A Human Liver-on-a-Chip Platform for Modeling Nonalcoholic Fatty Liver Disease

The effects of simvastatin-loaded nanoliposomes on human multilineage liver fibrosis microtissue

In this in vitro study, for the first time, we evaluate the effects of simvastatin-loaded liposome nanoparticles (SIM-LipoNPs) treatment on fibrosis-induced liver microtissues, as simvastatin (SIM) has shown potential benefits in the non-alcoholic fatty liver disease process. We developed multicellular liver microtissues composed of hepatic stellate cells, hepatoblastoma cells and human umbilical vein endothelial cells. The microtissues were supplemented with a combination of palmitic acid and oleic acid to develop fibrosis models. Subsequently, various groups of microtissues were exposed to SIM and SIM-LipoNPs at doses of 5 and 10 mg/mL. The effectiveness of the treatments was evaluated by analysing cell viability, production of reactive oxygen species (ROS) and nitric oxide (NO), the expression of Kruppel-like factor (KLF) 2, and pro-inflammatory cytokines (interleukin(IL)-1 α, IL-1 β, IL-6 and tumour necrosis factor-α), and the expression of collagen I. Our results indicated that SIM-LipoNPs application showed promising results. SIM-LipoNPs effectively amplified the SIM-klf2-NO pathway at a lower dosage compatible with a high dosage of free SIM, which also led to reduced oxidative stress by decreasing ROS levels. SIM-LipoNPs administration also resulted in a significant reduction in pro-inflammatory cytokines and Collagen I mRNA levels, as a marker of fibrosis. In conclusion, our study highlights the considerable therapeutic potential of using SIM-LipoNPs to prevent liver fibrosis progress, underscoring the remarkable properties of SIM-LipoNPs in activating the KLF2-NO pathway and anti-oxidative and anti-inflammatory response.

Biomimetic microfluidic chips for toxicity assessment of environmental pollutants

Various types of pollutants widely present in environmental media, including synthetic and natural chemicals, physical pollutants such as radioactive substances, ultraviolet rays, and noise, as well as biological organisms, pose a huge threat to public health. Therefore, it is crucial to accurately and effectively explore the human physiological responses and toxicity mechanisms of pollutants to prevent diseases caused by pollutants. The emerging toxicological testing method biomimetic microfluidic chips (BMCs) exhibit great potential in environmental pollutant toxicity assessment due to their superior biomimetic properties. The BMCs are divided into cell-on-chips and organ-on-chips based on the distinctions in bionic simulation levels. Herein, we first summarize the characteristics, emergence and development history, composition and structure, and application fields of BMCs. Then, with a focus on the toxicity mechanisms of pollutants, we review the applications and advances of the BMCs in the toxicity assessment of physical, chemical, and biological pollutants, respectively, highlighting its potential and development prospects in environmental toxicology testing. Finally, the opportunities and challenges for further use of BMCs are discussed.

Bioengineering scalable and drug-responsive in vitro human multicellular non-alcoholic fatty liver disease microtissues encapsulated in the liver extracellular matrix-derived hydrogel

Non-alcoholic fatty liver disease (NAFLD) is a high-prevalence and progressive disorder. Due to lack of reliable in vitro models to recapitulate the consecutive phases, the exact pathogenesis mechanism of this disease and approved therapeutic medications have not been revealed yet. It has been proven that the interplay between multiple hepatic cell types and liver extracellular matrix (ECM) are critical in NAFLD initiation and progression. Herein, a liver microtissue (LMT) consisting of Huh-7, THP-1, and LX-2 cell lines and human umbilical vein endothelial cells (HUVEC), which could be substituted for the main hepatic cells (hepatocyte, Kupffer, stellate, and sinusoidal endothelium, respectively), encapsulated in liver derived ECM-Alginate composite, was bioengineered. When the microtissues were treated with free fatty acids (FFAs) including Oleic acid (6.6×10-4M) and Palmitic acid (3.3×10-4M), they displayed the key features of NAFLD, including similar pattern of transcripts for genes involved in lipid metabolism, inflammation, insulin-resistance, and fibrosis, as well as pro-inflammatory and pro-fibrotic cytokines' secretions and intracellular lipid accumulation. Continuing FFAs supplementation, we demonstrated that the NAFLD phenomenon was established on day 3 and progressed to the initial fibrosis stage by day 8. Furthermore, this model was stable until day 12 post FFAs withdrawal on day 3. Moreover, administration of an anti-steatotic drug candidate, Liraglutide (15 μM), on the NAFLD microtissues significantly ameliorated the NAFLD phenomenon. Overall, we bioengineered a drug-responsive, cost-benefit liver microtissues which can simulate the initiation and progression of NAFLD. It is expected that this platform could potentially be used for studying molecular pathogenesis of NAFLD and high-throughput drug screening. See also the graphical abstract(Fig. 1).

The Effect of Mesenchymal Stem Cell-Derived Exosomes and miR17-5p Inhibitor on Multicellular Liver Fibrosis Microtissues

Background

Although several studies have been conducted on modeling human liver disease, it is still challenging to mimic nonalcoholic fatty liver disease in vitro. Here, we aimed to develop a fibrotic liver microtissue composed of hepatocytes, hepatic stellate, and endothelial cells. In addition, the therapeutic effects of umbilical cord mesenchymal stem cell-derived exosomes (UC-MSC-EXO) and anti-miR17-5p as new antifibrotic drugs were investigated.

Methods

To create an effective preclinical fibrosis model, multicellular liver microtissues (MLMs) consisting of HepG2, LX2, and HUVECs were cultured and supplemented with a mixture of palmitic acid and oleic acid for 96 hr. Then, MLMs were exposed to UC-MSC-EXO and anti-miR17-5p in different groups. The results of cell viability, reactive oxygen species (ROS) production, liver enzyme levels, inflammation, and histopathology were analyzed to assess the treatment efficacy. Furthermore, the expression of collagen I (COL I) and α-smooth muscle actin (α-SMA) as critical matrix components, transforming growth factor beta (TGF-β), and miR-17-5p were measured.

Results

Free fatty acid supplementation causes fibrosis in MLMs. Our results demonstrated that UC-MSC-EXO and anti-miR17-5p attenuated TGF-β1, interleukin-1β, and interleukin-6 in all experimental groups. According to the suppression of the TGF-β1 pathway, LX2 activation was inhibited, reducing extracellular matrix proteins, including COL I and α-SMA. Also, miR-17-5p expression was elevated in fibrosis conditions. Furthermore, we showed that our treatments decreased alanine aminotransferase and aspartate aminotransferase, and increased albumin levels in the culture supernatant. We also found that both MSC-EXO and MSC-EXO + anti-miR17-5p treatments could reduce ROS production.

