Emerging applications of stimuli-responsive polymer materials

Magnetic-Based Strategies for Regenerative Medicine and Tissue Engineering

The fabrication of biological substitutes to repair, replace, or enhance tissue- and organ-level functions is a long-sought goal of tissue engineering (TE). However, the clinical translation of TE is hindered by several challenges, including the lack of suitable mechanical, chemical, and biological properties in one biomaterial, and the inability to generate large, vascularized tissues with a complex structure of native tissues. Over the past decade, a new generation of "smart" materials has revolutionized the conventional medical field, transforming TE into a more accurate and sophisticated concept. At the vanguard of scientific development, magnetic nanoparticles (MNPs) have garnered extensive attention owing to their significant potential in various biomedical applications owing to their inherent properties such as biocompatibility and rapid remote response to magnetic fields. Therefore, to develop functional tissue replacements, magnetic force-based TE (Mag-TE) has emerged as an alternative to conventional TE strategies, allowing for the fabrication and real-time monitoring of tissues engineered in vitro. This review addresses the recent studies on the use of MNPs for TE, emphasizing the in vitro, in vivo, and clinical applications. Future perspectives of Mag-TE in the fields of TE and regenerative medicine are also discussed.

2D Materials Beyond Post-AI Era: Smart Fibers, Soft Robotics, and Single Atom Catalysts

Recent consecutive discoveries of various 2D materials have triggered significant scientific and technological interests owing to their exceptional material properties, originally stemming from 2D confined geometry. Ever-expanding library of 2D materials can provide ideal solutions to critical challenges facing in current technological trend of the fourth industrial revolution. Moreover, chemical modification of 2D materials to customize their physical/chemical properties can satisfy the broad spectrum of different specific requirements across diverse application areas. This review focuses on three particular emerging application areas of 2D materials: smart fibers, soft robotics, and single atom catalysts (SACs), which hold immense potentials for academic and technological advancements in the post-artificial intelligence (AI) era. Smart fibers showcase unconventional functionalities including healthcare/environmental monitoring, energy storage/harvesting, and antipathogenic protection in the forms of wearable fibers and textiles. Soft robotics aligns with future trend to overcome longstanding limitations of hard-material based mechanics by introducing soft actuators and sensors. SACs are widely useful in energy storage/conversion and environmental management, principally contributing to low carbon footprint for sustainable post-AI era. Significance and unique values of 2D materials in these emerging applications are highlighted, where the research group has devoted research efforts for more than a decade.

4D-printed needle panel meters coupled with enzymatic derivatization for reading urea and glucose concentrations in biological samples

On-site analytical techniques continue being developed with advances in modern technology. To demonstrate the applicability of four-dimensional printing (4DP) technologies in the direct fabrication of stimuli-responsive analytical devices for on-site determination of urea and glucose, we used digital light processing three-dimensional printing (3DP) and 2-carboxyethyl acrylate (CEA)-incorporated photocurable resins to fabricate all-in-one needle panel meters. When adding a sample having a value of pH above the pKa of CEA (ca. 4.6-5.0) into the fabricated needle panel meter, the [H+]-responsive layer of the needle, printed using the CEA-incorporated photocurable resins, swelled as a result of electrostatic repulsion among the dissociated carboxyl groups of the copolymer, leading to [H+]-dependent bending of the needle. When coupled with a derivatization reaction (urease-mediated hydrolysis of urea to decrease [H+]; glucose oxidase-mediated oxidization of glucose to increase [H+]), the bending of the needle allowed reliable quantification of urea or glucose when referencing pre-calibrated concentration scales. After method optimization, the method's detection limits for urea and glucose were 4.9 and 7.0 μM, respectively, within a working concentration range from 0.1 to 10 mM. We verified the reliability of this analytical method by determining the concentrations of urea and glucose in samples of human urine, fetal bovine serum, and rat plasma with spike analyses and comparing the results with those obtained using commercial assay kits. Our results confirm that 4DP technologies can allow the direct fabrication of stimuli-responsive devices for quantitative chemical analysis, and that they can advance the development and applicability of 3DP-enabling analytical methods.

Synthesis and characterization of chitosan/carbon quantum dots/Fe2O3 nanocomposite comprising curcumin for targeted drug delivery in breast cancer therapy

Curcumin, a natural compound with promising anti-cancerous features, suffers from a number of shortcomings such as low chemical stability, bioavailability, and solubility, which impedes its application as an alternative for conventional cancer therapy. In this study, curcumin comprising Fe2O3/Chitosan/CQDs was fabricated through double emulsion method (W/O/W) for the first time to exploit its anticancer features while alleviating its limitation, making this nanocomposite promising in targeted drug delivery. Chitosan, a hydrophilic biopolymer, has incorporated to constitute an adhesive pH-sensitive matrix that can trap the hydrophobic drug resulting in controlled drug release in cancerous environment. Carbon quantum dots render luminescence and water solubility properties, which is favorable for tracing drug release and bio imaging along with enhancement of biocompatibility. Fe2O3 can improve chemical stability and bioavailability in addition to anti-cancerous property. XRD and FTIR analysis confirmed the physical interaction between the drug and fabricated nano composite in addition to chemical bonding between the prepared nano composite. Matrix and spherical structure of the formed drug is corroborated by FESEM analysis. DLS analysis' results determine the mean size of the nano composite at about 227.2 nm and zeta potential result is indicative of perfect stability of the fabricated drug. Various kinetic models for drug release were fitted to experimental data in order to investigate the drug release in which Korsmeyer-Peppas' model was the predominant release system in cancerous environment. In vitro studies through flow cytometry and MTT assay exerted noticeable cytotoxicity effect on MCF-7 cell lines. It can be deduced from these results that curcumin encapsulated with CS/CQDs/Fe2O3 nanocomposites is an excellent alternative for targeted drug delivery.

SANS contrast matching for the unambiguous localization of anionic dye in cationic surfactant micelles

Contrast variation in small-angle neutron scattering (SANS) was successfully applied to localize the anionic azo dye Blue in co-assemblies with the cationic surfactant dodecyltrimethylammoniumbromide (DTAB). For this purpose, the scattering contrast between DTAB and the aqueous solvent was eliminated by SANS contrast matching, leaving only the scattering signal from Blue to be detected. Results obtained by contrast matching were confirmed by NOESY NMR-spectroscopy, showing that Blue interacts with the positively charged DTAB head groups and with up to the 4th neighbouring methylene group of the DTAB C12-alkyl chain. Its localization in the outer layer of the Blue-DTAB co-assembly explains the uniaxial growth of spheroidal DTAB micelles to wormlike micelles with increasing [Blue] : [DTAB] ratio from 0 : 1 to 1 : 3. This is in line with the concept of the packing parameter for amphiphilic substances.

Molecularly confined hydration in thermoresponsive hydrogels for efficient atmospheric water harvesting

Water scarcity is a pressing global issue, requiring innovative solutions such as atmospheric water harvesting (AWH), which captures moisture from the air to provide potable water to many water-stressed areas. Thermoresponsive hydrogels, a class of temperature-sensitive polymers, demonstrate potential for AWH as matrices for hygroscopic components like salts predominantly due to their relatively energy-efficient desorption properties compared to other sorbents. However, challenges such as limited swelling capacity due to the salting-out effect and difficulty in more complete water release hinder the effectiveness of conventional hydrogel sorbents. To overcome these limitations, we introduce molecularly confined hydration in thermoresponsive hydrogels by employing a bifunctional polymeric network composed of hygroscopic zwitterionic moieties and thermoresponsive moieties. Here, we show that this approach ensures stable water uptake, enables water release at relatively low temperatures, and exhibits rapid sorption-desorption kinetics. Furthermore, by incorporating photothermal absorbers, the sorbent can achieve solar-driven AWH with comparable water release performance. This work advances the design of AWH sorbents by introducing molecularly confined hydration in thermoresponsive hydrogels, leading to a more efficient and sustainable approach to water harvesting. Our findings offer a potential solution for advanced sorbent design with comprehensive performance to mitigate the freshwater crisis.

