Asymmetric Gradient Research Articles

Diatoms Inspired Green Janus Fabric for Efficient Fog Harvesting

AbstractFog harvesting is a promising path against the global freshwater scarcity. Asymmetric wettability fabric‐based fog collection materials inspired by the Namib desert beetle have been reported widely due to their easy access and adjustable structures. Nevertheless, the single drive force for water transportation produced by the asymmetric wettability is insufficient, causing a non‐ideal fog harvesting efficiency. Moreover, sustainability challenges persist for fog collection materials, primarily due to their heavy dependence on chemical treatments. Herein, a diatom‐inspired Janus fabric (Ly/Csp‐3) based on asymmetric wettability and aperture gradient is developed without additional physical or chemical treatment. The wettability gradient and aperture gradient generate dual directional drive forces that regulate the water transport direction more accurately and enhance the transportation rate more effectively. Ly/Csp‐3 reaches a one‐way transport index of 390.7% and a water collecting rate (WCR) of 1170.5 mg cm−2 h−1, while exhibiting the capability of anti‐acid rain and the resistance to sunlight. This work provides an efficient and programmable biomimetic design proposal for fibrous fog harvesting devices.

Research on Efficient Electromagnetic Shielding Performance and Modulation Mechanism of Aero/Organo/Hydrogels with Gravity-Induced Asymmetric Gradient Structure.

To eliminate electromagnetic pollution, it is a challenging task to develop highly efficient electromagnetic shielding materials that integrate microwave absorption (MA) performance with high shielding capability and achieve tunability in shielding performance. Asymmetrically structured aero/organo/hydrogels with a progressively changing concentration gradient of liquid metal nanoparticles (LMNPs), induced by gravity, are prepared by integrating the conductive fillers Ti3C2Tx MXene and LMNPs into a dual-network structure composed of polyvinyl alcohol and cellulose nanofibers. Benefiting from the unique structure, which facilitates the absorption-reflection-reabsorption process of electromagnetic waves along with conductive fillers and the porous structure, three types of gels demonstrate efficient shielding performance. HPCML achieves a total shielding effectiveness (SET) of up to 86.9dB and a reflection shielding effectiveness (SER) of as low as 2.85dB. Especially, APCML, with an ultra-low reflection coefficient (R) of 6.4%, achieves compatibility between shielding performance and MA properties. The relationship between dispersing media (air, water, and glycerol/water) and the shielding performance of aero/organo/hydrogels is explored, thereby achieving modulation of the shielding performance of the gel system. The work has paved a clear path for integrating absorption and shielding capabilities into a composite material, thereby providing a prototype of a highly efficient shielding material with MA performance.

Barrier Membrane with Janus Function and Structure for Guided Bone Regeneration.

Guided bone regeneration (GBR) technology has been demonstrated to be an effective method for reconstructing bone defects. A membrane is used to cover the bone defect to stop soft tissue from growing into it. The biosurface design of the barrier membrane is key to the technology. In this work, an asymmetric functional gradient Janus membrane was designed to address the bidirectional environment of the bone and soft tissue during bone reconstruction. The Janus membrane was simply and efficiently prepared by the multilayer self-assembly technique, and it was divided into the polycaprolactone isolation layer (PCL layer, GBR-A) and the nanohydroxyapatite/polycaprolactone/polyethylene glycol osteogenic layer (HAn/PCL/PEG layer, GBR-B). The morphology, composition, roughness, hydrophilicity, biocompatibility, cell attachment, and osteogenic mineralization ability of the double surfaces of the Janus membrane were systematically evaluated. The GBR-A layer was smooth, dense, and hydrophobic, which could inhibit cell adhesion and resist soft tissue invasion. The GBR-B layer was rough, porous, hydrophilic, and bioactive, promoting cell adhesion, proliferation, matrix mineralization, and expression of alkaline phosphatase and RUNX2. In vitro and in vivo results showed that the membrane could bind tightly to bone, maintain long-term space stability, and significantly promote new bone formation. Moreover, the membrane could fix the bone filling material in the defect for a better healing effect. This work presents a straightforward and viable methodology for the fabrication of GBR membranes with Janus-based bioactive surfaces. This work may provide insights for the design of biomaterial surfaces and treatment of bone defects.

