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ABSTRACT Micro to Macro: Translating the behavior of small molecules to functional materials through the use of external stimuli by Kyle Darrin Clark As the scientific community continues to develop a vast array of functional materials, the demand for improved control over a broad range of properties becomes all the more prevalent. Stimuli such as light and temperature have been employed consistently throughout history as easily accessible tools for chemists, and in recent years they have shown great promise as a means to control polymer property on-demand. The discovery of novel photo-responsive small molecules and temperature triggered reactions and applications of the materials are presented. Self-immolative polymers (SIPs) are a sub-class of stimuli-responsive materials that, when exposed to an appropriate stimulus, degrade end-to-end into their composite monomers and release a given cargo. One challenge with current SIPs is that once initiated, unraveling of the polymer typically occurs in an uncontrolled fashion. To address this challenge, we designed a SIP system capable of dual-stimulus activation, allowing on/off control of depolymerization. Specifically, furan-endcapped polyurethanes were prepared and the controlled depolymerization was studied with both acid and heat triggers. From these SIPs, a new class of temporally controlled degradable materials could be accessed which hold potential for on/off drug release. Photo-responsive polymers represent another class of stimuli responsive material with myriad of applications that range from controlled micelle rupture and surface patterning to mechanical actuators. Advances in this area has been fueled by photoswitching molecules – compounds that change molecular conformation and numerous properties in response to light. Donor–acceptor Stenhouse adducts (DASAs), a novel class of photochromic developed in our group, exhibit large changes in color, polarity and molecular volume upon visible light irradiation. The first generation of these photochromic molecules were limited to alkyl amine donors, absorbing green light. To expand their capabilities, we developed second and third generations DASA derivatives, vastly expanding the scope of both structure and properties. Second generation DASAs were synthesized and using aniline derivatives, yielding compounds with red-shifted absorption windows. Although advantageous, we discovered that these new derivatives lost control over the thermodynamic equilibrium between the open and closed state in the dark. As such, a third generation DASA derivative was developed. By modifying the acceptor unit, we demonstrated both tunable equilibria between the open and closed form and an expanded absorption window (550 to 750 nm). With optimized DASA derived photochromic material in hand, we focused on demonstrating the ability convert light into mechanical work. To accomplish this, we developed a new approach to liquid crystal elastomers (LCEs) based on mild, additive free Diels–Alder step-growth polymerization reaction. This approach expands the functional-group tolerance of current click chemistry platforms, enabling Michael-acceptor-bearing compounds such as DASAs to be incorporated into LCE networks. In addition, this new method provides a platform to study the performance of a multitude of photoswitches under a unified polymer system. This holds the potential to enable for the first time structure-property relationships between the photochromic material and LCE architecture that are needed to advance this field.

This article reviews recent progress in the use of stimuli-responsive polymers for soft robotics. First, we introduce different types of representative stimuli-responsive polymers, which include liquid crystal polymers and elastomers, hydrogels, shape memory polymers, magnetic elastomers, electroactive polymers, and thermal expansion actuators. We focus on the mechanisms of actuation and the evaluation of performance and discuss strategies for improvements. We then present examples of soft robotic applications based on stimuli-responsive polymers for bending, grasping, walking, swimming, flying, and sensing control. Finally, we discuss current opportunities and challenges of stimuli-responsive soft robots for future study.

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.

The hybridization of mechanically responsive molecular crystals with polymers has proven to be an efficient approach to fabricate smart hybrid materials that can produce multiple motions upon exter...

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

Natural bioactive ingredients have lower bioavailability because of their chemical instability and poor water solubility, which limits their applications in functional foods. Among diverse biopolymers that can be used to construct delivery systems of bioactives, chitosan has attracted extensive attention due to its unique cationic nature, excellent mucoadhesive properties and easy modification. In this review, chitosan and its composites-based food-grade delivery systems as well as the factors affecting their performance are summarized. Modification, crosslinking, combination with other biopolymer or utilization of coating material can effectively overcome the instability of pure chitosan-based carriers under acidic conditions, thereby constructing chitosan and its complex-based carriers with conspicuously improved performance. Furthermore, the applications of chitosan-based delivery systems in nutrition and health as well as their future development trends and challenges are discussed. Functional food ingredients, functional food packaging and biological health are potential applications of chitosan-based food-grade delivery systems. The research trends of nutraceutical delivery systems based on chitosan and its composites include co-delivery of nutrients and essential oils, targeted intestinal delivery, stimulus responsive/sustained release and their applications in real foods. In conclusion, food industry will be significantly promoted with the continuous innovation and development of chitosan-based nutraceutical delivery systems.

