticles inside a polymeric matrix. The alkylthiol-coated gold particles are designed to reversible agglomerate at certain temperatures, which changes the plasmonic coupling and thus optical properties. It is found that particles confined to the liquid inclusions inside the active composite retain this capability and cause macroscopic, temperature-dependent color change of the solid. The transition is fully reversible for at least 100 times and tunable in temperature via particle size and ligand. This method is suitable to "package" responsive dispersion in solid composites to exploit their dynamic properties in materials.