Functional differentiation of human pluripotent stem cells on a chip

Deep learning for quantifying spatial patterning and formation process of early differentiated human-induced pluripotent stem cells with micropattern images

Micropatterning is reliable method for quantifying pluripotency of human-induced pluripotent stem cells (hiPSCs) that differentiate to form a spatial pattern of sorted, ordered and nonoverlapped three germ layers on the micropattern. In this study, we propose a deep learning method to quantify spatial patterning of the germ layers in the early differentiation stage of hiPSCs using micropattern images. We propose decoding and encoding U-net structures learning labelled Hoechst (DNA-stained) hiPSC regions with corresponding Hoechst and bright-field micropattern images to segment hiPSCs on Hoechst or bright-field images. We also propose a U-net structure to extract extraembryonic regions on a micropattern, and an algorithm to compares intensities of the fluorescence images staining respective germ-layer cells and extract their regions. The proposed method thus can quantify the pluripotency of a hiPSC line with spatial patterning including cell numbers, areas and distributions of germ-layer and extraembryonic cells on a micropattern, and reveal the formation process of hiPSCs and germ layers in the early differentiation stage by segmenting live-cell bright-field images. In our assay, the cell-number accuracy achieved 86% and 85%, and the cell region accuracy 89% and 81% for segmenting Hoechst and bright-field micropattern images, respectively. Applications to micropattern images of multiple hiPSC lines, micropattern sizes, groups of markers, living and fixed cells show the proposed method can be expected to be a useful protocol and tool to quantify pluripotency of a new hiPSC line before providing it to the scientific community.

Multiscale engineering of brain organoids for disease modeling

Brain organoids hold great potential for modeling human brain development and pathogenesis. They recapitulate certain aspects of the transcriptional trajectory, cellular diversity, tissue architecture and functions of the developing brain. In this review, we explore the engineering strategies to control the molecular-, cellular- and tissue-level inputs to achieve high-fidelity brain organoids. We review the application of brain organoids in neural disorder modeling and emerging bioengineering methods to improve data collection and feature extraction at multiscale. The integration of multiscale engineering strategies and analytical methods has significant potential to advance insight into neurological disorders and accelerate drug development.

On-Chip Neural Induction Boosts Neural Stem Cell Commitment: Toward a Pipeline for iPSC-Based Therapies

The clinical translation of induced pluripotent stem cells (iPSCs) holds great potential for personalized therapeutics. However, one of the main obstacles is that the current workflow to generate iPSCs is expensive, time-consuming, and requires standardization. A simplified and cost-effective microfluidic approach is presented for reprogramming fibroblasts into iPSCs and their subsequent differentiation into neural stem cells (NSCs). This method exploits microphysiological technology, providing a 100-fold reduction in reagents for reprogramming and a ninefold reduction in number of input cells. The iPSCs generated from microfluidic reprogramming of fibroblasts show upregulation of pluripotency markers and downregulation of fibroblast markers, on par with those reprogrammed in standard well-conditions. The NSCs differentiated in microfluidic chips show upregulation of neuroectodermal markers (ZIC1, PAX6, SOX1), highlighting their propensity for nervous system development. Cells obtained on conventional well plates and microfluidic chips are compared for reprogramming and neural induction by bulk RNA sequencing. Pathway enrichment analysis of NSCs from chip showed neural stem cell development enrichment and boosted commitment to neural stem cell lineage in initial phases of neural induction, attributed to a confined environment in a microfluidic chip. This method provides a cost-effective pipeline to reprogram and differentiate iPSCs for therapeutics compliant with current good manufacturing practices.

Evaluating the antioxidant potential of resveratrol-gold nanoparticles in preventing oxidative stress in endothelium on a chip

Vascular endothelial cells play a vital role in the health and maintenance of vascular homeostasis, but hyperglycemia disrupts their function by increasing cellular oxidative stress. Resveratrol, a plant polyphenol, possesses antioxidant properties that can mitigate oxidative stress. Addressing the challenges of its limited solubility and stability, gold nanoparticles (GNps) were utilized as carriers. A microfluidic chip (MFC) with dynamic flow conditions was designed to simulate body vessels and to investigate the antioxidant properties of resveratrol gold nanoparticles (RGNps), citrate gold nanoparticles (CGNps), and free Resveratrol on human umbilical vein endothelial cells (HUVEC). The 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay was employed to measure the extracellular antioxidant potential, and cell viability was determined using the Alamar Blue test. For assessing intracellular oxidative stress, the 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) assay was conducted, and results from both the cell culture plate and MFC were compared. Free Resveratrol demonstrated peak DPPH scavenging activity but had a cell viability of about 24-35%. RGNPs, both 3.0 ± 0.5 nm and 20.2 ± 4.7 nm, consistently showed high cell viability (more than about 90%) across tested concentrations. Notably, RGNPs (20 nm) exhibited antioxidative properties through DPPH scavenging activity (%) in the range of approximately 38-86% which was greater than that of CGNps at about 21-32%. In the MFC,the DCFH-DA analysis indicated that RGNPs (20 nm) reduced cellular oxidative stress by 57-82%, surpassing both CGNps and free Resveratrol. Morphologically, cells in the MFC presented superior structure compared to those in traditional cell culture plates, and the induction of hyperglycemia successfully led to the formation of multinucleated variant endothelial cells (MVECs). The MFC provides a distinct advantage in observing cell morphology and inducing endothelial cell dysfunction. RGNps have demonstrated significant potential in alleviating oxidative stress and preventing endothelial cell disorders.

Guiding Hepatic Differentiation of Pluripotent Stem Cells Using 3D Microfluidic Co-Cultures with Human Hepatocytes

Human pluripotent stem cells (hPSCs) are capable of unlimited proliferation and can undergo differentiation to give rise to cells and tissues of the three primary germ layers. While directing lineage selection of hPSCs has been an active area of research, improving the efficiency of differentiation remains an important objective. In this study, we describe a two-compartment microfluidic device for co-cultivation of adult human hepatocytes and stem cells. Both cell types were cultured in a 3D or spheroid format. Adult hepatocytes remained highly functional in the microfluidic device over the course of 4 weeks and served as a source of instructive paracrine cues to drive hepatic differentiation of stem cells cultured in the neighboring compartment. The differentiation of stem cells was more pronounced in microfluidic co-cultures compared to a standard hepatic differentiation protocol. In addition to improving stem cell differentiation outcomes, the microfluidic co-culture system described here may be used for parsing signals and mechanisms controlling hepatic cell fate.

Microfluidic organoids-on-a-chip: The future of human models

Microfluidics opened the possibility to model the physiological environment by controlling fluids flows, and therefore nutrients supply. It allows to integrate external stimuli such as electricals or mechanicals and in situ monitoring important parameters such as pH, oxygen and metabolite concentrations. Organoids are self-organized 3D organ-like clusters, which allow to closely model original organ functionalities. Applying microfluidics to organoids allows to generate powerful human models for studying organ development, diseases, and drug testing. In this review, after a brief introduction on microfluidics, organoids and organoids-on-a-chip are described by organs (brain, heart, gastrointestinal tract, liver, pancreas) highlighting the microfluidic approaches since this point of view was overlooked in previously published reviews. Indeed, the review aims to discuss from a different point of view, primary microfluidics, the available literature on organoids-on-a-chip, standing out from the published literature by focusing on each specific organ.

