Engineering neurovascular organoids with 3D printed microfluidic chips

Vascularized platforms for investigating cell communication via extracellular vesicles

The vascular network plays an essential role in the maintenance of all organs in the body via the regulated delivery of oxygen and nutrients, as well as tissue communication via the transfer of various biological signaling molecules. It also serves as a route for drug administration and affects pharmacokinetics. Due to this importance, engineers have sought to create physiologically relevant and reproducible vascular systems in tissue, considering cell-cell and extracellular matrix interaction with structural and physical conditions in the microenvironment. Extracellular vesicles (EVs) have recently emerged as important carriers for transferring proteins and genetic material between cells and organs, as well as for drug delivery. Vascularized platforms can be an ideal system for studying interactions between blood vessels and EVs, which are crucial for understanding EV-mediated substance transfer in various biological situations. This review summarizes recent advances in vascularized platforms, standard and microfluidic-based techniques for EV isolation and characterization, and studies of EVs in vascularized platforms. It provides insights into EV-related (patho)physiological regulations and facilitates the development of EV-based therapeutics.

Shaping the Neurovascular Unit Exploiting Human Brain Organoids

Brain organoids, three-dimensional cell structures derived from pluripotent stem cells, closely mimic key aspects of the human brain in vitro, providing a powerful tool for studying neurodevelopment and disease. The neuroectodermal induction protocol employed for brain organoid generation primarily gives rise to the neural cellular component but lacks the vital vascular system, which is crucial for the brain functions by regulating differentiation, migration, and circuit formation, as well as delivering oxygen and nutrients. Many neurological diseases are caused by dysfunctions of cerebral microcirculation, making vascularization of human brain organoids an important tool for pathogenetic and translational research. Experimentally, the creation of vascularized brain organoids has primarily focused on the fusion of vascular and brain organoids, on organoid transplantation in vivo, and on the use of microfluidic devices to replicate the intricate microenvironment of the human brain in vitro. This review summarizes these efforts and highlights the importance of studying the neurovascular unit in a forward-looking perspective of leveraging their use for understanding and treating neurological disorders.

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.

Patient-Derived Organoids as Therapy Screening Platforms in Cancer Patients

Patient-derived organoids (PDOs) developed ex vivo and in vitro are increasingly used for therapeutic screening. They provide a more physiologically relevant model for drug discovery and development compared to traditional cell lines. However, several challenges remain to be addressed to fully realize the potential of PDOs in therapeutic screening. This paper summarizes recent advancements in PDO development and the enhancement of PDO culture models. This is achieved by leveraging materials engineering and microfabrication technologies, including organs-on-a-chip and droplet microfluidics. Additionally, this work discusses the application of PDOs in therapy screening to meet diverse requirements and overcome bottlenecks in cancer treatment. Furthermore, this work introduces tools for data processing and analysis of organoids, along with their microenvironment. These tools aim to achieve enhanced readouts. Finally, this work explores the challenges and future perspectives of using PDOs in drug development and personalized screening for cancer patients.

Vascularized tumor models for the evaluation of drug delivery systems: a paradigm shift

As the conversion rate of preclinical studies for cancer treatment is low, user-friendly models that mimic the pathological microenvironment and drug intake with high throughput are scarce. Animal models are key, but an alternative to reduce their use would be valuable. Vascularized tumor-on-chip models combine great versatility with scalable throughput and are easy to use. Several strategies to integrate both tumor and vascular compartments have been developed, but few have been used to assess drug delivery. Permeability, intra/extravasation, and free drug circulation are often evaluated, but imperfectly recapitulate the processes at stake. Indeed, tumor targeting and chemoresistance bypass must be investigated to design promising cancer therapeutics. In vitro models that would help the development of drug delivery systems (DDS) are thus needed. They would allow selecting good candidates before animal studies based on rational criteria such as drug accumulation, diffusion in the tumor, and potency, as well as absence of side damage. In this review, we focus on vascularized tumor models. First, we detail their fabrication, and especially the materials, cell types, and coculture used. Then, the different strategies of vascularization are described along with their classical applications in intra/extravasation or free drug assessment. Finally, current trends in DDS for cancer are discussed with an overview of the current efforts in the domain.

