Automation of three-dimensional cell culture in arrayed microfluidic devices

Surface modifications of COP-based microfluidic devices for improved immobilisation of hydrogel proteins: long-term 3D culture with contractile cell types and ischaemia model

The tissue microenvironment plays a crucial role in tissue homeostasis and disease progression. However, the in vitro simulation has been limited by the lack of adequate biomimetic models in the last decades. Thanks to the advent of microfluidic technology for cell culture applications, these complex microenvironments can be recreated by combining hydrogels, cells and microfluidic devices. Nevertheless, this advance has several limitations. When cultured in three-dimensional (3D) hydrogels inside microfluidic devices, contractile cells may exert forces that eventually collapse the 3D structure. Disrupting the compartmentalisation creates an obstacle to long-term or highly cell-concentrated assays, which are extremely relevant for multiple applications such as fibrosis or ischaemia. Therefore, we tested surface treatments on cyclic-olefin polymer-based microfluidic devices (COP-MD) to promote the immobilisation of collagen as a 3D matrix protein. Thus, we compared three surface treatments in COP devices for culturing human cardiac fibroblasts (HCF) embedded in collagen hydrogels. We determined the immobilisation efficiency of collagen hydrogel by quantifying the hydrogel transversal area within the devices at the studied time points. Altogether, our results indicated that surface modification with polyacrylic acid photografting (PAA-PG) of COP-MD is the most effective treatment to avoid the quick collapse of collagen hydrogels. As a proof-of-concept experiment, and taking advantage of the low-gas permeability properties of COP-MD, we studied the application of PAA-PG pre-treatment to generate a self-induced ischaemia model. Different necrotic core sizes were developed depending on initial HCF density seeding with no noticeable gel collapse. We conclude that PAA-PG allows long-term culture, gradient generation and necrotic core formation of contractile cell types such as myofibroblasts. This novel approach will pave the way for new relevant in vitro co-culture models where fibroblasts play a key role such as wound healing, tumour microenvironment and ischaemia within microfluidic devices.

Viral and non-viral gene therapy using 3D (bio)printing

The overall success in launching discovered drugs is tightly restricted to the high rate of late-stage failures, which ultimately inhibits the distribution of medicines in markets. As a result, it is imperative that methods reliably predict the effectiveness and, more critically, the toxicity of medicine early in the drug development process before clinical trials be continuously innovated. We must stay up to date with the fast appearance of new infections and diseases by rapidly developing the requisite vaccinations and medicines. Modern in vitro models of disease may be used as an alternative to traditional disease models, and advanced technology can be used for the creation of pharmaceuticals as well as cells, drugs, and gene delivery systems to expedite the drug discovery procedure. Furthermore, in vitro models that mimic the spatial and chemical characteristics of native tissues, such as a 3D bioprinting system or other technologies, have proven to be more effective for drug screening than traditional 2D models. Viral and non-viral gene delivery vectors are a hopeful tool for combinatorial gene therapy, suggesting a quick way of simultaneously deliver multiple genes. A 3D bioprinting system embraces an excellent potential for gene delivery into the different cells or tissues for different diseases, in tissue engineering and regeneration medicine, in which the precise nucleic acid is located in the 3D printed tissues and scaffolds. Non-viral nanocarriers, in combination with 3D printed scaffolds, are applied to their delivery of genes and controlled release properties. There remains, however, a big obstacle in reaching the full potential of 3D models because of a lack of in vitro manufacturing of live tissues. Bioprinting advancements have made it possible to create biomimetic constructions that may be used in various drug discovery research applications. 3D bioprinting also benefits vaccinations, medicines, and relevant delivery methods because of its flexibility and adaptability. This review discusses the potential of 3D bioprinting technologies for pharmaceutical studies.

