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Designing stimuli-responsive therapeutic scaffolds to deliver hydrophobic chemo drugs with controlled and sustained release at the tumour site would be promising in cancer treatment. In a quest for the stimuli-responsive drug delivery system with sustained release, herein we have fabricated active pharmaceutical ingredient based ionic liquid (IL) based hydrogel with self-healable and injectable properties. The ionic hydrogel makes a localized, long-term co-delivery system with self-healable, injectable, and stimuli-responsiveness. Further, the smart hybrid ionic hydrogel was constructed through encapsulating doxorubicin (DOX) within the 3D matrix of the ionic hydrogel, which responds to an intracellular biological stimulus (e.g., pH and temperature) and releases the DOX in 57 h. Experimental results of IL-IL, IL-DOX interactions are supported through Density Functional Theory (DFT) calculations. In vitro cellular studies revealed that DOX loaded hybrid ionic hydrogel shows a synergistic anticancer effect against MCF-07 cells. These results demonstrate the ability of the ionic hydrogel as a promising candidate for local cancer therapeutics.

Reversible tricolored mechanochromism and recyclable mechanoluminescence properties (new shoots) of a reported tetraphenylethene derivative (old roots) were explored.

A simple-structured super gelator with self-healability and multi-stimuli responses was reported herein, which exhibited multiple visual molecular recognition abilities. Multifunctional applications such as effective lubricants, safe fuels, high-efficient propellants, dyes adsorbents, enhanced fluorescence emission and separation of aldehydes from aqueous solutions are integrated into a single organogelator, which was rarely reported.

Targeted release of drugs is important for precision treatment at the desired site and preventing the indiscriminate release of drugs. Incorporating stimuli-responsiveness into drug carriers has been proposed to enable the carriers to have the ability to perform targeted release at specific sites. However, a vast majority of the many established carriers are not stimuli-responsive. The current methods used for the synthesis of stimuli-responsive carriers are mostly highly specific and ineffective (e.g., they either leak or cannot release completely). This manuscript describes a novel class of stimuli-responsive attachments that can be attached flexibly onto any type of soft carrier (i.e., loaded with chemicals or drugs), thus transforming the non-responsive carrier into a stimuli-responsive carrier. The attachment consists of a layer of stimuli-responsive hydrogel around the carrier and a partial rigid coating on the exterior. The attachment is general: non-responsive carrier materials of different types (e.g., liposomes and polymeric carriers) and different sizes (e.g., nanoscale and macroscopic) are shown to become stimuli-responsive for different types of stimuli. Importantly, the attachment is capable of exerting a large pressure for rupturing carriers with rigid and impermeable shells (e.g., highly crosslinked shells). Hence, these carriers with stimuli-responsive attachment effectively exhibit a full range of stimuli-responsiveness: they are not leaky due to their rigid shells, but can release their contents completely via rupture of their shells under the influence of the stimulus. The approach of using this novel class of stimuli-responsive attachments is thus general, simple, and effective. The large number and diverse range of well-established soft non-responsive drug carriers can be transformed into stimuli-responsive carriers conveniently without the constant need to find specific methods for different types of carriers.

Stimuli-responsive crystals have aroused tremendous interest due to their potential as smart materials. However, endowing mono-component crystals with multiple stimuli-responsive and multifunction properties is still a great challenge. Here, we report an anthracene derivative, 9-anthraldehyde, which can respond to mechanical force and light. It possesses two-dimensional (2D) elastic bending, plastic twisting and photoinduced bending properties. Unusual elastic bending of the plastic twisted crystal was achieved in one crystal. The crystal obtained in this work is a multi-dimensional elastic crystal, which is different from reported twistable materials. To reveal the mechanisms of the properties of 2D elastic bending, plastic twisting and photoinduced bending, nanoindentation tests, energy framework analysis and Hirshfeld surface analysis were used to study the property–structure relationship at the molecular level. It was found that these properties can be ascribed to the unique intermolecular interactions and types of molecular arrangement.

CRISPR-Cas9 promotes changes in identity or abundance of nucleic acids in live cells and is a programmable modality of broad biotechnological and therapeutic interest. To reduce off-target effects, tools for conditional control of CRISPR-Cas9 functions are under active research, such as stimuli-responsive guide RNA (gRNA). However, the types of physiologically relevant stimuli that can trigger gRNA are largely limited due to the lack of a versatile synthetic approach in chemistry to introduce diverse labile modifications into gRNA. In this work, we developed such a general method to prepare stimuli-responsive gRNA based on site-specific derivatization of 2′-O-methylribonucleotide phosphorothioate (PS-2′-OMe). We demonstrated CRISPR-Cas9-mediated gene editing in human cells triggered by oxidative stress and visible light, respectively. Our study tackles the synthetic challenge and paves the way for chemically modified RNA to play more active roles in gene therapy., Conditional control of CRISPR-Cas9 activity by reactive oxygen species and visible light is achieved using stimuli-responsive guide RNA synthesized by a general method based on RNA 2′-O-methylribonucleotide phosphorothioate.

