Phaseguides as tunable passive microvalves for liquid routing in complex microfluidic networks

A three-dimensional vessel-on-chip model to study Puumala orthohantavirus pathogenesis

Puumala orthohantavirus (PUUV) infection in humans can result in hemorrhagic fever with renal syndrome. Endothelial cells (ECs) are primarily infected with increased vascular permeability as a central aspect of pathogenesis. Historically, most studies included ECs cultured under static two-dimensional (2D) conditions, thereby not recapitulating the physiological environment due to their lack of flow and inherent pro-inflammatory state. Here, we present a high-throughput model for culturing primary human umbilical vein ECs in 3D vessels-on-chip in which we compared host responses of these ECs to those of static 2D-cultured ECs on a transcriptional level. The phenotype of ECs in vessels-on-chip more closely resembled the in vivo situation due to higher similarity in expression of genes encoding described markers for disease severity and coagulopathy, including IDO1, LGALS3BP, IL6 and PLAT, and more diverse endothelial-leukocyte interactions in the context of PUUV infection. In these vessels-on-chip, PUUV infection did not directly increase vascular permeability, but increased monocyte adhesion. This platform can be used for studying pathogenesis and assessment of possible therapeutics for other endotheliotropic viruses even in high biocontainment facilities.

A sequential liquid dispensing method in a centrifugal microfluidic device operating at a constant rotational speed for the multiplexed genetic detection of foodborne pathogens

This study proposes a sequential liquid dispensing method using a centrifugal microfluidic device operating at a constant rotational speed for the multiplexed genetic detection of nucleic acid targets across multiple samples in a single operation. A pair of passive valves integrated into each microchamber enabled the liquid to fill towards the center of rotation against the centrifugal force, facilitating the complete removal of air inside the microchamber. Liquid manipulation can be achievable without any surface coating of the device by exploiting the inherent hydrophobicity of the polymer. Furthermore, design guidelines for the optimization of microfluidic devices are clarified. Consequently, our proposed method allows direct liquid dispensing into the reaction chambers without cross-contamination while simultaneously metering the sample/reagent volume for the colorimetric loop-mediated isothermal amplification (LAMP) reaction. In addition, we demonstrated the simultaneous detection of four foodborne pathogens (Salmonella spp., Vibrio parahaemolyticus, Campylobacter spp., and norovirus genogroup II (GII)) across four samples in a centrifugal microfluidic device within 60 min. Furthermore, the device exhibited high quantitation (R 2 > 0.98) of the DNA concentration in the sample. Our proposed method enables a more compact design by eliminating the need for metering chambers and offers a point-of-care testing platform with high simplicity as it operates at a constant rotational speed.

A high-throughput gut-on-chip platform to study the epithelial responses to enterotoxins

Enterotoxins are a type of toxins that primarily affect the intestines. Understanding their harmful effects is essential for food safety and medical research. Current methods lack high-throughput, robust, and translatable models capable of characterizing toxin-specific epithelial damage. Pressing concerns regarding enterotoxin contamination of foods and emerging interest in clinical applications of enterotoxins emphasize the need for new platforms. Here, we demonstrate how Caco-2 tubules can be used to study the effect of enterotoxins on the human intestinal epithelium, reflecting toxins' distinct pathogenic mechanisms. After exposure of the model to toxins nigericin, ochratoxin A, patulin and melittin, we observed dose-dependent reductions in barrier permeability as measured by TEER, which were detected with higher sensitivity than previous studies using conventional models. Combination of LDH release assays and DRAQ7 staining allowed comprehensive evaluation of toxin cytotoxicity, which was only observed after exposure to melittin and ochratoxin A. Furthermore, the study of actin cytoskeleton allowed to assess toxin-induced changes in cell morphology, which were only caused by nigericin. Altogether, our study highlights the potential of our Caco-2 tubular model in becoming a multi-parametric and high-throughput tool to bridge the gap between current enterotoxin research and translatable in vivo models of the human intestinal epithelium.