Analysis of Static Molecular Gradients in a High-Throughput Drug Screening Microfluidic Assay

In this study, we thoroughly analyzed molecular gradient generation, its stability over time, and linearity in our high-throughput drug screening microfluidic assay (HTS). These parameters greatly affect the precision and accuracy of the device's analytical protocol. As part of the research, we developed a mathematical model of dependence of the concentration profile on the initial concentrations of active substances in reservoirs and the number of tilts, as well as the dependence of the active substance concentration profiles in the culture chambers on the concentration profile of the reference dye in the indicator chamber. The mean concentration prediction error of the proposed equations ranged from 1.4% to 2.4% for the optimized parameters of the procedure and did not increase with the incubation time. The concentration profile linearity index, Pearson's correlation coefficient reached -0.997 for 25 device tilts. The observed time stability of the profiles was very good. The mean difference between the concentration profile after 5 days of incubation and the baseline profile was only 7.0%. The newly created mathematical relationships became part of the new HTS biochip operating protocols, which are detailed in the article.

Engineering a Model to Study Viral Infections: Bioprinting, Microfluidics, and Organoids to Defeat Coronavirus Disease 2019 (COVID-19)

While the number of studies related to severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) is constantly growing, it is essential to provide a framework of modeling viral infections. Therefore, this review aims to describe the background presented by earlier used models for viral studies and an approach to design an "ideal" tissue model for SARS-CoV-2 infection. Due to the previous successful achievements in antiviral research and tissue engineering, combining the emerging techniques such as bioprinting, microfluidics, and organoid formation are considered to be one of the best approaches to form in vitro tissue models. The fabrication of an integrated multi-tissue bioprinted platform tailored for SARS-CoV-2 infection can be a great breakthrough that can help defeat coronavirus disease in 2019.

Hydrogels as artificial matrices for cell seeding in microfluidic devices

Hydrogel-based artificial scaffolds and its incorporation with microfluidic devices play a vital role in shifting in vitro models from two-dimensional (2D) cell culture to in vivo like three-dimensional (3D) cell culture

Cell Seeding Technology for Microarray-Based Quantitative Human Primary Skeletal Muscle Cell Analysis

Pipetting techniques play a crucial role in obtaining reproducible and reliable results, especially when seeding cells on small target areas, such as on microarrays, biochips or microfabricated cell culture systems. For very rare cells, such as human primary skeletal muscle cells (skMCs), manual (freehand) cell seeding techniques invariably result in nonuniform cell spreading and heterogeneous cell densities, giving rise to undesirable variations in myogenesis and differentiation. To prevent such technique-dependent variation, we have designed and fabricated a simple, low-cost pipet guidance device (PGD), and holder that works with hand-held pipettes. This work validates the accuracy and reproducibility of the PGD platform and compares its effectiveness with manual and robotic seeding techniques. The PGD system ensures reproducibility of cell seeding, comparable to that of more expensive robotic dispensing systems, resulting in a high degree of cell uniformity and homogeneous cell densities, while also enabling cell community studies. As compared to freehand pipetting, PGD-assisted seeding of C2C12 mouse myoblasts showed 5.3 times more myotube formation and likewise myotubes derived from PGD-seeded human primary skMCs were 3.6 times thicker and 2.2 times longer. These results show that this novel, yet simple PGD-assisted pipetting technique provides precise cell seeding on small targets, ensuring reproducible and reliable high-throughput cell assays.

Integrating 3D Cell Culture of PC12 Cells with Microchip-Based Electrochemical Detection

Developing in vitro cell culture models that accurately mimic in vivo processes in a manner that also enables near real-time analysis of neurotransmitters is an important research area. New technologies being developed such as 3D scaffolds for cell culture and 3D printed microfluidics provide an opportunity for such advancements. In this work, PC12 cells were used as a model system and they were immobilized onto a 3D scaffold of polystyrene (PS) fibers. These fibers were created by electrospinning onto PS sheets, which were laser cut and, after cell seeding, inserted into a 3D printed microfluidic device. The 3D printed device was designed with threads for connecting commercial fittings (to integrate automated pumps and a 4-port injection system) and a steel pin for simple coupling with PDMS/polystyrene analytical devices. A straight PDMS channel was used for simple (and continuous) flow-based detection by sealing onto a PS base containing an embedded gold array working electrode and a platinum pseudo-reference. Electrochemical detection of stimulated catecholamine release was demonstrated. The insert-based system was then integrated with a bilayer valving PDMS device (for microchip electrophoresis) sealed onto a PS base (with electrodes for electrochemical detection). This base was embedded with a Pd decoupler (for grounding the separation voltage and adsorbing hydrogen) and a 33 µm carbon fiber working electrode for in-channel detection. PC12 cells were stimulated in the 3D cell culture device, and the valving/electrophoresis microchip was able to separate and detect dopamine and norepinephrine release. This work demonstrates the ability to integrate 3D cell scaffolds with microchip-based analysis for detection of multiple analytes released from cells.