Microinstrumentation for Brain Organoids

Brain organoids are three-dimensional aggregates of self-organized differentiated stem cells that mimic the structure and function of human brain regions. Organoids bridge the gaps between conventional drug screening models such as planar mammalian cell culture, animal studies, and clinical trials. They can revolutionize the fields of developmental biology, neuroscience, toxicology, and computer engineering. Conventional microinstrumentation for conventional cellular engineering, such as planar microfluidic chips; microelectrode arrays (MEAs); and optical, magnetic, and acoustic techniques, has limitations when applied to three-dimensional (3D) organoids, primarily due to their limits with inherently two-dimensional geometry and interfacing. Hence, there is an urgent need to develop new instrumentation compatible with live cell culture techniques and with scalable 3D formats relevant to organoids. This review discusses conventional planar approaches and emerging 3D microinstrumentation necessary for advanced organoid-machine interfaces. Specifically, this article surveys recently developed microinstrumentation, including 3D printed and curved microfluidics, 3D and fast-scan optical techniques, buckling and self-folding MEAs, 3D interfaces for electrochemical measurements, and 3D spatially controllable magnetic and acoustic technologies relevant to two-way information transfer with brain organoids. This article highlights key challenges that must be addressed for robust organoid culture and reliable 3D spatiotemporal information transfer.

Limitations of human brain organoids to study neurodegenerative diseases: a manual to survive

In 2013, M. Lancaster described the first protocol to obtain human brain organoids. These organoids, usually generated from human-induced pluripotent stem cells, can mimic the three-dimensional structure of the human brain. While they recapitulate the salient developmental stages of the human brain, their use to investigate the onset and mechanisms of neurodegenerative diseases still faces crucial limitations. In this review, we aim to highlight these limitations, which hinder brain organoids from becoming reliable models to study neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and amyotrophic lateral sclerosis (ALS). Specifically, we will describe structural and biological impediments, including the lack of an aging footprint, angiogenesis, myelination, and the inclusion of functional and immunocompetent microglia—all important factors in the onset of neurodegeneration in AD, PD, and ALS. Additionally, we will discuss technical limitations for monitoring the microanatomy and electrophysiology of these organoids. In parallel, we will propose solutions to overcome the current limitations, thereby making human brain organoids a more reliable tool to model neurodegeneration.

Bioengineering methods for vascularizing organoids

Organoids, self-organizing three-dimensional (3D) structures derived from stem cells, offer unique advantages for studying organ development, modeling diseases, and screening potential therapeutics. However, their translational potential and ability to mimic complex in vivo functions are often hindered by the lack of an integrated vascular network. To address this critical limitation, bioengineering strategies are rapidly advancing to enable efficient vascularization of organoids. These methods encompass co-culturing organoids with various vascular cell types, co-culturing lineage-specific organoids with vascular organoids, co-differentiating stem cells into organ-specific and vascular lineages, using organoid-on-a-chip technology to integrate perfusable vasculature within organoids, and using 3D bioprinting to also create perfusable organoids. This review explores the field of organoid vascularization, examining the biological principles that inform bioengineering approaches. Additionally, this review envisions how the converging disciplines of stem cell biology, biomaterials, and advanced fabrication technologies will propel the creation of increasingly sophisticated organoid models, ultimately accelerating biomedical discoveries and innovations.

Microfluidic sensors for the detection of emerging contaminants in water: A review

In recent years, numerous emerging contaminants have been identified in surface water, groundwater, and drinking water. Developing novel sensing methods for detecting diverse emerging pollutants in water is urgently needed, as even at low concentrations, these pollutants can pose a serious threat to human health and environmental safety. Traditional testing methods are based on laboratory equipment, which is highly sensitive but complex to operate, costly, and not suitable for on-site monitoring. Microfluidic sensors offer several benefits, including rapid evaluation, minimal sample usage, accurate liquid manipulation, compact size, automation, and in-situ detection capabilities. They provide promising and efficient analytical tools for high-performance sensing platforms in monitoring emerging contaminants in water. In this paper, recent research advances in microfluidic sensors for the detection of emerging contaminants in water are reviewed. Initially, a concise overview is provided about the various substrate materials, corresponding microfabrication techniques, different driving forces, and commonly used detection techniques for microfluidic devices. Subsequently, a comprehensive analysis is conducted on microfluidic detection methods for endocrine-disrupting chemicals, pharmaceuticals and personal care products, microplastics, and perfluorinated compounds. Finally, the prospects and future challenges of microfluidic sensors in this field are discussed.

