Advancing Tissue Culture with Light-Driven 3D-Printed Microfluidic Devices

Three-dimensional (3D) printing presents a compelling alternative for fabricating microfluidic devices, circumventing certain limitations associated with traditional soft lithography methods. Microfluidics play a crucial role in the biomedical sciences, particularly in the creation of tissue spheroids and pharmaceutical research. Among the various 3D printing techniques, light-driven methods such as stereolithography (SLA), digital light processing (DLP), and photopolymer inkjet printing have gained prominence in microfluidics due to their rapid prototyping capabilities, high-resolution printing, and low processing temperatures. This review offers a comprehensive overview of light-driven 3D printing techniques used in the fabrication of advanced microfluidic devices. It explores biomedical applications for 3D-printed microfluidics and provides insights into their potential impact and functionality within the biomedical field. We further summarize three light-driven 3D printing strategies for producing biomedical microfluidic systems: direct construction of microfluidic devices for cell culture, PDMS-based microfluidic devices for tissue engineering, and a modular SLA-printed microfluidic chip to co-culture and monitor cells.

Talin mechanotransduction in disease

Talin protein (Talin 1/2) is a mechanosensitive cytoskeleton protein. The unique structure of the Talin plays a vital role in transmitting mechanical forces. Talin proteins connect the extracellular matrix to the cytoskeleton by linking to integrins and actin, thereby mediating the conversion of mechanical signals into biochemical signals and influencing disease progression as potential diagnostic indicators, therapeutic targets, and prognostic indicators of various diseases. Most studies in recent years have confirmed that mechanical forces also have a crucial role in the development of disease, and Talin has been found to play a role in several diseases. Still, more studies need to be done on how Talin is involved in mechanical signaling in disease. This review focuses on the mechanical signaling of Talin in disease, aiming to summarize the mechanisms by which Talin plays a role in disease and to provide references for further studies.

Opportunities and considerations for studying liver disease with microphysiological systems on a chip

Advances in microsystem engineering have enabled the development of highly controlled models of the liver that better recapitulate the unique in vivo biological conditions. In just a few short years, substantial progress has been made in creating complex mono- and multi-cellular models that mimic key metabolic, structural, and oxygen gradients crucial for liver function. Here we review: 1) the state-of-the-art in liver-centric microphysiological systems and 2) the array of liver diseases and pressing biological and therapeutic challenges which could be investigated with these systems. The engineering community has unique opportunities to innovate with new liver-on-a-chip devices and partner with biomedical researchers to usher in a new era of understanding of the molecular and cellular contributors to liver diseases and identify and test rational therapeutic modalities.

Glia Maturation Factor-β Supports Liver Regeneration by Remodeling Actin Network to Enhance STAT3 Proliferative Signals

BACKGROUND & AIMS

Glia maturation factor-β (GMFB) is a bona fide member of the actin depolymerizing factor homology family. Recently, emerging evidence suggested its implication in liver diseases, but data on its role in liver remain limited.

METHODS

Assessment of GMFB in liver histology, impact on liver regeneration and hepatocyte proliferation, and the underlying molecular pathways were conducted using mouse models with acute liver injury.

RESULTS

GMFB is widely distributed in normal liver. Its expression increases within 24 hours after partial hepatectomy (PHx). Adult Gmfb knockout mice and wild-type littermates are similar in gross appearance, body weight, liver function, and histology. However, compared with wild-type control, Gmfb knockout mice post-PHx develop more serious liver damage and steatosis and have delayed liver regeneration; the dominant change in liver transcriptome at 24 hours after PHx is the significantly suppressed acute inflammation pathways; the top down-regulated gene sets relate to interleukin (IL)6/Janus kinase/signal transducer and activator of transcription 3 (STAT3) signaling. Another mouse model intoxicated with carbon tetrachloride replicated these findings. Furthermore, Gmfb knockout and wild-type groups have the similar numbers of Kupffer cells, but Gmfb knockout Kupffer cells once stimulated produce less IL6, tumor necrosis factor, and IL1β. In hepatocytes treated with IL6, GMFB associates positively with cell proliferation and STAT3/cyclin D1 activation, but without any direct interaction with STAT3. In Gmfb knockout hepatocytes, cytoskeleton-related gene expression was changed significantly, with an abnormal-appearing morphology of actin networks. In hepatocyte modeling, actin-filament turnover, STAT3 activation, and metabolite excretion show a strong reliance on the status of actin-filament organization.