Reversible transformation of peptide assembly between densified-polysarcosine-driven kinetically and helix-orientation-driven thermodynamically stable morphologies

Stimuli-responsive transformable biomaterials development can be manipulated practically by fine-tuning the built-in molecular design of their structural segments. Here, we demonstrate a peptide assembly by the bola-type amphiphilic polypeptide, glycolic acid-polysarcosine (PSar)13-b-(L-Leu-Aib)6-b-PSar13-glycolic acid (S13L12S13), which shows morphological transformations between hydrophilic chain-driven and hydrophobic unit-driven morphologies. The hydrophobic α-helical unit (L-Leu-Aib)6 precisely controls packing in the hydrophobic layer of the assembly and induces tubule formation. The densified, hydrophilic PSar chain on the assembly surface becomes slightly more hydrophobic as the temperature increases above 70 °C, starting to disturb the helix-helix interaction-driven formation of tubules. As a result, the S13L12S13 peptide assembly undergoes a reversible vesicle-nanotube transformation following a time course at room temperature and a heat treatment above 80 °C. Using membrane fluidity analysis with DPH and TMA-DPH and evaluating the environment surrounding the PSar side chain with NMR, we clarify that the vesicle was in a kinetically stable state driven by the dehydrated PSar chain, while the nanotube was in a thermodynamically stable state.

Advances of nanotechnology for intracerebral hemorrhage therapy

Intracerebral hemorrhage (ICH), the most devastating subtype of stoke, is of high mortality at 5 years and even those survivors usually would suffer permanent disabilities. Fortunately, various preclinical active drugs have been approached in ICH, meanwhile, the therapeutic effects of these pharmaceutical ingredients could be fully boosted with the assistance of nanotechnology. In this review, besides the pathology of ICH, some ICH therapeutically available active drugs and their employed nanotechnologies, material functions, and therapeutic principles were comprehensively discussed hoping to provide novel and efficient strategies for ICH therapy in the future.

Recent Advances in Sources of Bio-Inspiration and Materials for Robotics and Actuators

Bionic robotics and actuators have made dramatic advancements in structural design, material preparation, and application owing to the richness of nature and innovative material design. Appropriate and ingenious sources of bio-inspiration can stimulate a large number of different bionic systems. After millennia of survival and evolutionary exploration, the mere existence of life confirms that nature is constantly moving in an evolutionary direction of optimization and improvement. To this end, bio-inspired robots and actuators can be constructed for the completion of a variety of artificial design instructions and requirements. In this article, the advances in bio-inspired materials for robotics and actuators with the sources of bio-inspiration are reviewed. The specific sources of inspiration in bionic systems and corresponding bio-inspired applications are summarized first. Then the basic functions of materials in bio-inspired robots and actuators is discussed. Moreover, a principle of matching biomaterials is creatively suggested. Furthermore, the implementation of biological information extraction is discussed, and the preparation methods of bionic materials are reclassified. Finally, the challenges and potential opportunities involved in finding sources of bio-inspiration and materials for robotics and actuators in the future is discussed.

Transition Metal-Based Therapies for Inflammatory Diseases

Inflammatory disease (ID) is a general term that covers all diseases in which chronic inflammation performs as the major manifestation of pathogenesis. Traditional therapies based on the anti-inflammatory and immunosuppressive drugs are palliative with the short-term remission. The emergence of nanodrugs has been reported to solve the potential causes and prevent recurrences, thus holding great potential for the treatment of IDs. Among various nanomaterial systems, transition metal-based smart nanosystems (TMSNs) with unique electronic structures possess therapeutic advantages owing to their large surface area to volume ratio, high photothermal conversion efficiency, X-ray absorption capacity, and multiple catalytic enzyme activities. In this review, the rationale, design principle, and therapeutic mechanisms of TMSNs for treatments of various IDs are summarized. Specifically, TMSNs can not only be designed to scavenge danger signals, such as reactive oxygen and nitrogen species and cell-free DNA, but also can be engineered to block the mechanism of initiating inflammatory responses. In addition, TMSNs can be further applied as nanocarriers to deliver anti-inflammatory drugs. Finally, the opportunities and challenges of TMSNs are discussed, and the future directions of TMSN-based ID treatment for clinical applications are emphasized.

Biomimetic redox-responsive smart coatings with resistance-release functions for reverse osmosis membranes

Membrane fouling induces catastrophic loss of separation performance and seriously restricts the applications of reverse osmosis (RO) membranes. Inspired by the mussel structure, polydopamine (PDA) and cystamine molecules (CA) with excellent anti-fouling properties were used to prepare accessible, biocompatible, and redox-responsive coatings for RO membranes. The PDA/CA-coated RO membranes exhibit a superior water flux of 65 L m-2 h-1 with a favourable NaCl rejection exceeding 99%. The water permeability through the PDA/CA-coated membrane is much higher than that of most membranes with similar rejection rates. Due to the formed protective hydration layers by PDA/CA coatings, anti-fouling properties against proteins, polysaccharides and surfactants were evaluated separately, and ultralow fouling properties were demonstrated. Moreover, the disulfide linkages in CA molecules can cleave in a reducing environment, yielding the degradation of PDA/CA coatings, thereby removing the foulants deposited on the coatings. The degradation endows the coated membranes with satisfying longtime anti-fouling properties, where the flux recovery reaches up to 90%. The construction of redox-responsive smart coatings not only provided a promising route to alleviate membrane fouling but can also be upscaled for use in numerous practical applications like sensors, medical devices, and drug delivery.

Adsorption of Preformed Microgel-Enzyme Complexes as a Novel Strategy toward Engineering Microgel-Based Enzymatic Biosensors

A novel approach to surface modification, which consists of the adsorption of microgel-enzyme complexes preformed in solution, is highlighted. Accordingly, the microgel-enzyme complexes were formed due to the electrostatic interaction of the oppositely charged interacting components, that is, a cationic poly(N-isopropylacrylamide)-based microgel and glucose oxidase taken as a model enzyme. The spontaneous adsorption of the prepared microgel-enzyme complexes, examined by means of quartz crystal microbalance with dissipation monitoring and atomic force microscopy, was observed, resulting in the formation of well-adhered microgel-enzyme coatings. Further, the preformed microgel-enzyme complexes were adsorbed onto the modified graphite-based screen-printed electrodes, and their enzymatic responses were determined by means of amperometry, demonstrating a remarkable analytical performance toward the quantification of β-D-glucose in terms of high sensitivity (0.0162 A × M-1 × cm-2), a low limit of detection (1 μM), and an expanded linear range (1-2000 μM). The fabricated microgel-enzyme biosensor constructs were found to be very stable against manifold-repeated measurements. Finally, the pH- or salt-induced release of glucose oxidase from the adsorbed preformed microgel-enzyme complexes was demonstrated. The findings obtained for the microgel-enzyme coatings prepared via adsorption of the preformed microgel-enzyme complexes were compared to those found for the microgel-enzyme coatings fabricated via a previously exploited two-stage sequential adsorption, which includes the adsorption of the microgel first, followed by the electrostatic binding of glucose oxidase by the adsorbed microgel.

