Smart Janus textiles for biofluid management in wearable applications

Summary

Janus textiles with asymmetric wettability have shown great potential in wearable applications due to their ability to manage biofluids efficiently. This review summarizes recent advances in smart Janus textiles for biofluid control and monitoring, focusing on wearable technologies. We first introduce the design configurations and fabrication approaches of Janus textiles, including asymmetric generation and asymmetric decoration strategies. We then highlight their diverse wearable applications spanning personal thermal management textiles, sweat sensors, hemostatic wound dressings, and protective equipment. These textiles offer innovative solutions for directional sweat transport, enhancing cooling and humidity control, and providing antibacterial properties. Finally, we discuss current limitations in durability, biocompatibility, and manufacturing scalability, alongside emerging opportunities in the field of smart Janus textiles.

Graphical abstract

Sensor; Bioelectronics

Introduction

Smart textiles have played a critical role in the development of point-of-care medicine facilitating early diagnosis and personalized therapies.^{1,2,3,4,5,6,7,8} These textiles, fabricated into wearable sensors, enable real-time, continuous monitoring of critical health parameters such as brainwave and muscle activity, temperature, biophotons, and specific biomarkers in sweat or breath, which is vital for managing abnormal physiological states.^{9,10,11,12,13,14,15,16,17,18,19,20,21} Additionally, textile-based lab-on-chip systems have been developed, integrating microfluidics for immediate, on-site analysis of biomarkers using minute biofluid samples, including sweat, saliva, or blood.^22,23 In wound care, intelligent bandages and biosensor-equipped dressings are transformative, enabling monitoring of healing and infection detection without the need for dressing removal, thus promoting personalized medical care.²⁴

Despite their numerous benefits, these wearable devices often face challenges in terms of comfort and skin compatibility, particularly during extended wear. Issues such as poor breathability and heat dissipation can lead to skin irritation.²⁵ High humidity levels at the epidermis can reduce sensing accuracy for skin conductance readings. Moisture regulation is also vital physically, as variations in temperature and humidity impact the body. Inadequate moisture wicking can lead to skin maceration, irritation, and even secondary infections. Excess humidity buildup inside wearables also risks short-circuiting electronic components, compromising utility.²⁶

In light of these issues, asymmetric wettability, where a material displays different wettability characteristics on each side, is a significant attribute.^27,28,29 A prime example of this in nature is the desert beetle, whose back with alternating hydrophobic and hydrophilic can collect the droplet and roll the droplet to the beetle’s mouth. Inspired by this natural phenomenon, smart Janus textiles with asymmetric wettability have emerged as a high-performance functional material category. Their applications are diverse, ranging from water harvesting,³⁰ oil-water separations,^31,32,33 smart clothing,³⁴ and medical applications.^35,36 While recent literature reviews have covered advancements in Janus membranes, the rapid progression in smart textiles featuring asymmetric wettability for biofluid management warrants a comprehensive review to summarize newer developments.

In this review, we summarized the latest research progress of smart Janus textiles for biofluid management, and a brief introduction to representative synthetic approaches of smart Janus textiles was also presented. The focal point of this review is the exploration of multifunctional smart Janus textiles for biofluid management in wearable applications, encompassing personal thermal management materials, sweat sensors, hemostatic materials, and wearable protection. Finally, we will address the current limitations, existing challenges, and future opportunities for smart Janus textiles. Our discussion attempts to cover advanced strategies, materials, and the associated opportunities and challenges in this dynamic field.

The design and preparation of smart Janus textile

In general, three configurations can be followed when designing membranes with asymmetric wettability: A-on-B, A-and-B, and A-to-B, as shown in Figure 1A.²⁸ For the first two types, the wettability of each layer is homogeneous, only the relative thicknesses of layers A and B are different. The A-on-B membrane is obtained by adding a thinner A layer to the B layer.^27,29 Despite the A layer being thinner than the B layer, it has a significant impact on the membrane surface properties. The A-and-B membrane is the configuration where the thickness of the A and B layers are similar. The third type is much different from the formers, a gradual change of wettability along the membrane can be observed in the structure of the A-to-B membrane.

Figure 1.

The design and preparation of smart Janus textile

(A) Three configurations of Janus membranes with asymmetric wettability. Schematic diagram of asymmetric generation (B) and asymmetric modification (C) for Janus membrane preparations.