The 3Rs in Experimental Liver Disease

Patients with cirrhosis present multiple physiological and immunological alterations that play a very important role in the development of clinically relevant secondary complications to the disease. Experimentation in animal models is essential to understand the pathogenesis of human diseases and, considering the high prevalence of liver disease worldwide, to understand the pathophysiology of disease progression and the molecular pathways involved, due to the complexity of the liver as an organ and its relationship with the rest of the organism. However, today there is a growing awareness about the sensitivity and suffering of animals, causing opposition to animal research among a minority in society and some scientists, but also about the attention to the welfare of laboratory animals since this has been built into regulations in most nations that conduct animal research. In 1959, Russell and Burch published the book "The Principles of Humane Experimental Technique", proposing that in those experiments where animals were necessary, everything possible should be done to try to replace them with non-sentient alternatives, to reduce to a minimum their number, and to refine experiments that are essential so that they caused the least amount of pain and distress. In this review, a comprehensive summary of the most widely used techniques to replace, reduce, and refine in experimental liver research is offered, to assess the advantages and weaknesses of available experimental liver disease models for researchers who are planning to perform animal studies in the near future.

A quantitative meta-analysis comparing cell models in perfused organ on a chip with static cell cultures

As many consider organ on a chip for better in vitro models, it is timely to extract quantitative data from the literature to compare responses of cells under flow in chips to corresponding static incubations. Of 2828 screened articles, 464 articles described flow for cell culture and 146 contained correct controls and quantified data. Analysis of 1718 ratios between biomarkers measured in cells under flow and static cultures showed that the in all cell types, many biomarkers were unregulated by flow and only some specific biomarkers responded strongly to flow. Biomarkers in cells from the blood vessels walls, the intestine, tumours, pancreatic island, and the liver reacted most strongly to flow. Only 26 biomarkers were analysed in at least two different articles for a given cell type. Of these, the CYP3A4 activity in CaCo2 cells and PXR mRNA levels in hepatocytes were induced more than two-fold by flow. Furthermore, the reproducibility between articles was low as 52 of 95 articles did not show the same response to flow for a given biomarker. Flow showed overall very little improvements in 2D cultures but a slight improvement in 3D cultures suggesting that high density cell culture may benefit from flow. In conclusion, the gains of perfusion are relatively modest, larger gains are linked to specific biomarkers in certain cell types.

Organs-on-chips technologies – A guide from disease models to opportunities for drug development

Current in-vitro 2D cultures and animal models present severe limitations in recapitulating human physiopathology with striking discrepancies in estimating drug efficacy and side effects when compared to human trials. For these reasons, microphysiological systems, organ-on-chip and multiorgans microdevices attracted considerable attention as novel tools for high-throughput and high-content research to achieve an improved understanding of diseases and to accelerate the drug development process towards more precise and eventually personalized standards. This review takes the form of a guide on this fast-growing field, providing useful introduction to major themes and indications for further readings. We start analyzing Organs-on-chips (OOC) technologies for testing the major drug administration routes: (1) oral/rectal route by intestine-on-a-chip, (2) inhalation by lung-on-a-chip, (3) transdermal by skin-on-a-chip and (4) intravenous through vascularization models, considering how drugs penetrate in the bloodstream and are conveyed to their targets. Then, we focus on OOC models for (other) specific organs and diseases: (1) neurodegenerative diseases with brain models and blood brain barriers, (2) tumor models including their vascularization, organoids/spheroids, engineering and screening of antitumor drugs, (3) liver/kidney on chips and multiorgan models for gastrointestinal diseases and metabolic assessment of drugs and (4) biomechanical systems recapitulating heart, muscles and bones structures and related diseases. Successively, we discuss technologies and materials for organ on chips, analyzing (1) microfluidic tools for organs-on-chips, (2) sensor integration for real-time monitoring, (3) materials and (4) cell lines for organs on chips. (Nano)delivery approaches for therapeutics and their on chip assessment are also described. Finally, we conclude with a critical discussion on current significance/relevance, trends, limitations, challenges and future prospects in terms of revolutionary impact on biomedical research, preclinical models and drug development.

A Microfluidic Device for Long-Term Maintenance of Organotypic Liver Cultures

Liver cultures may be used for disease modeling, testing therapies and predicting drug-induced injury. The complexity of the liver cultures has evolved from hepatocyte monocultures to co-cultures with non-parenchymal cells and finally to precision-cut liver slices. The latter culture format retains liver's native biomolecular and cellular complexity and therefore holds considerable promise for in vitro testing. However, liver slices remain functional for ~72 h in vitro and display limited utility for some disease modeling and therapy testing applications that require longer culture times. This paper describes a microfluidic device for longer-term maintenance of functional organotypic liver cultures. Our microfluidic culture system was designed to enable direct injection of liver tissue into a culture chamber through a valve-enabled side port. Liver tissue was embedded in collagen and remained functional for up to 31 days, highlighted by continued production of albumin and urea. These organotypic cultures also expressed several enzymes involved in xenobiotic metabolism. Conversely, matched liver tissue embedded in collagen in a 96-well plate lost its phenotype and function within 3-5 days. The microfluidic organotypic liver cultures described here represent a significant advance in liver cultivation and may be used for future modeling of liver diseases or for individualized liver-directed therapies.

Microfluidic Manipulation for Biomedical Applications in the Central and Peripheral Nervous Systems

Physical injuries and neurodegenerative diseases often lead to irreversible damage to the organizational structure of the central nervous system (CNS) and peripheral nervous system (PNS), culminating in physiological malfunctions. Investigating these complex and diverse biological processes at the macro and micro levels will help to identify the cellular and molecular mechanisms associated with nerve degeneration and regeneration, thereby providing new options for the development of new therapeutic strategies for the functional recovery of the nervous system. Due to their distinct advantages, modern microfluidic platforms have significant potential for high-throughput cell and organoid cultures in vitro, the synthesis of a variety of tissue engineering scaffolds and drug carriers, and observing the delivery of drugs at the desired speed to the desired location in real time. In this review, we first introduce the types of nerve damage and the repair mechanisms of the CNS and PNS; then, we summarize the development of microfluidic platforms and their application in drug carriers. We also describe a variety of damage models, tissue engineering scaffolds, and drug carriers for nerve injury repair based on the application of microfluidic platforms. Finally, we discuss remaining challenges and future perspectives with regard to the promotion of nerve injury repair based on engineered microfluidic platform technology.

