Abstract:
This invention includes the implementation of several unconventional droplet manipulations on a superhydrophobic-patterned surface microfluidic platform, which may be applied to automated biological analyzes and point-of-care diagnostic applications.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional patent application Ser. No. 61/780,268 filed on Mar. 13, 2013, incorporated herein by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with Government support under 0846502, awarded by the National Science Foundation. The Government has certain rights in the invention. 
    
    
     INCORPORATION-BY-REFERENCE OF COMPUTER PROGRAM APPENDIX 
     Not Applicable 
     NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains generally to a superhydrophobic textile, and more particularly to a micropatterned superhydrophobic textile for biofluidic transport. 
     2. Description of Related Art 
     Microfluidics has gained increasing popularity in the handling, transporting, and analyzing of minute volumes of biological and chemical fluids. Open-surface and interfacial microfluidics, where one or more gas-liquid interfaces exist as a boundary condition, are emerging directions in microfluidics from which several new and flexible operations have been established, including self-propelled motion, three-dimensional connectivity, open sample accessibility, direct reactivity and readability, in addition to conventional microflow manipulations. Specifically, paper-based testing strips, employing the capillarity force (also known as wicking force) generated by the microscopic fibrous/porous structures within the substrate, have been considered as the early historic implementation of interfacial microfluidics which are widely used in pH value indication and pregnancy testing. 
     The latest development of the concept of lab-on-a-paper has enabled biochemical assaying on multilayer micropatterned paper substrates fabricated by a simple printing process that form three-dimensional flow networks for multiplexed biochemical analyses (e.g., glucose, urine, and pH). In conjunction with conductive ink printing, this group has also successfully demonstrated quantitative electrochemical analysis on the paper-based devices by measuring the concentrations of heavy metal ions and glucose molecules. 
     More recently, the interfacial microfluidic concept has been extended to textile-based structures and surfaces (e.g., yarns and fabrics). Textile-based microfluidics utilize a similar wicking force as seen in paper that is produced by hydrophilic yarns (e.g., cotton yarns) to direct biological reagents along the fibrous structure which affords the aforementioned operational capacities of interfacial microfluidics while providing a low-cost and scalable solution based on well-established, traditional textile manufacturing techniques such as automatic weaving, knotting, and stitching. In particular, basic microfluidic functions, including pumping, mixing, separation, and networking, have been recently demonstrated on knotted yarn structures. Although the current development of capillarity-enabled interfacial microfluidics holds great promise to biofluidic manipulation, its intrinsically driven mechanism continues to be a major challenge for continuous and facilitated biofluidic transport. For instance, an external fluidic driver (e.g., capillary or syringe pumps) still remains necessary to provide continuous flow on the fabric network. 
     Competitive fabrics, featuring quick drying, such as CoolMax, utilize polyester fibers with irregular cross-sections to wick liquid from the surface of human skin and to spread the liquid to enhance evaporation. The only driving force is still capillary force, which diminishes when lots of liquid wets the surface. Once the textile is wetted with sweat, the gas permeability decreases and the weight increases. Moreover, the evaporation of the sweat is highly affected by the environmental humidity. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, the latest efforts for implementing surface tension-driven flow on the interfacial microfluidics have enabled a new approach to automated microflow operations. By harvesting Laplace pressure gradients from various sizes of liquid droplets, self-propelled flow in an open-channel configuration was achieved. Importantly, a surface tension-driven micropump can be achieved simply by lithographically defining hydrophilic flow paths on a superhydrophobic substrate to provide extensive pumping capacity, flexible pumping rates, as well as bidirectional control. 
     Textile-enabled interfacial microfluidics, utilizing fibrous hydrophilic yarns (e.g., cotton) to guide biological reagent flows, has been extended to various biochemical analyses recently. The restricted capillary-driving mechanism, however, persists to be a major challenge for continuous and facilitated biofluidic transport. In the subject invention, a novel interfacial microfluidic transport principle is described to drive three-dimensional liquid flows on a micropatterned superhydrophobic textile (MST) platform in a more autonomous and controllable manner. 
     Specifically, the MST system utilizes the surface tension-induced Laplace pressure to facilitate the liquid&#39;s motion along the hydrophilic yarn, in addition to the capillarity present in the fibrous structure. The fabrication of MST is accomplished by simply stitching hydrophilic cotton yarn into a superhydrophobic fabric substrate (contact angle 140±3°), from which well-controlled wetting patterns are established for interfacial microfluidic operations. The geometric configurations of the stitched micropatterns, e.g., the lengths and diameters of the yarn and bundled arrangement, can all influence the transport process. The surface tension-induced pressure as well as pumping speed can be highly controllable by the sizes of the stitching patterns of hydrophilic yarns and the confined liquid volume. The MST can be potentially applied to large volume and continuous biofluidic collection and removal. 
     Two operation modes, discrete and continuous transports, are also provided. In addition, the gravitational effect and the droplet removal process have also been considered and quantitatively analyzed during the transport process. In one embodiment, an MST design has been implemented on an artificial skin surface to collect and remove sweat in a highly efficient and facilitated means. The results have illustrated that the novel interfacial transport on the textile platform can be extended to a variety of biofluidic collection and removal applications. 
     This invention provides a new mechanism for removing liquid from the skin&#39;s surface by surface tension and merging of droplets. This mechanism stabilizes the transport rate that will not be affected by the moisture level of the fabric or environmental humidity. The superhydrophobic property of the fabric ensures the dryness of most of the skin&#39;s surface area and excellent air permeability. Moreover, since the liquid is not absorbed by most regions of the textile, the weight of the fabric remains light during the perspiration process. Additional features such as self-cleaning and waterproofing are also not available in former functional fabrics. 
     By way of example and not by limitation, the subject invention includes a novel type of textile that is able to transport sweat on the skin&#39;s surface to the outer sides of the fabric, where the liquid collects and drips off. The textile utilizes interfacial microfluidic principles and implements liquid transport spontaneously by micropatterns on the surface of superhydrophobic fabric. Embodiments of the invention provide a new dimension of transport to the textiles using surface tension force, in addition to the intrinsic capillary force in hydrophilic fibers. Several new features are present in this invention. For example, this is the first time that interfacial/surface microfluidics principles have been applied to body fluidic transport. Body fluid removal is facilitated through a well controlled flow rate and removal rate. The patterned wettability can handle both moisture and liquid removal. The textile is also self-cleaning and waterproof. 
     Accordingly, one aspect of the invention provides a means of fast sweat removal. This structure of hydrophilic material on a superhydrophobic substrate can quickly remove the sweat from the skin and transport it to the outside of the fabric, while keeping most areas dry and gas-permeable. 
     Another aspect of the invention provides an alternative to a diaper or maxi pad. This structure can facilitate bio-fluids to be uniformly distributed in the absorbent material and prevent leakage. 
     Another aspect of the invention provides a means of wound dressing for high-exudate wounds or chronic wounds. This structure can quickly transport the exudate from the wound to the outside of the dressing and remain gas permeable to the wound. 
     Another aspect of the invention provides a textile-based microfluidic chip. This provides an ideal structure for fabrication of low-cost microfluidic devices, for example, pregnancy test strips. 
     Another aspect of the invention provides a water collection network. This can be done by suspending this material in a high-humidity environment and allowing water droplets to condense on a network of hydrophilic channels. 
     Yet another aspect of the invention provides for water-oil separation by immersing this material in a water-oil mixture. The water droplets dispersed in the oil can be merged and collected. 
     Further aspects of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only: 