Conclusion

Our findings indicated that anti-miR17-5p and MSC-EXO might be promising therapeutic options for treating liver fibrosis. Furthermore, EXO + anti-miR had the best effects on boosting the fibrotic markers. Therefore, we propose this novel MLM model to understand fibrosis mechanisms better and develop new drugs.

NAFLD-Related HCC: Focus on the Latest Relevant Preclinical Models

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer and one of the deadliest cancers worldwide. Despite extensive research, the biological mechanisms underlying HCC's development and progression remain only partially understood. Chronic overeating and/or sedentary-lifestyle-associated obesity, which promote Non-Alcoholic Fatty Liver Disease (NAFLD), have recently emerged as worrying risk factors for HCC. NAFLD is characterized by excessive hepatocellular lipid accumulation (steatosis) and affects one quarter of the world's population. Steatosis progresses in the more severe inflammatory form, Non-Alcoholic Steatohepatitis (NASH), potentially leading to HCC. The incidence of NASH is expected to increase by up to 56% over the next 10 years. Better diagnoses and the establishment of effective treatments for NAFLD and HCC will require improvements in our understanding of the fundamental mechanisms of the disease's development. This review describes the pathogenesis of NAFLD and the mechanisms underlying the transition from NAFL/NASH to HCC. We also discuss a selection of appropriate preclinical models of NAFLD for research, from cellular models such as liver-on-a-chip models to in vivo models, focusing particularly on mouse models of dietary NAFLD-HCC.

The Growing Importance of Three-Dimensional Models and Microphysiological Systems in the Assessment of Mycotoxin Toxicity

Current investigations in the field of toxicology mostly rely on 2D cell cultures and animal models. Although well-accepted, the traditional 2D cell-culture approach has evident drawbacks and is distant from the in vivo microenvironment. To overcome these limitations, increasing efforts have been made in the development of alternative models that can better recapitulate the in vivo architecture of tissues and organs. Even though the use of 3D cultures is gaining popularity, there are still open questions on their robustness and standardization. In this review, we discuss the current spheroid culture and organ-on-a-chip techniques as well as the main conceptual and technical considerations for the correct establishment of such models. For each system, the toxicological functional assays are then discussed, highlighting their major advantages, disadvantages, and limitations. Finally, a focus on the applications of 3D cell culture for mycotoxin toxicity assessments is provided. Given the known difficulties in defining the safety ranges of exposure for regulatory agency policies, we are confident that the application of alternative methods may greatly improve the overall risk assessment.

Bioengineering liver microtissues for modeling non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) has become the world's most common chronic liver disease. However, due to the lack of reliable in vitro NAFLD models, drug development studies have faced many limitations, and there is no food and drug administration-approved medicine for NAFLD treatment. A functional biomimetic in vitro human liver model requires an optimized natural microenvironment using appropriate cellular composition, to provide constructive cell-cell interactions, and niche-specific bio-molecules to supply crucial cues as cell-matrix interplay. Such a suitable liver model could employ appropriate and desired biochemical, mechanical, and physical properties similar to native tissue. Moreover, bioengineered three-dimensional tissues, specially microtissues and organoids, and more recently using infusion-based cultivation systems such as microfluidics can mimic natural tissue conditions and facilitate the exchange of nutrients and soluble factors to improve physiological function in the in vitro generated constructs. This review highlights the key players involved in NAFLD initiation and progression and discussed the available cells and matrices for in vitro NAFLD modeling. The strategies for optimizing the liver microenvironment to generate a powerful and biomimetic in vitro NAFLD model were described as well. Finally, the current challenges and future perospective for promotion in this subject were discussed.

Spheroid Engineering in Microfluidic Devices

Two-dimensional (2D) cell culture techniques are commonly employed to investigate biophysical and biochemical cellular responses. However, these culture methods, having monolayer cells, lack cell-cell and cell-extracellular matrix interactions, mimicking the cell microenvironment and multicellular organization. Three-dimensional (3D) cell culture methods enable equal transportation of nutrients, gas, and growth factors among cells and their microenvironment. Therefore, 3D cultures show similar cell proliferation, apoptosis, and differentiation properties to in vivo. A spheroid is defined as self-assembled 3D cell aggregates, and it closely mimics a cell microenvironment in vitro thanks to cell-cell/matrix interactions, which enables its use in several important applications in medical and clinical research. To fabricate a spheroid, conventional methods such as liquid overlay, hanging drop, and so forth are available. However, these labor-intensive methods result in low-throughput fabrication and uncontrollable spheroid sizes. On the other hand, microfluidic methods enable inexpensive and rapid fabrication of spheroids with high precision. Furthermore, fabricated spheroids can also be cultured in microfluidic devices for controllable cell perfusion, simulation of fluid shear effects, and mimicking of the microenvironment-like in vivo conditions. This review focuses on recent microfluidic spheroid fabrication techniques and also organ-on-a-chip applications of spheroids, which are used in different disease modeling and drug development studies.

Design and engineering of organ-on-a-chip

Organ-on-a-chip (OOC) is an emerging interdisciplinary technology that reconstitutes the structure, function, and physiology of human tissues as an alternative to conventional preclinical models for drug screening. Over the last decade, substantial progress has been made in mimicking tissue- and organ-level functions on chips through technical advances in biomaterials, stem cell engineering, microengineering, and microfluidic technologies. Structural and engineering constituents, as well as biological components, are critical factors to be considered to reconstitute the tissue function and microenvironment on chips. In this review, we highlight critical engineering technologies for reconstructing the tissue microarchitecture and dynamic spatiotemporal microenvironment in OOCs. We review the technological advances in the field of OOCs for a range of applications, including systemic analysis tools that can be integrated with OOCs, multiorgan-on-chips, and large-scale manufacturing. We then discuss the challenges and future directions for the development of advanced end-user-friendly OOC systems for a wide range of applications.

Critical design parameters to develop biomimetic organ-on-a-chip models for the evaluation of the safety and efficacy of nanoparticles

INTRODUCTION

Organ-on-a-chip (OOC) models are based on microfluidics and can recapitulate the healthy and diseased microstructure of organs¹ and tissues and the dynamic microenvironment inside the human body. However, the use of OOC models to evaluate the safety and efficacy of nanoparticles (NPs) is still in the early stages.

AREAS COVERED

The different design parameters of the microfluidic chip and the mechanical forces generated by fluid flow play a pivotal role in simulating the human environment. This review discusses the role of different key parameters on the performance of OOC models. These include the flow pattern, flow rate, shear stress (magnitude, rate, and distribution), viscosity of the media, and the microchannel dimensions and shape. We also discuss how the shear stress and other mechanical forces affect the transport of NPs across biological barriers, cell uptake, and their biocompatibility.

