Direct Transport Research Articles

Continuous and spontaneous directional droplet transport on bioinspired serial-wedge-shaped groove with wettability gradient

We propose a serial-wedge-shaped groove with a wettability gradient to achieve continuous directional transport of droplets. Molecular dynamics simulations demonstrate that this design provides a sustained driving force and reduces energy barriers at junctions, facilitating continuous droplet motion. Moreover, higher temperatures and greater wettability gradients are shown to enhance the efficiency of continuous transport. Theoretical analysis further reveals that increasing surface hydrophobicity, width ratio, and droplet size can reduce energy barriers, thereby improving transport performance. These findings are expected to improve the understanding of continuous directional droplet transport and shed light on its manipulation.

Raman activity and high electron mobility of piezoelectric semiconductor GaSiX2 (X = N, P, and As) toward flexible nanoelectronic devices

Abstract Inspired by the urgent demand for novel multifunctional materials in advanced technology applications, herein, first-principles calculations are utilized to construct new two-dimensional GaSiX 2 (X = N, P, As) monolayers. After optimizing the GaSiX 2 crystal structures, their stabilities, Raman responses, piezoelectricity, and electronic/transport characteristics are systematically studied. Results from phonon dispersions, ab initio molecular dynamics simulations, elastic constants, and cohesive energies confirm the good dynamic, thermal, energetic, and mechanical stabilities of the proposed GaSiX 2 monolayers. Based on the Heyd–Scuseria–Ernzerhof approach, the GaSiX 2 exhibit semiconductor behaviors with favorable bandgaps for absorption of the visible spectrum of 1.82 for GaSiP2 and 1.43 eV for GaSiAs2 monolayer. In addition, the GaSiX 2 monolayers also show piezoelectric effects, and high in-plane piezoelectric coefficients d 11 are found for the GaSiP2 (−1.16 pm V − 1 ) and GaSiAs2 (−1.26 pm V − 1 ). The carrier mobilities of the GaSiX 2 are estimated by the deformation potential method for their transport properties. Along two in-plane transport directions, the carrier mobilities of the GaSiX 2 are anisotropy for holes and electrons. GaSiP2 and GaSiAs2 show large electron mobilities along the x axis of 2816.99 and 1211.41 cm2V−1s−1, respectively. Thus, the GaSiP2 and GaSiAs2 monolayers not only have high anisotropic electron mobilities but also favorable bandgaps and large piezoelectric coefficients, indicating potential applications of GaSiP2 and GaSiAs2 in electronic, photovoltaic, and piezoelectric devices. The findings of this study may provide insights into the GaSiX 2 monolayers for multifunctional applications.

Superfast nanodroplet propulsion in 2D nanochannels tuned by strain gradients.

Directional transport of droplets is crucial for industrial applications and chemical engineering processes, with significant potential demonstrated in water harvesting, microfluidics, and heat transfer. In this work, we present a novel approach to induce self-driving behavior in nanodroplets within a two-dimensional (2D) nanochannel using a strain gradient, as demonstrated through molecular dynamics simulations. Our findings reveal that a small strain gradient imposed along a nanochannel constructed by parallel surfaces can induce water transport at ultrafast velocities (O(102 m s-1)), far exceeding macroscale predictions. Certainly, a larger strain gradient further enhances droplet transport velocity. Additionally, combining a strain gradient with nonparallel surfaces results in up to a 150% increase in transport efficiency. Furthermore, we show that this spontaneous transport mechanism is applicable to nanochannels composed of various 2D materials and successfully establish a reliable theoretical model. These simulation results provide new insights into the directional transport of nanodroplets in 2D nanochannels, opening avenues for advanced applications in nanotechnology and fluid dynamics.

Diagnostic tools for stroke detection-from prehospital to diagnosis

Strokes are common neurological emergencies that require rapid diagnosis to minimize long-term damage. Prehospital detection and triage play acritical role in patient outcomes. How effective are different prehospital diagnostic tools for stroke detection, and which triage strategies optimize patient care? The article compares prehospital diagnostic tools for stroke detection and evaluates different transport strategies. Case studies illustrate their practical application. Traditional stroke diagnosis methods have limitations, particularly in identifying strokes in the posterior circulation. Newer diagnostic tools that incorporate additional symptoms, such as dizziness and vision problems, show higher sensitivity. The choice of triage strategy depends on the severity of symptoms and regional factors. Direct transport to specialized centers is beneficial for severe strokes, while initial stabilization at nearby units is more efficient in rural areas. Modern diagnostic tools offer better sensitivity for prehospital stroke detection. Regional cooperation and the selection of appropriate triage strategies are key to improving stroke care.

