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Significant progress in fabricating new multifunctional soft materials and the advances of additive manufacturing technologies have given birth to a new generation of soft robots with complex capabilities, such as crawling, swimming, jumping, gripping, and releasing. Within this vast array of responsive soft materials, hydrogels receive considerable attention due to their fascinating properties, including biodegradable, self-healing, stimuli-responsive, and large volume transformation. Konjac glucomannan (KGM) is an edible polysaccharide that forms a pH-responsive, self-healing hydrogel when crosslinked with borax, and it is the focus of this study. A novel KGM-Borax ink for three-dimensional (3D) printing of free-form structures and soft robots at room temperature is presented. A complete process from ink preparation to the fabrication of a completely cross-linked part is demonstrated. Print setting parameters, rheological properties of the ink and crosslinked gels were characterized. Print quality was found to be consistent across a wide range of print settings. The minimum line width achieved is 650 μm. Tensile testing was carried out to validate the self-healing capability of the KGM-Borax gel. Results show that KGM-Borax has a high self-healing efficiency of 98%. Self-healing underwater was also demonstrated, a rarity for crosslinked gels. The means to form complex structures via 3D printing, reacting to environmental stimuli and the resilience against damage, make this new KGM-Borax gel a promising candidate for the fabrication of the next generation of soft robots.

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.

Atherosclerosis (AS), mainly caused by the changed immune system functions and inflammation, is the central pathogenesis of cardiovascular disease, which is a leading cause of death in the world. In modern medicine, the development of carriers precisely delivering the therapeutic agents to the target sites is the primary goal, which could minimize the potential adverse effects and be more effective in treating lesions. Due to the precise location, real-time monitoring, AS microenvironment response, and low toxicity, stimuli-responsive nano-based drug delivery systems (NDDSs) have been a promising approach in AS treatments. Herein, we will systematically summarize the recent advances in stimuli-responsive NDDSs for AS treatment, including internal stimuli (reactive oxygen species, enzyme, shear stress, and pH) and external stimuli (light, ultrasound, and magnetism) responsive NDDSs. Besides, we will also summarize in detail the classification of stimuli-responsive NDDSs for AS, such as organic NDDSs (e.g., lipid-based and polymer-based nanomaterials), inorganic NDDSs (e.g., metal-based nanoparticles and nonmetallic nanomaterials), and composite multifunctional NDDSs. Finally, the critical challenges and prospects of this field will also be proposed and discussed.

Responsive emulsions are the emulsions that can be reversibly switched on-demand between “stable” and “unstable” by environmental stimulus or trigger, which allows a simple and effective adjustment approach to achieve emulsification and demulsification. In recent years, stimuli-responsive emulsions acting as smart soft material are received considerable attention with the advantages of simple manipulation, good reversibility, low cost, easy treatment, and little effect on the system. In this paper, the recent research progress of emulsions that can respond to external stimuli, including pH, light, magnetic field, CO2/N2 and dual responsive are reviewed. Also, the potential applications based on responsive emulsion are discussed, such as catalytic reactions, heavy oil recovery, polymer particles synthesis and optical sensor, aiming to summarize the latest achievements and put forward the possible development trends of responsive emulsions.

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...

Background: Metal-organic frameworks (MOFs), as attractive hybrid crystalline porous materials, are being increasingly investigated in biomedical applications owing to their exceptional properties, including high porosity, ultrahigh surface areas, tailorable composition and structure, and tunability and surface functionality. Of interest, in this review, is the design and development of MOF-based drug delivery systems (DDSs) that have excellent biocompatibility, good stability under physiological conditions, high drug loading capacity, and controlled/targeted drug release. Objective: This review highlights the latest advances in MOFs as anticancer drug delivery systems (DDSs) along with insights on their design, fabrication, and performance under different stimuli that are either internal or external. The synthesis methods of MOFs, along with their advantages and disadvantages, are briefly discussed. The emergence of multifunctional MOF-based theranostic platforms is also discussed. Finally, the future challenges facing the developments of MOFs in the field of drug delivery are discussed. Methods: The review was prepared by carrying out a comprehensive literature survey using relevant work published in various scientific databases. Results: Novel MOFs in biomedical applications, especially in drug delivery, have shown great potential. MOF-based DDSs can be classified into normal (non-controllable) DDSs, stimuli-responsive DDSs, and theranostic platforms. The normal DDSs are pristine MOFs loaded with therapeutic agents and offer little to no control over drug release. Stimuli-responsive DDSs offer better spatiotemporal control over drug release by responding to either endogenous (pH, redox, ions, ATP) or exogenous stimuli (light, magnetism, US, pressure, temperature). The theranostic platforms combine stimuli-responsive drug delivery with diagnostic imaging functionality, paving the road for imaging-guided drug delivery. Conclusion: This review presented a summary of the various methods utilized in MOF's synthesis along with the advantages and disadvantages of each method. Furthermore, the review highlighted and discussed the latest developments in the field of MOF-based DDSs and theranostic platforms. The review is focused on the characteristics of MOF-based DDSs, the encapsulation of different anticancer drugs as well as their stimuli-responsive release.