EXPERT OPINION

We describe several good practices and design parameters to consider for future OOC research. We submit that following these recommendations will help realize the full potential of the OOC models in the preclinical evaluation of novel therapies, including NPs.

Engineered Biomimetic Membranes for Organ-on-a-Chip

Organ-on-a-chip (OOC) systems are engineered nanobiosystems to mimic the physiochemical environment of a specific organ in the body. Among various components of OOC systems, biomimetic membranes have been regarded as one of the most important key components to develop controllable biomimetic bioanalysis systems. Here, we review the preparation and characterization of biomimetic membranes in comparison with the features of the extracellular matrix. After that, we review and discuss the latest applications of engineered biomimetic membranes to fabricate various organs on a chip, such as liver, kidney, intestine, lung, skin, heart, vasculature and blood vessels, brain, and multiorgans with perspectives for further biomedical applications.

State-of-the-art liver disease research using liver-on-a-chip

To understand disease pathophysiologies, models that recapitulate human functions are necessary. In vitro models that consist of human cells are preferred to ones using animal cells, because organ functions can vary from species to species. However, conventional in vitro models do not recapitulate human organ functions well. Organ-on-a-chip technology provides a reliable in vitro model of the functional units of human organs. Organ-on-a-chip technology uses microfluidic devices and their accessories to impart organ functions to human cells. Using microfluidic devices, we can co-culture multiple cell types that compose human organs. Moreover, we can culture human cells under physiologically relevant stresses, such as mechanical and shear stresses. Current organ-on-a-chip technology can reproduce the functions of several organs including the liver. Because it is difficult to maintain the function of human hepatocytes, which are the gold standard of in vitro liver models, under conventional culture conditions, the application of liver-on-a-chips to liver disease research is expected. This review introduces the current status and future prospects of liver-on-a-chips in liver disease research.

Toward 3D-Bioprinted Models of the Liver to Boost Drug Development

The main problems in drug development are connected to enormous costs related to the paltry success rate. The current situation empowered the development of high-throughput and reliable instruments, in addition to the current golden standards, able to predict the failures in the early preclinical phase. Being hepatotoxicity responsible for the failure of 30% of clinical trials, and the 21% of withdrawal of marketed drugs, the development of complex in vitro models (CIVMs) of liver is currently one of the hottest topics in the field. Among the different fabrication techniques, 3D-bioprinting is emerging as a powerful ally for their production, allowing the manufacture of three-dimensional constructs characterized by computer-controlled and customized geometry, and inter-batches reproducibility. Thanks to these, it is possible to rapidly produce tailored cell-laden constructs, to be cultured within static and dynamic systems, thus reaching a further degree of personalization when designing in vitro models. This review highlights and prioritizes the most recent advances related to the development of CIVMs of the hepatic environment to be specifically applied to pharmaceutical research, with a special focus on 3D-bioprinting, since the liver is primarily involved in the metabolism of drugs.

An in vitro fibrotic liver lobule model through sequential cell-seeding of HSCs and HepG2 on 3D-printed poly(glycerol sebacate) acrylate scaffolds

Cirrhosis is a major cause of global morbidity and mortality, and significantly leads to a heightened risk of liver cancer. Despite decades of efforts in seeking for cures for cirrhosis, this disease remains irreversible. To assist in the advancement of understanding toward cirrhosis as well as therapeutic options, various disease models, each with different strengths, are developed. With the development of three-dimensional (3D) cell culture in recent years, more realistic biochemical properties are observed in 3D cell models, which have gradually taken over the responsibilities of traditional 2D cell culture, and are expected to replace some of the animal models in the near future. Here, we propose a 3D fibrotic liver model inspired by liver lobules. In the model, 3D-printed poly(glycerol sebacate) acrylate (PGSA) scaffolds facilitated the formation of 3D tissues and guided the deposition of fibrotic structures. Through the sequential seeding of hepatic stellate cells (HSCs), HepG2 and HSCs, fibrotic septum-like tissues were created on PGSA scaffolds. As albumin secretion is considered a rather important function of the liver and is found only among hepatic cells, the detection of albumin secretion up to 30 days indicates the mimicking of basic liver functions. Moreover, the in vivo fibrotic tissue shows a high similarity to fibrotic septa. Finally, via complete encapsulation of HSCs, a down-regulated albumin secretion profile was observed in the capped model, which is a metabolic indicator that is important for the prognosis for liver cirrhosis. Looking forward, the incorporation of the vasculature will further upgrade the model into a sound tool for liver research and associated treatments.

Biomedical Applications of Microfluidic Devices: A Review

Both passive and active microfluidic chips are used in many biomedical and chemical applications to support fluid mixing, particle manipulations, and signal detection. Passive microfluidic devices are geometry-dependent, and their uses are rather limited. Active microfluidic devices include sensors or detectors that transduce chemical, biological, and physical changes into electrical or optical signals. Also, they are transduction devices that detect biological and chemical changes in biomedical applications, and they are highly versatile microfluidic tools for disease diagnosis and organ modeling. This review provides a comprehensive overview of the significant advances that have been made in the development of microfluidics devices. We will discuss the function of microfluidic devices as micromixers or as sorters of cells and substances (e.g., microfiltration, flow or displacement, and trapping). Microfluidic devices are fabricated using a range of techniques, including molding, etching, three-dimensional printing, and nanofabrication. Their broad utility lies in the detection of diagnostic biomarkers and organ-on-chip approaches that permit disease modeling in cancer, as well as uses in neurological, cardiovascular, hepatic, and pulmonary diseases. Biosensor applications allow for point-of-care testing, using assays based on enzymes, nanozymes, antibodies, or nucleic acids (DNA or RNA). An anticipated development in the field includes the optimization of techniques for the fabrication of microfluidic devices using biocompatible materials. These developments will increase biomedical versatility, reduce diagnostic costs, and accelerate diagnosis time of microfluidics technology.

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.

Constructing biomimetic liver models through biomaterials and vasculature engineering

The occurrence of various liver diseases can lead to organ failure of the liver, which is one of the leading causes of mortality worldwide. Liver tissue engineering see the potential for replacing liver transplantation and drug toxicity studies facing donor shortages. The basic elements in liver tissue engineering are cells and biomaterials. Both mature hepatocytes and differentiated stem cells can be used as the main source of cells to construct spheroids and organoids, achieving improved cell function. To mimic the extracellular matrix (ECM) environment, biomaterials need to be biocompatible and bioactive, which also help support cell proliferation and differentiation and allow ECM deposition and vascularized structures formation. In addition, advanced manufacturing approaches are required to construct the extracellular microenvironment, and it has been proved that the structured three-dimensional culture system can help to improve the activity of hepatocytes and the characterization of specific proteins. In summary, we review biomaterials for liver tissue engineering, including natural hydrogels and synthetic polymers, and advanced processing techniques for building vascularized microenvironments, including bioassembly, bioprinting and microfluidic methods. We then summarize the application fields including transplant and regeneration, disease models and drug cytotoxicity analysis. In the end, we put the challenges and prospects of vascularized liver tissue engineering.