Stimuli-responsive luminescent materials have received much attention as next-generation smart materials for various applications, including their use as biomedical probes, for the visualization of pollutants and sensing toxic gases. Boron-containing luminophores have been widely utilized to achieve such sensing materials because of their vacant 2pz orbital, which is responsible for their Lewis acidity, electron-accepting properties, and ability to form complexes. In addition, polymeric structures often enhance stimuli-responsivity because slight environmental changes around the molecules can dramatically affect their molecular motions, shapes and physical properties. This review describes the development of stimuli-responsive materials using various kinds of luminescent boron compounds, focusing on the mechanisms of the sensing abilities and the molecular designs.

Controlled drug delivery systems, which could release loaded therapeutics upon physicochemical changes imposed by physiological triggers in the desired zone and during the required period of time, offer numerous advantages over traditional drug carriers including enhanced therapeutic effects and reduced toxicity. A polypeptide is a biocompatible and biodegradable polymer, which can be conveniently endowed with stimuli-responsiveness by introducing natural amino acid residues with innate stimuli-responsive characteristics or introducing responsive moieties to its side chains using simple conjugating methods, rendering it an ideal biomedical material for controlled drug delivery. This feature article summarizes our recent work and other relevant studies on the development of polypeptide-based drug delivery systems that respond to single or multiple physiological stimuli (e.g., pH, redox potential, glucose, and hypoxia) for controlled drug delivery applications. The material designs, synthetic strategies, loading and controlled-release mechanisms of drugs, and biomedical applications of these stimuli-responsive polypeptides-based drug delivery systems are elaborated. Finally, the challenges and opportunities in this field are briefly discussed.

Stimuli-responsive temporary adhesives constitute a rapidly developing class of materials defined by the modulation of adhesion upon exposure to an external stimulus or stimuli. Engineering these materials to shift between two characteristic properties, strong adhesion and facile debonding, can be achieved through design strategies that target molecular functionalities. This perspective reviews the recent design and development of these materials, with a focus on the different stimuli that may initiate debonding. These stimuli include UV light, thermal energy, chemical triggers, and other potential triggers, such as mechanical force, sublimation, electromagnetism. The conclusion discusses the fundamental value of systematic investigations of the structure–property relationships within these materials and opportunities for unlocking novel functionalities in future versions of adhesives., Stimuli-responsive temporary adhesives emerge as next-generation multifunctional materials with advantages that include strong temporary adhesion, debonding on demand, and tunable reactivity.

Smart fibers with reversible optical properties have received extensive attention due to their wide potential for application in human health monitoring and wearable devices. However, achieving multi-stimuli-responsive luminescent fibers via a facile manufacturing process is challenging. Herein, novel independent multi-stimuli-responsive luminescent fibers are successfully fabricated via a facile wet-spinning process. The color of the fibers responds to ultraviolet (UV) and heat independently and in combination. The fibers emit bright red light emission (λem = 627 nm) after excitation (λex = 330 nm) which is attributed to Y2O2S:Eu3+,Mg2+,Ti4+ ceramics. The as-prepared fibers possess a tensile strength of around 9.39 MPa. The experimental results demonstrate that the multi-stimuli-responsive persistent luminescent fibers coupled with the facile preparation process make the multi-stimuli-responsive luminescent fibers a potential candidate for application in anti-counterfeiting and UV/heat detection devices.

Cancer is a multifactorial disease that involves unique tumor microenvironment (TEM) and abnormal organs with complex structures. Conventional anticancer drugs require high doses and systemic administration, and nonspecific tissue distribution causing serious side effects. Nanomaterials have far-reaching influences in cancer treatment, theranostics and imaging. Specifically, anticancer drug-loading into nanocarriers can avoid unnecessary systemic toxicity and achieve sustained drug release in response to all kinds of exogenous or endogenous stimuli. Nanocarriers can be stimulated by external (light irradiation and magnetic fields) or internal (pH, glutathione, enzymes and oxidative stress) elements, which have attracted growing attention in the field of drug delivery systems. On the basis of this powerful concept, environment-responsive nanocarriers have been designed to ensure delivery of the anticancer drug to the targeting lesion sites and effective release, which can overcome the biological barriers that limit conventional treatments and reduce the administered drug dose. Herein, this review will discuss the fundamentals of environment-responsive nanocarriers to enhance the permeability and retention (EPR) effect, and improve cancer therapy outcomes.

Photoacoustic imaging (PAI) relies on the use of contrast agents with high molar absorptivity in the NIR-I/NIR-II region. Expanded porphyrins, synthetic analogues of natural tetrapyrrolic pigments (e.g. heme and chlorophyll), constitute as potentially attractive platforms due to their NIR-II absorptivity and their ability to respond to stimuli. Here, we evaluate two expanded porphyrins, naphthorosarin (1) and octaphyrin (4), as stimuli responsive PA contrast agents for functional PAI. Both undergo proton-coupled electron transfer to produce species that absorb well in the NIR-II region. Octaphyrin (4) was successfully encapsulated into 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-poly(ethylene glycol) (DSPE-PEG2000) nanoparticles to afford OctaNPs. In combination with PAI, OctaNPs allowed changes in the acidic environment of the stomach to be visualized and cancerous versus healthy tissues to be discriminated., In this study, two expanded porphyrins, octaphyrin and naphthorosarin were evaluated as potential PA agents. The nanoparticle encapsulation of octaphyrin successfully enabled the visualization of acidic environments and the discrimination between cancerous and healthy tissues.

