Phosphonated Pillar[5]arene-Valved Mesoporous Silica Drug Delivery Systems

Macrocycle-Based Supramolecular Drug Delivery Systems: A Concise Review

Efficient delivery of therapeutic agents to the lesion site or specific cells is an important way to achieve "toxicity reduction and efficacy enhancement". Macrocycles have always provided many novel ideas for drug or gene loading and delivery processes. Specifically, macrocycles represented by crown ethers, cyclodextrins, cucurbit[n]urils, calix[n]arenes, and pillar[n]arenes have unique properties, which are different cavity structures, good biocompatibility, and good stability. Benefited from these diverse properties, a variety of supramolecular drug delivery systems can be designed and constructed to effectively improve the physical and chemical properties of guest molecules as needed. This review provides an outlook on the current application status and main limitations of macrocycles in supramolecular drug delivery systems.

Smart controlled-release nanopesticides based on metal-organic frameworks

The practical utilization rates of conventional pesticide formulations by target organisms are very low, which results in the pollution of ecological environments and the formation of pesticide residues in agricultural products. Water-based nanopesticide formulations could become alternative and effective formulations to eventually resolve the main issues of conventional pesticide formulations. In this feature article, we describe the design concept of smart (stimuli-responsive) controlled-release nanopesticides, which are created toward hierarchical targets (pests, pathogens, and foliage) in response to multidimensional stimuli from physiological and environmental factors (such as sunlight) of target organisms and plants, for achieving enhanced insecticidal and fungicidal efficacies. The pore sizes and functionalities of metal-organic frameworks (MOFs) can be fine-tuned through the choice of metal-containing units and organic ligands. Tailor-made MOF nanoparticles with large microporous or mesoporous sizes, as well as good biocompatibility and high thermal, mechanical, and chemical durabilities, are used to load pesticides within these pores followed by coating of plant polyphenols and natural polymers for stimuli-responsive controlled pesticide release. This feature article highlights our works on smart controlled-release MOF-based nanopesticides and also includes related works from other laboratories. The future challenges and promising prospects of smart controlled-release MOF-based nanopesticides are also discussed.

Recent Advances in Stimulus-Responsive Nanocarriers for Pesticide Delivery

In an effort to make pesticide use safer, more efficient, and sustainable, micro-/nanocarriers are increasingly being utilized in agriculture to deliver pesticide-active agents, thereby reducing quantities and improving effectiveness. In the use of nanopesticides, the choice to further design and prepare pesticide stimulus-responsive nanocarriers based on changes in the plant growth environment (light, temperature, pH, enzymes, etc.) has received more and more attention from researchers. Based on this, this paper examines recent advancements in nanomaterials for the design of stimulus-responsive micro-/nanocarriers. It delves into the intricacies of preparation methods, material enhancements, in vivo/ex vivo controlled release, and application techniques for controlled release formulations. The aim is to provide a crucial reference for harnessing nanotechnology to pursue reduced pesticide use and increased efficiency.

Core-shell inorganic NP@MOF nanostructures for targeted drug delivery and multimodal imaging-guided combination tumor treatment

It is well known that metal-organic framework (MOF) nanostructures have unique characteristics such as high porosity, large surface areas and adjustable functionalities, so they are ideal candidates for developing drug delivery systems (DDSs) as well as theranostic platforms in cancer treatment. Despite the large number of MOF nanostructures that have been discovered, conventional MOF-derived nanosystems only have a single biofunctional MOF source with poor colloidal stability. Accordingly, developing core-shell MOF nanostructures with good colloidal stability is a useful method for generating efficient drug delivery, multimodal imaging and synergistic therapeutic systems. The preparation of core-shell MOF nanostructures has been done with a variety of materials, but inorganic nanoparticles (NPs) are highly effective for drug delivery and imaging-guided tumor treatment. Herein, we aimed to overview the synthesis of core-shell inorganic NP@MOF nanostructures followed by the application of core-shell MOFs derived from magnetic, quantum dots (QDs), gold (Au), and gadolinium (Gd) NPs in drug delivery and imaging-guided tumor treatment. Afterward, we surveyed different factors affecting prolonged drug delivery and cancer therapy, cellular uptake, biocompatibility, biodegradability, and enhanced permeation and retention (EPR) effect of core-shell MOFs. Last but not least, we discussed the challenges and the prospects of the field. We envision this article may hold great promise in providing valuable insights regarding the application of hybrid nanostructures as promising and potential candidates for multimodal imaging-guided combination cancer therapy.

