Nanosphere Chain Model of Magnetic Fluid and Its Dynamic Performance

The magnetorheological effect is a critically important mechanical property of magnetic fluids. Accurately capturing the macroscopic properties of magnetorheological fluids with elongated particle forms, such as nanosphere chains, remains a challenging task, particularly due to the complexities arising from particle asymmetry. Traditional particle dynamics primarily utilize spherical particles as computational units, but this approach can lead to significant inaccuracies, especially when analyzing nonspherical magnetorheological fluids, due to the neglect of particle asymmetry. In this work, an advanced particle dynamics model has been developed by integrating the rotation and collision of these asymmetric particles, specifically tailored for the configuration of nanosphere chains. This model exhibits a significant reduction in error by a factor of 3.883, compared to conventional particle models. The results demonstrate that alterations in the geometric characteristics of magnetic nanosphere chains can cause changes in mesoscopic structures and magnetic potential energy, thereby influencing the mechanical properties at the macroscopic level. This work has developed an accurate mesoscopic simulation method for calculating chain-type magnetorheological fluids, establishing a connection between mesoscopic structures and macroscopic properties, and unveiling the tremendous potential for accelerating the design of next-generation magnetic fluids using this approach.

SiO2@AuAg/PDA hybrid nanospheres with photo-thermally enhanced synergistic antibacterial and catalytic activity

Wastewater discharged from industrial, agricultural and livestock production contains a large number of harmful bacteria and organic pollutants, which usually cause serious harm to human health. Therefore, it is urgent to find a "one-stone-two-birds" strategy with good antimicrobial and pollutant degradation activity for treating waste water. In this paper, SiO2@AuAg/Polydopamine (SiO2@AuAg/PDA) core/shell nanospheres, which possessed synergistic "Ag+-release-photothermal" antibacterial and catalytic behaviors, have been successfully prepared via a simple in situ redox polymerization method. The SiO2@AuAg/PDA nanospheres showed good catalytic activity in reducing 4-nitrophenol to 4-aminophenol (0.576 min-1 mg-1). Since the AuAg nanoclusters contain both gold and silver elements, they provided a high photothermal conversion efficiency (48.1%). Under NIR irradiation (808 nm, 2.5 W-2), the catalytic kinetics were improved by 2.2 times. Besides the intrinsic Ag+-release, the photothermal behavior originating from the AuAg bimetallic nanoclusters and the PDA component of SiO2@AuAg/PDA also critically improved the antibacterial performance. Both E. coli and S. aureus could be basically killed by SiO2@AuAg/PDA nanospheres at a concentration of 90 μg mL-1 under NIR irradiation. This "Ag+-release-photothermal" coupled sterilization offers a straightforward and effective approach to antimicrobial therapy, and further exhibits high potential in nanomedicine for combating bacterial contamination in environmental treatment and biological fields.

Size-dependent magnetomechanically enhanced photothermal antibacterial effect of Fe3O4@Au/PDA nanodurian

The global health crisis of bacterial resistance to antibiotics requires innovative antibacterial strategies. One promising solution is the exploitation of multifunctional nanoplatforms based on non-resistant antibacterial mechanisms. This work reports a novel Fe3O4@Au/polydopamine (PDA) nanodurian with excellent photothermal-magnetomechanic synergistic antibacterial effects. The one-step formed Au/PDA hybrid shell provides good photothermal properties and spiky surfaces for enhanced magnetomechanic effects. Upon near-infrared (NIR) irradiation, the Fe3O4@Au/PDA nanodurian (200 μg mL-1) achieved nearly 100% antibacterial effect against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The efficiency of photothermal antimicrobial activity was further enhanced by the application of a rotating magnetic field (RMF), with the sterilization efficiency being increased by up to more than a half compared to the action alone. Interestingly, the size of the nanodurian has a significant impact on the synergistic sterilization effect, with larger particles showing a superior performance due to stronger chain-like structures in the magnetic field. Finally, the Fe3O4@Au/PDA nanodurian also demonstrates effective biofilm removal, with larger particles exhibiting the best eradication effect under the photothermal-magnetomechanic treatment. Overall, this magnetic field enhanced photothermal antibacterial strategy provides a promising broad-spectrum antimicrobial solution to combat bacterial infections. Thus, it possesses great potential in future nanomedicine and pollution treatment.

Triple-Responsive Soft Actuator with Plastically Retentive Deformation and Magnetically Programmable Recovery

Multistimuli responsiveness and programmable shape recovery are crucial for soft actuators in soft robotics, electronics, and wearables. However, existing strategies for actuation cannot attain power-free shape retention after removing the external energy supply. Here, a self-assembled density deposition method was developed to fabricate an electrothermal-NIR-magnetic triple-response actuator which was composed of cellulose nanofiber/poly(vinyl alcohol)/liquid metal (CNF/PVA/LM) and magnetic polydimethylsiloxane (MPDMS) layer. Interestingly, the large deformation can be controllably fixed and the temporary configuration will be programmable recovered under a magnetic field due to the thermal-plastic transferring behavior of the CNF/PVA/LM. Rolling robot prepared based on soft actuators exhibits good ability to avoid obstacles. In addition, the object handling and programmable release capabilities of the carrier robots demonstrate that this actuation approach will contribute to a better understanding of how to more rationally utilize various stimuli for application purposes.

