Microfluidic Diagnostic Devices Research Articles

A market for diagnostic devices for extreme point-of-care testing: Are we ASSURED of an ethical outcome?

The World Health Organisation (WHO) is leading a global effort to deliver improved diagnostic testing to people living in low-resource settings. A reliance on the healthcare technologies marketplace and industry, shapes many aspects of the WHO project, and in this situation normative guidance comes by way of the ASSURED criteria - Affordable, Sensitive, Specific, User-friendly, Rapid and robust, Equipment-free, and Delivered. While generally improving access to diagnostics, I argue that the ASSURED approach to distributive justice - efficiency - and assessment of worth - productivity - may constrain efforts to deliver timely and accurate diagnosis in the developing world equitably by holding back new and innovative diagnostics and indirectly encouraging program and device design that may unfairly discriminate against certain groups. Even as we try to overcome the problem of global healthcare injustice, we may be entrenching disadvantage. I present my critique of ASSURED by 1) referencing Boltanski and Thévenot's theory of orders of worth to highlight the industrial and market foundations of the ASSURED guidelines; 2) comparing ASSURED with other normative guides that elevate the importance of civic responsibility in evaluations of distributive justice; 3) presenting a case study of the failed promise of microfluidic diagnostic devices. I conclude that a new approach to normative guidance is required to assess the value of developing world diagnostics, preferably, one that does not force global public goods into the marketplace.

Self-Assembling Graphene Layers for Electrochemical Sensors Printed in a Single Screen-Printing Process.

This article reports findings on screen-printed electrodes employed in microfluidic diagnostic devices. The research described includes developing a series of graphene- and other carbon form-based printing pastes compared to their rheological parameters, such as viscosity in static and shear-thinning conditions, yield stress, and shear rate required for thinning. In addition, the morphology, electrical conductivity, and electrochemical properties of the electrodes, printed with the examined pastes, were investigated. Correlation analysis was performed between all measured parameters for six electrode materials, yielding highly significant (p-value between 0.002 and 0.017) correlations between electron transfer resistance (Ret), redox peak separation, and static viscosity and thinning shear-rate threshold. The observed more electrochemically accessible surface was explained according to the fluid mechanics of heterophase suspensions. Under changing shear stress, the agglomeration enhanced by the graphene nanoplatelets' interparticle affinity led to phase separation. Less viscous pastes were thinned to a lesser degree, allowing non-permanent clusters to de-agglomerate. Thus, the breaking of temporary agglomerates yielded an unblocked electrode surface. Since the mechanism of phase ordering through agglomeration and de-agglomeration is affected by the pastes' rheology and stress during the printing process and requires no further treatment, it can be appropriately labeled as a self-assembling electrode material.

A microfluidic diagnostic device with air plug-in valves for the simultaneous genetic detection of various food allergens

The identification of accidental allergen contamination in processed foods is crucial for risk management strategies in the food processing industry to effectively prevent food allergy incidents. Here, we propose a newly designed passive stop valve with high pressure resistance performance termed an “air plug-in valve” to further improve microfluidic devices for the detection of target nucleic acids. By implementing the air plug-in valve as a permanent stop valve, a maximal allowable flow rate of 70 µL/min could be achieved for sequential liquid dispensing into an array of 10 microchambers, which is 14 times higher than that achieved with the previous valve arrangement using single-faced stop valves. Additionally, we demonstrate the simultaneous detection of multiple food allergens (wheat, buckwheat, and peanut) based on the colorimetric loop-mediated isothermal amplification assay using our diagnostic device with 10 microchambers compactly arranged in a 20-mm-diameter circle. After running the assays at 60 °C for 60 min, any combination of the three types of food allergens and tea plant, which were used as positive and negative control samples, respectively, yielded correct test results, without any cross-contamination among the microchambers. Thus, our diagnostic device will provide a rapid and easy sample-to-answer platform for ensuring food safety and security.

Deformation and rupture of microcapsules flowing through constricted capillary

The dynamics of deformable microcapsules flowing through constricted channels is relevant in target delivery of chemicals in physiological systems, porous media, microfluidic medical diagnostic devices and many other applications. In some situations, the microcapsules need to sustain the stress they are subjected to as they flow through constricted channels and in others, the stress may be the rupture trigger used to release the internal content. We experimentally investigate the flow of monodispersed gellan gum microcapsules through a constricted capillary tube by measuring the evolution of the pressure difference and flow visualization. The maximum pressure difference and capsule deformation is obtained for capsules with different diameter and shell thickness. We map the conditions, e.g. diameter and shell thickness, at which the capsule membrane ruptures during the flow, releasing its internal phase.

