Establishment of a novel microfluidic co-culture system for simultaneous analysis of multiple indicators of gefitinib sensitivity in colorectal cancer cells

The therapeutic effect of gefitinib on colorectal cancer (CRC) is unclear, but it has been reported that stromal cells in the tumor microenvironment may have an impact on drug sensitivity. Herein, we established a microfluidic co-culture system and explored the sensitivity of CRC cells co-cultured with cancer-associated fibroblasts (CAFs) to gefitinib. The system consisted of a multichannel chip and a Petri dish. The chambers in the chip and dish were designed to continuously supply nutrients for long-term cell survival and create chemokine gradients for driving cell invasion without any external equipment. Using this system, the proliferation and invasiveness of cells were simultaneously evaluated by quantifying the area of cells and the migration distance of cells. In addition, the system combined with live cell workstation could evaluate the dynamic drug response of co-cultured cells and track individual cell trajectories in real-time. When CRC cells were co-cultured with CAFs, CAFs promoted CRC cell proliferation and invasion and reduced the sensitivity of cells to gefitinib through the exosomes secreted by CAFs. Furthermore, the cells that migrated out of the chip were collected, and EMT-related markers were determined by immunofluorescent and western blot assays. The results demonstrated that CAFs affected the response of CRC cells to gefitinib by inducing EMT, providing new ideas for further research on the resistance mechanism of gefitinib. This suggests that targeting CAFs or exosomes might be a new approach to enhance CRC sensitivity to gefitinib, and our system could be a novel platform for investigating the crosstalk between tumor cells and CAFs and understanding multiple biological changes of the tumor cells in the tumor microenvironment.

Drug Evaluation Based on a Multi-Channel Cell Chip with a Horizontal Co-Culture

We developed a multi-channel cell chip containing a three-dimensional (3D) scaffold for horizontal co-culture and drug toxicity screening in multi-organ culture (human glioblastoma, cervical cancer, normal liver cells, and normal lung cells). The polydimethylsiloxane (PDMS) multi-channel cell chip (PMCCC) was based on fused deposition modeling (FDM) technology. The architecture of the PMCCC was an open-type cell chip and did not require a pump or syringe. We investigated cell proliferation and cytotoxicity by conducting 3-(4,5-dimethylthiazol-2-yl)-2,5-dphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays and analysis of oleanolic acid (OA)-treated multi-channel cell chips. The results of the MTT and LDH assays showed that OA treatment in the multi-channel cell chip of four cell lines enhanced chemoresistance of cells compared with that in the 2D culture. Furthermore, we demonstrated the feasibility of the application of our multi-channel cell chip in various analysis methods through Annexin V-fluorescein isothiocyanate/propidium iodide staining, which is not used for conventional cell chips. Taken together, the results demonstrated that the PMCCC may be used as a new 3D platform because it enables simultaneous drug screening in multiple cells by single point injection and allows analysis of various biological processes.

Co-Culturing of Endothelial and Cancer Cells in a Nanofibrous Scaffold-Based Two-Layer System

Angiogenesis is critical for local tumor growth. This study aimed to develop a three-dimensional two-layer co-culture system to investigate effects of cancer cells on the growth of endothelial cells (ECs). Poly(ε-caprolactone) (PCL) nanofibrous membranes were generated via electrospinning of PCL in chloroform (C-PCL-M) and chloroform and dimethylformamide (C/DMF-PCL-M). We assembled a two-layer co-culture system using C-PCL-M and C/DMF-PCL-M for EC growth in the upper layer with co-cultured cancer cells in the lower layer. In the absence of vascular endothelial growth factor (VEGF), growth of bEND.3 ECs decreased on C/DMF-PCL-M but not on C-PCL-M with time. Growth of bEND.3 cells on C/DMF-PCL-M was enhanced through co-culturing of CT26 cancer cells and enhanced growth of bEND.3 cells was abrogated with anti-VEGF antibodies and sorafenib. However, EA.hy926 ECs displayed steady growth and proliferation on C/DMF-PCL-M, and their growth was not further increased through co-culturing of cancer cells. Moreover, chemical hypoxia in CT26 cancer cells upon treatment with CoCl₂ enhanced the growth of co-cultured bEND.3 cells in the two-layer system. Thus, EC growth on the nanofibrous scaffold is dependent on the types of ECs and composition of nanofibers and this co-culture system can be used to analyze EC growth induced by cancer cells.

Patient-derived small intestinal myofibroblasts direct perfused, physiologically responsive capillary development in a microfluidic Gut-on-a-Chip Model

The development and physiologic role of small intestine (SI) vasculature is poorly studied. This is partly due to a lack of targetable, organ-specific markers for in vivo studies of two critical tissue components: endothelium and stroma. This challenge is exacerbated by limitations of traditional cell culture techniques, which fail to recapitulate mechanobiologic stimuli known to affect vessel development. Here, we construct and characterize a 3D in vitro microfluidic model that supports the growth of patient-derived intestinal subepithelial myofibroblasts (ISEMFs) and endothelial cells (ECs) into perfused capillary networks. We report how ISEMF and EC-derived vasculature responds to physiologic parameters such as oxygen tension, cell density, growth factors, and pharmacotherapy with an antineoplastic agent (Erlotinib). Finally, we demonstrate effects of ISEMF and EC co-culture on patient-derived human intestinal epithelial cells (HIECs), and incorporate perfused vasculature into a gut-on-a-chip (GOC) model that includes HIECs. Overall, we demonstrate that ISEMFs possess angiogenic properties as evidenced by their ability to reliably, reproducibly, and quantifiably facilitate development of perfused vasculature in a microfluidic system. We furthermore demonstrate the feasibility of including perfused vasculature, including ISEMFs, as critical components of a novel, patient-derived, GOC system with translational relevance as a platform for precision and personalized medicine research.

Plug-and-Play In Vitro Metastasis System toward Recapitulating the Metastatic Cascade

Microfluidic-based tumor models that mimic tumor culture environment have been developed to understand the cancer metastasis mechanism and discover effective antimetastatic drugs. These models successfully recapitulated key steps of metastatic cascades, yet still limited to few metastatic steps, operation difficulty, and small molecule absorption. In this study, we developed a metastasis system made of biocompatible and drug resistance plastics to recapitulate each metastasis stage in three-dimensional (3D) mono- and co-cultures formats, enabling the investigation of the metastatic responses of cancer cells (A549-GFP). The plug-and-play feature enhances the efficiency of the experimental setup and avoids initial culture failures. The results demonstrate that cancer cells tended to proliferate and migrate with circulating flow and intravasated across the porous membrane after a period of 3 d when they were treated with transforming growth factor-beta 1 (TGF-β1) or co-cultured with human pulmonary microvascular endothelial cells (HPMECs). The cells were also observed to detach and migrate into the circulating flow after a period of 20 d, indicating that they transformed into circulating tumor cells for the next metastasis stage. We envision this metastasis system can provide novel insights that would aid in fully understanding the entire mechanism of tumor invasion.

Microphysiological lung models to evaluate the safety of new pharmaceutical modalities: a biopharmaceutical perspective

The lung is a complex organ; it is both the initial barrier for inhaled agents and the site of metabolism and therapeutic effect for a subset of systemically administered drugs. Comprised of more than 40 cell types that are responsible for various important functions, the lung's complexity contributes to the subsequent challenges in developing complex in vitro co-culture models (also called microphysiological systems (MPS), complex in vitro models or organs-on-a-chip). Although there are multiple considerations and limitations in the development and qualification of such in vitro systems, MPS exhibit great promise in the fields of pharmacology and toxicology. Successful development and implementation of MPS models may enable mechanistic bridging between non-clinical species and humans, and increase clinical relevance of safety endpoints, while decreasing overall animal use. This article summarizes, from a biopharmaceutical industry perspective, essential elements for the development and qualification of lung MPS models. Its purpose is to guide MPS developers and manufacturers to expedite MPS utilization for safety assessment in the biopharmaceutical industry.

