Perfusion-based microfluidic device for three-dimensional dynamic primary human hepatocyte cell culture in the absence of biological or synthetic matrices or coagulants

Organ-on-a-Chip Approach for Accelerating Blood-Brain Barrier Nanoshuttle Discovery

Organ-on-a-chip, which recapitulates the dynamics of in vivo vasculature, has emerged as a promising platform for studying organ-specific vascular beds. However, its practical advantages in identifying vascular-targeted drug delivery systems (DDS) over traditional in vitro models remain underexplored. This study demonstrates the reliability and efficacy of the organ-on-a-chip in screening efficient DDS by comparing its performance with that of a conventional transwell, both designed to simulate the blood-brain barrier (BBB). The BBB nanoshuttles discovered through BBB Chip-based screening demonstrated superior functionality in vivo compared to those identified using transwell methods. This enhanced effectiveness is attributed to the BBB Chip's accurate replication of the structure and dynamics of the endothelial glycocalyx, a crucial protective layer within blood vessels, especially under shear stress. This capability of the BBB Chip has enabled the identification of molecular shuttles that efficiently exploit the endothelial glycocalyx, thereby enhancing transendothelial transport efficacy. Our findings suggest that organ-on-a-chip technology holds considerable promise for advancing research in vascular-targeted DDS due to its accurate simulation of molecular transport within endothelial systems.

Bone and Joint-on-Chip Platforms: Construction Strategies and Applications

Organ-on-a-chip, also known as "tissue chip," is an advanced platform based on microfluidic systems for constructing miniature organ models in vitro. They can replicate the complex physiological and pathological responses of human organs. In recent years, the development of bone and joint-on-chip platforms aims to simulate the complex physiological and pathological processes occurring in human bones and joints, including cell-cell interactions, the interplay of various biochemical factors, the effects of mechanical stimuli, and the intricate connections between multiple organs. In the future, bone and joint-on-chip platforms will integrate the advantages of multiple disciplines, bringing more possibilities for exploring disease mechanisms, drug screening, and personalized medicine. This review explores the construction and application of Organ-on-a-chip technology in bone and joint disease research, proposes a modular construction concept, and discusses the new opportunities and future challenges in the construction and application of bone and joint-on-chip platforms.

Recent advances in liver-on-chips: Design, fabrication, and applications

The liver is a multifunctional organ and the metabolic center of the human body. Most drugs and toxins are metabolized in the liver, resulting in varying degrees of hepatotoxicity. The damage of liver will seriously affect human health, so it is very important to study the prevention and treatment of liver diseases. At present, there are many research studies in this field. However, most of them are based on animal models, which are limited by the time-consuming processes and species difference between human and animals. In recent years, liver-on-chips have emerged and developed rapidly and are expected to replace animal models. Liver-on-chips refer to the use of a small number of liver cells on the chips to simulate the liver microenvironment and ultrastructure in vivo. They hold extensive applications in multiple fields by reproducing the unique physiological functions of the liver in vitro. In this review, we first introduced the physiology and pathology of liver and then described the cell system of liver-on-chips, the chip-based liver models, and the applications of liver-on-chips in liver transplantation, drug screening, and metabolic evaluation. Finally, we discussed the currently encountered challenges and future trends in liver-on-chips.

Primary Hepatocyte Isolation and Cultures: Technical Aspects, Challenges and Advancements

Hepatocytes are differentiated cells that account for 80% of the hepatic volume and perform all major functions of the liver. In vivo, after an acute insult, adult hepatocytes retain their ability to proliferate and participate in liver regeneration. However, in vitro, prolonged culture and proliferation of viable and functional primary hepatocytes have remained the major and the most challenging goal of hepatocyte-based cell therapies and liver tissue engineering. The first functional cultures of rat primary hepatocytes between two layers of collagen gel, also termed as the "sandwich cultures", were reported in 1989. Since this study, several technical developments including choice of hydrogels, type of microenvironment, growth factors and culture conditions, mono or co-cultures of hepatocytes along with other supporting cell types have evolved for both rat and human primary hepatocytes in recent years. All these improvements have led to a substantial improvement in the number, life-span and hepatic functions of these cells in vitro for several downstream applications. In the current review, we highlight the details, limitations and prospects of different technical strategies being used in primary hepatocyte cultures. We discuss the use of newer biomaterials as scaffolds for efficient culture of primary hepatocytes. We also describe the derivation of mature hepatocytes from other cellular sources such as induced pluripotent stem cells, bone marrow stem cells and 3D liver organoids. Finally, we also explain the use of perfusion-based bioreactor systems and bioengineering strategies to support the long-term function of hepatocytes in 3D conditions.

Construction of polysaccharide scaffold-based perfusion bioreactor supporting liver cell aggregates for drug screening

Rebuilding a suitable microenvironment of liver cells is the key challenge to enhancing the expression of hepatic functions for drug screening in vitro. To improve the microenvironment by providing the specific adhesive ligands for hepatocytes in the three-dimensional dynamic culture, a perfusion bioreactor with a pectin/alginate blend porous scaffold was constructed in this study. The galactosyl component in the main chain of pectin was able to be specifically recognized by the asialoglycoprotein receptor on the surface of hepatocytes, and subsequently promoted the adhesion and aggregation of hepatocytes co-cultured with hepatic non-parenchymal cells. The bioreactor was optimized for 4 h of dynamic inoculation followed by perfusion at a flow rate of 2 mL/min, which provided adequate oxygen supply and good mass transfer to the liver cells. During dynamic cultured in the bioreactor for 14 days, more multicellular aggregates were formed and were evenly distributed in the pectin/alginate blend scaffolds. The expressions of intercellular interaction and hepatic functions of the hepatocytes in aggregates were significantly enhanced in the three-dimensional dynamic group. Furthermore, the bioreactor not only markedly upregulated the cell polarity markers expression of hepatocytes but also enhanced their metabolic capacity to acetaminophen, isoniazid, and tolbutamide, which exhibited a significant concentration-dependent manner. Therefore, the pectin/alginate blend scaffold-based perfusion bioreactor appeared to be a promising candidate in the field of drug development and liver regeneration research.