MICROFLUIDIC DEVICES AS A TOOL FOR DRUG DELIVERY AND DIAGNOSIS: A REVIEW

Microfluidic devices are a good example of the collaboration of chemical, biological, and engineering sciences. Microfluidic devices emerge as an in fluent technology which provides an alternative to conventional laboratory methods. These devices are employed for the precise handling and transport precise quantities of drugs without toxicity. This system is emerging as a promising platform for designing advanced drug delivery systems and analysis of biological phenomena on miniature devices for easy diagnosis. Microfluidics enables the fabrication of drug carriers with controlled geometry and specific target sites. Microfluidic devices are also used for the diagnosis of cancer circulating tumor cells. In the current review, different microfluidic drug delivery systems and diagnostic devices have described.

A Microfluidic Diagnostic Device Capable of Autonomous Sample Mixing and Dispensing for the Simultaneous Genetic Detection of Multiple Plant Viruses.

As an efficient approach to risk management in agriculture, the elimination of losses due to plant diseases and insect pests is one of the most important and urgent technological challenges for improving the crop yield. Therefore, we have developed a polydimethylsiloxane (PDMS)-based microfluidic device for the multiplex genetic diagnosis of plant diseases and pests. It offers unique features, such as rapid detection, portability, simplicity, and the low-cost genetic diagnosis of a wide variety of plant viruses. In this study, to realize such a diagnostic device, we developed a method for the autonomous dispensing of fluid into a microchamber array, which was integrated with a set of three passive stop valves with different burst pressures (referred to as phaseguides) to facilitate precise fluid handling. Additionally, we estimated the mixing efficiencies of several types of passive mixers (referred to as chaotic mixers), which were integrated into a microchannel, through experimental and computational analyses. We first demonstrated the ability of the fabricated diagnostic devices to detect DNA-based plant viruses from an infected tomato crop based on the loop-mediated isothermal amplification (LAMP) method. Moreover, we demonstrated the simultaneous detection of RNA-based plant viruses, which can infect cucurbits, by using the reverse transcription LAMP (RT-LAMP) method. The multiplex RT-LAMP assays revealed that multiple RNA viruses extracted from diseased cucumber leaves were successfully detected within 60 min, without any cross-contamination between reaction microchambers, on our diagnostic device.

Integrated microfluidic pneumatic circuit for point-of-care molecular diagnostics

Developing simple, portable, rapid, and easy-to-use diagnostic technologies is essential for point-of-care (POC) blood molecular testing. Integrated microfluidic devices that include the functionalities of blood separation, microfluidic pumping, and molecular detection are desirable for POC testing; however, current technologies still rely on off-chip sample processing or require bulky equipment. We report a fully-integrated microfluidic diagnostic device, i.e., an integrated pneumatic microfluidic circuit (iPC), that can autonomously pump whole blood, continuously sort blood plasma, and readily enable blood plasma proteomic analysis. The iPC contains vacuum pillars as a vacuum source and waste reservoir, as well as microchannels connecting the pillars as a plasma separator or a flow stabilizer. We combined the iPC and a miniaturized fluorescence microscope to create a portable diagnostic platform that enables fluorescence-based biomarker detection. First, we performed systematic parametric studies to establish design rules for determining the transport and distribution of fluid streams in the iPC. We then demonstrated the capability of the iPC-based diagnostic platform by successfully separating blood plasma from microliter quantities of whole blood while simultaneously quantifying thrombin in blood samples using an aptamer beacon within 5 min of sample injection. Our platform holds potential as a rapid, field-deployable, essentially universal diagnostic tool in POC settings.

Instrument-free argentometric determination of chloride via trapezoidal distance-based microfluidic paper devices

Chloride (Cl−) is an inorganic anion present in a broad range of samples (e.g. biological, environmental, food, water, etc.), the determination of which is of widespread significance. In this work, we translate the well-established traditional argentometric method (Mohr's precipitation titration) into a small, simple, portable, and low-cost paper-based microfluidic diagnostic device, which provides rapid and quantitative analysis. The developed device enables the determination of chloride sample volumes as small as 5 μL. A distance-based detection method is implemented providing fully instrument-free quantitation. The beneficial effects of channel geometry (variable widths with constant heights) on analytical parameters were investigated. Trapezoidal channels (channel width changes linearly with height) were used to create a gradient of paper surface (titrant) available for the reaction, compared to the typical uniform rectangular channels (constant channel width). The trapezoid with increasing width offered higher sensitivity and lower detection limits (i.e. 0.05 mM vs 0.1 mM from the rectangular channel) for chloride determination across the concentration range of 0.05–25 mM. In addition, the effect of concentration of the deposited reagent on the obtained distance signals was investigated using varying concentrations of titrant (AgNO3), which allowed determination of chloride across a wider dynamic range (up to 200 mM). The utility of the paper devices was demonstrated by determination of chloride in a variety of matrices including body fluids (sweat, serum, and urine) and water samples (drinking, mineral, river water).

