Quantitative study of the dynamic tumor-endothelial cell interactions through an integrated microfluidic coculture system

Multiplexed microfluidic chip for cell co-culture

Paracrine signaling is challenging to study in vitro, as conventional culture tools dilute soluble factors and offer little to no spatiotemporal control over signaling. Microfluidic chips offer potential to address both of these issues. However, few solutions offer both control over onset and duration of cell-cell communication, and high throughput. We have developed a microfluidic chip designed to culture cells in adjacent chambers, separated by valves to selectively allow or prevent exchange of paracrine signals. The chip features 16 fluidic inputs and 128 individually-addressable chambers arranged in 32 sets of 4 chambers. Media can be continuously perfused or delivered by diffusion, which we model under different culture conditions to ensure normal cell viability. Immunocytochemistry assays can be performed in the chip, which we modeled and fine-tuned to reduce total assay time to 1 h. Finally, we validate the use of the chip for co-culture studies by showing that HEK293Ta cells respond to signals secreted by RAW 264.7 immune cells in adjacent chambers, only when the valve between the chambers is opened.

Oviduct-mimicking microfluidic chips decreased the ROS concentration in the in vitro fertilized embryos of CD-1 mice

BACKGROUND

The process of the assisted reproductive technology (ART) cycle is extremely complicated, and various factors in each step may influence the final clinical outcomes; thus, optimizing culture conditions for embryos is crucial in the ART cycle, particularly when the traditional petri-dish method remains unchanged for decades. In the current study, we intend to culture embryos in a dynamic environment on chips to optimize the embryo culture conditions.

METHODS

Multilayer soft lithography technology was utilized to establish a microfluidics-based oviduct. Mouse primary oviduct epithelial cells were identified by immunofluorescence staining and then loaded into the chip to coculture with the embryos. The development potential parameters of embryos on chips with cells, on chips without cells, and in drops were compared, as well as reactive oxygen species (ROS) in embryos.

RESULTS

There were no obvious differences regarding the fertilization rate, 4-Cell embryo rate, cleavage rate, high-quality embryo rate, or blastocyst formation rate. However, the intracellular ROS levels in 4-Cell stage embryos on chips with cells were statistically significantly lower than those in drops (P < 0.001). This organ-on-chip device allowed the probability of mammalian embryo culture in a microfluidic-based manner.

CONCLUSIONS

Our findings demonstrated that this novel oviduct-on-chip model may optimize embryo culture conditions by reducing intracellular ROS levels, which may be a competent alternative to the existing stable embryo culture system.

High-throughput probing macrophage-bacteria interactions at the single cell level with microdroplets

Pathogenic infections may lead to disruption of homeostasis, thus becoming a serious threat to the human health. Understanding the interactions between bacteria and macrophages is critical for therapeutic development against sepsis or inflammatory bowel disease. Here, we report a technique using droplet biosensors for the detection of nitric oxide (NO) secreted by a single macrophage under inflammatory stimuli. We demonstrated that the limit of detection can be promoted more than two orders of magnitude by our approach, in comparison to the conventional microplate format. The experiments of co-encapsulating single macrophages and different numbers of Escherichia coli (E. coli) enabled fluorescence monitoring of NO secretion by single macrophages over the incubation, and investigation of their interactions inside the isolated droplet for their separate fates. Our approach provides a unique platform to study the bacteria-macrophage interactions at the single cell level.

Microfluidic chip for precise trapping of single cells and temporal analysis of signaling dynamics

Microfluidic designs are versatile examples of technology miniaturisation that find their applications in various cell biology research, especially to investigate the influence of environmental signals on cellular response dynamics. Multicellular systems operate in intricate cellular microenvironments where environmental signals govern well-orchestrated and robust responses, the understanding of which can be realized with integrated microfluidic systems. In this study, we present a fully automated and integrated microfluidic chip that can deliver input signals to single and isolated suspension or adherent cells in a precisely controlled manner. In respective analyses of different single cell types, we observe, in real-time, the temporal dynamics of caspase 3 activation during DMSO-induced apoptosis in single cancer cells (K562) and the translocation of STAT-1 triggered by interferon γ (IFNγ) in single fibroblasts (NIH3T3). Our investigations establish the employment of our versatile microfluidic system in probing temporal single cell signaling networks where alternations in outputs uncover signal processing mechanisms.

Nidhi Sinha, Haowen Yang and colleagues report a microfluidic large-scale integration chip to probe temporal single-cell signalling networks via the delivery of patterns of input signalling molecules. The researchers use their device to investigate drug-induced cancer cell apoptosis and single cell transcription (STAT-1) protein signalling dynamics.

A microfluidic hanging drop-based spheroid co-culture platform for probing tumor angiogenesis

Co-culturing of embryoid bodies (EBs) and tumor spheroids (TSs) allows mimicking tumor angiogenesis in vitro. Here, we report a microfluidic hanging drop-based spheroid co-culture device (μ-CCD) that permits the generation and co-culturing of EBs and TSs using a simple manual operation procedure and setup. In brief, uniform-sized EBs and TSs can be generated on the device in eight pairs of hanging droplets from adjacent microfluidic channels, followed by the confrontation of EB and TS pairs by merging the droplet pairs to culture the EB-TS spheroids to investigate tumor-induced angiogenic sprouting. The physical parameters of the device were optimized to maintain the long-term stability of hanging droplets for up to ten days. The mouse embryonic stem cell line ES-D3 and breast cancer cell lines MDA-MB-231 and MCF-7 were used to generate EBs, invasive TSs, and non-invasive TSs respectively. Confocal imaging results showed that the vessel percentage area and total vessel length which are linked to tumor angiogenesis increased after 6 days of co-culturing. An anti-angiogenesis drug testing on the co-cultured EB-TS spheroids was also demonstrated in the device. The μ-CCD provides a simple yet high-efficiency method to generate and co-culture cell spheroids and may also be useful for other applications involving spheroid co-culturing.