3D ECM-rich environment sustains the identity of naive human iPSCs

The establishment of in vitro naive human pluripotent stem cell cultures opened new perspectives for the study of early events in human development. The role of several transcription factors and signaling pathways have been characterized during maintenance of human naive pluripotency. However, little is known about the role exerted by the extracellular matrix (ECM) and its three-dimensional (3D) organization. Here, using an unbiased and integrated approach combining microfluidic cultures with transcriptional, proteomic, and secretome analyses, we found that naive, but not primed, hiPSC colonies are characterized by a self-organized ECM-rich microenvironment. Based on this, we developed a 3D culture system that supports robust long-term feeder-free self-renewal of naive hiPSCs and also allows direct and timely developmental morphogenesis simply by modulating the signaling environment. Our study opens new perspectives for future applications of naive hiPSCs to study critical stages of human development in 3D starting from a single cell.

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.

Microfluidics for Neuronal Cell and Circuit Engineering

The widespread adoption of microfluidic devices among the neuroscience and neurobiology communities has enabled addressing a broad range of questions at the molecular, cellular, circuit, and system levels. Here, we review biomedical engineering approaches that harness the power of microfluidics for bottom-up generation of neuronal cell types and for the assembly and analysis of neural circuits. Microfluidics-based approaches are instrumental to generate the knowledge necessary for the derivation of diverse neuronal cell types from human pluripotent stem cells, as they enable the isolation and subsequent examination of individual neurons of interest. Moreover, microfluidic devices allow to engineer neural circuits with specific orientations and directionality by providing control over neuronal cell polarity and permitting the isolation of axons in individual microchannels. Similarly, the use of microfluidic chips enables the construction not only of 2D but also of 3D brain, retinal, and peripheral nervous system model circuits. Such brain-on-a-chip and organoid-on-a-chip technologies are promising platforms for studying these organs as they closely recapitulate some aspects of in vivo biological processes. Microfluidic 3D neuronal models, together with 2D in vitro systems, are widely used in many applications ranging from drug development and toxicology studies to neurological disease modeling and personalized medicine. Altogether, microfluidics provide researchers with powerful systems that complement and partially replace animal models.

Physiologically relevant microsystems to study viral infection in the human liver

Viral hepatitis is a leading cause of liver disease and mortality. Infection can occur acutely or chronically, but the mechanisms that govern the clearance of virus or lack thereof are poorly understood and merit further investigation. Though cures for viral hepatitis have been developed, they are expensive, not readily accessible in vulnerable populations and some patients may remain at an increased risk of developing hepatocellular carcinoma (HCC) even after viral clearance. To sustain infection in vitro, hepatocytes must be fully mature and remain in a differentiated state. However, primary hepatocytes rapidly dedifferentiate in conventional 2D in vitro platforms. Physiologically relevant or physiomimetic microsystems, are increasingly popular alternatives to traditional two-dimensional (2D) monocultures for in vitro studies. Physiomimetic systems reconstruct and incorporate elements of the native cellular microenvironment to improve biologic functionality in vitro. Multiple elements contribute to these models including ancillary tissue architecture, cell co-cultures, matrix proteins, chemical gradients and mechanical forces that contribute to increased viability, longevity and physiologic function for the tissue of interest. These microsystems are used in a wide variety of applications to study biological phenomena. Here, we explore the use of physiomimetic microsystems as tools for studying viral hepatitis infection in the liver and how the design of these platforms is tailored for enhanced investigation of the viral lifecycle when compared to conventional 2D cell culture models. Although liver-based physiomimetic microsystems are typically applied in the context of drug studies, the platforms developed for drug discovery purposes offer a solid foundation to support studies on viral hepatitis. Physiomimetic platforms may help prolong hepatocyte functionality in order to sustain chronic viral hepatitis infection in vitro for studying virus-host interactions for prolonged periods.

Liver-on-a-chip devices: the pros and cons of complexity

Physiologically relevant and broadly applicable liver cell culture platforms are of great importance in both drug development and disease modeling. Organ-on-a-chip systems offer a promising alternative to conventional, static two-dimensional (2-D) cultures, providing much-needed cues such as perfusion, shear stress, and three-dimensional (3-D) cell-cell communication. However, such devices cover a broad range of complexity both in manufacture and in implementation. In this review, we summarize the key features of the human liver that should be reflected in a physiologically relevant liver-on-a-chip model. We also discuss different material properties of importance in producing liver-on-a-chip devices and summarize recent and current progress in the field, highlighting different types of devices at different levels of complexity.

Timely delivery of cardiac mmRNAs in microfluidics enhances cardiogenic programming of human pluripotent stem cells

In the last two decades lab-on-chip models, specifically heart-on-chip, have been developed as promising technologies for recapitulating physiological environments suitable for studies of drug and environmental effects on either human physiological or patho-physiological conditions. Most human heart-on-chip systems are based on integration and adaptation of terminally differentiated cells within microfluidic context. This process requires prolonged procedures, multiple steps, and is associated with an intrinsic variability of cardiac differentiation. In this view, we developed a method for cardiac differentiation-on-a-chip based on combining the stage-specific regulation of Wnt/β-catenin signaling with the forced expression of transcription factors (TFs) that timely recapitulate hallmarks of the cardiac development. We performed the overall cardiac differentiation from human pluripotent stem cells (hPSCs) to cardiomyocytes (CMs) within a microfluidic environment. Sequential forced expression of cardiac TFs was achieved by a sequential mmRNAs delivery of first MESP1, GATA4 followed by GATA4, NKX2.5, MEF2C, TBX3, and TBX5. We showed that this optimized protocol led to a robust and reproducible approach to obtain a cost-effective hiPSC-derived heart-on-chip. The results showed higher distribution of cTNT positive CMs along the channel and a higher expression of functional cardiac markers (TNNT2 and MYH7). The combination of stage-specific regulation of Wnt/β-catenin signaling with mmRNAs encoding cardiac transcription factors will be suitable to obtain heart-on-chip model in a cost-effective manner, enabling to perform combinatorial, multiparametric, parallelized and high-throughput experiments on functional cardiomyocytes.

Human Pluripotent Stem Cell-Derived Micropatterned Ectoderm Allows Cell Sorting of Meso-Endoderm Lineages

The human developmental processes during the early post-implantation stage instruct the specification and organization of the lineage progenitors into a body plan. These processes, which include patterning, cell sorting, and establishment of the three germ layers, have been classically studied in non-human model organisms and only recently, through micropatterning technology, in a human-specific context. Micropatterning technology has unveiled mechanisms during patterning and germ layer specification; however, cell sorting and their segregation in specific germ layer combinations have not been investigated yet in a human-specific in vitro system. Here, we developed an in vitro model of human ectodermal patterning, in which human pluripotent stem cells (hPSCs) self-organize to form a radially regionalized neural and non-central nervous system (CNS) ectoderm. We showed that by using micropatterning technology and by modulating BMP and WNT signals, we can regulate the appearance and spatial distribution of the different ectodermal populations. This pre-patterned ectoderm can be used to investigate the cell sorting behavior of hPSC-derived meso-endoderm cells, with an endoderm that segregates from the neural ectoderm. Thus, the combination of micro-technology with germ layer cross-mixing enables the study of cell sorting of different germ layers in a human context.

