Dual-Responsive Bola-Type Supra-Amphiphile Constructed from Water-Soluble Pillar[5]arene and Naphthalimide-Containing Amphiphile for Intracellular Drug Delivery

Pillararene-Based Stimuli-Responsive Supramolecular Delivery Systems for Cancer Therapy

Cancer poses a significant challenge to global public health, seriously threatening human health and life. Although various therapeutic strategies, such as chemotherapy (CT), radiotherapy, phototherapy, and starvation therapy, are applied to cancer treatment, their limited therapeutic effect, severe side effects, and unsatisfactory drug release behavior need to be carefully considered. Thus, there is an urgent need to develop efficient drug delivery strategies for improving cancer treatment efficacy and realizing on-demand drug delivery. Notably, pillararenes, as an emerging class of supramolecular macrocycles, possess unique properties of highly tunable structures, superior host-guest chemistry, facile modification, and good biocompatibility, which are widely used in cancer therapy to achieve controllable drug release and reduce the toxic side effects on normal tissues under various internal/external stimuli conditions. This review summarizes the recent advance of stimuli-responsive supramolecular delivery systems (SDSs) based on pillararenes for tumor therapy from the perspectives of different assembly methods and hybrid materials, including molecular-scale SDSs, supramolecular nano self-assembly delivery systems, and nanohybrid SDSs. Moreover, the prospects and critical challenges of stimuli-responsive SDSs based on pillararenes for cancer therapy are also discussed.

Self-Assembly of Amphiphilic PDI and NDI Derivatives with Opposite Thermoresponsive Fluorescent Behaviors in Aqueous Solution

This work presents a study of the thermally induced aggregation of perylene diimide (PDI) and naphthalene diimide (NDI) derivatives modified with oligo ethylene glycol (OEG) chains in aqueous solution. Water-soluble and flexible OEG side chains were introduced into the π-core of glutamate-modified NDI and PDI structures, and the aggregation process was modulated by heating or cooling in water. Interestingly, a rare opposite temperature response of fluorescent behavior from the two amphiphilic chromophores was revealed, in which the PDI exhibited fluorescent enhancement, while fluorescent quenching upon temperature increase was observed from the NDI assembly. The mechanism of thermally induced aggregation is clearly explained by studies with various spectroscopic techniques including UV-visible, fluorescence, 1H NMR, 2D NMR spectroscopy, and SEM observation as well as control experiments operated in DMSO solution. It is found that although similar J-aggregates were formed by both amphiphilic chromophores in aqueous solution, the temperature response of the aggregates to temperature was opposite. The degree of PDI aggregation decreased, while that of NDI increased upon temperature rising. This research paves a valuable way for understanding the complicated supramolecular behaviors of amphiphilic chromophores.

Dual-Responsive Drug-Delivery System Based on PEG-Functionalized Pillararenes Containing Disulfide and Amido Bonds for Cancer Theranostics

The construction of a smart drug-delivery system based on amphiphilic pillararenes with multiple responsiveness properties has become an important way to improve the efficacy of tumor chemotherapy. Here, a new PEG-functionalized pillararene (EtP5-SS-PEG) containing disulfide and amido bonds was designed and synthesized, which has been used to construct a novel supramolecular nanocarrier through a host-guest interaction with a perylene diimide derivative (PDI-2NH4 ) and their supramolecular self-assembly. This nanocarrier showed good drug loading capability, and dual stimulus responsiveness to enzyme and GSH (glutathione). After loading of doxorubicin (DOX), the prepared nanodrugs displayed efficient DOX release and outstanding cancer theranostics ability.

The design strategy for pillararene based active targeted drug delivery systems

Pillararenes have columnar architectures with electron-rich cavities to endow themselves with unique host-guest complexation capability. Easy structural modifiability facilitates them to be used in many applications. Currently, pillararene based drug delivery systems (DDSs) have been developed as a powerful tool for precise diagnosis and treatment of cancer. Various functional guest molecules could be integrated with pillararenes to construct nanomaterials for cancer chemotherapy, phototherapy and chemodynamic therapy. In order to improve cancer therapy efficacy, active targeted DDSs have become particularly important. Benefiting from the good host-guest properties and structural variability of pillararenes, tumor targeting groups could be easily introduced into pillararene based DDSs to realize precise drug delivery at tumor sites. In this feature article, we provide a comprehensive summary of the present design strategy for pillararene based active targeted DDSs, which can be classified into three types namely host-guest complexation, charge reversal and targeted group modified pillararenes. Some important examples are selected to for a detailed discussion on their respective strengths and weaknesses.