Asymmetric multilayered cellulose nanofiber composite membranes with electrical-magnetic dual-gradient architectures towards excellent electromagnetic interference shielding performance

The structural design strategies of MXene-based nanocomposites have demonstrated critical significance for electromagnetic interference (EMI) shielding applications. Herein, novel asymmetric multilayered cellulose nanofiber/multiwalled carbon nanotube@ferroferric oxide/MXene (CNF/MWCNT@Fe3O4/MXene) composite membranes with electrical-magnetic dual-gradient structures were prepared via layered-by-layered self-assembly strategy. Briefly, CNF/MWCNT@Fe3O4 layers are designed as the negative gradient absorption layers which provide dielectric/magnetic double loss. Meanwhile, MXene layers serve as the positive gradient reflection layers which generate multiple reflections and conduct loss. Thus, gradient multilayered CNF/MWCNT@Fe3O4/MXene composite membranes exhibit a total electromagnetic interference shielding effectiveness (EMI SET) of 73.20 dB at the thickness of 180 μm and R-value of 0.99934 in the X-band. Furthermore, the asymmetric gradient multilayer composite membrane reveals a superior EMI shielding performance in comparison with that of homogeneous multilayered composite membranes. When electromagnetic waves (EMWs) pass through the gradient multilayered CNF/MWCNT@Fe3O4/MXene composite membrane, the rational asymmetric gradient multilayered structures contribute to a “gradually decreasing absorption-gradually increasing reflection” shielding mechanism. Thereby, the design strategy of asymmetric electrical-magnetic dual-gradient structures is advantageous in enhancing the EMI shielding ability of polymeric composites.

Bioinspired Superhydrophobic All-In-One Coating for Adaptive Thermoregulation.

The development of scalable and passive coatings that can adapt to seasonal temperature changes while maintaining superhydrophobic self-cleaning functions is crucial for their practical applications. However, the incorporation of passive cooling and heating functions with conflicting optical properties in a superhydrophobic coating is still challenging. Herein, an all-in-one coating inspired by the hierarchical structure of a lotus leaf that combines surface wettability, optical structure, and temperature self-adaptation is obtained through a simple one-step phase separation process. This coating exhibits an asymmetrical gradient structure with surface-embedded hydrophobic SiO2 particles and subsurface thermochromic microcapsules within vertically distributed hierarchical porous structures. Moreover, the coating imparts superhydrophobicity, high infrared emission, and thermo-switchable sunlight reflectivity, enabling autonomous transitions between radiative cooling and solar warming. The all-in-one coating prevents contamination and over-cooling caused by traditional radiative cooling materials, opening up new prospects for the large-scale manufacturing of intelligent thermoregulatory coatings.

Multifunctional bionanohybrids of graphene oxide/β-cyclodextrin for applications in methylene blue adsorption, solvent response, and smart light-driven

In this study, a multifunctional graphene oxide/β-cyclodextrin bionanohybrids (BWGO) was prepared successfully. The structure, morphology, adsorption capacity, solvent response, and light-driven properties of the BWGO were systematically investigated through the in-situ formation of an asymmetric gradient structure. The maximum adsorption value of BWGO based on bio-nanohybrids was 81.27 mg·g−1 for methylene blue (MB), which fitted the Langmuir isotherm in accordance with the pseudo-secondary kinetic model. Additionally, the host–guest interaction model of between BWGO and MB (in ratios of 1:1 or 1:2) was proposed by ROESY. Remarkably, the BWGO exhibited not only unique and exceptional responses to organic hazard solvents, self-driven, and photothermal responses, but also demonstrated controllable object loading and shape memory useful for soft grasping. More importantly, the related mechanisms of adsorption and behaviors driven by multiple stimuli (solvent, light) were elucidated through the host–guest interaction, wrinkled structure, gradient solvent swelling effects, and conformational changes in the macromolecular chain. This work not only introduces the multifunctional bionanohybrid materials with a wrinkled structure for the adsorption of organic dyes, but also opens avenues for potential applications in smart windows, soft grasping, and biomimetic industrial materials.

