Unidirectional Transport Research Articles

A multiple scattering formulation for elastic wave propagation in space–time modulated metamaterials

Space–time modulation of material parameters offers new possibilities for manipulating elastic wave propagation by exploiting time-reversal symmetry breaking. Here, we propose and validate a general framework based on the multiple scattering theory to model space–time modulated elastic metamaterials, namely elastic waveguides equipped with modulated resonators. The formulation allows to consider an arbitrary distribution of resonators with a generic space–time modulation profile and compute the wavefield within and outside the resonators’ region. Under appropriate assumptions, the same framework can be exploited to predict the waveguide dispersion relation. We demonstrate the capabilities of our formulation by revisiting the dynamics of two representative space–time modulated systems, e.g., the non-reciprocal propagation of (i) flexural waves along a metabeam and (ii) surface acoustic waves along a metasurface. Given its flexibility, the proposed method can facilitate the design of novel devices able to realize unidirectional transport of elastic energy for vibration isolation, signal processing and energy harvesting purposes.

Peristome-mimetic surfaces using three-dimensional microcavities for unidirectional liquid transport

Peristome-mimetic surfaces using three-dimensional microcavities for unidirectional liquid transport

Hierarchical nanofibrous and recyclable membrane with unidirectional water-transport effect for efficient solar-driven interfacial evaporation

Solar-driven interfacial evaporation technology has attracted significant attention for water purification. However, design and fabrication of solar-driven evaporator with cost-effective, excellent capability and large-scale production remains challenging. In this study, inspired by plant transpiration, a tri-layered hierarchical nanofibrous photothermal membrane (HNPM) with a unidirectional water transport effect was designed and prepared via electrospinning for efficient solar-driven interfacial evaporation. The synergistic effect of the hierarchical hydrophilic-hydrophobic structure and the self-pumping effect endowed the HNPM with unidirectional water transport properties. The HNPM could unidirectionally drive water from the hydrophobic layer to the hydrophilic layer within 2.5 s and prevent reverse water penetration. With this unique property, the HNPM was coupled with a water supply component and thermal insulator to assemble a self-floating evaporator for water desalination. Under 1 sun illumination, the water evaporation rates of the designed evaporator with HNPM in pure water and dyed wastewater reached 1.44 and 1.78 kg·m−2·h−1, respectively. The evaporator could achieve evaporation of 11.04 kg·m−2 in 10 h under outdoor solar conditions. Moreover, the tri-layered HNPM exhibited outstanding flexibility and recyclability. Our bionic hydrophobic-to-hydrophilic structure endowed the solar-driven evaporator with capillary wicking and transpiration effects, which provides a rational design and optimization for efficient solar-driven applications.

Janus membrane with asymmetric wettability for efficient oil/water separation

The rapid development of society and industry as well as the frequent occurrence of oil spills cause the shortage of fresh water resources, which not only affects human safety and life, but also impedes the world-wide sustainable development. To address these challenges, novel membrane materials with unique wettability properties have gained significant attention, particularly in the field of oil/water separation. In this research, we modified the hydrophobic PET fabric to achieve superhydrophilic characteristics using impregnation method. Subsequently, we electrospun hydrophobic PVDF fibers onto the superhydrophilic fabric surface, and PVDF/Ca10(PO4)6(OH)2@PET Janus membrane with asymmetric wettability was obtained. The membrane has an excellent unidirectional liquid transport capacity, and can effectively separate heavy oil or light oil, the separation efficiency is more than 90 %. The results also show that the Janus membrane can be used under alkaline conditions and has satisfactory tensile resistance and re-use performance. This work provides a new idea for Janus membrane design and effectively improves the application potential of the Janus membrane in the field of oil/water separation.