         FIG. 1  is a diagram of a fluidic network design in a radial pattern (multi-inlet-single-outlet) on the MST platform using the autonomous interfacial transport concept according to one embodiment. 
         FIG. 2A  is a schematic diagram of a top view of a fluid flow path on MST. 
         FIG. 2B  is a schematic diagram of a side view of a fluid flow path on MST. 
         FIG. 2C  is a schematic diagram of a side view of the discrete transport mode. 
         FIG. 2D  is a schematic diagram of a side view of the continuous transport mode. 
         FIG. 3A  through  FIG. 3D  are schematic diagrams of the fabrication process of MST with a multi-inlet-single-outlet design. 
         FIG. 4A  is an image of the artificial skin model. 
         FIG. 4B  is a schematic diagram of the artificial skin model. 
         FIG. 5A  is an image of the wetting and transport phenomena of MST: a 5 μL droplet sits on an original hydrophilic stitching substrate. 
         FIG. 5B  is a schematic diagram of  FIG. 5A . 
         FIG. 6A  is an image of the wetting and transport phenomena of MST: a 5 μL droplet sits on a superhydrophobic treated substrate. 
         FIG. 6B  is a schematic diagram of  FIG. 6A . 
         FIG. 7A  is an image of the wetting and transport phenomena of MST: a 5 μL droplet sits on a 2 mm circular hydrophilic micropattern. 
         FIG. 7B  is a schematic diagram of  FIG. 7A . 
         FIG. 8A  is an image of the 3D Laplace pressure-driven transport on MST. 
         FIG. 8B  is a schematic diagram of the 3D Laplace pressure-driven transport on MST. 
         FIG. 9A  is an image of the 3D Laplace pressure-driven transport on MST. 
         FIG. 9B  is a schematic diagram of the 3D Laplace pressure-driven transport on MST. 
         FIG. 10A  is an image of the 3D Laplace pressure-driven transport on MST. 
         FIG. 10B  is a schematic diagram of the 3D Laplace pressure-driven transport on MST. 
         FIG. 11A  is a schematic diagram of the cross-sections of yarn structures for single yarn (S), two separated yarns (TS) and a two-yarn bundle (TB) which were analysed for flow resistance. 
         FIG. 11B  is a plot of the flow resistance measurement of single yarn (S), two separated yarns (TS) and a two-yarn bundle (TB) at different yarn lengths (from 10 mm to 30 mm). 
         FIG. 12A  is a schematic diagram of the diameters of the inlet (D i ) and outlet (D o ) of the fluid flow path. 
         FIG. 12B  is a plot of the discrete transport mode—transport duration of a 4 μL droplet on MST with selected single-inlet-single-outlet dimensions (D i  and D o  in diameter, respectively). 
         FIG. 13  is a plot of the continuous transport mode—the relationship between the inlet pressure and the constant pumping rate Q with two-yarn bundles (10 mm and 20 mm) as the connection. 
         FIG. 14A  is a schematic diagram of a height difference between the inlet and outlet when the MST is tilted vertically. 
         FIG. 14B  is a plot of the transport duration of a 4 μL droplet when tilting a 2 mm-6 mm MST to produce a different height difference H between the inlet and outlet. 
         FIG. 14C  is a plot of the theoretical prediction and the measurement of the dripping volume on the outlet varying with the diameter D o  of the reservoir. 
         FIG. 15A  is a schematic diagram of the front side of the MST for sweat collection and removal. 
         FIG. 15B  is a schematic diagram of the back side of the MST for sweat collection and removal. 
         FIG. 16A  through  FIG. 16D  are images of the 3D discrete transport mode of the MST from  FIG. 15A  and  FIG. 15B  on the artificial skin model. 
         FIG. 17A  through  FIG. 17D  are images of the continuous transport mode of the MST from  FIG. 15A  and  FIG. 15B  on the artificial skin model. 
         FIG. 18A  and  FIG. 18B  are schematic diagrams of an alternative design of MST. 
         FIG. 18C  is schematic diagram of a preliminary test of an alternative design of MST on skin. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     I. Introduction 
     In recent decades, superhydrophobicity, also known as the remarkable water-repellent Lotus effect mimicked from nature, has been introduced to functional fabric development (e.g., water-repellent and anti-icing coatings). A number of convenient and robust manufacturing techniques have been implemented on various fabric materials to impart superhydrophobicity. For instance, a facile approach has been established using silica nanoparticles with fluorosilane modification on cotton-based fabrics, from which a water contact angle (CA) as high as 155°±2° has been repetitively achieved. Similar water repellence (CA&gt;150°) has been implemented on non-woven nylon fabrics by sequentially grafting polyacrylic acid (PAA) and fluoroamine molecules onto the original cloth. 
     Similarly, superhydrophilic textiles can be achieved in a comparable manner. For example, wool-based fabrics can be rendered superhydrophilic by depositing a thin layer of silica particles of 27 nm in diameter onto the textile. Furthermore, patterned hydrophobicity on fabric structures has also been investigated. An alternatively woven textile from both hydrophobic and hydrophilic yarns has been used to illustrate the capacity of autonomous water-oil separation. Moreover, predefined microfluidic channels woven by wetting and non-wetting silk yarns have been utilized for immunoassays. Similarly, pH sensing has been achieved by soaking the aqueous samples through amphiphilic channels created by selective surface modifications. 
     According to the following embodiments, an interfacial microfluidic transport principle to establish three-dimensional liquid flows on micropatterned superhydrophobic textiles (MST) in an autonomous, controllable and continuous fashion is presented. As the central concept, the interfacial microfluidic transport utilizes the surface tension-induced pressure gradient along the flow path defined by extreme wetting contrast to facilitate the liquid motion in the MST network in addition to the capillarity presented in the fibrous structure. The wetting contrast patterns are defined by stitching patterns of hydrophilic yarns (CA=0°) on the superhydrophobic textile (CA=140°) treated by coating a thin layer of fluoropolymer microparticles. The transport duration on MST can be highly-controlled by the dimensions of the hydrophilic pattern (inlet and outlet) and connecting yarns (channel). 
     Furthermore, two operation modes are provided for biofluidic transport: a) discrete transport—periodically adding a fixed volume of droplets to the inlet, and b) continuous transport—feeding a continuous flow to the inlet. In addition, a flow conductance model on different geometric patterns of yarns has also been analyzed (single yarn vs. yarn bundles) from which the microflow profiles on fibrous linear yarns can be interpreted. 
     Referring more specifically to the drawings, for illustrative purposes several embodiments of the system scheme of the present invention and the associated methods are depicted generally in  FIG. 1  through  FIG. 18C . It will be appreciated that the methods may vary as to the specific steps and sequence and the apparatus architecture may vary as to structural details, without departing from the basic concepts as disclosed herein. The method steps are merely exemplary of the order that these steps may occur. The steps may occur in any order that is desired, such that it still performs the goals of the claimed invention. 
     Referring now to  FIG. 1 , in one embodiment of the subject invention, a fluidic network design in a radial pattern  10  has been demonstrated to continuously extract inlet droplets  12  from six inlets  14  into one big outlet droplet  16  at the central outlet  18 , which shows the highly-efficient transport and collection capacity of the MST in this embodiment.  FIG. 1  illustrates a multi-inlet  14  single-outlet  18  yarn (or single thread or thread bundle)  20  design on the MST platform with a superhydrophobic-treated fabric substrate  22  using the autonomous interfacial transport concept. A fluidic network design  10  in a radial pattern simultaneously and continuously extracts inlet droplets  12  (each with a volume of 5 μL) from six small inlets  14  (2 mm) and merges them via channels  24  into one big outlet droplet  16  at the central outlet  18  (6 mm). The interfacial fluidic network design in a radial pattern  10  on MST may be applied to large volume and continuous biofluidic (e.g., sweat or urine) collection and removal. In comparison with current fabrics, the MST possesses high-efficiency in liquid transport while maintaining its high gas permeability from superhydrophobicity. 
     II. Theoretical Analysis 
     The MST design utilizes hydrophilic yarns micro-stitched on the superhydrophobic textile which possesses a very high CA (typically greater than 140°) and inherently low hysteresis. Once hydrophilic micropatterns are formed on the superhydrophobic textile, the extreme wetting contrast enables immobilization of the triple line of gas/liquid/solid phases along the pattern boundaries. Therefore, the internal pressure (ΔP) of any droplet deposited on MST can be directly related to its original volume (V) and the size of the hydrophilic pattern (of diameter D if circular) as described in the following equations derived from the classic Laplace&#39;s Law: 
                     Δ   ⁢           ⁢   P     =       16   ⁢           ⁢   h   ⁢           ⁢   γ         D   2     +     4   ⁢           ⁢     h   2                   (   1   )               V   =       π   24     ⁢     (       4   ⁢           ⁢     h   3       +     3   ⁢           ⁢     hD   2         )               (   2   )               
where h is the height of the droplet and γ is the surface tension of the fluid.
 