Pillar[5]arene-Derived Terpyridinepalladium(II) Complex: Synthesis, Characterization, and Application in Green Catalysis

Metal nanoparticle catalysts have attracted great interest because they possess high surface-to-volume ratios and exhibit a very large number of catalytically active sites per unit area. However, high surface-to-volume ratios will induce nanoparticle aggregates during the catalytic reactions, making them lose their catalytic activity. In this work, a monoterpyridine-unit-functionalized pillar[5]arene (TP5) was synthesized successfully, which can be used as anchoring sites for the controllable preparation of well-dispersed palladium nanoparticles [TP5/Pd(0) NPs]. The as-prepared TP5/Pd(0) NPs were fully characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, and powder X-ray diffraction. Importantly, the ultrafine TP5/Pd(0) NPs are found to be excellent and reusable catalysts for the reduction of nitrophenols in aqueous solution.

Controlled release of drug molecules by pillararene-modified nanosystems

Stimuli-responsive nanosystems have attracted the interest of researchers due to their intelligent function of controlled release regulated by a variety of external stimuli and have been applied in biomedical fields. Pillar[n]arenes with the advantages of a rigid structure, electron holes and easy functionalization are considered as excellent candidates for the construction of host-guest nanosystems. In recent years, many pillararene modified nanosystems have been reported in response to different stimuli. In this feature article, we summarize the advance of stimuli-responsive pillararene modified nanosystems for controlled release of drugs from the perspectives of decomposition release and gated release, focusing on the control principles of these nanosystems. We expect that this review can enlighten and guide investigators in the field of stimuli-responsive controlled release.

Pillar[5]arene based glyco-targeting nitric oxide nanogenerator for hyperthermia-induced triple-mode cancer therapy

Nitric oxide (NO)-mediated gas therapy (GT) and alkyl radical (R•) therapy (ART) are emerging cancer therapy modes, and multi-mode therapy has been recognized as an attractive strategy for enhancing anti-cancer efficacy. In this work, a thermal-responsive R• initiator 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (AIBI)-loaded glycol-targeting NO nanogenerator was constructed by first the covalent conjugation of thermal-responsive NO donor of S-nitrosothiols (RSNO) on the surface of mesoporous silica-coated gold nanorods (AuNRs@MSN), then the coating of a supramolecular complex of amino pillar[5]arene (NP5) and galactose derivative (G), and finally the loading of AIBI. The glycol-targeting NO nanogenerator demonstrated specific targeting ability to HepG2 cells owing to the recognition between galactose residues and asialoglycoprotein receptors (ASGPR). Specially, upon 808 nm near-infrared (NIR) irradiation, the AIBI-loaded NO nanogenerator generated hyperthermia to achieve photothermal therapy (PTT), and further GT and ART resulted from the thermal responsiveness of RSNO and AIBI, respectively. In vitro experiments revealed that the AIBI-loaded glyco-targeting NO nanogenerator had good biocompatibility and exhibited effective inhibition to the proliferation of HepG2 cells. This work provides a novel way to supramolecular hybrid drug delivery systems for triple-mode targeting therapy of PTT/GT/ART.

Ovotransferrin Antibacterial Peptide Coupling Mesoporous Silica Nanoparticle as an Effective Antibiotic Delivery System for Treating Bacterial Infection In Vivo

Antibiotic-resistant pathogens are a serious threat to global public health. The emergence of drug-resistant pathogens is due to the improper use of antibiotics, making the treatment of bacterial infections very challenging. Here, we reported an efficient antibiotic delivery nanoparticle to minimize antibiotic resistance. The nanoparticle was designed to target the bacterial membrane using mesoporous silica nanoparticles (MSNs) modified with an ovotransferrin-derived antimicrobial peptide (OVTp12), enabling the antibiotic to be delivered to the vicinity of the pathogenic bacteria. Moreover, we observed that OVTp12-modified nanoparticles effectively inhibited the growth of Escherichia coli in vitro and in vivo. The nanoparticle with high biosafety could significantly downregulate the expression of inflammation-related cytokines in infected tissues. Thus, this novel bacterial targeted nanoparticle provides advantages in minimizing bacterial drug resistance and treating bacterial infection.