Development of an in vitro insulin resistance dissociated model of hepatic steatosis by co-culture system

The evidence shows that there is an associated relationship between hepatosteatosis and insulin resistance. While some existing genetic induction animal and patient models challenge this relationship, indicating that hepatosteatosis is dissociated from insulin resistance. However, the molecular mechanisms of this dissociation remain poorly understood due to a lack of available, reliable, and simplistic setup models. Currently, we used primary rat hepatocytes (rHPCs), co-cultured with rat hepatic stellate cells (HSC-T6) or human foreskin fibroblast cells (HFF-1) in stimulation with high insulin and glucose, to develop a model of steatosis charactered as dissociated lipid accumulation from insulin resistance. Oil-Red staining significantly showed intracellular lipid accumulated in the developed model. Gene expression of sterol regulatory element-binding protein 1c (SREBP1c) and elongase of very-long-chain fatty acids 6 (ELOVL6), key genes responsible for lipogenesis, were detected and obviously increased in this model. Inversely, the insulin resistance related genes expression included phosphoenolpyruvate carboxykinase 1 (PCK1), pyruvate dehydrogenase lipoamide kinase isozyme 4 (PDK4), and glucose-6-phosphatase (G6pase) were decreased, suggesting a dissociation relationship between steatosis and insulin resistance in the developed model. As well, the drug metabolism of this developed model was investigated and showed up-regulation of cytochrome P450 3A (CYP3A) and down-regulation of cytochrome P450 2E1 (CYP2E1) and cytochrome P450 1A2 (CYP1A2). Taken together, those results demonstrate that the in vitro model of dissociated steatosis from insulin resistance was successfully created by our co-cultured cells in high insulin and glucose medium, which will be a potential model for investigating the mechanism of insulin resistance dissociated steatosis, and discovering a novel drug for its treatment.

Controlled fabrication of functional liver spheroids with microfluidic flow cytometric printing

Multicellular liver spheroids are 3D culture models useful in the development of therapies for liver fibrosis. While these models can recapitulate fibrotic disease, current methods for generating them via random aggregation are uncontrolled, yielding spheroids of variable size, function, and utility. Here, we report fabrication of precision liver spheroids with microfluidic flow cytometric printing. Our approach fabricates spheroids cell-by-cell, yielding structures with exact numbers of different cell types. Because spheroid function depends on composition, our precision spheroids have superior functional uniformity, allowing more accurate and statistically significant screens compared to randomly generated spheroids. The approach produces thousands of spheroids per hour, and thus affords a scalable platform by which to manufacture single-cell precision spheroids for disease modeling and high throughput drug testing.

Tissue Engineering Approaches to Uncover Therapeutic Targets for Endothelial Dysfunction in Pathological Microenvironments

Endothelial cell dysfunction plays a central role in many pathologies, rendering it crucial to understand the underlying mechanism for potential therapeutics. Tissue engineering offers opportunities for in vitro studies of endothelial dysfunction in pathological mimicry environments. Here, we begin by analyzing hydrogel biomaterials as a platform for understanding the roles of the extracellular matrix and hypoxia in vascular formation. We next examine how three-dimensional bioprinting has been applied to recapitulate healthy and diseased tissue constructs in a highly controllable and patient-specific manner. Similarly, studies have utilized organs-on-a-chip technology to understand endothelial dysfunction's contribution to pathologies in tissue-specific cellular components under well-controlled physicochemical cues. Finally, we consider studies using the in vitro construction of multicellular blood vessels, termed tissue-engineered blood vessels, and the spontaneous assembly of microvascular networks in organoids to delineate pathological endothelial dysfunction.

Gut-liver-axis microphysiological system for studying cellular fluidic shear stress and inter-tissue interaction

To clarify the physiological and pathological roles of gut-liver-axis (GLA) in the human body, a GLA microphysiological system (GLA-MPS) holds great potential. However, in current GLA-MPSs, the importance of a physiologically relevant flow for gut and liver cells' cultivation is not fully addressed. In addition, the integration of individual organ perfusion, circulation flow, and organ tissue functions in a single device has not been achieved. Here, we introduce a GLA-MPS by integrating two cell-culture chambers with individually applied perfusion flows and a circulation channel with an on-chip pneumatic micropump under cell-culture chambers via a porous membrane for interconnecting them. We analyzed the fluid shear stress (FSS) with computational fluid dynamics simulations and confirmed that the physiologically relevant FSS could be applied to the gut (Caco-2) (8 × 10-3 dyn cm-2) and liver (HepG2) cells (1.2 × 10-7 dyn cm-2). Under the physiologically relevant flow, the Caco-2 and HepG2 cells in the GLA-MPS maintained a cell survival rate of 95% and 92%, respectively. Furthermore, the expression of functional proteins such as zonula occludens 1 (in Caco-2) and albumin (in HepG2) was enhanced. To demonstrate the GLA interaction, the inflammatory bowel disease was recapitulated by applying lipopolysaccharide for only Caco-2 cells. The inflammatory proteins, such as inducible nitric oxide synthase, were induced in Caco-2 and HepG2 cells. The presented GLA-MPS can be adapted as an advanced in vitro model in various applications for disease modeling associated with inter-tissue interactions, such as inflammatory disease.

A cryopreservation method for bioengineered 3D cell culture models

Technologies to cryogenically preserve (a.k.a. cryopreserve) living tissue, cell lines and primary cells have matured greatly for both clinicians and researchers since their first demonstration in the 1950s and are widely used in storage and transport applications. Currently, however, there remains an absence of viable cryopreservation and thawing methods for bioengineered, three-dimensional (3D) cell models, including patients' samples. As a first step towards addressing this gap, we demonstrate a viable protocol for spheroid cryopreservation and survival based on a 3D carboxymethyl cellulose scaffold and precise conditions for freezing and thawing. The protocol is tested using hepatocytes, for which the scaffold provides both the 3D structure for cells to self-arrange into spheroids and to support cells during freezing for optimal post-thaw viability. Cell viability after thawing is improved compared to conventional pellet models where cells settle under gravity to form a pseudo-tissue before freezing. The technique may advance cryobiology and other applications that demand high-integrity transport of pre-assembled 3D models (from cell lines and in future cells from patients) between facilities, for example between medical practice, research and testing facilities.