Introduction: With the development of hydrogels from half a century ago, their application in various medical fields, including drug delivery has been widely expanded. Hydrogels used in this field are produced with synthetic polymers such as polyvinylpyrrolidone, polyvinyl alcohol, or natural polymers like chitosan, agarose, and hyaluronic acid to develop biocompatible, biodegradable, and non-immunogenic drug carriers. However, limitations such as inadequate response to stimulation, low homogeneity, and poor loading capacity for hydrophobic drugs have limited the use of hydrogels for drug delivery due to the hydrophilic nature of the hydrogel. The use of nanoparticles in the structure of hydrogels to produce hydrogel nanocomposites leads to more diverse interactions such as hydrogen and electrostatic bonds in addition to covalent interactions between hydrogel polymers. In addition to enhancing the mechanical properties of the hydrogel and further homogeneity, these interactions lead to the formation of platforms responsive to various stimuli, attaining sustained release, and ameliorating the poor loading of hydrophobic drugs used in cancer treatment and wound dressing. Conclusion: A review of a research conducted in the last 20 years represents that the application of nanocomposite hydrogels in drug delivery includes a wide range of production methods, nanoparticles to create various stimulation mechanisms, and therapeutic applications. Indeed, research has been focused on developing smart systems for controlled release with stimuli to reduce side effects of conventional cancer treatment methods, such as chemotherapy, by targeting drug delivery and reducing drug administration frequency and mitigating chronic wound complications by the release of growth factors.

Circularly polarized luminescence (CPL) materials have potential applications in 3D optical displays, information security encryption, sensors, and photoelectric devices because of their inherent a...

Nanotechnology has been widely applied to the fabrication of drug delivery systems in the past decades. Recently, with the progress made in microfabrication approaches, nanorobots are steadily becoming a promising means for tumor-targeting drug delivery. In general, nanorobots can be divided into two categories: nanomotors and stimuli-responsive nanorobots. Nanomotors are nanoscale systems with the ability to convert surrounding energies into mechanical motion, whereas stimuli-responsive nanorobots are featured with activatable capacity in response to various endogenous and exogenous stimulations. In this minireview, the dynamic control of nanomotors and the rational design of stimuli-responsive nanorobots are overviewed, with particular emphasis on their contribution to tumor-targeting therapy. Moreover, challenges and perspectives associated with the future development of nanorobots are presented.

Summary Halide perovskites have recently shown potential as stimuli-responsive materials (SRMs) for a range of important technologies such as smart windows, memory devices, data storage, and sensors. Here, we overview these emerging SRMs that are based on halide perovskite systems of switchable optical and electrical properties as well as discuss their switching characteristics and practical applications. We summarize the reversible chemical and structural transformations of these materials and categorize them by their switching mechanisms. Furthermore, to guide the community’s search for new designs of stimuli-responsive halide perovskites, we outline several important criteria for effective switchable materials. Finally, we provide our perspective on the current challenges and future developments of these emerging 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.

Nano- and microgels are promising soft polymer materials for different application fields: stabilizers, sensors, catalysts, selective sorbents, drug delivery carriers etc. They are composed of cross-linked polymer chains swollen with a solvent. The building blocks, synthesis approaches and architecture of nano- and microgels are reviewed. The mechanisms of responsiveness to various stimuli are described, examples of applications are provided. Micro- and nanogels are good objects for learning projects and the ideas for learning projects with microgels are described.