Pumpless platform for high-throughput dynamic multicellular culture and chemosensitivity evaluation

We report here a novel pumpless, 96-well plate-based platform for high-throughput dynamic multicellular culture and chemosensitivity evaluation. A gravity-driven flow strategy was developed to generate and sustain the flow rate of culture medium within 10% in the platform's 20 culture chambers. The ability of the platform to generate and sustain the medium flow was demonstrated by computational simulation, flow visualization, and ascertaining the previously known effect of flow-induced shear stress on the stimulated osteogenic differentiation of osteoblasts. The high-throughput utility of the platform was demonstrated by in situ cell staining and high content screening of chemosensitivity assays of multiple myeloma and osteoblast co-cultures. Endpoint characterization and data analyses for all 20 culture chambers required less than 1 hour.

Adipose-on-a-chip: a dynamic microphysiological in vitro model of the human adipose for immune-metabolic analysis in type II diabetes

Infiltration of immune cells into adipose tissue is associated with chronic low-grade inflammation in obese individuals. To better understand the crosstalk between immune cells and adipocytes, in vivo-like in vitro models are required. Conventionally transwell culture plates are used for studying the adipocyte-immune cell interaction; however, the static culture nature of this approach falls short of closely recapitulating the physiological environment. Here we present a compartmentalized microfluidic co-culture system which provides a constant-rate of nutrient supply as well as waste removal, resembling the microvascular networks of the in vivo environment. Human adipocytes and U937 cells were co-cultured in close proximity in an enclosed system. The porous barrier between the adjacent compartments comprises an array of microchannels, which enables paracrine interaction between cells in adjacent compartments and improved perfusion-based long term cell feeding. Human pre-adipocytes were fully differentiated into adipocytes on the chip and remained viable for several weeks. Upon co-culturing with immune cells, adipocytes showed a tendency to develop insulin resistance. The immune-metabolic correlation has been studied by monitoring adiponectin and IL-6 expression, as well as glucose uptake upon treatment with insulin. Our microfluidic system can be potentially used to develop physiologically relevant adipose tissue models to study obesity-associated diseases such as insulin resistance and type 2 diabetes and therefore, facilitate drug development to treat these diseases.

A Three-Dimensional Arrayed Microfluidic Blood-Brain Barrier Model With Integrated Electrical Sensor Array

OBJECTIVE

The blood-brain barrier (BBB) poses a unique challenge to the development of therapeutics against neurological disorders due to its impermeabi-lity to most of the chemical compounds. Most in vitro BBB models have limitations in mimicking in vivo conditions and functions. Here, we show a co-culture microfluidic BBB-on-a-chip that provides interactions between neurovascular endothelial cells and neuronal cells across a porous polycarbonate membrane, which better mimics the in vivo conditions, as well as allows in vivo level shear stress to be applied.

METHODS

A 4 × 4 intersecting microchannel array forms 16 BBB sites on a chip, with a multielectrode array integrated to measure the transendothelial electrical resistance (TEER) from all 16 different sites, which allows label-free real-time analysis of the barrier function. Primary mouse endothelial cells and primary astrocytes were co-cultured in the chip while applying in vivo level shear stress. The chip allows the barrier function to be analyzed through TEER measurement, dextran permeability, as well as immunostaining.

RESULTS

Co-culture between astrocytes and endothelial cells, as well as in vivo level shear stress applied, led to the formation of tighter junctions and significantly lower barrier permeability. Moreover, drug testing with histamine showed increased permeability when using only endothelial cells compared to almost no change when using co-culture.

CONCLUSION

Results show that the developed BBB chip more closely mimics the in vivo BBB environment.

SIGNIFICANCE

The developed multisite BBB chip is expected to be used for screening drug by more accurately predicting their permeability through BBB as well as their toxicity.

In Vitro Differentiation of T Cells: From Nonhuman Primate-Induced Pluripotent Stem Cells

In this chapter, we describe a protocol for hematopoietic differentiation of nonhuman primate (NHP)-induced pluripotent stem cells (iPSCs) derived from T cells and generation of T cells. Derivation of T cells from PSCs involves three steps: induction of PSCs to hematopoietic progenitor cells (HPCs), differentiation of HPCs into progenitor T cells, and maturation of progenitor T cells into mature T cells, in particular CD8 single-positive (SP) T cells.

CD107a Degranulation Assay to Evaluate Immune Cell Antitumor Activity

Cancer development is under surveillance by the immune system of the host. Tumor cells can be recognized and killed by cytotoxic lymphocytes- such as CD8+ T lymphocytes and natural killer (NK) cells-mainly through the immune secretion of lytic granules that kill target cells. This process involves the fusion of the granule membrane with the cytoplasmic membrane of the immune effector cell, resulting in surface exposure of lysosomal-associated proteins that are typically present on the lipid bilayer surrounding lytic granules, such as CD107a. Therefore, membrane expression of CD107a constitutes a marker of immune cell activation and cytotoxic degranulation. In this chapter, we detail the steps required to isolate peripheral blood mononuclear cells (PBMCs), coculture them with target tumor cell lines, and evaluate the cytotoxic immune function by means of flow cytometry evaluation of CD107a expression on the surface of NK cells.

Cytokine Profiling and Orthotopic Xenografing of Pancreatic Stellate Cells

Pancreatic ductal adenocarcinoma (PDAC) continues to be one of the most lethal human malignancies with a poor prognosis due to systemic metastasis and a high recurrence rate. Interactions between tumor and stromal cells play a critical role in tumor progression. However, the interaction between PSCs and pancreatic cancer cells (PCCs) and the underlying mechanisms are poorly understood. Coculture system with PSCs and PCCs is very useful technique platform for the in vitro and in vivo study of the interaction between these two cellular components. In this protocol, we aim to describe the cytokine profiling technique for in vitro study of PSC-PCC intercellular communication, and orthotopic xenografting animal model with coinjection of primary PSCs and PCC cell line.

A microfluidic co-cultivation platform to investigate microbial interactions at defined microenvironments

Interspecies interactions inside microbial communities bear a tremendous diversity of complex chemical processes that are by far not understood. Even for simplified, often synthetic systems, the interactions between two microbes are barely revealed in detail. Here, we present a microfluidic co-cultivation platform for the analysis of growth and interactions inside microbial consortia with single-cell resolution. Our device allows the spatial separation of two different microbial organisms inside adjacent microchambers facilitating sufficient exchange of metabolites via connecting nanochannels. Inside the cultivation chambers cell growth can be observed with high spatio-temporal resolution by live-cell imaging. In contrast to conventional approaches, in which single-cell activity is typically fully masked by the average bulk behavior, the small dimensions of the microfluidic cultivation chambers enable accurate environmental control and observation of cellular interactions with full spatio-temporal resolution. Our method enables one to study phenomena in microbial interactions, such as gene transfer or metabolic cross-feeding. We chose two different microbial model systems to demonstrate the wide applicability of the technology. First, we investigated commensalistic interactions between an industrially relevant l-lysine-producing Corynebacterium glutamicum strain and an l-lysine auxotrophic variant of the same species. Spatially separated co-cultivation of both strains resulted in growth of the auxotrophic strain due to secreted l-lysine supplied by the producer strain. As a second example we investigated bacterial conjugation between Escherichia coli S17-1 and Pseudomonas putida KT2440 cells. We could show that direct cell contact is essential for the successful gene transfer via conjugation and was hindered when cells were spatially separated. The presented device lays the foundation for further studies on contactless and contact-based interactions of natural and synthetic microbial communities.