A MXene@AgAu@PDA nanoplatform loaded with AgAu nanocages for enhancing catalytic activity and antibacterial performance

With the rapid development of social industrialization, environmental problems seriously threaten people's health, especially water pollution. Therefore, there is an urgent need to construct a multifunctional nanoplatform for different scenarios. Two-dimensional MXene@AgAu@PDA nanosheets loaded with AgAu bimetallic nanocages have been prepared by a one-step method. First, the in situ generated MXene@Ag is used as an auxiliary template, and then HAuCl4 and dopamine are added for in situ redox-oxidizing polymerization reactions to obtain AgAu catalytic nanocages and the protective polydopamine (PDA) layer which can improve the stability and biocompatibility. MXene and PDA have excellent photothermal conversion ability while hollow AgAu nanocages have strong absorption in the near-infrared region and a local surface plasmonic resonance effect. In comparison to the catalytic reaction rates under dark and room temperature conditions, the catalytic kinetic rate of MXene@AgAu@PDA nanosheets under near-infrared irradiation increases from 0.13 to 0.69 min-1 mg-1. Density functional theory (DFT) is used to study the electron transfer behavior between AgAu nanocages and MXene nanosheets, and the mechanism of the enhanced catalytic reaction rate is analyzed. Besides, due to its Ag ions and photothermal coupling antibacterial properties, 40 μg mL-1 MXene@AgAu@PDA nanosheets inactivates nearly all E. coli and S. aureus after irradiation with near-infrared light for 6 min.

Wearable Safeguarding Leather Composite with Excellent Sensing, Thermal Management, and Electromagnetic Interference Shielding

This work illustrates a "soft-toughness" coupling design method to integrate the shear stiffening gel (SSG), natural leather, and nonwoven fabrics (NWF) for preparing leather/MXene/SSG/NWF (LMSN) composite with high anti-impact protecting, piezoresistive sensing, electromagnetic interference (EMI) shielding, and human thermal management performance. Owing to the porous fiber structure of the leather, the MXene nanosheets can penetrate leather to construct a stable 3D conductive network; thus both the LM and LMSN composites exhibit superior conductivity, high Joule heating temperature, and an efficient EMI shielding effectiveness. Due to the excellent energy absorption of the SSG, the LMSN composites possess a huge force-buffering (about 65.5%), superior energy dissipation (above 50%), and a high limit penetration velocity of 91 m s-1 , showing extraordinary anti-impact performance. Interestingly, LMSN composites possess an unconventional opposite sensing behavior to piezoresistive sensing (resistance reduction) and impact stimulation (resistance growing), thus they can distinguish the low and high energy stimulus. Ultimately, a soft protective vest with thermal management and impact monitoring performance is further fabricated, and it shows a typical wireless impact-sensing performance. This method is expected to have broad application potential in the next-generation wearable electronic devices for human safeguarding.

Ultra-Stretchable Spiral Hybrid Conductive Fiber with 500%-Strain Electric Stability and Deformation-Independent Linear Temperature Response

Stretchable configuration occupies priority in devising flexible conductors used in intelligent electronics and implantable sensors. While most conductive configurations cannot suppress electrical variations against extreme deformation and ignore inherent material characteristics. Herein, a spiral hybrid conductive fiber (SHCF) composed of aramid polymeric matrix and silver nanowires (AgNWs) coating is fabricated through shaping and dipping processes. The homochiral coiled configuration mimicked by plant tendrils not only enables its high elongation (958%), but also generates a superior deformation-insensitive effect to existing stretchable conductors. The resistance of SHCF maintains remarkable stability against extreme strain (500%), impact damage, air exposure (90 days), and cyclic bending (150 000 times). Moreover, the thermal-induced densification of AgNWs on SHCF achieves precise and linear temperature response toward a broad range (-20 to 100 °C). Its sensitivity further manifests high independence to tensile strain (0%-500%), allowing for flexible temperature monitoring of curved objects. Such unique strain-tolerant electrical stability and thermosensation hold broad prospects for SHCF in lossless power transferring and expeditious thermal analysis.

NIR-induced improvement of catalytic activity and antibacterial performance over AuAg nanorods in Rambutan-like Fe3O4@AgAu@PDA magnetic nanospheres

Pathogenic bacteria and difficult-to-degrade pollutants in water have been serious problems that always plague people. Therefore, finding a "one stone-two birds" method that can quickly catalyze the degradation of pollutants and show effective antibacterial behavior become an urgent requirement. This work reports a facile one-step strategy for fabricating a Rambutan-like Fe₃O₄@AgAu@PDA (Fe₃O₄@AgAu@Polydopamine) core/shell nanosphere with both catalytic and antibacterial activities which can be critically improved by externally applying an NIR laser irradiation (NIR, 808 nm) and a rotating magnetic field. Typically, the Rambutan-like Fe₃O₄@AgAu@PDA nanosphere have a rather rough surface due to the AuAg bimetallic nanorods sandwiched between the Fe₃O₄ core and the PDA shell. Owing to the penetrated PDA shell, AgAu nanorods show high and magnetically recyclable photothermal-enhanced catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol and they can also be applied to initiate TMB oxidation under the help of NIR heating condition. Moreover, Fe₃O₄@AgAu@PDA shows a moderate antibacterial activity due to the weak release of Ag⁺. Under applying a rotating external magnetic field, the rough-surface Fe₃O₄@AgAu@PDA nanospheres produce a controllable magnetolytic force on the bacterial due to their good affinity. As a result, the Fe₃O₄@AgAu@PDA nanospheres show a "magnetolytic-photothermal-Ag⁺" synergistic antibacterial behavior against E. coli and S. aureus.

AgPd nanocages sandwiched between a MXene nanosheet and PDA layer for photothermally improved catalytic activity and antibacterial properties

In this work, a MXene@AgPd/polydopamine (PDA) nanosheet with excellent photothermal conversion efficiency was successfully synthesized by a simple redox-oxidative polymerization method. Interestingly, AgPd bimetallic nanocrystals sandwiched between a MXene nanosheet and PDA layer have cage-like nanostructure, which is favorable for high catalytic efficiency and antibacterial performance. Importantly, the MXene@AgPd/PDA nanosheet exhibits good catalytic activity for the reduction of 4-nitrophenol (1.2 min^-1 mg^-1) and the catalytic dynamics can be improved by about 1.2 times under NIR (near-infrared light, 808 nm, and 2.5 W cm^-2) irradiation. As the PDA shell is well protected, the MXene@AgPd/PDA nanosheet retained more than 90% catalytic activity after 6 cycles. In addition, due to the presence of the Ag component, the MXene@AgPd/PDA nanosheet exhibited good antibacterial activity against both Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria. Under near-infrared light irradiation, its antibacterial activity was further enhanced due to the NIR photothermal effect.