Background: Development of controlled drug delivery systems can improve the pharmacokinetic characteristics of drug molecules in the human body, thereby significantly improving the utilization rate of drugs and reducing toxicity and side effects caused by their high concentrations, which can occur when delivery is not controlled. Metal organic frameworks are a new class of very promising crystalline microporous materials, especially when the size is reduced to the nanometer range. Metal-organic frameworks exhibit large specific surface areas, tunable compositions, and easy functionalization. In recent years, an increasing number of studies have reported the remarkable advances in multifunctional nanoscale metal-organic frameworks in drug delivery. Objective: To review the latest research involving advances in stimuli-responsive nanoscale metal organic frameworks as drug delivery systems in controlled-release drugs. Discussion: We first introduce the two main strategies associated with nanoscale metal organic frameworks used in drug loading: direct assembly and post-encapsulation. We next focus on the latest discoveries of nanoscale metal-organic framework-based stimulus response systems for drug delivery, including pH, magnetics, light, ion, temperature, and other stimuli, as well as multiple stimulus- responsive drug delivery systems. Finally, we discuss the challenges and future developmental directions of nanoscale metal-organic framework-based controlled drug release.

Soft photonic materials formed from nanoscale colloidal crystals are versatile platforms for sensing and signaling in biomedical, chemical, and mechanical application scenarios. A particularly leve...

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

With the incessant improvement of requirements for optical anti-counterfeiting technology, it is essential to develop multifunctional luminescent materials with multiple models and adjustable lumin...

Diabetes is a serious global disease that threatens more than 400 million people’s health. Therefore, timely detection of body’s glucose level becomes extremely important for control, diagnosis and treatment of diabetes. Based on the feature of stimuli-responsive volume phase transition of hydrogel materials, this review will provide a systematic summary of glucose detection devices in recent years, including hydrogel preparation methods based on glucose-sensitive pattern, detection mechanisms based on signal transduction, current and emerging devices based on different body fluids and discuss the challenge, prospect the future development trend in the end.

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

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.

Metal substrates beneath polymeric coatings are susceptible to localized corrosion, which could result in lifetime reduction and catastrophic failure without timely repair treatment. In situ detection of corrosion and repair coating defects are in high demand yet challenging to fulfill so far. Herein, we report a smart polymeric coating by integrating nanosensors into the coating matrix, which is capable of efficient corrosion sensing and active anticorrosion protecting. The nanosensors were constructed by zeolitic imidazolate framework encapsulated with the polyethylene glycol-tannic acid complex. The morphology, chemical constitution, and stimulus responsiveness of nanosensors were systematically analyzed. The generation of local corrosion beneath coating can be promptly sensed and reported by a conspicuous purple color derived from tannic-iron ion coordinates. Meanwhile, local electrochemical impedance spectroscopy results proved that the metal degradation process at the defected interface can be largely inhibited, exhibiting active anticorrosion property. Furthermore, the constructed smart coating possessed superior impermeability and long-term protective performance under simulated seawater and harsh salts spray conditions. This feasible and effective strategy based on simple nanosensors to engineer smart coatings paves a new way to develop high environmental adaptability protective materials with protecting, corrosion sensing, and self-healing functions.

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.

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.

Molecular self-assembly is a widespread natural phenomenon and has inspired several researchers to synthesize a compendium of nano/microstructures with widespread applications. Biomolecules like proteins, peptides and lipids are used as building blocks to fabricate various nanomaterials. Supramolecular peptide self-assembly continue to play a significant role in forming diverse nanostructures with numerous biomedical applications; however, dipeptides offer distinctive supremacy in their ability to self-assemble and produce a variety of nanostructures. Though several reviews have articulated the progress in the field of longer peptides or polymers and their self-assembling behavior, there is a paucity of reviews or literature covering the emerging field of dipeptide-based nanostructures. In this review, our goal is to present the recent advancements in dipeptide-based nanostructures with their potential applications.

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.

Gels prepared from low-molecular-weight gelators (LMWGs) represent versatile soft materials. Self-assembly of LMWGs forms nanofibers and above critical gelation concentrations, the entanglement of which leads to self-supporting gels. Owing to the dynamic properties of the self-assembly process, stimuli-responsive LMWGs have prospered in the last decade. In addition, incorporating multiple LMWGs into one system brings the opportunity to achieve sophisticated designs and functions. This review covers recent advances in the field of supramolecular gels, from stimuli-responsive gelators to multicomponent systems that are self-sorting and/or co-assembling.

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.

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.