A lung/liver-on-a-chip platform for acute and chronic toxicity studies

The merging of three-dimensional in vitro models with multi-organ-on-a-chip (MOC) technology has taken in vitro assessment of chemicals to an unprecedented level. By connecting multiple organotypic models, MOC allows for the crosstalk between different organs to be studied to evaluate a compound's safety and efficacy better than with single cultures. The technology could also improve the toxicological assessment of aerosols that have been implicated in the development of chronic obstructive pulmonary disease, asthma, or lung cancer. Here we report the development of a lung/liver-on-a-chip, connecting in a single circuit, normal human bronchial epithelial (NHBE) cells cultured at the air-liquid interface (ALI), and HepaRG™ liver spheroids. Maintenance of the individual tissues in the chip increased NHBE ALI tissue transepithelial electrical resistance and decreased HepaRG™ spheroid adenosine triphosphate content as well as cytochrome P450 (CYP) 1A1/1B1 inducibility. CYP inducibility was partly restored when HepaRG™ spheroids were cocultured with NHBE ALI tissues. Both tissues remained viable and functional for 28 days when cocultured in the chip. The capacity of the HepaRG™ spheroids to metabolize compounds present in the medium and to modulate their toxicity was proven using aflatoxin B1 (AFB1). AFB1 toxicity in NHBE ALI tissues decreased when HepaRG™ spheroids were present in the same chip circuit, proving that the HepaRG™-mediated detoxification is protecting/decreasing from AFB1-mediated cytotoxicity. The lung/liver-on-a-chip platform presented here offers new opportunities to study the toxicity of inhaled aerosols or to demonstrate the safety and efficacy of new drug candidates targeting the human lung.

A Fluidic Culture Platform for Spatially Patterned Cell Growth, Differentiation, and Cocultures

Stem cell cultures within perfusion bioreactors, while efficient in obtaining cell numbers, often lack the similarity to native tissues and consequently cell phenotype. We develop a three-dimensional (3D)-printed fluidic chamber for dynamic stem cell culture, with emphasis on control over flow and substrate curvature in a 3D environment, two physiologic features of native tissues. The chamber geometry, consisting of an array of vertical cylindrical pillars, facilitates actin-mediated localization of human mesenchymal stem cells (hMSCs) within ∼200 μm distance from the pillars, enabling spatial patterning of hMSCs and endothelial cells in cocultures and subsequent modulation of calcium signaling between these two essential cell types in the bone marrow microenvironment. Flow-enhanced osteogenic differentiation of hMSCs in growth media imposes spatial variations of alkaline phosphatase expression, which positively correlates with local shear stress. Proliferation of hMSCs is maintained within the chamber, exceeding the cell expansion in conventional static culture. The capability to manipulate cell spatial patterning, differentiation, and 3D tissue formation through geometry and flow demonstrates the culture chamber's relevant chemomechanical cues in stem cell microenvironments, thus providing an easy-to-implement tool to study interactions among substrate curvature, shear stress, and intracellular actin machinery in the tissue-engineered construct.

New coculture system of Clostridium spp. and Megasphaera hexanoica using submerged hollow-fiber membrane bioreactors for caproic acid production

In this study, a coculture bioprocess was developed with Clostridium strains producing butyric acid and Megasphaera hexanoica producing caproic acid from the butyric acid. The two bacterial strains were each cultivated in two submerged hollow-fiber membrane bioreactors (s-HF/MBRs), separately. Each fermentation broth was filtered through the membrane modules, and the filtered broth was either interchanged on another reactor or obtained sequentially through. Using s-HF/MBRs, the caproic acid concentration increased to 10.08 g L^-1, with the fastest productivity of 0.69 g L^-1 h^-1, which higher than that previously reported.

A liver-immune coculture array for predicting systemic drug-induced skin sensitization

Drug-induced skin sensitization is prevalent worldwide and can trigger life-threatening health conditions, such as Stevens Johnson Syndrome. However, existing in vitro skin models cannot adequately predict the skin sensitization effects of drugs administered into the systemic circulation because dermal inflammation and injury are preceded by conversion of parent drugs into antigenic reactive metabolites in the liver and subsequent activation of the immune system. Here, we demonstrate that recapitulation of these early tandem cellular processes in a compartmentalized liver-immune coculture array is sufficient to predict the skin sensitization potential of systemic drugs. Human progenitor cell (HepaRG)-derived hepatocyte spheroids and U937 myeloid cells, a representative antigen presenting cell (APC), can maintain their respective functions in 2 concentric micro-chambers, which are connected by a diffusion microchannel network. Paradigm drugs that are reported to cause severe cutaneous drug reactions (i.e. carbamazepine, phenytoin and allopurinol) can be metabolized into their reactive metabolites, which diffuse efficiently into the adjoining immune compartment within a 48 hour period. By measuring the extent of U937 activation as indicated by IL8, IL1β and CD86 upregulation upon drug administration, we show that the liver-immune coculture array more consistently and reliably distinguish all 3-paradigm skin sensitizing drugs from a non-skin sensitizer than conventional bulk Transwell coculture. Given its miniaturized format, design simplicity and prediction capability, this novel in vitro system can be readily scaled into a screenable platform to identify the skin sensitization potential of systemically-administered drugs.

Harvesting prevascularized smooth muscle cell sheets from common polystyrene culture dishes

Cell sheet engineering has recently emerged as a promising strategy for scaffold-free tissue engineering. However, the primary method of harvesting cell sheets using temperature-responsive dishes has potential limitations. Here we report a novel cell sheet technology based on a coculture system in which SMCs are cocultured with EPCs on common polystyrene dishes. We found that an intact and highly viable cell sheet could be harvested using mechanical methods when SMCs and EPCs were cocultured on common polystyrene dishes at a ratio of 6:1 for 5 to 6 days; the method is simple, cost-effective and highly repeatable. Moreover, the cocultured cell sheet contained capillary-like networks and could secrete a variety of angiogenic factors. Finally, in vivo studies proved that the cocultured cell sheets were more favorable for the fabrication of vascularized smooth muscle tissues compared to single SMC sheets. This study provides a promising avenue for smooth muscle tissue engineering.

A pumpless body-on-a-chip model using a primary culture of human intestinal cells and a 3D culture of liver cells

We describe an expanded modular gastrointestinal (GI) tract-liver system by co-culture of primary human intestinal epithelial cells (hIECs) and 3D liver mimic. The two organ body-on-chip design consisted of GI and liver tissue compartments that were connected by fluidic medium flow driven via gravity. The hIECs and HepG2 C3A liver cells in the co-culture system maintained high viability for at least 14 days in which hIECs differentiated into major cell types found in native human intestinal epithelium and the HepG2 C3A cells cultured on 3D polymer scaffold formed a liver micro-lobe like structure. Moreover, the hIECs formed a monolayer on polycarbonate membranes with a tight junction and authentic TEER values of approximately 250 Ω cm2 for the native gut. The hIEC permeability was compared to a conventional permeability model using Caco-2 cell response for drug absorption by measuring the uptake of propranolol, mannitol and caffeine. Metabolic rates (urea or albumin production) of the cells in the co-culture GI-liver system were comparable to those of HepG2 C3A cells in a single-organ fluidic culture system, while induced CYP activities were significantly increased in the co-culture GI tract-liver system compared to the single-organ fluidic culture system. These results demonstrated potential of the low-cost microphysiological GI-liver model for preclinical studies to predict human response.

