Organoid and Organ-On-A-Chip Systems: New Paradigms for Modeling Neurological and Gastrointestinal Disease

Microphysiological Blood-Brain Barrier Systems for Disease Modeling and Drug Development

The blood-brain barrier (BBB) is a highly controlled microenvironment that regulates the interactions between cerebral blood and brain tissue. Due to its selectivity, many therapeutics targeting various neurological disorders are not able to penetrate into brain tissue. Pre-clinical studies using animals and other in vitro platforms have not shown the ability to fully replicate the human BBB leading to the failure of a majority of therapeutics in clinical trials. However, recent innovations in vitro and ex vivo modeling called organs-on-chips have shown the potential to create more accurate disease models for improved drug development. These microfluidic platforms induce physiological stressors on cultured cells and are able to generate more physiologically accurate BBBs compared to previous in vitro models. In this review, different approaches to create BBBs-on-chips are explored alongside their application in modeling various neurological disorders and potential therapeutic efficacy. Additionally, organs-on-chips use in BBB drug delivery studies is discussed, and advances in linking brain organs-on-chips onto multiorgan platforms to mimic organ crosstalk are reviewed.

Deciphering the Tumor Microenvironment of Colorectal Cancer and Guiding Clinical Treatment With Patient-Derived Organoid Technology: Progress and Challenges

Colorectal cancer (CRC) is one of the most prevalent malignant tumors of the digestive tract worldwide. Despite notable advancements in CRC treatment, there is an urgent requirement for preclinical model systems capable of accurately predicting drug efficacy in CRC patients, to identify more effective therapeutic options. In recent years, substantial strides have been made in the field of organoid technology, patient-derived organoid models can phenotypically replicate the original intra-tumor and inter-tumor heterogeneity of CRC, reflecting cellular interactions of the tumor microenvironment. Patient-derived organoid models have become an indispensable tool for investigating the pathogenesis of CRC and facilitating translational research. This review focuses on the application of organoid technology in CRC modeling, tumor microenvironment, and guiding clinical treatment, particularly in drug screening and personalized medicine. It also examines the existing challenges encountered in clinical organoid research and provides a prospective outlook on the future development directions of clinical organoid research, encompassing the standardization of organoid culture technology and the application of tissue engineering technology.

Tailoring biomaterials for biomimetic organs-on-chips

Organs-on-chips are microengineered microfluidic living cell culture devices with continuously perfused chambers penetrating to cells. By mimicking the biological features of the multicellular constructions, interactions among organs, vascular perfusion, physicochemical microenvironments, and so on, these devices are imparted with some key pathophysiological function levels of living organs that are difficult to be achieved in conventional 2D or 3D culture systems. In this technology, biomaterials are extremely important because they affect the microstructures and functionalities of the organ cells and the development of the organs-on-chip functions. Thus, herein, we provide an overview on the advances of biomaterials for the construction of organs-on-chips. After introducing the general components, structures, and fabrication techniques of the biomaterials, we focus on the studies of the functions and applications of these biomaterials in the organs-on-chips systems. Applications of the biomaterial-based organs-on-chips as alternative animal models for pharmaceutical, chemical, and environmental tests are described and highlighted. The prospects for exciting future directions and the challenges of biomaterials for realizing the further functionalization of organs-on-chips are also presented.

Strategic use of organoids and organs-on-chip as biomimetic tools

Organoid development and organ-on-a-chip are technologies based on differentiating stem cells, forming 3D multicellular structures resembling organs and tissues in vivo. Hence, both can be strategically used for disease modeling, drug screening, and host-pathogen studies. In this context, this review highlights the significant advancements in the area, providing technical approaches to organoids and organ-on-a-chip that best imitate in vivo physiology.

Human Stem Cells for Cardiac Disease Modeling and Preclinical and Clinical Applications—Are We on the Road to Success?

Cardiovascular diseases (CVDs) are pointed out by the World Health Organization (WHO) as the leading cause of death, contributing to a significant and growing global health and economic burden. Despite advancements in clinical approaches, there is a critical need for innovative cardiovascular treatments to improve patient outcomes. Therapies based on adult stem cells (ASCs) and embryonic stem cells (ESCs) have emerged as promising strategies to regenerate damaged cardiac tissue and restore cardiac function. Moreover, the generation of human induced pluripotent stem cells (iPSCs) from somatic cells has opened new avenues for disease modeling, drug discovery, and regenerative medicine applications, with fewer ethical concerns than those associated with ESCs. Herein, we provide a state-of-the-art review on the application of human pluripotent stem cells in CVD research and clinics. We describe the types and sources of stem cells that have been tested in preclinical and clinical trials for the treatment of CVDs as well as the applications of pluripotent stem-cell-derived in vitro systems to mimic disease phenotypes. How human stem-cell-based in vitro systems can overcome the limitations of current toxicological studies is also discussed. Finally, the current state of clinical trials involving stem-cell-based approaches to treat CVDs are presented, and the strengths and weaknesses are critically discussed to assess whether researchers and clinicians are getting closer to success.