Mixing Performance of a Planar Asymmetric Contraction-and-Expansion Micromixer

Micromixers are one of the critical components in microfluidic devices. They significantly affect the efficiency and sensitivity of microfluidics-based lab-on-a-chip systems. This study introduces an efficient micromixer with a simple geometrical feature that enables easy incorporation in a microchannel network without compromising the original design of microfluidic devices. The study proposes a newly designed planar passive micromixer, termed a planar asymmetric contraction-and-expansion (P-ACE) micromixer, with asymmetric vertical obstacle structures. Numerical simulation and experimental investigation revealed that the optimally designed P-ACE micromixer exhibited a high mixing efficiency of 80% or more within a microchannel length of 10 mm over a wide range of Reynolds numbers (0.13 ≤ Re ≤ 13), eventually attaining approximately 90% mixing efficiency within a 20 mm microchannel length. The highly asymmetric geometric features of the P-ACE micromixers enhance mixing because of their synergistic effects. The flow velocities and directions of the two fluids change differently while alternately crossing the longitudinal centerline of the microchannel, with the obstacle structures asymmetrically arranged on both sidewalls of the rectangular microchannel. This flow behavior increases the interfacial contact area between the two fluids, thus promoting effective mixing in the P-ACE micromixer. Further, the pressure drops in the P-ACE micromixers were experimentally investigated and compared with those in a serpentine micromixer with a perfectly symmetric mixing unit.

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.

Advances in Organ-on-a-Chip Materials and Devices

The organ-on-a-chip (OoC) paves a way for biomedical applications ranging from preclinical to clinical translational precision. The current trends in the in vitro modeling is to reduce the complexity of human organ anatomy to the fundamental cellular microanatomy as an alternative of recreating the entire cell milieu that allows systematic analysis of medicinal absorption of compounds, metabolism, and mechanistic investigation. The OoC devices accurately represent human physiology in vitro; however, it is vital to choose the correct chip materials. The potential chip materials include inorganic, elastomeric, thermoplastic, natural, and hybrid materials. Despite the fact that polydimethylsiloxane is the most commonly utilized polymer for OoC and microphysiological systems, substitute materials have been continuously developed for its advanced applications. The evaluation of human physiological status can help to demonstrate using noninvasive OoC materials in real-time procedures. Therefore, this Review examines the materials used for fabricating OoC devices, the application-oriented pros and cons, possessions for device fabrication and biocompatibility, as well as their potential for downstream biochemical surface alteration and commercialization. The convergence of emerging approaches, such as advanced materials, artificial intelligence, machine learning, three-dimensional (3D) bioprinting, and genomics, have the potential to perform OoC technology at next generation. Thus, OoC technologies provide easy and precise methodologies in cost-effective clinical monitoring and treatment using standardized protocols, at even personalized levels. Because of the inherent utilization of the integrated materials, employing the OoC with biomedical approaches will be a promising methodology in the healthcare industry.

In vitro grafting of hepatic spheroids and organoids on a microfluidic vascular bed

With recent progress in modeling liver organogenesis and regeneration, the lack of vasculature is becoming the bottleneck in progressing our ability to model human hepatic tissues in vitro. Here, we introduce a platform for routine grafting of liver and other tissues on an in vitro grown microvascular bed. The platform consists of 64 microfluidic chips patterned underneath a 384-well microtiter plate. Each chip allows the formation of a microvascular bed between two main lateral vessels by inducing angiogenesis. Chips consist of an open-top microfluidic chamber, which enables addition of a target tissue by manual or robotic pipetting. Upon grafting a liver microtissue, the microvascular bed undergoes anastomosis, resulting in a stable, perfusable vascular network. Interactions with vasculature were found in spheroids and organoids upon 7 days of co-culture with space of Disse-like architecture in between hepatocytes and endothelium. Veno-occlusive disease was induced by azathioprine exposure, leading to impeded perfusion of the vascularized spheroid. The platform holds the potential to replace animals with an in vitro alternative for routine grafting of spheroids, organoids, or (patient-derived) explants.