Cancer treatment is challenging due to late-stage diagnosis, drug resistance and systemic toxicity of chemotherapeutic agents. The formulation of the drug into nanoparticles (NPs) can enhance the treatment efficacy and effectiveness. Therefore, a new cationic niosomal formulation, which contains Tween 80, Tween 60, cholesterol and lysine amino acid as a platform model to enhance transfection efficacy and reach more acceptable stability, and curcumin (Cur) as a biological anti-cancer drug, are introduced. Here, the authors focused on the design and synthesis of novel lysine-mediated niosomal NPs for the effectual and controlled release of the antitumor agent, Cur, and turned to optimize niosome formulations, concerning the volume of cholesterol and surfactant to implement these anticancer agents, simultaneously. The characterization of NPs s was carried out and the results showed the successful synthesis of Cur-entrapped niosomal NPs with high efficacy, sufficient positive charges and a favorable size (95/33 nm). The in vitro studies have been performed to investigate the cytotoxicity, cellular uptake and apoptosis of normal and cancer cells treated by black niosome, free Cur and niosom-loaded Cur. The results showed that implementing agents by niosome caused enhanced cytotoxicity, uptake and anticancer activity in cancer cells in comparison with normal cells. Furthermore, the effect of this nanodrug was surveyed on the 4T1 xenografted Balb/C mouse tumor model. Cur delivery to cancer models caused a higher tumor inhibition rate than in other groups.

A judicious strategy was utilized to envision the substantial regio-positional effects of substituents on the photophysical properties of the 2H-chromen-2-one-3-benzothiazole scaffold-based push-pull framework, named 6-X-CUMs. Among them, 6-NEt2-CUM reveals prominent excited-state intramolecular charge transfer with a large change of dipole moment (Δμ ∼ 18.23 D), hence displaying remarkable emission solvatochromism from the green (536 nm in cyclohexane) to far-red region (714 nm in dimethyl sulfoxide) and a high-temperature sensitivity (-0.23 nm °C-1). These, together with unique basicity and acido-/vaporchromism upon acidification elucidated by NMR and photospectroscopic studies, show stark contrast to the conventional 7-NEt2-CUM. The new series of these tailored 6-X-CUMs represents a new dimension in tailoring the photophysical properties for the development of a promising class of multistimuli-responsive materials.

The objective of the present work was to develop stimuli-responsive PEGylated nanoparticles system comprising of xanthine oxidase, Bleomycin and diallyl trisulfide in order to promote their signifi...

Donor-acceptor Stenhouse adducts (DASAs) are a photo-switch class that undergoes triene cyclisation in response to visible light. Herein, electrochemical oxidation is demonstrated as an effective alternative stimulus for the triene cyclisation commonly associated with photo-switching.

Stimuli-responsive fibers are highly desirable for their potential applications in areas such as anti-counterfeiting, optical memory systems, colorimetric sensing, and bioimaging sensors. An iridescent luminescent fibers that can achieve multi-color with long afterglow and photochromic properties is always required in color-on-demand applications. Here, a set of distinct three-primary colors luminescent fibers based on red-green-blue (RGB) system. Y2O2S:Eu3+, Mg2+, Ti4+ (red), SrAl2O4:Eu2+, Dy3+ (green), Sr2MgSi2O7: Eu2+, Dy3+ (blue) are successfully synthesized. Spiropyran and as-prepared luminescent materials are introduced into PAN fibers by a one-step extrusion wet-spinning process to achieve distinct three-primary colors luminescent photochromic fiber. These as-prepared fibers emit bright lights under excitation of ultraviolet with long afterglow. These fibers exhibit outstanding tensile properties which allow knitting or weaving them into demonstrated functional designs for aesthetic designs and encryption/decryption protocols. Comparing with previous studied stimuli-responsive fibers, our research focus on distinct three-primary colors luminescent photochromic fibers present enormous potential in 3D printing, information encryption, and next generation smart fibers.

Microneedle (MN) patches consisting of miniature needles have emerged as a promising tool to perforate the stratum corneum and translocate biomolecules into the dermis in a minimally invasive manner. Stimuli-responsive MN patches represent emerging drug delivery systems that release cargos on-demand as a response to internal or external triggers. In this review, a variety of stimuli-responsive MN patches for controlled drug release are introduced, covering the mechanisms of action toward different indications. Future opportunities and challenges with respect to clinical translation are also discussed.