Copper fiber wick with scaly fins fabricated by multi-tooth cutting for directional heat transfer

Wicks with directional liquid transport properties are the decisive factor in fabricating high-performance directional heat transfer devices. Aiming at the lack of wicks that can maintain directional liquid transport performance after high-temperature processes, sintered copper fiber wicks (SCFWs) with scaly fins were prepared. The copper fibers with scaly fins were fabricated by multi-tooth cutting and the additional driving force of scaly fins on ethanol was used to achieve directional capillary flow. The effects of scaly fin direction, sintering parameters, and porosity on the capillary performance of SCFWs were studied. The results show that the direction of scaly fins can adjust the liquid flow direction. The capillary performance parameter of SCFW3, with the same fin direction as the flow direction of ethanol, is 65.5% higher than that of SCFW1 with the opposite fin direction. Sintering temperature and holding time affect the formation of sintered necks and micropores, which affects the capillary performances of SCFWs. The effects of sintered necks on the capillary performances of SCFWs are more obvious than micropores on copper fibers. In addition, the relatively low porosity in the range of 70–80% helps improve the capillary performance of SCFWs. The SCFWs provide a feasible method for the fabrication of phase change heat transfer devices with directional heat transfer performances.

Effect of defects on ballistic transport in a bilayer SnS2-based junction with Co intercalated electrodes.

This study theoretically investigates the defect-related electronic structure and transport properties in a device where a semiconductor bilayer SnS2 (BL-SnS2) serves as the central scattering region and bilayer SnS2 with cobalt atom intercalation (Co-SnS2) as the metallic electrodes. The Co-SnS2/BL-SnS2 junction forms an ohmic contact, which is robust to defects. Low contact resistances of 52.1 Ω μm and 56.2 Ω μm are obtained in the zigzag (ZZ) and armchair (AC) transport directions, respectively. Defects, whether near the interface or in the middle of the central region, reduce the barrier between metal and semiconductor and the contact resistance. In particular, defects in the middle of the central region introduce impurity states and may result in resonant tunneling processes. This causes leakage current in the AC direction but not in the ZZ direction because impurity-associated transmission peaks in the latter are always outside the bias window.

Electrically switched asymmetric interfaces for liquid manipulation.

External field driven fluid manipulation, in particular electric field, offers the advantages of real-time control and exceptional flexibility, rendering it highly promising for applications in microfluidic devices, liquid separation and energy catalysis. However, it is still challenging for controlled liquid transport and fine control of droplet splitting. Herein, we demonstrate a strategy to achieve direction-controlled liquid transport and fine droplet splitting on an anisotropic groove-microstructured electrode surface via an electrically switched asymmetric interface. The balance of asymmetric capillary force generated by microstructures and electro-capillary force is critical in determining directional liquid transport and fine droplet splitting. Asymmetric bubbles generated by liquid electrolysis form an asymmetric liquid-gas-solid interface and result in gradient liquid wetting behavior on the two neighboring electrode surfaces. The electric field further enhances the asymmetric wetting of a liquid droplet on the electrode surface, exhibiting electric field direction-dependent motion. Moreover, the groove-microstructured electrode surface can strengthen the liquid droplet anisotropic wetting and correspondingly refine the volume range of the splitting sub-droplet. Even unidirectional/bidirectional liquid droplet transport can be controlled in collaboration with the asymmetric groove-microstructure and electric field. Thus, this work provides a new route for liquid transport and droplet splitting, showing great potential in controllable separation, microreaction and microfluidic devices.

Unidirectional moisture-conducting green fabrics prepared by a one-step electrospray technique.

