Multiple Stimuli-responsiveness Research Articles

AgNWs/Ti3C2Tx MXene-based multi-responsive actuators for programmable smart devices

Thermal bimorph actuators have important applications in artificial muscles, switches, and microsensors for robotics and biomimetic devices. To broaden the adaptability of environments, it is essential to fabricate thermal actuators with multiple stimulus responses, including electricity, near-infrared (NIR) light, and ultraviolet (UV) light, with fast and large deformations. Herein, a thermal actuator with programmable stimuli response was designed by combining silver nanowires (AgNWs) with Ti3C2Tx MXene. Due to the synergistic effect of AgNWs with high plasmonic properties and electrical conductivity as well as Ti3C2Tx MXene with good flexibility and photothermal properties, the obtained actuator can roll up for 2200° at a low driving voltage (2 V) and shows a fast response speed of 0.4 s for a bending angle of 360° under NIR light. More remarkably, the obtained thermal actuator can curl 360° in 1.2s under UV light which has never been reported before. We believe that such thermal actuators are attractive for a wide range of innovative technologies involving soft-bodied robots, intelligent grippers, bionic worms, and information cryptography.

Organic‒inorganic semi-interpenetrating networks with orthogonal light- and magnetic-responsiveness for smart photonic gels

Living matter has the ability to perceive multiple stimuli and respond accordingly. However, the integration of multiple stimuli-responsiveness in artificial materials usually causes mutual interference, which makes artificial materials work improperly. Herein, we design composite gels with organic‒inorganic semi-interpenetrating network structures, which are orthogonally responsive to light and magnetic fields. The composite gels are prepared by the co-assembly of a photoswitchable organogelator (Azo-Ch) and superparamagnetic inorganic nanoparticles (Fe3O4@SiO2). Azo-Ch assembles into an organogel network, which shows photoinduced reversible sol-gel transitions. In gel or sol state, Fe3O4@SiO2 nanoparticles reversibly form photonic nanochains via magnetic control. Light and magnetic fields can orthogonally control the composite gel because Azo-Ch and Fe3O4@SiO2 form a unique semi-interpenetrating network, which allows them to work independently. The orthogonal photo- and magnetic-responsiveness enables the fabrication of smart windows, anti-counterfeiting labels, and reconfigurable materials using the composite gel. Our work presents a method to design orthogonally stimuli-responsive materials.

A Wearable Flexible Tactile Sensor with Textile Microstructure for Wirelessly Recognizing Human Activity

AbstractFlexible tactile sensors have attracted special attention in the detection of human posture and activity. However, achieving multiple stimulus responses is particularly challenging in terms of structural design and has not been fully addressed. Herein, a novel structural design inspired by combining the characteristics of a strain sensor and e‐textile into a hybrid interface to obtain stretchable multiple stimulus‐responsive tactile sensors (stretching stimulus, pressing stimulus, and bending stimulus) is proposed. The sensitive layer of the sensor is designed as a textile microstructure. The sensor, which has a stable performance with excellent ohm property and durability (>2 years), possesses an extraordinary gauge factor (≈200) and a fast response time (≈2.48 ms) under tensile strain, a high sensitivity (≈2.35 kPa−1) in a low‐pressure range (≈9 kPa) under pressure. It has excellent performance for Human Activity Recognition by being attached to human skin. In addition, a Bluetooth device that tracks muscle activity in real‐time and transmits the output signals to a smartphone application is utilized. These results imply the utility of this sensor for a diverse application of robotic e‐skins or e‐muscles.

Smart bionic applications based on a multiple stimulus response GO-PDANP/PDMS bilayer flexible actuator

Flexible actuators, important part of the field of smart materials, can convert one or more stimuli in the environment into mechanical motion, which have been widely used in information technology, biosensors, intelligent robotics and other fields.

Dual Dynamic Covalently Crosslinked Alginate Hydrogels with Tunable Properties and Multiple Stimuli-Responsiveness.