Three-Dimensional Organoids as a Model to Study Nonalcoholic Fatty Liver Disease

Despite the rising prevalence of nonalcoholic fatty liver disease (NAFLD), the underlying disease pathophysiology remains unclear. There is a great need for an efficient and reliable "human" in vitro model to study NAFLD and the progression to nonalcoholic steatohepatitis (NASH), which will soon become the leading indication for liver transplantation. Here, we review the recent developments in the use of three-dimensional (3D) liver organoids as a model to study NAFLD and NASH pathophysiology and possible treatments. Various techniques that are currently used to make liver organoids are discussed, such as the use of induced pluripotent stem cells versus primary cell lines and human versus murine cells. Moreover, methods for inducing lipid droplet accumulation and fibrosis to model NAFLD are explored. Finally, the limitations specific to the 3D organoid model for NAFLD/NASH are reviewed, highlighting the need for further development of multilineage models to include hepatic nonparenchymal cells and immune cells. The ultimate goal is to be able to accurately recapitulate the complex liver microenvironment in which NAFLD develops and progresses to NASH.

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.

Bioartificial livers: a review of their design and manufacture

Acute liver failure (ALF) is a rapidly progressive disease with high morbidity and mortality rates. Liver transplantation and artificial liver support systems, such as artificial livers (ALs) and bioartificial livers (BALs), are the two major therapies for ALF. Compared to ALs, BALs are composed of functional hepatocytes that provide essential liver functions, including detoxification, metabolite synthesis, and biotransformation. Furthermore, BALs can potentially provide effective support as a form of bridging therapy to liver transplantation or spontaneous recovery for patients with ALF. In this review, we systematically discussed the currently available state-of-the-art designs and manufacturing processes for BAL support systems. Specifically, we classified the cell sources and bioreactors that are applied in BALs, highlighted the advanced technologies of hepatocyte culturing and bioreactor fabrication, and discussed the current challenges and future trends in developing next generation BALs for large scale clinical applications.

Modular 3D In Vitro Artery-Mimicking Multichannel System for Recapitulating Vascular Stenosis and Inflammation

Inflammation and the immune response in atherosclerosis are complex processes involving local hemodynamics, the interaction of dysfunctional cells, and various pathological environments. Here, a modular multichannel system that mimics the human artery to demonstrate stenosis and inflammation and to study physical and chemical effects on biomimetic artery models is presented. Smooth muscle cells and endothelial cells were cocultured in the wrinkled surface in vivo-like circular channels to recapitulate the artery. An artery-mimicking multichannel module comprised four channels for the fabrication of coculture models and assigned various conditions for analysis to each model simultaneously. The manipulation became reproducible and stable through modularization, and each module could be replaced according to analytical purposes. A chamber module for culture was replaced with a microfluidic concentration gradient generator (CGG) module to achieve the cellular state of inflamed lesions by providing tumor necrosis factor (TNF)-α, in addition to the stenosis structure by tuning the channel geometry. Different TNF-α doses were administered in each channel by the CGG module to create functional inflammation models under various conditions. Through the tunable channel geometry and the microfluidic interfacing, this system has the potential to be used for further comprehensive research on vascular diseases such as atherosclerosis and thrombosis.

Microtechnology-based in vitro models: Mimicking liver function and pathophysiology

The liver plays important roles in drug metabolism and homeostasis. The metabolism and biotransformation can not only affect the efficacy of drugs but also result in hepatotoxicity and drug-induced liver injury. Understanding the complex physiology of the liver and the pathogenetic mechanisms of liver diseases is essential for drug development. Conventional in vitro models have limitations in the ability to predict drug effects, due to the lack of physiological relevance. Recently, the liver-on-a-chip platform has been developed to reproduce the microarchitecture and in vivo environment of the liver. These efforts have improved the physiological relevance of the liver tissue used in the platform and have demonstrated its applicability to drug screening and disease models. In this review, we summarize the recent development of liver-on-a-chip models that closely mimic the in vivo liver environments and liver diseases.

Design and Fabrication of the Vertical-Flow Bioreactor for Compaction Hepatocyte Culture in Drug Testing Application

The perfusion culture of primary hepatocytes has been widely adopted to build bioreactors for various applications. As a drug testing platform, a unique vertical-flow bioreactor (VfB) array was found to create the compaction culture of hepatocytes which mimicked the mechanic microenvironment in vivo while maintaining the 3D cell morphology in a 2D culture setup and enhancing the hepatic functions for a sustained culture. Here, we report the methodology in designing and fabricating the VfB to reach ideal bioreactor requirements, optimizing the VfB as a prototype for drug testing, and to demonstrate the enhanced hepatic function so as to demonstrate the performance of the bioreactor. This device enables the modular, scalable, and manufacturable construction of a functional drug testing platform through the sustained maintenance of model cells.

Hydrogels: The Next Generation Body Materials for Microfluidic Chips?

The integration of microfluidics with biomedical research is confronted with considerable limitations due to its body materials. With high content of water, hydrogels own superior biocompatibility and degradability. Can hydrogels become another material choice for the construction of microfluidic chips, particularly biofluidics? The present review aims to systematically establish the concept of hydrogel-based microfluidic chips (HMCs) and address three main concerns: i) why choosing hydrogels? ii) how to fabricate HMCs?, and iii) in which fields to apply HMCs? It is envisioned that hydrogels may be used increasingly as substitute for traditional materials and gradually act as the body material for microfluidic chips. The modifications of conventional process are highlighted to overcome issues arising from the incompatibility between the construction methods and hydrogel materials. Specifically targeting at the "soft and wet" hydrogels, an efficient flowchart of "i) high resolution template printing; ii) damage-free demolding; iii) twice-crosslinking bonding" is proposed. Accordingly, a broader microfluidic chip concept is proposed in terms of form and function. Potential biomedical applications of HMCs are discussed. This review also highlights the challenges arising from the material replacement, as well as the future directions of the proposed concept. Finally, the authors' viewpoints and perspectives for this emerging field are discussed.