Multifunctional nanocomposites have drawn great attention in clinical applications because of their ability to integrate diagnostic and therapeutic functions. Manganese dioxide (MnO2), owing to its biocompatibility and magnetic resonance imaging (MRI) properties, has been widely applied in biomedical research. Our previous work on biogenic MnO2 nanoparticles (Bio-MnO2 NPs) revealed that intrinsic photothermal properties and stimuli-responsive MRI imaging are particularly promising for the development of theranostic systems. However, further improvement in the photothermal therapy (PTT) performance of Bio-MnO2 NPs is still required. Herein, we have improved the PTT efficiency of Bio-MnO2 NPs by in situ synthesis of fluorescent polydopamine (PDA) while generating additional stimuli responsive fluorescence properties in this system, thus further broadening the scope of their theranostic functions. These synthesis conditions are mild and green. The fluorescence of PDA was quenched by capping Bio-MnO2 NPs and could be recovered upon degradation of Bio-MnO2 NPs inside tumour cells. Additionally, Mn2+ released from the nanoparticles can support T1-weighted MR imaging. Compared to the Bio-MnO2 NPs alone, the integration of Bio-MnO2 NPs and PDA significantly enhances the photothermal performance in vitro and in vivo. With their high biocompatibility, these multifunctional composite nanodevices hold great potential for fluorescence imaging and MRI-guided photothermal therapy.

A method for the synthesis of DNA-based acrylamide hydrogel microcapsules loaded with quantum dots as a readout signal is introduced. The shell of DNA-acrylamide hydrogel microcapsules is encoded with microRNA-responsive functionalities, being capable of the detection of cancer-associated microRNA. The microRNA-141 (miR-141), a potential biomarker in prostate cancer, was employed as a model target in the microcapsular biosensor. The sensing principle of the microcapsular biosensor is based on the competitive sequence displacement of target miR-141 with the bridging DNA in the microcapsule's shell, leading to the unlocking of DNA-acrylamide hydrogel microcapsules and the release of the readout signal provided by fluorescent quantum dots. The readout signal is intensified as the concentration of miR-141 increases. While miR-141 was directly measured by DNA-acrylamide hydrogel microcapsules, the linear range for the detection of miR-141 is 2.5 to 50 μM and the limit of detection is 1.69 μM. To improve the sensitivity of the microcapsular biosensor for clinical needs, the isothermal strand displacement polymerization/nicking amplification machinery (SDP/NA) process was coupled to the DNA-acrylamide hydrogel microcapsule sensor for the microRNA detection. The linear range for the detection of miR-141 is improved to the range of 102 to 105 pM and the limit of detection is 44.9 pM. Compared to direct microcapsular biosensing, the detection limit for miR-141 by microcapsules coupled with strand-displacement amplification is enhanced by four orders of magnitude.

Stimuli-responsive polymers (SRPs) are capable of changing their solubility, conformation, and volume in response to external stimuli. By understanding the nature of the responsivity and the synthetic challenges, new SRPs can be synthesized with enhanced responsivities at scales that will allow their use in the real world. In this review, many fundamental concepts and recent advances in SRPs for sensing and actuation are presented. A variety of sensors that can respond to physiologically relevant species and stimuli are reviewed, including temperature/pH, proteins, glucose and ions. The review also includes examples of the use of SRPs for artificial muscles, soft robots, cell culture, and drug delivery.

The combination of polymerization-induced self-assembly (PISA) and post-polymerization modification is a versatile route to prepare core-functionalized nanoaggregates. PISA is a useful approach for preparing in situ self-assembled nano-objects, in which morphological nanostructures are tunable with a high solid concentration that can afford scale-up syntheses. Herein, the preparation via PISA of diblock copolymers that have functional groups in their structures to be further post-functionalized using active modifiers has been reviewed. The resulting multifunctional nanoaggregates exhibit great potential for use in a wide range of applications, for example, crosslinked nano-objects having improved stability, stimuli responsive vehicles for drug delivery, and fluorescent nanomaterials for bioimaging.

Traditional textiles with hydrophilic properties can absorb sweat secreted from the skin, but cause an undesirable cold sensation and adhere to the skin. Textiles with an effect similar to an air conditioner and sensing properties have attracted great interest because of their desirable performance, comfort, and energy-saving properties. However, fabricating functional textiles with moisture management and pH identification properties remains a difficult challenge. Herein, we demonstrate a fluorine-free hydrophobic loofah fabric with embedded thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microspheres as microplugs, which endowed it with directional liquid transport and body temperature regulation depending on the temperature. Based on the phase separation of the microplugs and capillary gradients, the microplugs of the self-venting textile are opened and generate drying and cooling effects via high moisture transport in hot weather, whereas the pores of the microplugs close to retain heat in cold weather. Moreover, the multifunctional loofah textile exhibits hydrophobic or hydrophilic behaviour for droplets with different pH values, which can provide real-time liquid signal detection. The water repellency and the wicking, permeability, and mechanical properties of the hydrophobic outer surface of the loofah textile are not affected by harsh conditions. This study not only provides ideas for the design and preparation of textiles for personal comfort, but also environmentally friendly and acid/alkali-protective clothing with great potential applications in demanding situations.

