Multi-stimuli Responsiveness Research Articles

Stimuli-Responsive Nanoradiosensitizers for Enhanced Cancer Radiotherapy.

Radiotherapy (RT) has been a classical therapeutic method of cancer for several decades. It attracts tremendous attention for the precise and efficient treatment of local tumors with stimuli-responsive nanomaterials, which enhance RT. However, there are few systematic reviews summarizing the newly emerging stimuli-responsive mechanisms and strategies used for tumor radio-sensitization. Hence, this review provides a comprehensive overview of recently reported studies on stimuli-responsive nanomaterials for radio-sensitization. It includes four different approaches for sensitized RT, namely endogenous response, exogenous response, dual stimuli-response, and multi stimuli-response. Endogenous response involves various stimuli such as pH, hypoxia, GSH, and reactive oxygen species (ROS), and enzymes. On the other hand, exogenous response encompasses X-ray, light, and ultrasound. Dual stimuli-response combines pH/enzyme, pH/ultrasound, and ROS/light. Lastly, multi stimuli-response involves the combination of pH/ROS/GSH and X-ray/ROS/GSH. By elaborating on these responsive mechanisms and applying them to clinical RT diagnosis and treatment, these methods can enhance radiosensitive efficiency and minimize damage to surrounding normal tissues. Finally, this review discusses the additional challenges and perspectives related to stimuli-responsive nanomaterials for tumor radio-sensitization.

Multi-stimulus Response Behavior of Biomimetic Autocrine Waxy Materials for Potential Self-Constructing Surface Microstructures.

Many functions of terrestrial plant leaves rely on the regenerable epidermal wax layer. Biomimetic autocrine waxy materials (AWMs) inspired by renewable epidermal waxes are attracting increasing attention. However, the growth properties of the wax layer remain unclear, limiting the development of this promising material. This work focuses on the stimulated growth characteristics and microstructural regulation methods of the waxy layers. It is found that the wax layers exhibit a corresponding behavior of changing their surface micromorphology under force, heat, solvents, and other stimuli during the self-growth process, and as a result of which, various types of fine surface microstructures such as grids, rings, stripes, pattern copying, and printing can be self-built on their surfaces. The composition of the surface autocrine wax layer changes with the autocrine time, and this finding may be useful for the separation and purification of alkane mixtures. In addition, the surface wax layer possesses the ability to self-heal and strengthen itself at the damage site after being stimulated by injury, similar to the damage-response behavior of a bark surface. Such multi-stimulus response behavior described here provides a platform for the discovery of more functional materials and microstructural self-construction techniques and can also serve as a basis for their applications.

Polyacrylamide–Poly(vinyl alcohol)–Sodium Alginate–Reduced Graphene Oxide/Nylon Fabrics with Multistimuli Responses

Polyacrylamide–Poly(vinyl alcohol)–Sodium Alginate–Reduced Graphene Oxide/Nylon Fabrics with Multistimuli Responses

Construction of a logic gate sensitive monitoring system of Graphdiyne/Poly(N,N-dimethylacrylamide) binary structure films for environmental pollutant phenylhydrazine

In this work, binary hydrogel films based on Graphdiyne/Poly(N,N-dimethylacrylamide (GDY/PDEA) were successfully polymerized and assembled on pyrolytic graphite (PG) electrode surface. When phenylhydrazine (PHz) as an active electrochemical probe in solution exhibits reversible cyclic voltammetric (CV) behaviors in response to temperature, salt and pH at the membrane electrode. The CV signals of PHz were significantly enhanced by electrocatalysis of GDY layer of the films. And the mechanism of membrane reaction was discussed and studied. The presence of protonated PHz determines the pH-sensitive property of the system. During pH adjustment with esterase urease, in situ enzymatic electrocatalysis that may be accelerates the electron transfer rate at the electrode surface. The structural alterations of PDEA hydrogels under multiple conditions were attribute to the temperature response and salt concentration–response. GDY films can also have an effect on the CV response signals. In conclusion, a multi-stimulus response hydrogel film environmental sensor has been constructed, and a 5-input/5-output logic gate system including OR, AND and NOT has been successfully constructed. And constructed 2-to-4 decoder and 2-to-1 encoder two logic devices. It provides a new method to increase the complexity of the environmental pollutant monitoring calculation system.