Stimuli-Responsive Codelivery System Self-Assembled from in Situ Dynamic Covalent Reaction of Macrocyclic Disulfides for Cancer Magnetic Resonance Imaging and Chemotherapy

Supramolecular self-assembly has gained increasing attention to construct multicomponent drug delivery systems for cancer diagnosis and therapy. Despite that these self-assembled nanosystems present surprising properties beyond that of each subcomponent, the spontaneous nature of co-self-assembly causes significant difficulties in control of the synthesis process and consequently leads to unsatisfactory influences in downstream applications. Hence, we utlized an in situ dynamic covalent reaction based on thiol-disulfide exchange to slowly produce disulfide macrocycles, which subsequently triggered the co-self-assembly of an anticancer drug (doxorubicin, DOX) and a magnetic resonance imaging (MRI) contrast agent of ultrasmall iron oxide nanoparticles (IO NPs). It showed concentration regulation of macrocyclic disulfides, DOX, and IO NPs by a dynamic covalent self-assembly (DCS) strategy, resulting in a stable codelivery nanosystem with high drug loading efficiency of 37.36%. More importantly, disulfide macrocycles in the codelivery system could be reduced and broken by glutathione (GSH) in tumor cells, thus leading to disassembly of nanostructures and intellgent release of drugs. These stimuli-responsive performances have been investigated via morphologies and molecular structures, revealing greatly enhanced dual-modal MRI abilities and smart drug release under the trigger of GSH. Moreover, the codelivery system conjugated with a targeting molecule of cyclic Arg-Gly-Asp (cRGD) exhibited significant biocompatibility, MR imaging, and chemotherapeutic anticancer effect in vitro and in vivo. These results indicated that in situ dynamic covalent chemistry enhanced the control over co-self-assembly and paved the way to develop more potential drug delivery systems.

Using host-guest interactions at the interface of quantum dots to load drug molecules for biocompatible, safe, and effective chemo-photodynamic therapy against cancer

Combining photodynamic therapy (PDT) and chemotherapy (CHT) by loading an anti-cancer drug and a photosensitizer (PS) into the same delivery nanosystem has been proposed as an effective approach to achieve synergistic effects for a safe cancer treatment. However, exploring an ideal delivery nanosystem has been challenging, because the noncovalent interactions must be maintained between the multiple components to produce a stable yet responsive nanostructure that takes into account the encapsulation of drug molecules. We addressed this issue by engineering the interfacial interaction between Ag₂S quantum dots (QDs) using a pillararene derivative to direct the co-self-assembly of the entire system. The high surface area-to-volume ratio of the Ag₂S QDs provided ample hydrophobic space to accommodate the anti-drug molecule doxrubicine. Moreover, Ag₂S QDs served as PSs triggered by 808 nm near-infrared (NIR) light and also as carriers for high-efficiency delivery of drug molecules to the tumor site. Drug release experiments showed smart drug release under the acidic microenvironments (pH 5.5) in tumor cells. Additionally, the Ag₂S QDs demonstrated outstanding PDT ability under NIR light, as confirmed by extracellular and intracellular reactive oxygen species generation. Significant treatment efficacy of the chemo-photodynamic synergistic therapy for cancer using the co-delivery system was demonstrated via in vitro and in vivo studies. These findings suggest that our system offers intelligent control of CHT and PDT, which will provide a promising strategy for constructing hybrid systems with synergistic effects for advanced applications in biomedicine, catalysis, and optoelectronics.

Orthogonal Design of Supramolecular Prodrug Vesicles via Water-Soluble Pillar[5]arene and Betulinic Acid Derivative for Dual Chemotherapy

Supramolecular prodrug vesicles with efficient property for dual chemotherapy have been successfully constructed based on the orthogonal self-assembly between a water-soluble pillar[5]arene host (WP5) and a betulinic acid guest (BA-D) as well as doxorubicin (DOX). Under the acidic microenvironment of cancer cells, both the encapsulated anticancer drug DOX and prodrug BA-D can be effectively released from DOX-loaded WP5⊃BA-D prodrug vesicles for combinational chemotherapy. Furthermore, bioexperiments indicate that DOX-loaded prodrug vesicles can obviously enhance the anticancer efficiency based on the cooperative effect of DOX and BA-D, while remarkably reducing the systematic toxicity in tumor-mice, displaying great potential applications in combinational chemotherapy for cancer treatments.