Microengineered systems with iPSC-derived cardiac and hepatic cells to evaluate drug adverse effects

Hepatic and cardiac drug adverse effects are among the leading causes of attrition in drug development programs, in part due to predictive failures of current animal or in vitro models. Hepatocytes and cardiomyocytes differentiated from human induced pluripotent stem cells (iPSCs) hold promise for predicting clinical drug effects, given their human-specific properties and their ability to harbor genetically determined characteristics that underlie inter-individual variations in drug response. Currently, the fetal-like properties and heterogeneity of hepatocytes and cardiomyocytes differentiated from iPSCs make them physiologically different from their counterparts isolated from primary tissues and limit their use for predicting clinical drug effects. To address this hurdle, there have been ongoing advances in differentiation and maturation protocols to improve the quality and use of iPSC-differentiated lineages. Among these are in vitro hepatic and cardiac cellular microsystems that can further enhance the physiology of cultured cells, can be used to better predict drug adverse effects, and investigate drug metabolism, pharmacokinetics, and pharmacodynamics to facilitate successful drug development. In this article, we discuss how cellular microsystems can establish microenvironments for these applications and propose how they could be used for potentially controlling the differentiation of hepatocytes or cardiomyocytes. The physiological relevance of cells is enhanced in cellular microsystems by simulating properties of tissue microenvironments, such as structural dimensionality, media flow, microfluidic control of media composition, and co-cultures with interacting cell types. Recent studies demonstrated that these properties also affect iPSC differentiations and we further elaborate on how they could control differentiation efficiency in microengineered devices. In summary, we describe recent advances in the field of cellular microsystems that can control the differentiation and maturation of hepatocytes and cardiomyocytes for drug evaluation. We also propose how future research with iPSCs within engineered microenvironments could enable their differentiation for scalable evaluations of drug effects.

Microfluidic lumen-based systems for advancing tubular organ modeling

Microfluidic lumen-based systems are microscale models that recapitulate the anatomy and physiology of tubular organs. These technologies can mimic human pathophysiology and predict drug response, having profound implications for drug discovery and development. Herein, we review progress in the development of microfluidic lumen-based models from the 2000s to the present. The core of the review discusses models for mimicking blood vessels, the respiratory tract, the gastrointestinal tract, renal tubules, and liver sinusoids, and their application to modeling organ-specific diseases. We also highlight emerging application areas, such as the lymphatic system, and close the review discussing potential future directions.

An adaptable soft-mold embossing process for fabricating optically-accessible, microfeature-based culture systems and application toward liver stage antimalarial compound testing

Advanced cell culture methods for modeling organ-level structure have been demonstrated to replicate in vivo conditions more accurately than traditional in vitro cell culture. Given that the liver is particularly important to human health, several advanced culture methods have been developed to experiment with liver disease states, including infection with Plasmodium parasites, the causative agent of malaria. These models have demonstrated that intrahepatic parasites require functionally stable hepatocytes to thrive and robust characterization of the parasite populations' response to investigational therapies is dependent on high-content and high-resolution imaging (HC/RI). We previously reported abiotic confinement extends the functional longevity of primary hepatocytes in a microfluidic platform and set out to instill confinement in a microtiter plate platform while maintaining optical accessibility for HC/RI; with an end-goal of producing an improved P. vivax liver stage culture model. We developed a novel fabrication process in which a PDMS soft mold embosses hepatocyte-confining microfeatures into polystyrene, resulting in microfeature-based hepatocyte confinement (μHEP) slides and plates. Our process was optimized to form both microfeatures and culture wells in a single embossing step, resulting in a 100 μm-thick bottom ideal for HC/RI, and was found inexpensively amendable to microfeature design changes. Microfeatures improved intrahepatic parasite infection rates and μHEP systems were used to reconfirm the activity of reference antimalarials in phenotypic dose-response assays. RNAseq of hepatocytes in μHEP systems demonstrated microfeatures sustain hepatic differentiation and function, suggesting broader utility for preclinical hepatic assays; while our tailorable embossing process could be repurposed for developing additional organ models.

Establishment of ornithine transcarbamylase deficiency-derived primary human hepatocyte with hepatic functions

A long-term hepatocyte culture maintaining liver-specific functions is very essential for both basic research and the development of bioartificial liver devices in clinical application. However, primary hepatocytes rapidly lose their proliferation and hepatic functions over a few days in culture. This work is to establish an ornithine transcarbamylase deficiency (OTCD) patient-derived primary human hepatocyte (OTCD-PHH) culture with hepatic functions for providing an in vitro cell model. Liver tissue from an infant with OTCD was dispersed into single cells. The cells were cultured using conditional reprogramming. To characterize the cells, we assessed activities and mRNA expression of CYP3A4, 1A1, 2C9, as well as albumin and urea secretion. We found that the OTCD-PHH can be subpassaged for more than 15 passages. The cells do not express mRNA of fibroblast-specific maker, whereas they highly express markers of epithelial cells and hepatocytes. In addition, the OTCD-PHH retain native CYP3A4, 1A1, 2C9 activities and albumin secretion function at early passages. The OTCD-PHH at passages 2, 6, 9 and 13 have identical DNA fingerprint as the original tissue. Furthermore, under 3D culture environment, low urea production and hepatocyte marker staining of the OTCD-PHH were detected. The established OTCD-PHH maintain liver-specific functions at early passages and can be long-term cultured in vitro. We believe the established long-term OTCD-PHH culture is highly relevant to study liver diseases, particularly in infants with OTCD.

Long-term culture and characterization of patient-derived primary hepatocytes using conditional reprogramming

Cultivation of primary human hepatocytes (PHHs) often faces obstacles including failure of long-term in vitro culture, weak proliferation ability, rapid loss of liver-specific function and morphology, and tendency of fibrosis. Previous research focused on immortalization methods, such as telomerase and viral, to culture immortalized primary human hepatocytes, which may lose some of the normal properties. However, non-immortalized PHHs often fail to maintain long-term viability and functionality. These highlight the urgent need for developing new culture strategy for PHHs. In the present study, we isolated PHHs from fresh human liver tissues representing different liver diseases and age groups. We used conditional reprogramming, without permanent immortalization, for long-term in vitro primary human hepatocytes cultivation and characterization. For functional characterization, we assessed CYP3A4, 1A1 and 2C9 activities and measured the mRNA expression of albumin , s100a4 , krt8 , krt18 , cyp1a1 , cyp3a4 , cyp2b6 , cyp2c8 , cyp2c9 , and cyp2d6 . Additionally, we compared the DNA fingerprint of the cells against their original liver tissues using short tandem repeat (STR) analysis. We found that PHHs-derived from young patients can survive for more than three months, while the lifespan of primary human hepatocytes derived from adult patients ranges from two to three months, which is longer than most commercial primary hepatocytes. Importantly, the cells at early passages retain strong CYP3A4, 1A1 and 2C9 activities and the DNA fingerprints are identical with their original tissues. Through conditional programming, we achieved, for the first time, a high level of success rate in the long-term in vitro cultivation of primary human hepatocytes-derived patients representing diverse liver disease. Moreover, the conditional programming cell culture technology reported in this paper requires neither co-culture with additive cells, nor complex and expensive components, such as collagen sandwich or spheroid culture. We thus believe that the patient-derived PHHs cultivation using conditional programming may provide a viable and valuable cell model to study liver disease-related mechanisms.