Human Stem Cells for Cardiac Disease Modeling and Preclinical and Clinical Applications-Are We on the Road to Success?

Cardiovascular diseases (CVDs) are pointed out by the World Health Organization (WHO) as the leading cause of death, contributing to a significant and growing global health and economic burden. Despite advancements in clinical approaches, there is a critical need for innovative cardiovascular treatments to improve patient outcomes. Therapies based on adult stem cells (ASCs) and embryonic stem cells (ESCs) have emerged as promising strategies to regenerate damaged cardiac tissue and restore cardiac function. Moreover, the generation of human induced pluripotent stem cells (iPSCs) from somatic cells has opened new avenues for disease modeling, drug discovery, and regenerative medicine applications, with fewer ethical concerns than those associated with ESCs. Herein, we provide a state-of-the-art review on the application of human pluripotent stem cells in CVD research and clinics. We describe the types and sources of stem cells that have been tested in preclinical and clinical trials for the treatment of CVDs as well as the applications of pluripotent stem-cell-derived in vitro systems to mimic disease phenotypes. How human stem-cell-based in vitro systems can overcome the limitations of current toxicological studies is also discussed. Finally, the current state of clinical trials involving stem-cell-based approaches to treat CVDs are presented, and the strengths and weaknesses are critically discussed to assess whether researchers and clinicians are getting closer to success.

Incubator-independent perfusion system integrated with microfluidic device for continuous electrophysiology and microscopy readouts

Advances in primary and stem cell derived neuronal cell culture techniques and abundance of available neuronal cell types have enabledin vitroneuroscience as a substantial approach to modelin vivoneuronal networks. Survival of the cultured neurons is inevitably dependent on the cell culture incubators to provide stable temperature and humidity and to supply required CO₂levels for controlling the pH of culture medium. Therefore, imaging and electrophysiology recordings outside of the incubator are often limited to the short-term experimental sessions. This restricts our understanding of physiological events to the short snapshots of recorded data while the major part of temporal data is neglected. Multiple custom-made and commercially available platforms like integrated on-stage incubators have been designed to enable long-term microscopy. Nevertheless, long-term high-spatiotemporal electrophysiology recordings from developing neuronal networks needs to be addressed. In the present work an incubator-independent polydimethylsiloxane-based double-wall perfusion chamber was designed and integrated with multi-electrode arrays (MEAs) electrophysiology and compartmentalized microfluidic device to continuously record from engineered neuronal networks at sub-cellular resolution. Cell culture media underwent iterations of conditioning to the ambient CO₂and adjusting its pH to physiological ranges to retain a stable pH for weeks outside of the incubator. Double-wall perfusion chamber and an integrated air bubble trapper reduced media evaporation and osmolality drifts of the conditioned media for two weeks. Aligned microchannel-microfluidic device on MEA electrodes allowed neurite growth on top of the planar electrodes and amplified their extracellular activity. This enabled continuous sub-cellular resolution imaging and electrophysiology recordings from developing networks and their growing neurites. The on-chip versatile and self-contained system provides long-term, continuous and high spatiotemporal access to the network data and offers a robustin vitroplatform with many potentials to be applied on advanced cell culture systems including organ-on-chip and organoid models.

Microfluidics for Neuronal Cell and Circuit Engineering

The widespread adoption of microfluidic devices among the neuroscience and neurobiology communities has enabled addressing a broad range of questions at the molecular, cellular, circuit, and system levels. Here, we review biomedical engineering approaches that harness the power of microfluidics for bottom-up generation of neuronal cell types and for the assembly and analysis of neural circuits. Microfluidics-based approaches are instrumental to generate the knowledge necessary for the derivation of diverse neuronal cell types from human pluripotent stem cells, as they enable the isolation and subsequent examination of individual neurons of interest. Moreover, microfluidic devices allow to engineer neural circuits with specific orientations and directionality by providing control over neuronal cell polarity and permitting the isolation of axons in individual microchannels. Similarly, the use of microfluidic chips enables the construction not only of 2D but also of 3D brain, retinal, and peripheral nervous system model circuits. Such brain-on-a-chip and organoid-on-a-chip technologies are promising platforms for studying these organs as they closely recapitulate some aspects of in vivo biological processes. Microfluidic 3D neuronal models, together with 2D in vitro systems, are widely used in many applications ranging from drug development and toxicology studies to neurological disease modeling and personalized medicine. Altogether, microfluidics provide researchers with powerful systems that complement and partially replace animal models.