Flexible and Stretchable Elastomer Composites Based on Lightweight Liquid Metal Foam Spheres with Pod-like Contacts

Liquid metal (LM) is increasingly employed as a conductive filler in soft and flexible elastomer composites owing to its favorable conductivity and liquid fluidity. However, the high density of LM inevitably increases the weight of composites, which brings limitations in large-area and weight-sensitive applications. This work reports a flexible and stretchable elastomer composite composed of pod-like contacting lightweight LM foam spheres and polydimethylsiloxane matrix (LMS/PDMS). The lightweight LMS reduces the amount of LM used in the preparation process while imparting good electrical conductivity and deformability to the composite. The different contact modes of LMS endow the final composites with diverse strain sensitivity. The mechanism of interfacial contact conduction between the LMS with different melting points has been systematically studied, and the result shows that the liquid-solid contact mode of LMS further improves the strain sensitivity of the composite. Moreover, the composite also has satisfactory electrothermal properties and the temperature can quickly reach 70 °C within 30 s, showing good applicability in electric heating. Finally, the composites containing LMS with different contact modes can be developed as multifunctional sensors to detect human activities, temperature variation, and even underwater vibration, demonstrating the great potential in next-generation sensors and electronics.

Magnetic-Field-Induced Improvement of Photothermal Sterilization Performance by Fe3O4@SiO2@Au/PDA Nanochains

Due to the abuse of antibiotics, the sensitivity of patients to antibiotics is gradually reduced. This work develops a Fe₃O₄@SiO₂@Au/PDA nanochain which shows an interesting magnetic-field-induced improvement of its photothermal antibacterial property. First, SiO₂ was wrapped on Fe₃O₄ nanospheres assembled in a chain to form a Fe₃O₄@SiO₂ nanocomposite with a chain-like nanostructure. Then, the magnetic Fe₃O₄@SiO₂@Au/PDA nanochains were prepared using in situ redox-oxidization polymerization. Under the irradiation of an 808 nm NIR laser, the temperature rise of the Fe₃O₄@SiO₂@Au/PDA nanochain dispersion was obvious, indicating that they possessed a good photothermal effect. Originating from the Fe₃O₄, the Fe₃O₄@SiO₂@Au/PDA nanochain showed a typical soft magnetic behavior. Both the NIR and magnetic field affected the antimicrobial performance of the Fe₃O₄@SiO₂@Au/PDA nanochains. Escherichia coli and Staphylococcus aureus were used as models to verify the antibacterial properties. The experimental results showed that the Fe₃O₄@SiO₂@Au/PDA nanochains exhibited good antibacterial properties under photothermal conditions. After applying a magnetic field, the bactericidal effect was further significantly enhanced. The above results show that the material has a broad application prospect in inhibiting the growth of bacteria.

Nacre-Mimetic Hierarchical Architecture in Polyborosiloxane Composites for Synergistically Enhanced Impact Resistance and Ultra-Efficient Electromagnetic Interference Shielding

Pervasive mechanical impact is growing requirement for advanced high-performance protective materials, while the electromagnetic interference (EMI) confers severe risk to human health and equipment operation. Bioinspired structural composites achieving outstanding safeguards against a single threat have been developed, whereas the synergistic implementation of impact/EMI coupling protection remains a challenge. This work proposes the concept of nacre-mimetic hierarchical composite duplicating the "brick-and-mortar" arrangement, which consists of freeze-drying constructed chitosan/MXene lamellar architecture skeleton embedded in a shear stiffening polyborosiloxane matrix. The resulting composite effectively attenuates the impact force of 85.9%-92.8% with extraordinary energy dissipation capacity, in the coordinative manner of strain-rate enhancement, structural densification, lamella dislocation and crack propagation. Attributed to the alternate laminated structure promoting the reflection loss of electromagnetic waves, it demonstrates an ultraefficient EMI shielding effectiveness of 47.2-71.8 dB within extremely low MXene loadings of 1.1-1.3 wt %. Furthermore, it serves favorably in impact monitoring and wireless alarm systems and accomplishes performance optimization through the combination of multiple biomimetic strategies. In conclusion, this function-integrated structural composite is shown to be a competitive candidate for sophisticated environments by resisting impact damage and EMI hazards.

Injectable magnetic montmorillonite colloidal gel for the postoperative treatment of hepatocellular carcinoma

Bioactive materials have been extensively developed for the adjuvant therapy of cancer. However, few materials can meet the requirements for the postoperative resection of hepatocellular carcinoma (HCC) due to massive bleeding and high recurrence. In particular, combination therapy for HCC has been highly recommended in clinical practice, including surgical resection, interventional therapy, ablation therapy and chemotherapy. Herein, an injectable magnetic colloidal gel (MCG) was developed by controllable electrostatic attraction between clinically available magnetic montmorillonites and amphoteric gelatin nanoparticles. The optimized MCG exhibited an effective magnetic heating effect, remarkable rheological properties, and high gel network stability, realizing the synergistic treatment of postoperative HCC by stimuli-responsive drug delivery, hemostasis and magnetic hyperthermia. Furthermore, a minimal invasive MCG-induced interventional magnetic hyperthermia therapy (MHT) under ultrasound guidance was realized on hepatic tumor rabbits, providing an alternative therapeutics to treat the postoperative recurrence. Overall, MCG is a clinically available injectable formulation for adjuvant therapy after HCC surgical resection.