Extracellular phosphoprotein regulation is affected by culture system scale-down

BACKGROUND

Phosphorylated proteins are known to be present in multiple body fluids in normal conditions, and abnormally accumulated under some pathological conditions. The biological significance of their role in the extracellular space has started being elucidated only recently, for example in bone mineralization, neural development, and coagulation. Here, we address some criticalities of conventional culture systems for the study of the extracellular regulation of phosphorylation.

METHODS

We make use of microfluidics to scale-down the culture volume to a size comparable to the interstitial spaces occurring in vivo. The phosphoprotein content of conditioned media was analyzed by a colorimetric assay that detects global phosphorylation.

RESULTS

We found that miniaturization of the culture system increases phosphoprotein accumulation. Moreover, we demonstrated that in conventional culture systems dilution affects the extent of the phosphorylation reactions occurring within the extracellular space. On the other hand, in microfluidics the phosphorylation status was not affected by addition of adenosine triphosphate (ATP) and FAM20C Golgi Associated Secretory Pathway Kinase (FAM20C) ectokinase, as if their concentration was already not limiting for the phosphorylation reaction to occur.

CONCLUSIONS

The volume of the extracellular environment plays a role in the process of extracellular phosphorylation due to its effect on the concentration of substrates, enzymes and co-factors.

GENERAL SIGNIFICANCE

Thus, the biological role of extracellular phosphoregulation may be better appreciated within a microfluidic culture system.

Derivation and Differentiation of Human Pluripotent Stem Cells in Microfluidic Devices

An integrative approach based on microfluidic design and stem cell biology enables capture of the spatial-temporal environmental evolution underpinning epigenetic remodeling and the morphogenetic process. We examine the body of literature that encompasses microfluidic applications where human induced pluripotent stem cells are derived starting from human somatic cells and where human pluripotent stem cells are differentiated into different cell types. We focus on recent studies where the intrinsic features of microfluidics have been exploited to control the reprogramming and differentiation trajectory at the microscale, including the capability of manipulating the fluid velocity field, mass transport regime, and controllable composition within micro- to nanoliter volumes in space and time. We also discuss studies of emerging microfluidic technologies and applications. Finally, we critically discuss perspectives and challenges in the field and how these could be instrumental for bringing about significant biological advances in the field of stem cell engineering. Expected final online publication date for the Annual Review of Biomedical Engineering, Volume 24 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The emergence of the circadian clock network in hiPSC-derived hepatocytes on chip

The circadian clock has paramount implications in physiology and pathology. Although the circadian clock has been widely investigated in adults, up to now very little is known about how circadian rhythms emerge during embryonic development. Some studies about the ontology of the circadian system are focused on the development of the central pacemaker, whereas there is still no agreement about the development of the circadian clock in peripheral tissues. Our work represents the first attempt at investigating the onset of peripheral circadian clocks in the liver, which has a central role in controlling several aspects of human physiology. We profile the emergence of the circadian genes during the transition from the initial state of human pluripotency to the final state of hepatic maturation. We demonstrate that circadian rhythmicity is absent in human pluripotent stem cells, and it arises gradually during the process of hepatic commitment. The clock genes expression reaches a peak at the hepatic progenitor stage. At this point o hiPSC-derived f differentiation the gene oscillations start to be observed with a period of 13 h and approaches 24 h in a later stage when the clock primary feedback loop starts working properly. At the end of differentiation, circadian rhythmicity appears, with genes of primary and secondary feedback loops in antiphase (CLOCK, BMAL1 and REV-ERBα) a sign that the system becomes to be functional.

Detection of Pathological Markers of Neurodegenerative Diseases following Microfluidic Direct Conversion of Patient Fibroblasts into Neurons

Neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease are clinically diagnosed using neuropsychological and cognitive tests, expensive neuroimaging-based approaches (MRI and PET) and invasive and time-consuming lumbar puncture for cerebrospinal fluid (CSF) sample collection to detect biomarkers. Thus, a rapid, simple and cost-effective approach to more easily access fluids and tissues is in great need. Here, we exploit the chemical direct reprogramming of patient skin fibroblasts into neurons (chemically induced neurons, ciNs) as a novel strategy for the rapid detection of different pathological markers of neurodegenerative diseases. We found that FAD fibroblasts have a reduced efficiency of reprogramming, and converted ciNs show a less complex neuronal network. In addition, ciNs from patients show misfolded protein accumulation and mitochondria ultrastructural abnormalities, biomarkers commonly associated with neurodegeneration. Moreover, for the first time, we show that microfluidic technology, in combination with chemical reprogramming, enables on-chip examination of disease pathological processes and may have important applications in diagnosis. In conclusion, ciNs on microfluidic devices represent a small-scale, non-invasive and cost-effective high-throughput tool for protein misfolding disease diagnosis and may be useful for new biomarker discovery, disease mechanism studies and design of personalised therapies.

Current Status and Challenges of Human Induced Pluripotent Stem Cell-Derived Liver Models in Drug Discovery

The pharmaceutical industry is in high need of efficient and relevant in vitro liver models, which can be incorporated in their drug discovery pipelines to identify potential drugs and their toxicity profiles. Current liver models often rely on cancer cell lines or primary cells, which both have major limitations. However, the development of human induced pluripotent stem cells (hiPSCs) has created a new opportunity for liver disease modeling, drug discovery and liver toxicity research. hiPSCs can be differentiated to any cell of interest, which makes them good candidates for disease modeling and drug discovery. Moreover, hiPSCs, unlike primary cells, can be easily genome-edited, allowing the creation of reporter lines or isogenic controls for patient-derived hiPSCs. Unfortunately, even though liver progeny from hiPSCs has characteristics similar to their in vivo counterparts, the differentiation of iPSCs to fully mature progeny remains highly challenging and is a major obstacle for the full exploitation of these models by pharmaceutical industries. In this review, we discuss current liver-cell differentiation protocols and in vitro iPSC-based liver models that could be used for disease modeling and drug discovery. Furthermore, we will discuss the challenges that still need to be overcome to allow for the successful implementation of these models into pharmaceutical drug discovery platforms.

Advances in microfluidic 3D cell culture for preclinical drug development

Drug development is often a very long, costly, and risky process due to the lack of reliability in the preclinical studies. Traditional current preclinical models, mostly based on 2D cell culture and animal testing, are not full representatives of the complex in vivo microenvironments and often fail. In order to reduce the enormous costs, both financial and general well-being, a more predictive preclinical model is needed. In this chapter, we review recent advances in microfluidic 3D cell culture showing how its development has allowed the introduction of in vitro microphysiological systems, laying the foundation for organ-on-a-chip technology. These findings provide the basis for numerous preclinical drug discovery assays, which raise the possibility of using micro-engineered systems as emerging alternatives to traditional models, based on 2D cell culture and animals.