Pillararene-based molecular-scale porous materials

This review discusses the design and syntheses of molecular-scale pillar[n]arene-based porous materials with promising applications and summarises the development of using pillar[n]arenes as the building blocks of porous materials. From the perspective of "role of participation" in the syntheses of molecular-scale pillar[n]arene-based porous materials, the content can be divided into pillar[n]arenes serving as supramolecular nanovalves on surfaces and as ligands for metal-organic frameworks and covalent organic polymers. By integrating pillararenes, which possess rigid pillar-like structures, electron-rich cavities and desirable host-guest properties, with porous polymers of large surface areas and abundant active sites, applications of the resulting materials in drug release platforms, molecular recognition, sensing, detection, gas adsorption, removal of water pollution, organic photovoltaic materials and heterogeneous catalysis can be realised simultaneously and efficiently. Finally, in the conclusions and perspectives part, we put forward the challenges and viewpoints of the current research on pillar[n]arene-based porous materials. We hope this article can provide a timely and valuable reference for researchers interested in synthetic macrocycles and porous materials.

Gold Nanorods: The Most Versatile Plasmonic Nanoparticles

Gold nanorods (NRs), pseudo-one-dimensional rod-shaped nanoparticles (NPs), have become one of the burgeoning materials in the recent years due to their anisotropic shape and adjustable plasmonic properties. With the continuous improvement in synthetic methods, a variety of materials have been attached around Au NRs to achieve unexpected or improved plasmonic properties and explore state-of-the-art technologies. In this review, we comprehensively summarize the latest progress on Au NRs, the most versatile anisotropic plasmonic NPs. We present a representative overview of the advances in the synthetic strategies and outline an extensive catalogue of Au-NR-based heterostructures with tailored architectures and special functionalities. The bottom-up assembly of Au NRs into preprogrammed metastructures is then discussed, as well as the design principles. We also provide a systematic elucidation of the different plasmonic properties associated with the Au-NR-based structures, followed by a discussion of the promising applications of Au NRs in various fields. We finally discuss the future research directions and challenges of Au NRs.

Multifunctional Pillar[n]arene-Based Smart Nanomaterials

The construction of smart nanomaterials from host macrocycles that are responsive to specific stimuli has gained significant attention in recent years. The application of pillar[n]arenes has been of particular interest given their ease of functionalization and tunability of the intrinsic cavity electronic properties that allows them to encapsulate a great variety of guests and complex with metal ions with high selectivity via noncovalent interactions, endowing them with captivating properties and functions. Herein, we present the most recent advances in the design and functionalization of pillar[n]arene-based smart nanomaterials, and their applications for sensing, catalysis, drug delivery, and artificial transmembrane channels.

The assembly of silica species with alkylamines: Mechanism of wastewater-free synthesis and the application of gel as a catalyst

Silica species generated by the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) could assemble with alkylamines to form silica gel. Herein, it was evidenced that part of the added amines, including butylamine (BA), octylamine (OA) or dodecylamine (DA), was protonated in the mixture of water and ethanol. Therefore, besides the hydrogen bonding between neutral silica species and the micelles composed of the non-protonated amines (Tanev and Pinnavaia, 1995), there existed strong electrostatic attraction between negatively charged silica species and the micelles composed of the protonated amines. This coexisting assembly mechanism could explain why the uncalcined BA- and OA-gels were millimeter-sized small blocks with large porosities and synthesized without waste water emission, while the uncalcined DA-gel was almost non-porous and formed via precipitation from its reaction medium. The uncalcined BA gel was proved to be efficient as a solid basic catalyst, replacing the commonly used ammonia solution which is easily volatilized and has a pungent smell, for the hydrolysis and condensation of TEOS to prepare silica microspheres.