New advances in microfluidic flow cytometry.

In recent years, researchers are paying the increasing attention to the development of portable microfluidic diagnostic devices including microfluidic flow cytometry for the point-of-care testing. Microfluidic flow cytometry, where microfluidics and flow cytometry work together to realize novel functionalities on the microchip, provides a powerful tool for measuring the multiple characteristics of biological samples. The development of a portable, low-cost, and compact flow cytometer can benefit the health care in underserved areas such as Africa or Asia. In this article, we review recent advancements of microfluidics including sample pumping, focusing and sorting, novel detection approaches, and data analysis in the field of flow cytometry. The challenge of microfluidic flow cytometry is also examined briefly.

Cytocoded passwords: BioMEMS based barcoding of biological samples for user authentication in microfluidic diagnostic devices.

Smart and connected point-of-care (POC) medical devices are becoming ever more ubiquitous and have the potential to radically improve disease diagnosis and health monitoring. This emerging connectivity can potentially create serious security issues where patient privacy can be easily compromised. Protection of patient data from malicious cyber-physical attackers requires radical solutions at the BioMEMS level. Ideally, the information exchange between the patient and practitioner is an automated and transparent process for the patient. In practice, this exchange requires both the patient and the test results to be authenticated and validated respectively on the storage service to ensure that the medical diagnostic results are properly stored and their access is protected. This secure authentication phase is particularly critical for medical diagnostics: patient data exposure could lead to negative social effects. This work focuses on providing a transparent authentication mechanism for patient blood tests performed using impedance flow cytometry. The goal is twofold: first, to alleviate the user from security procedures, precisely an authentication step, while using the medical device; second, to provide a unique identifier for the test results when stored in a remote server. This paper describes a domain specific authentication method for impedance flow cytometry devices. We spike into the blood samples synthetic micro-beads of different sizes, at determined concentrations, to generate a unique authentication string that uniquely identify a test result on the remote storage service. These authentication strings are embedded in the test devices and can be used as a convenient alternative to generic authentication methods, such as logins and passwords. This alternative method removes the authentication burden from the user and protects patient's privacy further by preventing them from linking their personal information to their test results.

Immunoreaction-based Microfluidic Diagnostic Device for the Detection of Prostate-Specific Antigen

This paper addresses an immunoreaction period-independent microfluidic diagnostic method for the detection of prostate-specific antigen. Immunoreaction-based biosensors generally use sandwich binding of a capture antibody, followed by an antigen, and then a detection antibody with a fluorescent label. Fluorescent intensity is proportional not only to the antigen density in a sample but also to the immunoreaction period. Generally, immunoreaction-based sensors are dependent on the immunoreaction period because the amount of antigen bound to fluorescent labels increases as the immunoreaction period increases. A wash-out step is suggested to eliminate dependence on a specific reaction period. Further, the optimal time to start the wash-out step was investigated. For the conventional detection process, fluorescent intensity increases constantly as the immunoreaction period increases, even though the antigen concentration in the sample has not changed. After applying the wash-out process, however, the fluorescent intensity was maintained over a 15-min period. Consequently, even though a user may miss the optimal reading time for the assay, an accurate result can be reported because the wash-out step enables microfluidic diagnostic devices to maintain a constant fluorescent intensity.