Protein overexpression of toll-like receptor 4 and myeloid differentiation factor 88 in oral squamous cell carcinoma and clinical significance

Oral squamous cell carcinoma (OSCC) is the most common type of malignancy of the head and neck. In the present study, the expression of Toll-like receptor 4 (TLR4) and myeloid differentiation primary response gene 88 (MyD88) was evaluated in 55 OSCC tissues and their corresponding adjacent tissues using immunohistochemistry and reverse-transcription quantitative PCR. The results indicated that TLR4 and MyD88 were overexpressed in OSCC. Furthermore, high expression of MyD88 was negatively associated with a poor degree of differentiation, recurrence and metastasis of the tumor and was positively associated with underlying disease, including hypertension, heart disease and diabetes mellitus. Furthermore, high expression of TLR4 was positively associated with a long growth time of the tumor. In conclusion, the present study evaluated the expression levels of TLR4 and MyD88 in OSCC, as well as the association between them and clinicopathological factors, to provide markers for the prognosis and treatment of OSCC. These two genes may serve as biomarkers to optimize OSCC treatment, setting a new direction for stratifying patients and developing precise and personalized treatment regimens; the TLR4/MyD88 pathway may serve as a potential therapeutic target in the future.

Patient-Specific Organoid and Organ-on-a-Chip: 3D Cell-Culture Meets 3D Printing and Numerical Simulation

The last few decades have witnessed diversified in vitro models to recapitulate the architecture and function of living organs or tissues and contribute immensely to advances in life science. Two novel 3D cell culture models: 1) Organoid, promoted mainly by the developments of stem cell biology and 2) Organ-on-a-chip, enhanced primarily due to microfluidic technology, have emerged as two promising approaches to advance the understanding of basic biological principles and clinical treatments. This review describes the comparable distinct differences between these two models and provides more insights into their complementarity and integration to recognize their merits and limitations for applicable fields. The convergence of the two approaches to produce multi-organoid-on-a-chip or human organoid-on-a-chip is emerging as a new approach for building 3D models with higher physiological relevance. Furthermore, rapid advancements in 3D printing and numerical simulations, which facilitate the design, manufacture, and results-translation of 3D cell culture models, can also serve as novel tools to promote the development and propagation of organoid and organ-on-a-chip systems. Current technological challenges and limitations, as well as expert recommendations and future solutions to address the promising combinations by incorporating organoids, organ-on-a-chip, 3D printing, and numerical simulation, are also summarized.

Engineering organoids

Organoids are in vitro miniaturized and simplified model systems of organs that have gained enormous interest for modelling tissue development and disease, and for personalized medicine, drug screening and cell therapy. Despite considerable success in culturing physiologically relevant organoids, challenges remain to achieve real-life applications. In particular, the high variability of self-organizing growth and restricted experimental and analytical access hamper the translatability of organoid systems. In this Review, we argue that many limitations of traditional organoid culture can be addressed by engineering approaches at all levels of organoid systems. We investigate cell surface and genetic engineering approaches, and discuss stem cell niche engineering based on the design of matrices that allow spatiotemporal control of organoid growth and shape-guided morphogenesis. We examine how microfluidic approaches and lessons learnt from organs-on-a-chip enable the integration of mechano-physiological parameters and increase accessibility of organoids to improve functional readouts. Applying engineering principles to organoids increases reproducibility and provides experimental control, which will, ultimately, be required to enable clinical translation.

Fabrication techniques of biomimetic scaffolds in three-dimensional cell culture: A review

In the last four decades, several researchers worldwide have routinely and meticulously exercised cell culture experiments in two-dimensional (2D) platforms. Using traditionally existing 2D models, the therapeutic efficacy of drugs has been inappropriately validated due to the failure in generating the precise therapeutic response. Fortunately, a 3D model addresses the foregoing limitations by recapitulating the in vivo environment. In this context, one has to contemplate the design of an appropriate scaffold for favoring the organization of cell microenvironment. Instituting pertinent model on the platter will pave way for a precise mimicking of in vivo conditions. It is because animal cells in scaffolds oblige spontaneous formation of 3D colonies that molecularly, phenotypically, and histologically resemble the native environment. The 3D culture provides insight into the biochemical aspects of cell-cell communication, plasticity, cell division, cytoskeletal reorganization, signaling mechanisms, differentiation, and cell death. Focusing on these criteria, this paper discusses in detail, the diversification of polymeric scaffolds based on their available resources. The paper also reviews the well-founded and latest techniques of scaffold fabrication, and their applications pertaining to tissue engineering, drug screening, and tumor model development.