Blood vessels in a dish: the evolution, challenges, and potential of vascularized tissues and organoids

Vascular pathologies are prevalent in a broad spectrum of diseases, necessitating a deeper understanding of vascular biology, particularly in overcoming the oxygen and nutrient diffusion limit in tissue constructs. The evolution of vascularized tissues signifies a convergence of multiple scientific disciplines, encompassing the differentiation of human pluripotent stem cells (hPSCs) into vascular cells, the development of advanced three-dimensional (3D) bioprinting techniques, and the refinement of bioinks. These technologies are instrumental in creating intricate vascular networks essential for tissue viability, especially in thick, complex constructs. This review provides broad perspectives on the past, current state, and advancements in key areas, including the differentiation of hPSCs into specific vascular lineages, the potential and challenges of 3D bioprinting methods, and the role of innovative bioinks mimicking the native extracellular matrix. We also explore the integration of biophysical cues in vascularized tissues in vitro, highlighting their importance in stimulating vessel maturation and functionality. In this review, we aim to synthesize these diverse yet interconnected domains, offering a broad, multidisciplinary perspective on tissue vascularization. Advancements in this field will help address the global organ shortage and transform patient care.

The Edifice of Vasculature-On-Chips: A Focused Review on the Key Elements and Assembly of Angiogenesis Models

The conception of vascularized organ-on-a-chip models provides researchers with the ability to supply controlled biological and physical cues that simulate the in vivo dynamic microphysiological environment of native blood vessels. The intention of this niche research area is to improve our understanding of the role of the vasculature in health or disease progression in vitro by allowing researchers to monitor angiogenic responses and cell-cell or cell-matrix interactions in real time. This review offers a comprehensive overview of the essential elements, including cells, biomaterials, microenvironmental factors, microfluidic chip design, and standard validation procedures that currently govern angiogenesis-on-a-chip assemblies. In addition, we emphasize the importance of incorporating a microvasculature component into organ-on-chip devices in critical biomedical research areas, such as tissue engineering, drug discovery, and disease modeling. Ultimately, advances in this area of research could provide innovative solutions and a personalized approach to ongoing medical challenges.

Basic models to advanced systems: harnessing the power of organoids-based microphysiological models of the human brain

Understanding the complexities of the human brain's function in health and disease is a formidable challenge in neuroscience. While traditional models like animals offer valuable insights, they often fall short in accurately mirroring human biology and drug responses. Moreover, recent legislation has underscored the need for more predictive models that more accurately represent human physiology. To address this requirement, human-derived cell cultures have emerged as a crucial alternative for biomedical research. However, traditional static cell culture models lack the dynamic tissue microenvironment that governs human tissue function. Advancedin vitrosystems, such as organoids and microphysiological systems (MPSs), bridge this gap by offering more accurate representations of human biology. Organoids, which are three-dimensional miniaturized organ-like structures derived from stem cells, exhibit physiological responses akin to native tissues, but lack essential tissue-specific components such as functional vascular structures and immune cells. Recent endeavors have focused on incorporating endothelial cells and immune cells into organoids to enhance vascularization, maturation, and disease modeling. MPS, including organ-on-chip technologies, integrate diverse cell types and vascularization under dynamic culture conditions, revolutionizing brain research by bridging the gap betweenin vitroandin vivomodels. In this review, we delve into the evolution of MPS, with a particular focus on highlighting the significance of vascularization in enhancing the viability, functionality, and disease modeling potential of organoids. By examining the interplay of vasculature and neuronal cells within organoids, we can uncover novel therapeutic targets and gain valuable insights into disease mechanisms, offering the promise of significant advancements in neuroscience and improved patient outcomes.