(Keynote) New Microfluidic Platforms for Medical Screening and Diagnostics

I. Introduction The field of microfluidics continues to show promise for applications in medical screening and diagnostics, and the study of human health and disease. Microfluidics has the potential to miniaturize instrumentation usually limited to the laboratory table top, offering the possibility of highly portable or wearable instruments for medical screening and diagnostics including the monitoring of biomarkers in real time. Microfluidics also offers unique devices and methods that enable scientists to study health and disease in new ways, from studying individual and monolayers of biological cells to mimicking organs on a chip. In order to fully develop these applications, new microfluidic platforms are required that incorporate the results of ongoing research in fields such as materials, biology, microfabrication, electronics, and computer engineering. This presentation discusses several platforms for the development of microfluidic systems for applications in biomedicine and biology. These platforms employ multiple recent advances in nanocomposite polymers, polymer microfabrication, printed circuit board technology, reconfigurable systems, and flexible electronics. These platforms are employed toward the development of new microfluidic instruments, including a reconfigurable microfluidic diagnostic unit, inexpensive and flexible biomedical screening devices, and biological cell research platforms. II. Example Platforms A. Reconfigurable Microfluidic Platform There is a growing need for instruments that perform fast, accurate, and inexpensive biological sample manipulation and processing with high-throughput. Microfluidics offers great possibilities for small, portable systems to perform fast manipulation and sorting of large numbers of samples, as well as multiplexed analysis of a single sample. Successful microfluidic-based devices exist, but their portability and throughput has been limited as they either require separate microfluidic channels for each test, which translates to a large array of permanently configured channels with a large footprint; require large off-chip support devices; or are based on other technologies that have relatively strict requirements for fluid sample manipulation and sample transfer between devices. We present on-going work to develop an instrument to address these problems of simultaneous high-throughput and portability. This instrument, a collaboration between microfluidics and computer engineering labs at Simon Fraser University, offers a new approach that is accomplished through the merging of electronically controlled functional magnetic materials for microfluidics with state-of-the-art field programmable technology. The instrument employs a compact, reconfigurable, microfluidics platform that is a combination of an array of small, individually-programmable, magnetic polymer valves [1] to address microfluidic channels that connect chambers containing sensors [2], heaters [3], mixers [4], etc., and a field programmable technology control that allows the highly portable instrument to configure itself “on-the-fly” for analysis of multiple samples using multiple tests. We present the reconfigurable microfluidics unit paradigm, and discuss technologies and techniques taken from the fields of composite materials and polymer microfabrication to develop the hardware for the reconfigurable microfluidic platform. B. Cost-Effective PCB-Based Platforms Printed Circuit Board (PCB) technology is a well understood and well utilized platform for electronics. We present a new PCB-based platform for microfluidic biomedical and biological testing. The standardized platform features integrated functional units, three-dimensional (3D) configurations, convenient device-instrumentation interconnections, and industry-compatible precision manufacturing using a custom three-metal fabrication process. PCB technology is demonstrated to not only form an integrated platform but is also utilized in the fabrication of functional elements for biosensing and bioprocessing devices and systems, such as reconfigurable microfluidic systems for biosample analysis. Example elements include a chemistry-based enzyme assay [2], and a molecule-based quantitative polymerase chain reaction (qPCR) screening device [3]. C. Flexible Microfluidic Platforms We present our most recent work in the development of microfluidic instruments of flexible substrates. We have previously presented work on flexible microfluidic platforms containing multiple layers of interconnected microfluidic channels on flexible substrates [5, 6], as well as conductive and magnetic functional polymers for flexible sensor [7] and actuator devices [1, 2, 8]. We present now the concept of integrating these technologies towards development of flexible microfluidic instrumentation for biological cell research [9] and wearable biomedical monitors. References M. Rahbar, et. al., J Micromech Microeng 26(5), 055012 (2016).H.-Y. Tseng, et. al., Measurement 73:158-161 (2015).H.-Y. Tseng, et. al. Sensors Actuators B, 204:459-466 (2014).M. Rahbar, et. al., J Micromech Microeng, 24(2):025003 (2014).D. Chung & B.L. Gray, J Micromech Microeng, 27(11), (2017).6. Patel, et. al., J Micromech Microeng 23(6):065029 (2013).D. Chung, et. al., J Electrochemical Society 161(2):B3071-76 (2014).M. Rahbar & B.L. Gray, IEEE 17th International Conference on Nanotechnology (IEEE-NANO), Pittsburgh, (July 2017).B.L. Gray, et. al., IEEE 14th International Conference on Nanotechnology (IEEE-NANO), Toronto (August 2014), 986-990.

