Moisture Gradient Research Articles

A finite element framework on water vapor transmission rates by pinhole damages in inorganic ultrabarriers for flexible electronics

This work presents a computational framework to predict possible scenarios of pinhole distributions in hermetic barrier encapsulated organic layers to fill the lack of pinhole damage studies in thin film/organic electronics to a great extent. We describe various scenarios, including multiple pinhole damages of varying sizes and distances on a polymer film. An equation of water vapor transmission rates is proposed for polyimide films encapsulated with ALD ultrabarriers from computational experiments performed with different strategies. The validity of this equation covers pinhole damages ranging from 100 nm to 2.2 mm and any size of surface area of the film can be applied. Since the proposed equation does not include the interaction of wetness gradients with neighboring pinholes, the distance effect is investigated to estimate decreases in WVTR as the distance decreases between pinholes. An interactive, customized graphical user interface was created with ANSYS Parametric Design Language to make computational calculations user-friendly and widely available to researchers. Solution strategies of complete and unit cell runs, including standard and sub-modeling approaches, are proposed with advantages and disadvantages in computational time and accuracy of results.

A wettability and structure gradient electrospun membrane for highly efficient emulsion separation

The treatment of oily wastewater, especially emulsions by membranes attracts growing attention nowadays. However, the handling of industrial oily wastewater, especially emulsions, remains a challenging issue and high flux and efficiency in emulsion separation usually depend on energy-consuming external driving pressure. In this work, we report a functional gradient membrane (GM) with special wettability and structure gradient in the thickness direction for highly efficient emulsion separation. The GM is prepared by a one-step electrospinning strategy using PS-PAN and GO@PAN to tune the wettability of each layer in the membrane following a specially designed fabrication protocol. The prepared GM has a wettability gradient of superhydrophilicity to hydrophobicity and a structure gradient of spindles on fibers caused by GO content variation. The wettability gradient of GM generates remarkable unidirectional liquid transport properties and significantly higher fluxes for emulsion separation than the homogeneous GO@PAN membrane while the GO and the spindles on fibers facilitate the demulsification and coalesce of demulsified oil droplets. As a result, ultrahigh separation flux and efficiency have been obtained in surfactant-free oil-in-water emulsion separation only under gravity and an energy-efficient separation of surfactant-stabilized emulsions under low gravity condition has also been achieved by the GM. In addition, the GO spindle structure in GM makes it present favorable antifouling properties. After several cycles of separation, the emulsion flux can be restored to about 100% of the initial flux after simple cleaning. Thus, the special wettability and structure gradient endows the GM with excellent energy-efficient and stable separation performance, showing tremendous potential in the field of oil–water separation.

Simulation and experimental study of heat-moisture-solute transfer during drying process of porous media

Fruits and vegetables, being typical porous media, allow for the migration of nutrients (solutes) and the transport of moisture simultaneously during the drying process. To reveal the migration mechanism of heat-moisture-solute during the drying process of porous media, a comprehensive mathematical model was established that accounts for the coupled phenomena of heat and moisture transfer, along with solute migration. The model was simulated using COMSOL to provide insights into these complex interactions. Hot-air drying experiments were conducted using apple slices as the subject to validate the accuracy and reliability of the model. The simulation results and experimental results of temperature, moisture content, and sugar concentration were in good agreement. The findings demonstrate that as the drying process progresses, the interface between temperature, moisture gradients, and sugar concentration shifts from the outer layers toward the inner regions. We investigated the effects of hot air temperature, thickness, and porosity on the heat-moisture-solute transfer in porous media. The results provide support for accurately predicting the migration and transport mechanisms of solutes in porous media.

Grafting of Poly(ionic liquid) Brushes through Fe0-Mediated Surface-Initiated Atom Transfer Radical Polymerization for Marine Antifouling.

Surface-tethered poly(ionic liquid) brushes have attracted considerable attention in widespread fields, from bioengineering to marine antifouling. However, their applications have been constrained due to the poor polymerization efficiency and sophisticated operation process. In this work, we efficiently synthesized the poly(ionic liquid) brushes with unparalleled speed (up to 98 nm h-1) through Fe0-mediated surface-initiated atom transfer radical polymerization (Fe0 SI-ATRP) while consuming only microliter of monomer solution under ambient conditions. We also demonstrated that poly(ionic liquid) brushes with gradient thickness and wettability were easily accessible by regulating the distance between the opposite plates of Fe0 SI-ATRP. Moreover, the resultant poly(ionic liquid) brushes presented excellent antibacterial activities against Escherichia coli (99.2%) and Bacillus subtilis (88.1%) after 24 h and low attachment for proteins and marine algae (≤5%) for over 2 weeks. This research provided pathways to the facile and controllable fabrication of poly(ionic liquid) materials for marine antifouling applications.

