A vascularized model of the human liver mimics regenerative responses

Microfluidic human physiomimetic liver model as a screening platform for drug induced liver injury

The pre-clinical animal models often fail to predict intrinsic and idiosyncratic drug induced liver injury (DILI), thus contributing to drug failures in clinical trials, black box warnings and withdrawal of marketed drugs. This suggests a critical need for human-relevant in vitro models to predict diverse DILI phenotypes. In this study, a porcine liver extracellular matrix (ECM) based biomaterial ink with high printing fidelity, biocompatibility and tunable rheological and mechanical properties is formulated for supporting both parenchymal and non-parenchymal cells. Further, we applied 3D printing and microfluidic technology to bioengineer a human physiomimetic liver acinus model (HPLAM), recapitulating the radial hepatic cord-like structure with functional sinusoidal microvasculature network, biochemical and biophysical properties of native liver acinus. Intriguingly, the human derived hepatic cells incorporated HPLAM cultured under physiologically relevant microenvironment, acts as metabolic biofactories manifesting enhanced hepatic functionality, secretome levels and biomarkers expression over several weeks. We also report that the matured HPLAM reproduces dose- and time-dependent hepatotoxic response of human clinical relevance to drugs typically recognized for inducing diverse DILI phenotypes as compared to conventional static culture. Overall, the developed HPLAM emulates in vivo like functions and may provide a useful platform for DILI risk assessment to better determine safety and human risk.

Donor-Derived Engineered Microvessels for Cardiovascular Risk Stratification of Patients with Kidney Failure

Cardiovascular disease is the cause of death in ≈50% of hemodialysis patients. Accumulation of uremic solutes in systemic circulation is thought to be a key driver of the endothelial dysfunction that underlies elevated cardiovascular events. A challenge in understanding the mechanisms relating chronic kidney disease to cardiovascular disease is the lack of in vitro models that allow screening of the effects of the uremic environment on the endothelium. Here, a method is described for microfabrication of human blood vessels from donor cells and perfused with donor serum. The resulting donor-derived microvessels are used to quantify vascular permeability, a hallmark of endothelial dysfunction, in response to serum spiked with pathophysiological levels of indoxyl sulfate, and in response to serum from patients with chronic kidney disease and from uremic pigs. The uremic environment has pronounced effects on microvascular integrity as demonstrated by irregular cell-cell junctions and increased permeability in comparison to cell culture media and healthy serum. Moreover, the engineered microvessels demonstrate an increase in sensitivity compared to traditional 2D assays. Thus, the devices and the methods presented here have the potential to be utilized to risk stratify and to direct personalized treatments for patients with chronic kidney disease.

Morphological profiling for drug discovery in the era of deep learning

Morphological profiling is a valuable tool in phenotypic drug discovery. The advent of high-throughput automated imaging has enabled the capturing of a wide range of morphological features of cells or organisms in response to perturbations at the single-cell resolution. Concurrently, significant advances in machine learning and deep learning, especially in computer vision, have led to substantial improvements in analyzing large-scale high-content images at high throughput. These efforts have facilitated understanding of compound mechanism of action, drug repurposing, characterization of cell morphodynamics under perturbation, and ultimately contributing to the development of novel therapeutics. In this review, we provide a comprehensive overview of the recent advances in the field of morphological profiling. We summarize the image profiling analysis workflow, survey a broad spectrum of analysis strategies encompassing feature engineering- and deep learning-based approaches, and introduce publicly available benchmark datasets. We place a particular emphasis on the application of deep learning in this pipeline, covering cell segmentation, image representation learning, and multimodal learning. Additionally, we illuminate the application of morphological profiling in phenotypic drug discovery and highlight potential challenges and opportunities in this field.

TruD technology for the study of epi- and endothelial tubes in vitro

Beyond the smallest organisms, animals rely on tubes to transport cells, oxygen, nutrients, waste products, and a great variety of secretions. The cardiovascular system, lungs, gastrointestinal and genitourinary tracts, as well as major exocrine glands, are all composed of tubes. Paradoxically, despite their ubiquitous importance, most existing devices designed to study tubes are relatively complex to manufacture and/or utilize. The present work describes a simple method for generating tubes in vitro using nothing more than a low-cost 3D printer along with general lab supplies. The technology is termed "TruD", an acronym for true dimensional. Using this technology, it is readily feasible to cast tubes embedded in ECM with easy access to the lumen. The design is modular to permit more complex tube arrangements and to sustain flow. Importantly, by virtue of its simplicity, TruD technology enables typical molecular cell biology experiments where multiple conditions are assayed in replicate.