In this work, using supramolecular polyurethanes theories, two polycaprolactone-based polyurethanes with 2-ureido-4-[1H]-pyrimidinone (UPy) motifs capable of forming quadruple hydrogen bonds were synthetized and characterized, focusing our attention on their capability to show thermally activated shape-memory response. In particular, 1H NMR analyses confirmed the chemical structure of the supramolecular polyurethanes, while DSC showed their totally amorphous morphology. DMTA in tensile mode was used to study their thermally activated shape-memory properties. In our case, the UPy units are the switching domains while the network formed by the segregated hard segments is the permanent domain obtained materials with excellent shape-memory response at both 100 and 85 °C. These materials are promising for multi-responsive materials where bio-based and potentially recyclable polymers with excellent shape-memory properties are needed.

A pyridyl side arm porphyrin incorporating C[Formula: see text] alkyl chains at the periphery of the porphyrin suitable for surface immobilisation on HOPG has been synthesised and tested for two state switching in solution. Temperature switching, involving reversible complexation of a covalently appended pyridyl side arm to the Zn(II) porphyrin, was comprehensively characterised by using variable temperature 1H NMR (-30 to +100[Formula: see text]C) and UV-vis (10 to 90[Formula: see text]C) in toluene. Molecular modelling assisted in understanding strain within the complex.

Supramolecular self-assemblies and co-assemblies possess multiple noncovalent interactions, highly ordered structures, and multifunctional properties. Yet, the fundamental understanding of their "structure-property relationship" remains very challenging. Herein, two kinetically controlled supramolecular charge transfer (CT) complexes were conceptualized from a trimorphic molecular donor denoted as "twisted aromatic hydrocarbon" (TAH), with p-fluoranil (TFQ) and p-chloranil (TCQ) in water, organic solvent, and solvent-free methods. Elucidating their co-assembling mechanism revealed that segmentation of the TAH with molecules having planar deficient cores spontaneously formed a distinct "H-type mixed stack" and "J-type segregated stack", regulated by blue/red-shifted charge-transfer and π-π stacking including weak C-H···F and C-H···O noncovalent interactions. By utilizing the structural transformational ability of the self-assembled TAH, the mechanistic aspects for the rapid nanoscopic co-assembly formation were precisely demonstrated experimentally and theoretically. The trimorphs and co-crystals of TAH could be disassembled resulting in turn-on emission by applying various external stimuli and being repeatedly reconfigured, thus providing a unique structure-property relationship and new TAH-based materials. This unique concept offers color-specific polymorphism and CT-complex formation strategy involving a simple class of functional materials having cooperative network forming ability using the twisted molecular donor.

The widespread occurrence of infections from multidrug-resistant (MDR) bacteria is a global health problem. It has been amplified over the past few years due to the increase in adaptive traits in bacteria and lack of advanced treatment strategies. Because of the low bioavailability and limited penetration at infected sites, the existing antibiotics often fail to resist bacterial growth. Recently, developed stimuli-responsive drug delivery systems and combinatorial therapeutic systems based on nanoparticles, metal-organic frameworks, hydrogels, and organic chromophores offer the ability to improve the therapeutic efficacy of antibiotics by reducing drug resistance and other side effects. These therapeutic systems have been designed with the relevant chemical and physical properties that respond to specific triggers resulting in spatiotemporal controlled release and site-specific transportability. This review highlights the latest development of single and dual/multistimuli-responsive antibiotic delivery systems for combination therapies to treat MDR bacterial infections and biofilm eradication.

Stimuli-responsive polymer gels have recently attracted great attention due to their heat/solvent resistance, dimensional stability, and unique sensitivity to external stimuli. In this work, we synthesized thiol-functionalized tetraphenylethylene (TPE) and constructed polymer gels through thiol-ene click reaction. The synthetic process of the polymer gels could be monitored by fluorescence emission of TPE moieties based on aggregation-induced emission mechanism. In addition, due to the dual redoxand acid responsiveness of the polymer gels, in the presence of dithiothreitol and trifluoroacetic acid, fluorescence quenching of the polymer gels can be observed. This stimuli-responsive characteristics endows the polymer gels with potential applications in fluorescent sensing and imaging, cancer diagnosis and selfhealing materials.