Three-Dimensional Regeneration of Patient-Derived Intestinal Organoid Epithelium in a Physiodynamic Mucosal Interface-on-a-Chip

The regeneration of the mucosal interface of the human intestine is critical in the host-gut microbiome crosstalk associated with gastrointestinal diseases. The biopsy-derived intestinal organoids provide genetic information of patients with physiological cytodifferentiation. However, the enclosed lumen and static culture condition substantially limit the utility of patient-derived organoids for microbiome-associated disease modeling. Here, we report a patient-specific three-dimensional (3D) physiodynamic mucosal interface-on-a-chip (PMI Chip) that provides a microphysiological intestinal milieu under defined biomechanics. The real-time imaging and computational simulation of the PMI Chip verified the recapitulation of non-linear luminal and microvascular flow that simulates the hydrodynamics in a living human gut. The multiaxial deformations in a convoluted microchannel not only induced dynamic cell strains but also enhanced particle mixing in the lumen microchannel. Under this physiodynamic condition, an organoid-derived epithelium obtained from the patients diagnosed with Crohn's disease, ulcerative colitis, or colorectal cancer independently formed 3D epithelial layers with disease-specific differentiations. Moreover, co-culture with the human fecal microbiome in an anoxic-oxic interface resulted in the formation of stochastic microcolonies without a loss of epithelial barrier function. We envision that the patient-specific PMI Chip that conveys genetic, epigenetic, and environmental factors of individual patients will potentially demonstrate the pathophysiological dynamics and complex host-microbiome crosstalk to target a patient-specific disease modeling.

In vitro modeling of the neurovascular unit: advances in the field

The blood–brain barrier (BBB) is a fundamental component of the central nervous system. Its functional and structural integrity is vital in maintaining the homeostasis of the brain microenvironment. On the other hand, the BBB is also a major hindering obstacle for the delivery of effective therapies to treat disorders of the Central Nervous System (CNS). Over time, various model systems have been established to simulate the complexities of the BBB. The development of realistic in vitro BBB models that accurately mimic the physiological characteristics of the brain microcapillaries in situ is of fundamental importance not only in CNS drug discovery but also in translational research. Successful modeling of the Neurovascular Unit (NVU) would provide an invaluable tool that would aid in dissecting out the pathological factors, mechanisms of action, and corresponding targets prodromal to the onset of CNS disorders. The field of BBB in vitro modeling has seen many fundamental changes in the last few years with the introduction of novel tools and methods to improve existing models and enable new ones. The development of CNS organoids, organ-on-chip, spheroids, 3D printed microfluidics, and other innovative technologies have the potential to advance the field of BBB and NVU modeling. Therefore, in this review, summarize the advances and progress in the design and application of functional in vitro BBB platforms with a focus on rapidly advancing technologies.

Human iPS Cell-Derived Patient Tissues and 3D Cell Culture Part 2: Spheroids, Organoids, and Disease Modeling

Human induced pluripotent stem cells (HiPSCs) provide several advantages for drug discovery, but principally they provide a source of clinically relevant tissue. Furthermore, the use of HiPSCs cultured in three-dimensional (3D) systems, as opposed to traditional two-dimensional (2D) culture approaches, better represents the complex tissue architecture in vivo. The use of HiPSCs in 3D spheroid and organoid culture is now growing, but particularly when using myocardial, intestinal enteric nervous system, and retinal cell lines. However, organoid cell culture is perhaps making the most notable impact in research and drug discovery, in which 3D neuronal cell cultures allow direct modeling of cortical cell layering and neuronal circuit activity. Given the specific degeneration seen in discrete neuronal circuitry in Alzheimer’s disease (AD) and Parkinson’s disease (PD), HiPSC culture systems are proving to be a major advance. In the present review, the second part of a two-part review, we discuss novel methods in which 3D cell culture systems (principally organoids) are now being used to provide insights into disease mechanisms. (The use of HiPSCs in target identification was reviewed in detail in Part 1.)

Human iPSC-Derived Endothelial Cells and Microengineered Organ-Chip Enhance Neuronal Development

Human stem cell-derived models of development and neurodegenerative diseases are challenged by cellular immaturity in vitro. Microengineered organ-on-chip (or Organ-Chip) systems are designed to emulate microvolume cytoarchitecture and enable co-culture of distinct cell types. Brain microvascular endothelial cells (BMECs) share common signaling pathways with neurons early in development, but their contribution to human neuronal maturation is largely unknown. To study this interaction and influence of microculture, we derived both spinal motor neurons and BMECs from human induced pluripotent stem cells and observed increased calcium transient function and Chip-specific gene expression in Organ-Chips compared with 96-well plates. Seeding BMECs in the Organ-Chip led to vascular-neural interaction and specific gene activation that further enhanced neuronal function and in vivo-like signatures. The results show that the vascular system has specific maturation effects on spinal cord neural tissue, and the use of Organ-Chips can move stem cell models closer to an in vivo condition.