Stimuli-responsive metal-organic framework nanoparticles, NMOFs, provide a versatile platform for the controlled release of drugs and biomedical applications. The porous structure of NMOFs, their biocompatibility, low toxicity, and efficient permeability turn the NMOFs into ideal carriers for therapeutic applications. Two general methods to gate the drug-loaded NMOFs and to release the loads were developed: by one method, the loaded NMOFs are coated or surface-modified with stimuli-responsive gates being unlocked in the presence of appropriate chemical (e.g., ions or reducing agents), physical (e.g., light or heat), or biomarker (e.g., miRNA or ATP) triggers. By a second approach, the drug-loaded NMOFs include encoded structural information or co-added agents to induce the structural distortion or stimulate the degradation of the NMOFs. Different chemical triggers such as pH changes, ions, ATP, or redox agents, and physical stimuli such as light or heat are applied to degrade the NMOFs, resulting in the release of the loads. In addition, enzymes, DNAzymes, and disease-specific biomarkers are used to unlock the gated NMOFs. The triggered release of drugs for cancer therapy, anti-blood clotting, and the design of autonomous insulin-delivery systems ("artificial pancreas") are discussed. Specifically, multi-drug carrier systems and functional NMOFs exhibiting dual and cooperative therapeutic functions are introduced. The future perspectives and applications of stimuli-responsive particles are addressed.

Herein, we report the first example of two pure organic polymorphs with stimuli-responsive single/dual phosphorescence transformation. By analyzing the crystal structures and theoretical results, it could be understood that efficient intermolecular interactions could restrict the molecular movements and lock distinct molecular conformations, leading to different phosphorescence behaviors. Besides, single/dual phosphorescence could transform into each other by heating or under solvent vapor conditions. Considering such unique properties, logical sensors (AND gate and OR gate) were built by providing different emission colors as inputs. Our work provides not only important information for understanding the dual RTP mechanism but also unique stimuli-responsive pure organic phosphorescent materials to enrich material fields.

Stimuli responsiveness has long been a fascinating feature of smart material design. Polydopamine (PDA), a nature inspired polymeric pigment, exhibits excellent photo-responsive properties and has active surface functionality for loading various responsive motifs, making it a promising candidate for the construction of stimuli-responsive smart functional materials. PDA has long been considered as a robust coating material, but its responsive feature has rarely been emphasized in the past reviews. Herein, we present the first effort to summarize recent advances in the design strategies, responsive mechanisms, and diverse applications of stimuli-responsive PDA-based smart materials; the stimuli include light, pH, chemicals, temperature, humidity, electric fields, mechanical force, magnetic fields, and ultrasound. Moreover, the current trends, challenges, and future directions of stimuli-responsive PDA-based materials are also elaborated.

The functionality of multi-stimuli-responsive hydrogels in physiological states is the reason for the increased attention of hydrogels nowadays. Multi-stimuli-responsive hydrogels exhibit tunable changes in swelling or mechanical properties in response to predetermined combinations of stimuli such as pH, temperature, ionic strength, electric field, magnetic field, light, chemical triggers, enzyme concentration, redox species, reactive oxygen species (ROS), and glucose levels. This review summarizes the recent advances in multi-stimuli-responsive hydrogels used in medical approaches. The first part of the review highlights the medical applications of polymer-based and supramolecular hydrogels and emphasizes the priority of multi-stimuli hydrogels over single-stimuli hydrogels. Also, recent studies in medical applications of multi-stimuli-responsive hydrogels are collected with a focus on self-healing hydrogels, anti-bacterial materials, and drug-delivery systems.

The vinyl caprolactam (VCL) based microgel system has become the center of great attention due to its versatile properties. Copolymerization of VCL with an ionic monomer imparts pH responsive properties into the microgel system in addition to thermo-sensitivity. Stimuli responsive behavior of VCL-based microgels makes them prospective and appealing candidates for practical applications covering the fields of drug delivery, catalysis and optical devices. In the last few years, VCL-based microgels have been used as microreactors and stabilizers for the synthesis and stabilization of inorganic nanoparticles to obtain hybrid microgels. The present review article provides a summary of the present-day progress of fabrication, stabilization, categorization and analysis of VCL-based microgels and their hybrids with different morphologies. The stimuli responsive properties and applications of VCL-based hybrid microgels have been reviewed critically. The remaining problems which need to be addressed have been pointed out for further advancement in this field.

Graphene possesses a set of unique physicochemical properties including exceptional mechanical, thermal, and electrical properties, making it an excellent candidate for constructing materials for a wide range of applications including the vast field of separation technology using membranes. Separation membranes based on graphene and its derivatives have shown satisfactory results over the years when applied to environmental systems such as wastewater treatment and gas purification, which is a great contribution in sustainable development. However, membrane separation research is generally performed using conventional membranes with fixed driving force and separation properties that suffer from fouling and decline in performance upon long-term use or when a change in the environmental conditions occur. These issues can be solved by employing an emerging technology that makes use of graphene and its derivatives combined with polymeric materials to construct stimuli-responsive or “smart” membranes that respond to the changes in their environment such as chemical cues, temperature, pressure, and external fields, and have a self-regulated separation performance due to reversible physicochemical properties. In this review, we present a report on the recent advancements on graphene-based separation technology including a concise discussion on the basic structure and properties of graphene and its derivatives, various membrane fabrication methods, and their employment on the different areas of membrane separation. More importantly, the main focus of this paper is to evaluate the design and utilization of graphene-based smart separation membranes.