Recent advances of integrated microfluidic suspension cell culture system

Microfluidic devices with superior microscale fluid manipulation ability and large integration flexibility offer great advantages of high throughput, parallelisation and multifunctional automation. Such features have been extensively utilised to facilitate cell culture processes such as cell capturing and culturing under controllable and monitored conditions for cell-based assays. Incorporating functional components and microfabricated configurations offered different levels of fluid control and cell manipulation strategies to meet diverse culture demands. This review will discuss the advances of single-phase flow and droplet-based integrated microfluidic suspension cell culture systems and their applications for accelerated bioprocess development, high-throughput cell selection, drug screening and scientific research to insight cell biology. Challenges and future prospects for this dynamically developing field are also highlighted.

On-Chip Replication of Extremely Early-Stage Tumor Behavior

Cancer is a multistep progressive disease that generally involves tumor growth, invasion, and metastasis. It is crucial to understand tumor progression for tumor diagnosis and therapy. However, tumor progression at an extremely early stage (EES) is barely demonstrated because EES tumors are too small to be detected by imaging. Herein, we, for the first time, replicated tumor progression at the EES on a microfluidic chip and uncovered the tumor behaviors affected by the tumor microenvironment. To mimic the progression of a single solid tumor at the EES, a HeLa cell spheroid was seeded and cultured on the chip, and a microvascular network was developed to integrate the microphysiological contexts around the tumor. We revealed not only the growth patterns and cell behaviors of tumor spheroids of different sizes under angiogenesis and fibroblast conditions but also the effect of tumor progression on peritumoral angiogenesis. We found that smaller tumors were more aggressive and that endotheliocytes and fibroblasts significantly accelerated both the proliferation and migration of tumor cells. In addition, we also first present the dynamic epithelial-mesenchymal transition process of tumor cells and the formation of vasculogenic mimicry at the EES. This work can provide insights for understanding tumor progression at the EES and offer new ideas for tumor therapy.

Glioma-on-a-Chip Models

Glioma, as an aggressive type of cancer, accounts for virtually 80% of malignant brain tumors. Despite advances in therapeutic approaches, the long-term survival of glioma patients is poor (it is usually fatal within 12-14 months). Glioma-on-chip platforms, with continuous perfusion, mimic in vivo metabolic functions of cancer cells for analytical purposes. This offers an unprecedented opportunity for understanding the underlying reasons that arise glioma, determining the most effective radiotherapy approach, testing different drug combinations, and screening conceivable side effects of drugs on other organs. Glioma-on-chip technologies can ultimately enhance the efficacy of treatments, promote the survival rate of patients, and pave a path for personalized medicine. In this perspective paper, we briefly review the latest developments of glioma-on-chip technologies, such as therapy applications, drug screening, and cell behavior studies, and discuss the current challenges as well as future research directions in this field.

Droplet array for open-channel high-throughput SERS biosensing

Open-channel and high throughput are two important aspects of clinical diagnosis, correlation biochemical analysis, cell culture techniques and food safety. Here, we propose the mini-pillar based array for open-channel and high-throughput SERS detection of miRNA. The polydimethylsiloxane (PDMS) mini-pillars are used as a high-throughput platform, which have good anchoring and aggregation effects on microdroplets, greatly reducing the amount of analytical solution and facilitate the homogeneous sample distribution after evaporation. The deposited gold nanorods (Au NRs) on the pillars with optimized diameter served as SERS-active substrate, can greatly improve the sensitivity of SERS signal compared to other planar substrates. On the open-channel biological chip, sensitive, simultaneous, and specific detection of breast cancer marker miRNA-1246 can be performed. In this mini-pillar array SERS system, the limit of detection (LOD) is 10^-12 M. The mini-pillar array shows enormous potential for open channel, high-throughput biomolecular detection, providing an opportunity for biomedical point-of-care testing (POCT) and drug screening.

An integrated microfluidic 3D tumor system for parallel and high-throughput chemotherapy evaluation

The development of a microplatform with multifunctional integration allowing the dynamic and high-throughput exploration of three-dimensional (3D) cultures is promising for biomedical research. Here, we introduce an integrated microfluidic 3D tumor system with pneumatic manipulation and chemical gradient generation to investigate anticancer therapy in a parallel, controllable, dynamic, and high-throughput manner. The stability of the microfluidic system to realize precise and long-term chemical gradient production was developed. Serial manipulations including active cell trapping, array-like tumor self-assembly and formation, reliable gradient generation, parallel multi-concentration drug stimulation, and real-time tumor analysis were achieved in a single microfluidic device. The microfluidic platform was demonstrated to be stable for high-throughput cell trapping and 3D tumor formation with uniform quantities. On-chip analysis of phenotypic tumor responses to diverse chemotherapies with different concentrations can be conducted in this device. The microfluidic advancement holds great potential for applications in the development of high-performance and multi-functional biomimetic tumor systems and in the fields of cancer research and pharmaceutical development.