     Turning now to  FIG. 2A  through  FIG. 2D , it is shown that by connecting two reservoirs (i.e. an inlet  14  and an outlet  18 ) through a hydrophilic channel  24 , comprising for example single threads, thread bundles, a cotton yarn or glass fiber, a simple surface-tension driven microfluidic system can be devised.  FIG. 2A  shows a top view of a single fluid flow path  26  with the inlet  14 , outlet  18  and channel  24  connecting them.  FIG. 2B  is a side view of the fluid flow path  26  that shows how the inlet  14  is formed by stitching the thread or yarn  20  throughout the fabric substrate  22  (an embodiment of the MST superhydrophobic-treated fabric substrate of  FIG. 1 ) while the outlet  18  is formed by stitching the thread  20  only on the outer surface  30  of the fabric substrate  22  and not on the inner surface  32  (e.g. the surface in contact with skin). Once the surface tension-induced pressure gradient is established along the fluid flow path  26 , the liquid at the inlet  14  (of the diameter D i ) is automatically directed towards the outlet  18  (of the diameter D o ) via the hydrophilic channel  24  (i.e., the yarn). Given its laminar nature, the flow rate is approximately proportional to the Laplace pressure difference between the inlet  14  and outlet  18 , but inversely proportional to flow resistance of the thread  20 . 
     Based on the transport model of MST, two three-dimensional (3D) microfluidic operations have been proposed and analyzed.  FIG. 2C  shows a side view of the first mode, referred to as the discrete transport mode  34 . The discrete transport mode  34  is established as collecting individual aqueous droplets  36  periodically from a contact surface  38  (e.g. skin) with channels or pores  40  underneath the inlet  14  of the fluid flow path  26 . This operation is analogous to a charging/discharging capacitor in electronic circuitry. The inlet droplet  12  volume and reservoir size determine the radius of curvature and the corresponding Laplace pressure of the inlet droplet  12  under the high wettability contrast, which drive the collected inlet droplet  12  towards the outlet  18  on the other side. Thus, the droplet hydrodynamics can be uniquely determined by the initial conditions, as shown in  FIG. 2C . 
       FIG. 2D  shows a side view of the second mode, known as the continuous transport mode  42 , which occurs when the fluid flow path—and MST structure  26  of  FIG. 2B  is in close proximity to a contact surface  38  under pressure. When a continuous inflow (Q) is perfused to the inlet  14  from the surface contact on the inside layer  32  of the fabric substrate  22 , the inlet droplets  12  (fluid), while restricted to the hydrophilic fabric patterns, will be directed towards the outlet  18  on the outer surface  30  of the double-layer fabric substrate  22 . This embodiment is analogous to an electronic circuit powered by a current source. It is worth noting that the maximal flow rate under this mode is set by the largest pressure gradient produced by the inlet  14 , equal to the Laplace pressure in a hemispherical inlet droplet  12  of the size of the inlet  14  reservoir. Otherwise, it could lead to outflow instability. 
     Both modes have been characterized experimentally, in which various sizes of yarn patterns have been paired to form the self-propelled flow pump by collecting moisture from the underlying contact surfaces. Priming of the yarn patterns prior to the measurement becomes necessary to eliminate influences from capillarity. To analyze the transport parameters, a video-camera (of a 1920×1080 pixel resolution at 60 fps) installed on a stereomicroscope (Omano) was used to record the transport processes on MST. From these recordings, the elapsed times and the droplet shapes can be directly analyzed, and as a result, both the average flow rates (based on the volume change over time) and Laplace pressures inside droplets (according to the radius of curvature) can be computed accordingly. 
     III. Materials and Methods 
     a. Hydrophilic Cotton Yarns 
     Commercially available mercerized cotton yarns with a nominal diameter of 500 μm were purchased online (100% Mercerized ELS Cotton, Star®). However, these cotton yarns came with a layer of wax on the surface and cannot be easily primed with aqueous solutions. Therefore, a hydrophilic pre-treatment (degumming) process becomes necessary to remove the outer wax shielding. First, an aqueous solution, composed of sodium carbonate (1.5% wt) and hand soap (which is mainly composed of sodium laureth sulfate and ammonium lauryl sulfate, 1.5% wt), was prepared and boiled at 300° C. on a hotplate. Subsequently, the waxed yarns were immersed into the boiled bath for 60 minutes, followed by a complete washing in deionized water at room temperature. 
     b. Superhydrophobic Fabric 
     Superhydrophobic fabric substrates were prepared from off-the-shelf cotton fabrics. The woven cotton fabrics (Fabric Flair®) composed of two layers of mesh with 31 threads per inch were purchased from a local fabric store. Commercially available superhydrophobic coating (Fluoropel™ M1604V, Belsville) was obtained from Cytonix Company and spray-coated onto the cotton fabrics of a 3 cm 2  surface area by an airbrush at the pressure of 50 kPa. The coating thickness can be controlled by the volume of the treatment solution per unit surface area. To achieve complete coverage with optimal superhydrophobic performance, 2 mL of the coating solution was applied and coated onto the substrate. A reduced amount of the superhydrophobic coating can be used to achieve a similar superhydrophobicity. However, it may not be as durable and robust as a thicker coating. Subsequently, a thermal curing step was performed in a 100° C. convection oven for 30 minutes, during which time the cotton fabric was temporarily fixed to a flat, rigid surface (e.g., a 5 mm-thick glass plate) to prevent any possible heat-induced curvature. 
     c. Characterization of the Surface Wettability 
     Superhydrophobicity of the treated fabric was characterized by conventional contact area (CA) measurement. A 5 μL de-ionized water droplet was deposited onto the textile surface by a micropipette, where the profile of the droplet was recorded horizontally by a stereomicroscope equipped with a DSLR CCD camera (Rebel T3, Canon). The contact areas of the droplets were assessed from the photos with graphic software (e.g. CorelDraw). An average CA value was calculated from the measurements of three droplets deposited on different spots on the same surface. The hydrophilicity (in terms of CA) of cotton yarns was measured by laying a mesh of fibers on a superhydrophobic substrate, followed by depositing a DI water droplet on the surface. 
     d. 3D Microfluidic Networks Fabricated by Stereo-Stitching 
     Referring now to  FIG. 3A  through  FIG. 3D , several fluid flow paths  26  (see  FIG. 2B ) were formed by stitching treated hydrophilic cotton yarn  20  on the superhydrophobic-treated fabric substrate  22  to create a fluidic network design in a radial pattern  10  (see  FIG. 1  and  FIG. 3D ). Prior to the stitching, the superhydrophobic-treated fabric substrate  22  was fixed flat under tension using an embroidery hoop  44  (4 inches in diameter). A 28 gauge stitching needle  46  (0.362 mm in diameter) was used to sew cotton yarn  20  to form the fluid flow paths  26 . In order to achieve the 3D flow profile, a two-stage stereo-stitching technique, involving both penetrating and parallel stitching, was utilized to build the 3D hydrophilic structures in the inlet  14  and the outlet  18  (see also  FIG. 2B ). Specifically, an inlet  14  was fabricated by closely stitching the yarn  20  to penetrate through the superhydrophobic-treated fabric substrate  22  in a defined area until the fabric substrate  22  was fully covered by the yarn  20 . Alternatively, an outlet  18  was fabricated by stitching the yarn  20  in parallel through the meshes only presented in the outer surface  30  (or top layer) of the fabric substrate  22 . As a consequence, the hydrophilic yarns  20  of the outlet  18  were only exposed to the outer surface  30  surface of the superhydrophobic fabric substrate  22 , which left the inner surface  32  still covered with the superhydrophobic fabric substrate  22 . Following connecting the outlet  18  and inlet  14  micropatterns through cotton yarn  20  channels  24 , a 3D hydrophilic fluid flow path  26  was formed by the two-stage stereo-stitching technique. 
     e. Characterization of the Flow Resistance 
     A continuous transport mode  42  setup (see  FIG. 2D ) was devised to characterize the flow resistance of the hydrophilic cotton yarn  20  on the superhydrophobic fabric substrate  22  in different configurations. A simple capillary pump was constructed from two hydrophilic glass slides (75 mm×50 mm×1 mm) separated by two 370 μm-thick Polydimethylsiloxane (PDMS, Sylgard 184, Dow Corning; 10:1 base:crosslinker) spacers to generate a constant negative pressure head. According to the Laplace equation, the capillarity-induced pressure gradient was 394.5 Pa and matched well with our experimental observation (less than 4% deviation). During the flow resistance test, the cotton yarn  20  was placed on a superhydrophobic textile (fabric) substrate  22  and connected between the primed capillary pump and a small reservoir. The flow rate was calculated based on the transport (or depletion) time of a known volume from the reservoir assuming that the hydrostatic pressure in the reservoir could be ignored. Each data point was measured in triplicate. 
     f. Fabrication of Artificial Skin Model 