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.

Cell Microarray Technologies for High-Throughput Cell-Based Biosensors

Due to the recent demand for high-throughput cellular assays, a lot of efforts have been made on miniaturization of cell-based biosensors by preparing cell microarrays. Various microfabrication technologies have been used to generate cell microarrays, where cells of different phenotypes are immobilized either on a flat substrate (positional array) or on particles (solution or suspension array) to achieve multiplexed and high-throughput cell-based biosensing. After introducing the fabrication methods for preparation of the positional and suspension cell microarrays, this review discusses the applications of the cell microarray including toxicology, drug discovery and detection of toxic agents.

Microfluidics-based 3D cell culture models: Utility in novel drug discovery and delivery research

The implementation of microfluidic devices within life sciences has furthered the possibilities of both academic and industrial applications such as rapid genome sequencing, predictive drug studies, and single cell manipulation. In contrast to the preferred two‐dimensional cell‐based screening, three‐dimensional (3D) systems have more in vivo relevance as well as ability to perform as a predictive tool for the success or failure of a drug screening campaign. 3D cell culture has shown an adaptive response to the recent advancements in microfluidic technologies which has allowed better control over spheroid sizes and subsequent drug screening studies. In this review, we highlight the most significant developments in the field of microfluidic 3D culture over the past half‐decade with a special focus on their benefits and challenges down the lane. With the newer technologies emerging, implementation of microfluidic 3D culture systems into the drug discovery pipeline is right around the bend.

Single cell functional analysis of multiple myeloma cell populations correlates with diffusion profiles in static microfluidic coculture systems

Microfluidic cell culture systems are becoming increasingly useful for studying biology questions, particularly those involving small cell populations that are cultured within microscale geometries mimicking the complex cellular microenvironment. Depending on the geometry and spatial organization of these cell populations, however, paracrine signaling between cell types can depend critically on spatial concentration profiles of soluble factors generated by diffusive transport. In scenarios where single cell data are acquired to study cell population heterogeneities in functional response, uncertainty associated with concentration profiles can lead to interpretation bias. To address this issue and provide important evidence on how diffusion develops within typical microfluidic cell culture systems, a combination of experimental and computational approaches were applied to measure and predict concentration patterns within microfluidic geometries, and characterize the functional response of culture cells based on single-cell resolution transcription factor activation. Using a model coculture system consisting of multiple myeloma cells (MMCs) and neighboring bone marrow stromal cells (BMSCs), we measured concentrations of three cytokines (IL-6, VEGF, and TNF-α) in conditioned media collected from separate culture compartments using a multiplex ELISA system. A 3D numerical model was developed to predict biomolecular diffusion and resulting concentration profiles within the tested microsystems and compared with experimental diffusion of 20 kDa FITC-Dextran. Finally, diffusion was further characterized by controlling exogenous IL-6 diffusion and the coculture spatial configuration of BMSCs to stimulate STAT3 nuclear translocation in MMCs. Results showed agreement between numerical and experimental results, provided evidence of a shallow concentration gradient across the center well of the microsystem that did not lead to a bias in results, and demonstrated that microfluidic systems can be tailored with specific geometries to avoid spatial bias when desired.

Microfluidic cell chips for high-throughput drug screening

The current state of screening methods for drug discovery is still riddled with several inefficiencies. Although some widely used high-throughput screening platforms may enhance the drug screening process, their cost and oversimplification of cell-drug interactions pose a translational difficulty. Microfluidic cell-chips resolve many issues found in conventional HTS technology, providing benefits such as reduced sample quantity and integration of 3D cell culture physically more representative of the physiological/pathological microenvironment. In this review, we introduce the advantages of microfluidic devices in drug screening, and outline the critical factors which influence device design, highlighting recent innovations and advances in the field including a summary of commercialization efforts on microfluidic cell chips. Future perspectives of microfluidic cell devices are also provided based on considerations of present technological limitations and translational barriers.