Compressible thermoplastic polyurethane/silver nanorod foams for absorption dominant electromagnetic interference shielding

Conductive polymer composites (CPCs) have attracted significant interest in the field of flexible electromagnetic protection, but the challenge of balancing high electromagnetic interference shielding effectiveness (EMI SE) and low reflection losses still exists. Herein, thermoplastic polyurethane/silver nanorod (TPU/AgNR) composite foams have been successfully prepared using both the salt template and vacuum-assisted thermal compression methods. By varying the AgNRs content and employing a layer-by-layer bonding approach, a gradient structure with optimized impedance matching is achieved. The “absorb-reflect-reabsorb” EM attenuation mechanism of the asymmetric gradient EMI shielding in the internal structure is exploited, resulting in TPU/AgNR foam (TAF) with high EMI SE and significantly reduced EM reflection. Notably, the three-layer foams exhibit an average shielding efficacy of 35.5 dB and a reflected power coefficient (R) of 0.085 in the X-band, thereby substantially mitigating secondary EM wave reflections. Furthermore, these foams demonstrate exemplary compressive resilience, with the sample maintaining excellent EMI shielding stability even after undergoing 100 compression cycles at 50 % strain. Consequently, a straightforward approach is employed to fabricate materials with high EMI SE and low reflectivity, offering the potential for use in EM shielding applications of next-generation flexible electronic devices.

Energy absorption characteristics of asymmetric tree-like fractal gradient hierarchical structures

Bionic gradient hierarchy design as a design method that can effectively improve the structural crashworthiness, but its current research only focuses on the symmetric fractal method related to the discussion. In view of this, this article carries out the innovative design and research of asymmetric tree-like fractal gradient hierarchy structure (ATFGHS). The results show that the crashworthiness of the structure can be greatly improved by using the asymmetric tree-like fractal gradient hierarchy design method. Specifically, the ATFGHS-P3 showed a 98% increase in energy absorption (EA), a 98% increase in specific energy absorption (SEA), and an 84% increase in crush force efficiency (CFE) compared to a conventional hexagonal multicellular tube. The completion of this study provides valuable insights into the design and optimization of novel lightweight thin-walled energy-absorbing structures.

Infinite Self-Propulsion of Circularly On/Discharged Droplets.

Self-propulsion of droplets in a controlled and long path at a high-speed is crucial for organic synthesis, pathological diagnosis and programable lab-on-a-chip. To date, extensive efforts have been made to achieve droplet self-propulsion by asymmetric gradient, yet, existing structural, chemical, or charge density gradients can only last for a while (<50mm). Here, this work designs a symmetrical waved alternating potential (WAP) on a superhydrophobic surface to charge or discharge the droplets during the transport process. By deeply studying the motion mechanisms for neutral droplets and charged droplets, the circularly on/discharged droplets achieve the infinite self-propulsion (>1000mm) with an ultrahigh velocity of meters per second. In addition, after permutation and combination of two motion styles of the droplets, it can be competent for more interesting work, such as liquid diode and liquid logic gate. Being assembled into a microfluidic chip, the strategy would be applied in chemical synthesis, cell culture, and diagnostic kits.

Study of ischemic progression in different intestinal tissue layers during acute intestinal ischemia using swept-source optical coherence tomography angiography.

