Design of Nanofibrous and Microfibrous Channels for Fast Capillary Flow

The Fastest Capillary Flow in Root-like Networks under Gravity

Capillary flow has garnered significant attention due to its unique dynamic characteristics that require no external force. Creating a quantitative analytical model to evaluate capillary flow behaviors in root-like networks is essential for enhancing fluid control properties in functional textiles. In this study, we explore the capillary dynamics within root-like networks under the influence of gravity and derive the most rapid capillary flow via structural optimization. The flow time in a capillary is dominated by the capillary pressure, viscous pressure loss, and gravity, each of which exhibits diverse sensitivities to the structures of root-like networks. We scrutinize various structural parameters to understand their impact on capillary flow in root-like networks. Subsequently, optimal structural parameters (namely, the mother tube diameter and diameter ratio) are identified to minimize capillary flow time. Moreover, we discovered that the correlation between flow time and distance for capillary flow in root-like networks does not obey the classical Lucas-Washburn equation. These results affirm that root-like networks can enhance capillary flow, providing critical insights for numerous capillary-flow-dependent engineering applications.

Psoralea corylifolia formula extract-loaded silk fibroin/polycaprolactone fibrous membrane for the treatment of colorectal cancer

Intestinal obstructions caused by intestinal tumors pose life-threatening risks to patients. Adjuvant treatment using intestinal stents carrying drug loaded membranes has the advantages of timely relief of intestinal obstruction, as well as effective inhibition of tumor progression. The present work is to develop an intestinal stent loaded with a combination of traditional Chinese medicines capable of good biocompatibility, degradability, sustained drug release and anti-tumor properties. The drug combination extract was obtained from Psoralea corylifolia formula (PCF) and then was loaded into silk fibroin (SF)/polycaprolactone (PCL) fibrous membranes using emulsion electrospinning technology. Results showed that the membrane prepared by emulsion electrospinning technology has apparent core-shell structure, and the mechanical property and hydrophilicity of the membrane are gradually improved with the addition of PCF. Drug sustained release results demonstrated that there were no bursting phenomena, and showed a gradual sustained release up to 400 h. The antitumor efficacy was assessed in vitro using a human colorectal cancer cell line HCT-116 and an epithelial cell line NCM-460. Results showed that this drug-loaded membrane sustained antitumor cell growth performance, indicating its great potential for clinical treatment for intestinal cancer in the near future.

Capillary rise behavior of lubricant in micropores with spiral bulge structures

The highly efficient exudation of lubricant in porous self-lubricating materials significantly influences the formation of self-lubricating films. In this paper, micropores with inner spiral bulge structures are considered, and their influence on the capillary behaviors of the lubricant is discussed to reveal the capillary rising mechanism. The results show that the Taylor capillary lift phenomenon is produced in the spiral bulge structure of the micropore, and the capillary lift force is enhanced. The spiral structure decreases the effective diameter of micropores. The magnitudes of the pressure and velocity in the spiral structure pores are larger than those in smooth pores. The liquid in the upper part of the micropores forms a velocity vortex during its upward rotation along the spiral channel, which promotes the capillary rising behavior. For smaller pitches, the velocity vortex increases, and the rising speed of the lubricant grows. The inner spiral bulge structure gives the micropores an excellent capillary rising ability. The quantitative characterization and mechanism reveal that the capillary rising behavior can be used to guide the bionic designs of pores in self-lubricating materials.

A self-floating and integrated bionic mushroom for highly efficient solar steam generation

Solar desalination is considered as a promising approach to solve the shortage of fresh water resources. In this work, inspired by the transpiration of trees, a self-floating and integrated bionic mushroom solar steam generator (BMSSG) is proposed for highly efficient water evaporation. A wooden strip is used to mimic the stipe of the mushroom for water transportation, meanwhile polyvinyl alcohol (PVA) modified graphene aerogels (GA) is used to imitate the pileus of the mushroom for photothermal conversion. After optimizing compositions of the aerogel and sizes of the wooden strip, a high evaporation rate of 1.67 kg m^-2h^-1 is obtained, outcompeting most of other wood-based evaporators. Compared to traditional interfacial evaporation devices, BMSSG is an integrated structure without a thermal insulation layer and an absorbent wick, which not only increases the compactness that is good for stability and reliability, but also reduces the manufacturing cost. Moreover, the BMSSG can self-float on the water like a roly-poly. These advantages indicate that BMSSG will play a significant role in seawater desalination. The feasibility as well as stability and recyclability of the BMSSG for seawater desalination are demonstrated. This bioinspired design provides a low-cost and scalable SSG, which will have a profound impact in future practical applications.