A dendritic polyamidoamine supramolecular system composed of pillar[5]arene and azobenzene for targeting drug-resistant colon cancer

Fusobacterium nucleatum caused drug-resistant around tumor sites often leads to the failure of chemotherapy during colorectal cancer (CRC) treatment. Multifunctional cationic quaternary ammonium materials have been widely used as broad-spectrum antibacterial agents in antibacterial and anticancer fields. Herein, we design a smart supramolecular quaternary ammonium nanoparticle, namely quaternary ammonium PAMAM-AZO@CP[5]A (Q-P-A@CP[5]A), consisting of azobenzene (AZO)-conjugated dendritic cationic quaternary ammonium polyamidoamine (PAMAM) as the core and carboxylatopillar[5]arene (CP[5]A)-based switch, for antibacterial and anti-CRC therapies. The quaternary ammonium-PAMAM-AZO (Q-P-A) core endows the supramolecular system with enhanced antibacterial and anticancer properties. -N⁺CH₃ groups on the surface of Q-P-A are accommodated in the CP[5]A cavity under normal conditions, which significantly improves the biocompatibility of Q-P-A@CP[5]A. Meanwhile, the CP[5]A host can be detached from -N⁺CH₃ groups under pathological conditions, achieving efficient antibacterial and antitumor therapies. Furthermore, azoreductase in the tumor site can break the -NN- bonds of AZO in Q-P-A@CP[5]A, leading to the morphology recovery of supramolecular nanoparticles and CRC therapy through inducing cell membrane rupture. Both in vitro and in vivo experiments demonstrate that Q-P-A@CP[5]A possesses good biocompatibility, excellent antibacterial effect, and CRC treatment capability with negligible side effects. This supramolecular quaternary ammonium system provides an effective treatment method to overcome chemotherapy-resistant cancer caused by bacteria.

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.

Promoting the Spreading of Droplets on a Superhydrophobic Surface by Supramolecular Amphiphilic Complex-Based Host-Guest Chemistry

The spreading of pesticide droplets on the surface of superhydrophobic plants is an important process, which can prevent the inadequate retention such as bouncing, splashing, and drifting, thereby improving the efficiency of pesticide utilization and reducing soil and groundwater pollution. Herein, we report an approach to fabricate a supramolecular amphiphilic system that significantly contributes to this issue. The hydrophilic amino-pillar[5]arene was synthesized, which could form vesicles with the hydrophobic long-chain guest. This host-guest complex decreased the surface tension, which greatly promotes the spreading of droplets. This study provides a new strategy for prolonging pesticide retention and reducing pesticide loss.

Water compatible supramolecular polymers: recent progress

Water compatible supramolecular polymers (WCSPs) combine aqueous compatibility with the reversibility and environmental responsiveness of supramolecular polymers. WCSPs have seen application across a number of fields, including stimuli-responsive materials, healable materials, and drug delivery, and are attracting increasing attention from the design, synthesis, and materials perspectives. In this review, we summarize the chemistry of WCSPs from 2016 to mid-2021. For the sake of discussion, we divide WCSPs into five categories based on the core supramolecular approaches at play, namely hydrogen-bonding arrays, electrostatic interactions, large π-conjugated subunits, host-guest interactions, and peptide-based systems, respectively. We discuss both synthesis and polymer structure, as well as the underlying design expectations. The goal of this overview is to deepen our understanding of the strategies that have been exploited to prepare WCSPs, as well as their properties and uses. Thus, a section devoted to potential applications is included in this review.