Immunochromatographic thread-based test platform for diagnosis of infectious diseases

Patterning is an important step in fabrication of multiplexed microfluidic devices. Various approaches including cutting, photolithography, wax-printing, plotting and etching have been developed and tested. Recently, using threads has emerged as a convenient and low-cost approach for fabrication of microfluidic devices. We explored the application of threads in combination with nitrocellulose membrane to fabricate multi-channel immunochromatographic diagnostic devices. Microfluidic channels were made using hydrophilic threads and nitrocellulose membrane strips. Household sewing needle was used to weave hydrophilic thread into desired patterns through a double-sided mounting tape. Glass fibre discs were used as conjugate pads while nitrocellulose membrane was used for immobilisation of capture antibodies. Patterned threads were linked to nitrocellulose membrane strips by overlapping so that reagents flowing through threads were eventually transferred to the membrane. The design was tested using IgG, H. pylori and Hepatitis B surface antigen. Continuous flow was observed from hydrophilic threads to the nitrocellulose membrane, and a positive signal was visualised on the membrane within 5 min of sample application. The observed limit of detection ranged between 30 and 300 ng/ml for H. pylori and Hepatitis B, respectively. Using thread and tape offers a promising alternative for patterning of simple, low-cost multiplexed microfluidic diagnostic devices with potential point-of-care applications in resource-limited settings.

Automated Blood Sample Preparation Unit (ABSPU) for Portable Microfluidic Flow Cytometry.

Portable microfluidic diagnostic devices, including flow cytometers, are being developed for point-of-care settings, especially in conjunction with inexpensive imaging devices such as mobile phone cameras. However, two pervasive drawbacks of these have been the lack of automated sample preparation processes and cells settling out of sample suspensions, leading to inaccurate results. We report an automated blood sample preparation unit (ABSPU) to prevent blood samples from settling in a reservoir during loading of samples in flow cytometers. This apparatus automates the preanalytical steps of dilution and staining of blood cells prior to microfluidic loading. It employs an assembly with a miniature vibration motor to drive turbulence in a sample reservoir. To validate performance of this system, we present experimental evidence demonstrating prevention of blood cell settling, cell integrity, and staining of cells prior to flow cytometric analysis. This setup is further integrated with a microfluidic imaging flow cytometer to investigate cell count variability. With no need for prior sample preparation, a drop of whole blood can be directly introduced to the setup without premixing with buffers manually. Our results show that integration of this assembly with microfluidic analysis provides a competent automation tool for low-cost point-of-care blood-based diagnostics.

A Digital-Analog Microfluidic Platform for Patient-Centric Multiplexed Biomarker Diagnostics of Ultralow Volume Samples.

Microfluidic diagnostic devices have the potential to transform the practice of medicine. We engineered a multiplexed digital-analog microfluidic platform for the rapid and highly sensitive detection of 3-4 biomarkers in quadruplicate in 16 independent and isolated microfluidic unit cells requiring only a single 5 μL sample. We comprehensively characterized the platform by performing single enzyme and digital immunoassays, achieving single molecule detection and measured as low as ∼10 fM (330 fg/mL) GFP in buffer and ∼12 fM GFP in human serum. We applied our integrated digital detection mechanism to multiplexed detection of 1pM anti-Ebola IgG in human serum and were able to differentiate three common Ebola strains. To ascertain that the device can be applied in environments beyond clinical point-of-care settings, we developed a low-cost, portable hardware system to control and read out the microfluidic device and detected anti-Ebola IgG in ultralow volume whole blood samples to levels of 100 pM in a multiplexed assay format.

Human breast cancer cell enrichment by Dean flow driven microfluidic channels

Cell separation based on size by microfluidic devices has become a widely studied research area to facilitate the diagnosis of malaria and cancer, in particular. Conventional diagnostic systems are sophisticated but expensive; however, with microfluidic devices a broad range of laboratory applications can be accomplished in a hand-held device. In this work, we fabricate a series of devices as Dean force coupled curved mirochannels for separation of human breast cancer cell lines which are MCF-7 (~20 µm) and MD-MBA-231 (~15 µm). These curved channels were fabricated in four different dimensions: 400 µm wide × 81 µm high; 500 μm wide × 84 μm; 600 μm wide × 91 μm high; 700 μm wide × 86 μm high. These channels have one inlet and three outlets. Each channel experienced different flow rates to observe cell focusing and separation. The MCF-7 cell line was labeled with carboxyfluorescein succinimidyl ester, which has a fluorescence characteristic, whereas the MDA-MB-231 cell line was unlabeled. Fluorescence microscopy experiments were performed to determine the appropriate flow rates for focusing. The investigation of cell separation yield was performed by flow cytometry. Adjusting flow rates revealed that enrichment of MCF-7 cells requires very high flow rates. Flow cytometry analysis confirmed enrichment to occur at the second outlet of each channel. The efficiency of enrichment was observed in the microchannel with 500 µm width as high as 93 %. Our results suggest that these curved channels can be regarded as a prototype of a microfluidic diagnostic device due to their fast reaction time, relatively accurate results, low cost and miniaturized features.