Selection of natural biomaterials for micro-tissue and organ-on-chip models

The desired organ in micro-tissue models of organ-on-a-chip (OoC) devices dictates the optimum biomaterials, divided into natural and synthetic biomaterials. They can resemble biological tissues' biological functions and architectures by constructing bioactivity of macromolecules, cells, nanoparticles, and other biological agents. The inclusion of such components in OoCs allows them having biological processes, such as basic biorecognition, enzymatic cleavage, and regulated drug release. In this report, we review natural-based biomaterials that are used in OoCs and their main characteristics. We address the preparation, modification, and characterization methods of natural-based biomaterials and summarize recent reports on their applications in the design and fabrication of micro-tissue models. This article will help bioengineers select the proper biomaterials based on developing new technologies to meet clinical expectations and improve patient outcomes fusing disease modeling.

Livogrit Prevents Methionine-Cystine Deficiency Induced Nonalcoholic Steatohepatitis by Modulation of Steatosis and Oxidative Stress in Human Hepatocyte-Derived Spheroid and in Primary Rat Hepatocytes

The prevalence of nonalcoholic steatohepatitis (NASH), characterized by fatty liver, oxidative injury, and inflammation, has considerably increased in the recent years. Due to the complexity of NASH pathogenesis, compounds which can target different mechanisms and stages of NASH development are required. A robust screening model with translational capability is also required to develop therapies targeting NASH. In this study, we used HepG2 spheroids and rat primary hepatocytes to evaluate the potency of Livogrit, a tri-herbal Ayurvedic prescription medicine, as a hepatoprotective agent. NASH was developed in the cells via methionine and cystine-deficient cell culture media. Livogrit at concentration of 30 µg/mL was able to prevent NASH development by decreasing lipid accumulation, ROS production, AST release, NFκB activation and increasing lipolysis, GSH (reduced glutathione), and mitochondrial membrane potential. This study suggests that Livogrit might reduce the lipotoxicity-mediated ROS generation and subsequent production of inflammatory mediators as evident from the increased gene expression of FXR, FGF21, CHOP, CXCL5, and their normalization due to Livogrit treatment. Taken together, Livogrit showed the potential as a multimodal therapeutic formulation capable of attenuating the development of NASH. Our study highlights the potential of Livogrit as a hepatoprotective agent with translational possibilities.

Advanced Materials and Sensors for Microphysiological Systems: Focus on Electronic and Electrooptical Interfaces

Advanced in vitro cell culture systems or microphysiological systems (MPSs), including microfluidic organ-on-a-chip (OoC), are breakthrough technologies in biomedicine. These systems recapitulate features of human tissues outside of the body. They are increasingly being used to study the functionality of different organs for applications such as drug evolutions, disease modeling, and precision medicine. Currently, developers and endpoint users of these in vitro models promote how they can replace animal models or even be a better ethically neutral and humanized alternative to study pathology, physiology, and pharmacology. Although reported models show a remarkable physiological structure and function compared to the conventional 2D cell culture, they are almost exclusively based on standard passive polymers or glass with none or minimal real-time stimuli and readout capacity. The next technology leap in reproducing in vivo-like functionality and real-time monitoring of tissue function could be realized with advanced functional materials and devices. This review describes the currently reported electronic and optical advanced materials for sensing and stimulation of MPS models. In addition, an overview of multi-sensing for Body-on-Chip platforms is given. Finally, one gives the perspective on how advanced functional materials could be integrated into in vitro systems to precisely mimic human physiology.

Vascularized Co-Culture Clusteroids of Primary Endothelial and Hep-G2 Cells Based on Aqueous Two-Phase Pickering Emulsions

Three-dimensional cell culture has been extensively involved in biomedical applications due to its high availability and relatively mature biochemical properties. However, single 3D cell culture models based on hydrogel or various scaffolds do not meet the more in-depth requirements of in vitro models. The necrotic core formation inhibits the utilization of the 3D cell culture ex vivo as oxygen permeation is impaired in the absence of blood vessels. We report a simple method to facilitate the formation of angiogenic HUVEC (human umbilical vein endothelial cells) and Hep-G2 (hepatocyte carcinoma model) co-culture 3D clusteroids in a water-in-water (w/w) Pickering emulsions template which can overcome this limitation. This method enabled us to manipulate the cells proportion in order to achieve the optimal condition for stimulating the production of various angiogenic protein markers in the co-cultured clusteroids. The HUVEC cells respond to the presence of Hep-G2 cells and their byproducts by forming endothelial cell sprouts in Matrigel without the exogenous addition of vascular endothelial growth factor (VEGF) or other angiogenesis inducers. This culture method can be easily replicated to produce other types of cell co-culture spheroids. The w/w Pickering emulsion template can facilitate the fabrication of 3D co-culture models to a great extent and be further utilized in drug testing and tissue engineering applications.

Microfluidic Organ-on-a-Chip Devices for Liver Disease Modeling In Vitro

Mortality from liver disease conditions continues to be very high. As liver diseases manifest and progress silently, prompt measures after diagnosis are essential in the treatment of these conditions. Microfluidic organs-on-chip platforms have significant potential for the study of the pathophysiology of liver diseases in vitro. Different liver-on-a-chip microphysiological platforms have been reported to study cell-signaling pathways such as those activating stellate cells within liver diseases. Moreover, the drug efficacy for liver conditions might be evaluated on a cellular metabolic level. Here, we present a comprehensive review of microphysiological platforms used for modelling liver diseases. First, we briefly introduce the concept and importance of organs-on-a-chip in studying liver diseases in vitro, reflecting on existing reviews of healthy liver-on-a-chip platforms. Second, the techniques of cell cultures used in the microfluidic devices, including 2D, 3D, and spheroid cells, are explained. Next, the types of liver diseases (NAFLD, ALD, hepatitis infections, and drug injury) on-chip are explained for a further comprehensive overview of the design and methods of developing liver diseases in vitro. Finally, some challenges in design and existing solutions to them are reviewed

Development of digital organ-on-a-chip to assess hepatotoxicity and extracellular vesicle-based anti-liver cancer immunotherapy

Organ-on-a-chip systems have been increasingly recognized as attractive platforms to assess toxicity and to develop new therapeutic agents. However, current organ-on-a-chip platforms are limited by a “single pot” design, which inevitably requires holistic analysis and limits parallel processing. Here, we developed a digital organ-on-a-chip by combining a microwell array with cellular microspheres, which significantly increased the parallelism over traditional organ-on-a-chip for drug development. Up to 127 uniform liver cancer microspheres in this digital organ-on-a-chip format served as individual analytical units, allowing for analysis with high consistency and quick response. Our platform displayed evident anti-cancer efficacy at a concentration of 10 μM for sorafenib, and had greater alignment than the “single pot” organ-on-a-chip with a previous in vivo study. In addition, this digital organ-on-a-chip demonstrated the treatment efficacy of natural killer cell-derived extracellular vesicles for liver cancer at 50 μg/mL. The successful development of this digital organ-on-a-chip platform provides high-parallelism and a low-variability analytical tool for toxicity assessment and the exploration of new anticancer modalities, thereby accelerating the joint endeavor to combat cancer.