In acute intestinal ischemia, the progression of ischemia varies across different layers of intestinal tissue. We established a mouse model and used swept-source optical coherence tomography (OCT) to observe the intestinal ischemic process longitudinally in different tissue layers. Employing a method that combines asymmetric gradient filtering with adaptive weighting, we eliminated the vessel trailing phenomenon in OCT angiograms, reducing the confounding effects of superficial vessels on the imaging of deeper vasculature. We quantitatively assessed changes in vascular perfusion density (VPD), vessel length, and vessel average diameter across various intestinal layers. Our results showed a significant reduction in VPD in all layers during ischemia. The mucosa layer experienced the most significant impact, primarily due to disrupted capillary blood flow, followed by the submucosa layer, where vascular constriction or decreased velocity was the primary factor.

Structural design of asymmetric gradient alternating multilayered CNF/MXene/FeCo@rGO composite film for efficient and enhanced absorbing electromagnetic interference shielding

Asymmetrical and electromagnetic gradient multilayered CNF/MXene/FeCo@rGO composite film with efficient and enhanced absorbing EMI shielding property was constructed by alternating filtration of different dispersions.

Constructing asymmetric gradient structures to enhance the energy storage performance of PEI-based composite dielectrics.

Enhancing the high electric field resistance and energy storage capacity of polymer dielectrics has been a long-standing challenge for the iterations of power equipment. Synergistic inhibition of carrier injection and transport is vital to energy storage performance improvement. Herein, promising polymer polyetherimide (PEI) was employed as a matrix and wider bandgap boron nitride nanosheets (BNNSs) were used as a reinforcing filler. Utilizing high-throughput stochastic breakdown simulations with the distribution characteristics of BNNSs as parameters, a series of topological gradient structures with the potential to enhance performance were obtained, thereby shortening the experimental cycle. Changing the BNNS distribution of symmetric/asymmetric and positive/inverse gradients, as well as the total and gradient contents of BNNSs, means that the position and condition of the surface barrier layer and central hinder layer change, which influences the energy storage performance of the polymer at room temperature and high temperature. Remarkably, the asymmetric gradient structure composite dielectrics exhibited excellent performances. Among them, the PEI-based composite dielectric with 2 vol% BNNS asymmetric inverse gradient distribution (gradient content of 1 vol%) achieved energy densities of 8.26 and 4.78 J cm-3 at room temperature and 150 °C, respectively. The asymmetric gradient structure design strategy holds great promise for optimizing the energy storage capacity of polymer dielectric capacitors.

An Asymmetric Layer Structure Enables Robust Multifunctional Wearable Bacterial Cellulose Composite Film with Excellent Electrothermal/Photothermal and EMI Shielding Performance.

Highly robust flexible multifunctional film with excellent electromagnetic interference shielding and electrothermal/photothermal characteristics are highly desirable for aerospace, military, and wearable devices. Herein, an asymmetric gradient multilayer structured bacterial cellulose@Fe3O4/carbon nanotube/Ti3C2Tx (BC@Fe3O4/CNT/Ti3C2Tx) multifunctional composite film is fabricated with simultaneously demonstrating fast Joule response, excellent EMI shielding effectiveness (EMI SE) and photothermal conversion properties. The asymmetric gradient 6-layer composite film with 40% of Ti3C2Tx possesses excellent mechanical performance with exceptional tensile strength (76.1MPa), large strain (14.7%), and good flexibility. This is attributed to the asymmetric gradient multilayer structure designed based on the hydrogen bonding self-assembly strategy between Ti3C2Tx and BC. It achieved an EMI SE of up to 71.3dB, which is attributed to the gradient "absorption-reflection-reabsorption" mechanism. Furthermore, this composite film also exhibits excellent low-voltage-driven Joule heating (up to 80.3°C at 2.5V within 15s) and fast-response photothermal performance (up to 101.5°C at 1.0Wcm-2 within 10s), which is attributed to the synergistic effect of heterostructure. This work demonstrates the fabrication of multifunctional bacterial cellulose@Fe3O4/carbon nanotube/Ti3C2Tx composite film has promising potentials for next-generation wearable electronic devices in energy conversion, aerospace, and artificial intelligence.