Fibrosis-on-Chip: A Guide to Recapitulate the Essential Features of Fibrotic Disease

Fibrosis, which is primarily marked by excessive extracellular matrix (ECM) deposition, is a pathophysiological process associated with many disorders, which ultimately leads to organ dysfunction and poor patient outcomes. Despite the high prevalence of fibrosis, currently there exist few therapeutic options, and importantly, there is a paucity of in vitro models to accurately study fibrosis. This review discusses the multifaceted nature of fibrosis from the viewpoint of developing organ-on-chip (OoC) disease models, focusing on five key features: the ECM component, inflammation, mechanical cues, hypoxia, and vascularization. The potential of OoC technology is explored for better modeling these features in the context of studying fibrotic diseases and the interplay between various key features is emphasized. This paper reviews how organ-specific fibrotic diseases are modeled in OoC platforms, which elements are included in these existing models, and the avenues for novel research directions are highlighted. Finally, this review concludes with a perspective on how to address the current gap with respect to the inclusion of multiple features to yield more sophisticated and relevant models of fibrotic diseases in an OoC format.

Beyond the hype and toward application: liver complex in vitro models in preclinical drug safety

INTRODUCTION

Drug induced Liver-Injury (DILI) is a leading cause of drug attrition and complex in vitro models (CIVMs), including three dimensional (3D) spheroids, 3D bio printed tissues and flow-based systems, could improve preclinical prediction. Although CIVMs have demonstrated good sensitivity and specificity in DILI detection their adoption remains limited.

AREAS COVERED

This article describes DILI, the challenges with its prediction and the current strategies and models that are being used. It reviews data from industry-FDA collaborations and strategic partnerships and finishes with an outlook of CIVMs in preclinical toxicity testing. Literature searches were performed using PubMed and Google Scholar while product information was collected from manufacturer websites.

EXPERT OPINION

Liver CIVMs are promising models for predicting DILI although, a decade after their introduction, routine use by the pharmaceutical industry is limited. To accelerate their adoption, several industry-regulator-developer partnerships or consortia have been established to guide the development and qualification. Beyond this, liver CIVMs should continue evolving to capture greater immunological mimicry while partnering with computational approaches to deliver systems that change the paradigm of predicting DILI.

On-Chip Reconstitution of Uniformly Shear-Sensing 3D Matrix-embedded Multicellular Blood Microvessel

Preclinical human-relevant modeling of organ-specific vasculature offers a unique opportunity to recreate pathophysiological intercellular, tissue-tissue, and cell-matrix interactions for a broad range of applications. Here, we present a reliable, and simply reproducible process for constructing user-controlled long rounded extracellular matrix (ECM)-embedded vascular microlumens on-chip for endothelization and co-culture with stromal cells obtained from human lung. We demonstrate the critical impact of microchannel cross-sectional geometry and length on uniform distribution and magnitude of vascular wall shear stress, which is key when emulating in vivo-observed blood flow biomechanics in health and disease. In addition, we provide an optimization protocol for multicellular culture and functional validation of the system. Moreover, we show the ability to finely tune rheology of the three-dimensional natural matrix surrounding the vascular microchannel to match pathophysiological stiffness. In summary, we provide the scientific community with a matrix-embedded microvasculature on-chip populated with all-primary human-derived pulmonary endothelial cells and fibroblasts to recapitulate and interrogate lung parenchymal biology, physiological responses, vascular biomechanics, and disease biogenesis in vitro. Such a mix-and-match synthetic platform can be feasibly adapted to study blood vessels, matrix, and ECM-embedded cells in other organs and be cellularized with additional stromal cells.