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Advances in hydrogel-based vascularized tissues for tissue repair and drug screening

The construction of biomimetic vasculatures within the artificial tissue models or organs is highly required for conveying nutrients, oxygen, and waste products, for improving the survival of engineered tissues in vitro. In recent times, the remarkable progress in utilizing hydrogels and understanding vascular biology have enabled the creation of three-dimensional (3D) tissues and organs composed of highly complex vascular systems. In this review, we give an emphasis on the utilization of hydrogels and their advantages in the vascularization of tissues. Initially, the significance of vascular elements and the regeneration mechanisms of vascularization, including angiogenesis and vasculogenesis, are briefly introduced. Further, we highlight the importance and advantages of hydrogels as artificial microenvironments in fabricating vascularized tissues or organs, in terms of tunable physical properties, high similarity in physiological environments, and alternative shaping mechanisms, among others. Furthermore, we discuss the utilization of such hydrogels-based vascularized tissues in various applications, including tissue regeneration, drug screening, and organ-on-chips. Finally, we put forward the key challenges, including multifunctionalities of hydrogels, selection of suitable cell phenotype, sophisticated engineering techniques, and clinical translation behind the development of the tissues with complex vasculatures towards their future development.

Applied Hepatic Bioengineering: Modeling the Human Liver Using Organoid and Liver-on-a-Chip Technologies

The liver is the most important metabolic hub of endo and xenobiotic compounds. Pre-clinical studies using rodents to evaluate the toxicity of new drugs and cosmetics may produce inconclusive results for predicting clinical outcomes in humans, moreover being banned in the European Union. Human liver modeling using primary hepatocytes presents low reproducibility due to batch-to-batch variability, while iPSC-derived hepatocytes in monolayer cultures (2D) show reduced cellular functionality. Here we review the current status of the two most robust in vitro approaches in improving hepatocyte phenotype and metabolism while mimicking the hepatic physiological microenvironment: organoids and liver-on-chip. Both technologies are reviewed in design and manufacturing techniques, following cellular composition and functionality. Furthermore, drug screening and liver diseases modeling efficiencies are summarized. Finally, organoid and liver-on-chip technologies are compared regarding advantages and limitations, aiming to guide the selection of appropriate models for translational research and the development of such technologies.

Implementing organ-on-chip in a next-generation risk assessment of chemicals: a review

Organ-on-chip (OoC) technology is full of engineering and biological challenges, but it has the potential to revolutionize the Next-Generation Risk Assessment of novel ingredients for consumer products and chemicals. A successful incorporation of OoC technology into the Next-Generation Risk Assessment toolbox depends on the robustness of the microfluidic devices and the organ tissue models used. Recent advances in standardized device manufacturing, organ tissue cultivation and growth protocols offer the ability to bridge the gaps towards the implementation of organ-on-chip technology. Next-Generation Risk Assessment is an exposure-led and hypothesis-driven tiered approach to risk assessment using detailed human exposure information and the application of appropriate new (non-animal) toxicological testing approaches. Organ-on-chip presents a promising in vitro approach by combining human cell culturing with dynamic microfluidics to improve physiological emulation. Here, we critically review commercial organ-on-chip devices, as well as recent tissue culture model studies of the skin, intestinal barrier and liver as the main metabolic organ to be used on-chip for Next-Generation Risk Assessment. Finally, microfluidically linked tissue combinations such as skin-liver and intestine-liver in organ-on-chip devices are reviewed as they form a relevant aspect for advancing toxicokinetic and toxicodynamic studies. We point to recent achievements and challenges to overcome, to advance non-animal, human-relevant safety studies.

Engineering Modular 3D Liver Culture Microenvironments In Vitro to Parse the Interplay between Biophysical and Biochemical Microenvironment Cues on Hepatic Phenotypes

In vitro models of human liver functions are used across a diverse range of applications in preclinical drug development and disease modeling, with particular increasing interest in models that capture facets of liver inflammatory status. This study investigates how the interplay between biophysical and biochemical microenvironment cues influence phenotypic responses, including inflammation signatures, of primary human hepatocytes (PHH) cultured in a commercially available perfused bioreactor. A 3D printing-based alginate microwell system was designed to form thousands of hepatic spheroids in a scalable manner as a comparator 3D culture modality to the bioreactor. Soft, synthetic extracellular matrix (ECM) hydrogel scaffolds with biophysical properties mimicking features of liver were engineered to replace polystyrene scaffolds, and the biochemical microenvironment was modulated with a defined set of growth factors and signaling modulators. The supplemented media significantly increased tissue density, albumin secretion, and CYP3A4 activity but also upregulated inflammatory markers. Basal inflammatory markers were lower for cells maintained in ECM hydrogel scaffolds or spheroid formats than polystyrene scaffolds, while hydrogel scaffolds exhibited the most sensitive response to inflammation as assessed by multiplexed cytokine and RNA-seq analyses. Together, these engineered 3D liver microenvironments provide insights for probing human liver functions and inflammatory response in vitro.

Engineering liver microtissues to study the fusion of HepG2 with mesenchymal stem cells and invasive potential of fused cells

Increasing evidence from cancer cell fusion with different cell types in the tumor microenvironment has suggested a probable mechanism for how metastasis-initiating cells could be generated in tumors. Although human mesenchymal stem cells (hMSCs) have been known as promising candidates to create hybrid cells with cancer cells, the role of hMSCs in fusion with cancer cells is still controversial. Here, we fabricated a liver-on-a-chip platform to monitor the fusion of liver hepatocellular cells (HepG2) with hMSCs and study their invasive potential. We demonstrated that hMSCs might play dual roles in HepG2 spheroids. The analysis of tumor growth with different fractions of hMSCs in HepG2 spheroids revealed hMSCs' role in preventing HepG2 growth and proliferation, while the hMSCs presented in the HepG2 spheroids led to the generation of HepG2-hMSC hybrid cells with much higher invasiveness compared to HepG2. These invasive HepG2-hMSC hybrid cells expressed high levels of markers associated with stemness, proliferation, epithelial to mesenchymal transition, and matrix deposition, which corresponded to the expression of these markers for hMSCs escaping from hMSC spheroids. In addition, these fused cells were responsible for collective invasion following HepG2 by depositing Collagen I and Fibronectin in their surrounding microenvironment. Furthermore, we showed that hepatic stellate cells (HSCs) could also be fused with HepG2, and the HepG2-HSC hybrid cells possessed similar features to those from HepG2-hMSC fusion. This fusion of HepG2 with liver-resident HSCs may propose a new potential mechanism of hepatic cancer metastasis.