A Multistimuli Responsive, Flexible Luminescent Framework and Its Applicability in Anticounterfeiting.

A linear distyrylanthracene derivative (DDATAn) with two diaminotriazine (DAT) groups acting as the hydrogen bond (H-bond) units was designed and synthesized in order to construct flexible organic porous crystals. H-bonds between the DAT moieties helped the molecules to construct a double interpenetrated two-dimensional layer, and the stacking between layers provided a H-bonded organic framework (X-HOF-3) with one-dimensional solvent channels. When X-HOF-3 was placed in contact with methanol, the fluorescent colors of the HOF exhibited an apparent bathochromic shift. More interestingly, the methanol-activated HOF was able to rapidly adsorb water from the air, which was accompanied by a change in fluorescent color from yellow to red. Under heating, water was released from the HOF and the fluorescent color returned to yellow. Water molecules in the pores were also able to be released after an applied mechanical force disrupted the ordered structure of the HOF. Based on these stimuli-responsive properties, these HOFs can be used as advanced functional materials in anticounterfeiting applications.

MXene‐Based Soft Actuators with Multiresponse and Diverse Applications by a Simple Method

AbstractSmart actuators that can convert external energy stimuli into mechanical energy output have great potential in industrial, biomedical, and military applications. However, the existed disadvantage such as complex fabrication process, single stimulus source, and the requirement of artificial energy restrict their further development. Herein, a MXene/polyethylene (PE)‐based soft actuator with multistimulus response and the ability to be driven by natural sunlight and human humidity is proposed through a simple method. Owing to the excellent electrical conductivity, high photothermal conversion capability, and surface hydrophilicity of MXene, the MXene/PE actuator exhibits rapid and large bending deformation in response to external multistimuli such as light, electricity, heat, and humidity. Owing to the simple preparation, and anisotropic, tailorable and programmable properties of the MXene/PE actuator, a soft robot that can crawl directionally under light conditions is constructed. In addition, based on the high sensitivity response of the actuator to light and humidity, smart clothing that can generate reversible bending deformation under natural sunlight as well as sweat conditions is developed. These results provide a new inspiration for the design of high‐performance soft actuators with multistimulus response, and demonstrate the potential applications of the MXene/PE actuators in smart devices, bionic robots, and wearable clothing.

Hygrothermic Wood Actuated Robotic Hand (Adv. Mater. 22/2023)

Wood Actuators In article number 2211437, Wenshuai Chen, Swee Ching Tan, and co-workers report a wooden robotic hand for dexterous object–hand interactions and fire rescue that generates stretching and bending responses to moisture and heat/light stimulation. Multiple advantages are realized by one device, including good mechanical properties, multi-stimulus response, complex deformation, wide working temperature range, low manufacturing cost, and biocompatibility.

Investigation of quasistatic and dynamic mechanical properties of thermoplastic polyurethane magnetorheological elastomers

Thermoplastic magnetorheological elastomers (MRE) are soft magnetic materials with multi stimuli response. As the name suggests, thermoplastic MREs are formed by the suspension of magnetic particles in a thermoplastic elastomer matrix, whose rheological properties can be controlled by temperature. The composite itself can thus be controlled by temperature and magnetic field. In this article, we present the method and results of quasistatic and dynamic mechanical properties of thermoplastic polyurethane MREs (TPU-MREs) based on the observations made on the influence of hardener and plasticizer content from the composition point of view and the directional interdependence of strain and magnetic field on the magnetorheological (MR) effect. Quasistatic tensile and torsion tests followed by dynamic oscillation tests conducted within the linear elastic regime at three different temperatures with and without externally applied magnetic field are performed on the TPU-MRE samples. The tests are conducted with an inhouse developed test setup adapted to a commercial rheometer. The obtained results demonstrate a strong correlation to the change in moduli of the TPU-MRE with respect to change in composition and temperature. From the results obtained, one can conclude that samples with lower hardener content with plasticizer have the highest relative MR effect.