Bioinspired Engineering of Organ-on-Chip Devices

The human body can be viewed as an organism consisting of a variety of cellular and non-cellular materials interacting in a highly ordered manner. Its complex and hierarchical nature inspires the multi-level recapitulation of the human body in order to gain insights into the inner workings of life. While traditional cell culture models have led to new insights into the cellular microenvironment and biological control in vivo, deeper understanding of biological systems and human pathophysiology requires the development of novel model systems that allow for analysis of complex internal and external interactions within the cellular microenvironment in a more relevant organ context. Engineering organ-on-chip systems offers an unprecedented opportunity to unravel the complex and hierarchical nature of human organs. In this chapter, we first highlight the advances in microfluidic platforms that enable engineering of the cellular microenvironment and the transition from cells-on-chips to organs-on-chips. Then, we introduce the key features of the emerging organs-on-chips and their proof-of-concept applications in biomedical research. We also discuss the challenges and future outlooks of this state-of-the-art technology.

In Vitro Immune Organs-on-Chip for Drug Development: A Review

The current drug development practice lacks reliable and sensitive techniques to evaluate the immunotoxicity of drug candidates, i.e., their effect on the human immune system. This, in part, has resulted in a high attrition rate for novel drugs candidates. Organ-on-chip devices have emerged as key tools that permit the study of human physiology in controlled in vivo simulating environments. Furthermore, there has been a growing interest in developing the so called "body-on-chip" devices to better predict the systemic effects of drug candidates. This review describes existing biomimetic immune organs-on-chip, highlights their physiological relevance to drug development and discovery and emphasizes the need for developing comprehensive immune system-on-chip models. Such immune models can enhance the performance of novel drug candidates during clinical trials and contribute to reducing the high attrition rate as well as the high cost associated with drug development.

Primary hepatocytes and their cultures for the testing of drug-induced liver injury

Drug-induced liver injury is a major reason for discontinuation of drug development and withdrawal of drugs from the market. Intensive efforts in the last decades have focused on the establishment and finetuning of liver-based in vitro models for reliable prediction of hepatotoxicity triggered by drug candidates. Of those, primary hepatocytes and their cultures still are considered the gold standard, as they provide an acceptable reflection of the hepatic in vivo situation. Nevertheless, these in vitro systems cope with gradual deterioration of the differentiated morphological and functional phenotype. The present paper gives an overview of traditional and more recently introduced strategies to counteract this dedifferentiation process in an attempt to set up culture models that can be used for long-term testing purposes. The relevance and applicability of such optimized cultures of primary hepatocytes for the testing of drug-induced cholestatic liver injury is demonstrated.

Study of oxygen tension variation within live tumor spheroids using microfluidic devices and multi-photon laser scanning microscopy

Three-dimensional cell spheroid culture using microfluidic devices provides a convenient in vitro model for studying tumour spheroid structures and internal microenvironments. Recent studies suggest that oxygen deprived zones inside solid tumors are responsible for stimulating local cytokines and endothelial vasculature proliferation during angiogenesis. In this work, we develop an integrated approach combining microfluidic devices and multi-photon laser scanning microscopy (MPLSM) to study variations in oxygen tension within live spheroids of human osteosarcoma cells. Uniform shaped, size-controlled spheroids are grown and then harvested using a polydimethylsiloxane (PDMS) based microfluidic device. Fluorescence live imaging of the harvested spheroids is performed using MPLSM and a commercially available oxygen sensitive dye, Image-iT Red, to observe the oxygen tension variation within the spheroids and those co-cultured with monolayers of human umbilical vein endothelial cells (HUVECs). Oxygen tension variations are observed within the spheroids with diameters ranging from 90 ± 10 μm to 140 ± 10 μm. The fluorescence images show that the low-oxygenated cores diminish when spheroids are co-cultured with HUVEC monolayers for 6 hours to 8 hours. In the experiments, spheroids subjected to HUVEC conditioned medium treatment and with a cell adherent substrate are also measured and analyzed to study their significance on oxygen tension within the spheroids. The results show that the oxygenation within the spheroids is improved when the spheroids are cultured under those conditions. Our work presents an efficient method to study oxygen tension variation within live tumor spheroids under the influence of endothelial cells and conditioned medium. The method can be exploited for further investigation of tumor oxygen microenvironments during angiogenesis.

A glass-based, continuously zonated and vascularized human liver acinus microphysiological system (vLAMPS) designed for experimental modeling of diseases and ADME/TOX

The vLAMPS is a human, biomimetic liver MPS, in which the ECM and cell seeding of the intermediate layer prior to assembly, simplifies construction of the model and makes the platform user-friendly. This primarily glass microfluidic device is optimal for real-time imaging, while minimizing the binding of hydrophobic drugs/biologics to the materials that constitute the device. The assembly of the three layered device with primary human hepatocytes and liver sinusoidal endothelial cells (LSECs), and human cell lines for stellate and Kupffer cells, creates a vascular channel separated from the hepatic channel (chamber) by a porous membrane that allows communication between channels, recapitulating the 3D structure of the liver acinus. The vascular channel can be used to deliver drugs, immune cells, as well as various circulating cells and other factors to a stand-alone liver MPS and/or to couple the liver MPS to other organ MPS. We have successfully created continuous oxygen zonation by controlling the flow rates of media in the distinct vascular and hepatic channels and validated the computational modeling of zonation with oxygen sensitive and insensitive beads. This allows the direct investigation of the role of zonation in physiology, toxicology and disease progression. The vascular channel is lined with human LSECs, recapitulating partial immunologic functions within the liver sinusoid, including the activation of LSECs, promoting the binding of polymorphonuclear leukocytes (PMNs) followed by transmigration into the hepatic chamber. The vLAMPS is a valuable platform to investigate the functions of the healthy and diseased human liver using all primary human cell types and/or iPSC-derived cells.