Responsive polymers with properties designed to interact with their surrounding environment are enabling “smart” design features for custom biomaterials. Numerous applications are being innovated, ranging from diagnostics and imaging to tissue engineering and drug delivery. Herein, I feature a collection of research articles published in ACS Macro Letters that highlight an array of innovative chemical attributes such as pH-triggered hydrolytic degradation, reduction-based release, photomodulation, glucose responsiveness, thermal sensitivity, and membrane permeating peptides. The chemical, physical, mechanical, and morphological properties of polymeric structures can be custom tailored to enhance numerous features such as biological delivery, pharmaceutical potency and safety, disease diagnosis, and antigen/biomaker detection.

DNA nanostructures have recently attracted increasing interest in biological and biomedical applications by virtue of their unique properties, such as structural programmability, multi-functionality, stimuli-responsive behaviors, and excellent biocompatibility. In particular, the intelligent responsiveness of smart DNA nanostructures to specific stimuli has facilitated their extensive development in the field of high-performance biosensing and controllable drug delivery. This minireview begins with different self-assembly strategies for the construction of various DNA nanostructures, followed by the introduction of a variety of stimuli-responsive functional DNA nanostructures for assembling metastable soft materials and for facilitating amplified biosensing. The recent achievements of smart DNA nanostructures for controllable drug delivery are highlighted. Finally, the current challenges and possible developments of this promising research are discussed in the fields of intelligent nanomedicine.

In the past few years four-dimensional (4D) printing technologies have attained worldwide interest and they are now considered the "next big thing". The aim of this research is to provide three selected examples of stimuli-responsive polymer (SRP) applications additively manufactured (AM) by the fused filament fabrication (FFF) technique. To that end, a CCT BLUE filament of thermo-responsive polymer was chosen to produce a water temperature indicator, which changes colour from blue to white when temperature increases; a CCU RED filament of photo-responsive polymer was used to produce a sunlight / UV indicator bracelet; a transparent PLA CLEAR polymer, a CCU RED photo-responsive polymer, and an electrical conductive PLA polymer were selected to produce a smart business card stand. The temperature indicator capability was analysed based on examining colour changes as a function of temperature changes. The sunlight/UV indicator capability was analysed based on the inspection of colour change as a function of absorbed sun/ultraviolet light. The electrical conductivity of the conductive PLA polymer was examined by performing resistance measurements. All three objects were successfully produced and their functionality was demonstrated. We hope that these examples will catalyse the expansion of FFF 4D printed SRP applications, as much work remains to be done in designing the parts and developing FFF printing parameters that take advantage of the stimuli-responsive materials currently being developed for FFF technology.

Smart materials possess a high potential for application in process engineering. Among these smart materials, stimuli-responsive hydrogels exhibit the chemically inherent characteristic to signific...

With growing interest in polymers of natural origin, innumerable polysaccharides have gained attention for their biomedical application. Pullulan, one of the FDA approved nutraceuticals, possesses multiple unique properties which make them highly advantageous for biomedical applications. This present review encompasses the sources, production, properties and applications of pullulan. It highlights various pullulan based stimuli-responsive systems (temperature, pH, ultrasound, magnetic), subcellular targeted systems (mitochondria, Golgi apparatus/endoplasmic reticulum, lysosome, endosome), lipid-vesicular systems (solid-lipid nanoparticles, liposomes), polymeric nanofibres, micelles, inorganic (SPIONs, gold and silver nanoparticles), carbon-based nanoplatforms (carbon nanotubes, fullerenes, nanodiamonds) and quantum dots. This article also gives insight into different biomedical, therapeutic and diagnostic applications of pullulan viz., imaging, tumor targeting, stem cell therapy, gene therapy, vaccine delivery, cosmetic applications, protein delivery, tissue engineering, photodynamic therapy and chaperone-like activities. The review also includes the toxicological profile of pullulan which is helpful for the development of suitable delivery systems for clinical applications.

Over the last decade, stimuli-responsive microemulsions, that is, those that switch between stable and unstable states in response to certain stimuli, have attracted considerable attention because of their unique properties and potential for diverse applications. Herein, we highlight the recent advances in the development of microemulsions responsive to external triggers such as pH, redox reactions, light, CO2 gas, magnetic field and temperature; discuss the corresponding responses; and reveal important composition–microstructure–macroscopic property relationships to suggest future research directions and potential applications.

Shape-memory polymers (SMPs) enable the production of stimuli-responsive polymer-based materials with the ability to undergo a large recoverable deformation upon the application of an external stimulus. Academic and industrial research interest in the shape-memory effects (SMEs) of these SMP-based materials is growing for task-specific applications. This mini-review covers interesting aspects of SMP-based materials, their properties, how they may be investigated and highlights examples of the potential applications of these materials.