Micro 3D cell culture systems for cellular behavior studies: Culture matrices, devices, substrates, and in-situ sensing methods

Microfabricated systems equipped with 3D cell culture devices and in-situ cellular biosensing tools can be a powerful bionanotechnology platform to investigate a variety of biomedical applications. Various construction substrates such as plastics, glass, and paper are used for microstructures. When selecting a construction substrate, a key consideration is a porous microenvironment that allows for spheroid growth and mimics the extracellular matrix (ECM) of cell aggregates. Various bio-functionalized hydrogels are ideal candidates that mimic the natural ECM for 3D cell culture. When selecting an optimal and appropriate microfabrication method, both the intended use of the system and the characteristics and restrictions of the target cells should be carefully considered. For highly sensitive and near-cell surface detection of excreted cellular compounds, SERS-based microsystems capable of dual modal imaging have the potential to be powerful tools; however, the development of optical reporters and nanoprobes remains a key challenge. We expect that the microsystems capable of both 3D cell culture and cellular response monitoring would serve as excellent tools to provide fundamental cellular behavior information for various biomedical applications such as metastasis, wound healing, high throughput screening, tissue engineering, regenerative medicine, and drug discovery and development.

Automatic 3D Cell Analysis in High-Throughput Microarray Using Micropillar and Microwell Chips

Area-based and intensity-based 3D cell viability measurement methods are compared in high-throughput screening in order to analyze their effects on the assay results (doubling time and IC50) and their repeatability. Many other 3D cell-based high-throughput screening platforms had been previously introduced, but these had not clearly addressed the effects of the two methods on the assay results and assay repeatability. In this study, the optimal way to analyze 3D cultured cells is achieved by comparing day-to-day data of doubling times and IC50 values obtained from the two methods. In experiments, the U251 cell line is grown in chips. The doubling time, based on the area of the 3D cells, was 27.8 ± 1.8 h (standard deviation: 6.6%) and 27.8 ± 3.8 h (standard deviation: 13.7%) based on the intensity of the 3D cells. The doubling time calculated by area shows a smaller standard deviation than one calculated by intensity. IC50 values calculated by both methods are very similar. The standard deviations of IC50 values for the two methods were within ±3-fold. The IC50 variations of the 12 compounds were similar regardless of the viability measurement methods and were highly related to the shape of the dose–response curves.

Microfluidic model of ductal carcinoma in situ with 3D, organotypic structure

BACKGROUND

Ductal carcinoma in situ (DCIS) is a non-invasive form of breast cancer that is thought to be a precursor to most invasive and metastatic breast cancers. Understanding the mechanisms regulating the invasive transition of DCIS is critical in order to better understand how some types of DCIS become invasive. While significant insights have been gained using traditional in vivo and in vitro models, existing models do not adequately recapitulate key structure and functions of human DCIS well. In addition, existing models are time-consuming and costly, limiting their use in routine screens. Here, we present a microscale DCIS model that recapitulates key structures and functions of human DCIS, while enhancing the throughput capability of the system to simultaneously screen numerous molecules and drugs.

METHODS

Our microscale DCIS model is prepared in two steps. First, viscous finger patterning is used to generate mammary epithelial cell-lined lumens through extracellular matrix hydrogels. Next, DCIS cells are added to fill the mammary ducts to create a DCIS-like structure. For coculture experiments, human mammary fibroblasts (HMF) are added to the two side channels connected to the center channel containing DCIS. To validate the invasive transition of the DCIS model, the invasion of cancer cells and the loss of cell-cell junctions are then examined. A student t-test is conducted for statistical analysis.

RESULTS

We demonstrate that our DCIS model faithfully recapitulates key structures and functions of human mammary DCIS and can be employed to study the mechanisms involved in the invasive progression of DCIS. First, the formation of cell-cell junctions and cell polarity in the normal mammary duct, and the structure of the DCIS model are characterized. Second, coculture with HMF is shown to induce the invasion of DCIS. Third, multiple endpoint analyses are demonstrated to validate the invasion.