Based on the understanding of the Janus membrane structure, there are two strategies used to prepare Janus materials: asymmetric generation and asymmetric decoration.

Asymmetric generation

Asymmetric generation is a common method for obtaining Janus membranes. The Janus fabric is made by manufacturing one side of the membrane first and then preparing the other side using a unique crafting technique based on the surface (Figure 1B). Currently, available Janus membrane fabrication technologies include electrospinning,^37,38 vacuum filtration,³⁹ and phase separation.⁴⁰ Among them, electrospinning is extensively used for Janus fabric preparation due to its outstanding anisotropic wetting properties and accurate controllability on the microstructure.⁴¹ This method relies on the formation of Taylor cones caused by charged droplets in a high-voltage electric field, as well as utilizing the template effect of polymers, to produce ultrafine fibers with a customizable diameter range from nanometers to micrometers.⁴² The nanofiber membrane prepared by the electrospinning method has various structural and functional advantages that can be achieved by manipulating the governing factors such as the system, solution, instrumental, and ambient parameters.⁴³ For example, Jiang et al. fabricated hydrophilic polyacrylonitrile (PAN) nanofiber membranes by electrospinning and then coated with a layer of ultra-thin hydrophobic carbon nanotubes on one side to achieve efficient separation of water-in-oil.⁴⁴ The prepared membrane exhibited both satisfactory mechanical and chemical stability. However, the interfacial adhesion between the two membranes should be taken into consideration when using this technique to maintain the stability of the prepared fibers.²⁸

Asymmetric modification

Moreover, asymmetric modification serves as another frequently employed approach for obtaining Janus membranes (Figure 1C). In this method, the entire membrane is initially prepared and subsequently modified on one side to achieve an asymmetric structure. Solution immersion⁴⁵ and single-side electrospraying⁴⁶ are typical examples of this method. Solution immersion is the process of obtaining asymmetrically modified Janus membranes by floating or immobilizing the substrate in an impregnating solution. However, this approach could not control the thickness of the hydrophobic layer in Janus membranes. During the electrospraying process, the liquid filled in the spray gun is atomized by a strong electric field. The thickness of the resultant coating can be precisely modulated by the applied voltage, liquid properties, liquid flow rate, and operating time.^47,48,49 When the membranes are modified, there is no gap between the two sides of the layers but a wettability gradient is exhibited. Overall, the fabrics prepared by the electrospray method have better interface compatibility and higher interface bonding force.

Nevertheless, the diversity of Janus fabrics can be inherently constrained by using only one preparation method. A high-performance micro/nanofibrous material with opposite wettability can be constructed by combining a variety of asymmetric preparation methods. Since Janus membranes are prepared by a traditional polymerization deposition or spraying coating of hydrophilic materials onto the hydrophobic membrane surface, the membrane pores will be severely blocked, leading to a reduction in the membrane’s permeability. A strategy for fabricating a Janus fibrous membrane (FM) with asymmetrical superwettability was proposed to solve this problem, which was fabricated via sequential electrospinning and electrospraying.⁵⁰ The hydrophobic polyvinylidene fluoride (PVDF) fibrous membrane (FM) was fabricated by electrospinning of the as-prepared hybrid PVDF solution and then the superhydrophilic surface layer was obtained by electrospraying polyvinyl alcohol (PVA)/polyacrylic acid (PAA) solution on the membrane surface. This asymmetrical superwettability Janus membrane resulted in the hierarchical roughness and extremely low-surface-energy membrane surface to enhance the antiwetting and antifouling properties for the treatment of hypersaline wastewater. To produce a Janus fibrous membrane with improved properties in breathability, permeability, and directional water transportation, Zhang et al. applied electrospinning and dip-coating modification methods in their study.⁵¹ The single layer of polyacrylonitrile (PAN)/polydopamine (PDA) superhydrophilic membrane was obtained by surface dip-coating modification of the PAN nanofiber membrane. Subsequently, the bi-layered thermoplastic polyurethane (TPU)-PAN/PDA Janus fiber membrane was prepared by the electrospinning of the TPU/N, N-dimethylformamide (DMF) solution on one side of this superhydrophilic fiber membrane, which generates asymmetric thickness and surface energy gradients to enhance moisture-permeable and breathable performance.