Although the utilization of rigid particles can afford stable emulsions, some applications require eventual emulsion destabilization to release contents captured in the particle-covered droplet. This destabilizing effect is achieved when using stabilizers that respond to controlled changes in environment. Microgels can be synthesized as stimuli responsive polymeric gel networks that adsorb to oil/water interfaces and stabilize emulsions. These particles are commonly hydrogels that swell and collapse in water in response to environmental changes. However, amphiphilic functionality is desired to enhance the adsorption abilities of these hydrogels while maintaining their stimuli responsivity. Microfluidic techniques are used to synthesize Janus microgels with two opposing stimuli responsive hemispheres. The particles have a temperature responsive domain connected to a pH responsive network where each side changes its hydrophilicity in response to a change in temperature or pH, respectively. The Janus microgels are amphiphilic in acidic conditions at 19 °C and alkaline conditions at 40 °C, while the opposite conditions cause a reduction of the amphiphilicity. By stabilizing emulsions with these dual responsive microgels, "smart" droplets that respond to environmental cues are formed. Emulsion droplets remain stable with smaller diameters when aqueous solution conditions favor amphiphilic particles yet, coalesce to larger droplets upon changing pH or temperature. These responsive Janus microgels represent the advancing technology of responsive droplets and demonstrate the applicability of microgels as emulsion stabilizers.

In the past decades, metal-organic frameworks (MOFs) have attracted considerable interest not only for their intrinsic aesthetic appeal but also their wide potential applications. The most distinctive feature of MOFs is their flexibility, which makes them exhibit a much larger magnitude of responses toward external stimuli than traditional materials. In addition, the stimuli usually have a huge impact on the MOFs' performances. A fundamental understanding of the structure evolution process under external stimuli is critical to reveal the structure-property relationships in MOFs. In this feature article, we tried to summarize how the crystal structure changes toward external stimuli, such as guest insertion, temperature, pressure, electric field, and light.

Interaction of acridine orange (AOH+) dye with water soluble anionic p-sulfonatocalix[n]arene (SCXn) hosts, SCX4 and SCX6, having different cavity dimensions, has been investigated using multispectroscopic techniques. Intriguing modulation in the photophysical properties of AOH+ upon interaction with SCXn hosts indicate the formation of different host-guest complexes at different regions of the host concentrations. At lower host concentrations, AOH+ undergoes SCXn assisted aggregation, causing a drastic reduction in fluorescence intensity. At higher host concentrations, aggregated-AOH+-SCXn complexes disintegrate and monomeric-AOH+-SCXn exo and inclusion complexes are eventually formed, leading to a huge fluorescence enhancement finally. Observed effects are more pronounced with SCX6 as compared to SCX4 host. Time-resolved fluorescence studies indicate that at very high host concentrations, there is also a diffusion-controlled dynamic quenching for both monomeric-AOH+-SCXn exo and inclusion complexes, caused by the free SCXn present in the solution, a phenomenon not reported before for such host-guest systems. The aggregated-AOH+-SCXn complexes at lower host concentration were employed to investigate displacement study using an antiviral drug, 1-adamantanamine (AD) and a neurotransmitter, acetylcholine (AcCh), as the competitive binders cum external stimuli, which resulted in a drastic recovery of the fluorescence reduced initially due to aggregation process. Though both the AOH+-SCXn systems act as efficient supramolecular assemblies in sensing AD and AcCh as the analytes through fluorescence "OFF-ON" mechanism, the effect is more pronounced for AOH+-SCX4 system as compared to AOH+-SCX6. SCXn induced interesting modulation in the photophysical properties of AOH+ and the stimulus responsive dye displacement observed for aggregated-AOH+-SCXn systems can expectedly find applications in fluorescence OFF-ON sensing, supramolecular functional materials and similar others.

Chemical and biological/biochemical sensors are capable of generating readout signals that are proportional to the concentration of specific analytes of interest. Signal sensitivity and limit of detection/quantitation can be enhanced through the use of polymers, nanomaterials, and their hybrids. Of particular interest are stimuli-responsive polymers and nanomaterials due to their ability to change their physical and/or chemical characteristics in response to their environment, and/or in the presence of molecular/biomolecular species of interest. Their individual use for sensing applications have many benefits, although this review focuses on the utility of stimuli-responsive polymer and nanomaterial hybrids. We discuss three main topics: stimuli-responsive nanogels, stimuli-responsive network polymers doped with nanomaterials, and nanoparticles modified with stimuli-responsive polymers.

Corrosion is a financial and enviromental plague which leads to the deterioration of our infrastructures. Using corrosion inhibitors at low concentrations in coatings is one effective method for preventing corrosion. Inspired by the development of polymer-drug conjugates, corrosion inhibitors are incorporated in various polymer structures to create novel materials for hindering corrosion. We discuss the strategies to covalently integrate corrosion inhibitors in polymer structures to form polymer-inhibitor conjugates. Inhibitors are conjugated to polymers via non-labile or stimuli-labile linkages to allow the release of the inhibitors upon onset of corrosion. The application and anticorrosion performance of representative polymers are also discussed.

