Effect of biochemical and biomechanical factors on vascularization of kidney organoid-on-a-chip

From organoids to organoids-on-a-chip: Current applications and challenges in biomedical research

ABSTRACT

The high failure rates in clinical drug development based on animal models highlight the urgent need for more representative human models in biomedical research. In response to this demand, organoids and organ chips were integrated for greater physiological relevance and dynamic, controlled experimental conditions. This innovative platform-the organoids-on-a-chip technology-shows great promise in disease modeling, drug discovery, and personalized medicine, attracting interest from researchers, clinicians, regulatory authorities, and industry stakeholders. This review traces the evolution from organoids to organoids-on-a-chip, driven by the necessity for advanced biological models. We summarize the applications of organoids-on-a-chip in simulating physiological and pathological phenotypes and therapeutic evaluation of this technology. This section highlights how integrating technologies from organ chips, such as microfluidic systems, mechanical stimulation, and sensor integration, optimizes organoid cell types, spatial structure, and physiological functions, thereby expanding their biomedical applications. We conclude by addressing the current challenges in the development of organoids-on-a-chip and offering insights into the prospects. The advancement of organoids-on-a-chip is poised to enhance fidelity, standardization, and scalability. Furthermore, the integration of cutting-edge technologies and interdisciplinary collaborations will be crucial for the progression of organoids-on-a-chip technology.

Kidney Fibrosis In Vitro and In Vivo Models: Path Toward Physiologically Relevant Humanized Models

Chronic kidney disease (CKD) affects over 10% of the global population and is a leading cause of mortality. Kidney fibrosis, a key endpoint of CKD, disrupts nephron tubule anatomy and filtration function, and disease pathomechanisms are not fully understood. Kidney fibrosis is currently investigated with in vivo models, that gradually support the identification of possible mechanisms of fibrosis, but with limited translational research, as they do not fully recapitulate human kidney physiology, metabolism, and molecular pathways. In vitro 2D cell culture models are currently used, as a starting point in disease modeling and pharmacology, however, they lack the 3D kidney architecture complexity and functions. The failure of several therapies and drugs in clinical trials highlights the urgent need for advanced 3D in vitro models. This review discusses the urinary system's anatomy, associated diseases, and diagnostic methods, including biomarker analysis and tissue biopsy. It evaluates 2D and in vivo models, highlighting their limitations. The review explores the state-of-the-art 3D-humanized in vitro models, such as 3D cell aggregates, on-chip models, biofabrication techniques, and hybrid models, which aim to mimic kidney morphogenesis and functions. These advanced models hold promise for translating new therapies and drugs for kidney fibrosis into clinics.

Induced pluripotent stem cell-based tissue models to study malaria: a new player in the research game

Most in vitro studies on parasite development and pathogenesis in the human host have been conducted using traditional primary or immortalized cells, despite their inherent limitations. Breakthroughs in the field of induced pluripotent stem cells (iPSCs) are revolutionizing disease modeling, offering alternatives to traditional in vivo and in vitro infection models. Human iPSCs differentiate into all cell types, proliferate indefinitely, and offer experimental advantages, like genome editing and donor control. iPSCs can be engineered into complex 3D tissue models that closely mimic morphology and function of their in vivo counterparts and allow for precise experimental manipulation. The physiological complexity of iPSC-based tissue models has improved rapidly. Given Plasmodium's systemic impact across multiple organs, these models provide an invaluable resource for studying parasite-tissue interactions. This opinion article focuses on recent developments of iPSC-based models for Plasmodium research. We describe the main highlights and potential use of these systems while acknowledging current limitations.

Dissecting endothelial cell heterogeneity with new tools

The formation of a blood vessel network is crucial for organ development and regeneration. Over the past three decades, the central molecular mechanisms governing blood vessel growth have been extensively studied. Recent evidence indicates that vascular endothelial cells-the specialized cells lining the inner surface of blood vessels-exhibit significant heterogeneity to meet the specific needs of different organs. This review focuses on the current understanding of endothelial cell heterogeneity, which includes both intra-organ and inter-organ heterogeneity. Intra-organ heterogeneity encompasses arterio-venous and tip-stalk endothelial cell specialization, while inter-organ heterogeneity refers to organ-specific transcriptomic profiles and functions. Advances in single-cell RNA sequencing (scRNA-seq) have enabled the identification of new endothelial subpopulations and the comparison of gene expression patterns across different subsets of endothelial cells. Integrating scRNA-seq with other high-throughput sequencing technologies promises to deepen our understanding of endothelial cell heterogeneity at the epigenetic level and in a spatially resolved context. To further explore human endothelial cell heterogeneity, vascular organoids offer powerful tools for studying gene function in three-dimensional culture systems and for investigating endothelial-tissue interactions using human cells. Developing organ-specific vascular organoids presents unique opportunities to unravel inter-organ endothelial cell heterogeneity and its implications for human disease. Emerging technologies, such as scRNA-seq and vascular organoids, are poised to transform our understanding of endothelial cell heterogeneity and pave the way for innovative therapeutic strategies to address human vascular diseases.

Organoids-on-a-chip: microfluidic technology enables culture of organoids with enhanced tissue function and potential for disease modeling

Organoids are stem-cell derived tissue structures mimicking specific structural and functional characteristics of human organs. Despite significant advancements in the field over the last decade, challenges like limited long-term functional culture and lack of maturation are hampering the implementation of organoids in biomedical research. Culture of organoids in microfluidic chips is being used to tackle these challenges through dynamic and precise control over the organoid microenvironment. This review highlights the significant breakthroughs that have been made in the innovative field of "organoids-on-chip," demonstrating how these have contributed to advancing organoid models. We focus on the incorporation of organoids representative for various tissues into chips and discuss the latest findings in multi-organoids-on-chip approaches. Additionally, we examine current limitations and challenges of the field towards the development of reproducible organoids-on-chip systems. Finally, we discuss the potential of organoids-on-chip technology for both in vitro and in vivo applications.

Application progress of bio-manufacturing technology in kidney organoids

Kidney transplantation remains a pivotal treatment modality for kidney disease, yet its progress is significantly hindered by the scarcity of donor kidneys and ethical dilemmas surrounding their procurement. As organoid technology evolves and matures, the creation of bionic human kidney organoids offers profound potential for advancing kidney disease research, drug nephrotoxicity screening, and regenerative medicine. Nevertheless, current kidney organoid models grapple with limitations such as constrained cellular differentiation, underdeveloped functional structures, and a crucial absence of vascularization. This deficiency in vascularization, in particular, stunts organoid development, restricts their size, diminishes filtration capabilities, and may trigger immune inflammatory reactions through the resulting ischemic microenvironment. Hence, the achievement of vascularization within kidney organoids and the successful establishment of functional microvascular networks constitutes a paramount goal for their future progression. In this review, we provide an overview of recent advancements in biotechnology domains, encompassing organ-on-a-chip technology, biomimetic matrices, and bioprinting, with the aim of catalyzing technological breakthroughs that can enhance the vascularization of kidney organoids and broaden their applicability. These technologies hold the key to unlocking the full potential of kidney organoids as a transformative therapeutic option for kidney disease.

