Automated high-throughput microchannel assays for cell biology: Operational optimization and characterization

Wall-mounted flexible plates in a two-dimensional channel trigger early flow instabilities

A high level of mixing by passive means is a desirable feature in microchannels for various applications, and use of flexible obstacles (or plates) is one of the prime choices in that regard. To gain further insight, we carry out two-dimensional numerical simulations for flow past one or two flexible plates anchored to a channel's opposite walls using a fluid-structure interaction framework. For the inlet flow Reynolds number vs the Strouhal number plane, we observe a sudden flow change from a laminar to a time-periodic vortex shedding state when flexible plates are present in the channel. We found the critical Reynolds number to be Re_{cr}≈370 when a single plate is anchored on the channel wall and Re_{cr}≈290 or even lower when two plates are anchored. With an increase in the inlet flow Reynolds number (up to 3200), we found that vortices detach regularly at the plates' tips, which causes the flow to meander in the channel. In a two-plate anchored configuration, primary vortices generated at the first plate are constrained by the second plate and result in an energetic secondary vortex generation in the downstream side. The overall flow features and the energy dissipation in the channel are mainly controlled by the separation gap between the plates. At high-inlet-flow Reynolds numbers (≥1600), the probability density function (F) of the kinetic energy dissipation in a flexible plate configuration shows a stretched exponential shape in the form F(Z)∼1/sqrt[Z]e^{-pZ^{q}}, where Z is the normalized kinetic energy dissipation and the constants p=0.89 and q=0.86. The observed increase in energy dissipation comes at the cost of an increase in pressure loss in the channel, and we found that the loss is inversely related to the plates' separation gap. From our simulations, we found that if high mixing levels are desired, then two flexible plates anchored to the channel walls is a better choice than a channel flow without obstacles or flow past a single plate. The two-plate configuration with zero separation gap between the plates is best suited to achieve a high mixing level.

A Platform for High-Throughput Assessments of Environmental Multistressors

A platform compatible with microtiter plates to parallelize environmental treatments to test the complex impacts of multiple stressors, including parameters relevant to climate change and point source pollutants is developed. This platform leverages (1) the high rate of purely diffusive gas transport in aerogels to produce well-defined centimeter-scale gas concentration gradients, (2) spatial light control, and (3) established automated liquid handling. The parallel gaseous, aqueous, and light control provided by the platform is compatible with multiparameter experiments across the life sciences. The platform is applied to measure biological effects in over 700 treatments in a five-parameter full factorial study with the microalgae Chlamydomonas reinhardtii. Further, the CO2 response of multicellular organisms, Lemna gibba and Artemia salina under surfactant and nanomaterial stress are tested with the platform.

Multiwell capillarity-based microfluidic device for the study of 3D tumour tissue-2D endothelium interactions and drug screening in co-culture models

The tumour microenvironment is very complex, and essential in tumour development and drug resistance. The endothelium is critical in the tumour microenvironment: it provides nutrients and oxygen to the tumour and is essential for systemic drug delivery. Therefore, we report a simple, user-friendly microfluidic device for co-culture of a 3D breast tumour model and a 2D endothelium model for cross-talk and drug delivery studies. First, we demonstrated the endothelium was functional, whereas the tumour model exhibited in vivo features, e.g., oxygen gradients and preferential proliferation of cells with better access to nutrients and oxygen. Next, we observed the endothelium structure lost its integrity in the co-culture. Following this, we evaluated two drug formulations of TRAIL (TNF-related apoptosis inducing ligand): soluble and anchored to a LUV (large unilamellar vesicle). Both diffused through the endothelium, LUV-TRAIL being more efficient in killing tumour cells, showing no effect on the integrity of endothelium. Overall, we have developed a simple capillary force-based microfluidic device for 2D and 3D cell co-cultures. Our device allows high-throughput approaches, patterning different cell types and generating gradients without specialised equipment. We anticipate this microfluidic device will facilitate drug screening in a relevant microenvironment thanks to its simple, effective and user-friendly operation.

