Spheroid Formation and Evaluation of Hepatic Cells in a Three-Dimensional Culture Device

Fabrication Method for Shape-Controlled 3D Tissue Using High-Porosity Porous Structure

Shape-controlled 3D tissues resemble natural living tissues in human and animal bodies and are essential materials for developing and improving technologies in regenerative medicine, drug discovery, and biological robotics. In previous studies, shape-controlled 3D tissues were fabricated using scaffold structures or 3D bioprinting techniques. However, controlling the shape of 3D tissues without leaving non-natural materials inside the 3D tissue and efficiently fabricating them remains challenging. In this paper, we propose a novel method for fabricating shape-controlled 3D tissues free of non-natural materials using a flexible high-porosity porous structure (HPPS). The HPPS consisted of a micromesh with pore sizes of 14.87 ± 1.83 μm, lattice widths of 2.24 ± 0.10 μm, thicknesses of 9.96 ± 0.92 μm, porosity of 69.06 ± 3.30%, and an I-shaped microchamber of depth 555.26 ± 11.17 μm. U-87 human glioma cells were cultured in an I-shaped HPPS microchamber for 48 h. After cultivation, the 3D tissue was released within a few seconds while maintaining its I-shape. Specific chemicals, such as proteolytic enzymes, were not used. Moreover, the viability of the released cells composed of shape-controlled 3D tissues free of non-natural materials was above 90%. Therefore, the proposed fabrication method is recommended for shape-controlled 3D tissues free of non-natural materials without applying significant stresses to the cells.

Microfluidic design for in-vitro liver zonation-a numerical analysis using COMSOL Multiphysics

The liver is one of the most important organs, with a complex physiology. Current in-vitro approaches are not accurate for disease modeling and drug toxicity research. One of those features is liver zonation, where cells display different physiological states due to different levels of oxygen and nutrient supplements. Organ-on-a-chip technology employs microfluidic platforms that enable a controlled environment for in-vitro cell culture. In this study, we propose a microfluidic design embedding a gas channel (of ambient air), creating an oxygen gradient. We numerically simulate different flow rates and cell densities with the COMSOL Multiphysics package considering cell-specific consumption rates of oxygen and glucose. We establish the cell density and flow rate for optimum oxygen and glucose distribution in the cell culture chamber. Furthermore, we show that a physiologically relevant concentration of oxygen and glucose in the chip is reached after 24 h and 30 min, respectively. The proposed microfluidic design and optimal parameters we identify in this paper provide a tool for in-vitro liver zonation studies. However, the microfluidic design is not exclusively for liver cell experiments but is foreseen to be applicable in cell studies where different gas concentration gradients are critical, e.g., studying hypoxia or toxic gas impact.

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.

Functional Evaluation of 3D Liver Models Labeled with Polysaccharide Functionalized Magnetic Nanoparticles

Establishing a rapid in vitro evaluation system for drug screening is essential for the development of new drugs. To reproduce tissues/organs with functions closer to living organisms, in vitro three-dimensional (3D) culture evaluation using microfabrication technology has been reported in recent years. Culture on patterned substrates with controlled hydrophilic and hydrophobic regions (Cell-able^TM) can create 3D liver models (miniature livers) with liver-specific Disse luminal structures and functions. MRI contrast agents are widely used as safe and minimally invasive diagnostic methods. We focused on anionic polysaccharide magnetic iron oxide nanoparticles (Resovist^®) and synthesized the four types of nanoparticle derivatives with different properties. Cationic nanoparticles (TMADM) can be used to label target cells in a short time and have been successfully visualized in vivo. In this study, we examined the morphology of various nanoparticles. The morphology of various nanoparticles showed relatively smooth-edged spherical shapes. As 3D liver models, we prepared primary hepatocyte-endothelial cell heterospheroids. The toxicity, CYP3A, and albumin secretory capacity were evaluated in the heterospheroids labeled with various nanoparticles. As the culture period progressed, the heterospheroids labeled with anionic and cationic nanoparticles showed lower liver function than non-labeled heterospheroids. In the future, there is a need to improve the method of creation of artificial 3D liver or to design a low-invasive MRI contrast agent to label the artificial 3D liver.