Stimuli-responsive nanocarriers are gaining much attention due to their versatile multifunctional activities, including disease diagnosis and treatment. Recently, clinical applications of nano-drug delivery systems for cancer treatment pose a challenge due to their limited cellular uptake, low bioavailability, poor targetability, stability issues, and unfavourable pharmacokinetics. To overcome these issues, researchers are focussing on stimuli-responsive systems. Nanocarriers elicit their role through endogenous (pH, temperature, enzyme, and redox) or exogenous (temperature, light, magnetic field, ultrasound) stimulus. These systems were designed to overcome the shortcomings such as non-specificity and toxicity associated with the conventional drug delivery systems. The pH variation between healthy cells and tumor microenvironment creates a platform for the generation of pH-sensitive nano delivery systems. Herein, we propose to present an overview of various internal and external stimuli-responsive behavior-based drug delivery systems. Herein, the present review will focus specifically on the significance of various pH-responsive nanomaterials such as polymeric nanoparticles, nano micelles, inorganic-based pH-sensitive drug delivery carriers such as calcium phosphate nanoparticles, and carbon dots in cancer treatment. Moreover, this review elaborates the recent findings on pH-based stimuli-responsive drug delivery systems with special emphasis on our reported stimuli-responsive systems for cancer treatment.

A Cp*-Rh based D-shaped binuclear metallacycle and a template-free molecular Borromean ring (BR) were obtained in high yield using the semi-rigid thioether dipyridyl ligand 1,4-bis[(pyridin-4-ylthio)methyl]benzene (Bptmb). The topological transformation from a binuclear metallacycle and a BR to tetranuclear metallacycles was realized via the controlled oxidation of thioethers. The strategy used in this work can be regarded as a new form of stimuli-responsive post-synthesis modification (PSM).

The fluorescent functional material prepared by combining 16‐alkyl (ferrocenyl‐methyl) ammonium bromide (Fc16AB) and dye molecule Congo red (CR) via ionic self‐assembly strategy exhibits double stimuli‐responsive behavior triggered by redox and pH value. Both the fabrication and switching mechanism of aggregates are proposed according to the cooperative binding of noncovalent interactions, including π‐π stacking, electrostatic interactions, charge transfer interaction, and amphiphilic hydrophobic association. The optimal geometry and energy transfer between monomers and aggregate are studied by means of quantum chemistry calculation and wavefunction analysis, which provides a deep and theoretical understanding for formation mechanism of ionic self‐assemblies. Moreover, the fluorescent switching behavior of assemblies upon pH was studied in detail, which opens the new way for the construction of organic light‐emitting diode (OLED).

A dual stimuli-responsive nanoplatform was rationally designed for controlled drug delivery. The nanosheets of graphene oxide (GO) were first modified with aminated mesoporous silica (NH2-mSiO2), and then methotrexate (MTX) was loaded into the mesopores of mSiO2. Alginate (Alg) acted as the "gatekeeper" was then anchored to the MTX-loaded GO/NH2-mSiO2 by amidation reaction, achieving the encapsulation of MTX in the core-shell structured GO/mSiO2@Alg. Due to the high pH sensitivity of amide bond and the excellent photothermal conversion ability of GO, the constructed nanoplatform could be used for pH and near-infrared (NIR) controlled delivery of MTX. The results of cell viability test demonstrate the high inhibitory rate of the dual stimuli-responsive nanoplatform toward hepatoma (HepG2) cells.

Inspired by the coloring mechanism of insects, we demonstrated the preparation of metallic luster materials by a combination of dye absorption and specular reflection from layered microcrystals. Me...

Development of smart switchable surfaces to solve the inevitable bacteria attachment and colonization has attracted much attention; however, it proves very challenging to achieve on-demand regeneration for noncontaminated surfaces. We herein report a smart, host-guest interaction-mediated photo/temperature dual-controlled antibacterial surface, topologically combining stimuli-responsive polymers with nanobactericide. From the point of view of long-chain polymer design, the peculiar hydration layer generated by hydrophilic poly(2-hydroxyethyl methacrylate) (polyHEMA) segments severs the route of initial bacterial attachment and subsequent proliferation, while the synergistic effect on chain conformation transformation poly(N-isopropylacrylamide) (polyNIPAM) and guest complex dissociation azobenzene/cyclodextrin (Azo/CD) complex greatly promotes the on-demand bacterial release in response to the switch of temperature and UV light. Therefore, the resulting surface exhibits triple successive antimicrobial functions simultaneously: (i) resists ∼84.9% of initial bacterial attachment, (ii) kills ∼93.2% of inevitable bacteria attack, and (iii) releases over 94.9% of killed bacteria even after three cycles. The detailed results not only present a potential and promising strategy to develop renewable antibacterial surfaces with successive antimicrobial functions but also contribute a new antimicrobial platform to biomedical or surgical applications.