Tailored Mesoporous Inorganic Biomaterials: Assembly, Functionalization, and Drug Delivery Engineering

Infectious or immune diseases have caused serious threat to human health due to their complexity and specificity, and emerging drug delivery systems (DDSs) have evolved into the most promising therapeutic strategy for drug-targeted therapy. Various mesoporous biomaterials are exploited and applied as efficient nanocarriers to loading drugs by virtue of their large surface area, high porosity, and prominent biocompatibility. Nanosized mesoporous nanocarriers show great potential in biomedical research, and it has become the research hotspot in the interdisciplinary field. Herein, recent progress and assembly mechanisms on mesoporous inorganic biomaterials (e.g., silica, carbon, metal oxide) are summarized systematically, and typical functionalization methods (i.e., hybridization, polymerization, and doping) for nanocarriers are also discussed in depth. Particularly, structure-activity relationship and the effect of physicochemical parameters of mesoporous biomaterials, including morphologies (e.g., hollow, core-shell), pore textures (e.g., pore size, pore volume), and surface features (e.g., roughness and hydrophilic/hydrophobic) in DDS application are overviewed and elucidated in detail. As one of the important development directions, advanced stimuli-responsive DDSs (e.g., pH, temperature, redox, ultrasound, light, magnetic field) are highlighted. Finally, the prospect of mesoporous biomaterials in disease therapeutics is stated, and it will open a new spring for the development of mesoporous nanocarriers.

Laser-induced switching of the biological activity of phosphonate molecules

The effect of laser activation on butyrylcholinesterase inhibition by a series of phosphorylated arylaminomalonates with different substituents in the phenyl ring is demonstrated.

A Review of Mesoporous Silica Nanoparticle Delivery Systems in Chemo-Based Combination Cancer Therapies

Chemotherapy is an important anti-tumor treatment in clinic to date, however, the effectiveness of traditional chemotherapy is limited by its poor selectivity, high systemic toxicity, and multidrug resistance. In recent years, mesoporous silica nanoparticles (MSNs) have become exciting drug delivery systems (DDS) due to their unique advantages, such as easy large-scale production, adjustable uniform pore size, large surface area and pore volumes. While mesoporous silica-based DDS can improve chemotherapy to a certain extent, when used in combination with other cancer therapies MSN based chemotherapy exhibits a synergistic effect, greatly improving therapeutic outcomes. In this review, we discuss the applications of MSN DDS for a diverse range of chemotherapeutic combination anti-tumor therapies, including phototherapy, gene therapy, immunotherapy and other less common modalities. Furthermore, we focus on the characteristics of each nanomaterial and the synergistic advantages of the combination therapies. Lastly, we examine the challenges and future prospects of MSN based chemotherapeutic combination therapies.

Pillar[n]arene-Based Supramolecular Switches in Solution and on Surfaces

The design and synthesis of new synthetic macrocycles has driven the rapid development of supramolecular chemistry and materials. Pillar[n]arenes, as a new type of macrocyclic compounds, are used as a promising type of building blocks for switchable supramolecular systems due to their versatile functionalization and the ability of binding toward various guest molecules. A number of guests can form inclusion complexes with pillar[n]arenes and their derivatives in solution, which are sensitive to different external triggers. Interestingly, the pursuit of complex stimuli-responsive functional materials and devices has largely motivated the shift of pillar[n]arene-based switches from solution media to surfaces for controllable macroscopic motions on solid platforms. Facilitated by the facile modification of pillar[n]arenes on various solid supports and the dynamic binding of host-guest complexes, numerous functional hybrid materials with adjustable physical or chemical properties and integrated functionalities have been reported in the last decade. Here, the advance of supramolecular switches in solution and on surfaces based on pillar[n]arenes and derivatives with an emphasis on the efforts and the latest contributions from the field is discussed.

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.