Wearable application

Janus textiles with varying wettability can be used for several applications due to their directional biofluid transport features, such as thermal regulation, sweat detection, hemostatic dressings, and wearable protection. As illustrated in Figure 2, sweat collection and sensing are typically employed in personal thermal management and health monitoring, while hemostatic dressings are often employed in advanced wound care. Similarly, their application in wearable protection marks a notable advancement in personal protective equipment (PPE). This section will further explore the unique properties and current applications of Janus textiles, emphasizing their pivotal role in managing and sensing biofluids across various contexts.

Figure 2.

Wearable application of smart Janus textiles with asymmetric wettability, mainly including thermal management textiles, sweat sensors, hemostatic materials, and protective equipment

Thermal management textiles: Reproduced with permission from ref. 56. Copyright 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Sweat sensors: Reproduced with permission from ref. 74. Copyright 2019 American Chemical Society. Hemostatic materials: Reproduced with permission from ref. 78. Copyright 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Protective equipment: Reproduced with permission from ref. 82. Copyright 2022 Wiley-VCH GmbH.

Thermal management textiles: Regulating body temperature and sweat control

Thermal management textiles play a crucial role in personal comfort by balancing the heat exchange between the human body and surrounding environments, especially when managing sweat efficiently.⁵² These textiles are designed with microstructures whose surface wettability is key to determining the liquid transport process and sweat evaporation efficiency. Cotton and similar traditional fabrics are hydrophilic and easily wetted by sweat, which can lead to a wet and sticky sensation. On the other hand, textiles like polyester are hydrophobic, repelling water from both sides and blocking sweat transport from the skin to the outside. The development of thermal management textiles aims to modify the wettability on both sides of the textiles to enhance directional sweat-wicking and evaporation for personal cooling. This has been facilitated by the emergence of Janus membrane technologies, which allow for liquid directional transport due to asymmetric wettability.

Sweat evaporation is an important way of human thermal management. A trilayered textile with Janus wettability was demonstrated to pull out the moisture with the increased capillary from the inner layer to the outer layer (Figure 3A).⁵³ The trilayered fibrous membranes have a wettability gradient, leading to directional moisture transport and inner layer drying, where the transfer layer plays a crucial role during the moisture transfer process. Compared to a bilayered membrane, the trilayered Janus membrane showed higher breakthrough pressure (16.1 cm H₂O) in the reverse direction and a much higher one-way transport index (1021%), indicating enhanced sweat evaporation and human thermal management. Dai et al. designed a hydrophobic polyester (PE) and hydrophilic nitrocellulose (NC) Janus textile with conical micropores for effective thermal management as displayed in Figure 3B.⁵⁴ The hydrophilic conical micropores can rapidly transport and diffuse liquid to the outer surface, which can weaken undesired wet adhesion and heat loss. The Janus PE/NC textile will provide a warmer sensation than the cotton, increasing the textile’s thermal protection.

Figure 3.

The Janus textiles are designed for personal thermal management

(A) The trilayered fibrous membranes with Janus wettability provide a dry and comfortable microclimate for the wearer. Reproduced with permission from ref. 54. Copyright 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

(B) The Janus polyester/nitrocellulose textile transports sweat by asymmetric curvature of conical micropores. Reproduced with permission from ref. 55. Copyright 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

(C) The Janus fabric has smart double bonds, allowing reversible diode-like water transportation and adjustable thermal convection based on temperature changes. Reproduced with permission from ref. 56. Copyright 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

(D) The Janus particles textile exhibits thermal-stimuli wettability responsiveness to dynamically and intelligently construct wettability gradients in different environments. Reproduced with permission from ref. 57. Copyright 2023 Wiley-VCH GmbH.

(E) PU/Si₃N₄-FM is a nanoparticle-embedded material that cools through radiative, conductive, and evaporative heat dissipation. Reproduced with permission from ref. 60. Copyright 2022 American Chemical Society.

An innovative strategy in thermal management involves more than just directional moisture transport. It also encompasses dynamic regulation responsive to ambient temperature changes. Currently, this approach is exemplified by Wang et al.’s development, as illustrated in Figure 3C.⁵⁵ They introduced a double-sided synergetic Janus textile that excels in reversible biofluid transportation, adeptly adapting to temperature fluctuations. This unique capability allows the textile to adjust thermal convection, thereby maintaining optimal personal comfort under various environmental conditions. The outstanding feature of these Janus fabrics lies in their localized, temperature-triggered responses. The polymer networks within the fabric contract or expand in response to temperature changes, altering the surface energy and pore size. This mechanism is pivotal for generating drying and cooling effects, effectively regulating temperature and moisture for the wearer. Yang and colleagues presented a study on thermosensitive amino-silica@PDVB/PNIPAM Janus particles (JPs) as shown in Figure 3D.⁵⁶ These particles are synthesized for use in dynamic fabrics that can transport water directionally in response to temperature changes. When the temperature increases, the fabric becomes hydrophobic, repelling water, and when the temperature decreases, it becomes hydrophilic, absorbing water. This is achieved by the thermosensitive properties of the PNIPAM component in the JPs, which alters its physical state in response to temperature changes, thus enabling the dynamic switch in the fabric’s water transport properties. Two sides of the fabrics can construct the wettability gradient dynamically in different environments for sweat-wicking clothes.