Adaptation of a Simple Microfluidic Platform for High-Dimensional Quantitative Morphological Analysis of Human Mesenchymal Stromal Cells on Polystyrene-Based Substrates

Multipotent stromal cells (MSCs, often called mesenchymal stem cells) have garnered significant attention within the field of regenerative medicine because of their purported ability to differentiate down musculoskeletal lineages. Given the inherent heterogeneity of MSC populations, recent studies have suggested that cell morphology may be indicative of MSC differentiation potential. Toward improving current methods and developing simple yet effective approaches for the morphological evaluation of MSCs, we combined passive pumping microfluidic technology with high-dimensional morphological characterization to produce robust tools for standardized high-throughput analysis. Using ultraviolet (UV) light as a modality for reproducible polystyrene substrate modification, we show that MSCs seeded on microfluidic straight channel devices incorporating UV-exposed substrates exhibited morphological changes that responded accordingly to the degree of substrate modification. Substrate modification also effected greater morphological changes in MSCs seeded at a lower rather than higher density within microfluidic channels. Despite largely comparable trends in morphology, MSCs seeded in microscale as opposed to traditional macroscale platforms displayed much higher sensitivity to changes in substrate properties. In summary, we adapted and qualified microfluidic cell culture platforms comprising simple straight channel arrays as a viable and robust tool for high-throughput quantitative morphological analysis to study cell-material interactions.

A novel 96well-formatted micro-gap plate enabling drug response profiling on primary tumour samples

Drug-based treatments are the most widely used interventions for cancer management. Personalized drug response profiling remains inherently challenging with low cell count harvested from tumour sample. We present a 96well-formatted microfluidic plate with built-in micro-gap that preserves up to 99.2% of cells during multiple assay/wash operation and only 9,000 cells needed for a single reagent test (i.e. 1,000 cells per test spot x 3 selected concentration x triplication), enabling drug screening and compatibility with conventional automated workstations. Results with MCF7 and MDA-MB-231 cell lines showed that no statistical significance was found in dose-response between the device and conventional 96-well plate control. Primary tumour samples from breast cancer patients tested in the device also showed good IC₅₀ prediction. With drug screening of primary cancer cells must consider a wide range of scenarios, e.g. suspended/attached cell types and rare/abundant cell availability, the device enables high throughput screening even for suspended cells with low cell count since the signature microfluidic cell-trapping feature ensures cell preservation in a multiple solution exchange protocol.

High-density self-contained microfluidic KOALA kits for use by everyone

Cell-based assays are essential tools used by research labs in a wide range of fields, including cell biology, toxicology, and natural product discovery labs. However, in some situations, the need for cell-based assays does not justify the costs of maintaining cell culture facilities and retaining skilled staff. The kit-on-a-lid assay (KOALA) technology enables accessible low-cost and prepackageable microfluidic platforms that can be operated with minimal infrastructure or training. Here, we demonstrate and characterize high-density KOALA methods for high-throughput applications, achieving an assay density comparable to that of a 384-well plate and usability by hand with no liquid-handling equipment. We show the potential for high-content screening and complex assays such as quantitative immunochemistry assays requiring multiple steps and reagents.

Cellular microenvironment dictates androgen production by murine fetal Leydig cells in primary culture

Despite the fact that fetal Leydig cells are recognized as the primary source of androgens in male embryos, the mechanisms by which steroidogenesis occurs within the developing testis remain unclear. A genetic approach was used to visualize and isolate fetal Leydig cells from remaining cells within developing mouse testes. Cyp11a1-Cre mice were bred to mT/mG dual reporter mice to target membrane-tagged enhanced green fluorescent protein (GFP) within steroidogenic cells, whereas other cells expressed membrane-tagged tandem-dimer tomato red. Fetal Leydig cell identity was validated using double-labeled immunohistochemistry against GFP and the steroidogenic enzyme 3beta-HSD, and cells were successfully isolated as indicated by qPCR results from sorted cell populations. Because fetal Leydig cells must collaborate with neighboring cells to synthesize testosterone, we hypothesized that the fetal Leydig cell microenvironment defined their capacity for androgen production. Microfluidic culture devices were used to measure androstenedione and testosterone production of fetal Leydig cells that were cultured in cell-cell contact within a mixed population, were isolated but remained in medium contact via compartmentalized co-culture with other testicular cells, or were isolated and cultured alone. Results showed that fetal Leydig cells maintained their identity and steroidogenic activity for 3-5 days in primary culture. Microenvironment dictated proficiency of testosterone production. As expected, fetal Leydig cells produced androstenedione but not testosterone when cultured in isolation. More testosterone accumulated in medium from mixed cultures than from compartmentalized co-cultures initially; however, co-cultures maintained testosterone synthesis for a longer time. These data suggest that a combination of cell-cell contact and soluble factors constitute the ideal microenvironment for fetal Leydig cell activity in primary culture.