CONCLUSIONS

We have developed and characterized a novel in vitro model of normal and DCIS-inflicted mammary ducts with 3D lumen structures. These models will enable researchers to investigate the role of microenvironmental factors on the invasion of DCIS in more in vivo-like conditions.

Microscale screening systems for 3D cellular microenvironments: platforms, advances, and challenges

The increasing interest in studying cells using more in vivo-like three-dimensional (3D) microenvironments has created a need for advanced 3D screening platforms with enhanced functionalities and increased throughput. 3D screening platforms that better mimic in vivo microenvironments with enhanced throughput would provide more in-depth understanding of the complexity and heterogeneity of microenvironments. The platforms would also better predict the toxicity and efficacy of potential drugs in physiologically relevant conditions. Traditional 3D culture models (e.g., spinner flasks, gyratory rotation devices, non-adhesive surfaces, polymers) were developed to create 3D multicellular structures. However, these traditional systems require large volumes of reagents and cells, and are not compatible with high-throughput screening (HTS) systems. Microscale technology offers the miniaturization of 3D cultures and allows efficient screening of various conditions. This review will discuss the development, most influential works, and current advantages and challenges of microscale culture systems for screening cells in 3D microenvironments.

Building risk-on-a-chip models to improve breast cancer risk assessment and prevention

Preventive actions for chronic diseases hold the promise of improving lives and reducing healthcare costs. For several diseases, including breast cancer, multiple risk and protective factors have been identified by epidemiologists. The impact of most of these factors has yet to be fully understood at the organism, tissue, cellular and molecular levels. Importantly, combinations of external and internal risk and protective factors involve cooperativity thus, synergizing or antagonizing disease onset. Models are needed to mechanistically decipher cancer risks under defined cellular and microenvironmental conditions. Here, we briefly review breast cancer risk models based on 3D cell culture and propose to improve risk modeling with lab-on-a-chip approaches. We suggest epithelial tissue polarity, DNA repair and epigenetic profiles as endpoints in risk assessment models and discuss the development of 'risks-on-chips' integrating biosensors of these endpoints and of general tissue homeostasis. Risks-on-chips will help identify biomarkers of risk, serve as screening platforms for cancer preventive agents, and provide a better understanding of risk mechanisms, hence resulting in novel developments in disease prevention.

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.

Enabling screening in 3D microenvironments: probing matrix and stromal effects on the morphology and proliferation of T47D breast carcinoma cells

During breast carcinoma progression, the three-dimensional (3D) microenvironment is continuously remodeled, and changes in the composition of the extracellular matrix (ECM) occur. High throughput screening platforms have been used to decipher the complexity of the microenvironment and to identify ECM components responsible for cancer progression. However, traditional screening platforms are typically limited to two-dimensional (2D) cultures, and often exclude the influence of ECM and stromal components. In this work, a system that integrates 3-dimensional cell culture techniques with an automated microfluidic platform was used to create a new ECM screening platform that cultures cells in more physiologically relevant 3D in vitro microenvironments containing stromal cells and different ECM molecules. This new ECM screening platform was used to culture T47D breast carcinoma cells in mono- and co-culture with human mammary fibroblasts (HMF) with seven combinations of three different ECM proteins (collagen, fibronectin, laminin). Differences in the morphology of T47D clusters, and the proliferation of T47D cells were found in ECM compositions rich in fibronectin or laminin. In addition, an MMP enzyme activity inhibition screening showed the capabilities of the platform for small molecule screening. The platform presented in this work enables screening for the effects of matrix and stromal compositions and show promises for providing new insights in the identification of key ECM components involved in breast cancer.