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.

A deep and permeable nanofibrous oval-shaped microwell array for the stable formation of viable and functional spheroids

Despite the potential of a nanofibrous (NF) microwell array as a permeable microwell array to improve the viability and functions of spheroids, thanks to the superior permeability to both gases and solutes, there have still been difficulties regarding the stable formation of spheroids in the NF microwell array due to the low aspect ratio (AR) and the large interspacing between microwells. This study proposes a nanofibrous oval-shaped microwell array, named the NOVA microwell array, with both a high AR and a high well density, enabling us to not only collect cells in the microwell with a high cell seeding efficiency, but also to generate multiple viable and functional spheroids in a uniform and stable manner. To realize a deep NOVA microwell array with a high aspect ratio (AR = 0.9) and a high well density (494 wells cm^-2), we developed a matched-mold thermoforming process for the fabrication of both size- and AR-controllable NOVA microwell arrays with various interspacing between microwells while maintaining the porous nature of the NF membrane. The human hepatocellular carcinoma (HepG2) cell spheroids cultured on the deep NOVA microwell array not only had uniform size and shape, with a spheroid circularity of 0.80 ± 0.03 at a cell seeding efficiency of 94.29 ± 9.55%, but also exhibited enhanced viability with a small fraction of dead cells and promoted functionality with increased albumin secretion, compared with the conventional impermeable microwell array. The superior characteristics of the deep NOVA microwell array, i.e. a high AR, a high well density, and a high permeability, pave the way to the production of various viable and functional spheroids and even organoids in a scalable manner.

Squaramide-Based Supramolecular Materials Drive HepG2 Spheroid Differentiation

A major challenge in the use of HepG2 cell culture models for drug toxicity screening is their lack of maturity in 2D culture. 3D culture in Matrigel promotes the formation of spheroids that express liver-relevant markers, yet they still lack various primary hepatocyte functions. Therefore, alternative matrices where chemical composition and materials properties are controlled to steer maturation of HepG2 spheroids remain desired. Herein, a modular approach is taken based on a fully synthetic and minimalistic supramolecular matrix based on squaramide synthons outfitted with a cell-adhesive peptide, RGD for 3D HepG2 spheroid culture. Co-assemblies of RGD-functionalized squaramide-based and native monomers resulted in soft and self-recovering supramolecular hydrogels with a tunable RGD concentration. HepG2 spheroids are self-assembled and grown (≈150 µm) within the supramolecular hydrogels with high cell viability and differentiation over 21 days of culture. Importantly, significantly higher mRNA and protein expression levels of phase I and II metabolic enzymes, drug transporters, and liver markers are found for the squaramide hydrogels in comparison to Matrigel. Overall, the fully synthetic squaramide hydrogels are proven to be synthetically accessible and effective for HepG2 differentiation showcasing the potential of this supramolecular matrix to rival and replace naturally-derived materials classically used in high-throughput toxicity screening.

Chloroquine diphosphate suppresses liver cancer via inducing apoptosis in Wistar rats using interventional therapy

Liver cancer ranks as the second leading cause of cancer-associated mortality worldwide. To date, neither current ablation therapy nor chemotherapy are considered ideal in improving the outcome of liver cancer. Therefore, more effective therapies for treating this devastating disease are urgently required. Interventional therapy has been used for numerous years in the treatment of different types of cancer, and is characterized by the direct delivery of anticancer drugs into the tumor. It has been reported that antimalarial chloroquine diphosphate (CQ) exerts effective anticancer activity against several types of cancer. However, its effect on liver cancer remains unclear. Therefore, in the present study, 2D monolayer cell culture and 3D spheroid in vitro models, and a rat model, were utilized to investigate the effect of CQ on liver cancer. CQ demonstrated an effective anticancer effect on HepG2 cells and 3D liver spheroids. Furthermore, the drug significantly inhibited cell growth and viability in the 2D and 3D in vitro models. The CQ-based intervention treatment effectively attenuated tumor size and weight, increased food intake and consumption of drinking water, and improved body weight and survival rate of rats in the in vivo model. In addition, treatment with CQ potently increased the expression levels of the apoptosis-related genes. Taken together, the findings of the present study may provide a novel insight into the development of safe and effective treatments for liver cancer.