Fluid-solid coupling for microscale transport of nanoparticles in ultralong carbon nanotubes

Achieving microscale motion of nanoparticles is crucial for the development of various nanodevices. Here we propose a novel fluid-solid coupling device that leverages a thermally-induced water flow to enable long-range nanoparticle transport within carbon nanotubes (CNTs). Our device comprises an ultralong CNT composed of repeated units filled with water. Each unit experiences an asymmetrical thermal gradient induced by intentionally incorporating asymmetrical configurations of atomic vacancies on the CNT surface. Through molecular dynamics (MD) simulations, we demonstrate that these repeated units with periodic thermal fields effectively induce a steady water flow, enabling continuous transportation of a nanoparticle (e.g., a C60 fullerene) within the ultralong CNT over microscale distances. Moreover, we reveal that the device can be also designed with various alternative options (e.g., Stone–Wales defects or carbon/boron-nitride heterojunctions). Our proposed device holds promising potential for microscale nanoparticle transport applications.

Hydrophobic Composite Foams with Asymmetric Gradient Sandwich Structure for Excellent Electromagnetic Interference Shielding and Photothermal Response.

The evolution of contemporary electronics urgently requires the use of versatile electromagnetic interference (EMI) shielding materials in complex environments. Interlayer polydimethylsiloxane (PDMS)/Fe3O4@multiwalled carbon nanotubes (MWCNTs) foams were prepared by a simple physical foaming method with excellent flexibility and electromagnetic wave absorption. The bottom nickel aramid paper (NiP) layer creates a dense conductive network by chemical plating technology, which ensures excellent EMI effectiveness. The upper carbon black (CB)/Fe3O4 layer further improves the absorption performance via conductive loss and magnetic loss. With the effective layout of the impedance matching layer, absorbing layer, and conductive shielding layer, the CB/Fe3O4-PDMS/Fe3O4@MWCNTs-NiP composite material achieves an EMI shielding effectiveness (EMI SE) of 61.7 dB and an absorption coefficient of 0.58 at X-band. In addition, the composite foam provides photothermal conversion and hydrophobicity due to the effective stacking of PDMS and CB/Fe3O4. Thus, the multifunctional composite foam presents a broad range of possible applications, benefiting EMI shielding as well as other specific areas.

Balanced strength and ductility by asymmetric gradient nanostructure in AZ91 Mg alloy

High-strength Mg alloys have historically suffered from a challenge in achieving good ductility. Here, we report an asymmetric gradient nanostructure design prepared by ultrasonic severe surface rolling (USSR) at room temperature. Unlike conventional gradient-nanostructured materials that employ a hard-soft-hard sandwich structure, this new design incorporates a combined gradient distribution of grain microstructure and nanoprecipitates throughout the entire sample along the thickness direction. The nanoprecipitates are identified as the β-Mg17Al12 phase and are primarily generated through In-situ precipitation promoted by the USSR-induced high-density dislocations and temperature increment. Benefiting from this unique microstructure, an outstanding strength-ductility synergy is achieved, with a yield strength of 372.8 MPa, an ultimate tensile strength of 453.3 MPa, and an elongation of 11.5%. The enhanced strength can be attributed to several mechanisms, including grain boundary strengthening, dislocation strengthening, precipitation strengthening, twin strengthening, and hetero-deformation induced (HDI) strengthening. The HDI hardening and activation of multiple deformation modes also contribute to good ductility. This work provides a promising and effective method for overcoming the longstanding strength-ductility trade-off dilemma in Mg alloys.

Next-generation MRI scanner designed for ultra-high-resolution human brain imaging at 7 Tesla

To increase granularity in human neuroimaging science, we designed and built a next-generation 7 Tesla magnetic resonance imaging scanner to reach ultra-high resolution by implementing several advances in hardware. To improve spatial encoding and increase the image signal-to-noise ratio, we developed a head-only asymmetric gradient coil (200 mT m−1, 900 T m−1s−1) with an additional third layer of windings. We integrated a 128-channel receiver system with 64- and 96-channel receiver coil arrays to boost signal in the cerebral cortex while reducing g-factor noise to enable higher accelerations. A 16-channel transmit system reduced power deposition and improved image uniformity. The scanner routinely performs functional imaging studies at 0.35–0.45 mm isotropic spatial resolution to reveal cortical layer functional activity, achieves high angular resolution in diffusion imaging and reduces acquisition time for both functional and structural imaging.