In addition to sweat evaporation, the following key mechanisms control human thermal homeostasis: convection, conduction, and radiation.^57,58 These processes work together to dissipate heat from the body, helping to regulate temperature in varying environmental conditions. Based on integrated requirements, Miao et al. introduced an innovative textile designed for all-day personal cooling (Figure 3E).⁵⁹ It achieves this by integrating Janus wettability with efficient heat conduction in a hierarchically structured polyurethane/silicon nitride fibrous membrane (PU/Si₃N₄-FM). The textile is created using a scalable electrospinning method combined with a single-side hydrophilic plasma treatment. This process generates a fibrous membrane composed of polyurethane and silicon nitride, enabling efficient moisture management and directional water transport. The incorporation of silicon nitride, known for its high thermal conductivity, enhances the heat conduction properties of the textile. Furthermore, PU/Si₃N₄-FM shows its superior radiative cooling performance in both the daytime and nighttime. The ingenious combination of selective optical cooling and wick-evaporation cooling was also achieved in another Janus fabric.⁶⁰ It uses materials with high reflectivity in the visible light spectrum to reflect sunlight, while also being highly emissive in the infrared range to effectively emit body heat. Additionally, the fabric’s hierarchical structure is designed to enhance moisture absorption and evaporation, leveraging the cooling effect of evaporative heat loss. This multi-layered, strategic design allows the fabric to provide efficient thermal management, particularly in hot conditions.

Efficient sweat sensors: Sweat analysis and health monitoring

Textile-based sweat sensors, a key component in personalized healthcare, are adept at providing crucial insights for personal health monitoring and disease prevention by monitoring biomarkers in sweat, including electrolytes, metabolites, and hormones.^61,62 A major challenge with these sensors is ensuring user comfort during long-term wear, which heavily depends on the device’s design and material selection. Addressing this issue, Janus fabric, as explored in this article, presents several advantages for effective sweat monitoring. Its innovative design features a dual-sided structure with one side being superhydrophobic (water-repelling) and the other superhydrophilic (water-attracting), which enhances sweat capture and transport. This unique combination allows efficient separation and directed movement of sweat toward the sensor area, making Janus fabric a highly effective material for non-invasive, continuous monitoring of sweat composition, thereby providing valuable health insights.

Electrochemical sweat sensing

Electrochemical sweat sensing has emerged as a noninvasive, efficient health monitoring method. By analyzing sweat composition, this technology translates chemical data into electrical signals for precise analysis.^63,64 Traditional fabrics used in sweat sensing faced challenges in sweat management and comfort. Recent developments aim to create an optimal skin microenvironment, which is crucial for user comfort and accurate physiological monitoring.

Developed in 2020, a Janus-wettable textile band displayed in Figure 4A was fabricated by electrospinning a hydrophobic nanofiber array onto the gauze.⁶⁵ This unique textile technology combines hydrophobic polyurethane nanofiber arrays with super hydrophilic yarns, allowing efficient collection and guidance of sweat from the skin to the electrode surface for electrochemical biomarker detection. This design not only ensures effective sweat collection and transfer but also maintains physiological comfort during wear. Later, Li et al. developed a Janus nano-processed electronic textile (JNET) with optimized optical properties and wettability (Figure 4B).⁶⁶ This efficiently regulates heat and moisture, promoting a cooler and drier skin microenvironment. Furthermore, they incorporated fiber electrodes into the e-textile for the noninvasive tracking of sweat biomarkers, offering improved comfort and precise biofluid analysis.

Figure 4.

The Janus textiles allow for electrochemical sweat sensing

(A) Design of the integrated smart bands for self-pumping sweat sampling and electrochemical sensing. Reproduced with permission from ref. 66. Copyright 2020 American Chemical Society.