Photothermal and Humidity Stimulus-Responsive Self-Sensing Soft Actuators for Smart Packaging

Soft actuators with both actuation and self-sensing characteristics can better adapt to the environment and more effectively realize intelligent human–machine interactions, which is highly desired for the upcoming era of soft robotics. Herein, a multi-stimulus response actuator (MSRA) is constructed based on the asymmetric expansion principle, and the sensing function is simply and quickly integrated into the soft actuator by screen printing technology. Taking advantage of the good photothermal conversion performance of the dopamine-modified graphene oxide (DGO) layer and the difference in the expansion coefficient between the DGO layer and the poly(vinylidene fluoride)/polydimethylsiloxane layer, the soft actuators exhibit different actuation behaviors under photothermal and humidity stimuli, respectively. Meanwhile, the introduction of a printed carbon black/highly elastic transparent adhesive cement sensing layer gives MSRA a self-sensing function which can provide feedback on its actuation process in real time. In addition, various complex deformations can be achieved by the macroscopic assembly of several actuators. Finally, we show that this soft actuator can be used as a smart packaging material to realize smart packaging. We believe that actuators with sensing feedback are significant in soft robots and smart packaging.

A fast acid-responsive fluorescent porous polymer for acid-modified gas detection and optical anti-counterfeiting

Acid-stimulated responsive POP materials have received increased attention because of their intelligent photophysical properties and ability to translate changing environmental conditions into a specific response in the material. However, designing POP materials with new structures, excellent stability, and multi-stimulus response (simultaneous color and fluorescence response) remains challenging. Herein, a novel multi-stimulus responsive cyano-sp2c conjugated backbone POP-2 was designed and synthesized based on the synergistic effect of material protonation and intramolecular charge transfer (ICT). For the first time, we combined 2,4,6-Tri-(4-formyl-biphenyl-4-yl)-1,3,5-triazine (TFBT), a triazine-based monomer with biphenyl structure, with CPTD to synthesize a novel multi-responsive POP via sp2-C linkage (POP-2). POP-2 showed a dual response of color and fluorescence under acidic conditions. The introduction of the biphenyl structure increased the conjugation length and pore size of POP-2, which significantly improved the acid response behaviour of POP-2 due to the extended conjugation length, the conjugation effect, and the increase in pore size. Moreover, POP-2 can display aggregation-induced emission (AIE). Compared to the sp2-C-linked model compound TT-POP, POP-2 has a more significant fluorescence/color redshift and a lower response acid concentration under the same acidic conditions. This finding highlights the synergistic effect between conjugate length and pore size. In addition, we found that POP-2 exhibited a red shift of nearly 100 nm in aqueous hydrochloric acid at a concentration of 1 M, which was significantly better than most reported POPs. Interestingly, the resulting test strips produce a similar fluorescence response to HCl/NH3 gases with high sensitivity and reversibility. The POP material can be used as an intuitive and simple detection strategy for acidic and alkaline gases. In addition, its unique fluorescence response makes it valuable in optical anti-counterfeiting applications.