High-Performance Liquid Metal/Polyborosiloxane Elastomer toward Thermally Conductive Applications

With the combination of high flexibility and thermal property, thermally conductive elastomers have played an important role in daily life. However, traditional thermally conductive elastomers display limited stretchability and toughness, seriously restricting their further development in practical applications. Herein, a high-performance composite is fabricated by dispersing room-temperature liquid metal microdroplets (LM) into a polyborosiloxane elastomer (PBSE). Due to the unique solid-liquid coupling mechanism, the LM can deform with the PBSE matrix, achieving higher fracture strain (401%) and fracture toughness (2164 J/m²). Meanwhile, the existence of LM microdroplets improves the thermal conductivity of the composite. Interestingly, the LM/PBSE also exhibits remarkable anti-impact, adhesion capacities under complex loading environments. As a novel stretchable elastomer with enhanced mechanical and thermal behavior, the LM/PBSE shows good application prospects in the fields of thermal camouflages, stretchable heat-dissipation matrixes, and multifunctional shells for electronic devices.

3D Printing Ultraflexible Magnetic Actuators via Screw Extrusion Method

Soft magnetic actuators with programmable structure design and controllable deformation ability based on 3D printing technology have attracted extensive attention. In this paper, a novel 3D printing strategy is developed to manufacture the ultraflexible magnetic actuator, in which the printed material is composed of magnetic particles and thermoplastic rubber materials. Different from the traditional fused deposition printing, this printing strategy introduces screw extrusion technology to the heating components of the printer to overcome the problem of filament buckling in the flexible material. Thus, the tensile modulus of the printed products can be reduced to as low as ≈2 MPa. Based on the above method, biomimetic magnetic actuators of the sucker and the pump are constructed for adhering and releasing object and pumping liquid. The contraction performance of the magnetic actuator is studied via a series of experiments and the magnetic field-induced deformation is analyzed by the multiphysics-based finite element model. This work proves that ultraflexible magnetic actuators fabricated by this 3D printing strategy show broad prospects in the fields of soft robotics and bionics.

In situ Thermal-Responsive Magnetic Hydrogel for Multidisciplinary Therapy of Hepatocellular Carcinoma

Current surgical single modality treatments for hepatocellular carcinoma (HCC) were restricted by recurrence, blood loss, significant trauma, and poor prognostic. Although multidisciplinary strategies for HCC treatment have been highly recommended by the clinical guidelines, there was limited choice of materials and treatments. Herein, we reported an in situ formed magnetic hydrogel with promising bioapplicable thermal-responsiveness, strong adhesion in wet conditions, high magnetic hyperthermia, and biocompatibility, leading to efficient HCC multidisciplinary treatment including postoperative treatment and transarterial embolization therapy. In vivo results indicated that this hydrogel could reduce the postoperative recurrence rate. The hemostatic ability of the thermal-responsive hydrogel was further demonstrated in both the liver scratch model and liver tumor resection. Computed tomography imaging suggested that the hydrogel could completely embolize the arterial vessels of rabbit liver tumor by vascular intervention operation, which could serve as multidisciplinary responsive materials to external magnetic field and body temperature for HCC treatment.

Stretchable and Recyclable Liquid Metal Droplets Embedded Elastomer Composite with High Mechanically Sensitive Conductivity

Liquid metal (LM)-based elastomers have received growing interest for a wide range of applications such as soft robotics and flexible electronics. This work reports a stretchable and bendable liquid metal droplets embedded elastomer (LMDE) composite, which consists of liquid metal droplets (LMDs) filler and carbonyl iron particles (CIPs)/polydimethylsiloxane (PDMS) hybrid matrix. The reversible switching of the composite from an insulator to a conductor can be realized through the contact and noncontact process between the LMDs. The mechanism of constructing the controllable conductive path between the droplets under external deformations has been systematically studied, and this result also provides a basis model for analyzing the conductive networks in traditional LM-based flexible composites. The composites exhibit stable mechanical and electrical performance under different tensile strains and bending angles. Moreover, the fluidic nature of LM endows the composite with good electrically healing capability. The valuable LM can be easily recycled at a high recovery rate of 98%. Finally, the composite can be developed as a sensor for the detection of both compressive force and magnetic field, demonstrating a broad promising in flexible electronics, actuators, and wearable devices.

Near-infrared light-responsive photothermal α-Fe2O3@Au/PDA core/shell nanostructure with on-off controllable anti-bacterial effects

Antimicrobial materials are expected to be alternatives for antibiotics against multidrug-resistant bacteria. In this paper, non-spherical α-Fe₂O₃@Au/PDA core/shell nanoparticles with tunable shapes are synthesized by a one-step in situ oxidation-redox polymerization method toward near infrared light-responsive antibacterial therapy. The thickness and composition of the Au/PDA hybrid shell can be controlled by varying the concentration of HAuCl₄ and the dopamine precursor. Owing to the wonderful photothermal characteristics originating from the Au/PDA shell, the spindle α-Fe₂O₃@Au/PDA core shell nanoparticles exhibit excellent photothermal sterilization effects against both Escherichia coli and Staphylococcus aureus at low concentrations. Meanwhile, the NIR photothermal induced bactericidal performance indicates that α-Fe₂O₃@Au/PDA hybrid particles with tunable non-spherical shapes possess unique controllable antibacterial effects. As a result, this finding provides a simple strategy for fabricating high performance photothermal antibacterial agents and the final products possess high potential in synergistic antimicrobial therapy.

3D Printing Magnetic Actuators for Biomimetic Applications

Biomimetic actuators with stimuli-responsiveness, adaptivity, and designability have attracted extensive attention. Recently, soft intelligent actuators based on stimuli-responsive materials have been gradually developed, but it is still challenging to achieve various shape manipulations of actuators through a simple 3D printing technology. In this paper, a 3D printing strategy based on magneto-active materials is developed to manufacture various biomimetic magnetic actuators, in which the new printable magnetic filament is composed of a thermoplastic rubber material and magnetic particles. The continuous shape transformation of magnetic actuators is further demonstrated to imitate the motion characteristic of creatures, including the predation behavior of octopus tentacles, the flying behavior of the butterfly, and the flower blooming behavior of the plant. Furthermore, the magnetic field-induced deformation of the biomimetic structure can be simulated by the finite element method, which can further guide the structural design of the actuators. This work proves that the biomimetic actuator based on soft magneto-active materials has the advantages of programmable integrated structure, rapid prototyping, remote noncontact actuation, and rapid magnetic response. As a result, this 3D printing method possesses broad application prospects in soft robotics and other fields.