High-Throughput Incubation and Quantification of Agglutination Assays in a Microfluidic System

In this paper, we present a two-phase microfluidic system capable of incubating and quantifying microbead-based agglutination assays. The microfluidic system is based on a simple fabrication solution, which requires only laboratory tubing filled with carrier oil, driven by negative pressure using a syringe pump. We provide a user-friendly interface, in which a pipette is used to insert single droplets of a 1.25-µL volume into a system that is continuously running and therefore works entirely on demand without the need for stopping, resetting or washing the system. These assays are incubated by highly efficient passive mixing with a sample-to-answer time of 2.5 min, a 5⁻10-fold improvement over traditional agglutination assays. We study system parameters such as channel length, incubation time and flow speed to select optimal assay conditions, using the streptavidin-biotin interaction as a model analyte quantified using optical image processing. We then investigate the effect of changing the concentration of both analyte and microbead concentrations, with a minimum detection limit of 100 ng/mL. The system can be both low- and high-throughput, depending on the rate at which assays are inserted. In our experiments, we were able to easily produce throughputs of 360 assays per hour by simple manual pipetting, which could be increased even further by automation and parallelization. Agglutination assays are a versatile tool, capable of detecting an ever-growing catalog of infectious diseases, proteins and metabolites. A system such as this one is a step towards being able to produce high-throughput microfluidic diagnostic solutions with widespread adoption. The development of analytical techniques in the microfluidic format, such as the one presented in this work, is an important step in being able to continuously monitor the performance and microfluidic outputs of organ-on-chip devices.

A monolayer microfluidic device supporting mouse spermatogenesis with improved visibility

In our previous study, we produced a microfluidic device (MFD) which successfully maintained spermatogenesis for over 6 months in mouse testis tissues loaded in the device. In the present study, we developed a new MFD, a monolayer device (ML-D) with a barrier structure consisting of pillars and slits, which is simpler in design and easier to make. This ML-D was also effective for inducing mouse spermatogenesis and maintained it for a longer period than the conventional culture method. In addition, we devised a way of introducing sample tissue into the device during its production, just before bonding the upper layer of polydimethylsiloxane (PDMS) and bottom glass slide. The tissue can obtain nutrients horizontally from the medium running beside it and oxygen vertically from above through PDMS. In addition, the glass slide set at the bottom improved the visibility of the sample tissue with an inverted microscope. When we took photos of cultured tissue of the Acr-Gfp transgenic mouse testis in ML-D sequentially every day, morphological changes of the acrosome during spermiogenesis were successfully recorded. The ML-D is simple in design and useful for culturing testis tissue for inducing and maintaining spermatogenesis with clearer visibility. Due to the new method of sample loading, tissues other than testis should also be applicable.

Organs-on-a-Chip: A Fast Track for Engineered Human Tissues in Drug Development

Organs-on-a-chip (OOCs) are miniature tissues and organs grown in vitro that enable modeling of human physiology and disease. The technology has emerged from converging advances in tissue engineering, semiconductor fabrication, and human cell sourcing. Encompassing innovations in human stem cell technology, OOCs offer a promising approach to emulate human patho/physiology in vitro, and address limitations of current cell and animal models. Here, we review the design considerations for single and multi-organ OOCs, discuss remaining challenges, and highlight the potential impact of OOCs as a fast-track opportunity for tissue engineering to advance drug development and precision medicine.

Engineering 3D Hydrogels for Personalized In Vitro Human Tissue Models

There is a growing interest in engineering hydrogels for 3D tissue and disease models. The major motivation is to better mimic the physiological microenvironment of the disease and human condition. 3D tissue models derived from patients' own cells can potentially revolutionize the way treatment and diagnostic alternatives are developed. This requires development of tissue mimetic hydrogels with user defined and tunable properties. In this review article, a recent summary of 3D hydrogel platforms for in vitro tissue and disease modeling is given. Hydrogel design considerations and available hydrogel systems are summarized, followed by the types of currently available hydrogel models, such as bulk hydrogels, porous scaffolds, fibrous scaffolds, hydrogel microspheres, hydrogel sandwich systems, microwells, and 3D bioprinted constructs. Although hydrogels are utilized for a wide range of tissue models, this article focuses on liver and cancer models. This article also provides a detailed section on current challenges and future perspectives of hydrogel-based tissue models.

Organ-on-a-Chip Technology for Reproducing Multiorgan Physiology

In the drug development process, the accurate prediction of drug efficacy and toxicity is important in order to reduce the cost, labor, and effort involved. For this purpose, conventional 2D cell culture models are used in the early phase of drug development. However, the differences between the in vitro and the in vivo systems have caused the failure of drugs in the later phase of the drug-development process. Therefore, there is a need for a novel in vitro model system that can provide accurate information for evaluating the drug efficacy and toxicity through a closer recapitulation of the in vivo system. Recently, the idea of using microtechnology for mimicking the microscale tissue environment has become widespread, leading to the development of "organ-on-a-chip." Furthermore, the system is further developed for realizing a multiorgan model for mimicking interactions between multiple organs. These advancements are still ongoing and are aimed at ultimately developing "body-on-a-chip" or "human-on-a-chip" devices for predicting the response of the whole body. This review summarizes recently developed organ-on-a-chip technologies, and their applications for reproducing multiorgan functions.

Real-time measurement of cholesterol secreted by human hepatocytes using a novel microfluidic assay

The use of microfluidics has become widespread in recent years because of the use of lesser resources such as small size, low volume of reagents, and physiological representation of mammalian cells. One of the advantages of microfluidic-based cell culture is the ability to perfuse culture media which tends to improve cellular health and function. Although measurement of cellular function conventionally is carried out using well-plates and plate readers, these approaches are insufficient to carry out in-line analysis of perfused cell cultures because of mismatch between volumes and sensitivity. We report the development of a novel microfluidic device and assay that is carried out under perfusion, in-line to measure the cholesterol secreted from a human hepatocyte tissue-chip. The heart of the assay is the unique implementation of enzymatic chemistry that is carried out on a polystyrene bead. Using this approach, we successfully measured cholesterol secreted by the perfused human hepatocytes.