Vascular smooth muscle cell culture in microfluidic devices

This paper presents a microfluidic device enabling culture of vascular smooth muscle cells (VSMCs) where extracellular matrix coating, VSMC seeding, culture, and immunostaining are demonstrated in a tubing-free manner. By optimizing droplet volume differences between inlets and outlets of micro channels, VSMCs were evenly seeded into microfluidic devices. Furthermore, the effects of extracellular matrix (e.g., collagen, poly-l-Lysine (PLL), and fibronectin) on VSMC proliferation and phenotype expression were explored. As a platform technology, this microfluidic device may function as a new VSMC culture model enabling VSMC studies.

Characterizing asthma from a drop of blood using neutrophil chemotaxis

Asthma is a chronic inflammatory disorder that affects more than 300 million people worldwide. Asthma management would benefit from additional tools that establish biomarkers to identify phenotypes of asthma. We present a microfluidic solution that discriminates asthma from allergic rhinitis based on a patient's neutrophil chemotactic function. The handheld diagnostic device sorts neutrophils from whole blood within 5 min, and generates a gradient of chemoattractant in the microchannels by placing a lid with chemoattractant onto the base of the device. This technology was used in a clinical setting to assay 34 asthmatic (n = 23) and nonasthmatic, allergic rhinitis (n = 11) patients to establish domains for asthma diagnosis based on neutrophil chemotaxis. We determined that neutrophils from asthmatic patients migrate significantly more slowly toward the chemoattractant compared with nonasthmatic patients (P = 0.002). Analysis of the receiver operator characteristics of the patient data revealed that using a chemotaxis velocity of 1.55 μm/min for asthma yields a diagnostic sensitivity and specificity of 96% and 73%, respectively. This study identifies neutrophil chemotaxis velocity as a potential biomarker for asthma, and we demonstrate a microfluidic technology that was used in a clinical setting to perform these measurements.

Understanding the impact of 2D and 3D fibroblast cultures on in vitro breast cancer models

The utilization of 3D, physiologically relevant in vitro cancer models to investigate complex interactions between tumor and stroma has been increasing. Prior work has generally focused on the cancer cells and, the role of fibroblast culture conditions on tumor-stromal cell interactions is still largely unknown. Here, we focus on the stroma by comparing functional behaviors of human mammary fibroblasts (HMFs) cultured in 2D and 3D and their effects on the invasive progression of breast cancer cells (MCF10DCIS.com). We identified increased levels of several paracrine factors from HMFs cultured in 3D conditions that drive the invasive transition. Using a microscale co-culture model with improved compartmentalization and sensitivity, we demonstrated that HMFs cultured in 3D intensify the promotion of the invasive progression through the HGF/c-Met interaction. This study highlights the importance of the 3D stromal microenvironment in the development of multiple cell type in vitro cancer models.

Hormonally responsive breast cancer cells in a microfluidic co-culture model as a sensor of microenvironmental activity

Breast cancer cell growth and therapeutic response are manipulated extrinsically by microenvironment signals. Despite recognition of the importance of the microenvironment in a variety of tumor processes, predictive measures that incorporate the activity of the surrounding cellular environment are lacking. In contrast, tumor cell biomarkers are well established in the clinic. Expression of Estrogen Receptor-alpha (ERα) is the primary defining feature of hormonally responsive tumors and is the molecular target of therapy in the most commonly diagnosed molecular subtype of breast cancer. While a number of soluble factors have been implicated in ERα activation, the complexity of signaling between the cellular microenvironment and the cancer cell implies multivariate control. The cumulative impact of the microenvironment signaling, which we define as microenvironmental activity, is more difficult to predict than the sum of its parts. Here we tested the impact of an array of microenvironments on ERα signaling utilizing a microfluidic co-culture model. Quantitative immunofluorescence was employed to assess changes in ERα protein levels, combined with gene expression and phosphorylation status, as measures of activation. Analysis of microenvironment-induced growth under the same conditions revealed a previously undescribed correlation between growth and ERα protein down-regulation. These data suggest an expanded utility for the tumor biomarker ERα, in which the combination of dynamic regulation of ERα protein and growth in a breast cancer biosensor cell become a read-out of the microenvironmental activity.