Self-Amplified Cascade Degradation and Oxidative Stress Via Rational pH Regulation of Oxidation-Responsive Poly(ferrocene) Aggregates

Precise activation of polymer nanoparticles at lesion sites is crucial to achieve favorable therapeutic efficacy. However, conventional endogenous stimuli-responsive polymer nanoparticles probably suffer from few triggers to stimulate the polymer degradation and subsequent functions. Here, we describe oxidation-responsive poly(ferrocene) amphiphiles containing phenylboronic acid ester and ferrocene as the repeating backbone units. Upon triggering by hydrogen peroxide inside the tumor cells, the phenylboronic acid ester bonds are broken and poly(ferrocene) units are degraded to afford free ferrocene and noticeable hydroxide ions. The released hydroxide ions can immediately improve the pH value within the poly(ferrocene) aggregates, and the degradation rate of the phenylboronic acid ester backbone is further promoted by the upregulated pH; thereupon, the accelerated degradation can release much more additional hydroxide ions to improve the pH, thus achieving a positive self-amplified cascade degradation of poly(ferrocene) aggregates accompanied by oxidative stress boosting and efficient cargo release. Specifically, the poly(ferrocene) aggregates can be degraded up to ∼90% within 12 h when triggered by H2O2, while ferrocene-free control nanoparticles are degraded by only 30% within 12 days. In addition, the maleimide moieties tethered in the hydrophilic corona can capture blood albumin to form an albumin-rich protein corona and significantly improve favorable tumor accumulation. The current oxidation-responsive poly(ferrocene) amphiphiles can efficiently inhibit tumors in vitro and in vivo. This work provides a proof-of-concept paradigm for self-amplified polymer degradation and concurrent oxidative stress, which is promising in actively regulated precision medicine.

Transient regulation of gel properties by chemical reaction networks

Transient regulation of gel properties by chemical reaction networks (CRNs) represents an emerging and effective strategy to program or temporally control the structures, properties, and functions of gel materials in a self-regulated manner. CRNs provide significant opportunities to construct complex or sustainable gels with excellent dynamic features, thus expanding the application scope of these materials. CRN-based methods for transiently regulating the gel properties are receiving increasing attention, and the related fields are worth further studying. This feature article focuses on the CRN-mediated transient regulation of six properties of gels, which are transient gelation, transient liquefaction of gels, transient assembly of macroscopic gels, temporary actuation of gels, transient healing ability of kinetically inert gels, and cascade reaction-based self-reporting of external stimuli. Recent advances that showcase the six properties of gels controlled by CRNs are featured, the characterization and structural elucidation of gels are detailed, and the significance, achievements, and expectations of this field are discussed. The strategy of transient regulation of gel properties via CRNs is potentially useful for building the next generation of adaptive functional materials.

Tumor acidity-induced surface charge modulation in covalent nanonetworks for activated cellular uptake: targeted delivery of anticancer drugs and selective cancer cell death

A β-thioester and tertiary amine based covalently cross-linked nanoassembly coined as a nanonetwork (NN) endowed with dual pH responsive features (tumor acidity induced surface charge modulation and endosomal pH triggered controlled degradation) has been designed and synthesized for stable sequestration and sustained release of drug molecules in response to endosomal pH. An amphiphile integrated with tertiary amine and acrylate (ATA) functionalities was synthesized to fabricate the nanonetwork. This amphiphile showed entropically driven self-assembly and micellar nanostructures (nanoassemblies), which can sequester hydrophobic drug molecules at neutral pH. To further stabilize the nanoassemblies and the sequestered drug molecules even below its critical aggregation concentration (CAC), the micellar core was cross-linked via the thiol-acrylate Michael addition click reaction to generate multiple copies of acid labile β-thioester functionalities in the core, which undergo slow hydrolysis at endosomal pH (∼5.0), thus enabling sustained release of the anti-cancer drug doxorubicin at endosomal pH. The nanonetworks showed a significant decrease in drug leakage compared to the nanoassemblies (NAs), which was also justified by a low leakage coefficient calculated from the fluorescence resonance energy transfer experiment. The NN also exhibited dilution insensitivity and high serum stability, whereas the NA disassembled upon dilution and during serum treatment. The biological evaluation revealed tumor extracellular matrix pH (∼6.4-6.8) induced surface charge modulation and cancer cell (HeLa) selective activated cellular uptake of the doxorubicin loaded nanonetwork (NN-DOX). In contrast, the benign nature of NN-DOX towards normal cells (H9c2) suggests excellent cell specificity. Thus, we believe that the ease of synthesis, nanonetwork fabrication reproducibility, robust stability, smart nature of tumor microenvironment sensitive surface charge modulation, boosted tumoral-cell uptake, and triggered drug release will make this system a potential nanomedicine for chemotherapeutic treatments.

The morphological paradigm in robotics

In the paper, we are going to show how robotics is undergoing a shift in a bionic direction after a period of emphasis on artificial intelligence and increasing computational efficiency, which included isolation and extreme specialization. We assemble these new developments under the label of the morphological paradigm. The change in its paradigms and the development of alternatives to the principles that dominated robotics for a long time contains a more general epistemological significance. The role of body, material, environment, interaction and the paradigmatic status of biological and evolutionary systems for the principles of control are crucial here. Our focus will be on the introduction of the morphological paradigm in a new type of robotics and to contrast the interests behind this development with the interests shaping former models. The article aims to give a clear account of the changes in principles of orientation and control as well as concluding general observation in terms of historical epistemology, suggesting further political-epistemological analysis.

Trends in the Synthesis of Polymer Nano- and Microscale Materials for Bio-Related Applications

Polymeric nano- and microscale materials bear significant potential in manifold applications related to biomedicine. This is owed not only to the large chemical diversity of the constituent polymers, but also to the various morphologies these materials can achieve, ranging from simple particles to intricate self-assembled structures. Modern synthetic polymer chemistry permits the tuning of many physicochemical parameters affecting the behavior of polymeric nano- and microscale materials in the biological context. In this Perspective, an overview of the synthetic principles underlying the modern preparation of these materials is provided, aiming to demonstrate how advances in and ingenious implementations of polymer chemistry fuel a range of applications, both present and prospective.

Tris(pyridyl)borates: an emergent class of versatile and robust polydentate ligands for catalysis and materials applications

Tridentate ligands that incorporate pyridyl rather than pyrazolyl groups are emerging as an attractive class of "scorpionate"-type ligands with enhanced electron donation, increased stability, and divergent geometry at the metal centre relative to tris(pyrazolyl)borates originally introduced by Trofimenko. Following our initial reports, the tris(pyridyl)borate (Tpyb) ligand architecture has been adopted by several research groups in pursuit of functional metal complexes that offer new opportunities in catalysis and materials science. While earlier work had been focused on symmetric octahedral complexes, ML₂, which are advantageous as highly robust building blocks in materials sciences, recently introduced new ligand designs provide access to heteroleptic metal complexes with vacant sites that lend themselves to applications in catalysis. Signficant progress has also been made in the post-complexation functionalization of these ligands via electrophilic and nucleophilic substitution reactions at the boron centres, opening up new routes for integration of Tpyb complexes with diverse functional materials while also raising interesting mechanistic questions.