Alginate is a biopolymer that can be crosslinked with calcium ions to fabricate cytocompatible hydrogels. However, using calcium ions to crosslink alginate provides limited properties and functions to alginate hydrogels, restricting their biomedical applications. Here, phenylboronic acid-functionalized polyethyleneimine (PBA-PEI) was developed to introduce two orthogonal dynamic covalent crosslinks in the alginate hydrogels, where PBA-PEI was used to crosslink alginate dialdehyde (ADA) through imine bonds and boronate ester bonds. The grafting degree of PBA in the PEI structure was applied to fine-tune the properties of PBA-PEI/ADA hydrogels, including the rheological property, mechanical strength, swelling behavior, and antibacterial activity. In particular, the highly sensitive boronate ester bonds in the network enabled PBA-PEI/ADA hydrogels to be responsive to several stimuli, such as glucose, fructose, and hydrogen peroxide. Taken together, PBA-PEI/ADA hydrogels with tunable properties and multiple stimuli-responsiveness have been demonstrated as smart biomaterials for advanced biomedical applications.

Biomolecule-based stimuli-responsive nanohybrids for tumor-specific and cascade-enhanced synergistic therapy

Poor tumor specificity is one of the key obstacles for clinical applications of nanotheranostic agents, consequently leading to serious side effects and unsatisfactory therapeutic efficacy. Herein, biomolecule-based nanohybrids (named as Hb-PDA-GOx) with multiple stimuli-responsiveness were designed and fabricated to enhance tumor-specific therapy. The nanohybrids embodied two proteins, i.e., hemoglobin (Hb) and glucose oxidase (GOx), which exhibited cascade catalytic activity selectively within the tumor microenvironment (TME). Specifically, GOx catalyzes the overexpressed glucose into gluconic acid and hydrogen peroxide (H2O2), which not only initiated starvation therapy (ST) through cutting off the nutrition supply for carcinoma cells, but also provided H2O2 for sequential Fenton reaction induced by Hb that generating biotoxic hydroxyl radicals (•OH) for chemodynamic therapy (CDT). Moreover, localized heat generation from polydopamine (PDA) in the nanohybrids can implement photothermal therapy (PTT) and reinforce the CDT efficacy. Excitingly, effective eradication of solid tumors and significant suppression of metastatic tumors growth were achieved by utilizing Hb-PDA-GOx as a versatile theranostic agent. All these results had been verified by in vitro and/or in vivo experiments. In light of the superior anticancer effects and insignificant systemic toxicity, the as-fabricated biomolecule-based nanohybrids could be employed as a promising agent for tumor-specific therapy. More importantly, the high biocompatibility and biodegradability of the selected biomolecules would facilitate subsequent clinical translation. Statement of significance(1) A facile one-pot synthesis strategy was proposed to fabricate biomolecule-based tumor theranostic agent with high biocompatibility and biodegradability, which would facilitate subsequent clinical translation; (2) The as-developed theranostic agent was endowed with multiple stimuli-responsiveness for achieving tumor-specific and cascade-enhanced synergistic therapy; (3) The in vivo experiments demonstrated that the as-developed theranostic agent can not only effectively eradicate solid tumors, but also significantly suppress metastatic tumors growth.

Fabrication of sustainable, toughening epoxy thermosets with rapidly thermal and light‐triggered shape memory property

AbstractShape memory epoxy thermosets (SMETs) have attracted more and more attention in artificial intelligence applications. However, the fabrication of lightweight and high‐strength bio‐based SMET with multiple‐response shape memory properties remains a challenge. Herein, a thermal and light‐triggered bio‐based SMET with excellent mechanical property and toughness is prepared. To fabricate the SMET, a bio‐based curing agent (CFMA) derived from cardanol, menthane diamine and furfural is utilized to react with epoxy resin E51 to prepare the SMET. The curing kinetics of SMET is measured by non‐isothermal DSC, and the reaction order is 0.784. The SMETs have excellent thermal stability and mechanical strength. Based on the toughening effect of the bio‐based curing agent, the SMETs exhibit excellent stretchability, and the toughness of the SMETs improves gradually with the increase in curing agent content. Furthermore, the SMET exhibits excellent thermal and light‐triggered shape memory properties, and the SMET with broad glass transition shows triple‐shape memory property. These multiple stimulus–response bio‐based SMETs with lightweight and high strength have potential applications in the field of actuators and intelligent electronic devices.