A method of sequential liquid dispensing for the multiplexed genetic diagnosis of viral infections in a microfluidic device

In this study, we introduce polydimethylsiloxane (PDMS)-based microfluidic devices capable of sequential dispensing of samples into multiple reaction microchambers in a single operation to provide a fast and easy sample-to-answer platform for multiplexed genetic diagnosis of multiple viral infectious diseases. This approach utilizes the loop-mediated isothermal amplification (LAMP) method to amplify and detect specific nucleic acid (DNA/RNA) targets. We present a microfluidic flow control theory for sequential liquid dispensing phenomena, which provides design guidelines for device optimization. The device specifications, such as the possible dispensing number and maximal allowable flow rate, can be theoretically designed by optimizing the geometric dimensions of the microchannels and a pair of passive stop valves integrated into each microchamber together with the water contact angles of the materials used to fabricate the microfluidic devices. In addition, a passive stop valve with a vertical-type phaseguide structure was designed to improve device performance. We could simultaneously diagnose coronavirus disease 2019 (COVID-19) and other infectious diseases, such as severe acute respiratory syndrome (SARS), seasonal influenza A, and pandemic influenza A (H1N1) 2009. The colorimetric reverse transcription LAMP (RT-LAMP) assay suggests that the four viral infectious diseases can be detected within 30 min using a hue-based quantitative analysis, and the naked eye using our microfluidic devices.

TANDEM: biomicrofluidic systems with transverse and normal diffusional environments for multidirectional signaling

Biomicrofluidic systems that can recapitulate complex biological processes with precisely controlled 3D geometries are a significant advancement from traditional 2D cultures. To this point, these systems have largely been limited to either laterally adjacent channels in a single plane or vertically stacked single-channel arrangements. As a result, lateral (or transverse) and vertical (or normal) diffusion have been isolated to their respective designs only, thus limiting potential access to nutrients and 3D communication that typifies in vivo microenvironments. Here we report a novel device architecture called "TANDEM", an acronym for "T̲ransverse A̲nd N̲ormal D̲iffusional E̲nvironments for M̲ultidirectional Signaling", which enables multiplanar arrangements of aligned channels where normal and transverse diffusion occur in tandem to facilitate multidirectional communication. We developed a computational transport model in COMSOL and tested diffusion and culture viability in one specific TANDEM configuration, and found that TANDEM systems demonstrated enhanced diffusion in comparison to single-plane counterparts. This resulted in improved viability of hydrogel-embedded cells, which typically suffer from a lack of sufficient nutrient access during long-term culture. Finally, we showed that TANDEM designs can be expanded to more complex alternative configurations depending on the needs of the end-user. Based on these findings, TANDEM designs can utilize multidirectional enhanced diffusion to improve long-term viability and ultimately facilitate more robust and more biomimetic microfluidic systems with increasingly more complex geometric layouts.

A new drug testing platform based on 3D tri-culture in lab-on-a-chip devices

Drug discovery has a 90% rate of failure because preclinical platforms for drug testing do not mimic the in vivo conditions. Doxorubicin (DOX) is a commonly used drug to treat breast cancer patients even though it has side effects. Lab-on-a-chip (LOC) devices provide spatial control at the micrometer scale and can thus emulate the cancer microenvironment. Here, using a multidisciplinary approach, a new drug testing platform based on 3D tri-culture in LOC devices was developed. Breast cancer cells alone or with normal mammary epithelial cells and macrophages were cultured in matrigel in LOC devices. The platform was used to test DOX and (R)-4'-methylklavuzon (KLA), which is a new anti-cancer drug candidate. Results showed that DOX and KLA were equally effective on breast cancer cells in 3D monoculture. KLA produced 26% less death for breast cancer cells than DOX in 3D tri-culture. More importantly, DOX was not selective between breast cancer cells and normal mammary epithelial cells in 3D tri- culture whereas KLA caused 56% less cell death than DOX for normal mammary epithelial cells. Results strongly recommend that 3D tri-culture in LOC devices be used for assessment of drug toxicity at the preclinical stage.