Sequential-Stimuli Induced Stepwise-Response of Pyridylpyrenes

Stimuli-responsive materials, especially multi-stimuli-responsive materials, can sense external stimuli such as light, heat, and force, have shown great potential in drug delivery, data storage, encryption, energy-harvesting, and artificial intelligence. Conventional multi-stimuli-responsive materials are sensitive to each independent stimulus, causing losses in the diversity and accuracy of the identification for practical application. Herein, a unique phenomenon of sequential-stimuli induced stepwise-response generated from elaborately designed single-component organic materials is reported, which shows large bathochromic shifts up to 5800 cm-1 under sequential stimuli of force and light. In contrast to multi-stimuli-responsive materials, the response of these materials strictly relies on the sequence of stimuli, allowing logicality, rigidity, and accuracy to be integrated into one single-component material. The molecular keypad lock is built based on these materials, pointing promising to a future for this logical response in significant practical applications. This breakthrough gives a new drive to classical stimuli-responsiveness and provides a fundamental design strategy for new generations of high-performance stimuli-responsive materials.

Smart Polymers for Soft Materials: From Solution Processing to Organic Solids

Polymeric materials are ubiquitous in our everyday life, where they find a broad range of uses-spanning across common household items to advanced materials for modern technologies. In the context of the latter, so called "smart polymers" have received a lot of attention. These systems are soluble in water below their lower critical solution temperature Tℓ and often exhibit counterintuitive solvation behavior in mixed solvents. A polymer is known as smart-responsive when a slight change in external stimuli can significantly change its structure, functionm and stability. The interplay of different interactions, especially hydrogen bonds, can also be used for the design of lightweight high-performance organic solids with tunable properties. Here, a general scheme for establishing a structure-property relationship is a challenge using the conventional simulation techniques and also in standard experiments. From the theoretical side, a broad range of all-atom, multiscale, generic, and analytical techniques have been developed linking monomer level interaction details with macroscopic material properties. In this review, we briefly summarize the recent developments in the field of smart polymers, together with complementary experiments. For this purpose, we will specifically discuss the following: (1) the solution processing of responsive polymers and (2) their use in organic solids, with a goal to provide a microscopic understanding that may be used as a guiding tool for future experiments and/or simulations regarding designing advanced functional materials.

An Efficient Path Classification Algorithm Based on Variational Autoencoder to Identify Metastable Path Channels for Complex Conformational Changes

Conformational changes (i.e., dynamic transitions between pairs of conformational states) play important roles in many chemical and biological processes. Constructing the Markov state model (MSM) from extensive molecular dynamics (MD) simulations is an effective approach to dissect the mechanism of conformational changes. When combined with transition path theory (TPT), MSM can be applied to elucidate the ensemble of kinetic pathways connecting pairs of conformational states. However, the application of TPT to analyze complex conformational changes often results in a vast number of kinetic pathways with comparable fluxes. This obstacle is particularly pronounced in heterogeneous self-assembly and aggregation processes. The large number of kinetic pathways makes it challenging to comprehend the molecular mechanisms underlying conformational changes of interest. To address this challenge, we have developed a path classification algorithm named latent-space path clustering (LPC) that efficiently lumps parallel kinetic pathways into distinct metastable path channels, making them easier to comprehend. In our algorithm, MD conformations are first projected onto a low-dimensional space containing a small set of collective variables (CVs) by time-structure-based independent component analysis (tICA) with kinetic mapping. Then, MSM and TPT are constructed to obtain the ensemble of pathways, and a deep learning architecture named the variational autoencoder (VAE) is used to learn the spatial distributions of kinetic pathways in the continuous CV space. Based on the trained VAE model, the TPT-generated ensemble of kinetic pathways can be embedded into a latent space, where the classification becomes clear. We show that LPC can efficiently and accurately identify the metastable path channels in three systems: a 2D potential, the aggregation of two hydrophobic particles in water, and the folding of the Fip35 WW domain. Using the 2D potential, we further demonstrate that our LPC algorithm outperforms the previous path-lumping algorithms by making substantially fewer incorrect assignments of individual pathways to four path channels. We expect that LPC can be widely applied to identify the dominant kinetic pathways underlying complex conformational changes.

Molecular in situ monitoring of the pH-triggered response in adaptive polymers by two-dimensional Raman micro-correlation-spectroscopy

Stimuli-responsive polymers can switch specific physical properties in response to a change of the environmental conditions. This behavior offers unique advantages in applications where adaptive materials are needed. To tune the properties of stimuli-responsive polymers, a detailed understanding of the relationship between the applied stimulus and changes in molecular structure as well as the relationship between the latter and macroscopic properties is required, which until now has required laborious methods. Here, we present a straightforward way to investigate the progressing trigger, the change of the chemical composition of the polymer and the macroscopic properties simultaneously. Thereby, the response behavior of the reversible polymer is studied in situ with molecular sensitivity and spatial as well as temporal resolution utilizing Raman micro-spectroscopy. Combined with two-dimensional correlation analysis (2DCOS), this method reveals the stimuli-response on a molecular level and determines the sequence of changes and the diffusion rate inside the polymer. Due to the label-free and non-invasive approach, it is furthermore possible to combine this method with the investigation of macroscopic properties revealing the response of the polymer to the external stimulus on both the molecular and the macroscopic level.

3D printed swelling-driven shape-morphing pH-responsive hydrogel gripper

Stimuli-responsive soft robots have provided new directions for obtaining advanced biomedical healthcare systems, such as targeted drug delivery capsules, less-invasive biopsy tools, and untethered microsurgical robots. We designed, 3D printed, and tested diverse time-dependent shape changeable 3D pH-responsive soft grippers consisting of N-isopropylacrylamide (NIPAM) and N-isopropylacrylamide-co-acrylic acid (NIPAM-AAc) bilayer. We found that the swelling/deswelling-driven actuation of the pH-responsive NIPAM/NIPAM-AAc gripper is primarily affected by the volume percent (% v/v) of the acrylic acid (AAc) and intensity of UV light. We expect that this study can be applied to untethered pH-responsive soft grippers as smart drug delivery capsules or biopsy tools in biomedical healthcare systems.

Facile Ball Milling Preparation of Flame-Retardant Polymer Materials: An Overview

To meet the growing needs of public safety and sustainable development, it is highly desirable to develop flame-retardant polymer materials using a facile and low-cost method. Although conventional solution chemical synthesis has proven to be an efficient way of developing flame retardants, it often requires organic solvents and a complicated separation process. In this review, we summarize the progress made in utilizing simple ball milling (an important type of mechanochemical approach) to fabricate flame retardants and flame-retardant polymer composites. To elaborate, we first present a basic introduction to ball milling, and its crushing, exfoliating, modifying, and reacting actions, as used in the development of high-performance flame retardants. Then, we report the mixing action of ball milling, as used in the preparation of flame-retardant polymer composites, especially in the formation of multifunctional segregated structures. Hopefully, this review will provide a reference for the study of developing flame-retardant polymer materials in a facile and feasible way.

Targeting endosomal receptors, a new direction for polymers in nanomedicine

In this perspective, we outline a new opportunity for exploiting nanoparticle delivery of antagonists to target G-protein coupled receptors localized in intracellular compartments. We discuss the specific example of antagonizing endosomal receptors involved in pain to develop long-lasting analgesics but also outline the broader application potential of this delivery approach. We discuss the materials used to target endosomal receptors and indicate the design requirements for future successful applications.