Aggregation-Induced Emissive Silicone Elastomer with Multiple Stimuli Responsiveness

Stable and highly efficient fluorescent silicone elastomers have attracted tremendous attention. In this contribution, a series of fluorescent silicone elastomers are facilely fabricated by combining aggregation-induced emission (AIE)-active polymers with a silicone matrix. The investigated AIE-active macromolecules are synthesized by reversible addition–fragmentation chain-transfer polymerization of vinyl monomers containing a tetraphenylethylene pendant. Detailed experimental characterizations demonstrate that macromolecular fluorescent compounds have good dispersibility and leaching resistance in silicone elastomers. Especially, the fluorescence properties of the silicone elastomers can be modulated by changing the molecular weight or aggregation state of the fluorescent macromolecules. Moreover, the prepared fluorescent silicone films show multiple stimulus responsiveness to strain, temperature, and organic solvents. The present work provides a simple and universal strategy toward fluorescent silicone elastomers for both scientific research and future practical applications.

Printed asymmetric microcapsules: Facile loading and multiple stimuli-responsiveness.

Engineering of colloidal particles and capsules despite substantial progress is still facing a number of unsolved issues including low loading capacity, non-uniform size and shape of carriers, tailoring different functionalities and versatility to encapsulated cargo. In this work, we propose a method for defined-shaped functionally asymmetric polymer capsule fabrication based on a soft lithography approach. The developed capsules consist of two classes of polymers - the main part "cup" is made out of polyelectrolyte multilayers (PAH-PSS) and "lid" is made of biodegradable polyether (PLGA). Asymmetric capsules combine advantages from both traditional layer-by-layer capsules and recently developed printed "pelmeni" capsules. This combination provides stimuli-responsiveness due to polyelectrolyte multilayer properties differing from PLGA. The inner volume of capsules can be loaded with a variety of active compounds and the capsule's geometry is defined due to the soft-lithography method. Capsules have a core-shell structure and monodisperse size distribution. Three methods to trigger cargo release have been demonstrated, namely temperature treatment, ultrasonication and pH shift. Steroidal drug dexamethasone was used to illustrate the applicability of the systems for triggered drug release. The application of proposed asymmetric capsules includes but is not limited to pharmacology, diagnostics, sensors, micro- and nanoreactors and chemical actuators.

A flexible, multifunctional, optoelectronic anticounterfeiting device from high-performance organic light-emitting paper

As a primary anticounterfeiting technology, most paper anticounterfeiting devices take advantage of photoresponsive behaviors of certain security materials or structures, thus featuring low-security threshold, which has been a critical global issue. To incorporate optoelectronic devices into existing anticounterfeiting technology suggests a feasible avenue to address this challenge. Here we report a high-performance organic light-emitting paper-based flexible anticounterfeiting (FAC) device with multiple stimuli-responsiveness, including light, electricity, and their combination. Without sacrificing the preexisted security information on the paper, we fabricate FAC device in a facile, low-cost yet high-fidelity fashion by integrating patterned electro-responsive and photo-responsive organic emitters onto paper substrates. By introducing optical microcavities, the FAC device shows considerable color shift upon different viewing angle and applied voltage, which is easily discernible by naked eyes. Notably, the FAC device is bendable, unclonable, and durable (a half-lifetime over 4000 hours at 100 cd m−2).