Unidirectional moisture-conducting fabrics were prepared by electrospraying polyvinylidene fluoride (PVDF) and polyvinyl chloride (PVC) onto three green fabric substrates, namely cotton, hemp, and modal. Experiments were conducted to examine the effects of coating thickness, coating material, and substrate material on the moisture conductivity of the fabrics. The electrospraying technique was effective in forming uniform and strongly adhered PVDF and PVC coatings on the fabric substrates, and the coating thickness and material type had a significant effect on the fabric's moisture conductivity. The PVDF and PVC coatings significantly improved the unidirectional moisture conductivity of the fabric substrates, and although the unidirectional moisture conductivity effects differed among the substrates, all fabrics exhibited high directional water transport capacities (R values greater than 300%), high air permeabilities, and high water vapor transmission rates. Cotton and hemp substrates coated with hydrophobic layers showed more efficient unidirectional moisture transfer than modal fabrics. This study demonstrated that appropriate coating design and substrate selection can significantly improve the moisture conductivity of fabrics, providing a valuable reference for the development of high-performance functional textiles.

Linear PDI-based conjugated polymers with directional charge transport driving photocatalytic water oxidation

A linear conjugated organic polymer based on PDI was designed for directional charge transfer, it exhibits efficient charge separation that move along the chain direction. The above properties enable water oxidation for O2 production by PT-CB.

The well-defined three-dimensional matrix of a micro-sized silicon/carbon composite promoting lithium-ion transportation.

Micro-sized silicon is a promising anode material due to its high theoretical capacity and low cost. However, its bulk particle size poses a challenge during electrochemical cycling, and the long ion/electron transport paths within it limit the rate capability. Herein, we propose a structural engineering approach for establishing a well-defined three-dimensional (3D) micro-sized silicon/carbon matrix to achieve efficient omnidirectional ionic and electronic conductivity within micro-sized silicon and effectively mitigate the volume changes. The prepared materials, comprising ordered two-dimensional porous silicon nanosheets, offer direct two-dimensional electrolyte transport channels aligned parallel to the layer plane and porous channels oriented perpendicular to the layer plane. These well-defined omnidirectional pathways enable more efficient electrolyte mass transport than the disordered paths within the traditional 3D porous silicon anodes. A robust carbon shell, securely bonded to silicon through dual covalent bonding, effectively shields these pathways, buffering the volume changes and offering an electronically conductive 3D carbon network.

The multiple facets of Rab proteins modulating the cellular distribution of cholesterol from the late endosomal compartment.

Cholesterol is an essential lipid that ensures the functional integrity of mammalian cells. Most cells acquire cholesterol via endocytosis of low-density lipoproteins (LDL). Upon reaching late endosomes/lysosomes (LE/Lys), incoming ligands, including LDL-derived cholesterol, are distributed to other organelles. Niemann-Pick Type C1/2 (NPC1/2) proteins, members of the steroidogenic acute regulatory-related lipid transfer domain (StARD) and oxysterol-binding protein (OSBP) families facilitate the cellular distribution of cholesterol. NPC disease, a rare neurodegenerative disorder characterized by LE/Lys-cholesterol accumulation due to loss-of-function NPC1/2 mutations, underscores the physiological importance of LE/Lys-cholesterol distribution. Several Rab-GTPase family members, which play fundamental roles in directional membrane and lipid transport, including Rab7, 8 and 9, are critical for the delivery of cholesterol from LE/Lys to other organelles along vesicular and non-vesicular pathways. The insights gained from these regulatory circuits provide a foundation for the development of therapeutic strategies that could effectively address the cellular pathogenesis triggered by NPC1 deficiency and other lysosomal storage disorders.

Tuning interfacial charge transport via Ti-O-Sn bonds for efficient CO2 conversion.

Here, the clever design of forming an ohmic contact between SnS2 and MXene can regulate interfacial electron transport through Ti-O-Sn chemical bonds. This fast directional charge transport kinetics is attributed to the built-in electric field formed by the ohmic contact. As expected, the photoreduction CO2 activity of the optimized SSTC-5 catalyst is 10.4 times that of the original SnS2.

An esophagus-inspired magnetic-driven soft robot for directional transport of objects

An esophagus-inspired magnetic-driven soft robot can be used for orientation and antigravity object transport.