Recapitulating and Deciphering Tumor Microenvironment by Using 3D Printed Plastic Brick-Like Microfluidic Cell Patterning

Within the body, tumor cells are surrounded by neighboring counterparts, such as extracellular matrix, vasculature, and host stroma, which is also known as the tumor microenvironment. To understand tumorigenesis, it is essential to reconstitute the incorporative tumor niche with quantitative measurements in vitro. Here, a 3D printed plastic brick-like microfluidic gadget is developed for spatially patterning tumors and fibroblasts, enabling the recapitulation of tumor microenvironment with minimized microfluidic expertise and compatibility of standard pipetting. This method facilitates heterotypic coculturing, quantitative phenotype decoding, and downstream molecular assays with a small number of cells (less than 100). Phenotypic and gene/protein expression-based analysis of cell-cell interactions between fibrosarcoma cells and fibroblasts on this device reveals that the tumor and its counterparts show reciprocal synergism mainly by upregulation of proinflammatory cytokines. Notably, at the whole transcriptional landscape (RNA-seq), fibroblasts display a transition from normal to cancer-associated fibroblast (CAF)-like phase, and tumor cells exhibit a hyperactive ribosome biogenesis. The mouse xenograft model is also involved to validate the in vitro analysis. Given its easy-to-use feature, full compatibility with molecular analysis, and open-source accessibility, this approach provides an in vitro experimental system to advance knowledge of tumorigenesis and the corresponding tumor microenvironment.

A microfluidic mammary gland coculture model using parallel 3D lumens for studying epithelial-endothelial migration in breast cancer

In breast cancer development, crosstalk between mammary epithelial cells and neighboring vascular endothelial cells is critical to understanding tumor progression and metastasis, but the mechanisms of this dynamic interplay are not fully understood. Current cell culture platforms do not accurately recapitulate the 3D luminal architecture of mammary gland elements. Here, we present the development of an accessible and scalable microfluidic coculture system that incorporates two parallel 3D luminal structures that mimic vascular endothelial and mammary epithelial cell layers, respectively. This parallel 3D lumen configuration allows investigation of endothelial-epithelial crosstalk and its effects of the comigration of endothelial and epithelial cells into microscale migration ports located between the parallel lumens. We describe the development and application of our platform, demonstrate generation of 3D luminal cell layers for endothelial cells and three different breast cancer cell lines, and quantify their migration profiles based on number of migrated cells, area coverage by migrated cells, and distance traveled by individual migrating cells into the migration ports. Our system enables analysis at the single-cell level, allows simultaneous monitoring of endothelial and epithelial cell migration within a 3D extracellular matrix, and has potential for applications in basic research on cellular crosstalk as well as drug development.

Review on biofabrication and applications of heterogeneous tumor models

Resolving the origin and development of tumor heterogeneity has proven to be a crucial challenge in cancer research. In vitro tumor models have been widely used for both scientific and clinical research. Currently, tumor models based on 2D cell culture, animal models, and 3D cell-laden constructs are widely used. Heterogeneous tumor models, which consist of more than one cell type and mimic cell-cell as well as cell-matrix interactions, are attracting increasing attention. Heterogeneous tumor models can serve as pathological models to study the microenvironment and tumor development such as tumorigenesis, invasiveness, and malignancy. They also provide disease models for drug screening and personalized therapy. In this review, the current techniques, models, and oncological applications regarding 3D heterogeneous tumor models are summarized and discussed.

Integrating Organs-on-Chips: Multiplexing, Scaling, Vascularization, and Innervation

Organs-on-chips (OoCs) have attracted significant attention because they can be designed to mimic in vivo environments. Beyond constructing a single OoC, recent efforts have tried to integrate multiple OoCs to broaden potential applications such as disease modeling and drug discoveries. However, various challenges remain for integrating OoCs towards in vivo-like operation, such as incorporating various connections for integrating multiple OoCs. We review multiplexed OoCs and challenges they face: scaling, vascularization, and innervation. In our opinion, future OoCs will be constructed to have increased predictive power for in vivo phenomena and will ultimately become a mainstream tool for high quality biomedical and pharmaceutical research.

Establishment and application of a dynamic tumor-vessel microsystem for studying different stages of tumor metastasis and evaluating anti-tumor drugs

Tumor metastasis is one of the main causes of cancer-related death, and it is difficult to study the whole process of tumor metastasis in vivo due to the complex physiological environment in the body. Therefore, it's crucial to develop simple and physiologically relevant in vitro cancer models to study the metastasis process, especially different phases of tumor metastasis. A novel microfluidic tumor-vessel co-culture system was established to reproduce the different phases of cancer metastasis (proliferation, migration, intravasation and adherence) individually in vitro for the first time. It was observed that blood vessels with fluid flow had big impact on metastasis of liver cancer cells HepG2 and breast ones MDA-MB-231. In particular, it was found that both HepG2 and MDA-MB-231 cells migrated in the direction of “blood flow”. Furthermore, MDA-MB-231 cells invaded through paracellular mode disrupting the intercellular endothelial junctions, whereas HepG2 cells engaged in transcellular intravasation through transcellular process. Compared with traditional assays, much more potent inhibition of 5-fluorouracil (5-Fu) on different phases of tumor metastasis was observed on the microsystem. In summary, the microfluidic device yielded abundant information about each phase of tumor metastasis, and would provide a powerful platform for use in drug screening, toxicology studies, and personalized medicine in future.

The different stages of the cancer metastasis were reproduced individually on a novel tumor-vessel co-culture microsystem.