Wettability and/or shape gradient induced spontaneous droplet motion on solid surfaces

This research investigates the dynamics of spontaneous droplet motion induced by wettability and shape gradients on microscale substrates. The study compares and analyzes the effects of different driving sources, including wettability gradient, shape gradient, and their combination. Findings reveal that the combination of wettability and shape gradients on a wedge-shaped track produces unique droplet motion patterns. Results demonstrate that, despite a slower initial acceleration, the combined driving force on the wedge-shaped track leads to a larger peak velocity compared to tracks with individual gradients. Additionally, the study explores the impact of track end contact angle and wedge angle on droplet motion. It highlights the preference for uniform wettability tracks for faster droplet motion, emphasizing the role of overall contact angle and wetting area. The research concludes that track size influences droplet motion, with larger wedge angles promoting faster and more stable motion. Overall, the study provides valuable insights into controlling and understanding droplet dynamics on structured surfaces.

The droplet race: Optimization of a wettability gradient surface

Droplet behavior influenced by wettability distribution is a pertinent field of research with applications in lab-on-a-chip and heat transfer devices among others. Some have proposed patterned surfaces with controlled variation of wettability to orient the direction of the droplet motion or to increase its velocity. These patterns are arrived upon with experience and knowledge of this phenomenon. In this research paper, the authors used a mathematical approach to the physical problem by using a gradient based optimizer for maximizing droplet velocity. Given some initial conditions, the optimizer marches toward the optimum wettability distribution profile. The droplet motion is modeled in two dimensions (i.e., on the xy-plane), on a plate having a wettability distribution in one dimension (i.e., along the x axis). The single component pseudopotential model allows for the quantification of the wettability distribution as a distribution of a pseudodensity of the solid nodes of the flat plate. Starting with several monotonous analytical profiles, a quadratic convex profile allows us to reach the maximum mean velocity for the threshold droplet displacement. Different sets of initial profiles, length of the plate (L), and diameter of the droplet (D) are tested. For smaller L/D ratio, the optimal wettability distributions exhibit non-trivial features: profiles can be non-monotonous, and wettability gradient could be locally null. With the increase in the L/D ratio, these specificities tend to be less prominent and optimal profiles converge to the quadratic convex one. The main innovation and significance of the paper is that mathematical optimization algorithms have been used conjointly with a multiphase lattice Boltzmann model solver to address for the first time the droplet race defined as: “what is the best wettability profile in order for a droplet to reach a desired location as quickly as possible?”

Predicting the Electrical Conductivity of Partially Saturated Frozen Porous Media, a Fractal Model for Wide Ranges of Temperature and Salinity

AbstractThe quantitative determination of liquid water content and salinity in soils is crucial for the preservation of hydrological environments and engineering infrastructures, especially in frozen regions. Electrical conductivity, as a fundamental physical parameter in electrical and electromagnetic non‐destructive techniques, varies significantly with the physical and chemical properties, such as pore water conductivity, salinity, water saturation, and temperature. In this study, accounting for pore size and tortuous length following fractal distributions, we develop a new capillary bundle model for variation of electrical conductivity as a function of temperature in broad water saturation and salinity ranges. In this new model, we consider the contributions of bulk and surface conductivities to the total electrical conductivity. To test this model, a series of laboratory experiments were carried out for different initial water saturations and salinities using an electrical resistance apparatus and a nuclear magnetic resonance method. The experimental results show that unfrozen water saturation and ionic concentration affect the electrical conductivity of unsaturated frozen soils. Furthermore, the proposed model is capable of fitting the main trends of the experimental data from the literature and acquired in this study in unfrozen‐frozen conditions for different water contents. Relying on the proposed model, we also determine the expression of the apparent formation factor, which is significantly sensitive to porosity, water saturation, and temperature. The predicted values of the apparent formation factor also agree very well with the experimental data. This new capillary bundle model provides a new perspective in interpreting electrical monitoring to easily deduce changes in key variables in the cryosphere such as liquid water content and moisture gradients.