Hepatocyte cultures: From collagen gel sandwiches to microfluidic devices with integrated biosensors

Hepatocytes are parenchymal cells of the liver responsible for drug detoxification, urea and bile production, serum protein synthesis, and glucose homeostasis. Hepatocytes are widely used for drug toxicity studies in bioartificial liver devices and for cell-based liver therapies. Because hepatocytes are highly differentiated cells residing in a complex microenvironment in vivo, they tend to lose hepatic phenotype and function in vitro. This paper first reviews traditional culture approaches used to rescue hepatic function in vitro and then discusses the benefits of emerging microfluidic-based culture approaches. We conclude by reviewing integration of hepatocyte cultures with bioanalytical or sensing approaches.

Quantifying the progression of non-alcoholic fatty liver disease in human biomimetic liver microphysiology systems with fluorescent protein biosensors

Metabolic syndrome is a complex disease that involves multiple organ systems including a critical role for the liver. Non-alcoholic fatty liver disease (NAFLD) is a key component of the metabolic syndrome and fatty liver is linked to a range of metabolic dysfunctions that occur in approximately 25% of the population. A panel of experts recently agreed that the acronym, NAFLD, did not properly characterize this heterogeneous disease given the associated metabolic abnormalities such as type 2 diabetes mellitus (T2D), obesity, and hypertension. Therefore, metabolic dysfunction-associated fatty liver disease (MAFLD) has been proposed as the new term to cover the heterogeneity identified in the NAFLD patient population. Although many rodent models of NAFLD/NASH have been developed, they do not recapitulate the full disease spectrum in patients. Therefore, a platform has evolved initially focused on human biomimetic liver microphysiology systems that integrates fluorescent protein biosensors along with other key metrics, the microphysiology systems database, and quantitative systems pharmacology. Quantitative systems pharmacology is being applied to investigate the mechanisms of NAFLD/MAFLD progression to select molecular targets for fluorescent protein biosensors, to integrate computational and experimental methods to predict drugs for repurposing, and to facilitate novel drug development. Fluorescent protein biosensors are critical components of the platform since they enable monitoring of the pathophysiology of disease progression by defining and quantifying the temporal and spatial dynamics of protein functions in the biosensor cells, and serve as minimally invasive biomarkers of the physiological state of the microphysiology system experimental disease models. Here, we summarize the progress in developing human microphysiology system disease models of NAFLD/MAFLD from several laboratories, developing fluorescent protein biosensors to monitor and to measure NAFLD/MAFLD disease progression and implementation of quantitative systems pharmacology with the goal of repurposing drugs and guiding the creation of novel therapeutics.

Bioengineering platforms for cell therapeutics derived from pluripotent and direct reprogramming

Pluripotent and direct reprogramming technologies hold great potential for tissue repair and restoration of tissue and organ function. The implementation of induced pluripotent stem cells and directly reprogrammed cells in biomedical research has resulted in a significant leap forward in the highly promising area of regenerative medicine. While these therapeutic strategies are promising, there are several obstacles to overcome prior to the introduction of these therapies into clinical settings. Bioengineering technologies, such as biomaterials, bioprinting, microfluidic devices, and biostimulatory systems, can enhance cell viability, differentiation, and function, in turn the efficacy of cell therapeutics generated via pluripotent and direct reprogramming. Therefore, cellular reprogramming technologies, in combination with tissue-engineering platforms, are poised to overcome current bottlenecks associated with cell-based therapies and create new ways of producing engineered tissue substitutes.

The method to generate pulsatile circulatory fluid flow using microfluidics

Microfluidic chips provide versatile tools to mimic the biological effect of blood flow on pluripotent stem cells (PSC). This paper presents methods for the use of microfluidics to model embryonic circulation using differentiated PSC. Pulsatile circulatory flow is created with a microfluidics device with pressure-driven microvalves and ventricles. Silicone rubber devices are cast from moulds manufactured using standard and 3D laser lithography. The surface chemistry is modified to support the growth of human umbilical vein endothelial cells and pluripotent stem cells. Pulsatile circulatory fluid flow can be applied at specific stages of cell differentiation with direct observation of cellular responses by time-lapse fluorescent microscopy.•

Replicable manufacturing protocol of lab scale microfluidic device generating pulsatile fluid flow mimicry embryonic blood circulation.

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Integration of human cell lines on microfluidic chip.

Investigation of the hepatic development in the coculture of hiPSCs-derived LSECs and HLCs in a fluidic microenvironment

Interactions between the different liver cell types are critical to the maintenance or induction of their function in vitro. In this work, human-induced Pluripotent Stem Cells (hiPSCs)-derived Liver Sinusoidal Endothelial Cells (LSECs) and Hepatocytes-Like Cells (HLCs) were cultured and matured in a microfluidic environment. Both cell populations were differentiated in Petri dishes, detached, and inoculated in microfluidic biochips. In cocultures of both cell types, the tissue has exhibited a higher production of albumin (3.19 vs 5.31 μg/mL/106 cells in monocultures and cocultures) as well as a higher inducibility CYP450 over monocultures of HLCs. Tubular-like structures composed of LSECs and positive for the endothelial marker PECAM1, as well as a tissue more largely expressing Stabilin-2 were detected in cocultures only. In contrast, monocultures exhibited no network and less specific endothelial markers. The transcriptomic analysis did not reveal a marked difference between the profiles of both culture conditions. Nevertheless, the analysis allowed us to highlight different upstream regulators in cocultures (SP1, EBF1, and GATA3) and monocultures (PML, MECP2, and NRF1). In cocultures, the multi-omics dataset after 14 days of maturation in biochips has shown the activation of signaling related to hepatic maturation, angiogenesis, and tissue repair. In this condition, inflammatory signaling was also found to be reduced when compared to monocultures as illustrated by the activation of NFKB and by the detection of several cytokines involved in tissue injury in the latter. Finally, the extracted biological processes were discussed regarding the future development of a new generation of human in vitro hepatic models.

Highly parallelized human embryonic stem cell differentiation to cardiac mesoderm in nanoliter chambers on a microfluidic chip

Human stem cell-derived cells and tissues hold considerable potential for applications in regenerative medicine, disease modeling and drug discovery. The generation, culture and differentiation of stem cells in low-volume, automated and parallelized microfluidic chips hold great promise to accelerate the research in this domain. Here, we show that we can differentiate human embryonic stem cells (hESCs) to early cardiac mesodermal cells in microfluidic chambers that have a volume of only 30 nanoliters, using discontinuous medium perfusion. 64 of these chambers were parallelized on a chip which contained integrated valves to spatiotemporally isolate the chambers and automate cell culture medium exchanges. To confirm cell pluripotency, we tracked hESC proliferation and immunostained the cells for pluripotency markers SOX2 and OCT3/4. During differentiation, we investigated the effect of different medium perfusion frequencies on cell reorganization and the expression of the early cardiac mesoderm reporter MESP1mCherry by live-cell imaging. Our study demonstrates that microfluidic technology can be used to automatically culture, differentiate and study hESC in very low-volume culture chambers even without continuous medium perfusion. This result is an important step towards further automation and parallelization in stem cell technology.