Transport of lithium droplets between two nonparallel iron plates: A molecular dynamics study

The use of bionic structures for the efficient and passive directional transportation of liquid droplets is crucial in numerous industrial applications. Compared with conventional fluids, liquid metals are stable under a wide range of environmental conditions owing to their excellent physicochemical properties. However, the directional transportation of liquid metals remains challenging. Herein, inspired by the pecking feeding mode of shorebirds, we performed a series of systematic molecular dynamics simulations to study the directional transport of liquid lithium (Li) between non-parallel iron (Fe) plates. The simulations demonstrate that cyclically closing and opening the Fe plates induces the movement of Li droplets toward the tip of the beak-shaped plate. Increasing the opening angle and applying a positive strain of the Fe plates can increase the transport velocity of the Li droplets. Nevertheless, the dissolution of Fe atoms in the liquid Li due to corrosion hinders the transportation of Li droplet across the Fe plate. We simulated the impact of two surface nanostructures on Li transport behavior and found that saw-tooth nanostructures decrease transport efficiency and lead to droplet breakup, whereas nanogrooves improve transport capacity by promoting the capillary effect. This work indicates that understanding the mechanism and influencing factors of liquid Li transport between non-parallel plates is essential for the design of bionic structures for the efficient transport of liquid metals.

A diode-like integrated hydrogel for piezoionic generators and sensors

Wearable sensing electronic devices based on hydrogel are gradually developing towards multifunction and portability, however, efficiently harvesting energy from the surrounding environment to power traditional hydrogel-based wearable electronic devices is a major challenge. The assembly of multilayer heterogeneous hydrogels is a potential strategy to address this challenge. Herein, inspired by the structure of diodes, a diode-like integrated hydrogel composed of a three-tier structure of anionic polyelectrolyte hydrogel, polyacrylamide hydrogel and cationic polyelectrolyte hydrogel is developed. By the connection of polyacrylamide hydrogel, the composite hydrogel exhibits excellent structural stability and mechanical properties. Notably, due to the introduction of MXene ion-conducting microchannels, the directional transport of free cations and anions ionized by anionic and cationic polyelectrolytes is achieved, thereby improving the conductivity (74.58 mS/cm), sensing (gauge factor = 7.47) and piezoionic output performance of the composite hydrogel. The composite hydrogel-based sensor can sense tiny facial movements and recognize the direction of human movement, and the composite hydrogel-based piezoionic generator exhibit more efficient mechanical-electric conversion performance, which can output the maximum voltage of 1410mV, current of 28 μA, and power density of 2.9mW/m2 for a composite hydrogel of 5×5 cm2. The integration of multilayer heterogeneous hydrogels proposes a versatile strategy for the development of high-performance hydrogel-based self-powered sensing electronic devices, expanding the application of hydrogels in artificial intelligence and human-computer interaction.

Preparation of Aluminum-Based Dual-Gradient Surfaces for Directional Droplet Transport by Bioinspired Sarracenia Microstructures.

Inspired by the ultrafast directional water transport structure of Sarracenia trichomes, hierarchical textured surfaces with specific microgrooves were prepared based on laser processing combined with dip modification, in response to the growing problem of freshwater scarcity. The prepared surfaces were tested for droplet transport behavior to investigate the relationship between the surface structure and the driving force of directional water transport and their effects on the water transport distance and water transport velocity. The results showed that surfaces with a superhydrophobic background associated channels of multirib structures, and a dual-gradient surface of gradient hydrophobic background associated channels with gradient structure performed the best in terms of water transport efficiency. In addition, the water transport process of different samples under Mode II was simulated by CFD, and the dynamic evolution of water film mode formation was obtained to be divided into four phases, including film formation, transition state, mode formation, and stable water transport. This study provides a good reference for the development and preparation of surfaces for directional water transport.

HFM1 is essential for the germ cell intercellular bridge transport in primordial follicle formation in mice

The reproductive lifespan of female mammals is determined by the size of the primordial follicle pool, which comprises oocytes enclosed by a layer of flattened pre-granulosa cells. Oocyte differentiation needs acquiring organelles and cytoplasm from sister germ cells in cysts, but the mechanisms regulating this process remain unknown. Previously helicase for meiosis 1 (HFM1) is reported to be related to the development of premature ovarian insufficiency. Here, it is found that HFM1 is involved in oocyte differentiation through organelle enrichment from sister germ cells. Further study indicates that HFM1 is involved in intercellular directional transport through intercellular bridges via the RAC1/ANLN/E-cad signaling pathway, which is indispensable for oocyte differentiation and primordial follicle formation. These findings shed light on the critical role of HFM1 in intercellular bridge transport, which is essential for the establishment of the primordial follicle pool and presenting new horizons for female fertility protection.

Acidic pH of Early Endosomes Governs SARS-CoV-2 Transport in Host Cells.