Engineering liver microtissues for disease modeling and regenerative medicine

The burden of liver diseases is increasing worldwide, accounting for two million deaths annually. In the past decade, tremendous progress has been made in the basic and translational research of liver tissue engineering. Liver microtissues are small, three-dimensional hepatocyte cultures that recapitulate liver physiology and have been used in biomedical research and regenerative medicine. This review summarizes recent advances, challenges, and future directions in liver microtissue research. Cellular engineering approaches are used to sustain primary hepatocytes or produce hepatocytes derived from pluripotent stem cells and other adult tissues. Three-dimensional microtissues are generated by scaffold-free assembly or scaffold-assisted methods such as macroencapsulation, droplet microfluidics, and bioprinting. Optimization of the hepatic microenvironment entails incorporating the appropriate cell composition for enhanced cell-cell interactions and niche-specific signals, and creating scaffolds with desired chemical, mechanical and physical properties. Perfusion-based culture systems such as bioreactors and microfluidic systems are used to achieve efficient exchange of nutrients and soluble factors. Taken together, systematic optimization of liver microtissues is a multidisciplinary effort focused on creating liver cultures and on-chip models with greater structural complexity and physiological relevance for use in liver disease research, therapeutic development, and regenerative medicine.

Hydrogel microfluidic-based liver-on-a-chip: Mimicking the mass transfer and structural features of liver

Liver is fed by nutrition via diffusion across the vascular wall from blood flow. However, hepatocytes in liver models are directly exposed to the perfusion culture medium, where the shear stress reduces the cell viability and liver-specific functions. By mimicking the mass transfer and structural features of hepatic lobule, we designed a microfluidic liver-on-a-chip based on the di-acrylated pluronic F127 hydrogel. In the hydrogel chip, hepatocellular carcinoma HepG2 and human hepatic stellate cell LX-2 were statically cultured inside the microwells on the outer channel. These hepatic cells were fed by the diffused medium from the adjacent but separated inner channel with endothelial cell monolayers, which was perfused by the medium with physiologically relevant shear stress. As found, the hepatic cells in the liver-on-a-chip rapidly formed spheroids within 1-day incubation and expressed about one to two-fold higher viability/liver-specific functions than the corresponding static culture for at least 8 days. Moreover, the presence of endothelial cells also contributed to the expression of liver-specific functions in the liver-on-a-chip. Therefore, the proposed liver-on-a-chip provides a new concept for construction of 3D liver models in vitro, and shows the potential value for a variety of applications including bio-artificial livers and drug toxicity screening.

iPSC-Derived Liver Organoids: A Journey from Drug Screening, to Disease Modeling, Arriving to Regenerative Medicine

Liver transplantation is the most common treatment for patients suffering from liver failure that is caused by congenital diseases, infectious agents, and environmental factors. Despite a high rate of patient survival following transplantation, organ availability remains the key limiting factor. As such, research has focused on the transplantation of different cell types that are capable of repopulating and restoring liver function. The best cellular mix capable of engrafting and proliferating over the long-term, as well as the optimal immunosuppression regimens, remain to be clearly well-defined. Hence, alternative strategies in the field of regenerative medicine have been explored. Since the discovery of induced pluripotent stem cells (iPSC) that have the potential of differentiating into a broad spectrum of cell types, many studies have reported the achievement of iPSCs differentiation into liver cells, such as hepatocytes, cholangiocytes, endothelial cells, and Kupffer cells. In parallel, an increasing interest in the study of self-assemble or matrix-guided three-dimensional (3D) organoids have paved the way for functional bioartificial livers. In this review, we will focus on the recent breakthroughs in the development of iPSCs-based liver organoids and the major drawbacks and challenges that need to be overcome for the development of future applications.