Determination of Benzopyrene-Induced Lung Inflammatory and Cytotoxic Injury in a Chemical Gradient-Integrated Microfluidic Bronchial Epithelium System

Environmental pollution is one of the largest sources responsible for human diseases and premature death worldwide. However, the methodological development of a spatiotemporally controllable and high-throughput investigation of the environmental pollution-induced biological injury events is still being explored. In this study, we describe a chemical gradient generator-aided microfluidic cell system for the dynamic study of representative environmental pollutant-induced bronchial epithelium injury in a throughput manner. We demonstrated the stability and reliability of operation-optimized microfluidic system for precise and long-term chemical gradient production. We also performed a microenvironment-controlled microfluidic bronchial epithelium construction with high viability and structure integration. Moreover, on-chip investigation of bronchial epithelium injury by benzopyrene stimulation with various concentrations can be carried out in the single device. The varying bronchial inflammatory and cytotoxic responses were temporally monitored and measured based on the well-established system. The benzopyrene directionally led the bronchial epithelium to present observable cell shrinkage, cytoskeleton disintegration, Caspase-3 activation, overproduction of reactive oxygen species, and various inflammatory cytokine (TNF-α, IL-6, and IL-8) secretion, suggesting its significant inflammatory and cytotoxic effects on respiratory system. We believe the microfluidic advancement has potential applications in the fields of environmental monitoring, tissue engineering, and pharmaceutical development.

Microfluidic-based vascularized microphysiological systems

Microphysiological systems have emerged in the last decade to provide an alternative to in vivo models in basic science and pharmaceutical research. In the field of vascular biology, in particular, there has been a lack of a suitable in vitro model exhibiting a three-dimensional structure and the physiological function of vasculature integrated with organ-on-a-chip models. The rapid development of organ-on-a-chip technology is well positioned to fulfill unmet needs. Recently, functional integration of vasculature with diverse microphysiological systems has been increasing. This recent trend corresponds to emerging research interest in how the vascular system contributes to various physiological and pathological conditions. This innovative platform has undergone significant development, but adoption of this technology by end-users and researchers in biology is still a work in progress. Therefore, it is critical to focus on simplification and standardization to promote the distribution and acceptance of this technology by the end-users. In this review, we will introduce the latest developments in vascularized microphysiological systems and summarize their outlook in basic research and drug screening applications.

Advances in tumor-endothelial cells co-culture and interaction on microfluidics

The metastasis in which the cancer cells degrade the extracellular matrix (ECM) and invade to the surrounding and far tissues of the body is the leading cause of mortality in cancer patients. With a lot of advancement in the field, yet the biological cause of metastasis are poorly understood. The microfluidic system provides advanced technology to reconstruct a variety of in vivo-like environment for studying the interactions between tumor cells (TCs) and endothelial cells (ECs). This review gives a brief account of both two-dimensional models and three-dimensional microfluidic systems for the analysis of TCs-ECs co-culture as well as their applications to anti-cancer drug screening. Furthermore, the advanced methods for analyzing cell-to-cell interactions at single-cell level were also discussed.

Real-time detection and monitoring of the drug resistance of single myeloid leukemia cells by diffused total internal reflection

Real-time detection and monitoring of the drug resistance of single cells have important significance in clinical diagnosis and therapy. Traditional methods operate a number of times for each individual concentration, and innovation is required for the design of more simple and efficient manipulation platforms with necessary higher sensitivity. Here, we have developed a novel diffused total internal reflection (TIR) method to perform drug metabolism and cytotoxicity analysis of trapped myeloid leukemia cells. Molm-13 cells, a type of acute myeloid leukemia cell, were chosen and injected into the device and fittingly captured by cell traps. Differing from previous studies, a series of different concentrations of azelaic acid (AZA) drug could be used from 0 mM to 50 mM through convection and diffusion processes in a single chip, with each concentration region featuring 50 cells, with a total of 549 cell trapping units. Thanks to the high sensitivity of the TIR method, only cells with the same drug concentration could be illuminated in the detection process. By adjusting the incident angle, we could exactly detect and monitor the drug resistance of the cells using different drug concentrations and the experimental resolution of the drug concentration was as small as 5 mM. Images of the membrane integrity and morphology of the cells in the bright field were measured and we also monitored the cell viabilities in the dark field over 2 hours. The effects of AZA on the Molm-13 cells were explored in different concentrations at the single cell level. Compared with the results of the traditional MTT assay method, the experimental results are more simple and accurate. A cell death of 5% at an AZA concentration of 5 mM was observed after 30 minutes, while a concentration of 40 mM corresponded to a 98% cell death. The designed method in this study provides a novel toolkit to control and monitor drug resistance at the single cell level more easily with higher sensitivity and we believe it has significant potential application in single cell quality assessment and medicine analysis in clinical practice.

Microfluidic Tumor-Vascular Model to Study Breast Cancer Cell Invasion and Intravasation

Cancer is a major leading cause of disease-related death in the world. The severe impact of cancer can be attributed to poor understanding of the mechanisms involved in earliest steps of the metastatic cascade, specifically invasion into the surrounding stroma and intravasation into the blood capillaries. However, conducting integrated biological studies of invasion and intravasation have been challenging, within in vivo models and traditional in vitro assay, due to difficulties in establishing a precise tumor microenvironment. To that end, in this work, a novel 3D microfluidic platform comprised of concentric three-layer cell-laden hydrogels for simultaneous investigation of breast cancer cell invasion and intravasation as well as vasculature maturation influenced by tumor-vascular crosstalk is developed. It was demonstrated that the presence of spontaneously formed vasculature enhance MDA-MB-231 invasion into the 3D stroma. Following invasion, cancer cells are visualized intravasating into the outer vasculature. Additionally, invading cancer cells significantly reduce vessel diameter while increasing permeability, consistent with previous in vivo studies. Major signaling cytokines involved in tumor-vascular crosstalk that govern cancer cell invasion and intravasation are further identified. Taken together, this platform will enable unique insights of critical biological events within the metastatic cascade, with significant potential for developing efficient cancer therapeutics.