Tunable nanogels by host-guest interaction with carboxylate pillar[5]arene for controlled encapsulation and release of doxorubicin

Nanogels have become one of the most attractive systems for application as delivery vectors or for theragnostic approaches in nanomedicine, which is mainly related to the ease of their synthesis by precipitation polymerization. However, only a few suitable monomers have been reported so far and stabilization of the nanogels requires the incorporation of rather defined amounts of in most cases charged co-monomers, such as acrylic acid, which limits the flexibility in their design. Here, we present an alternative approach using a pyridinium based monomer, which not only provides stability due to the positive charge, but also allows the attachment of functional carboxylate-pillar[5]arene by the formation of a host-guest complex. This approach is tested on pH-sensitive nanogels based on the monomer N-[(2,2-dimethyl-1,3-dioxolane)methyl]acrylamide (DMDOMA) featuring an acetal group, which is hydrolysed under acidic conditions. As carboxylates are known to catalyze this hydrolysis, we tested different amounts of carboxylate-pillar[5]arenes to tune the hydrolysis rate of the acetal group and found a direct correlation. Additional encapsulation studies with doxorubicin (DOX) revealed that surface potential and charge density represent additional key factors not only for the loading capacity, but also for the release profile of the nanogels. The option to tune such properties simply by the addition of a co-factor, in this case, the carboxylate-pillar[5]arenes provides a powerful tool to optimize characteristics of functional nanogels for drug delivery or other applications.

A reversible, switchable pH-driven quaternary ammonium pillar[5]arene nanogate for mesoporous silica nanoparticles

Here we describe the assembly and pH-driven operation of two nanocarriers based on non-functionalized (MCM-41) and carboxylate-functionalized (MCM-41-COOH) containers loaded with the anticancer drug doxorubicin (DOX) and capped by quaternary ammonium pillar[5]arene (P[5]A) nanogates. MCM-41 and MCM-41-COOH containers were synthesized and transmission and scanning electron microscopies showed nanoparticles with spherical morphology and dimensions of 85 ± 13 nm. The nanochannels of MCM-41 loaded with DOX were gated through the electrostatic interactions between P[5]A and the silanolate groups formed at the silica-water interface, yielding the MCM-41-DOX-P[5]A nanocarrier. The second nanocarrier was gated through the electrostatic interactions between the carboxylate groups mounted on the surface of MCM-41 and P[5]A, resulting in the MCM-41-COO-DOX-P[5]A nanocarrier. The DOX release profiles from both nanocarriers were investigated by UV-vis spectroscopy at different pH values (2.0, 5.5 and 7.4) and also in the presence of ions, such as citrate^3- (19 mmol L^-1) and Zn²⁺ (1.2 and 50 mmol L^-1) at 37 °C. MCM-41-COO-DOX-P[5]A can be turned on and off eight times through the formation and breaking of electrostatic interactions. In vitro studies show that MCM-41-COO-DOX-P[5]A can penetrate and release DOX in the nucleus of human breast adenocarcinoma MCF-7 cancer cells leading to a pronounced cytotoxic effect. Therefore, the fabricated nanocarrier based on a water-soluble cationic pillar[5]arene nanogate, which is reversibly opened and closed by electrostatic interactions, can be considered as a promising drug transport and delivery technique for future cancer therapy.

Design, Preparation, and Characterization of Novel Calix[4]arene Bioactive Carrier for Antitumor Drug Delivery

An amphiphilic and bioactive calix[4]arene derivative 8 (CA) is designed and successfully synthesized from tert-butyl calix[4] arene 1 by sequential inverse F-C alkylation, nitration, O-alkylation, esterification, aminolysis, reduction, and acylation reaction. The blank micelles of FA-CA and doxorubicin (DOX) loaded micelles FA-CA-DOX are prepared subsequently undergoing self-assembly and dialysis of CA and DSPE-PEG₂₀₀₀-FA. The drug release kinetics curve of the encapsulated-DOX micelle demonstrates a rapid release under mild conditions, indicating the good pH-responsive ability. Furthermore, the cytotoxicity of DOX-loaded micelle respect to the blank micelle against seven different human carcinoma (A549, HeLa, HepG2, HCT116, MCF-7, MDA-MB231, and SW480) cells has been also investigated. The results confirm the more significant inhibitory effect of DOX-loaded micelle than those of DOX and the blank micelles. The CDI calculations show a synergistic effect between blank micelles and DOX in inducing tumor cell death. In conclusion, FA-CA micelles reported in this work was a promising drug delivery vehicle for tumor targeting therapy.