Mechanically toughened conductive hydrogels with shape memory behavior toward self-healable, multi-environmental tolerant and bidirectional sensors

• A toughened, self-healing, anti-freezing, anti-drying, and anti-swelling hydrogel is prepared. • Hydrogel sensors exhibit excellent self-healing capability and multi-environmental stability. • Hydrogel sensors display an attracting feature on distinguishing the direction of human motion. • Hydrogels possess significant shape memory and information storage functions even at −40 °C. Conductive hydrogels have considered as promising materials to revolutionize flexible electronics, biomedical devices and soft robotics. Despite significant progress has been made in the design of hydrogels, simultaneous realization of outstanding mechanical properties, self-healing capability, multi-environmental tolerance (e.g., freezing, drying, water, and oil), and multiple stimuli-responsiveness in a single hydrogel still remains a tremendous challenge. Herein, an extraordinary stretchable (1769%), toughened (0.46 MPa), self-healing, water-retaining (78% after 8 days), anti-freezing (below −40 °C), and anti-swelling (in water/organic solvents) conductive hydrogel is designed and prepared by simultaneously introducing zwitterionic proline, metal ions, and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) into vinyl hybrid silica nanoparticles cross-linked polyacrylic acid networks. Based on this hydrogel, the fabricated strain sensor exhibits excellent strain sensitivity (GF = 3.07), wide sensing range (from 5 to 700%), reliable stability (800 cycles at 200% strain), and accurate human motion detection along two opposite directions (bend down or bend up). In particular, it can not only withstand outstanding mechanical damages but also maintain stable sensing performances in water/organic solvent environments and freezing condition of −40 °C. More interestingly, under FeCl 3 -EG (ethylene glycol) and ascorbic acid-EG solution external stimuli, the resultant hydrogels also display the significant shape memory behaviors and repeated information recording/erasing capabilities even at an extremely cold temperature (−40 °C). These remarkable performances greatly expand the application fields of hydrogels in harsh environments.

Bz-8HQ: a novel supramolecular fluorochrome exhibiting multiple stimuli-responsiveness

A novel multifunctional fluorescent molecule (Bz-8HQ) was synthesized from the linkage of benzimidazole (Bz) and 8-hydroxyquinoline (8HQ) molecules and its response to multiple stimuli was investigated spectroscopically.

An Electrospinning Anisotropic Hydrogel with Remotely-Controlled Photo-Responsive Deformation and Long-Range Navigation for Synergist Actuation

As a soft/wet intelligent material, hydrogel actuators with multiple stimuli-responsiveness have been widely developed. However, it is still greatly difficult for them to integrate bi/multiple responsiveness together for bio-mimetic synergistic actuation. Here, we have explored a high-strength anisotropic bi-layer hydrogel actuator with P(NIPAM-ABP) layer and Fe3O4/PAN layer via electrospinning technique, which can provide programmable bi-functional synergistic movement. The Fe3O4/PAN layer can provide magnetic responsive navigation for long-range transportation on account of the magnetism of the Fe3O4 nanoparticles. Furthermore, the ultrahigh photothermal conversion efficiency of the Fe3O4 nanoparticles in the Fe3O4/PAN layer, can endow the P(NIPAM-ABP) layer with fast remotely-controlled photothermal-responsive deformation. Most importantly, this hydrogel actuator can achieve complex higher-level programmable movements than before based on the synergy of remotely-controlled deformation and the long-range transportation, which can be utilized to design various novel bio-mimetic soft-robots. Last but not least, the introduction of the electrospinning, not only can achieve high strength (4.59 MPa of tensile strength) of this bi-layer hydrogel, but also can provide both ultrafast (178°/s) and programmable complex photothermal-responsiveness, owing to the ultrahigh specific surface area (ultra-thin and porous structure) and excellent orientation of the thermal-responsive P(NIPAM-ABP) nanofibers respectively. This work will provide a general method via electrospinning for anisotropic hydrogel actuator with bi/multiple-functional synergy and will provide a new strategy for smart actuators and other bio-mimetic intelligent materials/systems.