MYOD modified mRNA drives direct on-chip programming of human pluripotent stem cells into skeletal myocytes

Drug screening and disease modelling for skeletal muscle related pathologies would strongly benefit from the integration of myogenic cells derived from human pluripotent stem cells within miniaturized cell culture devices, such as microfluidic platform. Here, we identified the optimal culture conditions that allow direct differentiation of human pluripotent stem cells in myogenic cells within microfluidic devices. Myogenic cells are efficiently derived from both human embryonic (hESC) or induced pluripotent stem cells (hiPSC) in eleven days by combining small molecules and non-integrating modified mRNA (mmRNA) encoding for the master myogenic transcription factor MYOD. Our work opens new perspective for the development of patient-specific platforms in which a one-step myogenic differentiation could be used to generate skeletal muscle on-a-chip.

A microfabricated multi-compartment device for neuron and Schwann cell differentiation

Understanding the complex communication between different cell populations and their interaction with the microenvironment in the central and peripheral nervous systems is fundamental in neuroscience research. The development of appropriate in vitro approaches and tools, able to selectively analyze and/or probe specific cells and cell portions (e.g., axons and cell bodies in neurons), driving their differentiation into specific cell phenotypes, has become therefore crucial in this direction. Here we report a multi-compartment microfluidic device where up to three different cell populations can be cultured in a fluidically independent circuit. The device allows cell migration across the compartments and their differentiation. We showed that an accurate choice of the device geometrical features and cell culture parameters allows to (1) maximize cell adhesion and proliferation of neuron-like human cells (SH-SY5Y cells), (2) control the inter-compartment cell migration of neuron and Schwann cells, (3) perform long-term cell culture studies in which both SH-SY5Y cells and primary rat Schwann cells can be differentiated towards specific phenotypes. These results can lead to a plethora of in vitro co-culture studies in the neuroscience research field, where tuning and investigating cell-cell and cell-microenvironment interactions are essential.

Induced Pluripotent Stem Cells on a Chip: A Self-Contained, Accessible, Pipette-less iPSC Culturing and Differentiation Kit

Over the past decade, induced pluripotent stem cells (iPSCs) have become a major focus of stem cell and developmental biology research, offering researchers a clinically relevant source of cells that are amenable to genetic engineering approaches. Though stem cells are promising for both research and commercial endeavors, iPSC-based assays require tedious protocols that include complex treatments, expensive reagents, and specialized equipment that limit their integration into academic curricula and cell biology research groups. Expanding on existing Kit-On-A-Lid-Assay (KOALA) technologies, we have developed a self-contained, injection molded, pipette-less iPSC culture and differentiation platform that significantly reduces associated costs and labor of stem cell maintenance and differentiation. The KOALA kit offers users the full range of iPSC culture necessities, including cell cryopreservation, media exchanges, differentiation, endpoint analysis, and a new capability, cell passaging. Using the KOALA kit, we were able to culture ~20,000 iPSCs per microchannel for at least 7 days, while maintaining stable expression of stemness markers (SSEA4 and Oct4) and normal iPSC phenotype. We also adapted protocols for differentiating iPSCs into neuroepithelial cells, cardiomyocytes, and definitive endodermal cells, a cell type from each germ layer of human development.

Multi-omics analysis of hiPSCs-derived HLCs matured on-chip revealed patterns typical of liver regeneration

Maturation of human-induced pluripotent stem cells (hiPSCs)-derived hepatocytes-like cells (HLCs) toward a complete hepatocyte phenotype remains a challenge as primitiveness patterns are still commonly observed. In this study, we propose a modified differentiation protocol for those cells which includes a prematuration in Petri dishes and a maturation in microfluidic biochip. For the first time, a large range of biomolecular families has been extracted from the same sample to combine transcriptomic, proteomic, and metabolomic analysis. After integration, these datasets revealed specific molecular patterns and highlighted the hepatic regeneration profile in biochips. Overall, biochips exhibited processes of cell proliferation and inflammation (via TGFB1) coupled with anti-fibrotic signaling (via angiotensin 1-7, ATR-2, and MASR). Moreover, cultures in this condition displayed physiological lipid-carbohydrate homeostasis (notably via PPAR, cholesterol metabolism, and bile synthesis) coupled with cell respiration through advanced oxidative phosphorylation (through the overexpression of proteins from the third and fourth complex). The results presented provide an original overview of the complex mechanisms involved in liver regeneration using an advanced in vitro organ-on-chip technology.

Engineered Microsystems for Spheroid and Organoid Studies

3D in vitro model systems such as spheroids and organoids provide an opportunity to extend the physiological understanding using recapitulated tissues that mimic physiological characteristics of in vivo microenvironments. Unlike 2D systems, 3D in vitro systems can bridge the gap between inadequate 2D cultures and the in vivo environments, providing novel insights on complex physiological mechanisms at various scales of organization, ranging from the cellular, tissue-, to organ-levels. To satisfy the ever-increasing need for highly complex and sophisticated systems, many 3D in vitro models with advanced microengineering techniques have been developed to answer diverse physiological questions. This review summarizes recent advances in engineered microsystems for the development of 3D in vitro model systems. The relationship between the underlying physics behind the microengineering techniques, and their ability to recapitulate distinct 3D cellular structures and functions of diverse types of tissues and organs are highlighted and discussed in detail. A number of 3D in vitro models and their engineering principles are also introduced. Finally, current limitations are summarized, and perspectives for future directions in guiding the development of 3D in vitro model systems using microengineering techniques are provided.

The Microfluidic Environment Reveals a Hidden Role of Self-Organizing Extracellular Matrix in Hepatic Commitment and Organoid Formation of hiPSCs

The specification of the hepatic identity during human liver development is strictly controlled by extrinsic signals, yet it is still not clear how cells respond to these exogenous signals by activating secretory cascades, which are extremely relevant, especially in 3D self-organizing systems. Here, we investigate how the proteins secreted by human pluripotent stem cells (hPSCs) in response to developmental exogenous signals affect the progression from endoderm to the hepatic lineage, including their competence to generate nascent hepatic organoids. By using microfluidic confined environment and stable isotope labeling with amino acids in cell culture-coupled mass spectrometry (SILAC-MS) quantitative proteomic analysis, we find high abundancy of extracellular matrix (ECM)-associated proteins. Hepatic progenitor cells either derived in microfluidics or exposed to exogenous ECM stimuli show a significantly higher potential of forming hepatic organoids that can be rapidly expanded for several passages and further differentiated into functional hepatocytes. These results prove an additional control over the efficiency of hepatic organoid formation and differentiation for downstream applications.