Understanding functional group and assembly dynamics in temperature responsive systems leads to design principles for enzyme responsive assemblies

Understanding the molecular rules behind the dynamics of supramolecular assemblies is fundamentally important for the rational design of responsive assemblies with tunable properties. Herein, we report that the dynamics of temperature-sensitive supramolecular assemblies is not only affected by the dehydration of oligoethylene glycol (OEG) motifs, but also by the thermally-promoted molecular motions. These counteracting features set up a dynamics transition point (DTP) that can be modulated with subtle variations in a small hydrophobic patch on the hydrophilic face of the amphiphilic assembly. Understanding the structural factors that control the dynamics of the assemblies leads to rational design of enzyme-responsive assemblies with tunable temperature responsive profiles.

High-Efficiency Synergistic Effect of Supramolecular Nanoparticles Based on Cyclodextrin Prodrug on Cancer Therapy

Novel cyclodextrin-prodrug supramolecular nanoparticles (NPs) with cooperative-enhancing cancer therapy were constructed from a reduction-sensitive disulfide bond-linked permethyl-β-cyclodextrin-camptothecin prodrug, water-soluble adamantane-porphyrin photosensitizer, and hyaluronic acid grafted by triphenylphosphine and β-cyclodextrin through an orthogonal host-guest recognition strategy, displaying uniform nanoparticles with a diameter around 100 nm as revealed by dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Compared with 293T normal cells, the supramolecular NPs could be easily taken up by mitochondria of A549 cancer cells, then release the active anticancer drug camptothecin (CPT) in situ via the cleavage of the disulfide bond by the overexpressed glutathione, and could initiate the effective singlet oxygen (¹O₂) generation by porphyrin under light irradiation, ultimately resulting in severe mitochondrial dysfunction and a rising cell death rate with increasing micromolar concentration of NPs. These multicomponent supramolecular nanoassemblies effectively combined the two-step synergistic chemo-photodynamic therapy of reduction-release of CPT and light-triggered ¹O₂ generation within cancer cells presenting the synergistic effect of supramolecular nanoparticles on cancer therapy, which provide a new approach for efficient step-by-step cancer therapy.

Nanomaterials with Supramolecular Assembly Based on AIE Luminogens for Theranostic Applications

One of the major pursuits of biomedical science is to develop advanced strategies for theranostics, which is expected to be an effective approach for achieving the transition from conventional medicine to precision medicine. Supramolecular assembly can serve as a powerful tool in the development of nanotheranostics with accurate imaging of tumors and real-time monitoring of the therapeutic process upon the incorporation of aggregation-induced emission (AIE) ability. AIE luminogens (AIEgens) will not only enable fluorescence imaging but will also aid in improving the efficacy of therapies. Furthermore, the fluorescent signals and therapeutic performance of these nanomaterials can be manipulated precisely owing to the reversible and stimuli-responsive characteristics of the supramolecular systems. Inspired by rapid advances in this field, recent research conducted on nanotheranostics with the AIE effect based on supramolecular assembly is summarized. Here, three representative strategies for supramolecular nanomaterials are presented as follows: a) supramolecular self-assembly of AIEgens, b) the loading of AIEgens within nanocarriers with supramolecular assembly, and c) supramolecular macrocycle-guided assembly via host-guest interactions. Meanwhile, the diverse applications of such nanomaterials in diagnostics and therapeutics have also been discussed in detail. Finally, the challenges of this field are listed in this review.

Supramolecular Vesicles Based on Amphiphilic Pillar[n]arenes for Smart Nano-Drug Delivery

Supramolecular vesicles are the most popular smart nano-drug delivery systems (SDDs) because of their unique cavities, which have high loading carrying capacity and controlled-release action in response to specific stimuli. These vesicles are constructed from amphiphilic molecules via host-guest complexation, typically with targeted stimuli-responsive units, which are particularly important in biotechnology and biomedicine applications. Amphiphilic pillar[n]arenes, which are novel and functional macrocyclic host molecules, have been widely used to construct supramolecular vesicles because of their intrinsic rigid and symmetrical structure, electron-rich cavities and excellent properties. In this review, we first explain the synthesis of three types of amphiphilic pillar[n]arenes: neutral, anionic and cationic pillar[n]arenes. Second, we examine supramolecular vesicles composed of amphiphilic pillar[n]arenes recently used for the construction of SDDs. In addition, we describe the prospects for multifunctional amphiphilic pillar[n]arenes, particularly their potential in novel applications.