Building multi-color emitters with tailored lanthanide-based supramolecular metallogels

Multicomponent lanthanide-based metallogel offers unique prospects to access versatile, dynamic supramolecular soft materials with hierarchical stimuli-responsiveness and tunable functions, particularly for applications in the optical display field. In this work, a novel ligand L bearing classical coordinating terpyridine (tpy) and hosting 24-Crown-8 (24C8) moieties was synthesized with a function-oriented design principle, which further allowed the complexation between L and a series of lanthanide ions (Ln). Interestingly, several L-Ln complexes with 1:1 stoichiometry were found to be able to gel the solvent toluene/CH3CN (1:1), and thus lanthanide-based metallogels were successfully prepared. The L-Eu and L-Tb gel was found to be emissive and further utilized to produce a white light emitter through fine adjustment of stoichiometry among Eu, Tb, and L. Importantly, the multicomponent gel strategy was employed, and additional non-coordinating chromophores were introduced into the metallogel system. Thus a broad-spectrum of emission was achieved, and these multicomponent emissive gels were successfully applied as a photo printer. The metallogels also showed multiple stimuli-responsiveness such as pH, guest molecules thanks to the anchoring of predesigned functional moieties such as tpy and 24C8 on the ligand L. It is assumed that our multicomponent metallogel research shown here may open new avenues towards the design and preparation of intelligent and tunable hybrid lanthanide-based optical materials.

Temperature-Stress Bimodal Sensing Conductive Hydrogel-Liquid Metal by Facile Synthesis for Smart Wearable Sensor.

Conductive hydrogels have attracted great attention due to their promising applications in wearable sensors. However, developing conductive hydrogels with excellent sensor properties and multiple stimuli responsiveness for smart wearable devices is still a challenge. This paper presents a facile synthetic method of a crosslinked chitosan quaternary ammonium salt and liquid metal (CHACC-LM) composite hydrogel with temperature-stress bimodal sensing for smart wearable sensor. LM as liquid fillers toughen the hydrogel matrix (stress: 1.11MPa) and enhance the hydrogel extensibility (strain: 233%). The CHACC-LM hydrogel exhibits conductivity , excellent antibacterial properties (> 99%), an electrical self-healing property, and strain sensitivity (GF = 1.6). In addition, the CHACC-LM hydrogel can be used as wearable flexible sensors with the ability of monitoring human activities directly and the distinguished ability of discerning subtle motions (handwriting). It also shows sensitivity in the external environment such as low temperature, thermal response, and water solution. Importantly, the composite hydrogel simultaneous response to different stress and temperature stimuli. Furthermore, the CHACC-LM hydrogel can be used for gesture recognition and to control the manipulator in human-computer interaction. All these properties provide a great scope for researchers to achieve practical advances in smart wearable sensors.

Self-assembly of multiple stimulus response copolymer by ATRP in different media

ABSTRACT The novel pH and thermo-sensitive amphiphilic triblock copolymer poly(methyl methacrylate)-block-poly(N-isopropylacrylamide)-block-poly[N,N-(dimethylamino) ethyl methacrylate] (PMMA-b-PNIPAM-b-PDMAEMA) was synthesized by ATRP. We have prepared the AB amphiphilic copolymer (PMMA-b-PNIPAM) and ABC amphiphilic triblock copolymer (PMMA-b-PNIPAM-b-PDMAEMA) of expected molecular mass. It was characterized by GPC,1HNMR and FT-IR spectroscopy. The AB amphiphilic copolymer ability of temperature response and the morphology of self-assembly micelles different in toluene, THF, and DMF. ABC amphiphilic triblock copolymer self-assembled petal structure in alkaline aqueous solution, and lamellar structure in acidic aqueous solution. Moreover, the transmittance of micellar solution changes with the increase of temperature; these changes reflect the pH and thermo-sensitivity of the block copolymer. The micelles behavior and morphology of the system were studied by transmission electron microscopy (TEM) and dynamic light scattering (DLS).