Plant oil-derived vitrimers-graphene composites with self-healing ability triggered by multiple stimuli

Bio-based polymer materials with multi-stimuli responsiveness and multichannel self-healing ability have received significant attention due to their increasing impact on intelligent device. In this study, we report a direct construction of bio-based epoxy vitrimer (EV) from green, renewable precursors including soybean oil and tung oil that could offer new opportunities for constructions of novel polymer network intrinsically containing favorable features such as multi-stimuli response and multichannel self-healing ability, repeatable processing and recycling. Epoxidized soybean oil (ESO) and tung maleic anhydride (TMA) was used to produce a full plant oil-based EV. Tensile strengths of EVs significantly increased from 1.27 MPa to 3.7 MPa, which was due to the formation of multiple H-bonds and increased crosslink density. EVs with micropores or cracks cut achieved self-healing after heating at 200 °C in oven after 60 min. A practicable strategy for fabricating full plant oil based EV composites using graphene was developed to produce multifunctional vitrimers with self-healing ability triggered by multiple stimuli. The electricity, heat, electromagnetic wave and IR light triggered self-healing of EV composite with graphene were achieved.

Hygrothermic Wood Actuated Robotic Hand.

Stimulus-responsive actuators play a vital role in the new generation of intelligent systems. However, poor mechanical performance, complicated fabrication processes, and the inability to complex deformation limit their practical applications. Herein, these challenges are overcome via designing a strong hygrothermic wood actuator with asymmetric water affinity. The actuator is readily constructed by sandwiching polypyrrole-coated wood with a Ni complex hygroscopic gel top layer for moisture absorption and a polyimide bottom layer as the water barrier. The resulting hygrothermic wood spontaneously stretches and bends itself in response to moisture and thermal/light stimulation. A robotic hand and a series of grippers made of hygrothermic wood demonstrate dexterous object-hand interactions during grasping and holding, while the reversible hygrothermic property allows the actuator to be potentially applied in fire rescue scenarios to rescue trapped objects. A combination of good mechanical properties, multi-stimulus-response, complex deformation, wide working temperature range, low manufacturing cost, and biocompatibility are simultaneously realized by one device. It is thus believed that such a strong wood actuator will open up a new avenue for building intelligent robotic hand systems.

A Smart Benzothiazole-Based Conjugated Polymer Nanoplatform with Multistimuli Response for Enhanced Synergistic Chemo-Photothermal Cancer Therapy

The combination of chemotherapy and phototherapy has received tremendous attention in multimodal cancer therapy. However, satisfactory therapeutic outcomes of chemo-photothermal therapy (chemo-PTT) still remain challenging. Herein, a biocompatible smart nanoplatform based on benzothiazole-linked conjugated polymer nanoparticles (CPNs) is rationally designed, for effectively loading doxorubicin (DOX) and Mo-based polyoxometalate (POM) through both dynamic chemical bond and intermolecular interactions, with an expectation to obtain new anticancer drugs with multiple stimulated responses to the tumor microenvironment (TME) and external laser irradiation. Controlled drug release of DOX from the obtained nanoformulation (CPNs-DOX-PEG-cRGD-BSA@POM) triggered by both endogenous stimulations (GSH and low pH) and exogenous laser irradiation has been well demonstrated by pharmacodynamics investigations. More intriguingly, incorporating POM into the nanoplatform not only enables the nanomedicine to achieve mild hyperthermia but also makes it exhibit self-assembly behavior in acidic TME, producing enhanced tumor retention. Benefiting from the versatile functions, the prepared CPNs-DOX-PEG-cRGD-BSA@POM exhibited excellent tumor targeting and therapeutic effects in murine xenografted models, showing great potential in practical cancer therapy.

Photoactuation, photochromism and acidochromism of styrylindazole-based crystalline materials