Towards new nanoporous biomaterials: self-assembly of sulfopillar[5]arenes with vitamin D3 into supramolecular polymers

Novel water-soluble, deca-substituted pillar[5]arenes containing thiasulfate and thiacarboxylate fragments were synthesized and characterized. UV-vis, 2D 1H-1H NOESY and DOSY NMR spectroscopy revealed the ability of pillar[5]arenes containing thiasulfate fragments to form an inclusion complex with cholecalciferol (vitamin D3) in a 1 : 2 ratio (lg Kass = 2.2). Using DLS and SEM it was found that upon concentration and/or evaporation of the solvent, the supramolecular polymer (pillar[5]arene/vitamin D3 (1 : 2)) forms a porous material with an average wall diameter of 53 nm. It was shown that the supramolecular polymer is stable during photolysis by UV radiation (k1 = 1.7 × 10-5 s-1).

Fulleropillar[4]arene: The Synthesis and Complexation Properties

A multihydroquinone ether dialdehyde derivative 2 was incidentally obtained through an unexpected ring opening of pillar[4]arene[1]quinone 1. And the Prato reaction of 2 with [60]fullerene led to [60]fullerene bisadducts, from which trans-4 cyclic regioisomer 3 was isolated and characterized. The fulleropillar[4]arene 3 showed a larger cavity and can accommodate a viologen derivative C₁₂V²⁺ with a much stronger affinity than permethyl pillar[5]arene (MP5) and pillar[4]arene[1]quinone 1.

Copillar[5]arene-rhodamine conjugate as a selective sensor for Hg2+ ions

A new copillar[5]arene-coupled rhodamine probe 1 shows selective sensing of Hg²⁺ ions over a series of metal ions in CH₃CN by exhibiting color change of the solution as well as turn on fluorescence. It also shows interaction with Cu²⁺ by exhibiting different color and spectral change. Tetrabutylammonium iodide distinguishes between Hg²⁺ and Cu²⁺ ions.

Micelles with Cyclic Poly(ε-caprolactone) Moieties: Greater Stability, Larger Drug Loading Capacity, and Slower Degradation Property for Controlled Drug Release

Polymer topology exerts a significant effect on its properties and performance for potential applications. Cyclic topology and its derived structures have been recently shown to outperform conventional linear analogues for drug delivery applications. However, an amphiphilic tadpole-shaped copolymer consisting of a cylic hydrophobic moiety has rarely been explored. For this purpose, a tadpole-shaped amphiphilic diblock copolymer of poly(ethylene oxide)-b-(cyclic poly(ε-caprolactone)) (mPEG-b-cPCL) was synthesized successfully via ring-opening polymerization (ROP) of ε-CL using a mPEG-based macroinitiator with both a hydroxyl and an azide termini and subsequent intrachain Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAc) click cyclization. A comparison study on the self-assembly behaviors, in vitro drug loading and drug release profiles, and degradation properties of the resulting mPEG-b-cPCL (C) with those of the linear counterpart (mPEG-b-PCL, L) revealed that mPEG-b-cPCL micelles are a better formulation than the micelles formed by the linear counterparts in terms of micelle stability, drug loading capacity, and the degradation property. Interestingly, compared to the single degradation of L, C exhibited a slower two-stage degradation process including the topological change from tadpole shape to linear conformation and the subsequent degradation of a linear polymer. This study therefore uncovered the topological effect of a hydrophobic moiety on the properties of the self-assembled micelles and developed a complementary alternative to enhance the micelle stability by introducing a cyclic hydrophobic segment.

Supramolecular nanostructures constructed by rod-coil molecular isomers: effect of rod sequences on molecular assembly

Coil-rod-coil molecules, composed of flexible oligoether chains and conjugated rod blocks, have a well-known ability to produce various nanostructures in bulk and in aqueous solution. Herein we report the synthesis and self-assembly of coil-rod-coil molecules based on the sequence of the rod building block and the type of oligoether coil chain. These molecules consist of conjugated rod segments, which are composed of biphenyl, terphenyl, and acetylenic bonds, with chiral oligoether chains as flexible coil segments. The experimental results imply that the sequence of the rod segments markedly influences the self-assembled nanostructures of coil-rod-coil molecules in the bulk state, and that the type of coil chain strongly affects the morphology of the supramolecular nanoassemblies of these molecules in aqueous solution. In the bulk state, molecules 1a and 1b, which contain biphenyl units connected to the end of the coil segments self-organize into a hexagonal perforated lamellar phase, and oblique columnar and body-centred tetragonal structures, respectively. However, molecules 2a and 2b bearing terphenyl units linked to the end of the coil segments self-assemble into lamellar, hexagonal perforated lamellar and hexagonal columnar structures. In aqueous solution, rod-coil molecular isomers with linear chiral oligoether chains self-assemble into helical nanofibres of various lengths. Meanwhile, isomers with chiral oligoether dendron chains self-organize into sheet-like nanoribbons of different sizes.