Construction of a multicolored emission tetraphenylethene derivative in response to multiple stimuli

Novel multiple stimuli-responsive fluorescent materials have diverse functions and are in high demand in practical applications. In this work, we reported a simple but versatile tetraphenylethene (TPE) derivative 1, whose appearance and fluorescence color were sensitive to mechanical, thermal, solvent vapor and UV light stimuli. It displayed tricolored mechanochromic and photochromic behavior with high contrast (variation of emissive wavelength is more than 100 nm). Moreover, the relationship between intermolecular interactions and fluorescence property was clarified through the investigation of its polymorphs. The multiple stimuli-responsiveness of compound 1 is ideal for preparing advanced anti-counterfeiting material.

Supramolecular Polymer Networks with Enhanced Mechanical Properties: The Marriage of Covalent Polymer and Metallacycle†

Main observation and conclusionSupramolecular polymer networks (SPNs) have always been the focus of research due to their novel features of good processability, stimuli‐responsiveness, self‐healing, and recyclability. Herein, we report the preparation of a metallacycle‐linked supramolecular gel via orthogonal metal‐ligand interactions and host‐guest interactions. A triangular metallacycle with three appended 21‐crown‐7 (21C7) units was obtained by the metal coordination of nickel(II)‐salen‐based dipyridyl ligands and platinum(II) acceptors. The integration of this metallacycle and traditional copolymer bearing secondary ammonium salts constructed a SPN via host‐guest recognition between 21C7 units and ammonium salts, and a supramolecular gel further formed at high concentration. Multiple stimulus responsiveness and self‐healing properties of gel were observed. The gel exhibited better stretchability compared to relative gel formed by copolymer alone owing to the synergistic effect of covalent bonds and supramolecular interactions. Moreover, compared to the model gel without metallacycles, the gel showed higher storage and loss moduli, and exhibited stronger stiffness in the self‐healing tests performed with rheometer, indicating the metallacycle played an important role in improving the stiffness and self‐healing of the gel. Therefore, the feasible approach to the formation of SPNs by the marriage of covalent polymers and metallacycles is expected to open a new way to design novel SPNs.

Supramolecular Gels Based on Azobenzene Derivatives

In the past years, azobenzene, as a common photoreactive group, has been widely used in intelligent photocontrolled supramolecular gels. In the field of biomedicine, a few supramolecular hydrogels based on azobenzene are regarded as carriers with low damage and high control in vivo due to their advantages in light response. In the environmental field, some hydrogels can also adsorb pollutants under the control of light through the interaction between host and guest. At the same time, supramolecular hydrogels based on azobenzene with multiple stimulus responses have been studied. It is difficult for most supramolecular organogels to have multiple stimulus responses simultaneously and the preparation conditions are also more complex. In this paper, I have summarized the latest research results of supramolecular hydrogels and organogels based on azobenzene in recent years so that researchers can have a deeper understanding of the preparation methods, properties and application of the supramolecular gels containing azobenzene.

Tunable and Nacre-Mimetic Multifunctional Electronic Skins for Highly Stretchable Contact-Noncontact Sensing.

Electronic skins (e-skins) have attracted great attention for their applications in disease diagnostics, soft robots, and human-machine interaction. The integration of high sensitivity, low detection limit, large stretchability, and multiple stimulus response capacity into a single e-skin remains an enormous challenge. Herein, inspired by the structure of nacre, an ultra-stretchable and multifunctional e-skin with tunable strain detection range based on nacre-mimetic multi-layered silver nanowires /reduced graphene oxide /thermoplastic polyurethane mats is fabricated. The e-skin possesses extraordinary strain response performance with a tunable detection range (50 to 200% strain), an ultralow response limit (0.1% strain), a high sensitivity (gauge factor up to 1902.5), a fast response time (20ms), and an excellent stability (stretching/releasing test of 11 000 cycles). These excellent response behaviors enable the e-skin to accurately monitor full-range human body motions. Additionally, the e-skin can detect relative humidity quickly and sensitively through a reversible physical adsorption/desorption of water vapor, and the assembled e-skin array exhibits excellent performance in noncontact sensing. The tunable and multifunctional e-skins show promising applications in motion monitoring and contact-noncontact human machine interaction.