Using Liver Organoids as Models to Study the Pathobiology of Rare Liver Diseases

Liver organoids take advantage of several important features of pluripotent stem cells that self-assemble in a three-dimensional culture matrix and reproduce many aspects of the complex organization found within their native tissue or organ counterparts. Compared to other 2D or 3D in vitro models, organoids are widely believed to be genetically stable or docile structures that can be programmed to virtually recapitulate certain biological, physiological, or pathophysiological features of original tissues or organs in vitro. Therefore, organoids can be exploited as effective substitutes or miniaturized models for the study of the developmental mechanisms of rare liver diseases, drug discovery, the accurate evaluation of personalized drug responses, and regenerative medicine applications. However, the bioengineering of organoids currently faces many groundbreaking challenges, including a need for a reasonable tissue size, structured organization, vascularization, functional maturity, and reproducibility. In this review, we outlined basic methodologies and supplements to establish organoids and summarized recent technological advances for experimental liver biology. Finally, we discussed the therapeutic applications and current limitations.

Recent Advances in Liver Tissue Engineering as an Alternative and Complementary Approach for Liver Transplantation

Acute and chronic liver diseases cause significant morbidity and mortality worldwide, affecting millions of people. Liver transplantation is the primary intervention method, replacing a non-functional liver with a functional one. However, the field of liver transplantation faces challenges such as donor shortage, postoperative complications, immune rejection, and ethical problems. Consequently, there is an urgent need for alternative therapies that can complement traditional transplantation or serve as an alternative method. In this review, we explore the potential of liver tissue engineering as a supplementary approach to liver transplantation, offering benefits to patients with severe liver dysfunctions.

Microfluidic Fabrication of MicroRNA-Induced Hepatocyte-Like Cells/Human Umbilical Vein Endothelial Cells-Laden Microgels for Acute Liver Failure Treatment

Acute liver failure (ALF) is a critical life-threatening disease that occurs due to a rapid loss in hepatocyte functions. Hepatocyte transplantation holds great potential for ALF treatment, as it rapidly supports liver biofunctions and enhances liver regeneration. However, hepatocyte transplantation is still limited by renewable and ongoing cell sources. In addition, intravenously injected hepatocytes are primarily trapped in the lungs and have limited efficacy because of the rapid clearance in vivo. Here, we designed a Y-shaped DNA nanostructure to deliver microRNA-122 (Y-miR122), which could induce the hepatic differentiation and maturation of human mesenchymal stem cells. mRNA sequencing analysis revealed that the Y-miR122 promoted important hepatic biofunctions of the induced hepatocyte-like cells including fat and lipid metabolism, drug metabolism, and liver development. To further improve hepatocyte transplantation efficiency and therapeutic effects in ALF treatment, we fabricated protective microgels for the delivery of Y-miR122-induced hepatocyte-like cells based on droplet microfluidic technology. When cocultured with human umbilical vein endothelial cells in microgels, the hepatocyte-like cells exhibited an increase in hepatocyte-associated functions, including albumin secretion and cytochrome P450 activity. Notably, upon transplantation into the ALF mouse model, the multiple cell-laden microgels effectively induced the restoration of liver function and enhanced liver regeneration. Overall, this study presents an efficient approach from the generation of hepatocyte-like cells to hepatocyte transplantation in ALF therapy.

Vascularized liver-on-a-chip model to investigate nicotine-induced dysfunction

The development of physiologically relevant in vitro systems for simulating disease onset and progression and predicting drug metabolism holds tremendous value in reducing drug discovery time and cost. However, many of these platforms lack accuracy in replicating the tissue architecture and multicellular interactions. By leveraging three-dimensional cell culture, biomimetic soft hydrogels, and engineered stimuli, in vitro models have continued to progress. Nonetheless, the incorporation of the microvasculature has been met with many challenges, specifically with the addition of parenchymal cell types. Here, a systematic approach to investigating the initial seeding density of endothelial cells and its effects on interconnected networks was taken and combined with hepatic spheroids to form a liver-on-a-chip model. Leveraging this system, nicotine's effects on microvasculature and hepatic function were investigated. The findings indicated that nicotine led to interrupted adherens junctions, decreased guanosine triphosphate cyclohydrolase 1 expression, impaired angiogenesis, and lowered barrier function, all key factors in endothelial dysfunction. With the combination of the optimized microvascular networks, a vascularized liver-on-a-chip was formed, providing functional xenobiotic metabolism and synthesis of both albumin and urea. This system provides insight into potential hepatotoxicity caused by various drugs and allows for assessing vascular dysfunction in a high throughput manner.