Development of 3D Hepatic Constructs Within Polysaccharide-Based Scaffolds with Tunable Properties

Organoids production is a key tool for in vitro studies of physiopathological conditions, drug-induced toxicity assays, and for a potential use in regenerative medicine. Hence, it prompted studies on hepatic organoids and liver regeneration. Numerous attempts to produce hepatic constructs had often limited success due to a lack of viability or functionality. Moreover, most products could not be translated for clinical studies. The aim of this study was to develop functional and viable hepatic constructs using a 3D porous scaffold with an adjustable structure, devoid of any animal component, that could also be used as an in vivo implantable system. We used a combination of pharmaceutical grade pullulan and dextran with different porogen formulations to form crosslinked scaffolds with macroporosity ranging from 30 µm to several hundreds of microns. Polysaccharide scaffolds were easy to prepare and to handle, and allowed confocal observations thanks to their transparency. A simple seeding method allowed a rapid impregnation of the scaffolds with HepG2 cells and a homogeneous cell distribution within the scaffolds. Cells were viable over seven days and form spheroids of various geometries and sizes. Cells in 3D express hepatic markers albumin, HNF4α and CYP3A4, start to polarize and were sensitive to acetaminophen in a concentration-dependant manner. Therefore, this study depicts a proof of concept for organoid production in 3D scaffolds that could be prepared under GMP conditions for reliable drug-induced toxicity studies and for liver tissue engineering.

Development of a tunable method to generate various three-dimensional microstructures by replenishing macromolecules such as extracellular matrix components and polysaccharides

Multicellular spheroids (spheroids) are expected to be a promising approach to mimic in vivo organ functions and cell microenvironments. However, conventional spheroids do not fully consider the existence of extracellular matrices (ECMs). In this study, we developed a tunable method for replenishing macromolecules, including ECM components and polysaccharides, into spheroids without compromising cell viability by injecting a microvolume cell suspension into a high density of methylcellulose dissolved in the culture medium. Adjusting the ECM concentration in the cell suspension enabled the generation of different three-dimensional microstructures, such as "ECM gel capsules", which contained individually separated cells, and "ECM-loaded spheroids", which had thin ECM layers between cells. ECM-loaded spheroids with a 30-fold dilution of Matrigel (0.3 mg/ml) showed significantly higher albumin secretion than control spheroids composed of Hep G2 or HuH-7 cells. Additionally, the expression levels of major CYP genes were decreased in ECM gel capsules with undiluted Matrigel (9 mg/ml) compared to those in control spheroids. However, 0.3 mg/ml Matrigel did not disrupt gene expression. Furthermore, cell polarity associated with tight junction proteins (ZO-1 and Claudin-1) and the transporter protein MRP2 was markedly induced by using 0.3 mg/ml Matrigel. Thus, high-performance three-dimensional tissues fabricated by this method are applicable to increasing the efficiency of drug screening and to regenerative medicine.

Engineered Liver-on-a-Chip Platform to Mimic Liver Functions and Its Biomedical Applications: A Review

Hepatology and drug development for liver diseases require in vitro liver models. Typical models include 2D planar primary hepatocytes, hepatocyte spheroids, hepatocyte organoids, and liver-on-a-chip. Liver-on-a-chip has emerged as the mainstream model for drug development because it recapitulates the liver microenvironment and has good assay robustness such as reproducibility. Liver-on-a-chip with human primary cells can potentially correlate clinical testing. Liver-on-a-chip can not only predict drug hepatotoxicity and drug metabolism, but also connect other artificial organs on the chip for a human-on-a-chip, which can reflect the overall effect of a drug. Engineering an effective liver-on-a-chip device requires knowledge of multiple disciplines including chemistry, fluidic mechanics, cell biology, electrics, and optics. This review first introduces the physiological microenvironments in the liver, especially the cell composition and its specialized roles, and then summarizes the strategies to build a liver-on-a-chip via microfluidic technologies and its biomedical applications. In addition, the latest advancements of liver-on-a-chip technologies are discussed, which serve as a basis for further liver-on-a-chip research.