Construction of Janus structures on thin silk fabrics via misting for wet–thermal comfort and antimicrobial activity

Owing to their small fiber diameter (10–15 μm), silk fabrics are always thin (32–90 g m−2). Therefore, construction of the Janus surfaces of silk fabrics that possess excellent multifunctionality remains a formidable challenge. Herein, first, silk fabrics were grafted using glycidyltrimethylammonium chloride to form a superhydrophilic surface (G-side). Then, a unilateral hydrophobic surface (O-side) was readily fabricated by mist coating octadecyltrichlorosilane-functionalized SiO2 nanoparticles (NPs) to produce hierarchical surface textures. To prevent NP penetration from the G-side to the O-side, a “fireproof isolation” method was employed. Consequently, Janus silk fabrics (JanSFs) bearing asymmetric wettability were prepared, and their wetting gradient could be conveniently regulated. With the mist time ranging from 4 to 7 min, the unidirectional transport index and efficiency of the unidirectional water transport increased and decreased by 13.2 and 10.4 times, respectively. Sweat could be effectively drained away from human skin to ensure that the skin was dry and comfortable. Compared with the surface temperature of the raw fabric, the raw fabric of JanSFs increased by 2.7 °C. Furthermore, the breathability of JanSF was negligibly affected, and the outer O-side of the JanSF showed substantial antibacterial activity. This study is important for designing JanSFs that exhibit unidirectional water transport.

Matter transport as fundamental property of acoustic solitons in plasma

A theoretical study of the phenomenon of unidirectional transport of charged particles by acoustic-type solitons in plasma without the magnetic field is presented. Using a one-dimensional ion-acoustic soliton as an example, it is shown that the transport of charged particles is a fundamental property of classical solitons, which cannot be neglected at small wave amplitudes. The analysis is based on the hydrodynamic model using the Sagdeev pseudopotential and the KdV equation. A brief generalization of the results to electron- and dust-acoustic modes is also discussed.

A mini‐review of polymeric porous membranes with vertically penetrative pores

AbstractMembrane separation technology plays a pivotal role in modern industry and scientific research. The key to developing and improving membrane separation processes lies in designing and fabricating customized porous membranes with specific physical parameters, including pore diameter, porosity, pore size distribution, pore length (membrane thickness), pore geometry, and pore connectivity. Polymeric porous membranes with vertically‐penetrative‐pores (PPMVs) represent a distinct category among the available membranes due to their unique characteristics such as short transport path, small trans‐membrane resistance, and simple pore geometry, as compared to other porous membranes with sponge‐like channels. In practical applications, PPMVs offer several advantages, including achieving higher flux rates, facilitating easier unidirectional transport, and enabling harmless biological extraction. Moreover, PPMVs can serve as ideal model systems for theoretical investigations on the fundamental mechanisms of separation and transport in academic research. With substantial advancements in fabrication technologies and application fields of PPMVs in recent years, it warrants a comprehensive perspective. In this mini‐review, we provide an overview of widely used fabrication methods for PPMVs, discuss their primary applications, and address the existing challenges and opportunities.

Multistep conformational changes leading to the gate opening of light-driven sodium pump rhodopsin

Membrane transport proteins require a gating mechanism that opens and closes the substrate transport pathway to carry out unidirectional transport. The "gating" involves large conformational changes and is achieved via multistep reactions. However, these elementary steps have not been clarified for most transporters due to the difficulty of detecting the individual steps. Here, we propose these steps for the gate opening of the bacterial Na+ pump rhodopsin, which outwardly pumps Na+ upon illumination. We herein solved an asymmetric dimer structure of Na+ pump rhodopsin from the bacterium Indibacter alkaliphilus. In one protomer, the Arg108 sidechain is oriented toward the protein center and appears to block a Na+ release pathway to the extracellular (EC) medium. In the other protomer, however, this sidechain swings to the EC side and then opens the release pathway. Assuming that the latter protomer mimics the Na+-releasing intermediate, we examined the mechanism for the swing motion of the Arg108 sidechain. On the EC surface of the first protomer, there is a characteristic cluster consisting of Glu10, Glu159, and Arg242 residues connecting three helices. In contrast, this cluster is disrupted in the second protomer. Our experimental results suggested that this disruption is a key process. The cluster disruption induces the outward movement of the Glu159-Arg242 pair and simultaneously rotates the seventh transmembrane helix. This rotation resultantly opens a space for the swing motion of the Arg108 sidechain. Thus, cluster disruption might occur during the photoreaction and then trigger sequential conformation changes leading to the gate-open state.