Turning enol* emission of SBOH via restricting twisted intramolecular charge transfer behavior by pressure

Stimuli-responsive luminogens with aggregation-induced emission and excited state intramolecular proton transfer (ESIPT) properties have applications in storage devices, anti-counterfeiting, imaging, and sensors. Nevertheless, group rotation appears in twisted intramolecular charge transfer (TICT) state, resulting in decreased fluorescence intensity. Inhibiting TICT remains a challenge based on their intrinsic molecular configuration. Herein, we present a simple facile pressure-induced method to restrict the TICT behavior. Steady-state spectroscopy measurement shows that fluorescence enhancement and color shifts can be achieved under high pressure. Combined with in situ high-pressure ultrafast spectroscopy and theoretical calculations, the TICT behavior was restricted in two aspects. The ESIPT process was damaged, hence more particles stored in the E* state, and transferred to the TICT state hardly. Also, the rotation of (E)-dimethyl5-((4-(diethylamino)-2-hydroxybenzylidene)amino)isophthalate (SBOH) was restricted, significantly increasing the fluorescence intensity. This approach provides a new strategy for the development of stimulus-responsive materials.

Smart multi stimuli-responsive electrospun nanofibers for on-demand drug release

Here, we report poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAm-co-AAc) microgel-loaded polycaprolactone (PCL) nanofibers as temperature-, pH- and electro-responsive materials. First, the PNIPAm-co-AAc microgels were prepared by precipitation polymerization and then electrospun with PCL. The morphology of the prepared materials, analysed by scanning electron microscopy, showed a narrow nanofiber distribution in the range of 500-800 nm, depending on microgel content. Refractometry measurements, performed at pH4 and 6.5, as well as in distilled water, indicated the thermo- and pH-responsive behaviour of the nanofibers between 31 and 34 °C. After being thoroughly characterized, the prepared nanofibers were loaded with crystal violet (CV) or gentamicin as model drugs. The application of a pulsed voltage led to a pronounced increase in drug release kinetics, which was also dependent on microgel content. In addition, long-term temperature- and pH-responsive release was demonstrated. Next, the prepared materials displayed switchable antibacterial activity against S. aureus and E. coli. Finally, cell compatibility tests showed that NIH 3T3 fibroblasts spread evenly over the nanofiber surface, confirming that the nanofibers serve as a favourable support for cell growth. Overall, the prepared nanofibers offer switchable drug release and appear to have considerable biomedical potential, particularly in wound healing.

Green synthesis of chitosan/polyacrylic acid/graphitic carbon nitride nanocarrier as a potential pH-sensitive system for curcumin delivery to MCF-7 breast cancer cells

A novel pH-sensitive nanocarrier containing chitosan (CS), polyacrylic acid (PAA), and graphitic carbon nitride (g-C₃N₄) was designed via water/oil/water (W/O/W) emulsification to administer curcumin (CUR) drug. g-C₃N₄ nanosheets with a high surface area and porous structure were produced via simple one-step pyrolysis process using thiourea as precursor, and incorporated into CS/PAA hydrogel. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) were used to assess the crystalline structure of the nanocarrier and the interactions between its components, respectively. Scanning electron microscopy (SEM) images revealed a spherical structure and confirmed the g-C₃N₄ impregnation into the CS/PAA matrix. Zeta potential and dynamic light scattering (DLS) provided information about the surface charge and average size distribution. High CUR loading and entrapment efficiencies were obtained, which were further improved upon addition of g-C₃N₄. The release kinetics of drug-loaded CS/PAA/g-C₃N₄ nanocomposites were investigated at pH = 5.4 and pH = 7.4, and the results showed an excellent controlled pH-sensitive release profile. Cell apoptosis and in vitro cytotoxicity were investigated using flow cytometry and MTT analyses. CS/PAA/g-C₃N₄/CUR resulted in the highest rate of apoptosis in MCF-7 breast cancer cells, demonstrating the excellent nanocomposite efficacy in eliminating cancerous cells. CS/PAA hydrogel coated with g-C₃N₄ shows great potential for pH-sensitive controlled drug release.

Globular Proteins and Where to Find Them within a Polymer Brush-A Case Study

Protein adsorption by polymerized surfaces is an interdisciplinary topic that has been approached in many ways, leading to a plethora of theoretical, numerical and experimental insight. There is a wide variety of models trying to accurately capture the essence of adsorption and its effect on the conformations of proteins and polymers. However, atomistic simulations are case-specific and computationally demanding. Here, we explore universal aspects of the dynamics of protein adsorption through a coarse-grained (CG) model, that allows us to explore the effects of various design parameters. To this end, we adopt the hydrophobic-polar (HP) model for proteins, place them uniformly at the upper bound of a CG polymer brush whose multibead-spring chains are tethered to a solid implicit wall. We find that the most crucial factor affecting the adsorption efficiency appears to be the polymer grafting density, while the size of the protein and its hydrophobicity ratio come also into play. We discuss the roles of ligands and attractive tethering surfaces to the primary adsorption as well as secondary and ternary adsorption in the presence of attractive (towards the hydrophilic part of the protein) beads along varying spots of the backbone of the polymer chains. The percentage and rate of adsorption, density profiles and the shapes of the proteins, alongside with the respective potential of mean force are recorded to compare the various scenarios during protein adsorption.

A Review of Research Progress on the Performance of Intelligent Polymer Gel

Intelligent polymer gel, as a popular polymer material, has been attracting much attention for its application. An intelligent polymer gel will make corresponding changes to adapt to the environment after receiving stimuli; therefore, an intelligent polymer gel can play its role in many fields. With the research on intelligent polymer gels, there is great potential for applications in the fields of drug engineering, molecular devices, and biomedicine in particular. The strength and responsiveness of the gels can be improved under different configurations in different technologies to meet the needs in these fields. There is no discussion on the application of intelligent polymer gels in these fields; therefore, this paper reviews the research progress of intelligent polymer gel, describes the important research of some intelligent polymer gel, summarizes the research progress and current situation of intelligent polymer gel in the environment of external stimulation, and discusses the performance and future development direction of intelligent polymer gel.

Nonequilibrium configurations of swelling polymer brush layers induced by spreading drops of weakly volatile oil

Polymer brush layers are responsive materials that swell in contact with good solvents and their vapors. We deposit drops of an almost completely wetting volatile oil onto an oleophilic polymer brush layer and follow the response of the system upon simultaneous exposure to both liquid and vapor. Interferometric imaging shows that a halo of partly swollen polymer brush layer forms ahead of the moving contact line. The swelling dynamics of this halo is controlled by a subtle balance of direct imbibition from the drop into the brush layer and vapor phase transport and can lead to very long-lived transient swelling profiles as well as nonequilibrium configurations involving thickness gradients in a stationary state. A gradient dynamics model based on a free energy functional with three coupled fields is developed and numerically solved. It describes experimental observations and reveals how local evaporation and condensation conspire to stabilize the inhomogeneous nonequilibrium stationary swelling profiles. A quantitative comparison of experiments and calculations provides access to the solvent diffusion coefficient within the brush layer. Overall, the results highlight the-presumably generally applicable-crucial role of vapor phase transport in dynamic wetting phenomena involving volatile liquids on swelling functional surfaces.

pH-Mediated Size-Selective Adsorption of Gold Nanoparticles on Diblock Copolymer Brushes