Assembly of a three-dimensional multitype bronchiole coculture model using magnetic levitation

A longstanding goal in biomedical research has been to create organotypic cocultures that faithfully represent native tissue environments. There is presently great interest in representative culture models of the lung, which is a particularly challenging tissue to recreate in vitro. This study used magnetic levitation in conjunction with magnetic nanoparticles as a means of creating an organized three-dimensional (3D) coculture of the bronchiole that sequentially layers cells in a manner similar to native tissue architecture. The 3D coculture model was assembled from four human cell types in the bronchiole: endothelial cells, smooth muscle cells (SMCs), fibroblasts, and epithelial cells (EpiCs). This study represents the first effort to combine these particular cell types into an organized bronchiole coculture. These cell layers were first cultured in 3D by magnetic levitation, and then manipulated into contact with a custom-made magnetic pen, and again cultured for 48 h. Hematoxylin and eosin staining of the resulting coculture showed four distinct layers within the 3D coculture. Immunohistochemistry confirmed the phenotype of each of the four cell types and showed organized extracellular matrix formation, particularly, with collagen type I. Positive stains for CD31, von Willebrand factor, smooth muscle α-actin, vimentin, and fibronectin demonstrate the maintenance of the phenotype for endothelial cells, SMCs, and fibroblasts. Positive stains for mucin-5AC, cytokeratin, and E-cadherin after 7 days with and without 1% fetal bovine serum showed that EpiCs maintained the phenotype and function. This study validates magnetic levitation as a method for the rapid creation of organized 3D cocultures that maintain the phenotype and induce extracellular matrix formation.

Platform for high-throughput testing of the effect of soluble compounds on 3D cell cultures

In vitro 3D culture could provide an important model of tissues in vivo, but assessing the effects of chemical compounds on cells in specific regions of 3D culture requires physical isolation of cells and thus currently relies mostly on delicate and low-throughput methods. This paper describes a technique ("cells-in-gels-in-paper", CiGiP) that permits rapid assembly of arrays of 3D cell cultures and convenient isolation of cells from specific regions of these cultures. The 3D cultures were generated by stacking sheets of 200-μm-thick paper, each sheet supporting 96 individual "spots" (thin circular slabs) of hydrogels containing cells, separated by hydrophobic material (wax, PDMS) impermeable to aqueous solutions, and hydrophilic and most hydrophobic solutes. A custom-made 96-well holder isolated the cell-containing zones from each other. Each well contained media to which a different compound could be added. After culture and disassembly of the holder, peeling the layers apart "sectioned" the individual 3D cultures into 200-μm-thick sections which were easy to analyze using 2D imaging (e.g., with a commercial gel scanner). This 96-well holder brings new utilities to high-throughput, cell-based screening, by combining the simplicity of CiGiP with the convenience of a microtiter plate. This work demonstrated the potential of this type of assays by examining the cytotoxic effects of phenylarsine oxide (PAO) and cyclophosphamide (CPA) on human breast cancer cells positioned at different separations from culture media in 3D cultures.

Microengineered tumor models: insights & opportunities from a physical sciences-oncology perspective

Prevailing evidence has established the fundamental role of microenvironmental conditions in tumorigenesis. However, the ability to identify, interrupt, and translate the underlying cellular and molecular mechanisms into meaningful therapies remains limited, due in part to a lack of organotypic culture systems that accurately recapitulate tumor physiology. Integration of tissue engineering with microfabrication technologies has the potential to address this challenge and mimic tumor heterogeneity with pathological fidelity. Specifically, this approach allows recapitulating global changes of tissue-level phenomena, while also controlling microscale variability of various conditions including spatiotemporal presentation of soluble signals, biochemical and physical characteristics of the extracellular matrix, and cellular composition. Such platforms have continued to elucidate the role of the microenvironment in cancer pathogenesis and significantly improve drug discovery and screening, particularly for therapies that target tumor-enabling stromal components. This review discusses some of the landmark efforts in the field of micro-tumor engineering with a particular emphasis on deregulated tissue organization and mass transport phenomena in the tumor microenvironment.

Pharmacology on microfluidics: multimodal analysis for studying cell-cell interaction

Understanding the mechanisms of cell-cell interaction is a key unanswered question in modern pharmacology, given crosstalk defects are at the basis of many pathologies. Microfluidics represents a valuable tool for analyzing intercellular communication mediated by transmission of soluble signals, as occurring for example between neurons and glial cells in neuroinflammation, or between tumor and surrounding cells in cancer. However, the use of microfluidics for studying cell behavior still encompasses many technical and biological challenges. In this review, a state of the art of successes, potentials and limitations of microfluidics applied to key biological questions in modern pharmacology is analyzed and commented.