A method to generate perfusable physiologic-like vascular channels within a liver-on-chip model

The human vasculature is essential in organs and tissues for the transport of nutrients, metabolic waste products, and the maintenance of homeostasis. The integration of vessels in in vitro organs-on-chip may, therefore, improve the similarity to the native organ microenvironment, ensuring proper physiological functions and reducing the gap between experimental research and clinical outcomes. This gap is particularly evident in drug testing and the use of vascularized models may provide more realistic insights into human responses to drugs in the pre-clinical phases of the drug development pipeline. In this context, different vascularized liver models have been developed to recapitulate the architecture of the hepatic sinusoid, exploiting either porous membranes or bioprinting techniques. In this work, we developed a method to generate perfusable vascular channels with a circular cross section within organs-on-chip without any interposing material between the parenchyma and the surrounding environment. Through this technique, vascularized liver sinusoid-on-chip systems with and without the inclusion of the space of Disse were designed and developed. The recapitulation of the Disse layer, therefore, a gap between hepatocytes and endothelial cells physiologically present in the native liver milieu, seems to enhance hepatic functionality (e.g., albumin production) compared to when hepatocytes are in close contact with endothelial cells. These findings pave the way to numerous further uses of microfluidic technologies coupled with vascularized tissue models (e.g., immune system perfusion) as well as the integration within multiorgan-on-chip settings.

Endothelial cell activation mediated by cold ischemia-released mitochondria is partially inhibited by defibrotide and impacts on early allograft function following liver transplantation

DAMPs (danger-associated molecular patterns) are self-molecules of the organism that appear after damage. The endothelium plays several roles in organ rejection, such as presenting alloantigens to T cells and contributing to the development of inflammation and thrombosis. This study aimed to assess whether DAMPs present in the organ preservation solution (OPS) after cold ischemic storage (CIS) contribute to exacerbating the endothelial response to an inflammatory challenge and whether defibrotide treatment could counteract this effect. The activation of cultured human umbilical vein endothelial cells (HUVECs) was analyzed after challenging with end-ischemic OPS (eiOPS) obtained after CIS. Additionally, transwell assays were performed to study the ability of eiOPS to attract lymphocytes across the endothelium. The study revealed that eiOPS upregulated the expression of MCP-1 and IL-6 in HUVECs. Moreover, eiOPS increased the membrane expression of ICAM-1and HLA-DR, which facilitated leukocyte migration toward a chemokine gradient. Furthermore, eiOPS demonstrated its chemoattractant ability. This activation was mediated by free mitochondria. Defibrotide was found to partially inhibit the eiOPS-mediated activation. Moreover, the eiOPS-mediated activation of endothelial cells (ECs) correlated with early allograft dysfunction in liver transplant patients. Our finding provide support for the hypothesis that mitochondria released during cold ischemia could trigger EC activation, leading to complications in graft outcomes. Therefore, the analysis and quantification of free mitochondria in the eiOPS samples obtained after CIS could provide a predictive value for monitoring the progression of transplantation. Moreover, defibrotide emerges as a promising therapeutic agent to mitigate the damage induced by ischemia in donated organs.

Placental scaffolds as a potential biological platform for embryonic stem cells differentiation into hepatic-like cells lineage: A pilot study