Organ-On-A-Chip Platforms: A Convergence of Advanced Materials, Cells, and Microscale Technologies

Significant advances in biomaterials, stem cell biology, and microscale technologies have enabled the fabrication of biologically relevant tissues and organs. Such tissues and organs, referred to as organ-on-a-chip (OOC) platforms, have emerged as a powerful tool in tissue analysis and disease modeling for biological and pharmacological applications. A variety of biomaterials are used in tissue fabrication providing multiple biological, structural, and mechanical cues in the regulation of cell behavior and tissue morphogenesis. Cells derived from humans enable the fabrication of personalized OOC platforms. Microscale technologies are specifically helpful in providing physiological microenvironments for tissues and organs. In this review, biomaterials, cells, and microscale technologies are described as essential components to construct OOC platforms. The latest developments in OOC platforms (e.g., liver, skeletal muscle, cardiac, cancer, lung, skin, bone, and brain) are then discussed as functional tools in simulating human physiology and metabolism. Future perspectives and major challenges in the development of OOC platforms toward accelerating clinical studies of drug discovery are finally highlighted.

A decade of progress in liver regenerative medicine

Liver diseases can be caused by viral infection, metabolic disorder, alcohol consumption, carcinoma or injury, chronically progressing to end-stage liver disease or rapidly resulting in acute liver failure. In either situation, liver transplantation is most often sought for life saving, which is, however, significantly limited by severe shortage of organ donors. Until now, tremendous multi-disciplinary efforts have been dedicated to liver regenerative medicine, aiming at providing transplantable cells, microtissues, or bioengineered whole liver via tissue engineering, or maintaining partial liver functions via extracorporeal support. In both directions, new compatible biomaterials, stem cell sources, and bioengineering approaches have fast-forwarded liver regenerative medicine towards potential clinical applications. Another important progress in this field is the development of liver-on-a-chip technologies, which enable tissue engineering, disease modeling, and drug testing under biomimetic extracellular conditions. In this review, we aim to highlight the last decade's progress in liver regenerative medicine from liver tissue engineering, bioartificial liver devices (BAL), to liver-on-a-chip platforms, and then to present challenges ahead for further advancement.

Orthogonal Screening of Anticancer Drugs Using an Open-Access Microfluidic Tissue Array System

Screening for potential drug combinations presents significant challenges to the current microfluidic cell culture systems, due to the requirement of flexibility in liquid handling. To overcome this limitation, we present here an open-access microfluidic tissue array system specifically designed for drug combination screening. The microfluidic chip features a key structure in which a nanoporous membrane is sandwiched by a cell culture chamber array layer and a corresponding media reservoir array layer. The microfluidic approach takes advantage of the characteristics of the nanoporous membrane: on one side, this membrane permits the flow of air but not liquid, thus acting as a flow-stop valve to enable automatic cell distribution; on the other side, it allows diffusion-based media exchange and thus mimics the endothelial layer. In synergy with a liquid-transferring platform, the open-access microfluidic system enables complex multistep operations involving long-term cell culture, medium exchange, multistep drug treatment, and cell-viability testing. By using the microfluidic protocol, a 10 × 10 tissue array was constructed in 90 s, followed by schedule-dependent drug testing. Morphological and immunohistochemical assays indicated that the resultant tumor tissue was faithful to that in vivo. Drug-testing assays showed that the incorporation of the nanoporous membrane further decreased killing efficacy of the anticancer agents, indicating its function as an endothelial layer. Robustness of the microfluidic system was demonstrated by implementing a three-factor, three-level orthogonal screening of anticancer drug combinations, with which 67% of the testing (9 vs. 27) was saved. Experimental results demonstrated that the microfluidic tissue system presented herein is flexible and easy-to-use, thus providing an ideal tool for performing complex multistep cell assays with high efficiencies.

A pump-free microfluidic 3D perfusion platform for the efficient differentiation of human hepatocyte-like cells

The practical application of microfluidic liver models for in vitro drug testing is partly hampered by their reliance on human primary hepatocytes, which are limited in number and have batch-to-batch variation. Human stem cell-derived hepatocytes offer an attractive alternative cell source, although their 3D differentiation and maturation in a microfluidic platform have not yet been demonstrated. We develop a pump-free microfluidic 3D perfusion platform to achieve long-term and efficient differentiation of human liver progenitor cells into hepatocyte-like cells (HLCs). The device contains a micropillar array to immobilize cells three-dimensionally in a central cell culture compartment flanked by two side perfusion channels. Constant pump-free medium perfusion is accomplished by controlling the differential heights of horizontally orientated inlet and outlet media reservoirs. Computational fluid dynamic simulation is used to estimate the hydrostatic pressure heads required to achieve different perfusion flow rates, which are experimentally validated by micro-particle image velocimetry, as well as viability and functional assessments in a primary rat hepatocyte model. We perform on-chip differentiation of HepaRG, a human bipotent progenitor cell, and discover that 3D microperfusion greatly enhances the hepatocyte differentiation efficiency over static 2D and 3D cultures. However, HepaRG progenitor cells are highly sensitive to the time-point at which microperfusion is applied. Isolated HepaRG cells that are primed as static 3D spheroids before being subjected to microperfusion yield a significantly higher proportion of HLCs (92%) than direct microperfusion of isolated HepaRG cells (62%). This platform potentially offers a simple and efficient means to develop highly functional microfluidic liver models incorporating human stem cell-derived HLCs. Biotechnol. Bioeng. 2017;114: 2360-2370. © 2017 Wiley Periodicals, Inc.