Water-Assisted Programmable Assembly of Flexible and Self-Standing Janus Membranes.

Janus membranes with asymmetric wettability have been considered cutting-edge for energy/environmental-sustainable applications like water/fog harvester, breathable skin, and smart sensor; however, technical challenges in fabrication and accurate regulation of asymmetric wettability limit their development. Herein, by using water-assisted hydrogen-bonded (H-bonded) assembly of small molecules at water/oil interface, a facile strategy is proposed for one-step fabrication of membranes with well-regulable asymmetric wettability. Asymmetric orderly patterns, beneficial for mass transport based on abundant high-permeability sites and large surface area, are constructed on opposite membrane surfaces. Upon tuning water-assisted H-bonding via H-sites/configuration design and temperature/pH modulation, double-hydrophobic, double-hydrophilic, and hydrophobic-hydrophilic membranes are facilely fabricated. The Janus membranes show smart vapor-responsive curling and unidirectional water transport with promising flux of 1158±25Lm-2 h-1 under natural gravity and 31500±670L·(m-2 h-1 bar-1 ) at negative pressure. This bottom-up approach offers a feasible-to-scalable avenue to precise-manipulation of Janus membranes for advanced applications, providing an effective pathway for developing tailor-made self-assembled nanomaterials.

Magnetic Lateral Ladder for Unidirectional Transport of Microrobots: Design Principles and Potential Applications of Cells-on-Chip.

Functionalized microrobots, which are directionally manipulated in a controlled and precise manner for specific tasks, face challenges. However, magnetic field-based controls constrain all microrobots to move in a coordinated manner, limiting their functions and independent behaviors. This article presents a design principle for achieving unidirectional microrobot transport using an asymmetric magnetic texture in the shape of a lateral ladder, which the authors call the "railway track." An asymmetric magnetic energy distribution along the axis allows for the continuous movement of microrobots in a fixed direction regardless of the direction of the magnetic field rotation. The authors demonstratedprecise control and simple utilization of this method. Specifically, by placing magnetic textures with different directionalities, an integrated cell/particle collectorcan collect microrobots distributed in a large area and move them along a complex trajectory to a predetermined location. The authors can leverage the versatile capabilities offered by this texture concept, including hierarchical isolation, switchable collection, programmable pairing, selective drug-response test, and local fluid mixing for target objects. The results demonstrate the importance of microrobot directionality in achieving complex individual control. This novel concept represents significant advancement over conventional magnetic field-based control technology and paves the way for further research in biofunctionalized microrobotics.

An extended B′ formulation for ablating-surface boundary conditions

The B′ formulation can be understood as a mass and energy conservation formalism at a reacting singular surface. In hypersonics applications, it is typically used to compute the chemical equilibrium properties of gaseous mixtures at ablating surfaces, and to estimate the recession velocity of the interface. In the first half of the paper, we derive the B′ formulation to emphasize first principles. In particular, while we eventually specialize to the commonly considered case of chemical equilibrium boundary layers that satisfy the heat and mass transfer analogy, we first derive a general interface jump condition that lets us highlight all the underlying assumptions of the well-known B′ equations. This procedure helps elucidate the nature of the B′ formalism and it also allows us to straightforwardly extend the original formulation. Specifically, when applied at the interface between a porous material and a boundary layer (as in thermal protection systems applications), the original formulation assumes unidirectional advective transport of gaseous species from the porous material to the boundary layer (i.e., blowing). However, under conditions that may appear in hypersonic flight or in ground-based wind tunnels, boundary layer gases can enter the porous material due to a favorable pressure gradient. We show that this scenario can be easily handled via a straightforward modification to the B′ formalism, and we demonstrate via examples that accounting for gas entering the material can impact the predicted recession velocity of ablating surfaces. In order to facilitate the implementation of the extended B′ formulation in existing material response codes, we present a short algorithm in section 5 and we also refer readers to a GitHub repository where the scripts used to generate the modified B′ tables are publicly available.