Microfluidic-Chip-Integrated Biosensors for Lung Disease Models

Lung diseases (e.g., infection, asthma, cancer, and pulmonary fibrosis) represent serious threats to human health all over the world. Conventional two-dimensional (2D) cell models and animal models cannot mimic the human-specific properties of the lungs. In the past decade, human organ-on-a-chip (OOC) platforms-including lung-on-a-chip (LOC)-have emerged rapidly, with the ability to reproduce the in vivo features of organs or tissues based on their three-dimensional (3D) structures. Furthermore, the integration of biosensors in the chip allows researchers to monitor various parameters related to disease development and drug efficacy. In this review, we illustrate the biosensor-based LOC modeling, further discussing the future challenges as well as perspectives in integrating biosensors in OOC platforms.

Human Hepatocytes Isolated from Explanted Livers: A Powerful Tool to Understand End-stage Liver Disease and Drug Screening

The use of primary human hepatocytes has been hampered by limited availability of adequate numbers of fresh and viable cells due to the ongoing shortage of liver donors. Thus, there is no surplus of healthy organs from which freshly isolated cells can be prepared when needed. However, primary hepatocytes can be successfully isolated from explanted liver specimens obtained from patients receiving orthotopic liver transplantation for decompensated liver cirrhosis or for metabolic liver disease without end-stage liver disease and are a valuable resource for the pharmaceutical industry research. This review focuses on the isolation, characterization and cryopreservation of hepatocytes derived from therapeutically resected livers with various hepatic diseases.

Tackling Current Biomedical Challenges With Frontier Biofabrication and Organ-On-A-Chip Technologies

In the last decades, biomedical research has significantly boomed in the academia and industrial sectors, and it is expected to continue to grow at a rapid pace in the future. An in-depth analysis of such growth is not trivial, given the intrinsic multidisciplinary nature of biomedical research. Nevertheless, technological advances are among the main factors which have enabled such progress. In this review, we discuss the contribution of two state-of-the-art technologies-namely biofabrication and organ-on-a-chip-in a selection of biomedical research areas. We start by providing an overview of these technologies and their capacities in fabricating advanced in vitro tissue/organ models. We then analyze their impact on addressing a range of current biomedical challenges. Ultimately, we speculate about their future developments by integrating these technologies with other cutting-edge research fields such as artificial intelligence and big data analysis.

Critical Considerations for the Design of Multi-Organ Microphysiological Systems (MPS)

Identification and approval of new drugs for use in patients requires extensive preclinical studies and clinical trials. Preclinical studies rely on in vitro experiments and animal models of human diseases. The transferability of drug toxicity and efficacy estimates to humans from animal models is being called into question. Subsequent clinical studies often reveal lower than expected efficacy and higher drug toxicity in humans than that seen in animal models. Microphysiological systems (MPS), sometimes called organ or human-on-chip models, present a potential alternative to animal-based models used for drug toxicity screening. This review discusses multi-organ MPS that can be used to model diseases and test the efficacy and safety of drug candidates. The translation of an in vivo environment to an in vitro system requires physiologically relevant organ scaling, vascular dimensions, and appropriate flow rates. Even small changes in those parameters can alter the outcome of experiments conducted with MPS. With many MPS devices being developed, we have outlined some established standards for designing MPS devices and described techniques to validate the devices. A physiologically realistic mimic of the human body can help determine the dose response and toxicity effects of a new drug candidate with higher predictive power.

A scalable and sensitive steatosis chip with long-term perfusion of in situ differentiated HepaRG organoids

Nonalcoholic fatty liver disease (NAFLD) is a significant liver disease without approved therapy, lacking human NAFLD models to aid drug development. Existing models are either under-performing or too complex to allow robust drug screening. Here we have developed a 100-well drug testing platform with improved HepaRG organoids formed with uniform size distribution, and differentiated in situ in a perfusion microfluidic device, SteatoChip, to recapitulate major NAFLD features. Compared with the pre-differentiated spheroids, the in situ differentiated HepaRG organoids with perfusion experience well-controlled chemical and mechanical microenvironment, and 3D cellular niche, to exhibit enhanced hepatic differentiation (albumin⁺ cells ratio: 66.2% in situ perfusion vs 46.1% pre-differentiation), enriched and uniform hepatocyte distribution in organoids, higher level of hepatocyte functions (5.2 folds in albumin secretion and 7.6 folds in urea synthesis), enhanced cell polarity and bile canaliculi structures. When induced with free fatty acid (FFA), cells exhibit significantly higher level of lipid accumulation (6.6 folds for in situ perfusion vs 4.4 folds for pre-differentiation), altered glucose regulation and reduced Akt phosphorylation in the organoids. SteatoChip detects reduction of steatosis when cells are incubated with three different anti-steatosis compounds, 78.5% by metformin hydrochloride, 71.3% by pioglitazone hydrochloride and 66.6% by obeticholic acid, versus the control FFA-free media (38% reduction). The precision microenvironment control in SteatoChip enables improved formation, differentiation, and function of HepaRG organoids to serve as a scalable and sensitive drug testing platform, to potentially accelerate the NAFLD drug development.

Rebuilding the Vascular Network: In vivo and in vitro Approaches

As the material transportation system of the human body, the vascular network carries the transportation of materials and nutrients. Currently, the construction of functional microvascular networks is an urgent requirement for the development of regenerative medicine and in vitro drug screening systems. How to construct organs with functional blood vessels is the focus and challenge of tissue engineering research. Here in this review article, we first introduced the basic characteristics of blood vessels in the body and the mechanism of angiogenesis in vivo, summarized the current methods of constructing tissue blood vessels in vitro and in vivo, and focused on comparing the functions, applications and advantages of constructing different types of vascular chips to generate blood vessels. Finally, the challenges and opportunities faced by the development of this field were discussed.