Diselenium-containing ultrathin polymer nanocapsules for highly efficient targeted drug delivery and combined anticancer effect

The combination of selenium and pillararenes to prepare selenium-containing pillararene-based biomaterials is of great significance for the development of biomedicine. Herein, using a covalent self-assembly strategy, we successfully developed new diselenium-containing ultrathin polymer nanocapsules based on lateral cross-linked pillararenes. The new system exhibited a very potent anticancer effect; additionally, the incorporation of the cleavable redox diselenium bond into the polymer nanocapsules provided a smart nanocarrier for drug delivery. Moreover, the polymer nanocapsules were developed for anticancer drug targeting delivery by loading an anticancer drug and introducing the tumor-penetrating peptide RGD through the host-guest interaction strategy. The targeting DOX-loaded diselenium-containing polymer nanocapsules exhibited enhanced stability, self-anticancer effect, targeted delivery and controlled drug release, resulting in effective combined inhibition of tumor progression.

Supramolecular nanotheranostics based on pillarenes

With the rapid development of supramolecular chemistry and nanomaterials, supramolecular nanotheranostics has attracted remarkable attention owing to the advantages compared with conventional medicine. Supramolecular architectures relying on non-covalent interactions possess reversible and stimuli-responsive features; endowing supramolecular nanotheranostics based on supramolecular assemblies great potentials for the fabrication of integrated novel nanomedicines and controlled drug delivery systems. In particular, pillarenes, as a relatively new class of synthetic macrocycles, are important candidates in the construction of supramolecular therapeutic systems due to their excellent features such as rigid and symmetric structures, facile substitution, and unique host-guest properties. This review summarizes the development of pillarene-based supramolecular nanotheranostics for applications in biological mimicking, virus inhibition, cancer therapy, and diagnosis, which contains the following two major parts: (a) pillarene-based hybrid supramolecular nanotheranostics upon hybridizing with porous materials such as mesoporous silica nanoparticles, metal-organic frameworks, metal nanoparticles, and other inorganic materials; (b) pillarene-based organic supramolecular therapeutic systems that include supramolecular amphiphilic systems, artificial channels, and prodrugs based on host-guest complexes. Finally, perspectives on how pillarene-based supramolecular nanotheranostics will advance the field of pharmaceuticals and therapeutics are given.

Supramolecular Nanomachines as Stimuli-Responsive Gatekeepers on Mesoporous Silica Nanoparticles for Antibiotic and Cancer Drug Delivery

Major objectives in nanomedicine and nanotherapy include the ability to trap therapeutic molecules inside of nano-carriers, carry therapeutics to the site of the disease with no leakage, release high local concentrations of drug, release only on demand - either autonomous or external, and kill the cancer cells or an infectious organism. This review will focus on mesoporous silica nanoparticle carriers (MSN) with a large internal pore volume suitable for carrying anticancer and antibiotic drugs, and supramolecular components that function as caps that can both trap and release the drugs on-command.

Caps that are especially relevant to this review are rotaxanes and pseudorotaxanes that consist of a long chain-like molecule threaded through a cyclic molecule. Under certain conditions discussed throughout this review, the cyclic molecule can be attracted to one end of the rotaxane and in the presence of a stimulus can slide to the other end. When the thread is attached near the pore opening on MSNs, the sliding cyclic molecule can block the pore when it is near the particle or open it when it slides away.

The design, synthesis and operation of supramolecular systems that act as stimuli-responsive pore capping devices that trap and release molecules for therapeutic or imaging applications are discussed. Uncapping can either be irreversible because the cap comes off, or reversible when the cyclic molecule is prevented from sliding off by a steric barrier. In the latter case the amount of cargo released (the dose) can be controlled. These nanomachines act as valves.

Examples of supramolecular systems stimulated by chemical signals (pH, redox, enzymes, antibodies) or by external physical signals (light, heat, magnetism, ultrasound) are presented. Many of the systems have been studied in vitro proving that they are taken up by cancer cells and release drugs and kill the cells when stimulated. Some have been studied in mouse models; after IV injection they shrink tumors or kill intracellular pathogens after stimulation. Supramolecular constructs offer fascinating, highly controllable and biologically compatible platforms for drug delivery.