1D selective confinement and diffusion of metal atoms on graphene

The role of moiré graphene superstructures in favoring confined adsorption of different metal atoms is an intriguing problem not yet completely solved. Graphene (G) grown on Ni(100) forms a striped moiré pattern of valleys, where G approaches the nickel substrate and interacts with it rather strongly, and ridges, where G stays far away from the substrate and acts almost free-standing. Combining density functional theory (DFT) calculations and scanning-tunneling microscopy (STM) measurements, we show that this peculiar moiré constitutes a regular nanostructured template on a 2D support, confining in 1D trails single metal atoms and few atoms clusters. DFT calculations show that the confinement is selective and highly dependent on the atomic species, with some species preferring to adsorb on ridges and the other showing preference for valleys. Co and Au adsorbates, for instance, have opposite behavior, as predicted by DFT and observed by STM. The origin of such disparate behavior is traced back to the electrostatic interaction between the charged adsorbate and the nickel surface. Moreover, the selectivity is not restricted to the adsorption process only, but persists as adsorbate starts its diffusion, resulting in unidirectional mass transport on a continuous 2D support. These findings hold great promise for exploiting tailored nanostructured templates in a wide range of potential applications involving mass transport along element-specific routes.

ENOS Regulates Lymphatic Valve Specification by Controlling β-Catenin Signaling During Embryogenesis in Mice.

Lymphatic valves play a critical role in ensuring unidirectional lymph transport. Loss of lymphatic valves or dysfunctional valves are associated with several diseases including lymphedema, lymphatic malformations, obesity, and ileitis. Lymphatic valves first develop during embryogenesis in response to mechanotransduction signaling pathways triggered by oscillatory lymph flow. In blood vessels, eNOS (endothelial NO synthase; gene name: Nos3) is a well-characterized shear stress signaling effector, but its role in lymphatic valve development remains unexplored. We used global Nos3-/- mice and cultured human dermal lymphatic endothelial cells to investigate the role of eNOS in lymphatic valve development, which requires oscillatory shear stress signaling. Our data reveal a 45% reduction in lymphatic valve specification cell clusters and that loss of eNOS protein inhibited activation of β-catenin and its nuclear translocation. Genetic knockout or knockdown of eNOS led to downregulation of β-catenin target proteins in vivo and in vitro. However, pharmacological inhibition of NO production did not reproduce these effects. Co-immunoprecipitation and proximity ligation assays reveal that eNOS directly binds to β-catenin and their binding is enhanced by oscillatory shear stress. Finally, genetic ablation of the Foxo1 gene enhanced FOXC2 expression and partially rescued the loss of valve specification in the eNOS knockouts. In conclusion, we demonstrate a novel, NO-independent role for eNOS in regulating lymphatic valve specification and propose a mechanism by which eNOS directly binds β-catenin to regulate its nuclear translocation and thereby transcriptional activity.

Translocation of linearized full-length proteins through an engineered nanopore under opposing electrophoretic force.

Nanopores have recently been used to identify and fingerprint proteins. However, because proteins, unlike DNA, do not have a uniform charge, the electrophoretic force cannot in general be used to translocate or linearize them. Here we show that the introduction of sets of charges in the lumen of the CytK nanopore spaced by ~1 nm creates an electroosmotic flow that induces the unidirectional transport of unstructured natural polypeptides against a strong electrophoretic force. Molecular dynamics simulations indicate that this electroosmotic-dominated force has a strength of ~20 pN at -100 mV, which is similar to the electric force on single-stranded DNA. Unfolded polypeptides produce current signatures as they traverse the nanopore, which may be used to identify proteins. This approach can be used to translocate and stretch proteins for enzymatic and non-enzymatic protein identification and sequencing.