Precise control of nanoparticles at interfaces can be achieved by designing stimuli-responsive surfaces that have tunable interactions with nanoparticles. In this study, we demonstrate that a polymer brush can selectively adsorb nanoparticles according to size by tuning the pH of the buffer solution. Specifically, we developed a facile polymer brush preparation method using a symmetric polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer deposited on a grafted polystyrene layer. This method is based on the assembly of a PS-b-P2VP thin film oriented with parallel lamellae that remains after exfoliation of the top PS-b-P2VP layer. We characterized the P2VP brush using X-ray reflectivity and atomic force microscopy. The buffer pH is used to tailor interactions between citrate-coated gold nanoparticles (AuNPs) and the top P2VP block that behaves like a polymer brush. At low pH (∼4.0) the P2VP brushes are strongly stretched and display a high density of attractive sites, whereas at neutral pH (∼6.5) the P2VP brushes are only slightly stretched and have fewer attractive sites. A quartz crystal microbalance with dissipation monitored the adsorption thermodynamics as a function of AuNP diameter (11 and 21 nm) and pH of the buffer. Neutral pH provides limited penetration depth for nanoparticles and promotes size selectivity for 11 nm AuNP adsorption. As a proof of concept, the P2VP brushes were exposed to various mixtures of large and small AuNPs to demonstrate selective capture of the smaller AuNPs. This study shows the potential of creating devices for nanoparticle size separations using pH-sensitive polymer brushes.

CO2-responsive gels

CO₂-responsive materials undergo a change in chemical or physical properties in response to the introduction or removal of CO₂. The use of CO₂ as a stimulus is advantageous as it is abundant, benign, inexpensive, and it does not accumulate in a system. Many CO₂-responsive materials have already been explored including polymers, latexes, surfactants, and catalysts. As a sub-set of CO₂-responsive polymers, the study of CO₂-responsive gels (insoluble, cross-linked polymers) is a unique discipline due to the unique set of changes in the gels brought about by CO₂ such as swelling or a transformed morphology. In the past 15 years, CO₂-responsive gels and self-assembled gels have been investigated for a variety of emerging potential applications, reported in 90 peer-reviewed publications. The two most widely exploited properties include the control of flow (fluids) via CO₂-triggered aggregation and their capacity for reversible CO₂ absorption-desorption, leading to applications in Enhanced Oil Recovery (EOR) and CO₂ sequestration, respectively. In this paper, we review the preparation, properties, and applications of these CO₂-responsive gels, broadly classified by particle size as nanogels, microgels, aerogels, and macrogels. We have included a section on CO₂-induced self-assembled gels (including poly(ionic liquid) gels).

Polymerization-Induced Self-Assembly: An Emerging Tool for Generating Polymer-Based Biohybrid Nanostructures

The combination of biomolecules and synthetic polymers provides an easy access to utilize advantages from both the synthetic world and nature. This is not only important for the development of novel innovative materials, but also promotes the application of biomolecules in various fields including medicine, catalysis, and water treatment, etc. Due to the rapid progress in synthesis strategies for polymer nanomaterials and deepened understanding of biomolecules' structures and functions, the construction of advanced polymer-based biohybrid nanostructures (PBBNs) becomes prospective and attainable. Polymerization-induced self-assembly (PISA), as an efficient and versatile technique in obtaining polymeric nano-objects at high concentrations, has demonstrated to be an attractive alternative to existing self-assembly procedures. Those advantages induce the focus on the fabrication of PBBNs via the PISA technique. In this review, current preparation strategies are illustrated based on the PISA technique for achieving various PBBNs, including grafting-from and grafting-through methods, as well as encapsulation of biomolecules during and subsequent to the PISA process. Finally, advantages and drawbacks are discussed in the fabrication of PBBNs via the PISA technique and obstacles are identified that need to be overcome to enable commercial application.

Dynamic and Reversible Decoration of DNA-Based Scaffolds

An approach to achieving dynamic and reversible decoration of DNA-based scaffolds is demonstrated here. To do this, rationally engineered DNA tiles containing enzyme-responsive strands covalently conjugated to different molecular labels are employed. These strands are designed to be recognized and degraded by specific enzymes (i.e., Ribonuclease H, RNase H, or Uracil DNA Glycosylase, UDG) inducing their spontaneous de-hybridization from the assembled tile and replacement by a new strand conjugated to a different label. Multiple enzyme-responsive strands that specifically respond to different enzymes allow for dynamic, orthogonal, and reversible decoration of the DNA structures. As a proof-of-principle of the strategy, the possibility to orthogonally control the distribution of different labels (i.e., fluorophores and small molecules) on the same scaffold without crosstalk is demonstrated. By doing so, DNA scaffolds that display different antibody recognition patterns are obtained. The approach offers the possibility to control the decoration of higher-order supramolecular assemblies (including origami) with several functional moieties to achieve functional biomaterials with improved adaptability, precision, and sensing capabilities.

Leveraging the Polymer Glass Transition to Access Thermally Switchable Shear Jamming Suspensions

Suspensions of polymeric nano- and microparticles are fascinating stress-responsive material systems that, depending on their composition, can display a diverse range of flow properties under shear, such as drastic thinning, thickening, and even jamming (reversible solidification driven by shear). However, investigations to date have almost exclusively focused on nonresponsive particles, which do not allow in situ tuning of the flow properties. Polymeric materials possess rich phase transitions that can be directly tuned by their chemical structures, which has enabled researchers to engineer versatile adaptive materials that can respond to targeted external stimuli. Reported herein are suspensions of (readily prepared) micrometer-sized polymeric particles with accessible glass transition temperatures (T _g) designed to thermally control their non-Newtonian rheology. The underlying mechanical stiffness and interparticle friction between particles change dramatically near T _g. Capitalizing on these properties, it is shown that, in contrast to conventional systems, a dramatic and nonmonotonic change in shear thickening occurs as the suspensions transition through the particles' T _g. This straightforward strategy enables the in situ turning on (or off) of the system's ability to shear jam by varying the temperature relative to T _g and lays the groundwork for other types of stimuli-responsive jamming systems through polymer chemistry.

Chitosan/PVA Nanofibers as Potential Material for the Development of Soft Actuators

Chitosan/PVA nanofibrous electroresponsive soft actuators were successfully obtained using an electrospinning process, which showed fast speed displacement under an acidic environment. Chitosan/PVA nanofibers were prepared and characterized, and their electroactive response was tested. Chitosan/PVA nanofibers were electrospun from a chitosan/PVA solution at different chitosan contents (2.5, 3, 3.5, and 4 wt.%). Nanofibers samples were characterized using Fourier transform infrared analyses, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), optical microscopy, and tensile test. The electroactive behavior of the nanofiber hydrogels was tested under different HCl pH (2-6) under a constant voltage (10 V). The electroactive response test showed a dependence between the nanofiber's chitosan content and pH with the bending speed displacement, reaching a maximum speed displacement of 1.86 mm^-1 in a pH 3 sample with a chitosan content of 4 wt.%. The results of the electroactive response were further supported by the determination of the proportion of free amine groups, though deconvoluting the FTIR spectra in the range of 3000-3700 cm^-1. Deconvolution results showed that the proportion of free amine increased as the chitosan content was higher, being 3.6% and 4.59% for nanofibers with chitosan content of 2.5 and 4 wt.%, respectively.