Construction of designable and high-temperature resistant composite foams for tunable electromagnetic shielding

Conductive polymer composite (CPC) foams have been extensively studied for electromagnetic interference (EMI) shielding due to their lower density and relatively low EM reflectivity. However, most CPC foams are difficult to structurally design to regulate performance, and also limited in high-temperature application scenarios owing to the low-temperature resistance of the matrix themselves. Herein, high-performance expanded polyetherimide (EPEI) foam beads were fabricated by subcritical foaming technology with organic solvents/CO2 as co-blowing agents, and designable EPEI/CNS (carbon nanostructures) composite foams with segregated networks and high-temperature resistance were then manufactured through CNS dip-coating and epoxy bonding. The resultant EPEI/CNS composite foams showed the shielding effectiveness (SE) of ∼11.9–39.5 dB with CNS loading of only ∼0.25–0.72 vol%, along with R coefficient of only ∼0.26–0.56. The construction of asymmetric gradient structure in the foams via orderly assembling can further reduce the EM reflection in comparison with uniform structure, thereby remitting the secondary EM pollution. Moreover, the EPEI/CNS composite foams can not only maintain the structural integrity after being treated at ∼200 °C, but also maintain relatively stable EMI SE and most of their mechanical properties, enabling their applications in high-temperature environments. This work provides a simple and effective method for constructing high-temperature resistant CPC foams for tunable EMI shielding.

An Asymmetric Interlocked Structure with Modulus Gradient for Ultrawide Piezocapacitive Pressure Sensing Applications

AbstractHighly sensitive electronic skin (e‐skin) sensors with considerable operating range offer great possibilities for health care, human–‐machine interfaces, and intelligent robotics. Although subtle microstructures have been used in recent years to improve the sensitivity and sensing range of e‐skin sensors, the trade‐off between these features remains a big challenge to overcome. Here, an asymmetric interlocked gradient elastic modulus (AIGM) structure is designed for the first time to provide sufficient deformation space to the traditional interlocked structure while ensuring high sensitivity, and the gradient elastic modulus further extends the sensing range of the AIGM structure‐based sensors, which exhibit a maximum sensitivity of as high as 9.89 kPa−1 with an ultrawide working range that extends to above 530 kPa at the same time. As a demo, this sensor is integrated into an intelligent adjustable mouse platform for physiological signal monitoring, pressure feedback, and modulus adjustment, providing a viable alternative for hand disease prevention.

Near-Infrared-II-Driven Pollen Micromotors for Inflammatory Bowel Disease Treatment.

Inflammatory bowel disease (IBD) is a common inflammatory bowel disease with a high incidence rate and serious consequences. Attempts in this area are focusing on developing efficient delivery systems for relieving IBD. Herein, we present a kind of near-infrared-II (NIR-II)-activated pollen-derived micromotor (PDMM) as an efficient delivery system for treating IBD. These PDMMs are pollen grains with half of them covered by a gold (Au) layer, which can result in an asymmetric thermal gradient around the PDMMs under NIR-II irradiation, thereby forming a thermophoretic force to drive PDMMs to move spontaneously. Besides, the inherent spiny and hollow architectures of pollen grains endowed the PDMMs with outstanding capacity of adherence and drug delivery, respectively. Based on these features, we have demonstrated that the PDMMs could move actively in vivo with the irradiation of NIR-II light and adhere to the surrounding tissues for drug delivery. Thus, the PDMMs loaded with dexamethasone show desirable curative effects on treating IBD. These results indicated that the proposed PDMM-based delivery system has great potential in clinic gastrointestinal administration.