Recognition Selectivities of Lasso-Type Pseudo[1]rotaxane Based on a Mono-Ester-Functionalized Pillar[5]arene

Two types of mono-ester-functionalized pillar[5]arenes, P1 and P2, bearing different side-chain groups, were synthesized. Their host–guest complexation and self-inclusion properties were studied by ¹H NMR and 2D nuclear overhauser effect spectroscopy (NOESY) NMR measurements. The results showed that the substituents on their phenolic units have a great influence on the self-assembly of both pillar[5]arenes, although they both could form stable pseudo[1]rotaxanes at room temperature. When eight bulky 4-brombutyloxy groups were capped on the cavity, instead of methoxy groups, pseudo[1]rotaxane P1 became less stable and its locked ester group in the inner space of cavity was not as deep as P2, leading to distinctly different host–guest properties between P1 and P2 with 1,6-dibromohexane. Moreover, pillar[5]arene P1 displayed effective molecular recognition toward 1,6-dichlorohexane and 1,2-bromoethane among the guest dihalides. In addition, the self-complex models and stabilities between P1 and P2 were also studied by computational modeling and experimental calculations.

Nanoscale Metal-Organic-Frameworks Coated by Biodegradable Organosilica for pH and Redox Dual Responsive Drug Release and High-Performance Anticancer Therapy

Responsive nanocarriers with biocompatibility and precise drug releasing capability have emerged as a prospective candidate for anticancer treatment. However, the challenges imposed by the complicated preparation process and limited loading capacities have seriously impeded the development of novel multifunctional drug delivery systems. Here, we developed a novel and dual-responsive nanocarrier based on a nanoscale ZIF-8 core and an organosilica shell containing disulfide bridges in its frameworks through a facile and efficient strategy. The prepared ZIF-8@DOX@organosilica nanoparticles (ZDOS NPs) exhibited a well-defined structure and excellent doxorubicin (DOX) loading capability (41.2%) with pH and redox dual-sensitive release properties. The degradation of the organosilica shell was observed after 12 h incubation with a 10 mM reducing agent. Confocal imaging and flow cytometry analysis further proved that the nanocarriers can efficiently enter cells and complete intracellular DOX release under the low pH and high glutathione concentrations, which resulted in an enhanced cytotoxicity of DOX for cancer cells. Meanwhile, subcellular localization experiments revealed that the ZDOS NPs entered cells mainly by endocytosis and then escaped from lysosomes into the cytosol. Moreover, in vivo assays also demonstrated that the ZDOS NPs exhibited negligible systemic toxicity and significantly enhanced anticancer efficiencies compared with free DOX. In summary, our prepared pH and redox dual-responsive nanocarriers provide a potential platform for controlled release and cancer treatment.

Supramolecular vesicles based on pillar[n]arenes: design, construction, and applications

Supramolecular vesicles have attracted considerable attention due to their advantages of facile construction, high-cargo-loading capacity, and good biocompatibility. Pillar[n]arenes are a unique family of supramolecular macrocycles, exhibiting excellent features and broad applications due to their intrinsic topology and high functionality. In the past decade, the construction of pillar[n]arene-based supramolecular vesicles has been continuously attempted and developed rapidly. In this review, we mainly summarize the significant advancements of such supramolecular vesicles in the last three years. By showing some representative examples, the design strategies, construction methods, and potential applications of these dynamic nanocarriers are discussed in detail. In particular, the responsiveness of such vesicles to various external stimuli and their applications in drug delivery are highlighted. The outstanding performance of pillar[n]arene-based supramolecular vesicles would definitely enrich the family of supramolecular vesicles and promote the development of dynamic supramolecular materials.