Micropassage-embedding composite hydrogel fibers enable quantitative evaluation of cancer cell invasion under 3D coculture conditions

Cell migration and invasion are of significant importance in physiological phenomena, including wound healing and cancer metastasis. Here we propose a new system for quantitatively evaluating cancer cell invasion in a three-dimensional (3D), in vivo tissue-like environment. This system uses composite hydrogel microfibers whose cross section has a relatively soft micropassage region and that were prepared using a multilayered microfluidic device; cancer cells are encapsulated in the core and fibroblasts are seeded in the shell regions surrounding the core. Cancer cell proliferation is guided through the micropassage because of the physical restriction imposed by the surrounding solid shell regions. Quantitative analysis of cancer cell invasion is possible simply by counting the cancer cell colonies that form outside the fiber. This platform enables the evaluation of anticancer drug efficacy (cisplatin, paclitaxel, and 5-fluorouracil) based on the degree of invasion and the gene expression of cancer cells (A549 cells) with or without the presence of fibroblasts (NIH-3T3 cells). The presented hydrogel fiber-based migration assays could be useful for studying cell behaviors under 3D coculture conditions and for drug screening and evaluation.

Human Tumor Tissue-Based 3D In Vitro Invasion Assays

Here we describe a protocol to utilize human benign leiomyoma tissue in in vitro 3D model that enables an assessment of cell invasion. The chapter also describes detailed instructions for image analysis to quantify the results. Leiomyoma is a benign tumor of the uterus which mimics authentic components of the tumor microenvironment including fibroblasts, vessels, collagen fibers, and extracellular protein composition. The leiomyoma invasion model represents a superior 3D model for cell invasion studies compared to the other non-human organotypic models.

Monitoring the Mitochondrial Dynamics in Mammalian Cells

Mitochondria exist in a dynamic state inside mammalian cells. They undergo processes of fusion and fission to adjust their shape according to the different cell needs. Different proteins tightly regulate these dynamics: Opa-1 and Mitofusin-1 and Mitofusin-2 are the main profusion proteins, while Drp1 and its different receptors (Mff, Fis1, MiD49, MiD51) regulate mitochondrial fission. The dynamic nature of the mitochondrial network has become evident and detectable, thanks to recent advances in live imaging video microscopy and to the availability of mitochondria-tagged fluorescent proteins. High-resolution confocal reconstruction of mitochondria over time allows researchers to visualize mitochondria shape changes in living cells, under different experimental conditions. Moreover, in recent years, different techniques in living cells have been developed to study the process of mitochondria fusion in more details. Among them are fluorescence recovery after photobleaching (FRAP) of mitochondria-tagged GFP (mtGFP), use of photoactivatable mtGFP, polyethylene glycol (PEG)-based fusion of mtGFP and mtRFP cells, and Renilla luciferase assay (for population studies). In addition, in combination with imaging, the analysis of the expression levels of the different mitochondria-shaping proteins, along with that of their activation status, represents a powerful tool to investigate potential modulations of the mitochondrial network. Here, we review this aspect and then mention a number of techniques, with particular attention to their relative protocols.

The Colorectal Cancer Microenvironment: Strategies for Studying the Role of Cancer-Associated Fibroblasts

Colorectal cancer (CRC) is a key public health concern and the second highest cause of cancer related death in Western society. A dynamic interaction exists between CRC cells and the surrounding tumor microenvironment, which can stimulate not only the development of CRC, but its progression and metastasis, as well as the development of resistance to therapy. In this chapter, we focus on the role of fibroblasts within the CRC tumor microenvironment and describe some of the key methods for their study, as well as the evaluation of dynamic interactions within this biological ecosystem.

A deep conical agarose microwell array for adhesion independent three-dimensional cell culture and dynamic volume measurement

Multicellular spheroids represent a well-established 3D model to study healthy and diseased cells in vitro. The use of conventional 3D cell culture platforms for the generation of multicellular spheroids is limited to cell types that easily self-assemble into spheroids because less adhesive cells fail to form stable aggregates. A high-precision micromoulding technique developed in our laboratory produces deep conical agarose microwell arrays that allow the cultivation of uniform multicellular aggregates, irrespective of the spheroid formation capacity of the cells. Such hydrogel arrays warrant a steady nutrient supply for several weeks, permit live volumetric measurements to monitor cell growth, enable immunohistochemical staining, fluorescence-based microscopy, and facilitate immediate harvesting of cell aggregates. This system also allows co-cultures of two distinct cell types either in direct cell-cell contact or at a distance as the hydrogel permits diffusion of soluble compounds. Notably, we show that co-culture of a breast cancer cell line with bone marrow stromal cells enhances 3D growth of the cancer cells in this system.

Controlled placement of multiple CNS cell populations to create complex neuronal cultures

In vitro brain-on-a-chip platforms hold promise in many areas including: drug discovery, evaluating effects of toxicants and pathogens, and disease modelling. A more accurate recapitulation of the intricate organization of the brain in vivo may require a complex in vitro system including organization of multiple neuronal cell types in an anatomically-relevant manner. Most approaches for compartmentalizing or segregating multiple cell types on microfabricated substrates use either permanent physical surface features or chemical surface functionalization. This study describes a removable insert that successfully deposits neurons from different brain areas onto discrete regions of a microelectrode array (MEA) surface, achieving a separation distance of 100 μm. The regional seeding area on the substrate is significantly smaller than current platforms using comparable placement methods. The non-permanent barrier between cell populations allows the cells to remain localized and attach to the substrate while the insert is in place and interact with neighboring regions after removal. The insert was used to simultaneously seed primary rodent hippocampal and cortical neurons onto MEAs. These cells retained their morphology, viability, and function after seeding through the cell insert through 28 days in vitro (DIV). Co-cultures of the two neuron types developed processes and formed integrated networks between the different MEA regions. Electrophysiological data demonstrated characteristic bursting features and waveform shapes that were consistent for each neuron type in both mono- and co-culture. Additionally, hippocampal cells co-cultured with cortical neurons showed an increase in within-burst firing rate (p = 0.013) and percent spikes in bursts (p = 0.002), changes that imply communication exists between the two cell types in co-culture. The cell seeding insert described in this work is a simple but effective method of separating distinct neuronal populations on microfabricated devices, and offers a unique approach to developing the types of complex in vitro cellular environments required for anatomically-relevant brain-on-a-chip devices.

Novel co-culture plate enables growth dynamic-based assessment of contact-independent microbial interactions

Interactions between microbes are central to the dynamics of microbial communities. Understanding these interactions is essential for the characterization of communities, yet challenging to accomplish in practice. There are limited available tools for characterizing diffusion-mediated, contact-independent microbial interactions. A practical and widely implemented technique in such characterization involves the simultaneous co-culture of distinct bacterial species and subsequent analysis of relative abundance in the total population. However, distinguishing between species can be logistically challenging. In this paper, we present a low-cost, vertical membrane, co-culture plate to quantify contact-independent interactions between distinct bacterial populations in co-culture via real-time optical density measurements. These measurements can be used to facilitate the analysis of the interaction between microbes that are physically separated by a semipermeable membrane yet able to exchange diffusible molecules. We show that diffusion across the membrane occurs at a sufficient rate to enable effective interaction between physically separate cultures. Two bacterial species commonly found in the cystic fibrotic lung, Pseudomonas aeruginosa and Burkholderia cenocepacia, were co-cultured to demonstrate how this plate may be implemented to study microbial interactions. We have demonstrated that this novel co-culture device is able to reliably generate real-time measurements of optical density data that can be used to characterize interactions between microbial species.

Reciprocal influence of hMSCs/HaCaT cultivated on electrospun scaffolds

Here, we investigated the synergistic effect of electrospun nanofibrous scaffolds made of gelatin /sulfated hyaluronan (sHA) or native hyaluronan (HA)/chondroitin sulfate (CS) and, keratinocytes (HaCaT)-human mesenchymal stem cells (hMSCs) contact co-culture on epithelial differentiation of hMSCs. The hMSCs were co-cultured in contact with HaCaT cells for 5 days on electrospun scaffold. Results show that electrospun scaffolds containing sulfated glycosaminoglycans (GAGs) stimulate epithelial differentiation in terms of various protein expression markers (keratin 14, ΔNp63α and Pan-cytokeratin) and gene expression of several dermal proteins (keratin 14, ΔNp63α). Electrospun scaffold independent of GAGs alone did not affect the epithelial differentiation of hMSCs but combination of keratinocyte-hMSC contact co-culture and electrospun scaffold promotes the epithelial differentiation of hMSCs.