High-content adhesion assay to address limited cell samples

Cell adhesion is a broad topic in cell biology that involves physical interactions between cells and other cells or the surrounding extracellular matrix, and is implicated in major research areas including cancer, development, tissue engineering, and regenerative medicine. While current methods have contributed significantly to our understanding of cell adhesion, these methods are unsuitable for tackling many biological questions requiring intermediate numbers of cells (10(2)-10(5)), including small animal biopsies, clinical samples, and rare cell isolates. To overcome this fundamental limitation, we developed a new assay to quantify the adhesion of ~10(2)-10(3) cells at a time on engineered substrates, and examined the adhesion strength and population heterogeneity via distribution-based modeling. We validated the platform by testing adhesion strength of cancer cells from three different cancer types (breast, prostate, and multiple myeloma) on both IL-1β activated and non-activated endothelial monolayers, and observed significantly increased adhesion for each cancer cell type upon endothelial activation, while identifying and quantifying distinct subpopulations of cell-substrate interactions. We then applied the assay to characterize adhesion of primary bone marrow stromal cells to different cardiac fibroblast-derived matrix substrates to demonstrate the ability to study limited cell populations in the context of cardiac cell-based therapies. Overall, these results demonstrate the sensitivity and robustness of the assay as well as its ability to enable extraction of high content, functional data from limited and potentially rare primary samples. We anticipate this method will enable a new class of biological studies with potential impact in basic and translational research.

Kit-On-A-Lid-Assays for accessible self-contained cell assays

Microscale methods for cell-based assays typically rely on macroscopic reagent handling and fluidic loading protocols that are technically challenging and do not scale with the number of assays favorably. Here, we demonstrate a microfluidic platform technology called "Kit-On-A-Lid-Assay" (KOALA), that enables the creation of self-contained microfluidic cell-based assays, integrating all the steps required to perform cell-based assays. The KOALA platform allows the pre-packaging of reagents, cryopreservation of cell suspensions, thawing of cell suspensions, culture of cells, and operation of whole cell-based assays. The operation of the KOALA platform is user-friendly and consists of bringing together a lid containing the microchannels, and a base containing the pre-packaged reagents, thereby causing fluidic exchange in all the channels simultaneously. We demonstrate that the KOALA cell-based assays can be simply operated from start to finish without any external laboratory equipment.

Tubeless microfluidic angiogenesis assay with three-dimensional endothelial-lined microvessels

The study of angiogenesis is important to understanding a variety of human pathologies including cancer, cardiovascular and inflammatory diseases. In vivo angiogenesis assays can be costly and time-consuming, limiting their application in high-throughput studies. While traditional in vitro assays may overcome these limitations, they lack the ability to accurately recapitulate the main elements of the tissue microenvironment found in vivo, thereby limiting our ability to draw physiologically relevant biological conclusions. To bridge the gap between in vivo and in vitro angiogenesis assays, several microfluidic methods have been developed to generate in vitro assays that incorporate blood vessel models with physiologically relevant three-dimensional (3D) lumen structures. However, these models have not seen widespread adoption, which can be partially attributed to the difficulty in fabricating these structures. Here, we present a simple, accessible method that takes advantage of basic fluidic principles to create 3D lumens with circular cross-sectional geometries through ECM hydrogels that are lined with endothelial monolayers to mimic the structure of blood vessels in vitro. This technique can be used to pattern endothelial cell-lined lumens in different microchannel geometries, enabling increased flexibility for a variety of studies. We demonstrate the implementation and application of this technique to the study of angiogenesis in a physiologically relevant in vitro setting.