Spheroids as a Type of Three-Dimensional Cell Cultures-Examples of Methods of Preparation and the Most Important Application

Cell cultures are very important for testing materials and drugs, and in the examination of cell biology and special cell mechanisms. The most popular models of cell culture are two-dimensional (2D) as monolayers, but this does not mimic the natural cell environment. Cells are mostly deprived of cell-cell and cell-extracellular matrix interactions. A much better in vitro model is three-dimensional (3D) culture. Because many cell lines have the ability to self-assemble, one 3D culturing method is to produce spheroids. There are several systems for culturing cells in spheroids, e.g., hanging drop, scaffolds and hydrogels, and these cultures have their applications in drug and nanoparticles testing, and disease modeling. In this paper we would like to present methods of preparation of spheroids in general and emphasize the most important applications.

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.

Capillary microfluidics in microchannels: from microfluidic networks to capillaric circuits

Microfluidics offer economy of reagents, rapid liquid delivery, and potential for automation of many reactions, but often require peripheral equipment for flow control. Capillary microfluidics can deliver liquids in a pre-programmed manner without peripheral equipment by exploiting surface tension effects encoded by the geometry and surface chemistry of a microchannel. Here, we review the history and progress of microchannel-based capillary microfluidics spanning over three decades. To both reflect recent experimental and conceptual progress, and distinguish from paper-based capillary microfluidics, we adopt the more recent terminology of capillaric circuits (CCs). We identify three distinct waves of development driven by microfabrication technologies starting with early implementations in industry using machining and lamination, followed by development in the context of micro total analysis systems (μTAS) and lab-on-a-chip devices using cleanroom microfabrication, and finally a third wave that arose with advances in rapid prototyping technologies. We discuss the basic physical laws governing capillary flow, deconstruct CCs into basic circuit elements including capillary pumps, stop valves, trigger valves, retention valves, and so on, and describe their operating principle and limitations. We discuss applications of CCs starting with the most common usage in automating liquid delivery steps for immunoassays, and highlight emerging applications such as DNA analysis. Finally, we highlight recent developments in rapid prototyping of CCs and the benefits offered including speed, low cost, and greater degrees of freedom in CC design. The combination of better analytical models and lower entry barriers (thanks to advances in rapid manufacturing) make CCs both a fertile research area and an increasingly capable technology for user-friendly and high-performance laboratory and diagnostic tests.

A multiplexed microfluidic system for evaluation of dynamics of immune-tumor interactions

Recapitulation of the tumor microenvironment is critical for probing mechanisms involved in cancer, and for evaluating the tumor-killing potential of chemotherapeutic agents, targeted therapies and immunotherapies. Microfluidic devices have emerged as valuable tools for both mechanistic studies and for preclinical evaluation of therapeutic agents, due to their ability to precisely control drug concentrations and gradients of oxygen and other species in a scalable and potentially high throughput manner. Most existing in vitro microfluidic cancer models are comprised of cultured cancer cells embedded in a physiologically relevant matrix, collocated with vascular-like structures. However, the recent emergence of immune checkpoint inhibitors (ICI) as a powerful therapeutic modality against many cancers has created a need for preclinical in vitro models that accommodate interactions between tumors and immune cells, particularly for assessment of unprocessed tumor fragments harvested directly from patient biopsies. Here we report on a microfluidic model, termed EVIDENT (ex vivo immuno-oncology dynamic environment for tumor biopsies), that accommodates up to 12 separate tumor biopsy fragments interacting with flowing tumor-infiltrating lymphocytes (TILs) in a dynamic microenvironment. Flow control is achieved with a single pump in a simple and scalable configuration, and the entire system is constructed using low-sorption materials, addressing two principal concerns with existing microfluidic cancer models. The system sustains tumor fragments for multiple days, and permits real-time, high-resolution imaging of the interaction between autologous TILs and tumor fragments, enabling mapping of TIL-mediated tumor killing and testing of various ICI treatments versus tumor response. Custom image analytic algorithms based on machine learning reported here provide automated and quantitative assessment of experimental results. Initial studies indicate that the system is capable of quantifying temporal levels of TIL infiltration and tumor death, and that the EVIDENT model mimics the known in vivo tumor response to anti-PD-1 ICI treatment of flowing TILs relative to isotype control treatments for syngeneic mouse MC38 tumors.