Recent advances in microfluidic technologies for cell-to-cell interaction studies

Microfluidic cell cultures are ideally positioned to become the next generation of in vitro diagnostic tools for biomedical research, where key biological processes such as cell signalling and dynamic cell-to-cell interactions can be reliably analysed under reproducible physiological cell culture conditions. In the last decade, a large number of microfluidic cell analysis systems have been developed for a variety of applications including drug target optimization, drug screening and toxicological testing. More recently, advanced in vitro microfluidic cell culture systems have emerged that are capable of replicating the complex three-dimensional architectures of tissues and organs and thus represent valid biological models for investigating the mechanism and function of human tissue structures, as well as studying the onset and progression of diseases such as cancer. In this review, we present the most important developments in single-cell, 2D and 3D microfluidic cell culture systems for studying cell-to-cell interactions published over the last 6 years, with a focus on cancer research and immunotherapy, vascular models and neuroscience. In addition, the current technological development of microdevices with more advanced physiological cell microenvironments that integrate multiple organ models, namely, the so-called body-, human- and multi-organ-on-a-chip, is reviewed.

Recent advances in the use of microfluidic technologies for single cell analysis

The inherent heterogeneity in cell populations has become of great interest and importance as analytical techniques have improved over the past decades. With the advent of personalized medicine, understanding the impact of this heterogeneity has become an important challenge for the research community. Many different microfluidic approaches with varying levels of throughput and resolution exist to study single cell activity. In this review, we take a broad view of the recent microfluidic developments in single cell analysis based on microwell, microchamber, and droplet platforms. We cover physical, chemical, and molecular biology approaches for cellular and molecular analysis including newly emerging genome-wide analysis.

Cell migration in microengineered tumor environments

Recent advances in microengineered cell migration platforms are discussed critically with a focus on how cell migration is influenced by engineered tumor microenvironments, the medical relevance being to understand how tumor microenvironments may promote or suppress the progression of cancer. We first introduce key findings in cancer cell migration under the influence of the physical environment, which is systematically controlled by microengineering technology, followed by multi-cues of physico-chemical factors, which represent the complexity of the tumor environment. Recognizing that cancer cells constantly communicate not only with each other but also with tumor-associated cells such as vascular, fibroblast, and immune cells, and also with non-cellular components, it follows that cell motility in tumor microenvironments, especially metastasis via the invasion of cancer cells into the extracellular matrix and other tissues, is closely related to the malignancy of cancer-related mortality. Medical relevance of forefront research realized in microfabricated devices, such as single cell sorting based on the analysis of cell migration behavior, may assist personalized theragnostics based on the cell migration phenotype. Furthermore, we urge development of theory and numerical understanding of single or collective cell migration in microengineered platforms to gain new insights in cancer metastasis and in therapeutic strategies.

Probing the Bi-directional Interaction Between Microglia and Gliomas in a Tumor Microenvironment on a Microdevice

It has been proven that microglia are involved in both early and late stages of glioma progression and contribute substantially to the tumor mass of gliomas. Because no appropriate in vitro or in vivo investigative approach is available, the dynamic interaction between microglia and gliomas during tumor formation remains unclear. In this study, three types of microfluidic assay were developed to examine the outcomes of the dynamic interaction between microglia and gliomas. Co-migration assay and two-dimensional cell co-culture assay have been used to show that microglial BV-2 cells migrate toward C6 glioma cells and inhibit tumor growth during the early stage of tumorigenesis. However, in three-dimensional cell spheres (three-dimensional cell co-culture assay) that contain a large amount of glioma cells, mimicking the late stage of glioma growth, the phagocytosis of microglia was suppressed, which suggests that glioma cells could reeducate classically activated microglia into a tumor-promoting state at some point during tumor progression. Notably, we found that microglia could contribute to tumor invasion and acquisition of the epithelial-mesenchymal transition phenotype in the glioma microenvironment during the early stage and the late stage of tumor progression. In conclusion, we have developed a potential quantitative method for in vitro study of glioma immunity and provided evidence for the duality of glioma-associated microglia.

Vasculature-On-A-Chip for In Vitro Disease Models

Vascularization, the formation of new blood vessels, is an essential biological process. As the vasculature is involved in various fundamental physiological phenomena and closely related to several human diseases, it is imperative that substantial research is conducted on characterizing the vasculature and its related diseases. A significant evolution has been made to describe the vascularization process so that in vitro recapitulation of vascularization is possible. The current microfluidic systems allow elaborative research on the effects of various cues for vascularization, and furthermore, in vitro technologies have a great potential for being applied to the vascular disease models for studying pathological events and developing drug screening platforms. Here, we review methods of fabrication for microfluidic assays and inducing factors for vascularization. We also discuss applications using engineered vasculature such as in vitro vascular disease models, vasculature in organ-on-chips and drug screening platforms.

Heterotypic 3D tumor culture in a reusable platform using pneumatic microfluidics

The construction of a micro-platform capable of microscale control for continuous, dynamic, and high-throughput biomimetic tumor manipulation and analysis plays a significant role in biological and clinical research. Here, we introduce a pneumatic microstructure-based microfluidic platform for versatile three-dimensional (3D) tumor cultures. The manipulative potential of pneumatic microstructures in a fabrication-optimized microfluidic device can be stimulated to achieve ultra-repetitive (tens of thousands of times) and persistent (over several months) microfluidic control. We demonstrated that the microfluidic platform is reusable (dozens of times) for stable, reproducible, and high-throughput generation of tumors with uniform size. Various heterotypic and homotypic 3D tumor arrays can be produced successfully in the device based on robust pneumatic control. On-chip monitoring and analysis of tumor phenotypes and responses to different culture conditions and chemotherapies were also achieved in real-time in the microfluidic platform. The results indicate that fibroblasts cocultured with tumor cells positively promote the phenotypical appearance of heterotypic tumors. This microfluidic advancement offers a new methodological approach for the development of high-performance and non-disposable 3D culture systems and for tissue-mimicking cancer research. We believe that it could be valuable for various tumor-related research fields such as oncology, pharmacology, tissue engineering, and bioimaging.