Understanding the Spatiotemporal Variability of Tropical Orographic Rainfall Using Convective Plume Buoyancy

Abstract Mechanical forcing by orography affects precipitating convection across many tropical regions, but controls on the intensity and horizontal extent of the orographic precipitation peak and rain shadow remain poorly understood. A recent theory explains this control of precipitation as arising from modulation of lower-tropospheric temperature and moisture by orographic mechanical forcing, setting the distribution of convective rainfall by controlling parcel buoyancy. Using satellite and reanalysis data, we evaluate this theory by investigating spatiotemporal precipitation variations in six mountainous tropical regions spanning South and Southeast Asia, and the Maritime Continent. We show that a strong relationship holds in these regions between daily precipitation and a measure of convective plume buoyancy. This measure depends on boundary layer thermodynamic properties and lower-free-tropospheric moisture and temperature. Consistent with the theory, temporal variations in lower-free-tropospheric temperature are primarily modulated by orographic mechanical lifting through changes in cross-slope wind speed. However, winds directed along background horizontal moisture gradients also influence lower-tropospheric moisture variations in some regions. The buoyancy measure is also shown to explain many aspects of the spatial patterns of precipitation. Finally, we present a linear model with two horizontal dimensions that combines mountain wave dynamics with a linearized closure exploiting the relationship between precipitation and plume buoyancy. In some regions, this model skillfully captures the spatial structure and intensity of rainfall; it underestimates rainfall in regions where time-mean ascent in large-scale convergence zones shapes lower-tropospheric humidity. Overall, these results provide new understanding of fundamental processes controlling subseasonal and spatial variations in tropical orographic precipitation.

Survival, growth, and functional traits of tropical wet forest tree seedlings across an experimental soil moisture gradient in Puerto Rico.

Droughts are predicted to become more frequent and intense in many tropical regions, which may cause shifts in plant community composition. Especially in diverse tropical communities, understanding how traits mediate demographic responses to drought can help provide insight into the effects of climate change on these ecosystems. To understand tropical tree responses to reduced soil moisture, we grew seedlings of eight species across an experimental soil moisture gradient at the Luquillo Experimental Forest, Puerto Rico. We quantified survival and growth over an 8-month period and characterized demographic responses in terms of tolerance to low soil moisture-defined as survival and growth rates under low soil moisture conditions-and sensitivity to variation in soil moisture-defined as more pronounced changes in demographic rates across the observed range of soil moisture. We then compared demographic responses with interspecific variation in a suite of 11 (root, stem, and leaf) functional traits, measured on individuals that survived the experiment. Lower soil moisture was associated with reduced survival and growth but traits mediated species-specific responses. Species with relatively conservative traits (e.g., high leaf mass per area), had higher survival at low soil moisture whereas species with more extensive root systems were more sensitive to soil moisture, in that they exhibited more pronounced changes in growth across the experimental soil moisture gradient. Our results suggest that increasing drought will favor species with more conservative traits that confer greater survival in low soil moisture conditions.

Rapid decrease of the Labrador Sea’s influence on black spruce ecosystems with distance inland

In eastern Canada, Black spruce (Picea mariana Mill. B.S.P.) grows in a wide variety of climates, from maritime-oceanic conditions near the Labrador Sea, to more continental climates, inland. Along this gradient, timing and provenance of heat and moisture that support growth are uncertain, weakening our capacity to predict the response of boreal ecosystems to climate variability. Here, we measured the stable oxygen isotopic composition of black spruce tree-ring cellulose at three sites in eastern Canada and provide evidence of a rapid decrease of Labrador Sea’s influence on adjacent ecosystems. Our results report a landwards decrease in the oxygen isotope composition of both tree-ring cellulose (δ18OTRC) and precipitation water (δ18Op). We also reveal a rapid landwards decoupling between δ18OTRC variability (1950-2013), maximum temperature and Sea Surface Temperature variations over the Northwest Atlantic. Thus, despite their apparent ecological homogeneity, eastern Canada’s black spruce ecosystems rely on heterogeneous sources of heat and moisture.

Control of Water Droplet Transport Using Anodic Porous Alumina with a Wettability Gradient.

Water droplets can spontaneously move on surfaces with a wettability gradient, and such surfaces can be used in various functional devices. In this study, surfaces with a wettability gradient were prepared from anodic porous alumina with different pore arrangement regularities. The evaluation of the water droplet transport distance on the surfaces of the prepared samples showed that the pore arrangement regularity of the anodic porous alumina had no effect on the droplet transport distance. It was also shown that the droplet transport distance was affected by the droplet size and the width of the wettability gradient structure. When two water droplets were formed at both ends of the anodic porous alumina with an increasing gradient of pore diameter from the center to both ends, they moved from the ends toward the center and merged. The method reported in this paper shows that by controlling the pore size of anodic porous alumina, one can fabricate a substrate on which droplets can move in any direction. The anodic porous alumina with a wettability gradient as obtained in this study has potential use for various applications such as microfluidic devices and analytical chips.