Construction of stable capillary networks using a microfluidic device

Construction of stable capillary networks is required to provide sufficient oxygen and nutrients to the deep region of thick tissues, which is important in the context of 3D tissue engineering. Although conventional in vitro culture models have been used to investigate the mechanism of capillary formation, recent advances in microfluidics technologies allowed us to control biophysical and biochemical culture environments more precisely, which led to the construction of functional and stable capillary networks. In this study, endothelial cells and mesenchymal stem cells were co-cultured in microfluidic devices to construct stable capillary networks, which resulted in the construction of luminal structures covered by pericytes. Interactions between endothelial cells and mesenchymal stem cells are also discussed in the context of capillary formation.

Modeling the Blood-Brain Barrier in a 3D triple co-culture microfluidic system

The need for a blood-brain barrier (BBB) model that accurately mimics the physiological characteristics of the in-vivo situation is well-recognized by researchers in academia and industry. However, there is currently no in-vitro model allowing studies of neuronal growth and/or function influenced by factors from the blood that cross through the BBB. Therefore, we established a 3D triple co-culture microfluidic system using human umbilical vein endothelial cells (HUVEC) together with primary rat astrocytes and neurons. Immunostaining confirmed the successful triple co-culture system consisting of an intact BBB with tight intercellular junctions in the endothelial monolayer. The BBB selective permeability was determined by a fluorescent-based assay using dextrans of different molecular weights. Finally, neuron functionality was demonstrated by calcium imaging.

A 3D neurovascular microfluidic model consisting of neurons, astrocytes and cerebral endothelial cells as a blood-brain barrier

The neurovascular unit is a complex, interdependent system composed of neurons and neural supporting cells, such as astrocytes, as well as cells that comprise the vascular system including endothelial cells, pericytes, and smooth muscle cells. Each cell type in the neurovascular unit plays an essential role, either in transmitting and processing neural signals or in maintaining the appropriate microenvironmental conditions for healthy neural function. In vitro neurovascular models can be useful for understanding the different roles and functions of the cells composing the neurovascular unit, as well as for assessing the effects on neural function of therapeutic compounds after crossing the endothelial barrier. Here, we report a novel three-dimensional neurovascular microfluidic model consisting of primary rat astrocytes and neurons together with human cerebral microvascular endothelial cells. These three cell types in our neurovascular chip (NVC) show distinct cell type-specific morphological characteristics and functional properties. In particular, morphological and functional analysis of neurons enables quantitative assessment of neuronal responses, while human cerebral endothelial cells form monolayers with size-selective permeability similar to existing in vitro blood-brain barrier (BBB) models.

Co-cultivation of microalgae and nitrifiers for higher biomass production and better carbon capture

The aim of this work was to study co-cultivation of nitrifiers with microalgae as a non-intrusive technique for selective removal of oxygen generated by microalgae. Biomass concentration was, at least, 23% higher in mixed-cultures where nitrifiers kept the dissolved oxygen concentration below 9.0μLL(-1) than in control Chlorella vulgaris axenic-cultures where the concentration of dissolved oxygen was higher than 10.0μLL(-1). This approach to eliminating oxygen inhibition of microalgal growth could become the basis for the development of advanced microalgae reactors for removal of CO2 from the atmosphere, and concentrated CO2 streams. CO2 sequestration would become a chemically and geologically safer and environmentally more sound technology provided it uses microalgal, or other biomass, instead of CO2, for carbon storage.

Microfluidic co-culture system for cancer migratory analysis and anti-metastatic drugs screening

Tumour metastasis is an important reason for cancer death, and cancer cell migration is an important step in the process of tumour metastasis. Studying cancer cell migration is of great significance. Here, we present a novel microfluidic co-culture system and establish mild, moderate and severe cancer models by using HMEpiC and MDA-MB-231 cells to study cancer cell migration and anti-cancer drug screening. Using this device, we achieved high cell viability (over 90%) and a stable analysis of the migration ability of cancer cells. We observed that the density of the cancer cells determined the probability of the occurrence of metastatic cells and that the induction of normal cells affected the metastatic velocity of each cancer cell. We verified that the increase in the migration ability of MDA-MB-231 cells co-cultured with HMEpiC cells was relative to the increased secretion of IL-6 and that this was verified by an IL-6 inhibitor assay. This co-culture also led to decreased CK-14 secretion and morphological changes in HMEpiC cells. Finally, significant inhibition of paclitaxel and tamoxifen on cancer migration was observed. Taken together, our microfluidic device could be a useful tool for the quantitation of the migratory capability and anti-metastatic drug screening.

A microfluidic cell-trapping device for single-cell tracking of host-microbe interactions

The impact of cellular individuality on host-microbe interactions is increasingly appreciated but studying the temporal dynamics of single-cell behavior in this context remains technically challenging. Here we present a microfluidic platform, InfectChip, to trap motile infected cells for high-resolution time-lapse microscopy. This approach allows the direct visualization of all stages of infection, from bacterial uptake to death of the bacterium or host cell, over extended periods of time. We demonstrate the utility of this approach by co-culturing an established host-cell model, Dictyostelium discoideum, with the extracellular pathogen Klebsiella pneumoniae or the intracellular pathogen Mycobacterium marinum. We show that the outcome of such infections is surprisingly heterogeneous, ranging from abortive infection to death of the bacterium or host cell. InfectChip thus provides a simple method to dissect the time-course of host-microbe interactions at the single-cell level, yielding new insights that could not be gleaned from conventional population-based measurements.

Single cell dual adherent-suspension co-culture micro-environment for studying tumor-stromal interactions with functionally selected cancer stem-like cells

Considerable evidence suggests that cancer stem-like cells (CSCs) are critical in tumor pathogenesis, but their rarity and transience has led to much controversy about their exact nature. Although CSCs can be functionally identified using dish-based tumorsphere assays, it is difficult to handle and monitor single cells in dish-based approaches; single cell-based microfluidic approaches offer better control and reliable single cell derived sphere formation. However, like normal stem cells, CSCs are heavily regulated by their microenvironment, requiring tumor-stromal interactions for tumorigenic and proliferative behaviors. To enable single cell derived tumorsphere formation within a stromal microenvironment, we present a dual adherent/suspension co-culture device, which combines a suspension environment for single-cell tumorsphere assays and an adherent environment for co-culturing stromal cells in close proximity by selectively patterning polyHEMA in indented microwells. By minimizing dead volume and improving cell capture efficiency, the presented platform allows for the use of small numbers of cells (<100 cells). As a proof of concept, we co-cultured single T47D (breast cancer) cells and primary cancer associated fibroblasts (CAF) on-chip for 14 days to monitor sphere formation and growth. Compared to mono-culture, co-cultured T47D have higher tumorigenic potential (sphere formation rate) and proliferation rates (larger sphere size). Furthermore, 96-multiplexed single-cell transcriptome analyses were performed to compare the gene expression of co-cultured and mono-cultured T47D cells. Phenotypic changes observed in co-culture correlated with expression changes in genes associated with proliferation, apoptotic suppression, tumorigenicity and even epithelial-to-mesechymal transition. Combining the presented platform with single cell transcriptome analysis, we successfully identified functional CSCs and investigated the phenotypic and transcriptome effects induced by tumor-stromal interactions.

Multi-channel cell co-culture for drug development based on glass microfluidic chip-mass spectrometry coupled platform

RATIONALE

Cell-based drug assay plays an essential role in drug development. By coupling a microfluidic chip with mass spectrometry (MS), we developed a multifunctional platform. Cell co-culture, cell apoptosis assay, fluorescence and MS detection of intracellular drug absorption could be simultaneously conducted on this platform.