A self-contained, programmable microfluidic cell culture system with real-time microscopy access

Utilizing microfluidics is a promising way for increasing the throughput and automation of cell biology research. We present a complete self-contained system for automated cell culture and experiments with real-time optical read-out. The system offers a high degree of user-friendliness, stability due to simple construction principles and compactness for integration with standard instruments. Furthermore, the self-contained system is highly portable enabling transfer between work stations such as laminar flow benches, incubators and microscopes. Accommodation of 24 individual inlet channels enables the system to perform parallel, programmable and multiconditional assays on a single chip. A modular approach provides system versatility and allows many different chips to be used dependent upon application. We validate the system's performance by demonstrating on-chip passive switching and mixing by peristaltically driven flows. Applicability for biological assays is demonstrated by on-chip cell culture including on-chip transfection and temporally programmable gene expression.

An inertia enhanced passive pumping mechanism for fluid flow in microfluidic devices

We describe and characterize a pumping mechanism that leverages the momentum present in small droplets ejected from a micro-nozzle to drive flow in an open microfluidic device. This approach allows driving flow in a microfluidic device in a regime that offers unique features different to those achievable with typical passive pumping or syringe-pump driven flow. Two flow regimes with specific flow characteristics are described: inertia enhanced passive pumping, in which fluid exchange times in the channel are significantly reduced, and inertia actuated flow, in which it is possible to initiate flow in an empty channel or against natural pressure gradients. Momentum is leveraged to create rapid fluid exchanges, instantaneous flow reversal, filling and mixing inside the microfluidic device.

Microscale functional cytomics for studying hematologic cancers

An important problem in translational cancer research is our limited ability to functionally characterize behaviors of primary patient cancer cells and associated stromal cell types, and relate mechanistic understanding to therapy selection. Functional analyses of primary samples face at least 3 major challenges: limited availability of primary samples for testing, paucity of functional information extracted from samples, and lack of functional methods accessible to many researchers. We developed a microscale cell culture platform that overcomes these limitations, especially for hematologic cancers. A key feature of the platform is the ability to compartmentalize small populations of adherent and nonadherent cells in controlled microenvironments that can better reflect physiological conditions and enable cell-cell interaction studies. Custom image analysis was developed to measure cell viability and protein subcellular localizations in single cells to provide insights into heterogeneity of cellular responses. We validated our platform by assessing viability and nuclear translocations of NF-κB and STAT3 in multiple myeloma cells exposed to different conditions, including cocultured bone marrow stromal cells. We further assessed its utility by analyzing NF-κB activation in a primary chronic lymphocytic leukemia patient sample. Our platform can be applied to myriad biological questions, enabling high-content functional cytomics of primary hematologic malignancies.

Automation of three-dimensional cell culture in arrayed microfluidic devices

The increasing interest in studying the interactions between cells and the extracellular matrix (ECM) has created a need for high throughput low-cost three-dimensional (3D) culture systems. The recent development of tubeless microfluidics via passive pumping provides a high throughput microchannel culture platform compatible with existing high throughput infrastructures (e.g., automated liquid handlers). Here, we build on a previously reported high throughput two-dimensional system to create a robust automated system for 3D culture. Operational controls including temperature and sample handling have been characterized and automated. Human mammary fibroblasts (HMFs) suspended in type I collagen are loaded and cultured in microchannel arrays and used to optimize the system operational parameters. A Peltier cooler maintains the collagen as a liquid at 4 °C during cell seeding, followed by polymerization at 37 °C. Optimization of this platform is discussed (e.g., controlling collagen contraction, increasing cell viability, preventing the removal of microchannel contents), and 3D distribution of HMFs is examined by fluorescent microscopy. Finally, we validate the platform by automating a previously developed 3D breast carcinoma coculture assay. The platform allows more efficient 3D culture experiments and lays the foundation for high throughput studies of cell-ECM interactions.