Evolution of branched peptides as novel biomaterials

Branched peptide-based materials draw inspiration from dendritic structures to emulate the complex architecture of native tissues, aiming to enhance the performance of biomaterials in medical applications. These innovative materials benefit from several key features: they exhibit slower degradation rates, greater stiffness, and the ability to self-assemble. These properties are crucial for maintaining the structural integrity and functionality of the materials over time. By integrating bioactive peptides and natural polymers within their branched frameworks, these materials offer modularity and tunability and can accommodate a range of mechanical properties, degradation rates, and biological functions making them suitable for biomedical applications, including drug delivery systems, wound healing scaffolds, and tissue engineering constructs. In drug delivery, these materials can be engineered to release therapeutic agents in a controlled manner, enhancing the efficacy and safety of treatments. In wound healing, they provide a supportive environment which promotes rapid and efficient tissue repair. The combination of biomimetic design and functional adaptability makes branched peptide-based materials a promising candidate for the development of next-generation biomaterials, paving the way for significant advancements in healthcare.

Human kidney organoids for modeling the development of different diseases

The increasing incidence of kidney diseases has highlighted the need for in vitro experimental models to mimic disease development and to test new therapeutic approaches. Traditional two-dimensional in vitro experimental models are not fully able to recapitulate renal diseases. Instead, kidney organoids represent three-dimensional models that better mimic the human organ from both structural and functional points of view. Human pluripotent stem cells (PSCs), both embryonic and induced, are ideal sources for generating renal organoids. These organoids contain all renal cell types and the protocols to differentiate PSCs into renal organoids consist of three different stages that recapitulate embryonic development: mesodermal induction, nephron progenitor formation, and nephron differentiation. Recently it has been establish a renal organoid model where collecting ducts are also present. In this case, the presence of ureteric bud progenitor cells is essential. Renal organoids are particularly useful for studying genetic diseases, by introducing the specific mutations in PSCs by genome editing or generating organoids from patient-derived PSCs. Moreover, renal organoids represent promising models in toxicology studies and testing new therapeutic approaches. Renal organoids can be established also from adult stem cells. This type of organoid, named tubuloid, is composed only of epithelial cells and recapitulates the tissue repair process. The tubuloids can be generated from adult stem or progenitor cells, obtained from renal biopsies or urine, and are promising in vitro models for studying tubular functions, diseases, and regeneration. Tubuloids can be derived from patients and permit the study of genetic diseases, performing personalized drug screening and modeling renal pathologies.

A multiphysics hybrid continuum - agent-based model of in vitro vascularized organoids

BACKGROUND

Organoids are 3D in vitro models that fulfill a hierarchical function, representing a small version of living tissues and, therefore, a good approximation of cellular mechanisms. However, one of the main disadvantages of these models is the appearance of a necrotic core due to poor vascularization. The aim of this work is the development of a numerical framework that incorporates the mechanical stimulation as a key factor in organoid vascularization. Parameters, such as fluid velocity and nutrient consumption, are analyzed along the organoid evolution.

METHODS

The mathematical model created for this purpose combines continuum and discrete approaches. In the continuum part, the fluid flow and the diffusion of oxygen and nutrients are modeled using a finite element method approach. Meanwhile, the growth of the organoid, blood vessel evolution, as well as their interaction with the surrounding environment, are modeled using agent-based methods.

RESULTS

Continuum model outcomes include the distribution of shear stress, pressure and fluid velocity around the organoid surface, in addition to the concentration of oxygen and nutrients in its interior. The agent models account for cell proliferation, differentiation, organoid growth and blood vessel morphology, for the different case studies considered.

CONCLUSIONS

Two main conclusions are achieved in this work: (i) the results of the study quantitatively predict in vitro data, with an enhanced blood vessel invasion under high fluid flow and (ii) the diffusion and consumption model parameters of the organoid cells determine the thickness of the proliferative, quiescent, hypoxic and necrotic layers.

Establishment of nasal and olfactory epithelium organoids for unveiling mechanism of tissue regeneration and pathogenesis of nasal diseases

Organoid is an ideal in vitro model with cellular heterogeneity and genetic stability when passaging. Currently, organoids are exploited as new tools in a variety of preclinical researches and applications for disease modeling, drug screening, host-microbial interactions, and regenerative therapy. Advances have been made in the establishment of nasal and olfactory epithelium organoids that are used to investigate the pathogenesis of smell-related diseases and cellular/molecular mechanism underlying the regeneration of olfactory epithelium. A set of critical genes are identified to function in cell proliferation and neuronal differentiation in olfactory epithelium organoids. Besides, nasal epithelium organoids derived from chronic rhinosinusitis patients have been established to reveal the pathogenesis of this disease, potentially applied in drug responses in individual patient. The present article reviews recent research progresses of nasal and olfactory epithelium organoids in fundamental and preclinical researches, and proposes current advances and potential future direction in the field of organoid research and application.

Engineering organoids-on-chips for drug testing and evaluation

Organoids-on-chips is an emerging innovative integration of stem cell-derived organoids with advanced organ-on-chip technology, providing a novel platform for the in vitro construction of biomimetic micro-physiological systems. The synergistic merger transcends the limitations of traditional drug screening and safety assessment methodologies, such as 2D cell cultures and animal models. In this review, we examine the prevailing challenges and prerequisites of preclinical models utilized for drug screening and safety evaluations. We highlighted the salient features and merits of organoids-on-chip, elucidating their capability to authentically replicate human physiology, thereby addressing contemporary impediments. We comprehensively overviewed the recent endeavors where organoids-on-chips have been harnessed for drug screening and safety assessment and delved into potential opportunities and challenges for evolving sophisticated, near-physiological organoids-on-chips. Based on current achievements, we further discuss how to enhance the practicality of organoids-on-chips and accelerate the translation from preclinical to clinical stages in healthcare and industry by utilizing multidisciplinary convergent innovation.

Lung cancer organoid-based drug evaluation models and new drug development application trends

Lung cancer is a malignant tumor with high incidence and mortality rates in both men and women worldwide. Although anticancer drugs are prescribed to treat lung cancer patients, individual responses to these drugs vary, making it crucial to identify the most suitable treatment for each patient. Therefore, it is necessary to develop an anticancer drug efficacy prediction model that can analyze drug efficacy before patient treatment and establish personalized treatment strategies. Unlike two-dimensional (2D) cultured lung cancer cells, lung cancer organoid (LCO) models have a three-dimensional (3D) structure that effectively mimics the characteristics and heterogeneity of lung cancer cells. Lung cancer patient-derived organoids (PDOs) also have the advantage of recapitulating histological and genetic characteristics similar to those of patient tissues under in vitro conditions. Due to these advantages, LCO models are utilized in various fields, including cancer research, and precision medicine, and are especially employed in various new drug development processes, such as targeted therapies and immunotherapy. LCO models demonstrate potential applications in precision medicine and new drug development research. This review discusses the various methods for implementing LCO models, LCO-based anticancer drug efficacy analysis models, and new trends in lung cancer-targeted drug development.