METHODS

Three micro-channels were fabricated through photolithography technology to conduct the cell co-culture. Cell apoptosis after drug treatment was assayed by fluorescent probes (Hoechst 33342). Intracellular Dox absorption was analyzed by confocal fluorescent microscopy. With a high voltage (~ 4.5 kV) applied onto the microfluidic chip, the ionization spray was successfully generated by dropping isopropanol onto it. By coupling with a Shimadzu LCMS-2010 A mass spectrometer, intracellular CPA absorption was detected on the microfluidic chip.

RESULTS

The microfluidic chip-MS coupled platform showed high biocompatibility. Distinction of cell apoptosis between co-cultured and mono-cultured cells was detected. The results of intracellular drug absorption well explained the different cell apoptosis rate.

CONCLUSIONS

Cell-based drug assay was facilely and successfully conducted on the microfluidic chip-MS coupled platform. This technology we have devised could promote MS application in the field of drug development. Copyright © 2016 John Wiley & Sons, Ltd.

Co-Culture of Tumor Spheroids and Fibroblasts in a Collagen Matrix-Incorporated Microfluidic Chip Mimics Reciprocal Activation in Solid Tumor Microenvironment

Multicellular 3D culture and interaction with stromal components are considered essential elements in establishing a ‘more clinically relevant’ tumor model. Matrix-embedded 3D cultures using a microfluidic chip platform can recapitulate the microscale interaction within tumor microenvironments. As a major component of tumor microenvironment, cancer-associated fibroblasts (CAFs) play a role in cancer progression and drug resistance. Here, we present a microfluidic chip-based tumor tissue culture model that integrates 3D tumor spheroids (TSs) with CAF in proximity within a hydrogel scaffold. HT-29 human colorectal carcinoma cells grew into 3D TSs and the growth was stimulated when co-cultured with fibroblasts as shown by 1.5-folds increase of % changes in diameter over 5 days. TS cultured for 6 days showed a reduced expression of Ki-67 along with increased expression of fibronectin when co-cultured with fibroblasts compared to mono-cultured TSs. Fibroblasts were activated under co-culture conditions, as demonstrated by increases in α-SMA expression and migratory activity. When exposed to paclitaxel, a survival advantage was observed in TSs co-cultured with activated fibroblasts. Overall, we demonstrated the reciprocal interaction between TSs and fibroblasts in our 7-channel microfluidic chip. The co-culture of 3D TS-CAF in a collagen matrix-incorporated microfluidic chip may be useful to study the tumor microenvironment and for evaluation of drug screening and evaluation.

Engineering a perfusable 3D human liver platform from iPS cells

In vitro models of human tissue are crucial to our ability to study human disease as well as develop safe and effective drug therapies. Models of single organs in static and microfluidic culture have been established and shown utility for modeling some aspects of health and disease; however, these systems lack multi-organ interactions that are critical to some aspects of drug metabolism and toxicity. Thus, as part of a consortium of researchers, we have developed a liver chip that meets the following criteria: (1) employs human iPS cells from a patient of interest, (2) cultures cells in perfusable 3D organoids, and (3) is robust to variations in perfusion rate so as to be compatible in series with other specialized tissue chips (e.g. heart, lung). In order to achieve this, we describe methods to form hepatocyte aggregates from primary and iPS-derived cells, alone and in co-culture with support cells. This necessitated a novel culture protocol for the interrupted differentiation of iPS cells that permits their removal from a plated surface and aggregation while maintaining phenotypic hepatic functions. In order to incorporate these 3D aggregates in a perfusable platform, we next encapsulated the cells in a PEG hydrogel to prevent aggregation and overgrowth once on chip. We adapted a C-trap chip architecture from the literature that enabled robust loading with encapsulated organoids and culture over a range of flow rates. Finally, we characterize the liver functions of this iHep organoid chip under perfusion and demonstrate a lifetime of at least 28 days. We envision that such this strategy can be generalized to other microfluidic tissue models and provides an opportunity to query patient-specific liver responses in vitro.

Modular, pumpless body-on-a-chip platform for the co-culture of GI tract epithelium and 3D primary liver tissue

We have developed an expandable modular body-on-a-chip system that allows for a plug-and-play approach with several in vitro tissues. The design consists of single-organ chips that are combined with each other to yield a multi-organ body-on-a-chip system. Fluidic flow through the organ chips is driven via gravity and controlled passively via hydraulic resistances of the microfluidic channel network. Such pumpless body-on-a-chip devices are inexpensive and easy to use. We tested the device by culturing GI tract tissue and liver tissue within the device. Integrated Ag/AgCl electrodes were used to measure the resistance across the GI tract cell layer. The transepithelial resistance (TEER) reached values between 250 to 650 Ω cm(2) throughout the 14 day co-culture period. These data indicate that the GI tract cells retained their viability and the GI tract layer as a whole retained its barrier function. Throughout the 14 day co-culture period we measured low amounts of aspartate aminotransferase (AST, ∼10-17.5 U L(-1)), indicating low rates of liver cell death. Metabolic rates of hepatocytes were comparable to those of hepatocytes in single-organ fluidic cell culture systems (albumin production ranged between 3-6 μg per day per million hepatocytes and urea production ranged between 150-200 μg per day per million hepatocytes). Induced CYP activities were higher than previously measured with microfluidic liver only systems.

Chemotaxis-driven assembly of endothelial barrier in a tumor-on-a-chip platform

The integration of three-dimensional micropatterning with microfluidics provides a unique opportunity to create perfusable tissue constructs in vitro. Herein, we have used this approach to create a tumor-on-a-chip with an endothelial barrier. Specifically, we photopatterned a mixture of endothelial cells and cancer spheroids within a gelatin methacrylate (GelMA) hydrogel inside a microfluidic device. The differential motility of endothelial and cancer cells in response to a controlled morphogen gradient across the cell-laden network drove the migration of endothelial cells to the periphery while maintaining the cancer cells within the interior of the hydrogel. The resultant endothelial cell layer forming cell-cell contact via VE-cadherin junctions was found to encompass the entire GelMA hydrogel structure. Furthermore, we have also examined the potential of such a tumor-on-a-chip system as a drug screening platform using doxorubicin, a model cancer drug.

Microfluidic co-culture platform to quantify chemotaxis of primary stem cells

Functional analysis of primary tissue-specific stem cells is hampered by their rarity. Here we describe a greatly miniaturized microfluidic device for the multiplexed, quantitative analysis of the chemotactic properties of primary, bone marrow-derived mesenchymal stem cells (MSC). The device was integrated within a fully customized platform that both increased the viability of stem cells ex vivo and simplified manipulation during multidimensional acquisition. Since primary stem cells can be isolated only in limited number, we optimized the design for efficient cell trapping from low volume and low concentration cell suspensions. Using nanoliter volumes and automated microfluidic controls for pulsed medium supply, our platform is able to create stable gradients of chemoattractant secreted from mammalian producer cells within the device, as was visualized by a secreted NeonGreen fluorescent reporter. The design was functionally validated by a CXCL/CXCR ligand/receptor combination resulting in preferential migration of primary, non-passaged MSC. Stable gradient formation prolonged assay duration and resulted in enhanced response rates for slowly migrating stem cells. Time-lapse video microscopy facilitated determining a number of migratory properties based on single cell analysis. Jackknife-resampling revealed that our assay requires only 120 cells to obtain statistically significant results, enabling new approaches in the research on rare primary stem cells. Compartmentalization of the device not only facilitated such quantitative measurements but will also permit future, high-throughput functional screens.