Transition to invasion in breast cancer: a microfluidic in vitro model enables examination of spatial and temporal effects

The transition of ductal carcinoma in situ (DCIS) to invasive ductal carcinoma (IDC) is a critical step in breast cancer progression. We introduce a simple microfluidic 3D compartmentalized system in which mammary epithelial cells (MCF-DCIS) are co-cultured with human mammary fibroblasts (HMFs), which promotes a transition from DCIS to IDC in vitro. The model enables control of both spatial (distance-dependence) and temporal (transition from larger clusters) aspects within the microenvironment, allowing recapitulation of the in vivo environment in ways not practical with existing experimental models. When HMFs were cultured some distance (0.5-1.5 mm) from the MCF-DCIS cells, we observed an initial morphological change, suggesting soluble factors can begin the transition. However, cell-cell contact with HMFs allowed the MCF-DCIS cells to complete the transition to invasion. Uniquely, the compartmentalized platform enables the analysis of the intrinsic second harmonic generation signal of collagen, providing a label-free quantitative analysis of DCIS-associated collagen remodeling. The arrayed microchannel-based model is compatible with existing infrastructure and, for the first time, provides a cost effective approach to test for inhibitors of pathways involved in DCIS progression to IDC allowing a screening approach to the identification of potential therapeutic targets. Importantly, the model can be easily adapted and generalized to a variety of cell-cell signaling studies.

Rapid prototyping of arrayed microfluidic systems in polystyrene for cell-based assays

Microfluidic cell-based systems have enabled the study of cellular phenomena with improved spatiotemporal control of the microenvironment and at increased throughput. While poly(dimethylsiloxane) (PDMS) has emerged as the most popular material in microfluidics research, it has specific limitations that prevent microfluidic platforms from achieving their full potential. We present here a complete process, ranging from mold design to embossing and bonding, that describes the fabrication of polystyrene (PS) microfluidic devices with similar cost and time expenditures as PDMS-based devices. Emphasis was placed on creating methods that can compete with PDMS fabrication methods in terms of robustness, complexity, and time requirements. To achieve this goal, several improvements were made to remove critical bottlenecks in existing PS embossing methods. First, traditional lithographic techniques were adapted to fabricate bulk epoxy molds capable of resisting high temperatures and pressures. Second, a method was developed to emboss through-holes in a PS layer, enabling creation of large arrays of independent microfluidic systems on a single device without need to manually create access ports. Third, thermal bonding of PS layers was optimized in order to achieve quality bonding over large arrays of microsystems. The choice of materials and methods was validated for biological function in two different cell-based applications to demonstrate the versatility of our streamlined fabrication process.

Microfluidic cell culture and its application in high-throughput drug screening: cardiotoxicity assay for hERG channels

Evaluation of drug cardiotoxicity is essential to the safe development of novel pharmaceuticals. Assessing a compound's risk for prolongation of the surface electrocardiographic QT interval and hence risk for life-threatening arrhythmias is mandated before approval of nearly all new pharmaceuticals. QT prolongation has most commonly been associated with loss of current through hERG (human ether-a-go-go related gene) potassium ion channels due to direct block of the ion channel by drugs or occasionally by inhibition of the plasma membrane expression of the channel protein. To develop an efficient, reliable, and cost-effective hERG screening assay for detecting drug-mediated disruption of hERG membrane trafficking, the authors demonstrate the use of microfluidic-based systems to improve throughput and lower cost of current methods. They validate their microfluidics array platform in polystyrene (PS), cyclo-olefin polymer (COP), and polydimethylsiloxane (PDMS) microchannels for drug-induced disruption of hERG trafficking by culturing stably transfected HEK cells that overexpressed hERG (WT-hERG) and studying their morphology, proliferation rates, hERG protein expression, and response to drug treatment. Results show that WT-hERG cells readily proliferate in PS, COP, and PDMS microfluidic channels. The authors demonstrated that conventional Western blot analysis was possible using cell lysate extracted from a single microchannel. The Western blot analysis also provided important evidence that WT-hERG cells cultured in microchannels maintained regular (well plate-based) expression of hERG. The authors further show that experimental procedures can be streamlined by using direct in-channel immunofluorescence staining in conjunction with detection using an infrared scanner. Finally, treatment of WT-hERG cells with 5 different drugs suggests that PS (and COP) microchannels were more suitable than PDMS microchannels for drug screening applications, particularly for tests involving hydrophobic drug molecules.