     In another embodiment of the subject invention, to demonstrate the utility of the interfacial microfluidic transport, a newly established MST structure was applied to sweat removal on artificial human skin. One of the major advantages of using the MST for sweat removal is that the superhydrophobic fabric substrate  22  is only covered by a limited patterned area of highly wettable yarn  20 , while achieving a high sweat removal rate on the hydrophilic fluid flow path  26  and maintaining high gas permittivity on a majority of the superhydrophobic region. Implemented by using the 3D stitching technique, sweat collection areas can be limited to a small fraction of the skin surface while a majority of surface microfluidic networks are running on the exterior fabric surface, in contrast to existing moisture-wicking fabrics. Accordingly, the interfacial microfluidics-enabled textile possesses high-efficiency in sweat transport and removal while maintaining low humidity and high gas permeability during intense sweating. 
     Referring now to  FIG. 4A  (image) and  FIG. 4B  (schematic), the artificial skin model  48  was devised on a 3-layer microfluidic structure. Microchannels  50  were cut into the bottom two pieces  52  and the top layer  54  was perforated with pores  56 . The diameter and density of the pores  56  were 60 μm and 114 pores/cm 2 , respectively, similar to the opening and density of human sweat glands on human backs (160±30 glands/cm 2 ). The device was fabricated from PDMS using a simple laser micromachining PDMS approach. In brief, thin layers of PDMS (Sylgard 184, Dow Corning; 10:1 base:crosslinker) were prepared by spin-coating on a clean glass slide, followed by post-baking on a 100° C. hotplate for 15 minutes. Subsequently, a desktop CO 2  laser machine (VersaLaser, Universal Laser Systems) directly engraved the designed microchannels  50  and pores  56  on the PDMS substrates with control parameters preset in the software panel. After cleaning each piece in ethanol, the three layers of PDMS were aligned aided by a mask aligner (ABM, Inc.) and compressed to bond the chip using PDMS&#39;s inherent adhesion. Finally, a syringe pump (not shown) was connected through tubes  58  and micro droplets  60  were generated on the surface to mimic the perspiration process at different flow rates. 
     g. Characterization of the Wetting Properties 
     In order to characterize the wetting properties of a fabric, four important parameters were measured, including the thickness, weight, electrical resistance (indicating the moisture level in the fabrics) and gas permeability. Specifically, the thickness of a fabric was measured by a linear gauge (EG-225, Ono Sokki) and the weight of the fabric was measured by an analytical balance (Classic Plus, Mettler Toledo). A multimeter (34401a, Agilent) was utilized to measure the electrical resistance on the fabric surface in a two-probe configuration. The resistance value was recorded once the probe tips formed an intimate contact on the fabric surface at a 3 mm separation. The average resistance was calculated from 9 measurements in different positions evenly distributed throughout the entire fabric. Moreover, the gas permeability of the fabric was evaluated by a constant gas flow setup. A rigid plastic tube of 2 cm in the inner diameter was utilized as the flow guiding channel, of which one end was connected to a pressurized gas task and a manometer (Sper Scientific). On the other end, the fabric was clamped by an elastic ring to seal the outlet, ensuring the gas flow completely passing through the textile. The gas velocity was measured by a vaneometer (Dwyer Instrument). All the weight, resistance and gas permeability assessments of each fabric were conducted before and after the fabrics were fully wetted. The wetting condition was simulated on the artificial skin surface, where a constant liquid flow was applied until the fabric became completely wetted and the measurements were repeated to record the changes between the dry and wet states. 
     IV. Results and Discussion 
     Fluidic network designs defined by the high wetting contrast between the superhydrophobic fabric substrates  22  and the hydrophilic yarns  20  provide a direct means to manipulate the internal Laplace pressure of liquid droplets, which can be utilized as a propulsion mechanism in interfacial microfluidic networks in addition to the intrinsic capillarity. In the following sections, the wettability of the MST will be discussed first, followed by characterization of the autonomous bi-droplet (single-inlet-single-outlet) transport on MST. Complete analyses on hydrophilic fluid flow paths  26  in different yarn configurations were included in the experiments. Furthermore, the distinct transport modes, discrete  34  and continuous  42  modes, will be demonstrated and characterized, followed by a discussion of the benefit of the multi-inlet-single-outlet structure. As a demonstration, an autonomous transport on MST has been performed on an artificial skin surface for rapid collection and removal of biofluid (e.g., sweat). 
     a. Micropatterned Superhydrophobic Textile 
     The off-the-shelf cross-stitching fabric, originally made from natural cotton, is hydrophilic. In addition, the inter-stitching spaces between cotton yarns form small capillary channels that provide strong wicking forces to aqueous solutions.  FIG. 5A  shows an image  62  of a 5 μL water droplet that has been rapidly absorbed into the hydrophilic cotton fabric substrate  64 .  FIG. 5B  is the schematic representation of the image  62  in  FIG. 5A . To alter wettability on the hydrophilic cotton fabric substrate  64 , a superhydrophobic surface coating was applied to the hydrophilic cotton fabric substrate  64 . A suspension of perfluoropolyether (PFPE) microparticles (of 4˜8 μm in diameter) was prepared as the surface coating material for the chemical inertness and microscopic topology. After the spray-coating, the microparticles were physically absorbed onto the surface of the hydrophilic cotton fabric substrate  64 , rendering the surface superhydrophobic with a water CA of 140±3°. As can be seen in the image  66  of  FIG. 6A , a water droplet  68  of 5 μL maintained a nearly spherical shape on the superhydrophobic-treated cotton fabric substrate  70 .  FIG. 6B  shows the schematic representation of the image  66  in  FIG. 6A . 
     As described previously, hydrophilic yarns  20  with a CA close to 0° were stitched onto a superhydrophobic fabric substrate  22 , forming highly wettable fluid flow path  26  micropatterns.  FIG. 7A  shows an image  72  of a 5 μL droplet  74  that was deposited onto a 2 mm circular hydrophilic pattern  76  and forms a semi-spherical shape as its boundary is pinned along the wetting-contrast pattern, i.e., the solid/liquid/gas triple line. Although this configuration is similar to the surface microfluidic setup fabricated by laser micromachining in our previous investigation, all the components used in the MST are obtained as off-the-shelf textile components instead.  FIG. 7B  shows a schematic representation of the image  72  in  FIG. 7A . 
     The bi-droplet transport can be extended to MST by connecting two circular reservoir (e.g. inlet and outlet) patterns (2 mm to 6 mm) through a hydrophilic yarn (10 cm) flow path, demonstrating the bi-droplet surface-tension driven transport on MST. Under the wetting contrast and the induced triple line pinning, a droplet placed in each end can form a specific radius of curvature, which is established by the droplet volume (V) and reservoir diameter (D). As a result, the Laplace pressure inside each droplet can be uniquely determined. According to fluid dynamics, the droplet with higher internal pressure will be pumped simultaneously toward the droplet at the other end. 
     This Laplace pressure-driven transport can overcome gravitational influence as illustrated in the images  78  of  FIG. 8A, 9A  and  FIG. 10A . Importantly, since the inlet  14  and the outlet  18  reservoirs are fabricated by the unique two-stage stereo-stitching technique as aforementioned, the liquid  80  traverses from one side of the fabric to the other in a well-confined 3D manner, under the superhydrophobic-defined microfluidic geometries.  FIG. 8B ,  FIG. 9B  and  FIG. 10B  are schematic representations of the images  78  in  FIG. 8A, 9A  and  FIG. 10A . 
     b. Flow Resistance of Hydrophilic Yarns 
     In addition to the Laplace pressure gradient generated by the surface tension of the curved droplet surfaces, the liquid transport can also be affected by the flow conductance of the connecting hydrophilic yarns. Various structural parameters, including the thread diameter, yarn porosity, and bundled arrangement (single vs. multi-yarn arrangements), could all factor into the flow resistance analysis. In general, a thicker thread with a larger diameter, though possessing a lower flow resistance, is more difficult to form micropatterns with due to the limited resolution. As the primary focus is on building the surface microfluidic networks using all off-the-shelf components, the internal fabric structures (e.g., yarn porosity) were not altered. 
       FIG. 11A  through  FIG. 13  show the experimental characterizations of the fluid transport on MST.  FIG. 11A  is a schematic diagram that demonstrates the flow profile on the cross-sections of yarn structures (single yarn (S), two separated yarns (TS) and a two-yarn bundle (TB)). Yarns with an average diameter of 500 μm were utilized for all the measurements.  FIG. 11B  is a graph which summarizes the experimental investigations on the flow resistance influenced by different fabric configurations and shows the flow resistance measurement of single yarn (S), two separated yarns (TS) and a two-yarn bundle (TB) at different yarn lengths (from 10 mm to 30 mm). 