Cytokines in adipose-derived mesenchymal stem cells promote the healing of liver disease

Adipose-derived mesenchymal stem cells (ADSCs) are a treatment cell source for patients with chronic liver injury. ADSCs are characterized by being harvested from the patient's own subcutaneous adipose tissue, a high cell yield (i.e., reduced immune rejection response), accumulation at a disease nidus, suppression of excessive immune response, production of various growth factors and cytokines, angiogenic effects, anti-apoptotic effects, and control of immune cells via cell-cell interaction. We previously showed that conditioned medium of ADSCs promoted hepatocyte proliferation and improved the liver function in a mouse model of acute liver failure. Furthermore, as found by many other groups, the administration of ADSCs improved liver tissue fibrosis in a mouse model of liver cirrhosis. A comprehensive protein expression analysis by liquid chromatography with tandem mass spectrometry showed that the various cytokines and chemokines produced by ADSCs promote the healing of liver disease. In this review, we examine the ability of expressed protein components of ADSCs to promote healing in cell therapy for liver disease. Previous studies demonstrated that ADSCs are a treatment cell source for patients with chronic liver injury. This review describes the various cytokines and chemokines produced by ADSCs that promote the healing of liver disease.

Innovation for hepatotoxicity in vitro research models: A review

Many categories of drugs can induce hepatotoxicity, so improving the prediction of toxic drugs is important. In vitro models using human hepatocytes are more accurate than in vivo animal models. Good in vitro models require an abundance of metabolic enzyme activities and normal cellular polarity. However, none of the in vitro models can completely simulate hepatocytes in the human body. There are two ways to overcome this limitation: enhancing the metabolic function of hepatocytes and changing the cultural environment. In this review, we summarize the current state of research, including the main characteristics of in vitro models and their limitations, as well as improved technology and developmental prospects. We hope that this review provides some new ideas for hepatotoxicity research.

Advances in Engineered Human Liver Platforms for Drug Metabolism Studies

Metabolism in the liver often determines the overall clearance rates of many pharmaceuticals. Furthermore, induction or inhibition of the liver drug metabolism enzymes by perpetrator drugs can influence the metabolism of victim drugs (drug-drug interactions). Therefore, determining liver-drug interactions is critical during preclinical drug development. Unfortunately, studies in animals are often of limited value because of significant differences in the metabolic pathways of the liver across different species. To mitigate such limitations, the pharmaceutical industry uses a continuum of human liver models, ranging from microsomes to transfected cell lines and cultures of primary human hepatocytes (PHHs). Of these models, PHHs provide a balance of high-throughput testing capabilities together with a physiologically relevant cell type that exhibits all the characteristic enzymes, cofactors, and transporters. However, PHH monocultures display a rapid decline in metabolic capacity. Consequently, bioengineers have developed several tools, such as cellular microarrays, micropatterned cocultures, self-assembled and bioprinted spheroids, and perfusion devices, to enhance and stabilize PHH functions for ≥2 weeks. Many of these platforms have been validated for drug studies, whereas some have been adapted to include liver nonparenchymal cells that can influence hepatic drug metabolism in health and disease. Here, we focus on the design features of such platforms and their representative drug metabolism validation datasets, while discussing emerging trends. Overall, the use of engineered human liver platforms in the pharmaceutical industry has been steadily rising over the last 10 years, and we anticipate that these platforms will become an integral part of drug development with continued commercialization and validation for routine screening use.

High-glucose 3D INS-1 cell model combined with a microfluidic circular concentration gradient generator for high throughput screening of drugs against type 2 diabetes

In vitro models for screening of drugs against type 2 diabetes are crucial for the pharmaceutical industry. This paper presents a new approach for integration of a three-dimensionally-cultured insulinoma cell line (INS-1 cell) incubated in a high concentration of glucose as a new model. In this model, INS-1 cells tended to aggregate in the 3D gel (basement membrane extractant, BME), in a similar way to 3D in vivo cell culture models. The proliferation of INS-1 cells in BME was initially promoted and then suppressed by the high concentration of glucose, and the function of insulin secretion also was initially enhanced and then inhibited by the high concentration of glucose. These phenomena were similar to hyperglycemia symptoms, proving the validity of the proposed model. This model can help find the drugs that stimulate insulin secretion. Then, we identified the difference between the new model and the traditional two-dimensional model in terms of cell morphology, inhibition rate of cell proliferation, and insulin secretion. Simultaneously, we developed a circular drug concentration gradient generator based on microfluidic technology. We integrated the high-glucose 3D INS-1 cell model and the circular concentration gradient generator in the same microdevice, tested the utility of this microdevice in the field of drug screening with glipizide as a model drug, and found that the microdevice was more sensitive than the traditional device to screen the anti-diabetic drugs.