The control of the conformational transformation of KLA peptides in response to external stimuli would be an important motif to design effective peptide therapeutic agents. In this report, we investigated the stimuli-responsive conformational transformation of KLA peptide ((KLAKLAK)2 sequence) with the azobenzene stapling units in the middle of the sequence and at both the terminal moieties. The KLA peptide with an azobenzene stapling unit in the middle of the sequence exhibited a stimuli-responsive conformational transformation triggered by both UV irradiation and reductive cleavage. The KLA peptide with azobenzene stapling at both the terminals exhibited stimulus-responsive conformational transformation triggered by reductive cleavage of the azobenzene unit, but not by UV irradiation.

Organic cocrystals, as an intelligent design strategy of functional materials, have received extensive attention in the scientific community over recent years. The presence of diverse molecular arrangements and rich intermolecular interactions, in particular intrinsic charge transfer in organic cocrystals, depicts such materials as ideal systems to control and tailor their physical properties for stimuli-responsive applications. However, as a continuous emerging research field, a systematic review to summarize this promising application area remains unexplored. Herein, we focus on recent research progress and potential advantages of organic cocrystals in the field of stimuli response. First, an overview of the basic characteristics of organic charge transfer cocrystals is discussed. Subsequently, the stimuli-responsive behaviors of organic cocrystals under mechanical force, solvent, acid–base, light and heat stimuli are highlighted. Lastly, the future developments and prospects of these materials in a stimuli-responsive field are outlined.

Nanosystems responsive to a tumor microenvironment (TME) have recently attracted great attention due to their potential in precision cancer theranostics. However, theranostic nanosystems with a TME-activated consecutive cascade for the accurate diagnosis and treatment of cancer have rarely been exploited. Herein, an activatable theranostic nanosystem (Bi2S3-Ag2S-DATS@BSA-N3 NYs) is designed and constructed on the basis of a one-pot biomineralization method and surface functional modification to improve second near-infrared (NIR-II) fluorescence/photoacoustic (PA) imaging-guided photothermal therapy (PTT)/gas therapy (GT). Based on enhanced penetration and retention (EPR) effect-mediated tumor accumulation, the tumor-overexpressed glutathione (GSH) can accelerate hydrogen sulfide (H2S) generation from the nanoparticles by reacting with the encapsulated diallyl trisulfide (DATS). Meanwhile, the in situ released H2S can be used not only for gas therapy, but also to start the reduction of -N3(-) to -NH2(+), thereby enhancing the tumor-specific aggregation of NYs. As a result, the activatable nanosystems with excellent tumor accumulation and biodistribution could achieve an accurate NIR-II/PA dual-modality imaging for guiding the synergistic anticancer efficacy (PTT/GT). Thus, this work provides a promising TME-mediated continuously responsive strategy for efficient anticancer therapy.

A bright difluoroboron β-diketonate derivative 1 showing four emission colors (green, yellow, orange and red) with high quantum yields (41–74%) in four polymorphs and one amorphous state is reported. Green-emissive crystals (1-G and 1-G′) exhibit dimeric aggregation structures due to the strong molecular π–π interaction but exhibit hypsochromic emission compared to yellow-emissive crystals (1-Y) with monomeric aggregation because of lacking such π–π interactions. These novel emission phenomena are rationalized by theoretical calculations. High fluorescence sensitivity of compound 1 to its molecular packing modes results in excellent responsive behavior to multiple external stimuli thereby showing reversible change of emission colors under mechanical grinding, heating, solvent fuming and hydrostatic pressure.

A tetraphenylethene-based Pd2L4 metallacage was self-assembled from four TPE-pyridine ligands with two Pd2+ ions. This metallacage with D4 symmetry exhibited a classical aggregation-induced emission property in different solvents and reversible stimuli-responsive behaviour with chloride ions and silver ions, successively.

Amphiphilic alternating copolymers (AACs) possess unique self-assembly behaviours owing to their unique regular architecture. In this work, we employed dissipative particle dynamics simulations to explore the self-assembly behaviours of AACs with rigid pendants in selective solvents. The effects of block lengths and copolymer concentrations on the morphology of aggregates were examined. Two morphology diagrams were mapped out to provide a comprehensive understanding of the effect of these factors. The self-assembly process and the structure of aggregates were analysed in detail. The result shows that the amphiphilic alternating architecture can dramatically disturb the tendency of the ordered arrangement of rigid blocks. Furthermore, a rod-to-coil conformation transition of rigid blocks was performed to investigate the stimuli-responsive self-assembly behaviours. A comparison between the simulation results and our previous experimental observations was made, and the agreement is achieved.

The external surfaces of two-dimensional (2D) nanoarchitectures are easily functionalized to confer attractive and unique properties in nanomedicine. On the basis of the high surface area for desired drug-loading capacity, efficient cell uptake, attractive biocompatibility, and established chemical functionalization routes, layered nanoarchitectures as hosts are significantly exploited to function as intelligent drug delivery platforms for chemotherapy and combined therapies. Additionally, functionalization on the surfaces of 2D nanomaterials is subsequently integrated with stimuli-responsive characteristics and, thus, 2D hybrid-based drug release platforms equipped with the characteristics of triggered cargo release contribute to improving therapy efficacy with simultaneously diminished side effects. Herein, we briefly introduce the classification of 2D nanomaterials integrated with chemical functionalization, with a complete list of responsive endogenous and exogenous triggers. Comparisons between diverse 2D nanoarchitectures are highlighted and proposed horizons are also presented for addressing current drawbacks that are affecting their potential clinical applications.