Radical anions are important for various uses. However, their generation and stabilization under ambient conditions, which are essential for actual applications, are challenging. A photogenerated N...

Rational molecular design enables the development of stimuli-responsive supramolecular hydrogels. Biocompatible supramolecular hydrogels have great potential for medicinal and pharmaceutical applic...

Over the past few decades, advanced polymeric materials have gained popularity in the development of sustainable agricultural applications. Smart polymeric systems have extensively contributed to the agricultural industry by increasing the efficiency of pesticides, herbicides, and fertilizers by facilitating controlled release systems and, therefore, enabling lower doses to be used. Superabsorbent polymeric materials have been used as soil conditioners to control the impact of drought, whereas polycationic polymers have been utilized for plant bioengineering. These functions in the environment are complemented by applications within plants as part of the developing range of tools for genetically transforming plants in order to increase productivity and disease resistance. This Review will summarize and discuss the recent developments in the design and application of advanced polymeric systems for precision agriculture related applications. The design criteria of the polymers employed to date, such as polymer structure, as well as the properties of polymer nanoparticles including shape and size will be discussed, and the key findings in the related area will be highlighted. Finally, we will identify future directions for the exploration of functional polymers with the ultimate aim of advancing sustainable agriculture.\ud \ud

A wide variety of synthetic molecular machines has been designed and synthesized to construct nanometer-scale assemblies whose molecular motions can be precisely controlled by external stimuli. A h...

Hydrogels serving as a drug carrier was realized by entrapping small-sized drug molecules within their cross-linked interstitial networks. After covering the targeted location, hydrogels interact with the physiological fluids and swell, resulting in an increased interspace between networks for the outside diffusion of drugs. However, inevitable in vivo inflammatory responses or bacterial infection on the implant materials and persistent cargo release are still challenging. Herein, we report the fabrication of dual-responsive hydrogels based on acid-sensitive poly(ethylenimine) (PEI) derivative (PEI(-COOH/-vinyl)), thiol-responsive camptothecin prodrug monomer (CPTM), and hydrophilic oligo(ethylene glycol) methyl ether acrylate (OEGMA) by a conventional radical polymerization. Curcumin was then solubilized into the hydrogels to endow them with antimicrobial and cancer resistance properties. The in vitro experiments exhibited sustained hydrogel dissolution and CPT release in a simulated physiological environment. The antimicrobial and cytotoxicity tests of drug-loaded hydrogels using methicillin-resistant

An easy one-pot method is utilized for the synthesis of carbon nanodots, which has been investigated primarily from material perspectives. However, this preferred one-pot synthesis method suffers f...

Nanocarriers are nanoscale delivery systems composed of natural or synthetic polymers, which are advantageous in reducing drug toxicity while improving drug targeting and utilization. With the advancement of biomedical technology, it is revealed that reactive oxygen species (ROS), a class of oxidative metabolites, show abnormal overexpression in disease-related parts of the body. Hence, ROS stimuli-responsive nanocarriers have gained increasing attention, and recent developments are expected to realize controllable drug release. Based on linkers with different ROS-responsive mechanisms, a series of ROS-responsive nanocarriers have been designed to achieve specific controlled drug release under the stimulation of the ROS at the disease site. This article mainly focuses on ROS-responsive linkers, which have been commonly used for the synthesis of nanocarriers in recent years. Accordingly, the linkers are classified as chalcogen-containing responsive linkers (thioether, thioketal, selenide, diselenide, and telluride) and responsive linkers containing other elements (arylboronic ester, ferrocene, and peroxalate ester). ROS stimuli-responsive nanocarriers are fabricated by introducing ROS-responsive linkers in different design principles. Owing to the ROS-responsive linkers, the nanocarriers follow different responsive mechanisms, including hydrophobic-to-hydrophilic phase transition and cleavage. This article discusses the degree of responsiveness of nanocarri-ers and the specific release of drugs from nanocarriers upon ROS-stimuli, as well as their applications in vivo. In particular, on the basis of intelligent drug release and precision medicine, this article also emphasizes the importance of the biocompatibility and biodegradability of nanocarriers.