Engineering Janus cellulose fabric with unidirectional water transport capability toward perspiration-induced cooling human body

Traditional cellulose fabric with high hydrophilic distinction realizes personal thermal management via perspiration-induced cooling for the human body. However, such behavior is restricted in high-humidity environments, where sweat/water transports from a high-humidity environment to the human body by hydrophilic cellulose fabric. Herein, we developed an environmentally friendly, low-cost, large-scale Janus cellulose fabric via one-side hydrophobic modification of hydrophilic cellulose. Our Janus cellulose fabric comprises hydrophobic cellulose side (water contact angle of 151°) and hydrophilic cellulose side (water contact angle of 19°). Such distinction endows Janus cellulose fabric with unidirectional water-transport capability, where water molecules are inclined to transport, diffuse and evaporate on the hydrophilic cellulose (diffusion area of 50 μl water is around 0.8 cm2) rather than the hydrophobic cellulose (less and even negligible diffusion area), correspondingly spontaneously leading to a 3–4 ℃ temperature drop of the human body when covering Janus cellulose fabric than pristine cellulose fabric. Janus cellulose fabric paves the way toward green, cost-effective, and cooling fabric in our sustainable society.

Adsorbate motors for unidirectional translation and transport.

Artificial molecular motors are designed to transform external energy into useful work in the form of unidirectional motion1. They have been studied mainly in solution2-4, but also on solid surfaces5,6, which provide fixed reference points, allowing for tracking of their movement. However, these molecules require sophisticated design and synthesis, because the motor function must be imprinted into the chemical structure, and show reduced functionality on surfaces compared with in solution5-8. DNA walkers9,10,on the other hand, impart high directionality as they include the surface as part of the motor function, but they require chemical surface patterning and sequential solvent modification for motor activation. Here we show how efficient motors can operate at much smaller length scales on a homogeneous metal surface without any liquid. This is realized by combining a surface with a simple molecule, which, by itself, does not contain any motor unit. The motion, which is tracked at the single-molecule level, is triggered by intramolecular proton transfer with a corresponding modulation of the potential energy surface. Each molecule moves with 100 percent unidirectionality along an atomically defined straight line. Proof of the motor performing meaningful work is shown by controlled transport of single carbon monoxide molecules. This simplistic concept could form the basis for the controlled bottom-up assembly of nanostructures at the atomic scale.

Hierarchical Weaving Metafabric for Unidirectional Water Transportation and Evaporative Cooling

AbstractSmart apparel with unidirectional sweat transportation functionality is highly desirable for wearing comfort. However, simultaneously achieving fast unidirectional water transport, mechanical robustness, human body comfortability, and industrialized fabrication is challenging because of the difficulty in fiber‐yarn‐fabric multiscale textile structure manipulation. Here, for the first time, a unidirectional water‐transportation metafabric (UWTM) with hierarchical weft‐double‐weave structure is developed using industrial‐producible weaving technology. The UWTM not only shows a fast unidirectional sweat transportation property, but also a robust mechanical property, air permeability, tailorability, and human body comfortability. The unidirectional water transportation is realized by a well‐engineered wettability gradient along fabric thickness direction by two‐set weft yarns and one‐set warp yarn. The UWTM shows a strong one‐way transport capacity of 984%, with a short water droplet transportation time of 4 s. In addition, the unidirectional water transportation leads to an evaporative cooling effect to the human body, resulting in a 1.6 °C cooling compared with the most used cotton fabrics, exhibiting excellent wet‐heat transfer responsiveness, and ensuring a comfortable microclimate between human skin and the environment. The facile and scalable method presented here paves a way for the design of fluorine‐free, robust, comfortable, and wearable unidirectional water transport fabrics.