     As expected, within the laminar flow region, the flow resistance shows a linear relationship with the length of the fluid flow path. In particular, as the yarn length increases from 10 mm to 30 mm, the flow resistance of a single yarn rises from 1.10×10 13  Pa·s·m −3  to 2.86×10 13  Pa·s·m −3 . However, including additive fluid flow paths in parallel would reduce the flow resistance according to the hydrodynamic theory, which has also been clearly shown in the measurements. If two yarns separated by 5 mm are connected in parallel between droplets, the overall resistance decreases to 5.44×10 12  Pa·s·m −3  and 1.56×10 13  Pa·s·m −3  for 10 mm and 30 mm long threads, respectively, which are half of the values of resistances for single threads, as predicted. 
     Notably, a bundled configuration of yarns, i.e., packing two yarns next to each other, would further reduce the flow resistance by a factor of five or more. For instance, at the same yarn length (of 10 mm), the flow resistance of the bundled configuration is measured at 1.04×10 12  Pa·s·m −3 , which approximates to only one fifth of that of the two separated yarns or 10% of that of the single yarn. This significant improvement on the fluid conductance can be attributed to the different flow profile for the two closely packed yarns. 
     As can be seen, the flows in the single and separated yarns are all confined by the physical boundaries of the fabrics, similar to the closed-channel microfluidics. Whereas, the bundled arrangement offers a suspended flow region with free-flow boundaries between the two yarns where a minimal liquid-solid contact area is retained under the surface tension, and thus, results in a substantially reduced flow resistance, analogous to the unbounded surface microflow. In brief, the flow resistance is linearly proportional to the length of the hydrophilic yarns and inversely proportional to the number of the separate fluidic pathways in parallel, while a bundled yarn arrangement can lead to an appreciable reduction in the flow resistance under the surface tension-induced suspended flow. 
     c. Transport Modes: Discrete Versus Continuous Transports 
     In the discrete transport mode, the size difference between the inlet and outlet reservoirs determines the pressure gradient and the pumping rate. In the experimental investigation, the transport durations were measured for various single-inlet-single-outlet configurations, given a fixed droplet volume (of 4 μL).  FIG. 12A  and  FIG. 12B  show the selected inlet-outlet dimensions in pairs: 1-2 mm, 1-3 mm, 1-4 mm, 1-5 mm and 1-6 mm; 2-4 mm, 2-5 mm, 2-6 mm; 3-5 mm and 3-6 mm. A two-yarn bundled pattern was utilized as the aqueous-conducting channel with a 10 mm separation between the inlet and outlet. 
     As expected, the larger outlet leads to an accelerated transport for the same size inlet. For instance, for an inlet of 1 mm in diameter, the transport duration decreases from 53 seconds to 11 seconds as the diameter of outlet extends from 2 mm to 6 mm. This is attributed to the fact that the same liquid droplet possess a lower profile on a larger size reservoir, and thereby, a smaller internal pressure. Conversely, a larger reservoir at the inlet will induce a slower transport given the same outlet dimension. As can be seen, the pump duration increases from 15 seconds to 75 seconds when the inlet reservoir size rises from 1 mm to 3 mm. Moreover, the highest average flow rate of 1.3 mL/h has been achieved at the 1-6 mm configuration. These results have clearly demonstrated the potential of the MST in manipulating flow rates by the micro-stitched geometries. 
     In the continuous pumping mode, the Laplace pressure of the droplet at the inlet is directly related to the pumping rate as well as the flow resistance of the channel.  FIG. 13  is a graph which demonstrates the measured internal pressure at the inlet as the flow rate varies with different thread/yarn configurations. The diameters of the inlet and outlet are 3 mm and 6 mm, respectively. According to the theoretical analysis, both a higher rate of pumping and a larger channel resistance could result in a larger internal pressure of the droplet. Moreover, the maximal pressure is reached at the inlet when the diameter of the droplet equals the reservoir size (97 Pa for a 3 mm reservoir). These results follow the prediction model well. For example, the average Laplace pressure at the inlet increases from 47 Pa to 96 Pa as the flow rate rises from 0.2 mL/h to 0.6 mL/h, given the fluidic path of 10 mm in length and two-yarn bundled. Furthermore, as the length of the bundle is doubled to 20 mm, the maximum pressure at the inlet of 97 Pa is obtained at 0.3 mL/h, compared with that of 59 Pa for the mm case. Overall, a higher flow rate can be established by yarn structures of a lower flow resistance. 
     d. Multi-Inlet-Single-Outlet Configuration 
     The maximal transport rate per unit area can be a critical measure for biofluidic transport applications. As previously discussed, the fluidic characterization of MST is based on a single-inlet-single-outlet (bi-droplet) configuration and a maximal flow rate of 1.3 mL/h was achieved on the MST for a 1-6 mm pattern (given the connecting yarn of 10 mm in length and 500 μm in diameter with bundled structure). The minimal inlet size that can be achieved is limited by the yarn diameter (which is 1 mm in this case), while an outlet of the diameter greater than 6 mm cannot provide noticeable improvement over transport rate according to our measurements, as shown in  FIG. 12B . 
       FIG. 12B  is a plot of the discrete transport mode. This plot shows the transport duration of a 4 μL droplet on MST with selected single-inlet-single-outlet dimensions (D i  and D o  in diameter, respectively, see  FIG. 12A ).  FIG. 13  is a plot of the continuous transport mode and shows the relationship between the inlet pressure and the constant pumping rate Q with two-yarn bundles (10 mm and 20 mm) as connection. 
     Given that the area of the micropattern is approximately 1 cm 2  (6 mm×17 mm), 1.3 mL/h per cm 2  was considered the maximal transporting rate achievable by the single-inlet-single-outlet configuration. Further improvement of the unit area transport rate of MST can be achieved by directing several collection spots to a common outlet to form a multi-inlet-single-outlet fluidic transport network (e.g. the fluidic network design in a radial pattern) as shown previously in  FIG. 1  and  FIG. 3D . Compared with the repeated one-inlet-one-outlet structures, the multi-inlet-single-outlet network design not only reduces the number of the outlets to one, but also improves the utility of the space among adjacent fluidic paths with the radial geometry design, which results in a considerably enhanced unit-area flow rate. For example, 10 individual single-inlet-single-outlet micropatterns (1-6 mm, 10 mm channel length), stitched closely side by side on a textile, would cover an area of about 10 cm 2  while achieving a maximal flow rate of approximately 1.3 mL·h 1 ·cm −2  as measured previously. 
     Alternatively, by connecting the ten inlets to one common outlet in a radial pattern as shown in  FIG. 1 , its total footprint is only 6.2 cm 2  (14 mm in radius). This is 40% more efficient than that of the former design, leading to a higher unit-area transport rate of 2.1 mL·h −1 ·cm −2 . The multi-inlet-single-outlet design can be significantly more efficient when additional inlets are directed to the shared outlet. However, the maximal number of the inlets to be added would be restrained by the fabrication resolution, i.e. the inlet size and channel width. In summary, a compact multi-inlet-single-outlet network design will further enhance fluid transport rate (per unit area) of the MST, leading to a higher transport capacity in handling a large biofluidic volume in a short period of time. 
     e. Interfacial Transport Under Gravitational Effects 
     The above discussions are all based on the simplified situation where the gravitational force is largely ignored, i.e., when the capillary length limits apply. If the gravitational effect is to be considered, two additional phenomena will be included in the analysis: the hydrostatic pressure generated by gravitation and the droplet removal under gravitation. 
     Whenever the fluidic inlet and outlet are not kept at the same hydrostatic level, the gravitational force will superpose a hydrostatic pressure gradient on the existing Laplace pressure gradient. The combined effects in a single experiment were calibrated by connecting two reservoirs (2 mm-6 mm) through a 10 mm yarn bundle and measuring the transport duration of a 4 μL droplet when tilting the fluidic network to produce various height differences.  FIG. 14B  shows that at zero height difference (as the chip is positioned horizontally), the transport measurements agree with the previous assessments conducted and shown in  FIG. 12B .  FIG. 14A  shows schematically that the height difference, H, is defined as one end of the inlet to the other end of the outlet in the vertical direction.  FIG. 14B  shows that as H gradually increases from 0 mm to 18 mm, the transport duration is reduced from 24 seconds to 12 seconds on average, nearly half of the value measured in the horizontal position. However, when the height changes in another direction, for example, under the height difference of 9 mm, the transport time increases to 72 seconds, which is three times slower than that of the horizontal situation. 
     Continuously increasing the height difference can eventually cease or even reverse the flow. At the height difference of 13 mm, no apparent flow has been observed in either direction, which agrees with the predicted value based on the balance of hydrostatic pressure and Laplace pressure, ΔP in Eq. (1). The gravitation can either promote or reduce the microfluidic transport on the MST by introducing the hydrostatic pressure gradient between the inlet and outlet reservoirs. 
     At the outlet, the droplet can be removed by the gravitational force as its own weight overrides the adhesion to the underside of the hydrophilic fabric. The maximum adhesive force (F A ) from a hydrophilic reservoir can be well predicted by the modified Furmidge equation:
 