Endocytosis is a prominent mechanism for SARS-CoV-2 entry into host cells. Upon internalization into early endosomes (EEs), the virus is transported to late endosomes (LEs), where acidic conditions facilitate spike protein processing and viral genome release. Dynein and kinesin motors drive EE transport along microtubules; dynein moves EEs to the perinuclear region, while kinesins direct them towards the plasma membrane, creating a tug-of-war over the direction of transport. Here, we identify that luminal pH of EEs is a key factor regulating the outcome of this tug-of-war. Among the known endosomal pH regulators, only the sodium-proton exchanger NHE9 has so far been genetically linked to severe COVID-19 risk. NHE9 functions as a proton leak pathway specifically on endosomes. We show that limiting acidification of EEs by increasing the expression of NHE9 leads to decreased infectivity of the SARS-CoV-2 spike-bearing virus in host cells. Our investigation identified the EE membrane lipid phosphatidylinositol-3-phosphate (PI3P) as a link between luminal pH changes and EE transport. Normally, as EEs mature, PI3P depletes. However, in cells with high NHE9 expression, PI3P persists longer on EEs. PI3P plays a pivotal role in the recruitment of motor proteins and the subsequent movement of EEs. Consistently, we observed NHE9 mediated alkalization of EEs hindered perinuclear movement. Specifically, EE speed and run-length were negatively impacted, ultimately leading to EEs falling off microtubules and impairing the delivery of viral cargo to LEs. NHE9 thus offers a unique opportunity as a viable therapeutic target to impede SARS-CoV-2 host cell entry.

Composite Nanofiber Membrane-Based Microfluidic Fluorescence Sensors for Sweat Analysis.

Microfluidic chips play a crucial role in wearable sensors for sweat collection. However, previously reported wearable microfluidic chips, such as those based on poly(dimethylsiloxane) (PDMS) and paper, encounter sweat accumulation at the skin-sensor interface in practical applications, which consequently affects both sensing stability and wearing comfort. Herein, we propose a composite nanofiber membrane (CNMF)-based microfluidic chip for in situ sweat collection. The CNMF with directional water transport capability was integrated with patterned PDMS to prepare microfluidic chips. On one hand, sweat can be automatically transported to the analysis area along the designed pathway. On the other hand, sweat transfers from the hydrophobic membrane close to the skin to the hydrophilic membrane, effectively avoiding sweat accumulation and facilitating a comfortable skin microenvironment. Subsequently, we constructed a CNMF-based microfluidic fluorescence sensor for the analysis of multiple targets in human sweat. A portable 3D-printed device was employed for the visual signal output. Results indicated that the microfluidic sensor exhibits excellent reliability for collecting and analyzing sweat. This work provides new insights into the construction of wearable microfluidic chips with enhanced wearing comfort.

Band alignment characterizations of grafted GaAs/(2¯01) Ga2O3 heterojunction via x-ray photoelectron spectroscopy

Research on gallium oxide (Ga2O3) has accelerated due to its exceptional properties, including an ultrawide bandgap, native substrate availability, and n-type doping capability. However, significant challenges remain, particularly in achieving effective p-type doping, which hinders the development of Ga2O3-based bipolar devices like heterojunction bipolar transistors (HBTs). To address this, we propose integrating mature III–V materials, specifically n-AlGaAs/p-GaAs as the emitter (E) and base (B) layers, with n-Ga2O3 as the collector (C) to form III–V/Ga2O3 n–p–n HBT. This hetero-material integration could be achieved using advanced semiconductor grafting techniques that could create arbitrary lattice-mismatched heterojunctions by introducing an ultrathin dielectric interfacial layer. This study focused on revealing the band alignment at the base–collector (B–C) junction using a n-Ga2O3(2¯01) orientated substrate combined with p-GaAs for potential HBT applications. We discovered a type-II band alignment between p-GaAs and Ga2O3(2¯01), with the p-GaAs conduction band approximately 0.614 eV higher than that of Ga2O3(2¯01). This staggered alignment allows for direct and efficient electron transport from the p-GaAs base to the n-Ga2O3 collector, avoiding the electron blocking issues present in p-GaAs/Ga2O3 (010) heterojunctions. Additionally, our study suggests the potentially existing type-II alignment between the (2¯01) and (010) Ga2O3 interfaces, highlighting the orientation-dependent band offsets. These findings are pivotal for developing high-performance Ga2O3-based HBTs, leveraging the strengths of Ga2O3 and well-established semiconductor materials to drive advancements in high-power electronics.