CONCLUSIONS

GMFB plays a significant role in liver regeneration by promoting acute inflammatory response in Kupffer cells and by intracellularly coordinating the responsive hepatocyte proliferation.

Endocardial/endothelial angiocrines regulate cardiomyocyte development and maturation and induce features of ventricular non-compaction

AIMS

Non-compaction cardiomyopathy is a devastating genetic disease caused by insufficient consolidation of ventricular wall muscle that can result in inadequate cardiac performance. Despite being the third most common cardiomyopathy, the mechanisms underlying the disease, including the cell types involved, are poorly understood. We have previously shown that endothelial cell-specific deletion of the chromatin remodeller gene Ino80 results in defective coronary vessel development that leads to ventricular non-compaction in embryonic mouse hearts. We aimed to identify candidate angiocrines expressed by endocardial and endothelial cells (ECs) in wildtype and LVNC conditions in Tie2Cre;Ino80fl/fltransgenic embryonic mouse hearts, and test the effect of these candidates on cardiomyocyte proliferation and maturation.

METHODS AND RESULTS

We used single-cell RNA-sequencing to characterize endothelial and endocardial defects in Ino80-deficient hearts. We observed a pathological endocardial cell population in the non-compacted hearts and identified multiple dysregulated angiocrine factors that dramatically affected cardiomyocyte behaviour. We identified Col15a1 as a coronary vessel-secreted angiocrine factor, downregulated by Ino80-deficiency, that functioned to promote cardiomyocyte proliferation. Furthermore, mutant endocardial and endothelial cells up-regulated expression of secreted factors, such as Tgfbi, Igfbp3, Isg15, and Adm, which decreased cardiomyocyte proliferation and increased maturation.

CONCLUSIONS

These findings support a model where coronary endothelial cells normally promote myocardial compaction through secreted factors, but that endocardial and endothelial cells can secrete factors that contribute to non-compaction under pathological conditions.

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.

Microfluidic organ-on-a-chip models of human liver tissue

The liver is the largest internal organ of the body with complex microarchitecture and function that plays critical roles in drug metabolism. Hepatotoxicity and drug-induced liver injury (DILI) caused by various drugs is the main reason for late-stage drug failures. Moreover, liver diseases are among the leading causes of death in the world, with the number of new cases arising each year. Although animal models have been used to understand human drug metabolism and toxicity before clinical trials, tridimensional microphysiological systems, such as liver-on-a-chip (Liver Chip) platforms, could better recapitulate features of human liver physiology and pathophysiology and thus, are often more predictive of human outcome. Liver Chip devices have shown promising results in mimicking in vivo condition by recapitulating the sinusoidal structure of the liver, maintaining high cell viability and cellular phenotypes, and emulating native liver functions. Here, we first review the cellular constituents and physiology of the liver and then critically discuss the state-of-the-art chip-based liver models and their applications in drug screening, disease modeling, and regenerative medicine. We finally address the pending issues of existing platforms and touch upon future directions for developing new, advanced on-chip models.

Hepatic Polarization Accelerated by Mechanical Compaction Involves HNF4α Activation

There remain few data about the role of homeostatic compaction in hepatic polarization. A previous study has found that mechanical compaction can accelerate hepatocyte polarization; however, the cellular mechanism underlying the effect is mostly unclear. Hepatocyte nuclear factor 4 alpha (HNF4α) is crucial for hepatic polarization in liver morphogenesis. Therefore, we sought to identify any possible involvement of HNF4α in the process of hepatocyte polarization accelerated by mechanical compaction. We first verified in the nonhepatic cell model HEK-293T, and the hepatic cell model primary hepatocytes that the mechanical compaction on cell aggregates simulated by using transient centrifugation can directly activate the expression of HNF4α promoters. Moreover, data using primary hepatocytes showed that the HNF4α expression is positively associated with the levels of compaction force: 2.1-folds higher at the mRNA level and 2.1-folds higher at the protein level for 500 g vs. 0 g. Furthermore, activated HNF4α expression is associated with the enhanced biliary canalicular formation and the increased production of albumin and urea. Pretreatment with Latrunculin B, an inhibitor of F-actin, and SHE78-7, an inhibitor of E-cadherin, which both interrupt the pathway of mechanical transduction, partially but significantly reduced the HNF4α expression and production of albumin and urea. In conclusion, HNF4α can be actively involved in the hepatic polarization in the context of environmental mechanical compaction.