 F   A   =D   o γ(cos θ R −cos θ A )  (3)
 
where γ is the surface tension of the liquid and θ A  and θ R  are the advancing and receding angles between the hydrophilic fabric and the underside of the superhydrophobic substrate, respectively. To demonstrate, various sizes of the outlet reservoirs (from 1 mm to 6 mm) were patterned. Subsequently, discrete and continuous flows were both applied to the study. In the discrete flow measurement, the dripping volume of the droplet, which is directly related to the maximum adhesion force F A , follows the diameter of the reservoir in a linear fashion, which has been verified experimentally, and is shown in  FIG. 14C . For example, the reservoir of 6 mm in diameter can hold a droplet of up to 62 μL until a droplet is detached and rolls down under the gravitational influence. As the droplets are manually added, disturbance of the droplet pressure can slightly affect the maximal removal rate and lead to deviations between the theoretical predications and experimental measurements. The droplet removal process can reset the pressure inside the outlet reservoir and enable continuous outflow.
 
     V. Demonstration 
     Sweat Collection and Removal 
     Sweat is secreted by the sweat glands distributed throughout the human body, which is composed mostly of water with various electrolytes. It serves as a primary means of thermoregulation (i.e., surface cooling), during which evaporation of sweat removes the latent heat from the skin underneath. During intensive physical activities, human sweat loss (or perspiration rate) can be as high as 2-4 liters per hour, equal to an average rate of 0.10 to 0.21 mL·h −1 ·cm −2  (provided that the overall skin area of 1.88 m 2  for an average male adult). Without efficient sweat removal, accumulative sweat can drastically increase the humidity level surrounding the skin surface, leading to elevated discomfort. 
     Therefore, fabric designs for sport activities have been focused on rapid removal of sweat and maintaining a low-humidity level on the skin surface. Specifically, natural cotton-based fabric is historically known for its high absorbance of sweat due to its intrinsically hydrophilic nature. However, after cotton-based fabric is fully hydrated, its weight drastically increases while the gas-permittivity sharply decreases creating limited capacity for sweat and humidity removal. The excessive liquid in the cotton makes the fabric wet and creates a heavy, sticky, and cold feeling on the skin. Newer fabric designs, such as Coolmax™ (Invista), utilize specialized polyester fibers with irregular woven cross-sections (known as tetra- or hexa-channels) to achieve efficient body moisture control. In principle, the smaller microchannels inside generate capillary force (in the order of 1 kPa) to extract the sweat and spread the fluid over a large area of the exterior fabric for facilitated evaporation. Meanwhile, the inter-fiber gap allows more air circulation and less moisture level on the skin surface for a comfortable and breathable sensation. However, the capillary-based absorption and evaporation are still subject to environmental temperature and humidity, and moreover, the fabric becomes heavier and less efficient under extensive perspiration conditions. 
     Accordingly, an artificial skin model was fabricated for demonstration of the MST using the method aforementioned for high-efficiency sweat management (see  FIG. 4A  and  FIG. 4B ). Referring now to  FIG. 15A  and  FIG. 15B , a micro-stitched pattern with a 1 mm inlet  14  and a 6 mm outlet  18  in a compact 5-inlet-1-outlet MST design  82  was utilized for efficient sweat removal. Both of the transport modes were applied to the MST design  82 , in addition to the gravitational effect, during the test.  FIG. 15A  shows the outer surface of the MST in contact with the outside  84  and  FIG. 15B  shows the inner surface of the MST in contact with the artificial skin model  86 . 
     Now referring to  FIG. 16A  through  FIG. 16D  and  FIG. 17A through 17D , as the human body keeps an up-right position throughout most of the day, it was reasonable to conduct our sweating collection from the outer MST surface  84  by placing the artificial skin model  48  vertically (75°). In the discrete mode, the substrate of the inner MST  86  is periodically put in contact with the artificial sweating surface of the artificial skin model  48  as shown in  FIG. 16B  and  FIG. 16D . As can be seen in  FIG. 15A  and  FIG. 15B , only the 5 inlet  14  collection sites are shown on both the front (outer surface  84 ) and backside (inner surface  86 ), which are in contact with the skin, while the conducting hydrophilic yarns  20  and outlet  18  reservoir are on the other side for liquid transport and removal. It has been observed that in each attaching and detaching cycle to the artificial skin model  48 , additional volumes are added and absorbed onto the hydrophilic inlets  14 , gradually transported to the outer surface  84  of the fabric, and eventually, collected at the outlet  18  opening under the Laplace pressure gradient imposed by the curved droplet surface. This 3D transport, enabled by the wetting contrast, ensures the unidirectional transport and the dryness on the MST surface that is in contact with the skin  86 . 
     After repetitive cycles of droplet collection and removal at the inlets  14 , collections from the multiple inlets  14  merge into a big droplet  16  at the outlet  18 , which detaches from the fabric as it overweighs the adhesion to the surface as shown in  FIG. 16D . 
     In the continuous transport mode, illustrated by  FIG. 17A  through  FIG. 17D , the MST  82  was placed in close contact with the artificial skin model  48  and fixed by an adhesive tape (Scotch®, 3M). As shown in  FIG. 17B , water adsorbed onto the hydrophilic inlets  14  is gradually transported to the outer surface  84  of the fabric  82  from the inner surface. Eventually, the water collects at the outlet  18  opening under the Laplace pressure gradient imposed by the curved droplet surface as seen in  FIG. 17C . 
     As can be seen in  FIG. 17D , similar to the phenomenon illustrated in the discrete mode, large droplets  16  consecutively form at the outlet  18  and drip off during the continuous pumping, while the superhydrophobic MST  82  remains dry and gas-permeable. 
     In order to quantitatively characterize the unique liquid transport performance of MST in the demonstration, several important parameters of a fabric were experimentally investigated, including the thickness, weight, electrical resistance, and gas permeability before and after the textile was completely wetted. Commercial cotton and CoolMax™ fabrics with the same surface area were prepared and tested as a comparison. The results are summarized in Table 1. As can be seen, the original thickness of the MST is comparable to that of the CoolMax™, but greater than the conventional cotton fabrics. Under completely wet conditions, the average weight per unit area of CoolMax™ varies from 0.0282 g·cm −2  to 0.1156 g·cm −2  (about 310% weight change) due to the high aqueous absorbance of the hydrophilic textile structures, which was similarly found in conventional cotton fabrics. Meanwhile, MST only shows a marginal increment of its unit area weight, from 0.0393 g·cm −2  to 0.0544 g·cm −2 , representing a 43% increase from its initial weight. The significant difference in weight change is contributed to the unique pattern-defined wettability of the MST, which was verified by the electrical resistance measurement in both wettable and non-wettable regions. 
     Under dry conditions, all three fabrics present open-circuit impedance. After full wetting, both the resistances of the cotton and CoolMax™ fabrics decreased to 0.21 MΩ throughout the entire fabric, which indicates a uniform distribution of a high water content present inside these fabrics. In contrast, the resistance of MST varies over the wettable and non-wettable regions. In particular, the resistance of the micropatterned hydrophilic region, covering only 4% of the entire inner surface, changed from an open circuit impedance to 0.86 MΩ, while the rest of the superhydrophobic MST fabric substrate maintained a high electrical resistance of 116 MΩ (which is believed to be caused by water moisture condensed inside the superhydrophobic fabric). In another measurement, it was found that the gas permittivity of MST (574.5 kPa·s·m −3 ) under a completely wetting condition was substantially lower than that of the cotton and CoolMax™, which was 3186.5 kPa·s·m −3  and 4336.5 kPa·s·m −3 , respectively (given that a forced air flow of 60 ft/m was constantly applied to the fabric surfaces). 
     The experimental measurements confirmed that the MST remains dry over the majority of the surface area and sustains high gas permittivity within a highly humid environment. Noticeably, this fluidic transport mechanism on MST is completely spontaneous and can be sustainable even under the wettest conditions, and more importantly, it is independent of the ambient temperature and humidity, unlike the conventional fabrics. This feature can be highly advantageous in conditions of heavy perspiration in humid weather, which is essential for the comfort of the human body during intensive exercise. In addition, the utility of the interfacial microfluidic transport on the MST can be extended to similar biofluidic transport applications, e.g., urine removal or collection, and drainage of wound exudates. Overall, the MST enables a surface tension-driven flow for controlled and facilitated transport of fluids on wettability-patterned textile surfaces. 
     VI. Conclusions 
     An interfacial microfluidic transport model has been presented and implemented on micropatterned superhydrophobic textiles (MST). The MST platform, utilizing the extreme wetting contrast between very hydrophilic yarns and a superhydrophobic textile substrate, confines the aqueous flow pathway and enables autonomous surface tension-driven microflow on the textile surface. As compared to the previously reported textile-based microfluidic systems, it is capable of achieving a continuous flow in a highly controllable manner without an external pumping system (e.g., capillary or syringe pumps). The maximal flow rate achieved by the MST after becoming completely wet was 1.3 mL/h (21 μL/min) in a discrete mode which is higher than reported capillary pumps and it can be continuously achieved even after the yarn is completely wet, under which the capillary/wicking force would eventually cease working. 
     Two 3D operation modes, discrete and continuous transports, have been introduced. By a unique two-stage stereo-stitching approach on the spray-coated superhydrophobic cotton fabric (CA=140±3), various micropattern designs (from diameters of 1 mm to 6 mm) have been fabricated and tested. In addition, the flow resistance on the hydrophilic pathway has also been modeled and evaluated. Measurements of flow resistance on single or multiple yarn configurations have been compared and analyzed, from which a closely packed bundle arrangement leads to the highest flow conductance due to formation of the surface tension-induced free flow region. Together, the MST system can provide a repeatable flow rate up to 1.3 mL/h. 