Dual-targeting nanoparticles with core-crosslinked and pH/redox-bioresponsive properties for enhanced intracellular drug delivery

Multifunctional nanoparticles (NPs) with high blood-stability, tumor-targeting ability, and stimuli-bioresponsive drug release behaviors are urgently demanded. Herein, folic acid (FA) and galactose (GAL) functionalized, core-crosslinked NPs (CC NPs) with dual-targeting and pH/redox-bioresponsive properties were developed based on amphiphilic FA-poly(6-O-methacryloyl-d-galactopyranose)-b-poly[2-(diisopropylamino) ethyl methacrylate-co-pyridyl disulfide methylacrylate] [FA-PMAgGP-b-P(DPA-co-PDEMA), termed as FA-PMgDP] block copolymers, and then investigated for facilitated hepatoma-targeting delivery of doxorubicin (DOX). A series of PMgDP copolymers were synthesized though two-step RAFT copolymerization followed by acid-induced acetal deprotection reaction. Their well-defined chemical structures and compositions were characterized by ¹H NMR and gel permeation chromatography. Nano-sized, non-crosslinked PMgDP NPs (PMgDP NC NPs) with sizes of less than 25 nm in aqueous solution were self-assembled via the solvent exchange method, and PMgDP CC NPs were readily prepared in the presence of dithiothreitol. The drug-loading content of PMgDP CC NPs was up to 15.8% and its entrapment efficiency was 89.0%. In normal physiological conditions, 11.6% of DOX was released from DOX-loaded PMgDP CC NPs at 25 h, whereas in analogous intracellular microenvironment, 95.5% was released at 11 h owing to the acid-induced protonation of tertiary amine and reductive cleavage of disulfide bond in the hydrophobic core. In a cellular uptake study, FA and GAL-mediated, active, dual-targeted DOX-loaded FA-PMgDP CC NPs showed a 3.54-fold increase in cellular uptake efficiency to HepG2 cells compared to that of shown by single GAL-targeted, DOX-loaded PMgDP NC NPs. Results of in vitro cytotoxicity study showed that blank FA-PMgDP CC NPs exhibited good biocompatibility, whereas dual-targeting DOX-loaded FA-PMgDP CC NPs increased cell apoptosis. Therefore, the above results indicated that the well-constructed FA-PMgDP CC NPs with multi-synergistic effect may serve as new nanocarriers in the field of precise hepatoma-targeting drug delivery.

Stimuli-responsive supramolecular nano-systems based on pillar[n]arenes and their related applications

Stimuli-responsive supramolecular nano-systems (SRNS) have been a trending interdisciplinary research area due to the responsiveness upon appropriate stimuli, which makes SRNS very attractive in multiple fields where precise control is vital.

Tuning the aggregation of an amphiphilic anionic calix[5]arene by selective host–guest interactions with bola-type dications

Bola-type dications of different length drive the formation of head-to-tail or capsular supramolecular amphiphiles and, in turn, that of the final aggregates.

Dual acid-responsive bola-type supramolecular vesicles for efficient intracellular anticancer drug delivery

Dual acid-responsive bola-type supramolecular vesicles have been successfully constructed for efficient intracellular anticancer drug delivery and controlled release.

Supramolecular delivery systems based on pillararenes

Supramolecular delivery systems (SDSs) fabricated via molecular assembly, which conveniently allow integration of multiple functions in a single system and structural diversity of systems, are a very active research area due to their enormous potential in biomedical applications, including drug delivery, cell imaging, diagnosis, and release monitoring. Pillararenes, a novel type of macrocyclic molecule, are gaining increasing interest as an important component in the construction of SDSs due to their unique structural and chemical properties. This feature article summarizes pillararene-based SDSs constructed via host-guest interactions via four strategies: (1) supramolecular host-guest complexation; (2) self-assembly of supramolecular amphiphiles; (3) self-assembly of amphiphilic supramolecular polymer conjugates; (4) hybridization with other porous materials, such as inorganic materials and metal-organic frameworks (MOFs). The various SDSs based on pillararenes for the delivery of different cargoes from anti-cancer drugs, fluorescent molecules, siRNAs, and insulin to antibiotics are reviewed. Furthermore, future challenges for advanced SDSs based on pillararenes and their broader applications are outlined.