A shape-deformable liquid-metal-filled magnetorheological plastomer sensor with a magnetic field "on-off" switch

Flexible viscoelastic sensors have gained significant attention in wearable devices owing to their exceptional strain-dependent electrical resistance. Most of the strain sensors are elastic composites, thus the internal stress is often preserved during the deformation when they are attached to the uneven target. Therefore, there is a pressing need for viscoelastic composites with highly self-adapted electromechanical properties sensitive to multiexternal circumstances. This work reports a liquid-metal-filled magnetorheological plastomer (LMMRP) that shows a high response behavior to the external stimulus such as magnetic field, temperature, and force. The shape-deformable LMMRP can transform from an insulator to a conductor under applying a magnetic field, thus the further viscoelastic sensor possesses a magnetic field “on-off” switch effect. The microstructure-dependent magnetic/thermal/mechanical-electrical coupling characteristics are investigated, and several proof-of-concept sensor applications, such as magnetic control, environment recognition, and motion monitoring, are demonstrated. These LMMRP composites show a broad potential in flexible sensors and soft electronics.

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A shape-deformable liquid-metal-filled magnetorheological plastomer was created.

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The plastomer is sensitive to magnetic field, temperature, and force.

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The evolution of the particle microstructure in the plastomer was simulated.

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The plastomer has great potential in flexible electronics with magnetic control.

Magnetism-Responsive Anisotropic Film with Self-Sensing and Multifunctional Shape Manipulation

At small scales, shape-programmable magnetic materials and self-sensing conductive materials have an enticing potential for realizing the functionalities that are unattainable by traditional machines. This work reports a facile preparation method of aself-sensing magnetism-responsive anisotropic films (SMAF) in which magnetic materials and conductive materials can be predesigned, oriented, and patterned without requiring an external magnetic field generator or other expensive devices. A variety of shaped magnetoactive films with complex chain-orientation structures that can achieve advanced actuation functions have been developed, such as magnetically driven flowers, windmills, and leaves. It is also verified that the as-prepared samples coated with the sensing layer can distinguish different actuation modes, such as inward bending, outward bending, twisting, and combined deformation, which would be conducive to further exploration and development of directionally responsive applications in the smart actuating system and soft robotics.

Fe3O4–Au–polydopamine hybrid microcapsules with photothermal–photodynamic synergistic anti-bacterial performance

A novel magnetic Fe3O4–Au–PDA hybrid microcapsule with both photothermal (PTT) and photodynamic (PDT) anti-bacterial functions has been developed, and the product exhibits higher antibacterial performance by the combined PTT/PDT treatment.

Hybrid Polydopamine/Ag Shell-Encapsulated Magnetic Fe3O4 Nanosphere with High Antibacterial Activity

The bacteria, which usually contaminate water environment, often cause terrible infectious diseases thus seriously threaten people's health. To meet the increasing requirement of the public health care, an easily separable nanomaterial with sustainable anti-bacteria performance is required. This work reports a Fe₃O₄@PDA/Ag/PDA core-shell nanosphere in which the Ag nanocrystals immobilized on the magnetic carrier are protected by an external polydopamine (PDA) layer. The magnetic hybrid nanospheres are constructed by a tunable coating method and the particle parameters can be effectively controlled by the experimental condition. The antibacterial potential of the nanospheres is evaluable by using the Staphylococcus aureus and Escherichia coli as the models. The results indicate the Fe₃O₄@PDA/Ag/PDA core-shell nanospheres have a high antibacterial performance by measuring the minimum inhibitory concentration and the minimum bactericidal concentration. Finally, the product is expected to have a sustainable activity because the protecting PDA layer reduce the releasing rate of the Ag⁺ ions and the materials can be magnetically recovered from the media after the disinfection procedure.

Three-Dimensional Structured Dual-Mode Flexible Sensors for Highly Sensitive Tactile Perception and Noncontact Sensing

This work reports a three-dimensional (3D) structured multifunctional sensor by connecting a magnetowhisker with a superflexible patterned skin film. Composed of percolation networks of silver nanowires, the patterned skin film is integrated via a simple template manufacturing method without increasing the complexity and sacrificing the flexibility. The as-prepared 3D structured sensor can realize the multimodal detection of out-of-plane tactile stimuli and details of noncontact environmental obstacles in multiple directions. Here, the sensor's perception behaviors on compression, pulling, magnetic field, sound waves, airflow, water level, water flow, and backwash are presented. Furthermore, the 3D structured sensor obtains outstanding mechanical robustness and stability for 8000 cycles, excellent sensitivity (12 800% when the applied pulling displacement was 3.5 mm; 152% T^-1 when the magnetic flux density variation was 40.6 mT), ultrahigh response time, and ultrahigh recovery time (∼5 ms), which may meet the industrial sensing requirement for artificial tactile electronics. Facile manufacturing processes and outstanding multimodal sensing characteristics make the 3D structured sensor to possess great potential to be implemented in the next-generation intelligent bionic equipment or systems.