96 perfusable blood vessels to study vascular permeability in vitro

Current in vitro models to test the barrier function of vasculature are based on flat, two-dimensional monolayers. These monolayers do not have the tubular morphology of vasculature found in vivo and lack important environmental cues from the cellular microenvironment, such as interaction with an extracellular matrix (ECM) and exposure to flow. To increase the physiological relevance of in vitro models of the vasculature, it is crucial to implement these cues and better mimic the native three-dimensional vascular architecture. We established a robust, high-throughput method to culture endothelial cells as 96 three-dimensional and perfusable microvessels and developed a quantitative, real-time permeability assay to assess their barrier function. Culture conditions were optimized for microvessel formation in 7 days and were viable for over 60 days. The microvessels exhibited a permeability to 20 kDa dextran but not to 150 kDa dextran, which mimics the functionality of vasculature in vivo. Also, a dose-dependent effect of VEGF, TNFα and several cytokines confirmed a physiologically relevant response. The throughput and robustness of this method and assay will allow end-users in vascular biology to make the transition from two-dimensional to three-dimensional culture methods to study vasculature.

3D capillary stop valves for versatile patterning inside microfluidic chips

The patterning of antibodies in microfluidics chips is always a delicate process that is usually done in an open chip before bonding. Typical bonding techniques such as plasma treatment can harm the antibodies with as result that they are removed from our fabrication toolbox. Here we propose a method, based on capillary phenomena using 3D capillary valves, that autonomously and conveniently allows us to pattern liquids inside closed chips. We theoretically analyse the system and demonstrate how our analysis can be used as a design tool for various applications. Chips patterned with the method were used for simple immunodetection of a cardiac biomarker which demonstrates its suitability for antibody patterning.

Gel integration for microfluidic applications

Molecular diffusive membranes or materials are important for biological applications in microfluidic systems. Hydrogels are typical materials that offer several advantages, such as free diffusion for small molecules, biocompatibility with most cells, temperature sensitivity, relatively low cost, and ease of production. With the development of microfluidic applications, hydrogels can be integrated into microfluidic systems by soft lithography, flow-solid processes or UV cure methods. Due to their special properties, hydrogels are widely used as fluid control modules, biochemical reaction modules or biological application modules in different applications. Although hydrogels have been used in microfluidic systems for more than ten years, many hydrogels' properties and integrated techniques have not been carefully elaborated. Here, we systematically review the physical properties of hydrogels, general methods for gel-microfluidics integration and applications of this field. Advanced topics and the outlook of hydrogel fabrication and applications are also discussed. We hope this review can help researchers choose suitable methods for their applications using hydrogels.

Differentiation of neuroepithelial stem cells into functional dopaminergic neurons in 3D microfluidic cell culture

A hallmark of Parkinson's disease is the progressive loss of nigrostriatal dopaminergic neurons. We derived human neuroepithelial cells from induced pluripotent stem cells and successfully differentiated them into dopaminergic neurons within phase-guided, three-dimensional microfluidic cell culture bioreactors. After 30 days of differentiation within the microfluidic bioreactors, in situ morphological, immunocytochemical and calcium imaging confirmed the presence of dopaminergic neurons that were spontaneously electrophysiologically active, a characteristic feature of nigrostriatal dopaminergic neurons in vivo. Differentiation was as efficient as in macroscopic culture, with up to 19% of differentiated neurons immunoreactive for tyrosine hydroxylase, the penultimate enzyme in the synthesis of dopamine. This new microfluidic cell culture model integrates the latest innovations in developmental biology and microfluidic cell culture to generate a biologically realistic and economically efficient route to personalised drug discovery for Parkinson's disease.