Multi-stimuli responsive (MSR) chromic materials which can exhibit a color change when exposed to external stimuli demonstrate huge potential in developing new intelligent devices. However, they commonly require complicated synthesis processes that are not suitable for mass production. To facilitate the fabrication of MSR devices, for the first time, we propose a facile 3D integration strategy to rationally assemble various commercial chromic materials, light shielding layers, and a stretchable substrate into a set of MSR devices equipped with thermo-/photo-/mechanochromic characteristics with negligible cross-interferences. Notably, the mechanochromic sensitivity can be readily adjusted to multiple levels via facile pre-stretching methods. Moreover, two types of MSR units are integrated into an interactive electronic device, which exhibits thermo-/photo-/electrochromic responses, and two levels of mechanochromic responses with color changes at 100% and 200% strain, respectively. In addition, another highly sensitive MSR unit is applied to a wearable motion/environmental monitoring chromic device, which can detect finger bending within 30% strain, and monitor environmental stimuli (UV, temperature) with thermal mapping capability. A smartphone-based colorimetric analysis app was also developed for finger bending detection. Comprehensive quantitative characterization and finite element analysis are used to elucidate the performance and intrinsic mechanisms of these MSR responses.

Emerging technologies are increasingly reliant on materials that deliver multiple functionality. For example, hydrogels using dynamic covalent crosslinks have proven well-suited for the preparation of functional systems with properties including self-healing, shape memory, and stimuli-induced stiffness changes. These covalent bonds are capable of exchanging, dissociating or switching in response to various stimuli. In this review stimuli responsive dynamic covalent hydrogels are discussed on the basis of their chemistry and how the gels are increasingly used in novel applications. Challenges and potential future developments of dynamic covalent hydrogels are also discussed.

Two multi-stimuli responsive compounds 1 and 2, obtained by the introduction of a carboxyl group to a cyanostilbene skeleton, revealed a fluorescence response to a change in the pH, amine vapors and mechanical stimulus. After scrutinizing their single crystal structures and comparing them with those of reference compounds 3 and 4, the molecules were found to demonstrate face-to-face stacking through multiple π–π interactions to restrain the non-radiative relaxation of the excited state, which led to mechanoluminescence (ML) during the fracturing process of the crystal. The discovery of these novel ML luminogens provides guidance for the design of pure organic ML materials.

Artificial supramolecular nanostructures showing transient properties have attracted significant attention in recent years. New discoveries in this area may provide insights into a better understanding of the sophisticated organization of complex biomolecular systems. Nevertheless, research concerning such materials is still limited. Better knowledge of the chemical reactivity and corresponding molecular transformations of self-assembling molecules, which guide their assembly/disassembly, may provide an opportunity to construct transient supramolecular nanostructures capable of showing chemical stimulus responsiveness. Herein, we report a short peptide derivative containing a hydrazone bond, which shows transient hydrogel formation (no only sol-to-gel but also gel-to-shrunken gel phase transition) accompanied by continuous transformation and growth of supramolecular nanostructures triggered by hydrazone-oxime exchange reaction in response to hydroxylamine. Such controlled shrinkage behavior of supramolecular hydrogels in response to specific chemical stimuli has rarely been explored compared with conventional polymer hydrogel systems.

CO2 capture and separation by using adsorbent materials have exhibited great potential for application in strategies that alleviate environmental degradation. Stimulus-responsive adsorbent materials, a kind of advanced functional materials, have recently attracted tremendous interest. These materials can recognize external stimuli and exhibit tunable physical or chemical properties, thus controlling CO2 adsorption and separation behaviors. This review highlights the recent developments of stimulus-responsive adsorbent materials that can modulate CO2 capture and separation properties in response to some specific stimuli, including pressure, temperature, light, electric field, magnetic field, guest molecules, and other newly emerging stimuli. To understand stimulus-responsive behaviors in depth, the response mechanisms are summarized and elucidated. This review also proposes future directions in the development of stimulus-responsive materials for CO2 capture and separation.

In nature, organisms control their deformation and locomotion through multi-functional synergy in response to environmental changes. Nowadays, most synthetic biomaterial systems are capable of realizing single-mode actuation movement under external triggers through biomimetic simulation, while complicated and continuous locomotion in artificial materials with multi-dimensional responsiveness remains to be explored. Here we report an anisotropic melem-formaldehyde polymer that is self-assembled from a one-dimensional (1D) chain into a two-dimensional (2D) film. The stimuli-responsive polymer film shows anisotropic responses in both radial and axial directions on contacting with different solvents (liquid or vapor) in a single material. Complex multi-dimensional motion patterns can be actuated and reversibly controlled by virtue of different interactions within the 1D line and 2D film as well as the gradients along the thickness direction. The developed architecture with tunable and programmable anisotropy is potentially applicable in soft material actuators that can operate in various environments.