Low-Temperature Airflow-Drying Cracking Coupling with Flexible Mechanical Deshelling for Camellia oleifera Fruit: Process and Mechanism

Addressing the problems of high seed-breaking ratio and difficult seed-shell separation in the current mechanical deshelling of Camellia Oleifera fruit (COF), this work innovatively proposed a strategy of low-temperature airflow-drying cracking coupling with flexible mechanical deshelling. The cracking ratio of COF reached 100% after airflow-drying at 20–50 °C for 4–10 h. Moreover, the tissue structure of the Camellia shell remained unchanged after airflow drying. The mechanical shelling ratio of cracked fruits (cracking gap 6 mm) reached 98.37%, and the shells present as integrated lamelliform for facilitating later sorting. The results of low-field nuclear magnetic resonance (LF-NMR) and shrinkage equation showed that the free water of outer layers in the Camellia shell evaporated first, then the free water of inner layers transferred to outer layers to further evaporate, creating a moisture gradient and moisture stress to cause the shrinkage of shell and cracking of COF.

Thermoresponsive Skin-like Fabric for Personal Comfort and Protection.

Acting as a "second skin", clothing plays an indispensable role in providing comfort and protection in the wide range of environments in which we live. However, comfort and protection are often competing requirements and are difficult to improve simultaneously. By mimicking the exceptional thermoresponsive one-way liquid transport property of human skin, here we developed a scalable and ecofriendly skin-like fabric that has a tunable directional water transport rate while having excellent water repellency. The water transport rate is also temperature-responsive, just like skin. As the temperature increases, the wettability gradient in the spatially distributed channels (acting like "sweat glands") increases, promoting sweat transport and evaporative heat dissipation. As the temperature decreases, on the other hand, the wettability gradient diminishes, reducing liquid transport and evaporative heat loss, thereby promoting heat retention. The fabric is highly suitable for sportswear and functional clothing and can have wider applications, such as oil-water separation, fog harvesting, etc.

The Stirring Tropics: Theory of Moisture Mode–Hadley Cell Interactions

Abstract Interactions between large-scale waves and the Hadley cell are examined using a linear two-layer model on an f plane. A linear meridional moisture gradient determines the strength of the idealized Hadley cell. The trade winds are in thermal wind balance with a weak temperature gradient (WTG). The mean meridional moisture gradient is unstable to synoptic-scale (horizontal scale of ∼1000 km) moisture modes that are advected westward by the trade winds, reminiscent of oceanic tropical depression–like waves. Meridional moisture advection causes the moisture modes to grow from “moisture-vortex instability” (MVI), resulting in a poleward eddy moisture flux that flattens the zonal-mean meridional moisture gradient, thereby weakening the Hadley cell. The amplification of waves at the expense of the zonal-mean meridional moisture gradient implies a downscale latent energy cascade. The eddy moisture flux is opposed by a regeneration of the meridional moisture gradient by the Hadley cell. These Hadley cell–moisture mode interactions are reminiscent of quasigeostrophic interactions, except that wave activity is due to column moisture variance rather than potential vorticity variance. The interactions can result in predator–prey cycles in moisture mode activity and Hadley cell strength that are akin to ITCZ breakdown. It is proposed that moisture modes are the tropical analog to midlatitude baroclinic waves. MVI is analogous to baroclinic instability, stirring latent energy in the same way that dry baroclinic eddies stir sensible heat. These results indicate that moisture modes stabilize the Hadley cell and may be as important as the latter in global energy transport. Significance Statement The tropics are characterized by steady circulations such as the Hadley cell as well as a menagerie of tropical weather systems. Despite progress in our understanding of both, little is known about how the mean circulations and the weather systems interact with one another. Here we show that tropical waves can grow by extracting moisture from the Hadley cell, thereby weakening it. They also transport moisture to higher latitudes. Our results challenge the notion that the Hadley cell is the sole transporter of energy out of the tropics and instead favor a view where tropical waves are also essential for the global energy balance. They dry the humid regions and moisten the drier regions via stirring.