Preparation and characterization of unidirectional water-transported bilayer PLA/ZnO-PAN/SPA nanofibrous membrane for wound healing

Wound infection caused by excessive exudate leads to overhydration of wounds and prevents wound healing. Thus, there is a need for a wound dressing to be developed that can unidirectionally export excess biological fluid while inhibiting bacterial infection. Herein, a nanofibrous bilayer membrane with a unidirectional water transport function was fabricated by electrospinning as a novel wound dressing, which can export excess biological fluid efficiently and further inhibit bacterial infection. The inner layer of the bilayer nanofiber membrane is polylactic acid (PLA)-zinc oxide (ZnO) nanofibers, which are hydrophobic and antibacterial. The outer layer is polyacrylonitrile (PAN)-sodium polyacrylate (SPA) nanofibers, which are hydrophilic and liquid-absorbent. The bilayer nanofibrous membrane's morphology, mechanics, thermal stability, wettability, water absorption, gas permeability, and unidirectional water transport ability were characterized and evaluated. The study showed that the nanofibrous bilayer membrane exhibited excellent physicochemical properties and biological performance, and its mechanical properties can reach 4.6 MPa. In addition, when the thickness of the hydrophobic layer is 3 µm and the thickness of the hydrophilic layer is 44 µm, the double-layer fiber membrane can effectively export the excess biological fluid in 5.09 s and prevent the wound from wetting again. The nanofibrous bilayer membrane with excellent water absorption, air permeability, thermal stability, and mechanical strength provides a feasible solution for chronic wound healing.

Unexpected water transfer enhancement through nanochannels via inserting an inner embedded nanochannel

Thermal fluctuations can significantly slow down water transfer rate, and result in low unidirectional transport efficiency. However, in this study, we employ molecular dynamics simulations to investigate water transport in nanochannels with large diameters. Surprisingly, we discover that the insertion of an inner embedded nanochannel unexpectedly enhances water transfer rate through the nanochannels. We attribute this enhancement to the increased water velocity, which occurs due to the decrease in the cross-section of the nanochannel upon inserting an inner nanochannel. These findings have important implications for optimizing water transport in nanochannels with large diameters.

Intramolecular interaction of NEP regulated by CRM1 ensures the unidirectional transport of M1 for the nuclear export of influenza viral ribonucleoprotein

IntroductionThe influenza virus genome consists of single-stranded RNAs and forms viral ribonucleoprotein (RNP) complexes. After viral genome replication in the nucleus, the viral RNP interacts with viral protein M1. The M1-viral RNP complex is exported to the cytoplasm via the CRM1-dependent pathway using NS2/NEP as an export adaptor protein. NEP is a 14 kDa protein and diffusely localizes in the nucleus and cytoplasm. Upon binding to the NLS motif of M1, NEP inhibits the nuclear accumulation of M1 and promotes the nuclear export of M1-viral RNP complex. However, the detail mechanism by which NEP binds to M1 only in the nucleus remains unclear.MethodsTo visualize the interaction of NEP with M1 in the formation of vRNP export complexes, we performed in situ proximity ligation assays. The close proximity of N-terminal and C-terminal domains of NEP was tested by split Renilla luciferase complementation assays in which the N-terminal and C-terminal fragments of Renilla luciferase were fused to the N-terminus and C-terminus of NEP, respectively.Results and discussionWe found that the intramolecular interaction of NEP inhibits the interaction of NEP with M1. The intramolecular interaction of NEP was mediated through the interaction of the N-terminal NES motif with the M1-binding domain at the C-terminus. By adding leptomycin B, a potent inhibitor of CRM1, the interaction of NEP with M1 was impaired. These results suggest that CRM1 disrupts the intramolecular interaction of NEP by recognizing the NES motif at the N-terminus of NEP, thereby promoting the interaction of NEP with M1. We also found that NEP mutant deficient in the intramolecular interaction was co-localized with M1 at the plasma membrane and did not show nuclear localization with M1. Based on these results, we propose that the intramolecular interaction of NEP regulated by CRM1 ensures the unidirectional transport of M1.