A bladder cancer microenvironment simulation system based on a microfluidic co-culture model

A tumor microenvironment may promote tumor metastasis and progression through the dynamic interplay between neoplastic cells and stromal cells. In this work, the most representative and significant stromal cells, fibroblasts, endothelial cells, and macrophages were used as vital component elements and combined with bladder cancer cells to construct a bladder cancer microenvironment simulation system. This is the first report to explore bladder cancer microenvironments based on 4 types of cells co-cultured simultaneously. This simulation system comprises perfusion equipment, matrigel channel units, a medium channel and four indirect contact culture chambers, allowing four types of cells to simultaneously interact through soluble biological factors and metabolites. With this system, bladder cancer cells (T24) with a tendency to form a ‘reticular’ structure under 3 dimensional culture conditions were observed in real time. The microenvironment characteristics of paracrine interactions and cell motility were successfully simulated in this system. The phenotype change process in stromal cells was successfully reproduced in this system by testing the macrophage effector molecule Arg-1. Arg-1 was highly expressed in the simulated tumor microenvironment group. To develop “precision medicine” in bladder cancer therapy, bladder cancer cells were treated with different clinical ‘neo-adjuvant’ chemotherapy schemes in this system, and their sensitivity differences were fully reflected. This work provides a preliminary foundation for neo-adjuvant chemotherapy in bladder cancer, a theoretical foundation for tumor microenvironment simulation and promotes individual therapy in bladder cancer patients.

Evaluating Biomaterial- and Microfluidic-Based 3D Tumor Models

Cancer is a major cause of morbidity and mortality worldwide, with a disease burden estimated to increase over the coming decades. Disease heterogeneity and limited information on cancer biology and disease mechanisms are aspects that 2D cell cultures fail to address. Here, we review the current ‘state-of-the-art’ in 3D tissue-engineering (TE) models developed for, and used in, cancer research. We assess the potential for scaffold-based TE models and microfluidics to fill the gap between 2D models and clinical application. We also discuss recent advances in combining the principles of 3D TE models and microfluidics, with a special focus on biomaterials and the most promising chip-based 3D models.

Programmable v-type valve for cell and particle manipulation in microfluidic devices

A new microfluidic valve or a "v-type valve" which can be flexibly actuated to focus a fluid flow and block a specific area of a microchannel is demonstrated. Valves with different design parameters were fabricated by multilayer soft lithography and characterized at various operating pressures. To evaluate the functionality of the valve, single microparticles (∅ 7 μm and ∅ 15 μm) and single cells were trapped from flowing suspensions. Continuous processes of particle capture and release were achieved by controlling the actuation and deactuation of the valve. Integration of the v-type valve with poly(dimethyl siloxane) (PDMS) monolithic valves in microfluidic devices was demonstrated to illustrate the potential of the system in various applications such as the creation of a solid phase column, the isolation of a specific number of particles in reactors, and the capture and release of particles or cells in the flow of two immiscible liquids. We believe that this new valve system will be suitable for manipulating particles and cells in a broad range of applications.

Biomimetic tumor-induced angiogenesis and anti-angiogenic therapy in a microfluidic model

Mimickingin vivoangiogenesis on a microfluidic model and application on testing drug potential to inhibit angiogenesis.

Automated profiling of individual cell-cell interactions from high-throughput time-lapse imaging microscopy in nanowell grids (TIMING)

MOTIVATION

There is a need for effective automated methods for profiling dynamic cell-cell interactions with single-cell resolution from high-throughput time-lapse imaging data, especially, the interactions between immune effector cells and tumor cells in adoptive immunotherapy.

RESULTS

Fluorescently labeled human T cells, natural killer cells (NK), and various target cells (NALM6, K562, EL4) were co-incubated on polydimethylsiloxane arrays of sub-nanoliter wells (nanowells), and imaged using multi-channel time-lapse microscopy. The proposed cell segmentation and tracking algorithms account for cell variability and exploit the nanowell confinement property to increase the yield of correctly analyzed nanowells from 45% (existing algorithms) to 98% for wells containing one effector and a single target, enabling automated quantification of cell locations, morphologies, movements, interactions, and deaths without the need for manual proofreading. Automated analysis of recordings from 12 different experiments demonstrated automated nanowell delineation accuracy >99%, automated cell segmentation accuracy >95%, and automated cell tracking accuracy of 90%, with default parameters, despite variations in illumination, staining, imaging noise, cell morphology, and cell clustering. An example analysis revealed that NK cells efficiently discriminate between live and dead targets by altering the duration of conjugation. The data also demonstrated that cytotoxic cells display higher motility than non-killers, both before and during contact.