Spheroid culture as a tool for creating 3D complex tissues

3D cell culture methods confer a high degree of clinical and biological relevance to in vitro models. This is specifically the case with the spheroid culture, where a small aggregate of cells grows free of foreign materials. In spheroid cultures, cells secrete the extracellular matrix (ECM) in which they reside, and they can interact with cells from their original microenvironment. The value of spheroid cultures is increasing quickly due to novel microfabricated platforms amenable to high-throughput screening (HTS) and advances in cell culture. Here, we review new possibilities that combine the strengths of spheroid culture with new microenvironment fabrication methods that allow for the creation of large numbers of highly reproducible, complex tissues.

Microfluidic 3D cell culture: potential application for tissue-based bioassays

Current fundamental investigations of human biology and the development of therapeutic drugs commonly rely on 2D monolayer cell culture systems. However, 2D cell culture systems do not accurately recapitulate the structure, function or physiology of living tissues, nor the highly complex and dynamic 3D environments in vivo. Microfluidic technology can provide microscale complex structures and well-controlled parameters to mimic the in vivo environment of cells. The combination of microfluidic technology with 3D cell culture offers great potential for in vivo-like tissue-based applications, such as the emerging organ-on-a-chip system. This article will review recent advances in the microfluidic technology for 3D cell culture and their biological applications.

A digital microfluidic method for multiplexed cell-based apoptosis assays

Digital microfluidics (DMF), a fluid-handling technique in which picolitre-microlitre droplets are manipulated electrostatically on an array of electrodes, has recently become popular for applications in chemistry and biology. DMF devices are reconfigurable, have no moving parts, and are compatible with conventional high-throughput screening infrastructure (e.g., multiwell plate readers). For these and other reasons, digital microfluidics has been touted as being a potentially useful new tool for applications in multiplexed screening. Here, we introduce the first digital microfluidic platform used to implement parallel-scale cell-based assays. A fluorogenic apoptosis assay for caspase-3 activity was chosen as a model system because of the popularity of apoptosis as a target for anti-cancer drug discovery research. Dose-response profiles of caspase-3 activity as a function of staurosporine concentration were generated using both the digital microfluidic method and conventional techniques (i.e., pipetting, aspiration, and 96-well plates.) As expected, the digital microfluidic method had a 33-fold reduction in reagent consumption relative to the conventional technique. Although both types of methods used the same detector (a benchtop multiwell plate reader), the data generated by the digital microfluidic method had lower detection limits and greater dynamic range because apoptotic cells were much less likely to de-laminate when exposed to droplet manipulation by DMF relative to pipetting/aspiration in multiwell plates. We propose that the techniques described here represent an important milestone in the development of digital microfluidics as a useful tool for parallel cell-based screening and other applications.

A practical method for patterning lumens through ECM hydrogels via viscous finger patterning

Extracellular matrix (ECM) hydrogels with patterned lumens have been used as a framework to generate more physiologically relevant models of tissues, such as vessels and mammary ducts, for biological investigations. However, these models have not found widespread use in research labs or in high-throughput screening applications in large part because the basic methods for generating the lumen structures are generally cumbersome and slow. Here we present viscous finger patterning, a technique to generate lumens through ECM hydrogels in microchannels that can be accomplished using manual or automated pipetting. Passive pumping is used to flow culture media through an unpolymerized hydrogel, creating a lumen through the hydrogel that is subsequently polymerized. Viscous finger patterning takes advantage of viscous fingering, the fluid dynamics phenomenon where a less viscous fluid will flow through and displace a more viscous fluid. We have characterized the technique and used it to create a variety of channel geometries and ECM hydrogel compositions, as well as for the generation of lumens surrounded by multiple hydrogel layers. Because viscous finger patterning can be performed with automated liquid handling systems, high-throughput generation of ECM hydrogels with patterned lumen is enabled. The ability to rapidly and cost-effectively create large numbers of lumens in natural polymers overcomes a critical barrier to the use of more physiologically relevant tissue models in a variety of biological studies and drug screening applications.