Highly Flexible Multilayered e-Skins for Thermal-Magnetic-Mechanical Triple Sensors and Intelligent Grippers

This work reports a novel triple-functional electronic skin (e-skin) which shows both wonderful thermal-magnetic-mechanical sensing performance and interesting magnetic actuation behavior. The flexible e-skin comprises thermo-sensitive, magnetic, and conductive tri-components, and their sensitive characteristics under 5-70 °C, 0-1200 mT, and 0.1-5.1 MΩ are studied, respectively. Owing to the unique piezoresistive characteristic and magnetorheological effect, the e-skin exhibits a rapid response time (38 ms) to the external stimuli. The assembled e-skin with the triple-layer structure can act as a functional sensor to monitor various human motions, magnetic fields, and environmental temperatures. Based on this e-skin, an intelligent magneto-active gripper is further developed, and it can be used to grasp and transport targets by the actuated force of magnetic field under various working conditions. Importantly, the multi-functional sensing capability endows the gripper with real-time deformation and ambient temperature perception characteristics. As a result, because of the ideal multi-field coupling sensing and magnetic active features, this e-skin shows a wide prospect in wearable electronics, man-machine interactions, and intelligent transport systems.

Polydopamine protected hollow nanosphere with AuAg-nanoframe-core@Carbon@AuAg-nanocrystals-satellite hybrid nanostructure (AuAg@C@AuAg/PDA) for enhancing nanocatalysis

This work reported a facile method for fabricating multi-layered polydopamine (PDA) encapsulated AuAg@C@AuAg core/shell nanosphere with a hollow interior. During the synthetic process, the preliminary Ag@C nanosphere is easily covered by an AuAg/PDA hybrid layer through the in situ redox-oxidized polymerization to form the Ag-AuAg@C@AuAg/PDA precursor, in which the AuAg bimetallic nanocrystals are simultaneously obtained via the electrochemical substitution reaction. After etching the residue Ag core, the final AuAg@C@AuAg/PDA hybrid nanosphere is achieved and the inner AuAg shows a unique nanoframe-like nanostructure. The carbon shell plays an important role for the formation and structure evolution of the AuAg@C@AuAg/PDA, and the composition can be modulated by varying the polymerization process. Owing to the well distributed AuAg nanocrystals and inner AuAg nanoframes, the AuAg@C@AuAg/PDA shows better performance than Ag-AuAg@C@AuAg/PDA precursor in catalyzing 4-nitrophenol, and the rate constant (K) to catalyst weight ratio reaches as high as 3.63 min^-1 •mg^-1. As a result, this work not only offers a hybrid bi-metallic nanocatalyst with excellent performance, but also has valuable implications for compositional modulation of hollow interior multi-layered nanostructure in adsorption, drug delivery, and nanocatalysis.

A Hydrophobic, Self-Powered, Electromagnetic Shielding PVDF-Based Wearable Device for Human Body Monitoring and Protection

With the rapid development of the electronics, information technology, and wearable devices, problems of the power crisis and electromagnetic radiation pollution have emerged. A piezoelectric wearable textile combined with electromagnetic shielding performance has become a favorable solution. Herein, a multifunctional PVDF-based wearable sensor with both electromagnetic shielding function and human body monitoring performance is proposed by incorporating silver nanowires (Ag NWs) and multiwall carbon nanotubes (MWCNTs) hybrid-networks into PVDF-casted commercial nonwoven fabrics (NWF). The coordination of Ag NWs and MWCNTs networks ensures the ideal electrical conductivity and mechanical strength. The maximum shielding value of the developed sensor reaches up to 34 dB when the area densities of the Ag NWs and MWCNT are kept at 1.9 and 2.0 mg/cm², respectively. Additionally, the hydrophobicity of the as-proposed sensor (water contact angle of ∼110.0°) ensures the self-cleaning function and makes it resistive against water and dirt. Moreover, the sensor possesses a force-sensing property by generating different piezoelectric voltages (0, 0.4, 1.0, and 1.5 V) when stimulated by various forces (0, 20, 44, and 60 N). Not only can it respond to different external stress in a timely manner (response sensitivity of ∼0.024 V/N, response time of ∼35 ms), but it can also monitor different body movements, such as joint bending, running, and jumping. This work opens up a new prospect of monitoring the human body as well as protecting human health from electromagnetic radiation surroundings.

Controlling Hydrogel Properties by the Cooperative Harvesting of the Components of Sunlight

The utilization of the full spectrum of sunlight from ultraviolet to infrared to cooperatively control the properties of hydrogels is the key to developing efficient sunlight-responsive hydrogels, but there are significant challenges. The photoresponsive hydrogel developed here formed by azobenzene-containing polyzwitterionic chains possesses capabilities for simultaneously utilizing light from the ultraviolet to the infrared to cooperatively facilitate the gel-to-sol transitions. The ultraviolet and visible light can be converted into mechanical energy simultaneously to synergistically power the dynamic wagging of azobenzene groups, while the infrared light can be converted into kinetic energy of the zwitterionic groups to promote the wagging of the azobenzene groups. Cooperative action between the major components of sunlight can be applied to control a range of important properties of the hydrogel including wettability, adhesion, molecular release, self-healing, and mineralization. The work presented here demonstrates a novel strategy for harvesting all the major components of sunlight to control the properties of photoresponsive materials.

Experiments and Simulations on the Magnetorheology of Magnetic Fluid Based on Fe3O4 Hollow Chains

This work reports an experiment/simulation combination study on the magnetorheological (MR) mechanism of magnetic fluid based on Fe₃O₄ hollow chains. The decrease of shear stress versus the increasing magnetic field was observed in a dilute magnetic fluid. Hollow chains exhibited a higher MR effect than pure Fe₃O₄ hollow nanospheres under a small magnetic field. A modified particle level simulation method including the translational and rotational motion of chains was developed to comprehend the correlation between rheological properties and microstructures. Sloping cluster-like microstructures were formed under a weak external field (24 mT), while vertical column-like microstructures were observed under a strong field (240 mT). The decrease of shear stress was due to the strong reconstruction process of microstructures and the agglomeration of chains near the boundaries. The chain morphology increased the dip angle of microstructures and thus improved the MR effect under a weak field. This advantage made Fe₃O₄ hollow chains to be widely applied for small and low-power devices in the biomedical field. Dimensionless viscosity as a function of the Mason number was collapsed onto linear master curves. Magnetic fluid in Poiseuille flow in a microfluidic channel was also observed and simulated. A qualitative and quantitative correspondence between simulations and experiments was obtained.