Quantitative Image-Based Cell Viability (QuantICV) Assay for Microfluidic 3D Tissue Culture Applications

Microfluidic 3D tissue culture systems are attractive for in vitro drug testing applications due to the ability of these platforms to generate 3D tissue models and perform drug testing at a very small scale. However, the minute cell number and liquid volume impose significant technical challenges to perform quantitative cell viability measurements using conventional colorimetric or fluorometric assays, such as MTS or Alamar Blue. Similarly, live-dead staining approaches often utilize metabolic dyes that typically label the cytoplasm of live cells, which makes it difficult to segment and count individual cells in compact 3D tissue cultures. In this paper, we present a quantitative image-based cell viability (QuantICV) assay technique that circumvents current challenges of performing the quantitative cell viability assay in microfluidic 3D tissue cultures. A pair of cell-impermeant nuclear dyes (EthD-1 and DAPI) were used to sequentially label the nuclei of necrotic and total cell populations, respectively. Confocal microscopy and image processing algorithms were employed to visualize and quantify the cell nuclei in the 3D tissue volume. The QuantICV assay was validated and showed good concordance with the conventional bulk MTS assay in static 2D and 3D tumor cell cultures. Finally, the QuantICV assay was employed as an on-chip readout to determine the differential dose responses of parental and metastatic 3D oral squamous cell carcinoma (OSCC) to Gefitinib in a microfluidic 3D culture device. This proposed technique can be useful in microfluidic cell cultures as well as in a situation where conventional cell viability assays are not available.

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.

Liver microsystems in vitro for drug response

Engineering approaches were adopted for liver microsystems to recapitulate cell arrangements and culture microenvironments in vivo for sensitive, high-throughput and biomimetic drug screening. This review introduces liver microsystems in vitro for drug hepatotoxicity, drug-drug interactions, metabolic function and enzyme induction, based on cell micropatterning, hydrogel biofabrication and microfluidic perfusion. The engineered microsystems provide varied microenvironments for cell culture that feature cell coculture with non-parenchymal cells, in a heterogeneous extracellular matrix and under controllable perfusion. The engineering methods described include cell micropatterning with soft lithography and dielectrophoresis, hydrogel biofabrication with photolithography, micromolding and 3D bioprinting, and microfluidic perfusion with endothelial-like structures and gradient generators. We discuss the major challenges and trends of liver microsystems to study drug response in vitro.

From a common progenitor to distinct liver epithelial phenotypes

The vertebrate liver presents a fascinating case study for how cell form is optimized for function. To execute its duties the liver assembles two distinct lumen-forming epithelial phenotypes: Firstly, cords with a branched, capillary-like luminal network formed between hepatocytes (bile canaliculi); and secondly, tubular ducts formed by biliary epithelial cells arranged around a central cavity and connected to the bile canaliculi. How these remarkably different epithelial polarity phenotypes are generated and joined into a contiguous luminal network are major unresolved questions. Recent studies have characterized the divergence of the two epithelial lineages from common progenitors, described the coordination of bile canaliculi formation with bile duct branching during biliary tree morphogenesis and implicated RhoA-dependent E-cadherin adhesion in the decision to polarize with hepatocytic or biliary phenotype.

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.