A genetically inducible endothelial niche enables vascularization of human kidney organoids with multilineage maturation and emergence of renin expressing cells

Vascularization plays a critical role in organ maturation and cell-type development. Drug discovery, organ mimicry, and ultimately transplantation hinge on achieving robust vascularization of in vitro engineered organs. Here, focusing on human kidney organoids, we overcame this hurdle by combining a human induced pluripotent stem cell (iPSC) line containing an inducible ETS translocation variant 2 (ETV2) (a transcription factor playing a role in endothelial cell development) that directs endothelial differentiation in vitro, with a non-transgenic iPSC line in suspension organoid culture. The resulting human kidney organoids show extensive endothelialization with a cellular identity most closely related to human kidney endothelia. Endothelialized kidney organoids also show increased maturation of nephron structures, an associated fenestrated endothelium with de novo formation of glomerular and venous subtypes, and the emergence of drug-responsive renin expressing cells. The creation of an engineered vascular niche capable of improving kidney organoid maturation and cell type complexity is a significant step forward in the path to clinical translation. Thus, incorporation of an engineered endothelial niche into a previously published kidney organoid protocol allowed the orthogonal differentiation of endothelial and parenchymal cell types, demonstrating the potential for applicability to other basic and translational organoid studies.

Force versus Response: Methods for Activating and Characterizing Mechanosensitive Ion Channels and GPCRs

Mechanotransduction is the process whereby cells convert mechanical signals into electrochemical responses, where mechanosensitive proteins mediate this interaction. To characterize these critical proteins, numerous techniques have been developed that apply forces and measure the subsequent cellular responses. While these approaches have given insight into specific aspects of many such proteins, subsequent validation and cross-comparison between techniques remain difficult given significant variations in reported activation thresholds and responses for the same protein across different studies. Accurately determining mechanosensitivity responses for various proteins, however, is essential for understanding mechanotransduction and potential physiological implications, including therapeutics. This critical review provides an assessment of current and emerging approaches used for mechanosensitive ion channel and G-Coupled Receptors (GPCRs) stimulation and measurement, with a specific focus on the ability to quantitatively measure mechanosensitive responses.

Epigenetics of Hypertensive Nephropathy

Hypertensive nephropathy (HN) is a leading cause of chronic kidney disease (CKD) and end-stage renal disease (ESRD), contributing to significant morbidity, mortality, and rising healthcare costs. In this review article, we explore the role of epigenetic mechanisms in HN progression and their potential therapeutic implications. We begin by examining key epigenetic modifications-DNA methylation, histone modifications, and non-coding RNAs-observed in kidney disease. Next, we discuss the underlying pathophysiology of HN and highlight current in vitro and in vivo models used to study the condition. Finally, we compare various types of HN-induced renal injury and their associated epigenetic mechanisms with those observed in other kidney injury models, drawing inferences on potential epigenetic therapies for HN. The information gathered in this work indicate that epigenetic mechanisms can drive the progression of HN by regulating key molecular signaling pathways involved in renal damage and fibrosis. The limitations of Renin-Angiotensin-Aldosterone System (RAAS) inhibitors underscore the need for alternative treatments targeting epigenetic pathways. This review emphasizes the importance of further research into the epigenetic regulation of HN to develop more effective therapies and preventive strategies. Identifying novel epigenetic markers could provide new therapeutic opportunities for managing CKD and reducing the burden of ESRD.

Unveiling the Heart's Hidden Enemy: Dynamic Insights into Polystyrene Nanoplastic-Induced Cardiotoxicity Based on Cardiac Organoid-on-a-Chip

Exposure to micro- and nanoplastics (MNPs) has been implicated in potential cardiotoxicity. However, in vitro models based on cardiomyocyte cell lines lack crucial cardiac characteristics, while interspecies differences in animal models compromise the reliability of the conclusions. In addition, current research has predominantly focused on single-time point exposures to MNPs, neglecting comparative analyses of cardiac injury across early and late stages. Moreover, there remains a large gap in understanding the susceptibility to MNPs under pathological conditions. To address these limitations, this study integrated cardiac organoids (COs) and organ-on-a-chip (OoC) technology to develop the cardiac organoid-on-a-chip (COoC), which was validated for cardiotoxicity evaluation through multiple dimensions. Based on COoC, we conducted a dynamic observation of the cardiac damage caused by short- and long-term exposure to polystyrene nanoplastics (PS-NPs). Oxidative stress, inflammation, disruption of calcium ion homeostasis, and mitochondrial dysfunction were confirmed as the potential mechanisms of PS-NP-induced cardiotoxicity and the crucial events in the early stages, while cardiac fibrosis emerged as a prominent feature in late stages. Notably, low-dose exposure exacerbated myocardial infarction symptoms under pathological states, despite no significant cardiotoxicity shown in healthy models. In conclusion, these findings further deepened our understanding of PS-NP-induced cardiotoxic effects and introduced a promising in vitro platform for assessing cardiotoxicity.

Recent advances in extracellular matrix manipulation for kidney organoid research

The kidney plays a crucial role in maintaining the body's microenvironment homeostasis. However, current treatment options and therapeutic agents for chronic kidney disease (CKD) are limited. Fortunately, the advent of kidney organoids has introduced a novel in vitro model for studying kidney diseases and drug screening. Despite significant efforts has been leveraged to mimic the spatial-temporal dynamics of fetal renal development in various types of kidney organoids, there is still a discrepancy in cell types and maturity compared to native kidney tissue. The extracellular matrix (ECM) plays a crucial role in regulating cellular signaling, which ultimately affects cell fate decision. As a result, ECM can refine the microenvironment of organoids, promoting their efficient differentiation and maturation. This review examines the existing techniques for culturing kidney organoids, evaluates the strengths and weaknesses of various types of kidney organoids, and assesses the advancements and limitations associated with the utilization of the ECM in kidney organoid culture. Additionally, it presents a discussion on constructing specific physiological and pathological microenvironments using decellularized extracellular matrix during certain developmental stages or disease occurrences, aiding the development of kidney organoids and disease models.

Dynamic culture of cerebral organoids using a pillar/perfusion plate for the assessment of developmental neurotoxicity

Despite the potential toxicity of commercial chemicals to the development of the nervous system (known as developmental neurotoxicity or DNT), conventionalin vitrocell models have primarily been employed for the assessment of acute neuronal toxicity. On the other hand, animal models used for the assessment of DNT are not physiologically relevant due to the heterogenic difference between humans and animals. In addition, animal models are low-throughput, time-consuming, expensive, and ethically questionable. Recently, human brain organoids have emerged as a promising alternative to assess the detrimental effects of chemicals on the developing brain. However, conventional organoid culture systems have several technical limitations including low throughput, lack of reproducibility, insufficient maturity of organoids, and the formation of the necrotic core due to limited diffusion of nutrients and oxygen. To address these issues and establish predictive DNT models, cerebral organoids were differentiated in a dynamic condition in a unique pillar/perfusion plate, which were exposed to test compounds to evaluate DNT potential. The pillar/perfusion plate facilitated uniform, dynamic culture of cerebral organoids with improved proliferation and maturity by rapid, bidirectional flow generated on a digital rocker. Day 9 cerebral organoids in the pillar/perfusion plate were exposed to ascorbic acid (DNT negative) and methylmercury (DNT positive) in a dynamic condition for 1 and 3 weeks, and changes in organoid morphology and neural gene expression were measured to determine DNT potential. As expected, ascorbic acid did not induce any changes in organoid morphology and neural gene expression. However, exposure of day 9 cerebral organoids to methylmercury resulted in significant changes in organoid morphology and neural gene expression. Interestingly, methylmercury did not induce adverse changes in cerebral organoids in a static condition, thus highlighting the importance of dynamic organoid culture in DNT assessment.