Optical oxygen sensors for applications in microfluidic cell culture

The presence and concentration of oxygen in biological systems has a large impact on the behavior and viability of many types of cells, including the differentiation of stem cells or the growth of tumor cells. As a result, the integration of oxygen sensors within cell culture environments presents a powerful tool for quantifying the effects of oxygen concentrations on cell behavior, cell viability, and drug effectiveness. Because microfluidic cell culture environments are a promising alternative to traditional cell culture platforms, there is recent interest in integrating oxygen-sensing mechanisms with microfluidics for cell culture applications. Optical, luminescence-based oxygen sensors, in particular, show great promise in their ability to be integrated with microfluidics and cell culture systems. These sensors can be highly sensitive and do not consume oxygen or generate toxic byproducts in their sensing process. This paper presents a review of previously proposed optical oxygen sensor types, materials and formats most applicable to microfluidic cell culture, and analyzes their suitability for this and other in vitro applications.

3D microchannel co-culture: method and biological validation

Conventional 3D culture is typically performed in multi-well plates (e.g. 12 wells). The volumes and dimensions necessitate relatively large numbers of cells and fluid exchange steps are not easily automated limiting throughput. 3D microchannel culture can overcome these challenges simplifying 3D culture processes. However, the adaptation of immunocytochemical endpoint measurements and the validation of microchannel 3D culture with conventional 3D culture are needed before widespread adoption can occur. Here we use a breast carcinoma growth model governed by complex and reciprocal interactions between epithelial carcinoma cells and mesenchymal fibroblasts to validate the 3D microculture system. Specifically, we report the use of a 3D microchannel co-culture assay platform to interrogate paracrine signalling pathways in breast cancer. Using a previously validated 3D co-culture of human mammary fibroblasts and T47D breast carcinoma cells, we demonstrate the use of arrayed microchannels to analyze paracrine signalling pathways and screen for inhibitors. Results in both conventional format (multiwell plate) and microchannels were comparable. This technology represents a significant advancement for high-throughput screening in individual patients and for drug discovery by enabling the use of 3D co-culture models via smaller sample requirements and compatibility with existing HTS infrastructure (e.g. automated liquid handlers, scanners).

Expanding the available assays: adapting and validating In-Cell Westerns in microfluidic devices for cell-based assays

Microfluidic methods for cellular studies can significantly reduce costs due to reduced reagent and biological specimen requirements compared with many traditional culture techniques. However, current types of readouts are limited and this lack of suitable readouts for microfluidic cultures has significantly hindered the application of microfluidics for cell-based assays. The In-Cell Western (ICW) technique uses quantitative immunocytochemistry and a laser scanner to provide an in situ measure of protein quantities in cells grown in microfluidic channels of arbitrary geometries. The use of ICWs in microfluidic channels was validated by a detailed comparison with current macroscale methods and shown to have excellent correlation. Transforming growth factor-β-induced epithelial-to-mesenchymal transition of an epithelial cell line was used as an example for further validation of the technique as a readout for soluble-factor-based assays performed in high-throughput microfluidic channels. The use of passive pumping for sample delivery and laser scanning for analysis opens the door to high-throughput quantitative microfluidic cell-based assays that integrate seamlessly with existing high-throughput infrastructure.

Fundamentals of microfluidic cell culture in controlled microenvironments

Microfluidics has the potential to revolutionize the way we approach cell biology research. The dimensions of microfluidic channels are well suited to the physical scale of biological cells, and the many advantages of microfluidics make it an attractive platform for new techniques in biology. One of the key benefits of microfluidics for basic biology is the ability to control parameters of the cell microenvironment at relevant length and time scales. Considerable progress has been made in the design and use of novel microfluidic devices for culturing cells and for subsequent treatment and analysis. With the recent pace of scientific discovery, it is becoming increasingly important to evaluate existing tools and techniques, and to synthesize fundamental concepts that would further improve the efficiency of biological research at the microscale. This tutorial review integrates fundamental principles from cell biology and local microenvironments with cell culture techniques and concepts in microfluidics. Culturing cells in microscale environments requires knowledge of multiple disciplines including physics, biochemistry, and engineering. We discuss basic concepts related to the physical and biochemical microenvironments of the cell, physicochemical properties of that microenvironment, cell culture techniques, and practical knowledge of microfluidic device design and operation. We also discuss the most recent advances in microfluidic cell culture and their implications on the future of the field. The goal is to guide new and interested researchers to the important areas and challenges facing the scientific community as we strive toward full integration of microfluidics with biology.