In situ redox-oxidation polymerization for magnetic core-shell nanostructure with polydopamine-encapsulated-Au hybrid shell

This work reports a facile one-step method for the fabricating Fe₃O₄@Au/polydopamine sandwich-like core-shell nanostructure, in which the Au/polydopamine (Au/PDA) hybrid shell is obtained via an in situ redox-oxidation polymerization between the HAuCl₄ and dopamine. The content of Au nanocrystals, shell thickness, and particle sizes are tunable by varying the experimental parameters. Intriguingly, this general method can be applied for different functional nanostructures such as the β-FeOOH@Au/PDA, SiO₂@Au/PDA, and CNT@Au/PDA nanocomposites. A possible formation mechanism is proposed and it is found that the surface interaction plays a key role in determining the final nanostructure. The as-prepared Fe₃O₄@Au/PDA exhibited eminent catalytic activity on the reduction of 4-nitrophenol. Since the external PDA shell prevents the Au nanocrystals from leaching during the reduction, the cycling activity has been maintained as high as 95% after seven times of catalytic reaction.

Magnetic microspheres with polydopamine encapsulated ultra-small noble metal nanocrystals as mimetic enzymes for the colorimetric detection of H2O2 and glucose

A novel sandwich-structured magnetic microsphere with ultra-small noble metal nanocrystals as a mimetic enzyme for the colorimetric detection of H₂O₂ and glucose.

ZIF-8 self-etching method for Au/polydopamine hybrid cubic microcapsules with modulated nanostructures

A one-step strategy combining in situ redox-oxidation polymerization and a ZIF-8 sacrifice template is reported for constructing Au/PDA cubic microcapsules.

Magneto-thermochromic coupling Janus sphere for dual response display

This work demonstrates a simple microfluidic device to synthesize a magneto-thermochromic sphere with Janus inner structure. The Janus sphere is composed of Fe₃O₄ microspheres, thermochromic particles, and polyacrylamide matrix. Because the Fe₃O₄ microspheres are assembled together in one pole, the Janus sphere can turn around by varying the direction of the external magnetic field. Originating from the temperature-dependent property of the thermochromic particles, the final Janus sphere can change its color from red to pale blue when the temperature is increased from 5 to 45 °C. The detailed formation process and the magneto-thermochromic mechanism are carefully investigated. Due to the magnetic switch and thermochromism, these Janus spheres can be applied as colorful displays by controlling the magnetic field and temperature. The results demonstrate that the dual responsive Janus spheres possess broad application potential in temperature sensors and displays.

This work demonstrates a simple microfluidic device to synthesize a magneto-thermochromic sphere with Janus inner structure.

Stress and Magnetic Field Bimode Detection Sensors Based on Flexible CI/CNTs-PDMS Sponges

This work reports porous carbonyl iron particles/multiwalled carbon nanotubes-polydimethylsiloxane composites (PCMCs) with high flexibility and low density. In comparison to the solid product, the porous PCMC possesses a larger elongation and deformation. Because of the excellent magnetic-mechanic-electric coupling performance, the flexible composite exhibits bimode sensitivity to both the external stresses and magnetic field. Typically, the normalized resistance variation (Δ R/ R) of PCMC reaches 82.8% and 52.2% when the compression strain and tension strain are 60% and 50%, respectively. Moreover, the Δ R/ R induced by bending, twisting, and magnetostress also changes remarkably. When a 144 mT magnetic field is applied, the Δ R/ R of PCMC increases with 3.6%. To further understand the magnetic-mechanic-electric coupling mechanism, a conductive network sensing model is proposed and analyzed. Finally, on the basis of the bimode PCMC sensor array, a smart chessboard which can precisely discriminate special chesses with different masses and magnets is developed. This study provides a new fabrication method for next-generation three-dimensional smart sensors toward artificial electronics and soft robotics.

Simulation of the optimal diameter and wall thickness of hollow Fe3O4 microspheres in magnetorheological fluids

This work reported a simulation study on the optimal diameter (D) and wall thickness (H) of hollow Fe3O4 microspheres to improve the magnetorheological (MR) effect. Modified formulae for the magnetic dipolar force, van der Waals force, and hydrodynamic drag force were employed in the simulation model. Typical evolution of shear stress and microstructures in steady shear flow was obtained. The shear stress-strain curve was divided into linear, fluctuant, and homeostasis regions, which were related to the inclination of particle chains and the lateral aggregation. For hollow Fe3O4 microspheres with different diameters and wall thicknesses, the shear stress curves collapsed onto a quadratic master curve. The best wall thickness was H = 0.39D for a 20 wt% MR fluid and H = 0.35D for a 40 wt% MR fluid, while the optimal diameter was D = 1000 nm and D = 100 nm, respectively. The maximum shear stress of the 40 wt% MR fluid was twice that of the 20 wt% MR fluid. The change of shear stress was due to the competition that results among the magnetic interaction, number of neighbors, tightness, and orientation of the particle chains. Simulated dimensionless viscosity data as a function of Mason number for various diameters, wall thicknesses, and weight fractions collapsed onto a single master curve. The simulated shear stress under both a magnetic field and shear rate sweep matched well with experiments.