A ruthenium complex showing multi-stimuli-responsive isomerization was synthesized. The catalytic activity of this complex toward water oxidation showed responses to visible-light irradiation and heat due to photoisomerization and thermal back-isomerization, respectively. DFT calculations suggested that a pendant moiety in the complex was key to controlling the catalytic activity.

Platinum(II) complexes with various π-conjugated ligands have received great attention thanks to their exceptional spectroscopic properties and applications in optical devices, chemical sensors, and bio-imaging. Their unique square-planar structures and coordinate-unsaturation characteristics induce the propensity to form self-assembled phosphorescent materials through metal–metal, π–π stacking, and other intermolecular interactions. In this review, we mainly describe the photophysical properties and structure–property relationships of multi-chelating platinum(II) complexes as well as the construction and application of phosphorescent supramolecular materials in recent years.

Efficient transformation of ACQ materials to AIE luminogens using simple design principles of positional isomerization and C-C bond exclusion is presented here. Consequently, the bond link, position and packing influence the photophysical properties that can be utilized in erasable secret inks, pressure sensors and chemical warfare sensors.

A bean-shaped and dual-functionalized organic-inorganic hybrid supramolecular system with a GSH-dependent turn-on fluorescence enhancement property and stimuli-responsive drug delivery function endowed with leaning towerarene-based switches has been constructed for simultaneous tumor inhibition and imaging.

Aggregation induced emission (AIE) materials are in the spotlight of current materials development due to their unique properties and potential applications in light-emitting devices, bio-imaging and sensors. In this work we synthesised and thoroughly studied a novel luminogen based on bis(4-((9H-fluoren-9-ylidene)methyl)phenyl)thiophene (BFMPT) showing polymorph-dependent AIE. BFMPT crystallises in two polymorphs of different crystal shapes and colours, however both of them are highly-luminescent with the same photoluminescence (PL) quantum yield of 40%. Polymorph I can undergo irreversible phase transition to polymorph II. Deep quantum chemical study of BFMPT revealed that inter- and intramolecular interactions in both polymorphs are very similar and the main contributor to the optical difference between the polymorphs is a variation of BFMPT conformation. The thermal stress was demonstrated to negligibly affect the PL efficiency of BFMPT crystals. Due to high intrinsic torsional freedom and high solid-state PL efficiency, BFMPT could serve as a basis for the molecular design of high performance AIE materials.

We report the design and fabrication of a multifunctional persistent luminescent nanoprobe for imaging guided dual-stimulus responsive and triple-synergistic therapy of drug resistant tumor. The integration of the dual-stimulus of an acidic microenvironment and laser irradiation with the triple-synergistic therapy of doxorubicin, photothermal and siRNA offers excellent therapeutic performance for drug resistant tumor cells with high specificity and little side effects.

For many decades, stimuli-responsive materials have been studied and utilized in various fields, ranging from chemical sensors to controlled drug release. Among these responsive materials are self-immolative polymers (SIPs) that allow for end-to-end depolymerization and the ability to release a desired cargo on demand or amplify analyte detection. However, in typical SIP systems, the triggering event leads to a relatively uncontrolled degradation process. Herein we present a multi-stimuli trigger that utilizes the combination of heat and acid to impart control over the trigger event and thus the degradation process. By controlling this reaction, we achieve temporal control over the trigger cleavage and subsequent depolymerization and release of cargo from the SIP.

Stimuli-responsive supramolecular nano-systems (SRNS) have been a trending interdisciplinary research area due to flexibly being able to switch functions through exposure to appropriate stimuli, which makes the systems very attractive in multiple fields where precise control is key. Pillar[n]arenes, as a new generation of macrocyclic host molecules, possess captivating properties including versatile chemical modifiability, rigid electron-rich structure and tuneable size of the cavity, and have become extremely valuable molecules/building blocks in constructing SRNS via non-covalent interactions. Significantly, numerous SRNS based on pillar[n]arenes have been fabricated in the past few years and found extensive applications in hydrogels, sensors, bioimaging, diagnosis, and, importantly, controlled drug release. In this review, we highlight the advances of SRNS based on pillar[n]arenes, which are categorised in terms of response factors including pH, redox, enzymes, temperature, light and ions. The related applications of pillar[n]arenes are then summarized into the following areas: fluorescent chemosensors, drug delivery, molecular switches, and other functional materials. In addition, the future potential for construction of SRNS based on pillar[n]arenes and their applications are discussed.

Cyclodextrins (CDs) with highly branched hydroxyl moieties and hydrophobic cavities, have been widely employed as building blocks for the construction of CD-based nanoplatforms. By the incorporation of responsive functionalities, these nanoplatforms can be responsive to various stimuli, such as pH, temperature, redox, enzymes, light and magnetic fields. In this review, we summarize recent advances of stimuli-responsive CD-based nanoplatforms for cancer treatment and theranostics. Firstly, we introduce the synthesis of CD-based derivatives, CD-conjugated polymers and CD-decorated inorganic nanoparticles. Afterwards, the construction and respective properties of stimuli-responsive CD-based nanoplatforms are elaborated. Thirdly, we highlight their various biomedical applications, especially for cancer treatment and theranostics. At the end, the current challenges and new opportunities of CD-based nanoplatforms are also discussed.