Progress and breakthroughs in human kidney organoid research

The three-dimensional (3D) kidney organoid is a breakthrough model for recapitulating renal morphology and function in vitro, which is grown from stem cells and resembles mammalian kidney organogenesis. Currently, protocols for cultivating this model from induced pluripotent stem cells (iPSCs) and patient-derived adult stem cells (ASCs) have been widely reported. In recent years, scientists have focused on combining cutting-edge bioengineering and bioinformatics technologies to improve the developmental accuracy of kidney organoids and achieve high-throughput experimentation. As a remarkable tool for mechanistic research of the renal system, kidney organoid has both potential and challenges. In this review, we have described the evolution of kidney organoid establishment methods and highlighted the latest progress leading to a more sophisticated kidney transformation research model. Finally, we have summarized the main applications of renal organoids in exploring kidney disease.

Establishment of advanced tumor organoids with emerging innovative technologies

Tumor organoids have emerged as a crucial preclinical model for multiple cancer research. Their high establishment rates, stability, and ability to replicate key biological features of original tumor cells in vivo render them invaluable for exploring tumor molecular mechanisms, discovering potential anti-tumor drugs, and predicting clinical drug efficacy. Here, we review the establishment of tumor organoid models and provide an extensive overview of organoid culturing strategies. We also emphasize the significance of integrating cellular components of the tumor microenvironment and physicochemical factors in the organoid culturing system, highlighting the importance of artificial intelligence technology in advancing organoid construction. Moreover, we summarize recent advancements in utilizing organoid systems for novel anti-cancer drug screening and discuss promising trends for enhancing advanced organoids in next-generation disease modeling.

Fenestrated Endothelial Cells across Organs: Insights into Kidney Function and Disease

In the human body, the vascular system plays an indispensable role in maintaining homeostasis by supplying oxygen and nutrients to cells and organs and facilitating the removal of metabolic waste and toxins. Blood vessels-the key constituents of the vascular system-are composed of a layer of endothelial cells on their luminal surface. In most organs, tightly packed endothelial cells serve as a barrier separating blood and lymph from surrounding tissues. Intriguingly, endothelial cells in some tissues and organs (e.g., choroid plexus, liver sinusoids, small intestines, and kidney glomerulus) form transcellular pores called fenestrations that facilitate molecular and ionic transport across the vasculature and mediate immune responses through leukocyte transmigration. However, the development and unique functions of endothelial cell fenestrations across organs are yet to be fully uncovered. This review article provides an overview of fenestrated endothelial cells in multiple organs. We describe their development and organ-specific roles, with expanded discussions on their contributions to glomerular health and disease. We extend these discussions to highlight the dynamic changes in endothelial cell fenestrations in diabetic nephropathy, focal segmental glomerulosclerosis, Alport syndrome, and preeclampsia, and how these unique cellular features could be targeted for therapeutic development. Finally, we discuss emerging technologies for in vitro modeling of biological systems, and their relevance for advancing the current understanding of endothelial cell fenestrations in health and disease.

Global Literature Analysis of Organoid and Organ-on-Chip Research

Organoids and cells in organ-on-chip platforms replicate higher-level anatomical, physiological, or pathological states of tissues and organs. These technologies are widely regarded by academia, the pharmacological industry and regulators as key biomedical developments. To map advances in this emerging field, a literature analysis of 16,000 article metadata based on a quality-controlled text-mining algorithm is performed. The analysis covers titles, keywords, and abstracts of categorized academic publications in the literature and preprint databases published after 2010. The algorithm identifies and tracks 149 and 107 organs or organ substructures modeled as organoids and organ-on-chip, respectively, stem cell sources, as well as 130 diseases, and 16 groups of organisms other than human and mouse in which organoid/organ-on-chip technology is applied. The analysis illustrates changing diversity and focus in organoid/organ-on-chip research and captures its geographical distribution. The downloadable dataset provided is a robust framework for researchers to interrogate with their own questions.

Advances in Microfluidic Technologies in Organoid Research

Organoids have emerged as major technological breakthroughs and novel organ models that have revolutionized biomedical research by recapitulating the key structural and functional complexities of their in vivo counterparts. The combination of organoid systems and microfluidic technologies has opened new frontiers in organoid engineering and offers great opportunities to address the current challenges of existing organoid systems and broaden their biomedical applications. In this review, the key features of the existing organoids, including their origins, development, design principles, and limitations, are described. Then the recent progress in integrating organoids into microfluidic systems is highlighted, involving microarrays for high-throughput organoid manipulation, microreactors for organoid hydrogel scaffold fabrication, and microfluidic chips for functional organoid culture. The opportunities in the nascent combination of organoids and microfluidics that lie ahead to accelerate research in organ development, disease studies, drug screening, and regenerative medicine are also discussed. Finally, the challenges and future perspectives in the development of advanced microfluidic platforms and modified technologies for building organoids with higher fidelity and standardization are envisioned.

From Organ-on-a-Chip to Human-on-a-Chip: A Review of Research Progress and Latest Applications

Organ-on-a-Chip (OOC) technology, which emulates the physiological environment and functionality of human organs on a microfluidic chip, is undergoing significant technological advancements. Despite its rapid evolution, this technology is also facing notable challenges, such as the lack of vascularization, the development of multiorgan-on-a-chip systems, and the replication of the human body on a single chip. The progress of microfluidic technology has played a crucial role in steering OOC toward mimicking the human microenvironment, including vascularization, microenvironment replication, and the development of multiorgan microphysiological systems. Additionally, advancements in detection, analysis, and organoid imaging technologies have enhanced the functionality and efficiency of Organs-on-Chips (OOCs). In particular, the integration of artificial intelligence has revolutionized organoid imaging, significantly enhancing high-throughput drug screening. Consequently, this review covers the research progress of OOC toward Human-on-a-chip, the integration of sensors in OOCs, and the latest applications of organoid imaging technologies in the biomedical field.

Development of Cell Culture Platforms for Study of Trabecular Meshwork Cells and Glaucoma Development

BACKGROUND

Various cell culture platforms that could display native environmental cue-mimicking stimuli were developed, and effects of environmental cues on cell behaviors were studied with the cell culture platforms. Likewise, various cell culture platforms mimicking native trabecular meshwork (TM) composed of juxtacanalicular, corneoscleral and uveal meshwork located in internal scleral sulcus were used to study effects of environmental cues and/or drug treatments on TM cells and glaucoma development. Glaucoma is a disease that could cause blindness, and cause of glaucoma is not clearly identified yet. It appears that aqueous humor (AH) outflow resistance increased by damages on pathway of AH outflow can elevate intraocular pressure (IOP). These overall possibly contribute to development of glaucoma.