Magnetically Separable Nanocatalyst with the Fe3O4 Core and Polydopamine-Sandwiched Au Nanocrystal Shell

This work reports a novel Fe₃O₄@polydopamine/Au/polydopamine core/shell nanocomposite toward a magnetically separable nanocatalyst. Because the polydopamine (PDA) layer-sandwiched Au nanocrystals were prepared by a layer-by-layer method, the content of Au could be controlled by varying the Au shell number (such as burger-like Fe₃O₄@PDA/Au/PDA/Au/PDA). Fe₃O₄@PDA/Au/PDA exhibited excellent catalytic activity in reducing p-nitrophenol because the substrate could penetrate the PDA shell. Owing to the protection of the PDA shell, Fe₃O₄@PDA/Au/PDA presented higher cyclability than Fe₃O₄@PDA/Au. The activity of Fe₃O₄@PDA/Au/PDA maintained 95% after 7 cycles, while that of Fe₃O₄@PDA/Au was only 61%. The detailed cycling catalytic mechanism was investigated, and it was found that the catalytic rate of Fe₃O₄@PDA/Au/PDA/Au/PDA was faster than that of Fe₃O₄@PDA/Au/PDA because of the higher Au content. Interestingly, this method could be extended for other magnetic nanocomposites with two different kinds of noble metal nanocrystals integrated within one particle, such as Fe₃O₄@PDA/Au/PDA/Ag/PDA and Fe₃O₄@PDA/Au/PDA/Pd/PDA.

Smart wearable Kevlar-based safeguarding electronic textile with excellent sensing performance

A novel S-ST/MWCNT/Kevlar-based wearable electronic textile (WET) with enhanced safeguarding performance and force sensing ability was fabricated. Stab resistance performance tests under quasi-static and dynamic conditions show that the maximum resistance force and penetration impact energy for the WET are 18 N and 11.76 J, which represent a 90% and 50% increment with respect to the neat Kevlar, respectively. Dynamic impact resistance tests show that the WET absorbs all the impact energy. The maximum resistance force of the WET is 1052 N, which represents an improvement of about 190% with respect to neat Kevlar. With the incorporation of multi-walled carbon nanotubes (MWCNTs), the WET can achieve a stable electrical conductivity of ∼10^-2 S m^-1, and the conductivity is highly sensitive to external mechanic forces. Notably, the sensing fabric also exhibits an outstanding ability to detect and analyze external forces. In addition, it can be fixed at any position of the human body and exhibits an ideal monitoring performance. Because of its flexibility, high sensitivity to various types of deformations and excellent safeguarding performance, the WET has a strong potential for wearable monitoring devices that simultaneously provide body protection and monitor the movements of the human body under various conditions.

Magnetorheology of a magnetic fluid based on Fe3O4immobilized SiO2core–shell nanospheres: experiments and molecular dynamics simulations

The MR effect of an Fe₃O₄-immobilized-SiO₂-nanosphere based magnetic fluid was 25 times larger than that of an Fe₃O₄based magnetic fluid.

The normal stress of an electrorheological fluid in compression mode

This work studied the normal stress of an ER fluid in compression mode through both experiment and simulation.

Stretchable Polyurethane Sponge Scaffold Strengthened Shear Stiffening Polymer and Its Enhanced Safeguarding Performance

A simple and scalable "dip and dry" method was developed for fabricating stretchable polyurethane sponge-based polymer composite with excellent shear stiffening effect, creep resisting and adhesion property. The stiffness of the composite was tunable, the storage modulus (G') could automatically increase 3 orders of magnitude with the increasing of shear frequency, and the G'max could reach to as high as 1.55 MPa. Importantly, the composite with ideal damping capacity reduced the impact force by 2 orders of magnitude even under 26 cycles of consecutive dynamic impact loading with no obvious mechanical degradation. Moreover, an enhancing mechanism was proposed and it was found the "B-O cross bond" and the entanglement of polymer chains were attributed to the shear stiffening characteristic. Finally, the excellent adhesion ability and hydrophobicity guarantee the composite with reliable mechanical performance and longer lifespan.

A facile one-step method to synthesize SiO2@polydopamine core–shell nanospheres for shear thickening fluid

An illustration of the synthesis of SiO₂@PDA core/shell nanospheres, in which the coating on the surface of the SiO₂nanospheres improves the rheological behavior of the resulting STFs.

Magnetic field dependent electro-conductivity of the graphite doped magnetorheological plastomers

In this work we reported a novel graphite doped conductive magnetorheological plastomer (GMRP) with magnetic field dependent electro-conductivity. The conductivity of the GMRPs increased by increasing the content of the graphite particles, while it decreased with the graphite size. When the graphite content reached 15 wt%, the conductivity of GMRPs is approximately 10 000 times higher than the non-doped MRP. Because the iron particles in the GMRPs were magnetic, the conductivity of the GMRPs was magnetically sensitive. Upon applying a 780 mT magnetic field, the electric conductivity could increase about 1000 times larger than the one under zero magnetic field. A particle-particle resistance model was developed to investigate the influence of the magnetic field and graphite doping on the conductivity, and the fitting curve matched the experimental results very well. Finally, a magnetically controllable on-off switch based on GMRPs was proposed and its working mechanism was discussed.

Rod-like β-FeOOH@poly(dopamine)–Au–poly(dopamine) nanocatalysts with improved recyclable activities

A novel rod-like β-FeOOH@poly(dopamine)–Au–poly(dopamine) core–shell nanocomposite with significantly improved recyclability is developed for catalysis.

Computational models on quantitative prediction of bioactivity of HIV-1 integrase 3' processing inhibitors

In this study, four computational quantitative structure-activity relationship (QSAR) models were built to predict the bioactivity of 3' processing (3'P) inhibitors of HIV-1 integrase. Some 453 inhibitors whose bioactivity values were detected by the radiolabelling method were collected. The molecular structures were represented with MOE descriptors. In total, 21 descriptors were selected for modelling. All inhibitors were divided into a training set and a test set with two methods: (1) by a Kohonen's self-organizing map (SOM); (2) by a random selection. For every training set and test set, a multilinear regression (MLR) analysis and a support vector machine (SVM) were used to establish models, respectively. For the training/test set divided by SOM, the correlation coefficients (r) were over 0.84, and for the training/test set split randomly, the r values were over 0.86. Some molecular properties such as hydrogen bond donor capacity, atomic partial charge properties, molecular refractivity, the number of aromatic bonds and molecular surface area, volume and shape properties played important roles for inhibiting 3' processing step of HIV-1 integrase.