Development of a microfluidic approach for the real-time analysis of extrinsic TGF-β signalling

Autocrine and paracrine signalling are traditionally difficult to study due to the sub-micromolar concentrations involved. This has proven to be especially limiting in the study of embryonic stem cells that rely on such signalling for viability, self-renewal, and proliferation. Microfluidics allows to achieve local concentrations of ligands representative of the in vivo stem cell niche, gaining more precise control over the cell microenvironment, as well as to manipulate ligands availability with high temporal resolution and minimal amount of reagents. Here we developed a microfluidics-based system for monitoring the dynamics of TGF-β pathway activity by means of a SMAD2/3-dependent luciferase reporter. We first validated our system by showing dose-dependent transcriptional activation. We then tested the effects of pulsatile stimulation and delayed inhibition of TGF-β activity on signalling dynamics. Finally, we show that our microfluidic system, unlike conventional culture systems, can detect TGF-β ligands secreted in the conditioned medium from hESCs.

Organ-on-a-Chip

Limitations of the current tools used in the drug development process, cell cultures, and animal models have highlighted the need for a new powerful tool that can emulate the human physiology in vitro. Advances in the field of microfluidics have made the realization of this tool closer than ever. Organ-on-a-chip platforms have been the first step forward, leading to the combination and integration of multiple organ models in the same platform with human-on-a-chip being the ultimate goal. Despite the current progress and technological developments, there are still several unmet engineering and biological challenges curtailing their development and widespread application in the biomedical field. The potentials, challenges, and current work on this unprecedented tool are being discussed in this chapter.

Microfluidic perfusion modulates growth and motor neuron differentiation of stem cell aggregates

Microfluidic technologies provide many advantages for studying differentiation of three-dimensional (3D) stem cell aggregates, including the ability to control the culture microenvironment, isolate individual aggregates for longitudinal tracking, and perform imaging-based assays. However, applying microfluidics to studying mechanisms of stem cell differentiation requires an understanding of how microfluidic culture conditions impact cell phenotypes. Conventional cell culture techniques cannot directly be applied to the microscale, as microscale culture varies from macroscale culture in multiple aspects. Therefore, the objective of this work was to explore key parameters in microfluidic culture of 3D stem cell aggregates and to understand how these parameters influence stem cell behavior and differentiation. These studies were done in the context of differentiation of embryonic stem cells (ESCs) to motor neurons (MNs). We assessed how media exchange frequency modulates the biochemical microenvironment, including availability of exogenous factors (e.g. nutrients, small molecule additives) and cell-secreted molecules, and thereby impacts differentiation. The results of these studies provide guidance on how key characteristics of 3D cell cultures can be considered when designing microfluidic culture parameters. We demonstrate that discontinuous perfusion is effective at supporting stem cell aggregate growth. We find that there is a balance between the frequency of media exchange, which is needed to ensure that cells are not nutrient-limited, and the need to allow accumulation of cell-secreted factors to promote differentiation. Finally, we show how microfluidic device geometries can influence transport of biomolecules and potentially promote asymmetric spatial differentiation. These findings are instructive for future work in designing devices and experiments for culture of cell aggregates.

A circular RNA map for human induced pluripotent stem cells of foetal origin

BACKGROUND

Adult skin fibroblasts represent the most common starting cell type used to generate human induced pluripotent stem cells (F-hiPSC) for clinical studies. Yet, a foetal source would offer unique advantages, primarily the absence of accumulated somatic mutations. Herein, we generated hiPSC from cord blood multipotent mesenchymal stromal cells (MSC-hiPSC) and compared them with F-hiPSC. Assessment of the full activation of the pluripotency gene regulatory network (PGRN) focused on circular RNA (circRNA), recently proposed to participate in the control of pluripotency.

METHODS

Reprogramming was achieved by a footprint-free strategy. Self-renewal and pluripotency of cord blood MSC-hiPSC were investigated in vitro and in vivo, compared to parental MSC, to embryonic stem cells and to F-hiPSC. High-throughput array-based approaches and bioinformatics analyses were applied to address the PGRN.

FINDINGS

Cord blood MSC-hiPSC successfully acquired a complete pluripotent identity. Functional comparison with F-hiPSC showed no differences in terms of i) generation of mesenchymal-like derivatives, ii) their subsequent adipogenic, osteogenic and chondrogenic commitment, and iii) their hematopoietic support ability. At the transcriptional level, specific subsets of mRNA, miRNA and circRNA (n = 4,429) were evidenced, casting a further layer of complexity on the PGRN regulatory crosstalk.

INTERPRETATION

A circRNA map of transcripts associated to naïve and primed pluripotency is provided for hiPSC of clinical-grade foetal origin, offering insights on still unreported regulatory circuits of the PGRN to consider for the optimization and development of efficient differentiation protocols for clinical translation.

FUNDING

This research was funded by Ricerca Corrente 2012-2018 by the Italian Ministry of Health.

Deconstructing, Replicating, and Engineering Tissue Microenvironment for Stem Cell Differentiation

One of the most crucial components of regenerative medicine is the controlled differentiation of embryonic or adult stem cells into the desired cell lineage. Although most of the reported protocols of stem cell differentiation involve the use of soluble growth factors, it is increasingly evident that stem cells also undergo differentiation when cultured in the appropriate microenvironment. When cultured in decellularized tissues, for instance, stem cells can recapitulate the morphogenesis and functional specialization of differentiated cell types with speed and efficiency that often surpass the traditional growth factor-driven protocols. This suggests that the tissue microenvironment (TME) provides stem cells with a holistic "instructive niche" that harbors signals for cellular reprogramming. The translation of this into medical applications requires the decoding of these signals, but this has been hampered by the complexity of TME. This problem is often addressed by a reductionist approach, in which cells are exposed to substrates decorated with simple, empirically designed geometries, textures, and chemical compositions ("bottom-up" approach). Although these studies are invaluable in revealing the basic principles of mechanotransduction mechanisms, their physiological relevance is often uncertain. This review examines the recent progress of an alternative, "top-down" approach, in which the TME is treated as a holistic biological entity. This approach is made possible by recent advances in systems biology and fabrication technologies that enable the isolation, characterization, and reconstitution of TME. It is hoped that these new techniques will elucidate the nature of niche signals so that they can be extracted, replicated, and controlled. This review summarizes these emerging techniques and how the data they generated are changing our view on TME. Impact statement This review summarizes the current state of art of the understanding of instructive niche in the field of tissue microenvironment. Not only did we survey the use of different biochemical preparations as stimuli of stem cell differentiation and summarize the recent effort in dissecting the biochemical composition of these preparations, through the application of extracellular matrix (ECM) arrays and proteomics, but we also introduce the use of open-source, high-content immunohistochemistry projects in contributing to the understanding of tissue-specific composition of ECM. We believe this review would be highly useful for our peer researching in the same field. "Mr. Tulkinghorn is always the same… so oddly out of place and yet so perfectly at home." -Charles Dickens, Bleak House.