Integrating Stimuli-Responsive Properties in Host-Guest Supramolecular Drug Delivery Systems

Host-guest motifs are likely the most recognizable manifestation of supramolecular chemistry. These complexes are characterized by the organization of small molecules on the basis of preferential association of a guest within the portal of a host. In the context of their therapeutic use, the primary application of these complexes has been as excipients which enhance the solubility or improve the stability of drug formulations, primarily in a vial. However, there may be opportunities to go significantly beyond such a role and leverage key features of the affinity, specificity, and dynamics of the interaction itself toward "smarter" therapeutic designs. One approach in this regard would seek stimuli-responsive host-guest recognition, wherein a complex forms in a manner that is sensitive to, or can be governed by, externally applied triggers, disease-specific proteins and analytes, or the presence of a competing guest. This review will highlight the general and phenomenological design considerations governing host-guest recognition and the specific types of chemistry which have been used and are available for different applications. Finally, a discussion of the molecular engineering and design approaches which enable sensitivity to a variety of different stimuli are highlighted. Ultimately, these molecular-scale approaches offer an assortment of new chemistry and material design tools toward improving precision in 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.

Mechanised lubricating silica nanoparticles for on-command cargo release on simulated surfaces of joint cavities

Supramolecular mechanised silica nanoparticles for controlled cargo release and lubrication enhancement are demonstrated.

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.

Gold Nanorods/Polypyrrole/m-SiO2 Core/Shell Hybrids as Drug Nanocarriers for Efficient Chemo-Photothermal Therapy

Combination therapy as a novel strategy with the combination of photothermal therapy and chemotherapy (photothermal-chemotherapy) has aroused the tremendously increasing interest owing to the synergistic therapeutic effect on destroying cancer cells because the hyperthermia generated from photothermal therapy can promote drug delivery into tumors, which would highly increase therapeutic efficacy as compared to those sole treatments. Herein, we fabricated a novel nanomaterial-based carrier composed of gold nanorods (GNRs), polypyrrole (PPy), and mesoporous silica to form GNRs/PPy/m-SiO₂ core/shell hybrids. After loading the anticancer drug of doxorubicin (DOX), the photothermal effect and the drug-release behavior of GNRs/PPy@m-SiO₂-DOX hybrids were investigated. The in vitro and in vivo near-infrared (NIR) photothermal-chemotherapy were also revealed. The results indicated that the NIR-induced photothermal effect was beneficial to promote the release of the drug. In addition, combination therapy demonstrated the enhanced synergistic efficacy and excellent treatment efficacy for cancer therapy.

The synthesis of water-soluble phosphate pillar[5]arenes functionalized graphene as a fluorescent probe for sensitive detection of paraquat

We describe a selective and sensitive fluorescence platform for the detection of paraquat (PQ) based on competitive host-guest recognition between phosphate pillar[5]arenes (PWP5) and probe (Safranine T, ST) with using PWP5 functionalized reduced graphene (PWP5-rGO) as the receptor. PQ is a positive charge molecule that is captured by PWP5 via electrostatic interactions. The host-guest interaction between PWP5 and PQ is studied by ¹H NMR. Therefore, a selective and sensitive fluorescence sensing of detection PQ is developed. It has a linear response ranges of 0.01-2.0 and 2.0-50.0 μM and a low detection limit of 0.0035 μM (S/N = 3) for PQ. The sensing platform is also used to test PQ in two water samples with satisfying results. It suggests that this approach has potential applications for the determination of PQ.

Gated Materials: Installing Macrocyclic Arenes-Based Supramolecular Nanovalves on Porous Nanomaterials for Controlled Cargo Release

Supramolecular nanovalves are an emerging class of important elements that are functionalized on the surfaces of inorganic or hybrid nanocarriers in the constructions of smart cargo delivery systems. Taking advantage of the pseudorotaxane structure via host-guest complexation and the dynamic nature of supramolecular interactions, macrocyclic arene-based supramolecular nanovalves have shown great promise in the applications of drug delivery and controlled release. Careful selection of diverse external stimuli, such as pH variations, temperature changes, redox, enzymes, light irradiation, and competitive binding, can activate the opening and closing of the nanovalves by altering the supramolecular structure or binding affinities. Meanwhile, the porous solid supports in controlled release systems also play an important role in the functionalities of the nanocarriers, which include, but not limited to, mesoporous silica nanoparticles (MSNs), metal-organic frameworks (MOFs), core-shell nanomaterials, and rare-earth porous nanomaterials. The elaborate decoration by macrocyclic arenes-based supramolecular nanovalves on porous nanomaterials has provided intelligent controlled release platforms. In this review, we will focus on the overview of supramolecular nanovalves based on two typical macrocyclic arenes, that is, calixarenes and pillarenes, and their operation manners in the controlled release processes.