Making a hydrophoretic focuser tunable using a diaphragm.

Microfluidic diagnostic devices often require handling particles or cells with different sizes. In this investigation, a tunable hydrophoretic device was developed which consists of a polydimethylsiloxane (PDMS) slab with hydrophoretic channel, a PDMS diaphragm with pressure channel, and a glass slide. The height of the hydrophoretic channel can be tuned simply and reliably by deforming the elastomeric diaphragm with pressure applied on the pressure channel. This operation allows the device to have a large operating range where different particles and complex biological samples can be processed. The focusing performance of this device was tested using blood cells that varied in shape and size. The hydrophoretic channel had a large cross section which enabled a throughput capability for cell focusing of ∼15 000 cells s(-1), which was more than the conventional hydrophoretic focusing and dielectrophoresis (DEP)-active hydrophoretic methods. This tunable hydrophoretic focuser can potentially be integrated into advanced lab-on-a-chip bioanalysis devices.

Hydroxypropyl Cellulose Methacrylate as a Photo‐Patternable and Biodegradable Hybrid Paper Substrate for Cell Culture and Other Bioapplications

In addition to the choice of appropriate material properties of the tissue construct to be used, such as its biocompatibility, biodegradability, cytocompatibility, and mechanical rigidity, the ability to incorporate microarchitectural patterns in the construct to mimic that found in the cellular microenvironment is an important consideration in tissue engineering and regenerative medicine. Both these issues are addressed by demonstrating a method for preparing biodegradable and photo-patternable constructs, where modified cellulose is cross-linked to form an insoluble structure in an aqueous environment. Specifically, hydroxypropyl cellulose (HPC) is rendered photocrosslinkable by grafting with methylacrylic anhydride, whose linkages also render the cross-linked construct hydrolytically degradable. The HPC is then cross-linked via a photolithography-based fabrication process. The feasibility of functionalizing these HPC structures with biochemical cues is verified post-fabrication, and shown to facilitate the adhesion of mesenchymal progenitor cells. The HPC constructs are shown to be biocompatible and hydrolytically degradable, thus enabling cell proliferation and cell migration, and therefore constituting an ideal candidate for long-term cell culture and implantable tissue scaffold applications. In addition, the potential of the HPC structure is demonstrated as an alternative substrate to paper microfluidic diagnostic devices for protein and cell assays.

Applications of microfluidics for molecular diagnostics.

Diagnostic assays implemented in microfluidic devices have developed rapidly over the past decade and are expected to become commonplace in the next few years. Hundreds of microfluidics-based approaches towards clinical diagnostics and pathogen detection have been reported with a general theme of rapid and customizable assays that are potentially cost-effective. This chapter reviews microfluidics in molecular diagnostics based on application areas with a concise review of microfluidics in general. Basic principles of microfabrication are briefly reviewed and the transition to polymer fabricated devices is discussed. Most current microfluidic diagnostic devices are designed to target a single disease, such as a given cancer or a variety of pathogens, and there will likely be a large market for these focused devices; however, the future of molecular diagnostics lies in highly multiplexed microfluidic devices that can screen for potentially hundreds of diseases simultaneously.

Control of Microfluidic Flow in Amphiphilic Fabrics

Woven textile fabrics were designed and constructed from hydrophilic and hydrophobic spun yarns to give planar substrates containing amphiphilic microchannels with defined orientations and locations. Polypropylene fibers were spun to give hydrophobic yarns, and the hydrophilic yarns were spun from a poly(ethylene terephthalate) copolyester. Water wicking rates into the fabrics were measured by video microscopy from single drops, relevant for point-of-care microfluidic diagnostic devices, and from reservoirs. intra-yarn microchannels in the hydrophilic polyester yarns were shown to selectively transport aqueous fluids, with the flow path governed by the placement of the hydrophilic yarns in the fabric. By comparing fluid transport in fabric constructions with systematic variations in the numbers of adjacent parallel and orthogonal hydrophilic yarns, it was found that inter-yarn microchannels significantly increased wicking rates. Simultaneous wicking of an aqueous and hydrocarbon fluid into the hydrophilic and hydrophobic microchannels of an amphiphilic fabric was successfully demonstrated. The high degree of interfacial contact and micrometer-scale diffusion lengths of such coflowing immiscible fluid streams inside amphiphilic fabrics suggest potential applications as highly scalable and affordable microcontactors for liquid-liquid extractions.