Hepatic microenvironment plays an essential role in liver regeneration, providing the necessary conditions for cell proliferation, differentiation and tissue rearrangement. One of the key factors for hepatic tissue reconstruction is the extracellular matrix (ECM), which through collagenous and non-collagenous proteins provide a three-dimensional structure that confers support for cell adhesion and assists on their survival and maintenance. In this scenario, placental ECM may be eligible for hepatic tissue reconstruction, once these scaffolds hold the major components required for cell support. Therefore, this preliminary study aimed to access the possibility of mouse embryonic stem cells differentiation into hepatocyte-like cells on placental scaffolds in a three-dimensional dynamic system using a Rotary Cell Culture System. Following a four-phase differentiation protocol that simulates liver embryonic development events, the preliminary results showed that a significant quantity of cells adhered and interacted with the scaffold through outer and inner surfaces. Positive immunolabelling for alpha fetus protein and CK7 suggest presence of hepatoblast phenotype cells, and CK18 and Albumin positive immunolabelling suggest the presence of hepatocyte-like phenotype cells, demonstrating the presence of a heterogeneous population into the recellularized scaffolds. Periodic Acid Schiff-Diastase staining confirmed the presence of glycogen storage, indicating that differentiate cells acquired a hepatic-like phenotype. In conclusion, these preliminary results suggested that mouse placental scaffolds might be used as a biological platform for stem cells differentiation into hepatic-like cells and their establishment, which may be a promissing biomaterial for hepatic tissue reconstruction.

Application of colloidal photonic crystals in study of organoids

As alternative disease models, other than 2D cell lines and patient-derived xenografts, organoids have preferable in vivo physiological relevance. However, both endogenous and exogenous limitations impede the development and clinical translation of these organoids. Fortunately, colloidal photonic crystals (PCs), which benefit from favorable biocompatibility, brilliant optical manipulation, and facile chemical decoration, have been applied to the engineering of organoids and have achieved the desirable recapitulation of the ECM niche, well-defined geometrical onsets for initial culture, in situ multiphysiological parameter monitoring, single-cell biomechanical sensing, and high-throughput drug screening with versatile functional readouts. Herein, we review the latest progress in engineering organoids fabricated from colloidal PCs and provide inputs for future research.

Improvements in Maturity and Stability of 3D iPSC-Derived Hepatocyte-like Cell Cultures

Induced pluripotent stem cell (iPSC) technology enables differentiation of human hepatocytes or hepatocyte-like cells (iPSC-HLCs). Advances in 3D culturing platforms enable the development of more in vivo-like liver models that recapitulate the complex liver architecture and functionality better than traditional 2D monocultures. Moreover, within the liver, non-parenchymal cells (NPCs) are critically involved in the regulation and maintenance of hepatocyte metabolic function. Thus, models combining 3D culture and co-culturing of various cell types potentially create more functional in vitro liver models than 2D monocultures. Here, we report the establishment of 3D cultures of iPSC-HLCs alone and in co-culture with human umbilical vein endothelial cells (HUVECs) and adipose tissue-derived mesenchymal stem/stromal cells (hASCs). The 3D cultures were performed as spheroids or on microfluidic chips utilizing various biomaterials. Our results show that both 3D spheroid and on-chip culture enhance the expression of mature liver marker genes and proteins compared to 2D. Among the spheroid models, we saw the best functionality in iPSC-HLC monoculture spheroids. On the contrary, in the chip system, the multilineage model outperformed the monoculture chip model. Additionally, the optical projection tomography (OPT) and electrical impedance tomography (EIT) system revealed changes in spheroid size and electrical conductivity during spheroid culture, suggesting changes in cell-cell connections. Altogether, the present study demonstrates that iPSC-HLCs can successfully be cultured in 3D as spheroids and on microfluidic chips, and co-culturing iPSC-HLCs with NPCs enhances their functionality. These 3D in vitro liver systems are promising human-derived platforms usable in various liver-related studies, specifically when using patient-specific iPSCs.

A microwell platform for high-throughput longitudinal phenotyping and selective retrieval of organoids

Organoids are powerful experimental models for studying the ontogeny and progression of various diseases including cancer. Organoids are conventionally cultured in bulk using an extracellular matrix mimic. However, bulk-cultured organoids physically overlap, making it impossible to track the growth of individual organoids over time in high throughput. Moreover, local spatial variations in bulk matrix properties make it difficult to assess whether observed phenotypic heterogeneity between organoids results from intrinsic cell differences or differences in the microenvironment. Here, we developed a microwell-based method that enables high-throughput quantification of image-based parameters for organoids grown from single cells, which can further be retrieved from their microwells for molecular profiling. Coupled with a deep learning image-processing pipeline, we characterized phenotypic traits including growth rates, cellular movement, and apical-basal polarity in two CRISPR-engineered human gastric organoid models, identifying genomic changes associated with increased growth rate and changes in accessibility and expression correlated with apical-basal polarity. A record of this paper's transparent peer review process is included in the supplemental information.