Regulation of molecular transport in polymer membranes with voltage-controlled pore size at the angstrom scale

Polymer membranes have been used extensively for Angstrom-scale separation of solutes and molecules. However, the pore size of most polymer membranes has been considered an intrinsic membrane property that cannot be adjusted in operation by applied stimuli. In this work, we show that the pore size of an electrically conductive polyamide membrane can be modulated by an applied voltage in the presence of electrolyte via a mechanism called electrically induced osmotic swelling. Under applied voltage, the highly charged polyamide layer concentrates counter ions in the polymer network via Donnan equilibrium and creates a sizeable osmotic pressure to enlarge the free volume and the effective pore size. The relation between membrane potential and pore size can be quantitatively described using the extended Flory-Rehner theory with Donnan equilibrium. The ability to regulate pore size via applied voltage enables operando modulation of precise molecular separation in-situ. This study demonstrates the amazing capability of electro-regulation of membrane pore size at the Angstrom scale and unveils an important but previously overlooked mechanism of membrane-water-solute interactions.

Multiple Responsive Hydrogel Films Based on Dynamic Phenylboronate Bond Linkages with Simple but Practical Linear Response Mode and Excellent Glucose/Fructose Response Speed

Multiple responsive hydrogels are usually constructed by the addition of many different functional groups. Generally, these groups have different responsive behaviors which lead to interleaved and complex modes of the multi-response system. It is difficult to get a practical application. In this study, we show that multi-response hydrogels can also be constructed using dynamic bonds as crosslinks. The multiple responsive hydrogel films with thicknesses on the sub-micrometer or micrometer scale can be fabricated from P(DMAA-3-AAPBA), a copolymer of N,N-dimethylacrylamide, 3-(acrylamido)phenylboronic acid, and poly(vinylalcohol) (PVA) though a simple layer-by-layer (LbL) technique. The driving force for the film build up is the in situ-formed phenylboronate ester bonds between the two polymers. The films exhibit Fabry-Perot fringes on their reflection spectra which can be used to calculate the equilibrium swelling degree (SD_e) of the film so as to characterize its responsive behaviors. The results show that the films are responsive to temperature, glucose, and fructose with simple and practical linear response modes. More importantly, the speed of which the films respond to glucose or fructose is quite fast, with characteristic response times of 45 s and 7 s, respectively. These quick response films may have potential for real-time, continuous glucose or fructose monitoring. With the ability to bind with these biologically important molecules, one can expect that hydrogels may find more applications in biomedical areas in the future.

Geometry Controlled Oscillations in Liquid Crystal Polymer Films Triggered by Thermal Feedback

Light-induced oscillatory behavior of liquid crystal polymer network (LCN) films has been demonstrated by several researchers in the past decade. Similarly, oscillations in LCN films under constant thermal stimulus have been reported recently, although the mechanism and the factors that govern the oscillatory behavior are not well understood. In this work, we study the dynamics of self-sustained oscillations exhibited by LCN films under a constant thermal stimulus through experiments and simulations. Geometrically asymmetric films such as a right triangle and an equilateral triangle are obtained from a twisted nematic square film. A multiphysics computational framework using the finite element method is developed to simulate the oscillatory behavior of the LCN films kept on a hot plate. The framework accounts for a coupling between heat transfer and mechanical deformations during the oscillations. Small temperature fluctuations (≈ 1 °C) coupled with gravity induced torque are shown to drive the oscillatory behavior at a specific plate temperature. We show for the first time that self-sustained oscillations can also be achieved in symmetric shapes, such as square films, by creating a thickness tapering between two opposite edges. The frequency of the oscillations is found to be in the range of 0.5 to 2.5 Hz for different geometries studied. The oscillation temperature depends on the mean thickness, size, and thickness profile of the films. As a possible application, we demonstrate a thermally actuated optical chopper using the oscillatory response of the films.

Active Control of Contact Angles of Various Liquids from the Response of Self-Assembled Thiol Molecules to Electric Current

The ability to change wettability in situ would realize active surfaces that can change their functionality and adapt to different environments. This article reports a new and easy method that controls surface wettability in situ. In doing so, three hypotheses were to be proven. First, thiol molecules with dipole moments at the end that were adsorbed onto gold could change the contact angles of nonpolar or slightly polar liquids when an electric current was provided at the gold surface without having to ionize the dipole. It was also hypothesized that the molecules would undergo conformation changes as their dipoles would align with the magnetic field induced by the applied current. Second, the ability to change contact angles was modified by mixing ethanethiol, a much shorter thiol with no dipole, with the abovementioned thiol molecules because it would provide space for the thiol molecules to undergo conformation changes. Third, the indirect evidence of the conformation change was verified with attenuated total reflection Fourier transform infrared (FT-IR) spectroscopy. Four thiol molecules that controlled the contact angles of deionized water and hydrocarbon liquids were identified. The abilities of those four molecules in changing the contact angles were modified by adding ethanethiol. A quartz crystal microbalance was used to infer the possible change in the distance between the adsorbed thiol molecules by investigating adsorption kinetics. The changes in FT-IR peaks with respect to applied currents were also presented as indirect evidence for the conformation change. This method was compared with other reported methods that control wettability in situ. The differences between the voltage-driven method to induce conformation changes of thiol molecules and the method presented in this paper were further discussed to emphasize that the mechanism by which the conformation change was induced in this article was most likely because of the dipole-electric current interaction.

Tunable metalensing based on plasmonic resonators embedded on thermosresponsive hydrogel

Metalenses of adjustable power and ultrathin flat zoom lens system have emerged as a promising and key photonic device for integrated optics and advanced reconfigurable optical systems. Nevertheless, realizing an active metasurface retaining lensing functionality in the visible frequency regime has not been fully explored to design reconfigurable optical devices. Here, we present a focal tunable metalens and intensity tunable metalens in the visible frequency regime through the control of the hydrophilic and hydrophobic behavior of freestanding thermoresponsive hydrogel. The metasurface is comprised of plasmonic resonators embedded on the top of hydrogel which serves as dynamically reconfigurable metalens. It is shown that the focal length can be continuously tuned by adjusting the phase transition of hydrogel, the results reveal that the device is diffraction limited in different states of hydrogel. In addition, the versatility of hydrogel-based metasurfaces is further explored to design intensity tunable metalens, that can dynamically tailor the transmission intensity and confined it into the same focal spot under different states, i.e., swollen and collapsed. It is anticipated that the non-toxicity and biocompatibility make the hydrogel-based active metasurfaces suitable for active plasmonic devices with ubiquitous roles in biomedical imaging, sensing, and encryption systems.

Turn-on stimuli-responsive switch: strategies for activating a new fluorescence channel by pressure

The stimulus-responsive smart switching of aggregation-induced emission (AIE) features has attracted considerable attention in 4D information encryption, optical sensors and biological imaging. Nevertheless, for some AIE-inactive triphenylamine (TPA) derivatives, activating the fluorescence channel of TPA remains a challenge based on their intrinsic molecular configuration. Here, we took a new design strategy for opening a new fluorescence channel and enhancing AIE efficiency for (E)-1-(((4-(diphenylamino)phenyl)imino)methyl)naphthalen-2-ol. The turn-on methodology employed is based on pressure induction. Combining ultrafast and Raman spectra with high-pressure in situ showed that activating the new fluorescence channel stemmed from restraining intramolecular twist rotation. Twisted intramolecular charge transfer (TICT) and intramolecular vibration were restricted, which induced an increase in AIE efficiency. This approach provides a new strategy for the development of stimulus-responsive smart-switch materials.