CONTACT

broysam@central.uh.edu or nvaradar@central.uh.edu

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Physical supports from liver cancer cells are essential for differentiation and remodeling of endothelial cells in a HepG2-HUVEC co-culture model

Blood vessel remodeling is crucial in tumor growth. Growth factors released by tumor cells and endothelium-extracellular matrix interactions are highlighted in tumor angiogenesis, however the physical tumor-endothelium interactions are highly neglected. Here, we report that the physical supports from hepatocellular carcinoma, HepG2 cells, are essential for the differentiation and remodeling of endothelial cells. In a HepG2-HUVEC co-culture model, endothelial cells in direct contact with HepG2 cells could differentiate and form tubular structures similar to those plated on matrigel. By employing HepG2 cell sheet as a supportive layer, endothelial cells formed protrusions and sprouts above it. In separate experiments, fixed HepG2 cells could stimulate endothelial cells differentiation while the conditioned media could not, indicating that physical interactions between tumor and endothelial cells were indispensable. To further investigate the endothelium-remodeling mechanisms, the co-culture model was treated with inhibitors targeting different angiogenic signaling pathways. Inhibitors targeting focal adhesions effectively inhibited the differentiation of endothelial cells, while the growth factor receptor inhibitor displayed little effect. In conclusion, the co-culture model has provided evidences of the essential role of cancer cells in the differentiation and remodeling of endothelial cells, and is a potential platform for the discovery of new anti-angiogenic agents for liver cancer therapy.

A microfluidic live cell assay to study anthrax toxin induced cell lethality assisted by conditioned medium

It is technically challenging to investigate the function of secreted protein in real time by supply of conditioned medium that contains secreted protein of interest. The internalization of anthrax toxin is facilitated by a secreted protein Dickkopf-1 (DKK1) and its receptor, and eventually leads to cell lethality. To monitor the dynamic interplay between these components in live cells, we use an integrated microfluidic device to perform the cell viability assays with real-time controlled culture microenvironment in parallel. Conditioned medium, which contains the secreted proteins from specific cell lines, can be continuously pumped towards the cells that exposed to toxin. The exogenous DKK1 secreted from distant cells is able to rescue the sensitivity to toxin for those DKK1-knocked-down cells. This high-throughput assay allows us to precisely quantify the dynamic interaction between key components that cause cell death, and provide independent evidence of the function of DKK1 in the complex process of anthrax toxin internalization.

An artificial blood vessel implanted three-dimensional microsystem for modeling transvascular migration of tumor cells

Reproducing a tumor microenvironment consisting of blood vessels and tumor cells for modeling tumor invasion in vitro is particularly challenging. Here, we report an artificial blood vessel implanted 3D microfluidic system for reproducing transvascular migration of tumor cells. The transparent, porous and elastic artificial blood vessels are obtained by constructing polysaccharide cellulose-based microtubes using a chitosan sacrificial template, and possess excellent cytocompatibility, permeability, and mechanical characteristics. The artificial blood vessels are then fully implanted into the collagen matrix to reconstruct the 3D microsystem for modeling transvascular migration of tumor cells. Well-defined simulated vascular lumens were obtained by proliferation of the human umbilical vein endothelial cells (HUVECs) lining the artificial blood vessels, which enables us to reproduce structures and functions of blood vessels and replicate various hemodynamic parameters. Based on this model, the adhesion and transvascular migration of tumor cells across the artificial blood vessel have been well reproduced.

Synthetic tumor networks for screening drug delivery systems

Tumor drug delivery is a complex phenomenon affected by several elements in addition to drug or delivery vehicle's physico-chemical properties. A key factor is tumor microvasculature with complex effects including convective transport, high interstitial pressure and enhanced vascular permeability due to the presence of "leaky vessels". Current in vitro models of the tumor microenvironment for evaluating drug delivery are oversimplified and, as a result, show poor correlation with in vivo performance. In this study, we report on the development of a novel microfluidic platform that models the tumor microenvironment more accurately, with physiologically and morphologically realistic microvasculature including endothelial cell lined leaky capillary vessels along with 3D solid tumors. Endothelial cells and 3D spheroids of cervical tumor cells were co-cultured in the networks. Drug vehicle screening was demonstrated using GFP gene delivery by different formulations of nanopolymers. The synthetic tumor network was successful in predicting in vivo delivery efficiencies of the drug vehicles. The developed assay will have critical applications both in basic research, where it can be used to develop next generation delivery vehicles, and in drug discovery where it can be used to study drug transport and delivery efficacy in realistic tumor microenvironment, thereby enabling drug compound and/or delivery vehicle screening.

High throughput and multiplex localization of proteins and cells for in situ micropatterning using pneumatic microfluidics

We present a micropatterning method for protein/cell localization by using pneumatically controllable microstructures in an integrated microfluidic device.

Quantifying biased response of axon to chemical gradient steepness in a microfluidic device

Axons are very sensitive to molecular gradients and can discriminate extremely small differences in gradient steepness. Microfluidic devices capable of generating chemical gradients and adjusting their steepness could be used to quantify the sensitivity of axonal response. Here, we present a versatile and robust microfluidic device that can generate substrate-bound molecular gradients with evenly varying steepness on a single chip to precisely quantify axonal response. In this device, two solutions are perfused into a central channel via two inlets while partially flowing into two peripheral channels through interconnecting grooves, which gradually decrease the fluid velocity along the central channel. Molecular gradients with evenly and gradually decreased steepness can therefore be generated with a high resolution that is less than 0.05%/mm. In addition, the overall distribution range and resolution of the gradient steepness can be highly and flexibly controlled by adjusting various parameters of the device. Using this device, we quantified the hippocampal axonal response to substrate-bound laminin and ephrin-A5 gradients with varying steepnesses. Our results provided more detailed information on how and to what extent different steepnesses guide hippocampal neuron development during the initial outgrowth. Furthermore, our results show that axons can sensitively respond to very shallow laminin and ephrin-A5 gradients, which could effectively initiate biased differentiation of hippocampal neurons in the steepness range investigated in this study.