Fluid flow to mimic organ function in 3D in vitro models

Many different strategies can be found in the literature to model organ physiology, tissue functionality, and disease in vitro; however, most of these models lack the physiological fluid dynamics present in vivo. Here, we highlight the importance of fluid flow for tissue homeostasis, specifically in vessels, other lumen structures, and interstitium, to point out the need of perfusion in current 3D in vitro models. Importantly, the advantages and limitations of the different current experimental fluid-flow setups are discussed. Finally, we shed light on current challenges and future focus of fluid flow models applied to the newest bioengineering state-of-the-art platforms, such as organoids and organ-on-a-chip, as the most sophisticated and physiological preclinical platforms.

Liver dECM-Gelatin Composite Bioink for Precise 3D Printing of Highly Functional Liver Tissues

In recent studies, liver decellularized extracellular matrix (dECM)-based bioinks have gained significant attention for their excellent compatibility with hepatocytes. However, their low printability limits the fabrication of highly functional liver tissue. In this study, a new liver dECM-gelatin composite bioink (dECM gBioink) was developed to overcome this limitation. The dECM gBioink was prepared by incorporating a viscous gelatin mixture into the liver dECM material. The novel dECM gBioink showed 2.44 and 10.71 times higher bioprinting resolution and compressive modulus, respectively, than a traditional dECM bioink. In addition, the new bioink enabled stable stacking with 20 or more layers, whereas a structure printed with the traditional dECM bioink collapsed. Moreover, the proposed dECM gBioink exhibited excellent hepatocyte and endothelial cell compatibility. At last, the liver lobule mimetic structure was successfully fabricated with a precisely patterned endothelial cell cord-like pattern and primary hepatocytes using the dECM gBioink. The fabricated lobule structure exhibited excellent hepatic functionalities and dose-dependent responses to hepatotoxic drugs. These results demonstrated that the gelatin mixture can significantly improve the printability and mechanical properties of the liver dECM materials while maintaining good cytocompatibility. This novel liver dECM gBioink with enhanced 3D printability and resolution can be used as an advanced tool for engineering highly functional liver tissues.

Surface modifications of COP-based microfluidic devices for improved immobilisation of hydrogel proteins: long-term 3D culture with contractile cell types and ischaemia model

The tissue microenvironment plays a crucial role in tissue homeostasis and disease progression. However, the in vitro simulation has been limited by the lack of adequate biomimetic models in the last decades. Thanks to the advent of microfluidic technology for cell culture applications, these complex microenvironments can be recreated by combining hydrogels, cells and microfluidic devices. Nevertheless, this advance has several limitations. When cultured in three-dimensional (3D) hydrogels inside microfluidic devices, contractile cells may exert forces that eventually collapse the 3D structure. Disrupting the compartmentalisation creates an obstacle to long-term or highly cell-concentrated assays, which are extremely relevant for multiple applications such as fibrosis or ischaemia. Therefore, we tested surface treatments on cyclic-olefin polymer-based microfluidic devices (COP-MD) to promote the immobilisation of collagen as a 3D matrix protein. Thus, we compared three surface treatments in COP devices for culturing human cardiac fibroblasts (HCF) embedded in collagen hydrogels. We determined the immobilisation efficiency of collagen hydrogel by quantifying the hydrogel transversal area within the devices at the studied time points. Altogether, our results indicated that surface modification with polyacrylic acid photografting (PAA-PG) of COP-MD is the most effective treatment to avoid the quick collapse of collagen hydrogels. As a proof-of-concept experiment, and taking advantage of the low-gas permeability properties of COP-MD, we studied the application of PAA-PG pre-treatment to generate a self-induced ischaemia model. Different necrotic core sizes were developed depending on initial HCF density seeding with no noticeable gel collapse. We conclude that PAA-PG allows long-term culture, gradient generation and necrotic core formation of contractile cell types such as myofibroblasts. This novel approach will pave the way for new relevant in vitro co-culture models where fibroblasts play a key role such as wound healing, tumour microenvironment and ischaemia within microfluidic devices.