A dual redox-responsive supramolecular amphiphile fabricated by selenium-containing pillar[6]arene-based molecular recognition

A dual redox-responsive pillar[6]arene-based supramolecular amphiphile was fabricated in water. The self-assembly behavior of this supramolecular amphiphile in response to dual redox stimuli was investigated.

GSH-Responsive supramolecular nanoparticles constructed by β-d-galactose-modified pillar[5]arene and camptothecin prodrug for targeted anticancer drug delivery

Supramolecular construction of a targeted and stimuli-responsive drug delivery system is still a challenging task. Herein, GSH-responsive supramolecular prodrug nanoparticles were constructed by the host-guest complexation between a β-d-galactose-functionalized water-soluble pillar[5]arene (GalP5) and a disulfide bond containing camptothecin prodrug (G). The obtained prodrug nanoparticles were stable under physiological conditions, whereas efficient drug release was triggered in a simulated tumor environment with high GSH concentration. In vitro studies revealed that these prodrug nanoparticles preferentially entered asialoglycoprotein receptor-overexpressing HepG2 cells due to the active targeting effect of galactose units. This active targeting effect resulted in the maximization of anticancer efficacy and reduction of the undesirable side effects to normal cells.

Hybrid Molecular Container Based on Glycoluril and Triptycene: Synthesis, Binding Properties, and Triggered Release

We designed and synthesized a "hybrid" molecular container 1, which is structurally related to both cucurbit[n]uril (CB[n]) and pillar[n]arene type receptors. Receptor 1 was fully characterized by ¹ H NMR, ¹³ C NMR, IR, MS and X-ray single crystal diffraction. The self-association behavior, host-guest recognition properties of 1, and the [salt] dependence of K_a were investigated in detail by ¹ H NMR and isothermal titration calorimetry (ITC). Optical transmittance and TEM measurements provide strong evidence that receptor 1 undergoes co-assemble with amphiphilic guest C10 in water to form supramolecular bilayer vesicles (diameter 25.6±2.7 nm, wall thickness ≈3.5 nm) that can encapsulate the hydrophilic anticancer drug doxorubicin (DOX) and the hydrophobic dye Nile red (NR). The release of encapsulated DOX or NR from the vesicles can be triggered by hexamethonium (8 c) or spermine (10) which leads to the disruption of the supramolecular vesicles.

Reversible fabrication and self-assembly of a gemini supra-amphiphile driven by dynamic covalent bonds

A smart gemini supra-amphiphile behaving with pH/CO2 dual-sensitive hierarchical self-assembly was fabricated under the effect of dynamic covalent bonds. In the presence of an amino-functionalized cation, water-insoluble terephthalaldehyde, and an amphiphilic anion, the benzoic imine bond can initiate the transformation from a single-tailed supra-amphiphile to a gemini supra-amphiphile with increasing pH, followed by the subsequent evolution from micelles to vesicles. Reversible self-assembly and disassembly of the gemini supra-amphiphile can be realized via CO2/N2 treatment, thus inducing the fission and reversion of vesicles. Interestingly, the flexible nature of supra-amphiphiles allows for the hierarchical assembly of vesicles, leading to the formation of aqueous two-phase systems. Multiple responsive supra-amphiphiles have useful applications in the fabrication of smart supra-molecular materials, including self-healing materials, nanocarriers and chemosensors.

Pillararene-based self-assembled amphiphiles

Pillararenes are a unique group of supramolecular macrocycles, presenting important features and potential applications on account of their intrinsic structural properties and functionality. Developing pillararene-based self-assembled amphiphiles (PSAs) is an efficient approach to translate pillararenes into functional systems and materials for facilitating their practical applications. In this review article, we highlight recent significant advancements in PSAs. A new standard according to the number, solubility, and amphiphilicity of building blocks is employed for dividing PSAs into different categories. The fabrication of PSAs based on various building blocks and supramolecular interactions, and the formation of amphiphile-based self-assemblies are then discussed based on this standard. Furthermore, interesting stimulus-responsiveness to various factors, such as pH, redox, temperature, light, ionic effect, and host-guest competition, generated by the functional groups on various building blocks is summarized, and the corresponding supramolecular interactions in PSAs and their self-assemblies are elaborated. In addition, some important applications of PSAs and their assemblies are discussed. This review not only provides fundamental findings on the construction of PSAs, but also foresees future research directions in this rapidly developing area.