Standing surface acoustic wave based cell coculture

Precise reconstruction of heterotypic cell-cell interactions in vitro requires the coculture of different cell types in a highly controlled manner. In this article, we report a standing surface acoustic wave (SSAW)-based cell coculture platform. In our approach, different types of cells are patterned sequentially in the SSAW field to form an organized cell coculture. To validate our platform, we demonstrate a coculture of epithelial cancer cells and endothelial cells. Real-time monitoring of cell migration dynamics reveals increased cancer cell mobility when cancer cells are cocultured with endothelial cells. Our SSAW-based cell coculture platform has the advantages of contactless cell manipulation, high biocompatibility, high controllability, simplicity, and minimal interference of the cellular microenvironment. The SSAW technique demonstrated here can be a valuable analytical tool for various biological studies involving heterotypic cell-cell interactions.

Engineering interconnected 3D vascular networks in hydrogels using molded sodium alginate lattice as the sacrificial template

Engineering 3D perfusable vascular networks in vitro and reproducing the physiological environment of blood vessels is very challenging for tissue engineering and investigation of blood vessel function. Here, we engineer interconnected 3D microfluidic vascular networks in hydrogels using molded sodium alginate lattice as sacrificial templates. The sacrificial templates are rapidly replicated in polydimethylsiloxane (PDMS) microfluidic chips via Ca⁺²-crosslinking and then fully encapsulated in hydrogels. Interconnected channels with well controlled size and morphology are obtained by dissolving the monolayer or multilayer templates with EDTA solution. The human umbilical vein endothelial cells (HUVECs) are cultured on the channel linings and proliferated to form vascular lumens. The strong cell adhesion capability and adaptive response to shear stress demonstrate the excellent cytocompatibility of both the template and template-sacrificing process. Furthermore, the barrier function of the endothelial layer is characterized and the results show that a confluent endothelial monolayer is fully developed. Taken together, we develop a facile and rapid approach to engineer a vascular model that could be potentially used in physiological studies of vascular functions and vascular tissue engineering.

Advantages and challenges of microfluidic cell culture in polydimethylsiloxane devices

Culture of cells using various microfluidic devices is becoming more common within experimental cell biology. At the same time, a technological radiation of microfluidic cell culture device designs is currently in progress. Ultimately, the utility of microfluidic cell culture will be determined by its capacity to permit new insights into cellular function. Especially insights that would otherwise be difficult or impossible to obtain with macroscopic cell culture in traditional polystyrene dishes, flasks or well-plates. Many decades of heuristic optimization have gone into perfecting conventional cell culture devices and protocols. In comparison, even for the most commonly used microfluidic cell culture devices, such as those fabricated from polydimethylsiloxane (PDMS), collective understanding of the differences in cellular behavior between microfluidic and macroscopic culture is still developing. Moving in vitro culture from macroscopic culture to PDMS based devices can come with unforeseen challenges. Changes in device material, surface coating, cell number per unit surface area or per unit media volume may all affect the outcome of otherwise standard protocols. In this review, we outline some of the advantages and challenges that may accompany a transition from macroscopic to microfluidic cell culture. We focus on decisive factors that distinguish macroscopic from microfluidic cell culture to encourage a reconsideration of how macroscopic cell culture principles might apply to microfluidic cell culture.

Microfluidics-based in vivo mimetic systems for the study of cellular biology

The human body is a complex network of molecules, organelles, cells, tissues, and organs: an uncountable number of interactions and transformations interconnect all the system’s components. In addition to these biochemical components, biophysical components, such as pressure, flow, and morphology, and the location of all of these interactions play an important role in the human body. Technical difficulties have frequently limited researchers from observing cellular biology as it occurs within the human body, but some state-of-the-art analytical techniques have revealed distinct cellular behaviors that occur only in the context of the interactions. These types of findings have inspired bioanalytical chemists to provide new tools to better understand these cellular behaviors and interactions.

What blocks us from understanding critical biological interactions in the human body? Conventional approaches are often too naïve to provide realistic data and in vivo whole animal studies give complex results that may or may not be relevant for humans. Microfluidics offers an opportunity to bridge these two extremes: while these studies will not model the complexity of the in vivo human system, they can control the complexity so researchers can examine critical factors of interest carefully and quantitatively. In addition, the use of human cells, such as cells isolated from donated blood, captures human-relevant data and limits the use of animals in research. In addition, researchers can adapt these systems easily and cost-effectively to a variety of high-end signal transduction mechanisms, facilitating high-throughput studies that are also spatially, temporally, or chemically resolved. These strengths should allow microfluidic platforms to reveal critical parameters in the human body and provide insights that will help with the translation of pharmacological advances to clinical trials.

In this Account, we describe selected microfluidic innovations within the last 5 years that focus on modeling both biophysical and biochemical interactions in cellular communication, such as flow and cell–cell networks. We also describe more advanced systems that mimic higher level biological networks, such as organ on-a-chip and animal on-a-chip models. Since the first papers in the early 1990s, interest in the bioanalytical use of microfluidics has grown significantly. Advances in micro-/nanofabrication technology have allowed researchers to produce miniaturized, biocompatible assay platforms suitable for microfluidic studies in biochemistry and chemical biology. Well-designed microfluidic platforms can achieve quick, in vitro analyses on pico- and femtoliter volume samples that are temporally, spatially, and chemically resolved. In addition, controlled cell culture techniques using a microfluidic platform have produced biomimetic systems that allow researchers to replicate and monitor physiological interactions. Pioneering work has successfully created cell–fluid, cell–cell, cell–tissue, tissue–tissue, even organ-like level interfaces. Researchers have monitored cellular behaviors in these biomimetic microfluidic environments, producing validated model systems to understand human pathophysiology and to support the development of new therapeutics.