Herein, three new fluorostyrylindazoles bearing one, three and five fluorine atoms (FPIZ, TFPIZ and PFPIZ) have been synthesized. Interestingly, the crystal of PFPIZ bent back away from the lighht source at the initial stage of 365 nm light irradiation, and then it showed phototropic bending when prolong the irradiation time without changing the irradiation direction. It was found that the photo-induced [2 + 2] cycloaddition could lead to the expansion and contraction of the unit cell in different directions, and in turn trigger the crystal to exhibit macroscopic mechanical moving. Meanwhile, the photochemical reaction was reasonable for the photochromism of the PFPIZ, which is helpful for the visual observation of the photomechanical effects. For instance, the fluorescence of the crystals of PFPIZ was changed from blue-purple to white under 365 nm irradiation. Besides, TFA (trifluoroacetic acid) could quench the emission of the synthesized fluorostyrylindazoles to different degree in solutions as well as in the films. The acidochromism of the styrylindazole derivatives was originated from the protonation of indazole by acid. The design of multi-stimuli response crystalline materials would be helpful for the fabrication of intelligent photoactuators and fluorescence sensors.

Stimulus-Responsive Drug Delivery Nanoplatforms for Osteoarthritis Therapy.

Osteoarthritis (OA) is one of the most prevalent age-related degenerative diseases. With an increasingly aging global population, greater numbers of OA patients are providing clear economic and societal burdens. Surgical and pharmacological treatments are the most common and conventional therapeutic strategies for OA, but often fall considerably short of desired or optimal outcomes. With the development of stimulus-responsive nanoplatforms has come the potential for improved therapeutic strategies for OA. Enhanced control, longer retention time, higher loading rates, and increased sensitivity are among the potential benefits. This review summarizes the advanced application of stimulus-responsive drug delivery nanoplatforms for OA, categorized by either those that depend on endogenous stimulus (reactive oxygen species, pH, enzyme, and temperature), or those that depend on exogenous stimulus (near-infrared ray, ultrasound, magnetic fields). The opportunities, restrictions, and limitations related to these various drug delivery systems, or their combinations, are discussed in areas such as multi-functionality, image guidance, and multi-stimulus response. The remaining constraints and potential solutions that are represented by the clinical application of stimulus-responsive drug delivery nanoplatforms are finally summarized.

Multi-stimuli, color switchable emitter by solvent induced polymorph synthesis

Polymorphism has drawn great attention in tuning organic solid-state luminescent materials by alteration of molecular packing structure and has considerable potential application in optoelectronic devices and fluorescence sensors. Herein, two polymorphs based on dicyanodistyrylbenzene (DCS) compound were obtained by solvent induced synthesis. We have comprehensively investigated photophysical properties (such as photoluminescence colors, lifetime and PL quantum yield) of the two polymorphs, blue one αDCFDCS (Aqua) and green one αDCFDCS (Green). The single crystal structure analysis and XRD powder pattern shows that there is a slightly packing dislocation in a-axis account for the difference between the two phases. Mechanical grinding can lead to an alternation in photoluminescence color from blue to green. The differential thermal analysis (DTA) measurement discloses αDCFDCS (Aqua) is the metastable state of the compound. Both of two polymorphs show thermochromic and can be reversibly switched upon heating and cooling, which is attributing to the crystal cell expansion with the temperature increasing revealed by in situ XRD. Moreover, fuming with NH3 also causes the color change via Lewis acid base reaction. Upon heating or being exposed to HCl, it will return to the original state. The results of the polymorphism not only provide an insight into molecular packing and emission properties, but also pave the way for understanding the solid luminescence change by the multi-stimuli response.

Fiber-reinforced liquid crystalline elastomer composite actuators with multi-stimulus response properties and multi-directional morphing capabilities

Liquid crystalline elastomers (LCEs) are promising materials for soft actuations. LCE composites (LCECs), via the inclusion of fillers into LCEs, bring diverse functionalities and stimuli-responsive capabilities. It is still a challenge to improve the mechanical properties of LCEC and ensure that the material can perform reversible transformations. Here we present a cost-effective LCEC design and fabrication method by dispersing continuous carbon fibers and carbon nanotubes into LCEs, forming a new type of LCEC actuator. We found that through adjusting the angle (such as 45° and 90°) between the carbon fiber and the stretching axis of LCEC matrix, complex deformable geometries can be easily achieved including bending and twisting structures with enhanced storage modulus (400.9 MPa at 25 °C). Furthermore, the LCEC actuators could be driven by various stimuli including heat (120 °C), light (800 mW cm−2), and electricity (2.0 V). As a result, our new LCEC actuator outperforms other LCE actuators by having the largest number of morphing geometries and stimulus-responsive modes. Our LCEC design and manufacturing strategy represents a promising general methodology that can be easily extended to other continuous fibers (such as glass fiber, aramid fiber, etc.) filled LCECs, bringing even rich shape-changing capabilities that are needed for soft robots and beyond.