(B) The design of the Janus e-textile with optimized optical properties and wettability is developed for comfortable biofluid monitoring. Reproduced with permission from ref. 67. Copyright 2023 Elsevier B.V.

(C) Janus water-diode membrane with asymmetric surface wettability. Reproduced with permission from ref. 68. Copyright 2021 Elsevier Inc.

(D) The hybrid Janus membrane with dual-asymmetry integration of wettability and conductivity. Reproduced with permission from ref. 69. Copyright 2022 American Chemical Society.

(E) Janus silk e-textile for efficient biofluid monitoring. Reproduced with permission from ref. 70. Copyright 2021 American Chemical Society.

Another challenge of electrochemical sweat sensing is to achieve micro-volume and high-sensitivity detection. In 2021, as shown in Figure 4C, a porous polyethersulfone membrane exhibited dynamic transport of micro-volume liquid with the Janus membrane prepared by dip-coating and roller-assisted liquid printing.⁶⁷ This unique characteristic allows for diode-like water permeability and focused transmembrane transport, enhancing the detection signal in biosensing applications like glucose detection. After that, they reported a hybrid Janus membrane through a specialized fabrication method, which improves upon the previous research by incorporating dual asymmetry in wettability and conductivity (Figure 4D).⁶⁸ This advancement enables more effective handling and analysis of ultra-low-volume sweat. The membrane’s advanced features, including unidirectional liquid transport, higher breakthrough pressure, rapid self-pumping rate, and improved flexible conductivity, provide superior real-time analysis of sweat in wearable biosensors, improving health monitoring and diagnostics.

Rapid response time is vital in healthcare for real-time physiological monitoring. To address this need, He et al. developed a Janus electronic textile (e-textile) for noninvasive analysis with a faster response time and less required liquid volume, preventing wet sticking as displayed in Figure 4E.⁶⁹ This e-textile incorporates silk yarn electrodes woven into its hydrophilic side. The specific design of the textile enhances its ability to quickly absorb and transport sweat due to the natural properties of silk. This efficient sweat management allows for rapid detection and analysis of biofluids, contributing to faster response time in monitoring and sensing applications. Meanwhile, faster response time and less required liquid volume minimize the potential for sample degradation or evaporation, allowing for more efficient data collection and analysis.

Overall, the Janus fabric-based sensor offers amounts of solutions for achieving efficient sweat collection by utilizing its unique properties and design to facilitate the transfer and analysis of sweat components.

Colorimetric sweat sensing

Colorimetric sweat sensing is a method that analyzes the composition of sweat by measuring color changes, and accurately quantifying the analytes present.⁷⁰ However, a challenge arises as colorimetric reagents can easily detach from their carrier, leading to the reagent backflowing onto the skin, causing contamination. One solution to this issue is the use of microfluidic chips, but these designs are complex and costly.^71,72

Recently, the use of Janus fabric in colorimetric sweat sensing has been extensively explored. As shown in Figure 5A, He et al. designed and prepared the superwettable colorimetric sensing bands for sweat sampling and analysis.⁷³ The band combines superhydrophobic-superhydrophilic microarrays with nano-dendritic colorimetric biosensors. These microarrays enable precise control of sweat droplet formation and positioning, ensuring that the droplets are confined to specific superhydrophilic areas. This targeted confinement enhances the accuracy and efficiency of the sensing process, as it allows for better interaction between the sweat and the biosensors. Additionally, the superhydrophobic background minimizes cross-contamination and interference from external factors, leading to more reliable and sensitive detection of analytes in sweat.

Figure 5.

The Janus textiles are designed for colorimetric sweat sensing

(A) The Janus bands, consisting of a superhydrophobic coating, superhydrophilic microwells, and an adhesive layer, enable sweat sampling and monitoring for multiplex target analysis. Reproduced with permission from ref. 74. Copyright 2019 American Chemical Society.

(B) The Janus fabric, designed for unidirectional sweat sampling and skin-friendly colorimetric detection, is utilized alongside pristine fabric in residual and colorimetric reagent detection. Reproduced with permission from ref. 75. Copyright 2023 Elsevier B.V.