Fabric-based in situ synthesis of gold nanoparticles for continuous enhanced heterogeneous chemiluminescence online detection of carbon dioxide

A novel method to achieve real-time and long-term continuous measurement of CO2 based on in situ synthesis of AuNPs on fabrics is reported. A heterogeneous CO2 detection method and the application of continuous catalytic chemiluminescence immobilized by nanoparticles were also developed.

Pumpless three-dimensional photo paper-based microfluidic analytical device for automatic detection of thioredoxin-1 using enzyme-linked immunosorbent assay

Microfluidic-based biosensors have been developed for their precise automatic reaction control. However, these biosensors require external devices that are difficult to transport and use. To overcome this disadvantage, our group made an easy-to-use, cheap, and light pumpless three-dimensional photo paper-based microfluidic analytical device (3D-μPAD; weight: 1.5 g). Unlike conventional paper-based microfluidic analytical devices, the 3D-μPAD can be used to control fluid flow in a 3D manner, thus allowing sophisticated multi-step reaction control. This device can control fluid flow speed and direction accurately using only the capillary-driven flow without an external device like a pump. The flow speed is controlled by the width of the microfluidic channel and its surface property. In addition, fluid speed control and 3D-bridge structure enable the control of fluid flow direction. Using these methods, multi-step enzyme-linked immunosorbent assay (ELISA) can be done automatically in sequence by injecting solutions (sample, washing, and enzyme's substrate) at the same time in the 3D-μPAD. All the steps can be performed in 14 min, and data can be analyzed immediately. To test this device, thioredoxin-1 (Trx-1), a biomarker of breast cancer, is used as the target. In the 3D-μPAD, it can detect 0-200 ng/mL of Trx-1, and the prepared 3D-μPAD Trx-1 sensor displays excellent selectivity. Moreover, by analyzing the concentration of Trx-1 in real patients and healthy individuals' blood serum samples using the 3D-μPAD, and comparing results to ELISA, it can be confirmed that the 3D-μPAD is a good tool for cancer diagnosis.

Intelligent Polymers, Fibers and Applications

Intelligent materials, also known as smart materials, are capable of reacting to various external stimuli or environmental changes by rearranging their structure at a molecular level and adapting functionality accordingly. The initial concept of the intelligence of a material originated from the natural biological system, following the sensing–reacting–learning mechanism. The dynamic and adaptive nature, along with the immediate responsiveness, of the polymer- and fiber-based smart materials have increased their global demand in both academia and industry. In this manuscript, the most recent progress in smart materials with various features is reviewed with a focus on their applications in diverse fields. Moreover, their performance and working mechanisms, based on different physical, chemical and biological stimuli, such as temperature, electric and magnetic field, deformation, pH and enzymes, are summarized. Finally, the study is concluded by highlighting the existing challenges and future opportunities in the field of intelligent materials.

Electrical Resistance of Stainless Steel/Polyester Blended Knitted Fabrics for Application to Measure Sweat Quantity

Skin wetness and body water loss are important indexes to reflect the heat strain of the human body. According to ISO 7933 2004, the skin wetness and sweat rate are calculated by the evaporative heat flow and the maximum evaporative heat flow in the skin surface, etc. This work proposes the soft textile-based sensor, which was knitted by stainless steel/polyester blended yarn on the flat knitting machine. It investigated the relationship between electrical resistance in the weft/warp directions and different water absorption ratio (0-70%), different sample size (2 cm × 2 cm, 2 cm × 4 cm, 2 cm × 6 cm and 2 cm × 8 cm). The hydrophilic treatment effectively improved the water absorption ratio increasing from 40% to 70%. The weft and warp direction exhibited different electrical behaviors when under dry and wet conditions. It suggested the weft direction of knitted fabrics was recommended for detecting the electrical resistance due to its stable sensitivity and linearity performance. It could be used as a flexible sensor integrated into a garment for measuring the skin wetness and sweat rate in the future instead of traditional measurements.