Organ-on-a-chip for assessing environmental toxicants

Man-made xenobiotics, whose potential toxicological effects are not fully understood, are oversaturating the already-contaminated environment. Due to the rate of toxicant accumulation, unmanaged disposal, and unknown adverse effects to the environment and the human population, there is a crucial need to screen for environmental toxicants. Animal models and in vitro models are ineffective models in predicting in vivo responses due to inter-species difference and/or lack of physiologically-relevant 3D tissue environment. Such conventional screening assays possess limitations that prevent dynamic understanding of toxicants and their metabolites produced in the human body. Organ-on-a-chip systems can recapitulate in vivo like environment and subsequently in vivo like responses generating a realistic mock-up of human organs of interest, which can potentially provide human physiology-relevant models for studying environmental toxicology. Feasibility, tunability, and low-maintenance features of organ-on-chips can also make possible to construct an interconnected network of multiple-organs-on-chip toward a realistic human-on-a-chip system. Such interconnected organ-on-a-chip network can be efficiently utilized for toxicological studies by enabling the study of metabolism, collective response, and fate of toxicants through its journey in the human body. Further advancements can address the challenges of this technology, which potentiates high predictive power for environmental toxicology studies.

Human Liver Sinusoid on a Chip for Hepatitis B Virus Replication Study

We have developed a miniature human liver (liver-sinusoid-on-a-chip) model using a dual microchannel separated by a porous membrane. Primary human hepatocytes and immortalized bovine aortic endothelial cells were co-cultured on opposite sides of a microporous membrane in a dual microchannel with continuous perfusion. Primary human hepatocytes in this system retained their polygonal morphology for up to 26 days, while hepatocytes cultured in the absence of bovine aortic endothelial cells lost their morphology within a week. In order to demonstrate the utility of our human-liver-sinusoid-on-a-chip, human hepatocytes in this system were directly infected by Hepatitis B Virus (HBV). Expression of the HBV core antigen was detected in human hepatocytes in the microchannel system. HBV replication, measured by the presence of cell-secreted HBV DNA, was also detected. Importantly, HBV is hepatotropic, and expression of HBV RNA transcripts is dependent upon expression of hepatocyte-specific factors. Moreover, HBV infection requires expression of the human-hepatocyte-specific HBV cell surface receptor. Therefore, the ability to detect HBV replication and Hepatitis B core Antigen (HBcAg) expression in our microfluidic platform confirmed that hepatocyte differentiation and functions were retained throughout the time course of our studies. We believe that our human-liver-sinusoid-on-a-chip could have many applications in liver-related research and drug development.

Idiosyncratic Drug-Induced Liver Injury (IDILI): Potential Mechanisms and Predictive Assays

Idiosyncratic drug-induced liver injury (IDILI) is a significant source of drug recall and acute liver failure (ALF) in the United States. While current drug development processes emphasize general toxicity and drug metabolizing enzyme- (DME-) mediated toxicity, it has been challenging to develop comprehensive models for assessing complete idiosyncratic potential. In this review, we describe the enzymes and proteins that contain polymorphisms believed to contribute to IDILI, including ones that affect phase I and phase II metabolism, antioxidant enzymes, drug transporters, inflammation, and human leukocyte antigen (HLA). We then describe the various assays that have been developed to detect individual reactions focusing on each of the mechanisms described in the background. Finally, we examine current trends in developing comprehensive models for examining these mechanisms. There is an urgent need to develop a panel of multiparametric assays for diagnosing individual toxicity potential.

Generation of human pluripotent stem cell-derived hepatocyte-like cells for drug toxicity screening

Because drug-induced liver injury is one of the main reasons for drug development failures, it is important to perform drug toxicity screening in the early phase of pharmaceutical development. Currently, primary human hepatocytes are most widely used for the prediction of drug-induced liver injury. However, the sources of primary human hepatocytes are limited, making it difficult to supply the abundant quantities required for large-scale drug toxicity screening. Therefore, there is an urgent need for a novel unlimited, efficient, inexpensive, and predictive model which can be applied for large-scale drug toxicity screening. Human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells are able to replicate indefinitely and differentiate into most of the body's cell types, including hepatocytes. It is expected that hepatocyte-like cells generated from human ES/iPS cells (human ES/iPS-HLCs) will be a useful tool for drug toxicity screening. To apply human ES/iPS-HLCs to various applications including drug toxicity screening, homogenous and functional HLCs must be differentiated from human ES/iPS cells. In this review, we will introduce the current status of hepatocyte differentiation technology from human ES/iPS cells and a novel method to predict drug-induced liver injury using human ES/iPS-HLCs.

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.

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

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

Biology-inspired microphysiological system approaches to solve the prediction dilemma of substance testing

The recent advent of microphysiological systems - microfluidic biomimetic devices that aspire to emulate the biology of human tissues, organs and circulation in vitro - is envisaged to enable a global paradigm shift in drug development. An extraordinary US governmental initiative and various dedicated research programs in Europe and Asia have led recently to the first cutting-edge achievements of human single-organ and multi-organ engineering based on microphysiological systems. The expectation is that test systems established on this basis would model various disease stages, and predict toxicity, immunogenicity, ADME profiles and treatment efficacy prior to clinical testing. Consequently, this technology could significantly affect the way drug substances are developed in the future. Furthermore, microphysiological system-based assays may revolutionize our current global programs of prioritization of hazard characterization for any new substances to be used, for example, in agriculture, food, ecosystems or cosmetics, thus, replacing laboratory animal models used currently. Thirty-six experts from academia, industry and regulatory bodies present here the results of an intensive workshop (held in June 2015, Berlin, Germany). They review the status quo of microphysiological systems available today against industry needs, and assess the broad variety of approaches with fit-for-purpose potential in the drug development cycle. Feasible technical solutions to reach the next levels of human biology in vitro are proposed. Furthermore, key organ-on-a-chip case studies, as well as various national and international programs are highlighted. Finally, a roadmap into the future is outlined, to allow for more predictive and regulatory-accepted substance testing on a global scale.

Organ-on-a-Chip Systems: Microengineering to Biomimic Living Systems

"Organ-on-a-chip" systems integrate microengineering, microfluidic technologies, and biomimetic principles to create key aspects of living organs faithfully, including critical microarchitecture, spatiotemporal cell-cell interactions, and extracellular microenvironments. This creative platform and its multiorgan integration recapitulating organ-level structures and functions can bring unprecedented benefits to a diversity of applications, such as developing human in vitro models for healthy or diseased organs, enabling the investigation of fundamental mechanisms in disease etiology and organogenesis, benefiting drug development in toxicity screening and target discovery, and potentially serving as replacements for animal testing. Recent advances in novel designs and examples for developing organ-on-a-chip platforms are reviewed. The potential for using this emerging technology in understanding human physiology including mechanical, chemical, and electrical signals with precise spatiotemporal controls are discussed. The current challenges and future directions that need to be pursued for these proof-of-concept studies are also be highlighted.