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.

Multi-stimuli-responsive supramolecular gel constructed by pillar[5]arene-based pseudorotaxanes for efficient detection and separation of multi-analytes in aqueous solution

Here, a novel pseudorotaxanes-type crosslinker of a supramolecular polymer network (WP5-PN) has been constructed from a host water-soluble pillar[5]arene (WP5) and a guest naphthalene dimethylamine derivative (PN) via a stepwise process involving multiple non-covalent interactions. The obtained supramolecular polymers were able to transform into a supramolecular polymer gel (WP5-PN-G) and show AIE properties in DMSO-H2O binary solution. Interestingly, due to the dynamic and reversible nature of non-covalent interactions, the resultant supramolecular polymer gels exhibited external stimuli-responsiveness to different parameters, such as temperature, acid-base, competitive guest and mechanical stress. Moreover, WP5-PN-G showed fluorescent response for Fe3+ and Cu2+, while its xerogel showed excellent recyclable separation properties for these metal ions with adsorption rates up to 98.07% and 95.38%, respectively. Moreover, by rational introduction of these metal ions into the WP5-PN-G, corresponding metal ion coordinated metallogels, such as WP5-PN-FeG and WP5-PN-CuG were obtained. These metallogels could selectively and sensitively sense F- and CN-, respectively. The detection limits of these metallogels for F- and CN- were about 1 × 10-8 M. The WP5-PN-G has potential applications in multi-analytes detection and separation as well as fluorescent display materials.

Easily Tunable Membrane Thickness of Microcapsules by Using a Coordination Assembly on the Liquid-Liquid Interface

A model solvent, 1,3,5-trimethylbenzene, was encapsulated using coordination assembly between metal ions and tannic acid to reveal the deposition of coordination complexes on the liquid-liquid interface. The deposition was confirmed by zeta potential, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Scanning electron microscopy and transmission electron microscopy were integrated to characterize the microcapsules (MCs). According to atomic force microscopy height analysis, membrane thickness of the MCs increased linearly with sequential deposition. For MCs prepared using the Fe3+-TA system, the average membrane thicknesses of MCs prepared with 2, 4, 6, and 8 deposition cycles were determined as 31.3 ± 4.6, 92.4 ± 15.0, 175.4 ± 22.1, and 254.8 ± 24.0 nm, respectively. Dissolution test showed that the release profiles of all the four tested MCs followed Higuchi kinetics. Membrane thicknesses of MCs prepared using the Ca2+-TA system were much smaller. We can easily tune the membrane thickness of the MCs by adjusting metal ions or deposition cycles according to the application requirements. The convenient tunability of the membrane thickness can enable an extensive use of this coordination assembly strategy in a broad range of applications.

Supramolecular Polymer-Based Fluorescent Microfibers for Switchable Optical Waveguides

We report the switchable optical waveguide microfibers based on fluorescent supramolecular polymer for the first time. The pillar[5]arene-based supramolecular polymeric microfibers were prepared easily from the viscous solution of bispillar[5]arene host (bisP5A) and diphenylanthracene-derived guest (GD). The resulting microfibers  act as an active optical waveguide material with long propagation distance (400 μm) and low optical propagation loss (0.01 dB/μm). When photoresponsive dithienylethene-derived guest (GDTE) was added, the resulting ternary microfibers show switchable optical waveguide by the noninvasive control of UV/vis light with negligible fatigue over four cycles. This convenient preparation method is also applied for the quadruple-hydrogen-bonded fluorescent supramolecular polymeric microfibers which imply good light propagation property with an optical loss coefficient of 0.02 dB/μm.