Bioengineered Multicellular Liver Microtissues for Modeling Advanced Hepatic Fibrosis Driven Through Non-Alcoholic Fatty Liver Disease

Despite considerable efforts in modeling liver disease in vitro, it remains difficult to recapitulate the pathogenesis of the advanced phases of non-alcoholic fatty liver disease (NAFLD) with inflammation and fibrosis. Here, a liver-on-a-chip platform with bioengineered multicellular liver microtissues is developed, composed of four major types of liver cells (hepatocytes, endothelial cells, Kupffer cells, and stellate cells) to implement a human hepatic fibrosis model driven by NAFLD: i) lipid accumulation in hepatocytes (steatosis), ii) neovascularization by endothelial cells, iii) inflammation by activated Kupffer cells (steatohepatitis), and iv) extracellular matrix deposition by activated stellate cells (fibrosis). In this model, the presence of stellate cells in the liver-on-a-chip model with fat supplementation showed elevated inflammatory responses and fibrosis marker up-regulation. Compared to transforming growth factor-beta-induced hepatic fibrosis models, this model includes the native pathological and chronological steps of NAFLD which shows i) higher fibrotic phenotypes, ii) increased expression of fibrosis markers, and iii) efficient drug transport and metabolism. Taken together, the proposed platform will enable a better understanding of the mechanisms underlying fibrosis progression in NAFLD as well as the identification of new drugs for the different stages of NAFLD.

Modeling Endothelialized Hepatic Tumor Microtissues for Drug Screening

Compared to various traditional 2D approaches, the scaffold-based 3D tumor models have emerged as an effective strategy to investigate the complex mechanisms behind cancer progression and responses to drug treatments, by providing biomimetic extracellular matrix and stromal-like microenvironments including the vascular elements. Herein, the development of a 3D endothelialized hepatic tumor microtissue model based on the fusion of multicellular aggregates of human hepatocellular carcinoma cells and human umbilical vein endothelial cells cocultured in poly(lactic-co-glycolic acid)-based porous microspheres (PLGA PMs) is reported. In contrast to the conventional 2D culture, the cells within the PLGA PMs exhibit significantly higher half-maximal inhibitory concentration values against anticancer drugs, including doxorubicin and cisplatin. Furthermore, the feasibility of coculturing other cell types, such as fibroblasts (L929) and HepG2 cells, is investigated. Together, the findings emphasize the significance of engineered 3D hepatic tumor microtissue models using PLGA PM-based multicellular aggregates for drug screening applications.

The Future Application of Organ-on-a-Chip Technologies as Proving Grounds for MicroBioRobots

An evolving understanding of disease pathogenesis has compelled the development of new drug delivery approaches. Recently, bioinspired microrobots have gained traction as drug delivery systems. By leveraging the microscale phenomena found in physiological systems, these microrobots can be designed with greater maneuverability, which enables more precise, controlled drug release. Their function could be further improved by testing their efficacy in physiologically relevant model systems as part of their development. In parallel with the emergence of microscale robots, organ-on-a-chip technologies have become important in drug discovery and physiological modeling. These systems reproduce organ-level functions in microfluidic devices, and can also incorporate specific biological, chemical, and physical aspects of a disease. This review highlights recent developments in both microrobotics and organ-on-a-chip technologies and envisions their combined use for developing future drug delivery systems.

Gut-on-a-chip: Current progress and future opportunities

Organ-on-a-chip technology tries to mimic the complexity of native tissues in vitro. Important progress has recently been made in using this technology to study the gut with and without microbiota. These in vitro models can serve as an alternative to animal models for studying physiology, pathology, and pharmacology. While these models have greater physiological relevance than two-dimensional (2D) cell systems in vitro, endocrine and immunological functions in gut-on-a-chip models are still poorly represented. Furthermore, the construction of complex models, in which different cell types and structures interact, remains a challenge. Generally, gut-on-a-chip models have the potential to advance our understanding of the basic interactions found within the gut and lay the foundation for future applications in understanding pathophysiology, developing drugs, and personalizing medical treatments.

Novel Strategies in Artificial Organ Development: What Is the Future of Medicine?

The technology of tissue engineering is a rapidly evolving interdisciplinary field of science that elevates cell-based research from 2D cultures through organoids to whole bionic organs. 3D bioprinting and organ-on-a-chip approaches through generation of three-dimensional cultures at different scales, applied separately or combined, are widely used in basic studies, drug screening and regenerative medicine. They enable analyses of tissue-like conditions that yield much more reliable results than monolayer cell cultures. Annually, millions of animals worldwide are used for preclinical research. Therefore, the rapid assessment of drug efficacy and toxicity in the early stages of preclinical testing can significantly reduce the number of animals, bringing great ethical and financial benefits. In this review, we describe 3D bioprinting techniques and first examples of printed bionic organs. We also present the possibilities of microfluidic systems, based on the latest reports. We demonstrate the pros and cons of both technologies and indicate their use in the future of medicine.

Microfluidic Control of Tumor and Stromal Cell Spheroids Pairing and Merging for Three-Dimensional Metastasis Study

Three-dimensional cell culture provides an efficient way to simulate the in vivo tumorigenic microenvironment where tumor-stroma interaction intrinsically plays a pivotal role. Conventional three-dimensional (3D) culture is inadequate to address precise coexistential heterogeneous pairing and quantitative measurement in a parallel algorithm format. Herein, we implemented a set of microwell array microfluidic devices to study the cell spheroids-based tumor-stromal metastatic process in vitro. This approach enables accurate one-to-one pairing between tumor and fibroblast spheroid for dissecting 3D tumor invasion in the manner of high-content imaging. On one single device, 240 addressable tumor-stroma pairings can be formed with convenient pipetting and centrifugation within a small area of 1 cm². Consequential confocal imaging analysis disclosed that the tumor spheroid could envelop the fibroblast spheroid. Specific chemicals can effectively hamper or promote this 3D metastasis. Due to the addressable time-resolved measurements of the merging process of hundreds of doublets, our approach allows us to decipher the metastatic phenotype between different tumor spheroids. Compared with traditional protocols, massive heterogeneous cellular spheroids pairing and merging using this method is well-defined with microfluidic control, which leads to a favorable high-content tumor-stroma doublet metastasis analysis. This simple technique will be a useful tool for investigating heterotypic spheroid-spheroid interactions.

The Influence of Chronic Liver Diseases on Hepatic Vasculature: A Liver-on-a-chip Review

In chronic liver diseases and hepatocellular carcinoma, the cells and extracellular matrix of the liver undergo significant alteration in response to chronic injury. Recent literature has highlighted the critical, but less studied, role of the liver vasculature in the progression of chronic liver diseases. Recent advancements in liver-on-a-chip systems has allowed in depth investigation of the role that the hepatic vasculature plays both in response to, and progression of, chronic liver disease. In this review, we first introduce the structure, gradients, mechanical properties, and cellular composition of the liver and describe how these factors influence the vasculature. We summarize state-of-the-art vascularized liver-on-a-chip platforms for investigating biological models of chronic liver disease and their influence on the liver sinusoidal endothelial cells of the hepatic vasculature. We conclude with a discussion of how future developments in the field may affect the study of chronic liver diseases, and drug development and testing.