METHODS

For the study of glaucoma, static and dynamic cell culture platforms were developed. Particularly, the dynamic platforms exploiting AH outflow-mimicking perfusion or increased IOP-mimicking increased pressure were used to study how perfusion or increased pressure could affect TM cells. Overall, potential mechanisms of glaucoma development, TM structures and compositions, TM cell culture platform types and researches on TM cells and glaucoma development with the platforms were described in this review.

RESULTS AND CONCLUSION

This will be useful to improve researches on TM cells and develop enhanced therapies targeting glaucoma.

Research progress on the application of organoids in gynecological tumors

Organoids are in vitro 3D models that maintain their own tissue structure and function. They largely overcome the limitations of traditional tumor models and have become a powerful research tool in the field of oncology in recent years. Gynecological malignancies are major diseases that seriously threaten the life and health of women and urgently require the establishment of models with a high degree of similarity to human tumors for clinical studies to formulate individualized treatments. Currently, organoids are widely studied in exploring the mechanisms of gynecological tumor development as a means of drug screening and individualized medicine. Ovarian, endometrial, and cervical cancers as common gynecological malignancies have high morbidity and mortality rates among other gynecological tumors. Therefore, this study reviews the application of modelling, drug efficacy assessment, and drug response prediction for ovarian, endometrial, and cervical cancers, thereby clarifying the mechanisms of tumorigenesis and development, and providing precise treatment options for gynecological oncology patients.

Extracellular vesicles as nanotheranostic platforms for targeted neurological disorder interventions

Central Nervous System (CNS) disorders represent a profound public health challenge that affects millions of people around the world. Diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and traumatic brain injury (TBI) exemplify the complexities and diversities that complicate their early detection and the development of effective treatments. Amid these challenges, the emergence of nanotechnology and extracellular vesicles (EVs) signals a new dawn for treating and diagnosing CNS ailments. EVs are cellularly derived lipid bilayer nanosized particles that are pivotal in intercellular communication within the CNS and have the potential to revolutionize targeted therapeutic delivery and the identification of novel biomarkers. Integrating EVs with nanotechnology amplifies their diagnostic and therapeutic capabilities, opening new avenues for managing CNS diseases. This review focuses on examining the fascinating interplay between EVs and nanotechnology in CNS theranostics. Through highlighting the remarkable advancements and unique methodologies, we aim to offer valuable perspectives on how these approaches can bring about a revolutionary change in disease management. The objective is to harness the distinctive attributes of EVs and nanotechnology to forge personalized, efficient interventions for CNS disorders, thereby providing a beacon of hope for affected individuals. In short, the confluence of EVs and nanotechnology heralds a promising frontier for targeted and impactful treatments against CNS diseases, which continue to pose significant public health challenges. By focusing on personalized and powerful diagnostic and therapeutic methods, we might improve the quality of patients.

Advancements in therapeutic development: kidney organoids and organs on a chip

The use of animal models in therapeutic development has long been the standard practice. However, ethical concerns and the inherent species differences have prompted a reevaluation of the experimental approach in human disease studies. The urgent need for alternative model systems that better mimic human pathophysiology has led to the emergence of organoids, innovative in vitro models, to simulate human organs in vitro. These organoids have gained widespread acceptance in disease models and drug development research. In this mini review, we explore the recent strides made in kidney organoid differentiation and highlight the synergistic potential of incorporating organ-on-chip systems. The emergent use of microfluidic devices reveals the importance of fluid flow in the maturation of kidney organoids and helps decipher pathomechanisms in kidney diseases. Recent research has uncovered their potential applications across a wide spectrum of kidney research areas, including hemodynamic forces at stake in kidney health and disease, immune cell infiltration, or drug delivery and toxicity. This convergence of cutting-edge technologies not only holds promise for expediting therapeutic development but also reflects an acknowledgment of the need to embrace innovative and more human-centric research models.

Dynamic culture of cerebral organoids using a pillar/perfusion plate for the assessment of developmental neurotoxicity

Despite the potential toxicity of commercial chemicals to the development of the nervous system (known as developmental neurotoxicity or DNT), conventional in vitro cell models have primarily been employed for the assessment of acute neuronal toxicity. On the other hand, animal models used for the assessment of DNT are not physiologically relevant due to the heterogenic difference between humans and animals. In addition, animal models are low-throughput, time-consuming, expensive, and ethically questionable. Recently, human brain organoids have emerged as a promising alternative to assess the detrimental effects of chemicals on the developing brain. However, conventional organoid culture systems have several technical limitations including low throughput, lack of reproducibility, insufficient maturity of organoids, and the formation of the necrotic core due to limited diffusion of nutrients and oxygen. To address these issues and establish predictive DNT models, cerebral organoids were differentiated in a dynamic condition in a unique pillar/perfusion plate, which were exposed to test compounds to evaluate DNT potential. The pillar/perfusion plate facilitated uniform, dynamic culture of cerebral organoids with improved proliferation and maturity by rapid, bidirectional flow generated on a digital rocker. Day 9 cerebral organoids in the pillar/perfusion plate were exposed to ascorbic acid (DNT negative) and methylmercury (DNT positive) in a dynamic condition for 1 and 3 weeks, and changes in organoid morphology and neural gene expression were measured to determine DNT potential. As expected, ascorbic acid didn't induce any changes in organoid morphology and neural gene expression. However, exposure of day 9 cerebral organoids to methylmercury resulted in significant changes in organoid morphology and neural gene expression. Interestingly, methylmercury did not induce adverse changes in cerebral organoids in a static condition, thus highlighting the importance of dynamic organoid culture in DNT assessment.

Top Five Stories of the Cellular Landscape and Therapies of Atherosclerosis: Current Knowledge and Future Perspectives

Atherosclerosis (AS) is characterized by impairment and apoptosis of endothelial cells, continuous systemic and focal inflammation and dysfunction of vascular smooth muscle cells, which is documented as the traditional cellular paradigm. However, the mechanisms appear much more complicated than we thought since a bulk of studies on efferocytosis, transdifferentiation and novel cell death forms such as ferroptosis, pyroptosis, and extracellular trap were reported. Discovery of novel pathological cellular landscapes provides a large number of therapeutic targets. On the other side, the unsatisfactory therapeutic effects of current treatment with lipid-lowering drugs as the cornerstone also restricts the efforts to reduce global AS burden. Stem cell- or nanoparticle-based strategies spurred a lot of attention due to the attractive therapeutic effects and minimized adverse effects. Given the complexity of pathological changes of AS, attempts to develop an almighty medicine based on single mechanisms could be theoretically challenging. In this review, the top stories in the cellular landscapes during the initiation and progression of AS and the therapies were summarized in an integrated perspective to facilitate efforts to develop a multi-targets strategy and fill the gap between mechanism research and clinical translation. The future challenges and improvements were also discussed.