Drivers of heterogeneity in tundra vegetation productivity on the Yamal Peninsula, Siberia, Russia

The direction and magnitude of tundra vegetation productivity trends inferred from the normalized difference vegetation index (NDVI) have exhibited spatiotemporal heterogeneity over recent decades. This study examined the spatial and temporal drivers of Moderate Resolution Imaging Spectroradiometer Max NDVI (a proxy for peak growing season aboveground biomass) and time-integrated (TI)-NDVI (a proxy for total growing season productivity) on the Yamal Peninsula, Siberia, Russia between 2001 and 2018. A suite of remotely-sensed environmental drivers and machine learning methods were employed to analyze this region with varying climatological conditions, landscapes, and vegetation communities to provide insight into the heterogeneity observed across the Arctic. Summer warmth index, the timing of snowmelt, and physiognomic vegetation unit best explained the spatial distribution of Max and TI-NDVI on the Yamal Peninsula, with the highest mean Max and TI-NDVI occurring where summer temperatures were higher, snowmelt occurred earlier, and erect shrub and wetland vegetation communities were dominant. Max and TI-NDVI temporal trends were positive across the majority of the Peninsula (57.4% [5.0% significant] and 97.6% [13.9% significant], respectively) between 2001 and 2018. Max and TI-NDVI trends had variable relationships with environmental drivers and were primarily influenced by coastal-inland gradients in summer warmth and soil moisture. Both Max and TI-NDVI were negatively impacted by human modification, highlighting how human disturbances are becoming an increasingly important driver of Arctic vegetation dynamics. These findings provide insight into the potential future of Arctic regions experiencing warming, moisture regime shifts, and human modification, and demonstrate the usefulness of considering multiple NDVI metrics to disentangle the effects of individual drivers across heterogeneous landscapes. Further, the spatial heterogeneity in the direction and magnitude of interannual covariation between Max NDVI, TI-NDVI, and climatic drivers highlights the difficulty in generalizing the effects of individual drivers on Arctic vegetation productivity across large regions.

Aeolian Sand Sorting and Soil Moisture in Arid Namibian Fairy Circles

We studied fairy circles 20 km west of Sesriem at one of the driest locations of fairy circles in Namibia, at the foot of the popular Sossusvlei dunes. These fairy circles lack the typical hexagonal order of the Namibian fairy circles. After years of drought, their pattern is more similar to that of vegetation rings, due to the sparse vegetation in the area between the circles. Cross-section measurements of the soil water content (SWC) show that the upper layer (12 cm) is very dry (~1%) and much below the wilting point of Stipagrostis ciliata grasses, whereas the deeper soil layer is wetter (4%). The grain size distribution of soil samples taken from inside and outside the fairy circles reveals considerable heterogeneity in the size fractions due to aeolian (wind-driven) sand sorting. The bare soil inside the fairy circles contains coarser grains, and the ground surface is covered by sand megaripples. There is a linear trend between the vertical soil moisture gradient and the median grain diameter. Fine particles trapped on the vegetated edges of the fairy circle result in small nebkhas that increase the soil water retention at the surface. The dry and loose coarser topsoil inside the fairy circles may prevent the recolonization of new seedlings with short root lengths inside the fairy circles. Our results highlight the role of aeolian sand transport and deposition in desert vegetation environments and seem to support the notion that fairy circle formation may be affected by the interplay between sand sorting and soil moisture gradients.

Effect of Wettability Gradient on the Scale Formation in Falling Film Flow

Abstract Mitigation of scale formation and performance degradation remains a vital challenge for falling film evaporators in various industries. In this work, an experimental study of falling film flow on a horizontal tube is conducted to investigate the effects of wettability gradients on thermal, hydraulic, and fouling behavior. It is revealed that certain hydrophobic coating patterns, such as strip, ring, and grid patterns, lead to unwetted heat transfer area, which results in decreased heat transfer compared to fully wetted plain tube. By adjusting the geometry and position of the wettability gradient, the hybrid coating demonstrates improved heat transfer performance. Based on the characteristics of horizontal tube falling film flow, impinging jet, thin film flow, and liquid retention at the tube bottom, a hybrid coating pattern is developed to improve surface wetting and mitigate the scaling coverage. It is revealed that scale deposition is regulated by wettability gradient. Crystals tend to be dense and compact in hydrophilic areas, while they appear scattered or even absent in hydrophobic regions, depending on the dimension of the hydrophobic area. While at the hydrophilic/hydrophobic boundary, a noticeable scale thickness step is observed, which raises the potential for self-cleaning. The balance of minimization of scaling layer coverage and maximization of wetting area requires an optimal design in coating dimensions, for which a systemic study of both flow dynamics and fouling characteristics on the falling film is necessary in the future.