Bio-based dynamically crosslinked networks/Fe3O4 nanoparticles composites with self-healing ability driven by multiple stimuli for non-contact welding

Polymers with repairability driven by multiple stimuli and its functional composite materials are desired for practical applications. However, to date, study on dynamically crosslinked networks with multi-stimuli response or multichannel self-healing ability derived from green, renewable precursors has been rarely reported. Herein, bio-based dynamically crosslinked network based on Schiff base (dynamic imine bonds) and multiple hydrogen bonds were fabricated from soybean oil and vanillin. The reprocessing and self-healing properties could be customized by varying the ratio of methacrylation of the obtained fatty amide (MASO) UV-curable prepolymer and methacrylate functionalized vanillin (MAV). The introduction of Schiff base and hydrogen bonds endowed reprocessability for the material. Moreover, the resulting bio-based dynamically crosslinked network exhibited outstanding self-healing performance stimulated by heat, organic solvent, infrared radiation, and microwave. The bio-based composites with Fe3O4 nanoparticles were also investigated to realize non-contact welding of fracture. This study provided a promising strategy for the development of biomass resources and bio-based dynamically crosslinked network composites with good repairability.

Multi-stimuli responsiveness of pyrimidine bishydrazone: AIE, tuneable luminescence, white light emission, mechanochromism, acidochromism and its anticounterfeiting applications

The development of multifunctional properties associated with a single molecule being a centre of attention in the material science research area has been more focused in recent days. An aggregation-induced emissive (AIE) molecule having various aspects of stimuli-responsiveness such as mechanochromism, and acidochromism, along with white-light emitting behavior within a molecule will give rise to enormous applications in near future. A simple strategy to fabricate white-light emitting material from a single component system is beneficial for applications in the field of flat-panel displays and other optoelectronic devices. Herein, we have designed a D-A-D triad-based AIE active organic molecule HYPY-DESALvia a facile one-step Schiff-base condensation reaction between 4,6-dihydrazinopyrimidine (HYPY) and 4-(N,N-diethylamino)salicylaldehyde (DESAL) containing ESIPT as well as ICT properties. This AIE-active molecule exhibits white light emission (fw ≈ 49%) feature in addition to the tunable emission characteristics in its aggregated states which can be utilized for various light emitting diode applications. The compound revealed exceptional solid-state stimuli responsiveness such as mechanofluorochromism and acidochromism. HYPY-DESAL exhibited acidochromic features with a remarkable red shift in emission wavelength greater than 150 nm in the solid state. The specific site of protonation upon TFA addition was confirmed via1H NMR titration as well as TD-DFT experiments. The interesting reversible switching characteristics of the compound upon exposure to TFA/TEA are successfully utilized for several coding-decoding, information storage, and anti-counterfeiting applications in paper strips as well as PMMA-based thin films. Taken together, the combined features of the newly designed and readily accessible molecule exhibiting multi-stimuli responsive features such as AIE, tuneable luminescence, white light emission, mechanochromism, acidochromism, vapor phase sensing applicability using paper strips as well as thin films is unique, if not unprecedented.

Multi-stimulus responsive properties of a Cd-MOF based on tetraphenylethylene

The three-dimensional MOF Cd-tcbpe undergoes ligand conformational compression under multi stimulus response conditions, resulting in sensitive and reversible fluorescence color changes. This multi stimulus response behavior could be widely applied.