Biomechanics in liver regeneration after partial hepatectomy

The liver is a complicated organ within the body that performs wide-ranging and vital functions and also has a unique regenerative capacity after hepatic tissue injury and cell loss. Liver regeneration from acute injury is always beneficial and has been extensively studied. Experimental models including partial hepatectomy (PHx) reveal that extracellular and intracellular signaling pathways can help the liver recover to its equivalent size and weight prior to an injury. In this process, mechanical cues possess immediate and drastic changes in liver regeneration after PHx and also serve as main triggering factors and significant driving forces. This review summarized the biomechanics progress in liver regeneration after PHx, mainly focusing on PHx-based hemodynamics changes in liver regeneration and the decoupling of mechanical forces in hepatic sinusoids including shear stress, mechanical stretch, blood pressure, and tissue stiffness. Also discussed were the potential mechanosensors, mechanotransductive pathways, and mechanocrine responses under varied mechanical loading in vitro. Further elucidating these mechanical concepts in liver regeneration helps establish a comprehensive understanding of the biochemical factors and mechanical cues in this process. Proper adjustment of mechanical loading within the liver might preserve and restore liver functions in clinical settings, serving as an effective therapy for liver injury and diseases.

Liver Regeneration and Immunity: A Tale to Tell

The physiological importance of the liver is demonstrated by its unique and essential ability to regenerate following extensive injuries affecting its function. By regenerating, the liver reacts to hepatic damage and thus enables homeostasis to be restored. The aim of this review is to add new findings that integrate the regenerative pathway to the current knowledge. An optimal regeneration is achieved through the integration of two main pathways: IL-6/JAK/STAT3, which promotes hepatocyte proliferation, and PI3K/PDK1/Akt, which in turn enhances cell growth. Proliferation and cell growth are events that must be balanced during the three phases of the regenerative process: initiation, proliferation and termination. Achieving the correct liver/body weight ratio is ensured by several pathways as extracellular matrix signalling, apoptosis through caspase-3 activation, and molecules including transforming growth factor-beta, and cyclic adenosine monophosphate. The actors involved in the regenerative process are numerous and many of them are also pivotal players in both the immune and non-immune inflammatory process, that is observed in the early stages of hepatic regeneration. Balance of Th17/Treg is important in liver inflammatory process outcomes. Knowledge of liver regeneration will allow a more detailed characterisation of the molecular mechanisms that are crucial in the interplay between proliferation and inflammation.

Liver-on-a-chip: Considerations, advances, and beyond

The liver is the largest internal organ in the human body with largest mass of glandular tissue. Modeling the liver has been challenging due to its variety of major functions, including processing nutrients and vitamins, detoxification, and regulating body metabolism. The intrinsic shortfalls of conventional two-dimensional (2D) cell culture methods for studying pharmacokinetics in parenchymal cells (hepatocytes) have contributed to suboptimal outcomes in clinical trials and drug development. This prompts the development of highly automated, biomimetic liver-on-a-chip (LOC) devices to simulate native liver structure and function, with the aid of recent progress in microfluidics. LOC offers a cost-effective and accurate model for pharmacokinetics, pharmacodynamics, and toxicity studies. This review provides a critical update on recent developments in designing LOCs and fabrication strategies. We highlight biomimetic design approaches for LOCs, including mimicking liver structure and function, and their diverse applications in areas such as drug screening, toxicity assessment, and real-time biosensing. We capture the newest ideas in the field to advance the field of LOCs and address current challenges.

The Influence of Interdisciplinary Work towards Advancing Knowledge on Human Liver Physiology

The knowledge accumulated throughout the years about liver regeneration has allowed a better understanding of normal liver physiology, by reconstructing the sequence of steps that this organ follows when it must rebuild itself after being injured. The scientific community has used several interdisciplinary approaches searching to improve liver regeneration and, therefore, human health. Here, we provide a brief history of the milestones that have advanced liver surgery, and review some of the new insights offered by the interdisciplinary work using animals, in vitro models, tissue engineering, or mathematical models to help advance the knowledge on liver regeneration. We also present several of the main approaches currently available aiming at providing liver support and overcoming organ shortage and we conclude with some of the challenges found in clinical practice and the ethical issues that have concomitantly emerged with the use of those approaches.

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.