Engineering physiological environments to advance kidney organoid models from human pluripotent stem cells

During embryogenesis, the mammalian kidney arises because of reciprocal interactions between the ureteric bud (UB) and the metanephric mesenchyme (MM), driving UB branching and nephron induction. These morphogenetic processes involve a series of cellular rearrangements that are tightly controlled by gene regulatory networks and signaling cascades. Here, we discuss how kidney developmental studies have informed the definition of procedures to obtain kidney organoids from human pluripotent stem cells (hPSCs). Moreover, bioengineering techniques have emerged as potential solutions to externally impose controlled microenvironments for organoid generation from hPSCs. Next, we summarize some of these advances with major focus On recent works merging hPSC-derived kidney organoids (hPSC-kidney organoids) with organ-on-chip to develop robust models for drug discovery and disease modeling applications. We foresee that, in the near future, coupling of different organoid models through bioengineering approaches will help advancing to recreate organ-to-organ crosstalk to increase our understanding on kidney disease progression in the human context and search for new therapeutics.

Engineering the Physical Microenvironment into Neural Organoids for Neurogenesis and Neurodevelopment

Understanding the signals from the physical microenvironment is critical for deciphering the processes of neurogenesis and neurodevelopment. The discovery of how surrounding physical signals shape human developing neurons is hindered by the bottleneck of conventional cell culture and animal models. Notwithstanding neural organoids provide a promising platform for recapitulating human neurogenesis and neurodevelopment, building neuronal physical microenvironment that accurately mimics the native neurophysical features is largely ignored in current organoid technologies. Here, it is discussed how the physical microenvironment modulates critical events during the periods of neurogenesis and neurodevelopment, such as neural stem cell fates, neural tube closure, neuronal migration, axonal guidance, optic cup formation, and cortical folding. Although animal models are widely used to investigate the impacts of physical factors on neurodevelopment and neuropathy, the important roles of human stem cell-derived neural organoids in this field are particularly highlighted. Considering the great promise of human organoids, building neural organoid microenvironments with mechanical forces, electrophysiological microsystems, and light manipulation will help to fully understand the physical cues in neurodevelopmental processes. Neural organoids combined with cutting-edge techniques, such as advanced atomic force microscopes, microrobots, and structural color biomaterials might promote the development of neural organoid-based research and neuroscience.

Monolithically Integrated Complementary Ferroelectric FET XNOR Synapse for the Binary Neural Network

Neuromorphic computing, which mimics the structure and principles of the human brain, has the potential to facilitate the hardware implementation of next-generation artificial intelligence systems and process large amounts of data with very low power consumption. Among them, the XNOR synapse-based Binary Neural Network (BNN) has been attracting attention due to its compact neural network parameter size and low hardware cost. The previous XNOR synapse has drawbacks, such as a trade-off between cell density and accuracy. In this work, we show nonvolatile XNOR synapses with high density and accuracy using a monolithically stacked complementary ferroelectric field-effect transistor (C-FeFET) composed of a p-type Si MFMIS-FeFET at the bottom and a 3D stackable n-type Al:IZTO MFS-FeTFT, achieving 60F2 per cell (2C-FeFET). For adjusting the threshold voltage and improving the switching speed (100 ns) of n-type ferroelectric TFT, we employed a dual-gate configuration and a unique operation scheme, making it comparable to those of Si-based FeFETs. We performed array-level simulation with a 512 × 512 subarray size and a 3-bit flash ADC, demonstrating that the image recognition accuracies using the MNIST and CIFAR-10 data sets were increased by 3.17 and 14.07%, respectively, in comparison to other nonvolatile XNOR synapses. In addition, we performed system-level analysis on a 512 × 512 XNOR C-FeFET, exhibiting an outstanding throughput of 717.37 GOPS and an energy efficiency of 196.7 TOPS/W. We expect that our approach would contribute to the high-density memory systems, logic-in-memory technology, and hardware implementation of neural networks.

Microfluidics: a concise review of the history, principles, design, applications, and future outlook

Microfluidic technologies have garnered significant attention due to their ability to rapidly process samples and precisely manipulate fluids in assays, making them an attractive alternative to conventional experimental methods. With the potential for revolutionary capabilities in the future, this concise review provides readers with insights into the fascinating world of microfluidics. It begins by introducing the subject's historical background, allowing readers to familiarize themselves with the basics. The review then delves into the fundamental principles, discussing the underlying phenomena at play. Additionally, it highlights the different aspects of microfluidic device design, classification, and fabrication. Furthermore, the paper explores various applications, the global market, recent advancements, and challenges in the field. Finally, the review presents a positive outlook on trends and draws lessons to support the future flourishing of microfluidic technologies.

Human organoids-on-chips for biomedical research and applications

Human organoids-on-chips (OrgOCs) are the synergism of human organoids (HOs) technology and microfluidic organs-on-chips (OOCs). OOCs can mimic extrinsic characteristics of organs, such as environmental clues of living tissue, while HOs are more amenable to biological analysis and genetic manipulation. By spatial cooperation, OrgOCs served as 3D organotypic living models allowing them to recapitulate critical tissue-specific properties and forecast human responses and outcomes. It represents a giant leap forward from the regular 2D cell monolayers and animal models in the improved human ecological niche modeling. In recent years, OrgOCs have offered potential promises for clinical studies and advanced the preclinical-to-clinical translation in medical and industrial fields. In this review, we highlight the cutting-edge achievements in OrgOCs, introduce the key features of OrgOCs architectures, and share the revolutionary applications in basic biology, disease modeling, preclinical assay and precision medicine. Furthermore, we discuss how to combine a wide range of disciplines with OrgOCs and accelerate translational applications, as well as the challenges and opportunities of OrgOCs in biomedical research and applications.

Vascularized microfluidic models of major organ structures and cancerous tissues

Organ-on-a-chip devices are powerful modeling systems that allow researchers to recapitulate the in vivo structures of organs as well as the physiological conditions those tissues are subject to. These devices are useful tools in modeling not only the behavior of a healthy organ but also in modeling disease pathology or the effects of specific drugs. The incorporation of fluidic flow is of great significance in these devices due to the important roles of physiological fluid flows in vivo. Recent developments in the field have led to the production of vascularized organ-on-a-chip devices, which can more accurately reproduce the conditions observed in vivo by recapitulating the vasculature of the organ concerned. This review paper will provide a brief overview of the history of organ-on-a-chip devices, before discussing developments in the production of vascularized organs-on-chips, and the implications these developments hold for the future of the field.

Mammary Microvessels are Sensitive to Menstrual Cycle Sex Hormones

The mammary gland is a highly vascularized organ influenced by sex hormones including estrogen (E2) and progesterone (P4). Beyond whole-organism studies in rodents or cell monocultures, hormonal effects on the breast microvasculature remain largely understudied. Recent methods to generate 3D microvessels on-chip have enabled direct observation of complex vascular processes; however, these models often use non-tissue-specific cell types, such as human umbilical vein endothelial cells (HUVECs) and fibroblasts from various sources. Here, novel mammary-specific microvessels are generated by coculturing primary breast endothelial cells and fibroblasts under optimized culture conditions. These microvessels are mechanosensitive (to interstitial flow) and require endothelial-stromal interactions to develop fully perfusable vessels. These mammary-specific microvessels are also responsive to exogenous stimulation by sex hormones. When treated with combined E2 and P4, corresponding to the four phases of the menstrual cycle (period, follicular, ovular, and luteal), vascular remodeling and barrier function are altered in a phase-dependent manner. The presence of high E2 (ovulation) promotes vascular growth and remodeling, corresponding to high depletion of proangiogenic factors, whereas high P4 concentrations (luteal) promote vascular regression. The effects of combined E2 and P4 hormones are not only dose-dependent but also tissue-specific, as are shown by similarly treating non-tissue-specific HUVEC microvessels.