     Finally, its applicability toward facilitated and controlled biofluid removal, such as skin surfaces experiencing heavy perspiration, was demonstrated. As one of the main innovations, the MST continuously removes the sweat by collecting the moistures from the skin surface, transports the fluidic contents to the exterior surface, and collects them into miniature droplets, which can eventually, without friction roll over on the superhydrophobic surface once their weights exceed the adhesion to the substrate. In fact, during this process, the MST maintains extremely low humidity and ultrahigh air permittivity, unlike the conventional fabrics, and therefore, it allows significantly improved evaporation process on human skin. In summary, the intriguing interfacial microfluidics, established on MST, offers a novel autonomous means to manipulate aqueous flow on a textile platform, which can be readily utilized for industrial manufacturing, and can be further extended to biofluid transport applications, which require high-efficiency and controlled fluidic flow. 
     The present invention is a new type of textile construction that is able to transport liquid on the skin&#39;s surface to the outer side of a fabric, where the liquid collects and drips off. The textile utilizes interfacial microfluidic principles and implements liquid transport spontaneously using hydrophilic micropatterns on a superhydrophobic/hydrophobic fabric surface. The invention provides a new dimension of transport to the textile: surface tension force, in addition to intrinsic capillary force in hydrophilic fibers. The invention exhibits several novel features which include, but are not limited to, the following: (1) Applies interfacial/surface microfluidics principle to body fluidic transport; (2) Facilitates body fluidic removal; (3) Models microfluidic transport on patterned hydrophobic and superhydrophobic fabrics; (4) Provides well controlled flow rate and removal rate of the fluid; (5) Is capable of both moisture and liquid removal due to patterned wettability; (6) Uses a fabrication process that is simple and compatible with the large-scale cloth manufacturing; and (7) Is self-cleaning and waterproof. 
     VII. Alternative Embodiments 
     The subject invention material comprises hydrophilic yarn and hydrophobic fabrics, which is distinguished by the contact angle (CA). A material&#39;s CA smaller than 90 degrees is hydrophilic while a CA larger than 90 degrees is hydrophobic. Several common materials are listed in both categories and any combination from these two categories can form the MST structure in the application. 
     The hydrophilic yarn can comprise, for example, cotton, nylon, hemp, polyester, etc. The hydrophobic fabrics can comprise, for example, grafted nylon fabric, hydrophobic material coated cotton and wool, non-wetting silk, etc. 
     An alternative design of MST  88  is illustrated in  FIG. 18A ,  FIG. 18B  and  FIG. 18C . It comprises a thin layer of hydrophobic material  90 , on which channel-like patterns  92  are cut and formed. This material can be fixed on the skin  94  under compression with adhesive tape  96  or any equivalent thereof.  FIG. 18C  shows a schematic diagram  98  of a human hand  100  with the alternative design of MST  88  fixed on the skin  94 . Since the human skin  94  is hydrophilic by nature, the bottom skin surface serves as the hydrophilic substrate for the alternative design MST  88  and the boundary of the channel is defined by the patterned hydrophobic material  90 . According to preliminary tests, microflow similar to the process previously described can be established with this new alternative design of MST  88 . 
     In summary, the start shape of the MST has a minimum of only one fluid flow path, with one inlet and one outlet. The more fluid flow paths in one design, the more efficient the unit area transport rate. The maximum number of fluid flow paths in one design depends on the resolution of the stitching technique. 
     From the discussion above it will be appreciated that the invention can be embodied in various ways, including the following: 
     1. A method of transporting fluid on a fabric, the method comprising: (a) creating a fluid flow path on a hydrophobic fabric; (b) wherein said fluid flow path comprises a hydrophilic material; (c) wherein said fluid flow path comprises an inlet and an outlet connected by a channel; (d) wherein said fluid flows continuously and autonomously along said fluid flow path; and (e) wherein said fluid flow is not affected by the absorption ability of the fabric and environmental humidity. 
     2. The method of any preceding embodiment, wherein the hydrophobic fabric has a fluid contact angle of at least 90°. 
     3. The method of any preceding embodiment, wherein the hydrophobic fabric has a fluid contact angle of between 90° and 140°. 
     4. The method of any preceding embodiment, wherein said hydrophilic material has a fluidic contact angle smaller than 90°. 
     5. The method of any preceding embodiment, wherein said inlet and said outlet can accumulate fluid to form a curved fluid surface. 
     6. The method of any preceding embodiment, wherein said channel comprises single threads or thread bundles. 
     7. The method of any preceding embodiment, wherein said outlet is larger than said channel. 
     8. The method of any preceding embodiment: (a) wherein the hydrophobic fabric comprises a first surface and a second surface; (b) wherein the inlet is formed throughout the hydrophobic fabric such that the inlet is present on the first surface and the second surface; (c) wherein the channel and the outlet are formed on the hydrophobic fabric such that the channel and the outlet are only present on the second surface of the hydrophobic fabric; and (d) wherein when a fluid contacts the inlet, the fluid is transported from the first surface to the second surface, along the channel and to the outlet. 
     9. The method of any preceding embodiment, wherein the continuous and autonomous fluid flow is maintained by the Laplace Pressure of liquid. 
     10. The method of any preceding embodiment, wherein the fluid can be removed from said outlet by droplet formation and dripping. 
     11. The method of any preceding embodiment, wherein a plurality of said hydrophilic fluid flow paths are configured to flow and terminate at one or more said outlets, creating a fluidic network design. 
     12. The method of any preceding embodiment, wherein a plurality of said fluidic network designs are configured on a piece of wearable hydrophobic fabric. 
     13. A method of transporting fluid across skin, the method comprising: (a) cutting a hollow pattern in a hydrophobic fabric; and (b) fixing said patterned hydrophobic fabric to skin; (c) wherein said skin forms a hydrophilic fluid flow path; (d) wherein said fluid flow path comprises an inlet and an outlet connected by a channel for said fluid; (e) wherein said fluid flows continuously and autonomously along said fluid flow path; and (f) wherein said fluid flow is not affected by environmental humidity. 
     14. The method of any preceding embodiment, wherein the hydrophobic fabric has a fluid contact angle of at least 90°. 
     15. The method of any preceding embodiment, wherein the hydrophobic fabric has a fluid contact angle of between 90° and 140°. 
     16. The method of any preceding embodiment, wherein said inlet and outlet can accumulate fluid to form a curved fluid surface. 
     17. The method of any preceding embodiment, wherein said outlet is larger than said channel. 
     18. The method of any preceding embodiment, wherein the continuous and autonomous fluid flow is maintained by the Laplace Pressure of liquid. 
     19. The method of any preceding embodiment, wherein the fluid can be removed from said outlet by droplet formation and dripping. 
     20. The method of any preceding embodiment, wherein a plurality of said hydrophilic fluid flow paths are configured to flow and terminate at one or more said outlets, creating a fluidic network design. 
     21. The method of any preceding embodiment, wherein a plurality of said fluidic network designs are configured on a piece of wearable hydrophobic fabric. 
     22. A fabric capable of transporting fluids, the fabric comprising: (a) a hydrophobic fabric material; and (b) a fluid flow path formed on said hydrophobic fabric material; (c) wherein said fluid flow path comprises a hydrophilic material; (d) wherein said fluid flow path comprises an inlet and an outlet connected by a channel; (e) wherein said fluid flows continuously and autonomously along said fluid flow path; and (f) wherein said fluid flow is not affected by the absorption ability of the fabric environmental humidity. 
     23. The fabric of any preceding embodiment, wherein the hydrophobic fabric has a fluid contact angle of at least 90°. 
     24. The fabric of any preceding embodiment, wherein the hydrophobic fabric has a fluid contact angle of between 90° and 140°. 
     25. The fabric of any preceding embodiment, wherein said hydrophilic material has a fluidic contact angle smaller than 90°. 
     26. The fabric of any preceding embodiment, wherein said inlet and outlet can accumulate fluid to form a curved fluid surface. 
     27. The fabric of any preceding embodiment, wherein said channel comprises single threads or thread bundles. 
     28. The fabric of any preceding embodiment, wherein said outlet is larger than said channel. 
     29. The fabric of any preceding embodiment: (a) wherein the hydrophobic fabric comprises a first surface and a second surface; (b) wherein the inlet is formed throughout the hydrophobic fabric such that the inlet is present on the first surface and the second surface; (c) wherein the channel and the outlet are formed on the hydrophobic fabric such that the channel and the outlet are only present on the second surface of the hydrophobic fabric; and (d) wherein when a fluid contacts the inlet, the fluid is transported from the first surface to the second surface, along the channel and to the outlet. 
     30. The fabric of any preceding embodiment, wherein the continuous and autonomous fluid flow is maintained by the Laplace Pressure of liquid. 
     31. The fabric of any preceding embodiment, wherein the fluid can be removed from said outlet by droplet formation and dripping. 
     32. The fabric of any preceding embodiment, wherein a plurality of said hydrophilic fluid flow paths are configured to flow and terminate at one or more said outlets, creating a fluidic network design. 
     33. The fabric if any preceding embodiment, wherein a plurality of said fluidic network designs are configured on a piece of wearable hydrophobic fabric. 
     Although the description above contains many details, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.” 
     In addition to any other claims, the applicant(s)/inventor(s) claim each and every embodiment of the invention described herein, as well as any aspect, component, or element of any embodiment described herein, and any combination of aspects, components or elements of any embodiment described herein. 
     