Modulation of wetting of stimulus responsive polymer brushes by lipid vesicles: experiments and simulations

The interactions between vesicle and substrate have been studied by simulation and experiment. We grafted polyacrylic acid brushes containing cysteine side chains at a defined area density on planar lipid membranes. Specular X-ray reflectivity data indicated that the addition of Cd²⁺ ions induces the compaction of the polymer brush layer and modulates the adhesion of lipid vesicles. Using microinterferometry imaging, we determined the onset level, [CdCl₂] = 0.25 mM, at which the wetting of the vesicle emerges. The characteristics of the interactions between vesicle and brush were quantitatively evaluated by the shape of the vesicle near the substrate and height fluctuations of the membrane in contact with brushes. To analyze these experiments, we have systematically studied the shape and adhesion of axially symmetric vesicles for finite-range membrane-substrate interaction, i.e., a relevant experimental characteristic, through simulations. The wetting of vesicles sensitively depends on the interaction range and the approximate estimates of the capillary length change significantly, depending on the adhesion strength. We found, however, that the local transversality condition that relates the maximal curvature at the edge of the adhesion zone to the adhesion strength remains rather accurate even for a finite interaction range as long as the vesicle is large compared to the interaction range.

Relatively homogeneous network structures of temperature-responsive gels synthesized via atom transfer radical polymerization

The network structures of poly(N-isopropylacrylamide) (PNIPAAm) gels prepared by atom transfer radical polymerization (ATRP) were compared with those prepared by free radical polymerization (FRP), as a conventional radical polymerization. Temperature-responsive shrinkage was observed in the PNIPAAm gels prepared by ATRP and FRP (ATRP and FRP gels), which depended on the cross-linker content. From the light-scattered intensities, 〈I〉_T, measured at the different sample positions, we used the partial heterodyne method to determine the dynamic fluctuation, 〈I〉_F, spatial component, 〈I〉_C, and correlation length, ξ, of the ATRP and FRP gels, as a function of the cross-linker content and temperature. While there is little difference in 〈I〉_F and ξ between the ATRP and FRP gels, 〈I〉_C of the ATRP gel was smaller than that of the FRP gel. In addition, we calculated the standard deviation of 〈I〉_T for the ATRP and FRP gels, as a function of temperature to quantify the inhomogeneity of the gel networks. The standard deviation revealed that increasing cross-linker content and temperature makes the gel networks more inhomogeneous. The dynamic light scattering (DLS) measurement used to characterize the gel network revealed that ATRP suppresses inhomogeneity more effectively than FRP. The standard deviation of the scattered intensity is used in this study to quantify the inhomogeneity of the network structures. Quantitative evaluations of the inhomogeneity of the network structures by the standard deviation of the scattered intensity are useful in the investigation of the structure-property relationships of gels.

A novel biosynthesis of MgO/PEG nanocomposite for organic pollutant removal from aqueous solutions under sunlight irradiation

The novel synthesis of MgO from Laurus nobilis L. leaves was prepared using the green synthesis method. It is using direct blending process to decorate MgO/PEG nanocomposite to enhance the photodegradation properties and examine its physical properties using diverse characterization techniques, including XRD, FTIR, SEM, EDX, and UV-Vis. X-ray diffraction reveals a cubic phase of MgO with a 37-nm grain size. SEM images confirm spherical nanoparticles with a diameter size of 22.9 nm. The optical energy gap of MgO NPs was 4.4 eV, and the MgO/PEG nanocomposite was 4.1 eV, which made it an efficient catalyst under sunlight. The photocatalytic activity of Rose Bengal (RB) and Toluidine Blue (TB) dyes at 5 × 10^-5 mol/l dye concentration indicates excellent degradation efficiencies of 98% and 95% in 120 min, respectively, under sunlight irradiation. MgO/PEG is an excellent candidate nanocomposite for applications of photodegradation and could be used for its potential capability to develop conventionally used techniques.

The pH Response of a Peptoid Oligomer

Polypeptoids are N-substituted glycine polymers, which differ from peptides in the placement of the side chain on the amide nitrogen rather than the C_α carbon. A peptoid with a chiral side chain containing both an aromatic group and carboxylic acid has a structure that responds to pH changes. All-atom molecular dynamics simulations using a force field specifically tuned for peptoids were carried out with an advanced sampling method for the peptoid (S)-N-(1-carboxy-2-phenylethyl)glycine in the high and low pH limits. The simulations show that the structure changes from mostly cis amide bonds at low pH to mostly trans bonds at high pH. The structural changes are driven by side chain-backbone hydrogen bonds at low pH and side chain repulsions and increased water contact at high pH.

Hierarchical network relaxation of a dynamic cross-linked polyolefin elastomer for advanced reversible shape memory effect

Reversible shape-memory polymers (RSMPs) are highly desired for soft actuators due to the repeatability of deformation. Herein, a polyolefin elastomer vitrimer (POEV) was prepared by constructing a dynamic cross-linked network based on boronic ester bonds. POEV showed varied network relaxation in a wide temperature range due to hierarchical network relaxation, and then the entropy decreased and the relaxation of POEV chains was facilely controlled by temperature. The controllable relaxation of POEV by programming the temperature enabled the actuation domain with a reduction in entropy and the skeleton domain with a relatively high entropy can be built in POEV, greatly affecting the reversible shape memory effects (RSMEs). The topological rearrangement resulted from the activated exchange of dynamic covalent bonds, which enables POEV with good shape reconfigurability, and allows for complicated 3D shapes and shape-shifting on demand. More interestingly, combining the decreasing entropy of POEV chains and fully topological rearrangement tailored by temperature, hybrid aligned carbon nanotubes (CNTs) can be constructed in POEV via a two-stage training. Then, the aligned CNTs can enhance the elasticity and act as a hybrid skeleton for RSMEs, avoiding the negative impact of CNTs on the reversible actuation strain. The hierarchical network relaxation facilitates combining all these unusual properties in one shape memory network synergistically, paving new avenues for realizing smart materials with advanced RSME.

Surface engineering of mixed conjugated/polyelectrolyte brushes - Tailoring interface structure and electrical properties

HYPOTHESIS

Mixed polymer brushes (MPBs) could be synthesized by surface dilution of homopolymer brushes and subsequent grafting of other type of chains in the formed voids. Nanophase separation and dynamics of surface-grafted chains could be tailored by modification of their molecular architecture. Mixed polyelectrolyte and conjugated chains contribute synergistically to tailor properties of the coating.

EXPERIMENTS

A new synthetic strategy that allowed spatially controlled grafting of poly(sodium 4-styrenesulfonate) chains (PSSNa) in close neighborhood of poly(3-methylthienyl methacrylate) (PMTM) brushes (precursors of the conjugated chains) using surface-initiated polymerizations was developed. The final mixed conjugated/polyelectrolyte brushes were prepared by template polymerization of pendant thiophene groups in PMTM chains. Surface dynamics and nanophase separation of MPBs were studied by nanoscale resolution IR imaging, SIMS profiling and AFM mapping in selective solvents.

FINDINGS

Unconjugated MPBs were shown to undergo vertical, and horizontal nanophase separation, while the size and shape of the nanodomains were dependent on molar ratio of the mixed chains and their relative lengths. Generation of the conjugated chains led to diminishing of nanophase separation thanks to stronger mutual interactions of conjugated PMTM and PSSNa (macromolecular mixing). The obtained systems demonstrated tunable interfacial structure and resistance switching phenomenon desired in construction of smart surfaces or memristive devices.