Generative models of morphogenesis in developmental biology

Understanding the mechanism by which cells coordinate their differentiation and migration is critical to our understanding of many fundamental processes such as wound healing, disease progression, and developmental biology. Mathematical models have been an essential tool for testing and developing our understanding, such as models of cells as soft spherical particles, reaction-diffusion systems that couple cell movement to environmental factors, and multi-scale multi-physics simulations that combine bottom-up rule-based models with continuum laws. However, mathematical models can often be loosely related to data or have so many parameters that model behaviour is weakly constrained. Recent methods in machine learning introduce new means by which models can be derived and deployed. In this review, we discuss examples of mathematical models of aspects of developmental biology, such as cell migration, and how these models can be combined with these recent machine learning methods.

Advanced in vitro models for renal cell carcinoma therapy design

Renal cell carcinoma (RCC) and its principal subtype, clear cell RCC, are the most diagnosed kidney cancer. Despite substantial improvement over the last decades, current pharmacological intervention still fails to achieve long-term therapeutic success. RCC is characterized by a high intra- and inter-tumoral heterogeneity and is heavily influenced by the crosstalk of the cells composing the tumor microenvironment, such as cancer-associated fibroblasts, endothelial cells and immune cells. Moreover, multiple physicochemical properties such as pH, interstitial pressure or oxygenation may also play an important role. These elements are often poorly recapitulated in in vitro models used for drug development. This inadequate recapitulation of the tumor is partially responsible for the current lack of an effective and curative treatment. Therefore, there are needs for more complex in vitro or ex vivo drug screening models. In this review, we discuss the current state-of-the-art of RCC models and suggest strategies for their further development.

[Research progress on vascularization of organoids]

Organoids are three-dimensional structures formed by self-organizing growth of cells in vitro, which own many structures and functions similar with those of corresponding in vivo organs. Although the organoid culture technologies are rapidly developed and the original cells are abundant, the organoid cultured by current technologies are rather different with the real organs, which limits their application. The major challenges of organoid cultures are the immature tissue structure and restricted growth, both of which are caused by poor functional vasculature. Therefore, how to develop the vascularization of organoids has become an urgent problem. We presently reviewed the progresses on the original cells of organoids and the current methods to develop organoids vascularization, which provide clues to solve the above-mentioned problems.

Genetically engineering endothelial niche in human kidney organoids enables multilineage maturation, vascularization and de novo cell types

Vascularization plays a critical role in organ maturation and cell type development. Drug discovery, organ mimicry, and ultimately transplantation in a clinical setting thereby hinges on achieving robust vascularization of in vitro engineered organs. Here, focusing on human kidney organoids, we overcome this hurdle by combining an inducible ETS translocation variant 2 (ETV2) human induced pluripotent stem cell (iPSC) line, which directs endothelial fate, with a non-transgenic iPSC line in suspension organoid culture. The resulting human kidney organoids show extensive vascularization by endothelial cells with an identity most closely related to endogenous kidney endothelia. Vascularized organoids also show increased maturation of nephron structures including more mature podocytes with improved marker expression, foot process interdigitation, an associated fenestrated endothelium, and the presence of renin+ cells. The creation of an engineered vascular niche capable of improving kidney organoid maturation and cell type complexity is a significant step forward in the path to clinical translation. Furthermore, this approach is orthogonal to native tissue differentiation paths, hence readily adaptable to other organoid systems and thus has the potential for a broad impact on basic and translational organoid studies.

A quantitative meta-analysis comparing cell models in perfused organ on a chip with static cell cultures

As many consider organ on a chip for better in vitro models, it is timely to extract quantitative data from the literature to compare responses of cells under flow in chips to corresponding static incubations. Of 2828 screened articles, 464 articles described flow for cell culture and 146 contained correct controls and quantified data. Analysis of 1718 ratios between biomarkers measured in cells under flow and static cultures showed that the in all cell types, many biomarkers were unregulated by flow and only some specific biomarkers responded strongly to flow. Biomarkers in cells from the blood vessels walls, the intestine, tumours, pancreatic island, and the liver reacted most strongly to flow. Only 26 biomarkers were analysed in at least two different articles for a given cell type. Of these, the CYP3A4 activity in CaCo2 cells and PXR mRNA levels in hepatocytes were induced more than two-fold by flow. Furthermore, the reproducibility between articles was low as 52 of 95 articles did not show the same response to flow for a given biomarker. Flow showed overall very little improvements in 2D cultures but a slight improvement in 3D cultures suggesting that high density cell culture may benefit from flow. In conclusion, the gains of perfusion are relatively modest, larger gains are linked to specific biomarkers in certain cell types.

Biosensors integrated 3D organoid/organ-on-a-chip system: A real-time biomechanical, biophysical, and biochemical monitoring and characterization

As a full-fidelity simulation of human cells, tissues, organs, and even systems at the microscopic scale, Organ-on-a-Chip (OOC) has significant ethical advantages and development potential compared to animal experiments. The need for the design of new drug high-throughput screening platforms and the mechanistic study of human tissues/organs under pathological conditions, the evolving advances in 3D cell biology and engineering, etc., have promoted the updating of technologies in this field, such as the iteration of chip materials and 3D printing, which in turn facilitate the connection of complex multi-organs-on-chips for simulation and the further development of technology-composite new drug high-throughput screening platforms. As the most critical part of organ-on-a-chip design and practical application, verifying the success of organ model modeling, i.e., evaluating various biochemical and physical parameters in OOC devices, is crucial. Therefore, this paper provides a logical and comprehensive review and discussion of the advances in organ-on-a-chip detection and evaluation technologies from a broad perspective, covering the directions of tissue engineering scaffolds, microenvironment, single/multi-organ function, and stimulus-based evaluation, and provides a more comprehensive review of the progress in the significant organ-on-a-chip research areas in the physiological state.

Strategies for Improving Vascularization in Kidney Organoids: A Review of Current Trends

Kidney organoids possess the potential to revolutionize the treatment of renal diseases. However, their growth and maturation are impeded by insufficient growth of blood vessels. Through a PubMed search, we have identified 34 studies that attempted to address this challenge. Researchers are exploring various approaches including animal transplantation, organ-on-chips, and extracellular matrices (ECMs). The most prevalent method to promote the maturation and vascularization of organoids involves transplanting them into animals for in vivo culture, creating an optimal environment for organoid growth and the development of a chimeric vessel network between the host and organoids. Organ-on-chip technology permits the in vitro culture of organoids, enabling researchers to manipulate the microenvironment and investigate the key factors that influence organoid development. Lastly, ECMs have been discovered to aid the formation of blood vessels during organoid differentiation. ECMs from animal tissue have been particularly successful, although the underlying mechanisms require further research. Future research building upon these recent studies may enable the generation of functional kidney tissues for replacement therapies.