Bioengineered Liver Models for Drug Testing and Cell Differentiation Studies

In vitro models of the human liver are important for the following: (1) mitigating the risk of drug-induced liver injury to human beings, (2) modeling human liver diseases, (3) elucidating the role of single and combinatorial microenvironmental cues on liver cell function, and (4) enabling cell-based therapies in the clinic. Methods to isolate and culture primary human hepatocytes (PHHs), the gold standard for building human liver models, were developed several decades ago; however, PHHs show a precipitous decline in phenotypic functions in 2-dimensional extracellular matrix-coated conventional culture formats, which does not allow chronic treatment with drugs and other stimuli. The development of several engineering tools, such as cellular microarrays, protein micropatterning, microfluidics, biomaterial scaffolds, and bioprinting, now allow precise control over the cellular microenvironment for enhancing the function of both PHHs and induced pluripotent stem cell-derived human hepatocyte-like cells; long-term (4+ weeks) stabilization of hepatocellular function typically requires co-cultivation with liver-derived or non-liver-derived nonparenchymal cell types. In addition, the recent development of liver organoid culture systems can provide a strategy for the enhanced expansion of therapeutically relevant cell types. Here, we discuss advances in engineering approaches for constructing in vitro human liver models that have utility in drug screening and for determining microenvironmental determinants of liver cell differentiation/function. Design features and validation data of representative models are presented to highlight major trends followed by the discussion of pending issues that need to be addressed. Overall, bioengineered liver models have significantly advanced our understanding of liver function and injury, which will prove useful for drug development and ultimately cell-based therapies.

The Microwell-mesh: A high-throughput 3D prostate cancer spheroid and drug-testing platform

Treatment following early diagnosis of Prostate cancer (PCa) is increasingly successful, whilst the treatment of advanced and metastatic PCa remains challenging. A major limitation in the development of new therapies is the prediction of drug efficacy using in vitro models. Classic in vitro 2-dimensional (2D) cell monolayer cultures are hypersensitive to anti-cancer drugs. As a result, there has been a surge in the development of platforms that enable three dimensional (3D) cultures thought to better replicate natural physiology and better predict drug efficacy. A deficiency associated with most 3D culture systems is that their complexity reduces the number of replicates and combination therapies that can be feasibly evaluated. Herein, we describe the use of a microwell platform that utilises a nylon mesh to retain 3D micro-tumours in discrete microwells; termed the Microwell-mesh. The Microwell-mesh enables the manufacture of ~150 micro-tumours per well in a 48-well plate, and response to anti-tumour drugs can be readily quantified. Our results demonstrate that 3D micro-tumours, unlike 2D monolayers, are not hypersensitive to Docetaxel or Abiraterone Acetate, providing a superior platform for the evaluation of sequential drug treatment. In summary, the Microwell-mesh provides an efficient 3D micro-tumour platform for single and sequential drug screening.

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

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

Advances in Engineered Liver Models for Investigating Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a major cause of drug attrition. Testing drugs on human liver models is essential to mitigate the risk of clinical DILI since animal studies do not always suffice due to species-specific differences in liver pathways. While primary human hepatocytes (PHHs) can be cultured on extracellular matrix proteins, a rapid decline in functions leads to low sensitivity (<50%) in DILI prediction. Semiconductor-driven engineering tools now allow precise control over the hepatocyte microenvironment to enhance and stabilize phenotypic functions. The latest platforms coculture PHHs with stromal cells to achieve hepatic stability and enable crosstalk between the various liver cell types towards capturing complex cellular mechanisms in DILI. The recent introduction of induced pluripotent stem cell-derived human hepatocyte-like cells can potentially allow a better understanding of interindividual differences in idiosyncratic DILI. Liver models are also being coupled to other tissue models via microfluidic perfusion to study the intertissue crosstalk upon drug exposure as in a live organism. Here, we review the major advances being made in the engineering of liver models and readouts as they pertain to DILI investigations. We anticipate that engineered human liver models will reduce drug attrition, animal usage, and cases of DILI in humans.