Another investigation was made by Xi et al., who synthesized a Janus fabric using electrospinning polyurethane (PU) technology (Figure 5B).⁷⁴ This fabric’s directional sweat-wicking performance not only aids in adequate sweat sampling but also prevents the backflow of colorimetric reagents toward the skin, reducing potential epidermal contamination and irritation. The Janus colorimetric fabric enhances skin safety and ensures the continuity of epidermal sweat sampling. Researchers have successfully utilized this fabric for the visual and portable detection of sweat biomarkers, including chloride, pH, and urea.

Hemostatic materials: Wound healing and bleeding control

Efficient management of bleeding is crucial in saving lives. Compared to other materials, cotton gauze is the most commonly used in hemostatic dressing due to its low skin irritation, softness, breathability, and affordability. However, it primarily adsorbs water from the blood to achieve coagulation. This process can lead to significant blood loss, as cotton gauze neither enhances platelet activation nor promotes clot formation.

To tackle this issue, Zhu et al. proposed a hemostatic Janus gauze that hastens coagulation by exploiting the superhydrophilic section of the Janus to absorb blood water, while the superhydrophobic portion obstructs further penetration of blood.⁷⁵ And the Janus fabrics have a bloodstain-free and dry outer layer, blocking the pathway for bacteria to the wound and reducing the risk of infection. As shown in Figure 6A, compared to standard hemostatic fabrics, Janus fabric significantly reduces blood loss and extends survival time in animal models. Similarly, Wang et al. demonstrated that a cotton-based Janus fabric provided effective hemostasis by promoting clot formation and controlling blood absorption.⁷⁶

Figure 6.

The Janus textiles are designed for hemostatic dressing

(A) The Janus fabrics with hemostatic performances in different animal models. Reproduced with permission from ref. 76. Copyright 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

(B) The Janus sponges with effective bleeding control. Reproduced with permission from ref. 78. Copyright 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

(C) The Janus cellulose-based dressings with pH-responsive properties for diabetic wound care. Reproduced with permission from ref. 79. Copyright 2023 Wiley-VCH GmbH.

(D) The Janus membrane with blood clotting, wet tissue adhesion, and anti-infection. Reproduced with permission from ref. 80. Copyright 2023 Elsevier B.V.

Innovations extend to hybrid materials like cellulose, offering robust mechanical properties and biodegradability. Cheng et al. developed a sponge with Janus character, which is achieved by incorporating chitosan into the cellulose nanofiber (CNF) matrix, as seen in Figure 6B.⁷⁷ Chitosan, a natural biopolymer known for its antimicrobial properties, is blended with the CNFs during the sponge preparation process. The hybrid sponges integrated the hemostatic property of chitosan with the physical barrier of Janus wettability, achieving effective bleeding control with nearly 50% less blood loss. For diabetic wounds, which are more prone to infection, Xu’s group proposed cellulose-based pH-responsive Janus dressings composed of a hydrophilic spinning layer (cellulose-anthocyanin, Cell-An) and a hydrophobic electrospun layer (polycaprolactone chlorhexidine, PCL-Ch) for diabetic wound care.⁷⁸ The pH-detection functionality in the Janus dressing is added for monitoring the healing progress of diabetic wounds. By integrating pH sensitivity, the dressing changes color in response to pH variations, allowing for a non-invasive and real-time assessment of wound condition. These multifunctional Janus dressings, with rapid moisture-draining and non-adhesive characteristics, are effective against bacterial proliferation and diabetic wound infection, as demonstrated in Figure 6C.

Traditional hemostatic bandages with fibrous membranes struggle with adhering effectively to the wound site. Inspired by Collocalia birds’ nest-building technique, Chao et al. introduced a biomimetic Janus-structured bandage, as shown in Figure 6D.⁷⁹ This innovative bandage integrates self-gelling powders with nanofibers to create a dual-function membrane. Its asymmetric wettability features a hydrophilic side for enhancing blood coagulation and a hydrophobic side for antibacterial protection. Crucially, the bandage forms a cohesive, adherent layer upon contact with wet tissue, ensuring secure wound sealing and strong adhesion. Compared to medical gauze and gelatin hemostatic sponges, the Janus fabric reduces hemostasis time to 1/5 (1.16 ± 0.28 min) and blood loss to 1/3 (111 ± 11 mg). Therefore, the bandage shows strong wet tissue adhesion, rapid blood coagulation, and effective sealing of wounds, demonstrating potential as a new material for hemostasis and wound care.