Label-free and non-destructive identification of naïve and primed embryonic stem cells based on differences in cellular metabolism

Pluripotent stem cells (PSCs) exist in naïve or primed states based on their origin. For in vitro culture, these PSCs require different supplements and growth factors. However, owing to their similar phenotypic features, identifying both cell types without harming cellular functions is challenging. This study reports an electrochemical method that enables simple, label-free, and non-destructive detection of naïve embryonic stem cells (ESCs) derived from mouse ESCs, based on the differences in cellular metabolism. Two major metabolic pathways to generate adenosine triphosphate (ATP)-glycolysis and oxidative phosphorylation (OXPHOS)-were blocked, and it was found that mitochondrial energy generation is the origin of the strong electrochemical signals of naïve ESCs. The number of ESCs is quantified when mixed with primed ESCs or converted from naïve-primed switchable metastable ESCs. The mouse PSCs derived from doxycycline-inducible mouse embryonic fibroblasts (MEFs) are also sensitively identified among other cell types such as unconverted MEFs and primed PSCs. The developed sensing platform operates in a non-invasive and label-free manner. Thus, it can be useful in the development of stem cell-derived therapeutics.

Vascularized Tissue Organoids

Tissue organoids hold enormous potential as tools for a variety of applications, including disease modeling and drug screening. To effectively mimic the native tissue environment, it is critical to integrate a microvasculature with the parenchyma and stroma. In addition to providing a means to physiologically perfuse the organoids, the microvasculature also contributes to the cellular dynamics of the tissue model via the cells of the perivascular niche, thereby further modulating tissue function. In this review, we discuss current and developing strategies for vascularizing organoids, consider tissue-specific vascularization approaches, discuss the importance of perfusion, and provide perspectives on the state of the field.

Effect of gut microbiome-derived metabolites and extracellular vesicles on hepatocyte functions in a gut-liver axis chip

Metabolism, is a complex process involving the gut and the liver tissue, is difficult to be reproduced in vitro with conventional single cell culture systems. To tackle this challenge, we developed a gut-liver-axis chip consisting of the gut epithelial cell chamber and three-dimensional (3D) uniform-sized liver spheroid chamber. Two cell culture chamber compartments were separated with a porous membrane to prevent microorganisms from passing through the chamber. When the hepG2 spheroids cultured with microbiota-derived metabolites, we observed the changes in the physiological function of hepG2 spheroids, showing that the albumin and urea secretion activity of liver spheroids was significantly enhanced. Additionally, the functional validation of hepG2 spheroids treated with microbiota-derived exosome was evaluated that the treatment of the microbiota-derived exosome significantly enhanced albumin and urea in hepG2 spheroids in a gut-liver axis chip. Therefore, this gut-liver axis chip could be a potentially powerful co-culture platform to study the interaction of microbiota and host cells.

Role of extracellular matrix components and structure in new renal models in vitro

The extracellular matrix (ECM), a complex set of fibrillar proteins and proteoglycans, supports the renal parenchyma and provides biomechanical and biochemical cues critical for spatial-temporal patterning of cell development and acquisition of specialized functions. As in vitro models progress towards biomimicry, more attention is paid to reproducing ECM-mediated stimuli. ECM's role in in vitro models of renal function and disease used to investigate kidney injury and regeneration is discussed. Availability, affordability, and lot-to-lot consistency are the main factors determining the selection of materials to recreate ECM in vitro. While simpler components can be synthesized in vitro, others must be isolated from animal or human tissues, either as single isolated components or as complex mixtures, such as Matrigel or decellularized formulations. Synthetic polymeric materials with dynamic and instructive capacities are also being explored for cell mechanical support to overcome the issues with natural products. ECM components can be used as simple 2D coatings or complex 3D scaffolds combining natural and synthetic materials. The goal is to recreate the biochemical signals provided by glycosaminoglycans and other signaling molecules, together with the stiffness, elasticity, segmentation, and dimensionality of the original kidney tissue, to support the specialized functions of glomerular, tubular, and vascular compartments. ECM mimicking also plays a central role in recent developments aiming to reproduce renal tissue in vitro or even in therapeutical strategies to regenerate renal function. Bioprinting of renal tubules, recellularization of kidney ECM scaffolds, and development of kidney organoids are examples. Future solutions will probably combine these technologies.

Kidney organoids: a pioneering model for kidney diseases

The kidney is a vital organ that regulates the bodily fluid and electrolyte homeostasis via tailored urinary excretion. Kidney injuries that cause severe or progressive chronic kidney disease have driven the growing population of patients with end-stage kidney disease, leading to substantial patient morbidity and mortality. This irreversible kidney damage has also created a huge socioeconomical burden on the healthcare system, highlighting the need for novel translational research models for progressive kidney diseases. Conventional research methods such as in vitro 2D cell culture or animal models do not fully recapitulate complex human kidney diseases. By contrast, directed differentiation of human induced pluripotent stem cells enables in vitro generation of patient-specific 3D kidney organoids, which can be used to model acute or chronic forms of hereditary, developmental, and metabolic kidney diseases. Furthermore, when combined with biofabrication techniques, organoids can be used as building blocks to construct vascularized kidney tissues mimicking their in vivo counterpart. By applying gene editing technology, organoid building blocks may be modified to minimize the process of immune rejection in kidney transplant recipients. In the foreseeable future, the universal kidney organoids derived from HLA-edited/deleted induced pluripotent stem cell (iPSC) lines may enable the supply of bioengineered organotypic kidney structures that are immune-compatible for the majority of the world population. Here, we summarize recent advances in kidney organoid research coupled with novel technologies such as organoids-on-chip and biofabrication of 3D kidney tissues providing convenient platforms for high-throughput drug screening, disease modelling, and therapeutic applications.

Creating a kidney organoid-vasculature interaction model using a novel organ-on-chip system

Kidney organoids derived from human induced pluripotent stem cells (iPSCs) have proven to be a valuable tool to study kidney development and disease. However, the lack of vascularization of these organoids often leads to insufficient oxygen and nutrient supply. Vascularization has previously been achieved by implantation into animal models, however, the vasculature arises largely from animal host tissue. Our aim is to transition from an in vivo implantation model towards an in vitro model that fulfils the advantages of vascularization whilst being fully human-cell derived. Our chip system supported culturing of kidney organoids, which presented nephron structures. We also showed that organoids cultured on chip showed increased maturation of endothelial populations based on a colocalization analysis of endothelial markers. Moreover, we observed migration and proliferation of human umbilical vein endothelial cells (HUVECs) cultured in the channels of the chip inside the organoid tissue, where these HUVECs interconnected with endogenous endothelial cells and formed structures presenting an open lumen resembling vessels. Our results establish for the first-time vascularization of kidney organoids in HUVEC co-culture conditions using a microfluidic organ-on-chip. Our model therefore provides a useful insight into kidney organoid vascularization in vitro and presents a tool for further studies of kidney development and drug testing, both for research purposes and pre-clinical applications.