Enhanced Adipogenic Differentiation of Human Adipose-Derived Stem Cells in an In Vitro Microenvironment: The Preparation of Adipose-Like Microtissues Using a Three-Dimensional Culture

The application of stem cells for cell therapy has been extensively studied in recent years. Among the various types of stem cells, human adipose tissue-derived stem cells (ASCs) can be obtained in large quantities with relatively few passages, and they possess a stable quality. ASCs can differentiate into a number of cell types, such as adipose cells and ectodermal cells. We therefore focused on the in vitro microenvironment required for such differentiation and attempted to induce the differentiation of human stem cells into microtissues using a microelectromechanical system. We first evaluated the adipogenic differentiation of human ASC spheroids in a three-dimensional (3D) culture. We then created the in vitro microenvironment using a 3D combinatorial TASCL device and attempted to induce the adipogenic differentiation of human ASCs. The differentiation of human ASC spheroids cultured in maintenance medium and those cultured in adipocyte differentiation medium was evaluated via Oil red O staining using lipid droplets based on the quantity of accumulated triglycerides. The differentiation was confirmed in both media, but the human ASCs in the 3D cultures contained higher amounts of triglycerides than those in the 2D cultures. In the short culture period, greater adipogenic differentiation was observed in the 3D cultures than in the 2D cultures. The 3D culture using the TASCL device with adipogenic differentiation medium promoted greater differentiation of human ASCs into adipogenic lineages than either a 2D culture or a culture using a maintenance medium. In summary, the TASCL device created a hospitable in vitro microenvironment and may therefore be a useful tool for the induction of differentiation in 3D culture. The resultant human ASC spheroids were "adipose-like microtissues" that formed spherical aggregation perfectly and are expected to be applicable in regenerative medicine as well as cell transplantation.

Engineered Liver Platforms for Different Phases of Drug Development

Drug-induced liver injury (DILI) remains a leading cause of drug withdrawal from human clinical trials or the marketplace. Owing to species-specific differences in liver pathways, predicting human-relevant DILI using in vitro human liver models is crucial. Microfabrication tools allow precise control over the cellular microenvironment towards stabilizing liver functions for weeks. These tools are used to engineer human liver models with different complexities and throughput using cell lines, primary cells, and stem cell-derived hepatocytes. Including multiple human liver cell types can mimic cell-cell interactions in specific types of DILI. Finally, organ-on-a-chip models demonstrate how drug metabolism in the liver affects multi-organ toxicities. In this review we survey engineered human liver platforms within the needs of different phases of drug development.

Characterization of a functional C3A liver spheroid model

More predictive in vitro liver models are a critical requirement for preclinical screening of compounds demonstrating hepatotoxic liability. 3D liver spheroids have been shown to have an enhanced functional lifespan compared to 2D monocultures; however a detailed characterisation of spatiotemporal function and structure of spheroids still needs further attention before widespread use in industry. We have developed and characterized the structure and function of a 3D liver spheroid model formed from C3A hepatoma cells. Spheroids were viable and maintained a compact in vivo-like structure with zonation features for up to 32 days. MRP2 and Pgp transporters had polarised expression on the canalicular membrane of cells in the spheroids and were able to functionally transport CMFDA substrate into these canalicular structures. Spheroids expressed CYP2E1 and were able to synthesise and secrete albumin and urea to a higher degree than monolayer C3A cultures. Penetration of doxorubicin throughout the spheroid core was demonstrated. Spheroids showed increased susceptibility to hepatotoxins when compared to 2D cultures, with acetaminophen having an IC50 of 7.2 mM in spheroids compared to 33.8 mM in monolayer culture. To conclude, we developed an alternative method for creating C3A liver spheroids and demonstrated cellular polarisation and zonation, as well as superior liver-specific functionality and more sensitive toxicological response compared to standard 2D liver models, confirming a more in vivo-like liver model.