In vitro micro-physiological immune-competent model of the human skin

Skin allergy, in particular, allergic contact dermatitis and irritant contact dermatitis, are common occupational and environmental health problems affecting the quality of life of a significant proportion of the world population. Since all new ingredients to be incorporated into a product are potential skin allergens, it is essential that these ingredients be first tested for their allergenic potential. However, despite the considerable effort using animal models to understand the underlying mechanism of skin sensitization, to date, the molecular and cellular responses due to skin contact with sensitizers are still not fully understood. To replace animal testing and to improve the prediction of skin sensitization, significant attention has been directed to the use of reconstructed organotypic in vitro models of human skin. Here we describe a miniaturized immune competent in vitro model of human skin based on 3D co-culture of immortalized human keratinocytes (HaCaT) as a model of the epidermis barrier and human leukemic monocyte lymphoma cell line (U937) as a model of human dendritic cells. The biological model was fitted in a microfluidic-based cell culture system that provides a dynamic cellular environment that mimics the in vivo environment of skin. The dynamic perfusion of culture media significantly improved the tight junction formation as evidenced by measuring higher values of TEER compared to static culture. This setting also maintained the high viability of cells over extended periods of time up to 17 days. The perfusion-based culture also allows growth of the cells at the air-liquid interface by exposing the apical side of the cells to air while providing the cell nutrients through a basolateral fluidic compartment. The microsystem has been evaluated to investigate the effect of the chemical and physical (UV irradiation) stimulation on the skin barrier (i.e. the TJ integrity). Three-tiered culture differential stimulation allowed the investigation of the role of the keratinocyte layer as a protection barrier to chemical/biological hazards.

Directed differentiation of basal forebrain cholinergic neurons from human pluripotent stem cells

BACKGROUND

Basal forebrain cholinergic neurons (BFCNs) play critical roles in learning, memory and cognition. Dysfunction or degeneration of BFCNs may connect to neuropathology, such as Alzheimer's disease, Down's syndrome and dementia. Generation of functional BFCNs may contribute to the studies of cell-based therapy and pathogenesis that is related to learning and memory deficits.

NEW METHOD

Here we describe a detail method for robust generation of BFCNs from human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs). In this method, BFCN progenitors are patterned from hESC or hiPSC-derived primitive neuroepithelial cells, with the treatment of sonic hedgehog (SHH) or combination with its agonist Purmorphamine, and by co-culturing with human astrocytes.

RESULTS

At day 20, ∼90% hPSC-derived progenitors expressed NKX2.1, which is a transcriptional marker for MGE. Moreover, around 40% of NKX2.1+ cells co-expressed OLIG2 and ∼15% of NKX2.1+ cells co-expressed ISLET1, which are ventral markers. At day 35, ∼40% neurons robustly express ChAT, most of which are co-labeled with NKX2.1, ISLET1 and FOXG1, indicating the basal forebrain-like identity. At day 45, these neurons express mature neuronal markers MAP2, Synapsin, and VAChT.

COMPARISON WITH EXISTING METHOD(S)

In this method, undefined conditions including genetic modification or cell-sorting are avoided. As a choice, feeder free conditions are used to avoid ingredients of animal origin. Moreover, Purmorphamine can be substituted for SHH to induce ventral progenitors effectively and economically.

CONCLUSION

We provide an efficient method to generate BFCNs from multiple hPSC lines, which offers the potential application for disease modeling and pharmacological studies.

In Vitro Reconstruction of Neuronal Networks Derived from Human iPS Cells Using Microfabricated Devices

Morphology and function of the nervous system is maintained via well-coordinated processes both in central and peripheral nervous tissues, which govern the homeostasis of organs/tissues. Impairments of the nervous system induce neuronal disorders such as peripheral neuropathy or cardiac arrhythmia. Although further investigation is warranted to reveal the molecular mechanisms of progression in such diseases, appropriate model systems mimicking the patient-specific communication between neurons and organs are not established yet. In this study, we reconstructed the neuronal network in vitro either between neurons of the human induced pluripotent stem (iPS) cell derived peripheral nervous system (PNS) and central nervous system (CNS), or between PNS neurons and cardiac cells in a morphologically and functionally compartmentalized manner. Networks were constructed in photolithographically microfabricated devices with two culture compartments connected by 20 microtunnels. We confirmed that PNS and CNS neurons connected via synapses and formed a network. Additionally, calcium-imaging experiments showed that the bundles originating from the PNS neurons were functionally active and responded reproducibly to external stimuli. Next, we confirmed that CNS neurons showed an increase in calcium activity during electrical stimulation of networked bundles from PNS neurons in order to demonstrate the formation of functional cell-cell interactions. We also confirmed the formation of synapses between PNS neurons and mature cardiac cells. These results indicate that compartmentalized culture devices are promising tools for reconstructing network-wide connections between PNS neurons and various organs, and might help to understand patient-specific molecular and functional mechanisms under normal and pathological conditions.

Microfluidic co-cultures with hydrogel-based ligand trap to study paracrine signals giving rise to cancer drug resistance

Targeted cancer therapies are designed to deactivate signaling pathways used by cancer cells for survival. However, cancer cells are often able to adapt by activating alternative survival pathways, thereby acquiring drug resistance. An emerging theory is that autocrine or paracrine growth factor signaling in the cancer microenvironment represent an important mechanism of drug resistance. In the present study we wanted to examine whether paracrine interactions between groups of melanoma cells result in resistance to vemurafenib - an FDA approved drug targeting the BRAF mutation in metastatic melanoma. We used a vemurafenib-resistant melanoma model which secretes fibroblast growth factor (FGF)-2 to test our hypothesis that this is a key paracrine mediator of resistance to vemurafenib. Sensitive cells treated with media conditioned by resistant cells did not protect from the effects of vemurafenib. To query paracrine interactions further we fabricated a microfluidic co-culture device with two parallel compartments, separated by a 100 μm wide hydrogel barrier. The gel barrier prevented resorting/contact of cells while permitting paracrine cross-talk. In this microfluidic system, sensitive cells did become refractive to the effects of vemurafenib when cultured adjacent to resistant cells. Importantly, incorporation of FGF-2 capture probes into the gel barrier separating the two cell types prevented onset of resistance to vemurafenib. Microfluidic tools described here allow for more sensitive analysis of paracrine signals, may help better understand signaling in the cancer microenvironment and may enable development of more effective cancer therapies.

Liver injury-on-a-chip: microfluidic co-cultures with integrated biosensors for monitoring liver cell signaling during injury

Tissue injury triggers complex communication between cells via secreted signaling molecules such as cytokines and growth factors. Discerning when and where these signals begin and how they propagate over time is very challenging with existing cell culture and analysis tools. The goal of this study was to develop new tools in the form of microfluidic co-cultures with integrated biosensors for local and continuous monitoring of secreted signals. Specifically, we focused on how alcohol injury affects TGF-β signaling between two liver cell types, hepatocytes and stellate cells. Activation of stellate cells happens early during liver injury and is at the center of liver fibrosis. We demonstrated that alcohol injury to microfluidic co-cultures caused significantly higher levels of stellate cell activation compared to conditioned media and transwell injury experiments. This highlighted the advantage of the microfluidic co-culture: placement of two cell types in close proximity to ensure high local concentrations of injury-promoting secreted signals. Next, we developed a microsystem consisting of five chambers, two for co-culturing hepatocytes with stellate cells and three additional chambers containing miniature aptamer-modified electrodes for monitoring secreted TGF-β. Importantly, the walls separating microfluidic chambers were actuatable; they could be raised or lowered to create different configurations of the device. The use of reconfigurable microfluidics and miniature biosensors revealed that alcohol injury causes hepatocytes to secrete TGF-β molecules, which diffuse over to neighboring stellate cells and trigger production of additional TGF-β from stellate cells. Our results lend credence to the emerging view of hepatocytes as active participants of liver injury. Broadly speaking, our microsystem makes it possible to monitor paracrine crosstalk between two cell types communicating via the same signaling molecule (e.g. TGF-β).