       
         
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Comparison of wetting characteristics among cotton, CoolMax ™ and MST. 
               
             
          
           
               
                   
                   
                   
                   
                   
                   
                 Original 
                 Wetted 
               
               
                   
                   
                   
                   
                 Original 
                 Wetted 
                 Gas 
                 Gas 
               
               
                   
                   
                 Original 
                 Wetted 
                 Electrical 
                 Electrical 
                 Permeability 
                 Permeability 
               
               
                 Textile 
                 Thickness 
                 Weight 
                 Weight 
                 Resistance 
                 Resistance 
                 (kPa · s · 
                 (kPa · s · 
               
               
                 Type 
                 (mm) 
                 (g/cm 2 ) 
                 (g/cm 2 ) 
                 (Ω) †   
                 (MΩ) †   
                 m −3 ) ‡   
                 m −3 ) ‡   
               
               
                   
               
               
                 Cotton 
                 0.260 
                 0.0181 ± 0.0040 
                 0.0843 ± 0.0100 
                 Open 
                 0.21 ± 0.02 
                 N/A 
                 3186.5 ± 52.5  
               
               
                   
                   
                   
                   
                 Circuit 
               
               
                 CoolMax ™ 
                 0.470 
                 0.0282 ± 0.0020 
                 0.1156 ± 0.0100 
                 Open 
                 0.21 ± 0.01 
                 N/A 
                 4336.5 ± 157.0 
               
               
                   
                   
                   
                   
                 Circuit 
               
               
                 MST 
                 0.550 
                 0.0393 ± 0.0020 
                 0.0544 ± 0.0100 
                 Open 
                 Micropatterns 
                 N/A 
                 574.5 ± 52.0 
               
               
                   
                   
                   
                   
                 Circuit 
                 (4%): 
               
               
                   
                   
                   
                   
                   
                 0.86 ± 0.65 
               
               
                   
                   
                   
                   
                   
                 SH 
               
               
                   
                   
                   
                   
                   
                 substrate 
               
               
                   
                   
                   
                   
                   
                 (96%): 
               
               
                   
                   
                   
                   
                   
                 116 ± 22  
               
               
                   
               
               
                   † The resistance data were measured between 2 points 3 mm apart from each other on the side in contact with the artificial skin. 
               
               
                   ‡ The gas resistance was measured by passing gas flow at 60 ft/min through a circular piece of textile with diameter of 2 cm; the gas permeability of dry textile is too small to be accurately measured by the setup.