Opportunities and challenges for the use of induced pluripotent stem cells in modelling neurodegenerative disease

Adult-onset neurodegenerative diseases are among the most difficult human health conditions to model for drug development. Most genetic or toxin-induced cell and animal models cannot faithfully recapitulate pathology in disease-relevant cells, making it excessively challenging to explore the potential mechanisms underlying sporadic disease. Patient-derived induced pluripotent stem cells (iPSCs) can be differentiated into disease-relevant neurons, providing an unparalleled platform for in vitro modelling and development of therapeutic strategies. Here, we review recent progress in generating Alzheimer's, Parkinson's and Huntington's disease models from patient-derived iPSCs. We also describe novel discoveries of pathological mechanisms and drug evaluations that have used these patient iPSC-derived neuronal models. Additionally, current human iPSC technology allows researchers to model diseases with 3D brain organoids, which are more representative of tissue architecture than traditional neuronal cultures. We discuss remaining challenges and emerging opportunities for the use of three-dimensional brain organoids in modelling brain development and neurodegeneration.

Modular operation of microfluidic chips for highly parallelized cell culture and liquid dosing via a fluidic circuit board

Microfluidic systems enable automated and highly parallelized cell culture with low volumes and defined liquid dosing. To achieve this, systems typically integrate all functions into a single, monolithic device as a "one size fits all" solution. However, this approach limits the end users' (re)design flexibility and complicates the addition of new functions to the system. To address this challenge, we propose and demonstrate a modular and standardized plug-and-play fluidic circuit board (FCB) for operating microfluidic building blocks (MFBBs), whereby both the FCB and the MFBBs contain integrated valves. A single FCB can parallelize up to three MFBBs of the same design or operate MFBBs with entirely different architectures. The operation of the MFBBs through the FCB is fully automated and does not incur the cost of an extra external footprint. We use this modular platform to control three microfluidic large-scale integration (mLSI) MFBBs, each of which features 64 microchambers suitable for cell culturing with high spatiotemporal control. We show as a proof of principle that we can culture human umbilical vein endothelial cells (HUVECs) for multiple days in the chambers of this MFBB. Moreover, we also use the same FCB to control an MFBB for liquid dosing with a high dynamic range. Our results demonstrate that MFBBs with different designs can be controlled and combined on a single FCB. Our novel modular approach to operating an automated microfluidic system for parallelized cell culture will enable greater experimental flexibility and facilitate the cooperation of different chips from different labs.

In vitro metabolic zonation through oxygen gradient on a chip

Among the multiple metabolic signals involved in the establishment of the hepatic zonation, oxygen could play a key role. Indeed, depending on hepatocyte position in the hepatic lobule, gene expression and metabolism are differently affected by the oxygen gradient present across the lobule. The aim of this study is to understand whether an oxygen gradient, generated in vitro in our developed device, is sufficient to instruct a functional metabolic zonation during the differentiation of human embryonic stem cells (hESCs) from endoderm toward terminally differentiated hepatocytes, thus mimicking the in vivo situation. For this purpose, a microfluidic device was designed for the generation of a stable oxygen gradient. The oxygen gradient was applied to differentiating hESCs at the pre-hepatoblast stage. The definitive endoderm and hepatic endoderm cells were characterized by the expression of the transcription factor SOX-17 and alpha-fetoprotein (AFP). Immature and mature hepatocytes were characterized by hepatocyte nuclear factor 4-alpha (HNF-4α) and albumin (ALB) expression and also analyzed for cytochrome P450 (CYP3A4) zonation and glycogen accumulation through PAS staining. Metabolic zonated genes expression was assessed through quantitative real time PCR. Application of the oxygen gradient during differentiation induced zonated glycogen storage, which was higher in the hepatocytes grown in high pO₂ compared to those grown in low pO₂. The mRNA levels of glutamine synthetase (GLUL), beta-catenin (CTNNB) and its direct target cyclin D1 (CCND1) showed significantly higher expression in the cells grown in low pO₂ compared to those grown in high pO₂. On the contrary, carbamoyl-phosphate synthetase 1 (CPS1), ALB, the proliferative marker ki67 (MKI67) and cyclin A (CCNA) resulted to be significantly higher expressed in cells cultured in high pO₂ compared to those cultured in low pO₂. These results indicate that the oxygen gradient generated in our device can instruct the establishment of a functional metabolic zonation in differentiating hESCs. The possibility to obtain differentiated hepatocytes in vitro may allow in the future to deepen our knowledge about the physiology/pathology of hepatocytes in relation to the oxygen content.

Autologous induced pluripotent stem cell-derived four-organ-chip

Microphysiological systems play a pivotal role in progressing toward a global paradigm shift in drug development. Here, we designed a four-organ-chip interconnecting miniaturized human intestine, liver, brain and kidney equivalents. All four organ models were predifferentiated from induced pluripotent stem cells from the same healthy donor and integrated into the microphysiological system. The coculture of the four autologous tissue models in one common medium deprived of tissue specific growth factors was successful over 14-days. Although there were no added growth factors present in the coculture medium, the intestine, liver and neuronal model maintained defined marker expression. Only the renal model was overgrown by coexisting cells and did not further differentiate. This model platform will pave the way for autologous coculture cross-talk assays, disease induction and subsequent drug testing.

Autologous induced pluripotent stem cell-derived four-organ-chip

Microphysiological systems play a pivotal role in progressing toward a global paradigm shift in drug development. Here, we designed a four-organ-chip interconnecting miniaturized human intestine, liver, brain and kidney equivalents. All four organ models were predifferentiated from induced pluripotent stem cells from the same healthy donor and integrated into the microphysiological system. The coculture of the four autologous tissue models in one common medium deprived of tissue specific growth factors was successful over 14-days. Although there were no added growth factors present in the coculture medium, the intestine, liver and neuronal model maintained defined marker expression. Only the renal model was overgrown by coexisting cells and did not further differentiate. This model platform will pave the way for autologous coculture cross-talk assays, disease induction and subsequent drug testing.

Automated sensing and splitting of stem cell colonies on microraft arrays

Human induced pluripotent stem cells (hiPSCs) are widely used for disease modeling, tissue engineering, and clinical applications. Although the development of new disease-relevant or customized hiPSC lines is of high importance, current automated hiPSC isolation technologies rely largely on the fluorescent labeling of cells, thus limiting the cell line development from many applications. The objective of this research was to develop a platform for high-throughput hiPSC cytometry and splitting that utilized a label-free cell sensing approach. An image analysis pipeline utilizing background subtraction and standard deviation projections was implemented to detect hiPSC colonies from bright-field microscopy data. The pipeline was incorporated into an automated microscopy system coupling quad microraft cell-isolation arrays, computer-based vision, and algorithms for smart decision making and cell sorting. The pipeline exhibited a hiPSC detection specificity of 98% and a sensitivity of 88%, allowing for the successful tracking of growth for hundreds of microcolonies over 7 days. The automated platform split 170 mother colonies from a microarray within 80 min, and the harvested daughter biopsies were expanded into viable hiPSC colonies suitable for downstream assays, such as polymerase chain reaction (PCR) or continued culture. Transmitted light microscopy offers an alternative, label-free modality for isolating hiPSCs, yet its low contrast and specificity for adherent cells remain a challenge for automation. This novel approach to label-free sensing and microcolony subsampling with the preservation of the mother colony holds the potential for hiPSC colony screening based on a wide range of properties including those measurable only by a cell destructive assay.