Investigating the Influence of HUVECs in the Formation of Glioblastoma Spheroids in High-Throughput Three-Dimensional Microwells

Glioblastoma (GBM) is the most common form of primary brain tumor with a high infiltrative capacity, increased vascularity, and largely elusive tumor progression mechanism. The current GBM treatment methods do not increase the patient survival rate and studies using two-dimensional (2D) cell cultures and in vivo animal models to investigate GBM behavior and mechanism have limitations. Therefore, there is an increasing need for in vitro three-dimensional (3D) models that closely mimic in vivo microenvironment of the GBM tumors to understand the underlying mechanisms of the tumor progression. In this study we propose to use a 3D in vitro model to overcome these limitations, using poly (ethylene glycol) dimethyl acrylate (PEGDA) hydrogel-based microwells and co-culture GBM (U87) cells and endothelial cells (HUVEC) in the 3D microwells to provide a 3D in vitro simulation of the tumor microenvironment. Furthermore, we investigated the gene expression differences of co-cultures by quantitative real-time PCR. Our results suggested that the relative expression profiles of tumor angiogenesis markers, PECAM1/CD31, and VEGFR2, in co-cultures are consistent with in vivo GBM studies. Furthermore, we suggest that our microwell platform could provide robust and useful 3D co-culture models for high-throughput drug screening and treatment of the GBM.

Nanothin Coculture Membranes with Tunable Pore Architecture and Thermoresponsive Functionality for Transfer-Printable Stem Cell-Derived Cardiac Sheets

Coculturing stem cells with the desired cell type is an effective method to promote the differentiation of stem cells. The features of the membrane used for coculturing are crucial to achieving the best outcome. Not only should the membrane act as a physical barrier that prevents the mixing of the cocultured cell populations, but it should also allow effective interactions between the cells. Unfortunately, conventional membranes used for coculture do not sufficiently meet these requirements. In addition, cell harvesting using proteolytic enzymes following coculture impairs cell viability and the extracellular matrix (ECM) produced by the cultured cells. To overcome these limitations, we developed nanothin and highly porous (NTHP) membranes, which are ∼20-fold thinner and ∼25-fold more porous than the conventional coculture membranes. The tunable pore size of NTHP membranes at the nanoscale level was found crucial for the formation of direct gap junctions-mediated contacts between the cocultured cells. Differentiation of the cocultured stem cells was dramatically enhanced with the pore size-customized NTHP membrane system compared to conventional coculture methods. This was likely due to effective physical contacts between the cocultured cells and the fast diffusion of bioactive molecules across the membrane. Also, the thermoresponsive functionality of the NTHP membranes enabled the efficient generation of homogeneous, ECM-preserved, highly viable, and transfer-printable sheets of cardiomyogenically differentiated cells. The coculture platform developed in this study would be effective for producing various types of therapeutic multilayered cell sheets that can be differentiated from stem cells.

Development and validation of a microfluidic immunoassay capable of multiplexing parallel samples in microliter volumes

Immunoassays are widely utilized due to their ability to quantify a vast assortment of biomolecules relevant to biological research and clinical diagnostics. Recently, immunoassay capabilities have been improved by the development of multiplex assays that simultaneously measure multiple analytes in a single sample. However, these assays are hindered by high costs of reagents and relatively large sample requirements. For example, in vitro screening systems currently dedicate individual wells to each time point of interest and this limitation is amplified in screening studies when the investigation of many experimental conditions is necessary; resulting in large volumes for analysis, a correspondingly high cost and a limited temporal experimental design. Microfluidics based immunoassays have been developed in order to overcome these drawbacks. Together, previous studies have demonstrated on-chip assays with either a large dynamic range, high performance sensitivity, and/or the ability to process samples in parallel on a single chip. In this report, we develop a multiplex immunoassay possessing all of these parallel characteristics using commercially available reagents, which allows the analytes of interest to be easily changed. The device presented can measure 6 proteins in 32 samples simultaneously using only 4.2 μL of sample volume. High quality standard curves are generated for all 6 analytes included in the analysis, and spiked samples are quantified throughout the working range of the assay. In addition, we demonstrate a strong correlation (R(2) = 0.8999) between in vitro supernatant measurements using our device and those obtained from a bench-top multiplex immunoassay. Finally, we describe cytokine secretion in an in vitro inflammatory hippocampus culture system, establishing proof-of-concept of the ability to use this platform as an in vitro screening tool. The low-volume, multiplexing abilities of the microdevice described in this report could be broadly applied to numerous situations where sample volumes and costs are limiting.

Dual-Microstructured Porous, Anisotropic Film for Biomimicking of Endothelial Basement Membrane

Human endothelial basement membrane (BM) plays a pivotal role in vascular development and homeostasis. Here, a bioresponsive film with dual-microstructured geometries was engineered to mimic the structural roles of the endothelial BM in developing vessels, for vascular tissue engineering (TE) application. Flexible poly(ε-caprolactone) (PCL) thin film was fabricated with microscale anisotropic ridges/grooves and through-holes using a combination of uniaxial thermal stretching and direct laser perforation, respectively. Through optimizing the interhole distance, human mesenchymal stem cells (MSCs) cultured on the PCL film's ridges/grooves obtained an intact cell alignment efficiency. With prolonged culturing for 8 days, these cells formed aligned cell multilayers as found in native tunica media. By coculturing human umbilical vein endothelial cells (HUVECs) on the opposite side of the film, HUVECs were observed to build up transmural interdigitation cell-cell contact with MSCs via the through-holes, leading to a rapid endothelialization on the PCL film surface. Furthermore, vascular tissue construction based on the PCL film showed enhanced bioactivity with an elevated total nitric oxide level as compared to single MSCs or HUVECs culturing and indirect MSCs/HUVECs coculturing systems. These results suggested that the dual-microstructured porous and anisotropic film could simulate the structural roles of endothelial BM for vascular reconstruction, with aligned stromal cell multilayers, rapid endothelialization, and direct cell-cell interaction between the engineered stromal and endothelial components. This study has implications of recapitulating endothelial BM architecture for the de novo design of vascular TE scaffolds.

A four-organ-chip for interconnected long-term co-culture of human intestine, liver, skin and kidney equivalents

Systemic absorption and metabolism of drugs in the small intestine, metabolism by the liver as well as excretion by the kidney are key determinants of efficacy and safety for therapeutic candidates. However, these systemic responses of applied substances lack in most in vitro assays. In this study, a microphysiological system maintaining the functionality of four organs over 28 days in co-culture has been established at a minute but standardized microsystem scale. Preformed human intestine and skin models have been integrated into the four-organ-chip on standard cell culture inserts at a size 100,000-fold smaller than their human counterpart organs. A 3D-based spheroid, equivalent to ten liver lobules, mimics liver function. Finally, a barrier segregating the media flow through the organs from fluids excreted by the kidney has been generated by a polymeric membrane covered by a monolayer of human proximal tubule epithelial cells. A peristaltic on-chip micropump ensures pulsatile media flow interconnecting the four tissue culture compartments through microfluidic channels. A second microfluidic circuit ensures drainage of the fluid excreted through the kidney epithelial cell layer. This four-organ-chip system assures near to physiological fluid-to-tissue ratios. In-depth metabolic and gene analysis revealed the establishment of reproducible homeostasis among the co-cultures within two to four days, sustainable over at least 28 days independent of the individual human cell line or tissue donor background used for each organ equivalent. Lastly, 3D imaging two-photon microscopy visualised details of spatiotemporal segregation of the two microfluidic flows by proximal tubule epithelia. To our knowledge, this study is the first approach to establish a system for in vitro microfluidic ADME profiling and repeated dose systemic toxicity testing of drug candidates over 28 days.