A vertical-flow bioreactor array compacts hepatocytes for enhanced polarity and functions

Although hepatocytes in vivo experience intra-abdominal pressure (IAP), pressure is typically not incorporated in hepatocyte culture systems. The cuboidal cell shape and extent of intercellular contact between cultured hepatocytes are critical parameters that influence the differentiated hepatic phenotype. Using a microfluidic device, the application of pressure to artificially compact cells and forge cell-cell interactions was previously demonstrated to be effective in accelerating hepatic repolarization. In seeking to implement this approach to higher throughput culture platforms for potential drug screening applications, we specifically designed a vertical-flow compaction bioreactor array (VCBA) that compacts hepatocytes within the range of IAP and portal pressure in vivo in a multi-well setup. As a result of vertical perfusion-generated forces, hepatocytes not only exhibited accelerated repolarization, an in vivo-like cuboidal morphology, but also better maintained hepatic functions in long-term culture as compared to the same cells cultured under static conditions. As a novel engineering tool to modulate cell compaction and intercellular interactions, this platform is a promising approach to confer tight control over hepatocyte repolarization for in vitro culture.

Interactions of Hepatitis B Virus Infection with Nonalcoholic Fatty Liver Disease: Possible Mechanisms and Clinical Impact

Hepatitis B virus (HBV) infection is a major etiology of chronic liver disease worldwide. In the past decade, nonalcoholic fatty liver disease (NAFLD) has emerged as a common liver disorder in general population. Accordingly, the patient number of chronic hepatitis B (CHB) concomitant with NAFLD grows rapidly. The present article reviewed the recent studies aiming to explore the relationship between CHB and NAFLD from different aspects, including the relevant pathogenesis of CHB and NAFLD, the intracellular molecular mechanisms overlaying HBV infection and hepatic steatosis, and the observational studies with animal models and clinical cohorts for analyzing the coincidence of the two diseases. It is concluded that although numerous cross-links have been suggested between the molecular pathways in HBV infection and NAFLD pathogenesis, regarding whether HBV infection can substantially interfere with the occurrence of NAFLD or vice versa in the patients, there is still far from a conclusive agreement.

Engineering liver

Interest in "engineering liver" arises from multiple communities: therapeutic replacement; mechanistic models of human processes; and drug safety and efficacy studies. An explosion of micro- and nanofabrication, biomaterials, microfluidic, and other technologies potentially affords unprecedented opportunity to create microphysiological models of the human liver, but engineering design principles for how to deploy these tools effectively toward specific applications, including how to define the essential constraints of any given application (available sources of cells, acceptable cost, and user-friendliness), are still emerging. Arguably less appreciated is the parallel growth in computational systems biology approaches toward these same problems-particularly in parsing complex disease processes from clinical material, building models of response networks, and in how to interpret the growing compendium of data on drug efficacy and toxicology in patient populations. Here, we provide insight into how the complementary paths of engineering liver-experimental and computational-are beginning to interplay toward greater illumination of human disease states and technologies for drug development.

Bioreactor technologies to support liver function in vitro

Liver is a central nexus integrating metabolic and immunologic homeostasis in the human body, and the direct or indirect target of most molecular therapeutics. A wide spectrum of therapeutic and technological needs drives efforts to capture liver physiology and pathophysiology in vitro, ranging from prediction of metabolism and toxicity of small molecule drugs, to understanding off-target effects of proteins, nucleic acid therapies, and targeted therapeutics, to serving as disease models for drug development. Here we provide perspective on the evolving landscape of bioreactor-based models to meet old and new challenges in drug discovery and development, emphasizing design challenges in maintaining long-term liver-specific function and how emerging technologies in biomaterials and microdevices are providing new experimental models.

Accelerating drug discovery via organs-on-chips

Considerable advances have been made in the development of micro-physiological systems that seek to faithfully replicate the complexity and functionality of animal and human physiology in research laboratories. Sometimes referred to as "organs-on-chips", these systems provide key insights into physiological or pathological processes associated with health maintenance and disease control, and serve as powerful platforms for new drug development and toxicity screening. In this Focus article, we review the state-of-the-art designs and examples for developing multiple "organs-on-chips", and discuss the potential of this emerging technology to enhance our understanding of human physiology, and to transform and accelerate the drug discovery and preclinical testing process. This Focus article highlights some of the recent technological advances in this field, along with the challenges that must be addressed for these technologies to fully realize their potential.