Protective equipment: Advanced protective barrier and vapor transmission

Increasing air pollution has necessitated the use of PPE such as masks.⁷ Traditional masks, however, fall short in efficiently transmitting water vapor and blocking harmful microorganisms. This can result in discomfort, particularly for those wearing glasses, as exhaled moisture accumulates inside the mask. Xu et al. developed a Janus nanofibrous porous mask.⁸⁰ This membrane is tailored for particulate matter (PM) filtration, volatile organic compound (VOC) adsorption, and moisture control. The water vapor or condensed water droplets exhaled by the human body could penetrate the membranes from hydrophobic sides to hydrophilic sides, and then be directed to the outside of the mask to reduce the uncomfortable feeling of dampness, as demonstrated in Figure 7A. Moreover, the unique structure of the nanofibers and their arrangement within the membrane contribute to their high filtration efficiency. The membranes capture and remove airborne particles, thereby purifying the air that passes through them.

Figure 7.

The Janus textiles are designed for wearable protection

(A) Janus nanofibrous porous membranes are used to filter particulate matter and adsorb volatile organic compounds. Reproduced with permission from ref. 81. Copyright 2021 American Chemical Society.

(B) Janus microsphere membranes are designed for filtration of particulate matter, directional transfer of water vapor, and high-efficiency broad-spectrum sterilization. Reproduced with permission from ref. 82. Copyright 2022 Wiley-VCH GmbH.

The pandemics of highly infectious diseases like COVID-19 have further increased the demand for PPE. Deng and colleagues made Janus masks by laminating the microsphere membrane on the cotton fiber substrate after quenching crystallization (Figure 7B).⁸¹ Janus microsphere membranes enhanced the water vapor transmission rate by more than 20% compared to monolayer hydrophobic microsphere membranes. Additionally, these masks incorporate halicin, a potent antibiotic, into the microspheres, providing broad-spectrum bactericidal properties. The Janus microsphere technology holds promise beyond masks, with potential applications in protective suits and multifunctional filters. Its unique combination of moisture control, filtration efficiency, and sterilization capabilities marks a significant advancement in wearable protective products.

Conclusions and outlook

In this review, we highlighted the significant progress in smart Janus textiles with asymmetric wettability, including the design and fabrication of Janus textiles and the development of the various functions of wearable devices based on Janus textiles for wearable applications. These textiles have revolutionized wearable devices with their dual-sided structure, enabling efficient directional transport of fluids like sweat, thus enhancing moisture wicking and evaporation. This is a stark contrast to traditional materials, which often struggle with efficient moisture management, making Janus textiles superior for maintaining an optimal microclimate next to the skin. In applications such as sweat sensors and wound dressings, Janus textiles excel in actively pumping and confining biofluids. This is a notable advancement over conventional materials, as it significantly improves detection accuracy and biosafety. Furthermore, their use in protective equipment like masks and gloves, leveraging moisture permeability and broad-spectrum antimicrobial features, is unparalleled in current technologies.

However, further research is required to address limitations in durability, skin biocompatibility, and scalable manufacturing which currently constrain the widespread adoption of Janus textiles. Specifically, the long-term robustness and abrasion resistance need evaluation for sustained use in daily wearables. Testing skin irritation and allergies from extended skin contact will also be vital for patient safety. In terms of production scalability, transitioning from lab-based fabrication to industrial-scale manufacturing could facilitate the integration of Janus textiles into commercial products.

Moving forward, new dynamic Janus textiles with responsive surface properties that automatically adapt to ambient conditions show great potential in smart garments. Additionally, advanced materials like nanocelluloses, hydrogels, and MXenes can equip Janus textiles with auxiliary functionalities like self-healing ability, electrical conductivity, and antimicrobial activity. Three-dimensional (3D) printing could also contribute to more complex asymmetric structures beyond flat membranes. Such multifunctional smart Janus textiles through hierarchical design have expansive applications from humidity-regulating textiles, to wound monitoring platforms, to extreme environment gear. Despite existing limitations, Janus textiles’ unique anisotropic fluid transport capabilities make them an extremely versatile and disruptive platform for next-generation biofluid management and healthcare technologies. Addressing current challenges through interdisciplinary efforts will help advance Janus textiles from proof-of-concept studies toward real-world implementation.

Limitations of the study

This review only focuses on textile-based biofluid management, employing Janus wettability. Various other materials not covered in this review could offer differing results and insights into the management of biofluids. The exclusion of these alternative materials signifies a limitation of our study, suggesting an avenue for future research to explore a broader spectrum of solutions beyond textiles.