Enhancement of lubricant replenishment for starved lubrication by laser-induced wettability gradient surface

This paper addresses the lubrication issues experienced by rolling element bearings operating under limited lubricant supply (LLS) or starvation conditions. A novel three-dimensional comb-tooth-groove (CTG) surface pattern is introduced to promote oil replenishment through unidirectional force. The transport of oil droplets on the CTG pattern is examined to evaluate this force, while groove length and depth are characterized as key factors influencing the surface force. More practically, the impact of CTG patterns on bearing lubrication under LLS conditions is assessed through experiments on bearings modified with CTG surface arrays. These modified bearings exhibit reduced torque and temperature rise, highlighting the significant advantages of CTG surfaces in enhancing bearing performance.

Fabrication of a superhydrophobic cotton fabric with efficient antibacterial properties and asymmetric wettability via synergistic effect of quaternized chitosan/TiO2/Ag

A superhydrophobic cotton fabric with unidirectional moisture transfer ability, antibacterial, and oil-water separation capabilities was fabricated by combining a simple coating method and oxygen plasma etching. Polydimethylsiloxane (PDMS) was employed to impart low surface energy to the cotton fabric, thereby endowing it with hydrophobic characteristics. The synthesized quaternized chitosan/TiO2/Ag (CTA) compound was subsequently applied onto the cotton fabric surface to introduce a desirable level of surface roughness, thus enhancing its hydrophobic properties and conferring excellent antibacterial efficacy. The cotton was subsequently treated by oxygen plasma to trigger asymmetrical wetting on both sides. The experimental findings reveal that the optimally treated cotton fabric exhibits hydrophobic properties on the bottom surface, with a water contact angle (WCA) reaching 162.8°, while the upper surface displays hydrophilic behavior, establishing a wetting gradient along the thickness direction. Notably, even under the influence of reverse gravity, water droplets are capable of transferring from the back to the top surface within 2 s, while preventing reverse penetration of liquid. Moreover, the synthesized compound CTA endows the cotton fabric with efficient and long-lasting antibacterial properties through two modes (contact and release sterilization modes) and three sterilization mechanisms (electrostatic interaction, plasma surface resonance effect, and reactive oxygen species). Remarkably, within a time frame of only 1 h, the modified cotton fabric is able to achieve a kill rate exceeding 99% against Escherichia coli and Staphylococcus aureus. Moreover, the aforementioned properties demonstrate outstanding durability against repeated washing, continuous abrasion, exposure to strong acid/base, and ultraviolet radiation. Additionally, this modified cotton fabric exhibits remarkable efficiency in terms of oil-water separation, effectively separating both light and heavy oil from water. It is worth noting that the preparation process is cost-effective, environmentally friendly, and free from fluorine.

Hydrogel-Functionalized Bandages with Janus Wettability for Efficient Unidirectional Drug Delivery and Wound Care.

Chronic wounds have imposed a severe physical and economic burden on the global healthcare system, which are usually treated by the delivery of drugs or bioactive molecules to the wound bed through wound dressings. In this work, we have demonstrated a hydrogel-functionalized bandage with Janus wettability in a bilayer structure to achieve unidirectional drug delivery and multifunctional wound care. The Janus patterned bandage with porous gradient wetting channels on the upper layer is responsible for the unidirectional transport of the drug from the outside to the wound bed (up to 90% drug transport efficiency) while preventing drug diffusion in unwanted directions (<8%). The hydrogel composed of chitosan quaternary ammonium salt (HACC), poly(vinyl alcohol) (PVA), and poly(acrylic acid) (PAA) at the bottom layer further functionalized such a bandage with biocompatibility, excellent antibacterial properties, and hemostatic ability to promote wound healing. Especially, the hydrogel-functionalized bandage with Janus wettability exhibits excellent mechanical flexibility (∼198% strain), which can comply well with skin deformation (stretching, bending, or twisting) and maintain unidirectional drug delivery behavior without any leakage. The in vivo full-thickness skin wound model confirms that the hydrogel-functionalized bandage can significantly facilitate epithelialization and collagen deposition and improve drug delivery efficiency, thus promoting wound closure and healing (the wound healing ratio was 98.10% at day 15). Such a synergistic strategy of unidirectional drug delivery and multifunctional wound care provides a more efficient, economical, and direct method to promote wound healing, which could be used as a potential high-performance wound dressing for clinical application.