Bioinspired textile with dual-stimuli responsive wettability for body moisture management and signal expression

A smart bioinspired loofah textile with biosafe wettability shows high directional liquid transport capacity and the ability to identify liquids with different pH values.

Analysis of Capillary Flow in a Parallel Microchannel-Based Wick Structure with Circular and Noncircular Geometries

Capillary flow in porous media is of great significance to many different applications including microfluidics, chromatography, and passive thermal management. For example, heat pipe has been widely used in the thermal management of electronic system due to its high flexibility and low thermal resistance. However, the critical heat flux of heat pipe is often limited by the maximum capillary-driven liquid transport rate through the wicking material. A significant number of novel porous material with complex structures have been proposed in past studies to provide enhanced capillary-driven flow without substantial reduction in pore size and porosity. However, the increasing level of structural complexity often leads to a more tortuous flow path, which deprives the merits of enhanced capillarity. In this study, we examined the capillary performance of a porous material with simple geometric structures both analytically and numerically. Specifically, the capillary rate of rise of water in parallel hollow microchannels with different cross-sectional shapes is derived by solving the momentum transport equation. The relationships between the capillary flow rate and wicking height are further validated by two-phase flow simulation based on the conservative level-set method. The results demonstrate that parallel microchannel configuration, despite its geometric simplicity, provides superior capillary performance than most existing porous media in terms of both capillary flow rate and ultimate wicking height. In addition, design of noncircular cross section reduces the viscous drag and increases the packing density of the microchannels in the bulk solid without affecting the capillary pumping pressure. These features contribute to a further enhancement in the capillary performance by up to 32%. These results provide important guidance to the rational design of porous material with enhanced fluid transport property in a variety of microfluidic systems.

Microfluidic Behavior of Alumina Nanotube-Based Pathways within Hydrophobic CNT Barriers

The use of porous micro-and nanostructured materials within microfluidic devices results in unique fluid transport characteristics. In this paper, we investigate the microfluidic behavior of hybrid alumina nanotube-based pathways within the hydrophobic carbon nanotube (CNT) barriers. These hybrid systems provide unique benefits for potential liquid transport control in porous structures with real-time sensing of fluids. In particular, we examine how the alignment of the alumina nanostructures with high internal porosity enables increased capillary action and sensitivity of detection. Based on the Lucas and Washburn model (LW) and the modified LW models, the microfluidic behavior of these systems is detailed. The time exponent prediction from the models for capillary transport in porous media is determined to be ≤0.5. The experimental results demonstrate that the average capillary rise in the nanostructured media driven by a capillary force follows t^0.7. The hydrophilic/electrically insulating and hydrophobic/electrically conductive patterned structures of the device are used for electronic measurements within the microfluidic channels. The device structure enables the detection of fluid samples of very low analyte concentrations (1 μM) that can be achieved due to the very high surface area of the hybrid structure combined with the electrical conductivity of the CNT support structure.

A Flexible Method for Nanofiber-based 3D Microfluidic Device Fabrication for Water Quality Monitoring

Water pollution seriously affects human health. Accurate and rapid detection and timely treatment of toxic substances in water are urgently needed. A stacked multilayer electrostatic printing technique was developed for making nanofiber-based microfluidic chips for water-quality testing. Nanofiber membrane matrix structures for microfluidic devices were fabricated by electrospinning. A hydrophobic barrier was then printed through electrostatic wax printing. This process was repeatedly performed to create three-dimensional nanofiber-based microfluidic analysis devices (3D-µNMADs). Flexible printing enabled one-step fabrication without the need for additional alignment or adhesive bonding. Practical applications of 3D-µNMADs include a colorimetric platform to quantitatively detect iron ion concentrations in water. There is also great potential for personalized point-of-care testing. Overall, the devices offer simple fabrication processes, flexible prototyping, potential for mass production, and multi-material integration.