Microtechnology-based organ systems and whole-body models for drug screening

After drug administration, the drugs are absorbed, distributed, metabolized, and excreted (ADME). Because ADME processes affect drug efficacy, various in vitro models have been developed based on the ADME processes. Although these models have been widely accepted as a tool for predicting the effects of drugs, the differences between in vivo and in vitro systems result in high attrition rates of drugs during the development process and remain a major limitation. Recent advances in microtechnology enable more accurate mimicking of the in vivo environment, where cellular behavior and physiological responses to drugs are more realistic; this has led to the development of novel in vitro systems, known as "organ-on-a-chip" systems. The development of organ-on-a-chip systems has progressed to include the reproduction of multiple organ interactions, which is an important step towards "body-on-a-chip" systems that will ultimately predict whole-body responses to drugs. In this review, we summarize the application of microtechnology for the development of in vitro systems that accurately mimic in vivo environments and reconstruct multiple organ models.

Advances and Challenges in Recapitulating Human Pulmonary Systems: At the Cusp of Biology and Materials

The aim of this review is to provide an overview of physiologically relevant microengineered lung-on-a-chip (LoC) platforms for a variety of different biomedical applications with emphasis on drug screening. First, a brief outline of lung anatomy and physiology is presented followed by discussion of the lung parenchyma and its extracellular matrix. Next, we point out the technical challenges in recapitulating the complexity of lung in conventional static two-dimensional microenvironments and the need for alternate lung platforms. The importance of scaling laws is also emphasized in designing these in vitro microengineered lung platforms. The review then discusses current LoC platforms that have been used for testing the efficacy of drugs or as model systems for investigating disorders of the lung parenchyma. Finally, the design parameters in developing an ideal physiologically relevant LoC platform are presented. As this emerging field of organ-on-a-chip can serve an alternative platform for animal testing of drugs or modeling human diseases in vitro, it has significant potential to impact the future of pharmaceutical research.

Validation of Bioreactor and Human-on-a-Chip Devices for Chemical Safety Assessment

Equipment and device qualification and test assay validation in the field of tissue engineered human organs for substance assessment remain formidable tasks with only a few successful examples so far. The hurdles seem to increase with the growing complexity of the biological systems, emulated by the respective models. Controlled single tissue or organ culture in bioreactors improves the organ-specific functions and maintains their phenotypic stability for longer periods of time. The reproducibility attained with bioreactor operations is, per se, an advantage for the validation of safety assessment. Regulatory agencies have gradually altered the validation concept from exhaustive "product" to rigorous and detailed process characterization, valuing reproducibility as a standard for validation. "Human-on-a-chip" technologies applying micro-physiological systems to the in vitro combination of miniaturized human organ equivalents into functional human micro-organisms are nowadays thought to be the most elaborate solution created to date. They target the replacement of the current most complex models-laboratory animals. Therefore, we provide here a road map towards the validation of such "human-on-a-chip" models and qualification of their respective bioreactor and microchip equipment along a path currently used for the respective animal models.

A pump-free membrane-controlled perfusion microfluidic platform

In this article, we present a microfluidic platform for passive fluid pumping for pump-free perfusion cell culture, cell-based assay, and chemical applications. By adapting the passive membrane-controlled pumping principle from the previously developed perfusion microplate, which utilizes a combination of hydrostatic pressure generated by different liquid levels in the wells and fluid wicking through narrow strips of a porous membrane connecting the wells to generate fluid flow, a series of pump-free membrane-controlled perfusion microfluidic devices was developed and their use for pump-free perfusion cell culture and cell-based assays was demonstrated. Each pump-free membrane-controlled perfusion microfluidic device comprises at least three basic components: an open well for generating fluid flow, a micron-sized deep chamber/channel for cell culture or for fluid connection, and a wettable porous membrane for controlling the fluid flow. Each component is fluidically connected either by the porous membrane or by the micron-sized deep chamber/channel. By adapting and incorporating the passive membrane-controlled pumping principle into microfluidic devices, all the benefits of microfluidic technologies, such as small sample volumes, fast and efficient fluid exchanges, and fluid properties at the micro-scale, can be fully taken advantage of with this pump-free membrane-controlled perfusion microfluidic platform.

On-chip three-dimensional cell culture in phaseguides improves hepatocyte functions in vitro

The in vitro study of liver functions and liver cell specific responses to external stimuli deals with the problem to preserve the in vivo functions of primary hepatocytes. In this study, we used the biochip OrganoPlate(TM) (MIMETAS) that combines different advantages for the cultivation of hepatocytes in vitro: (1) the perfusion flow is achieved without a pump allowing easy handling and placement in the incubator; (2) the phaseguides allow plating of matrix-embedded cells in lanes adjacent to the perfusion flow without physical barrier; and (3) the matrix-embedding ensures indirect contact of the cells to the flow. In order to evaluate the applicability of this biochip for the study of hepatocyte's functions, Matrigel(TM)-embedded HepG2 cells were cultured over three weeks in this biochip and compared to a static Matrigel culture (3D) and a monolayer culture (2D). Chip-cultured cells grew in spheroid-like structures and were characterized by the formation of bile canaliculi and a high viability over 14 days. Hepatocyte-specific physiology was achieved as determined by an increase in albumin production. Improved detoxification metabolism was demonstrated by strongly increased cytochrome P450 activity and urea production. Additionally, chip-cultured cells displayed increased sensitivity to acetaminophen. Altogether, the OrganoPlate seems to be a very useful alternative for the cultivation of hepatocytes, as their behavior was strongly improved over 2D and static 3D cultures and the results were largely comparable and partly superior to the previous reports on biochip-cultured hepatocytes. As for the low technical needs, this platform has the appearance of being highly applicable for further studies of hepatocytes' responses to external stimuli.