Gravity Drawing of Micro- and Nanofibers for Additive Manufacturing of Well-Organized 3D-Nanostructured Scaffolds

This work introduces a gravity fiber drawing (GFD) method of making single filament nanofibers from polymer solutions and precise alignment of the fibers in 3D scaffolds. This method is advantageous for nanofiber 3D alignment in contrast to other known methods. GFD provides a technology for the fabrication of freestanding filament nanofibers of well-controlled diameter, draw ratio, and 3D organization with controllable spacing and angular orientation between nanofibers. The GFD method is capable of fabricating complex 3D scaffolds combining fibers with different diameters, chemical compositions, mechanical properties, angular orientations, and multilayer structures in the same construct. The scaffold porosity can be as high as 99% to secure transport of nutrients and space for cell infiltration and differentiation in tissue engineering and 3D cell culture applications.

Wettability Control in Tree Structure-Based 1D Fiber Assemblies for Moisture Wicking Functionality

One of the fundamental properties of natural systems is their water transport ability, and living systems have efficient moisture management features. Here, a unique structure, inspired by the water transfer behavior in trees, was designed for one-dimensional (1D) fiber assemblies. In this 1D fiber assembly structure, a differential capillary effect enabling rapid water transfer at the interface between traditional cotton fibers and electrospun nanofibers was explored. A tree-like structure yarn was constructed successfully by novel electrospinning technology, and the effect was quantitatively controlled by precisely regulating the fibers' wettability. Fabrics based on these tree-like core-spun yarns possessed advanced moisture-wicking performance, a high one-way transport index (R) of 1034.5%, and a desirable overall moisture management capability of 0.88, which are over two times higher than those of conventional fabrics. This moisture-wicking regime endowed these 1D fiber assemblies with unique water transfer channels, providing a new strategy for moisture-heat transmission, microfluidics, and biosensor applications.

Biomimetic Fibrous Murray Membranes with Ultrafast Water Transport and Evaporation for Smart Moisture-Wicking Fabrics

Both antigravity directional water transport and ultrafast evaporation are critical to achieving a high-performance moisture-wicking fabric. The transpiration in vascular plants possess both of these features, which is due to their optimized hierarchical structure composed of multibranching porous networks following Murray's law. However, it remains a great challenge to simultaneously realize the ultrafast water transport and evaporation by mimicking nature's Murray networks in the synthetic materials. Here, we report a synergistic assembly strategy to create a biomimetic micro- and nanofibrous membrane with antigravity directional water transport and quick-dry performance by combining a multibranching porous structure and surface energy gradient, overcoming previous limitations. The resulting fiber-based porous Murray membranes exhibit an ultrahigh one-way transport capability ( R) of 1245%, a desired overall moisture management capability (OMMC) of 0.94, and an outstanding water evaporation rate of 0.67 g h^-1 (5.8 and 2.1 times higher than the cotton fabric and Coolmax fabric, respectively). Overall, the successful synthesis of these biomimetic porous Murray membranes should serve as a source of inspiration for the development of moisture-wicking technologies, providing personal comfort in hot or humid environments.

Continuous, Spontaneous, and Directional Water Transport in the Trilayered Fibrous Membranes for Functional Moisture Wicking Textiles

Directional water transport is a predominant part of functional textiles used for continuous sweat release in daily life. However, it has remained a great challenge to design such textiles which ensure continuous directional water transport and superior prevention of water penetration in the reverse direction. Here, a scalable strategy is reported to create trilayered fibrous membranes with progressive wettability by introducing a transfer layer, which can guide the directional water transport continuously and spontaneously, thus preventing the skin from being rewetted. The resulting trilayered fibrous membranes exhibit a high one-way transport index R (1021%) and a desired breakthrough pressure (16.1 cm H₂ O) in the reverse direction, indicating an ultrahigh directional water transport capacity. Moreover, on the basis of water transport behavior, a plausible mechanism is proposed to provide insight into the integrative and cooperative driving forces at the interfaces of trilayered hydrophobic/transfer/superhydrophilic fibrous membranes. The successful synthesis of such fascinating materials would be valuable for the design of functional textiles with directional water transport properties for personal drying applications.