High-resolution low-cost LCD 3D printing for microfluidics and organ-on-a-chip devices

The fabrication of microfluidic devices has progressed from cleanroom manufacturing to replica molding in polymers, and more recently to direct manufacturing by subtractive (e.g., laser machining) and additive (e.g., 3D printing) techniques, notably digital light processing (DLP) photopolymerization. However, many methods require technical expertise and DLP 3D printers remain expensive at a cost ∼15-30 K USD with ∼8 M pixels that are 25-40 μm in size. Here, we introduce (i) the use of low-cost (∼150-600 USD) liquid crystal display (LCD) photopolymerization 3D printing with ∼8-58 M pixels that are 18-35 μm in size for direct microfluidic device fabrication, and (ii) a poly(ethylene glycol) diacrylate-based ink developed for LCD 3D printing (PLInk). We optimized PLInk for high resolution, fast 3D printing and biocompatibility while considering the illumination inhomogeneity and low power density of LCD 3D printers. We made lateral features as small as 75 μm, 22 μm-thick embedded membranes, and circular channels with a 110 μm radius. We 3D printed microfluidic devices previously manufactured by other methods, including an embedded 3D micromixer, a membrane microvalve, and an autonomous capillaric circuit (CC) deployed for interferon-γ detection with excellent performance (limit of detection: 12 pg mL-1, CV: 6.8%). We made PLInk-based organ-on-a-chip devices in 384-well plate format and produced 3420 individual devices within an 8 h print run. We used the devices to co-culture two spheroids separated by a vascular barrier over 5 days and observed endothelial sprouting, cellular reorganization, and migration. LCD 3D printing together with tailored inks pave the way for democratizing access to high-resolution manufacturing of ready-to-use microfluidic and organ-on-a-chip devices by anyone, anywhere.

Models of Herpes Simplex Virus Latency

Our current understanding of HSV latency is based on a variety of clinical observations, and in vivo, ex vivo, and in vitro model systems, each with unique advantages and drawbacks. The criteria for authentically modeling HSV latency include the ability to easily manipulate host genetics and biological pathways, as well as mimicking the immune response and viral pathogenesis in human infections. Although realistically modeling HSV latency is necessary when choosing a model, the cost, time requirement, ethical constraints, and reagent availability are also equally important. Presently, there remains a pressing need for in vivo models that more closely recapitulate human HSV infection. While the current in vivo, ex vivo, and in vitro models used to study HSV latency have limitations, they provide further insights that add to our understanding of latency. In vivo models have shed light on natural infection routes and the interplay between the host immune response and the virus during latency, while in vitro models have been invaluable in elucidating molecular pathways involved in latency. Below, we review the relative advantages and disadvantages of current HSV models and highlight insights gained through each.

Vascularized organoid-on-a-chip: design, imaging, and analysis

Vascularized organoid-on-a-chip (VOoC) models achieve substance exchange in deep layers of organoids and provide a more physiologically relevant system in vitro. Common designs for VOoC primarily involve two categories: self-assembly of endothelial cells (ECs) to form microvessels and pre-patterned vessel lumens, both of which include the hydrogel region for EC growth and allow for controlled fluid perfusion on the chip. Characterizing the vasculature of VOoC often relies on high-resolution microscopic imaging. However, the high scattering of turbid tissues can limit optical imaging depth. To overcome this limitation, tissue optical clearing (TOC) techniques have emerged, allowing for 3D visualization of VOoC in conjunction with optical imaging techniques. The acquisition of large-scale imaging data, coupled with high-resolution imaging in whole-mount preparations, necessitates the development of highly efficient analysis methods. In this review, we provide an overview of the chip designs and culturing strategies employed for VOoC, as well as the applicable optical imaging and TOC methods. Furthermore, we summarize the vascular analysis techniques employed in VOoC, including deep learning. Finally, we discuss the existing challenges in VOoC and vascular analysis methods and provide an outlook for future development.

Bioengineering toolkits for potentiating organoid therapeutics

Organoids are three-dimensional, multicellular constructs that recapitulate the structural and functional features of specific organs. Because of these characteristics, organoids have been widely applied in biomedical research in recent decades. Remarkable advancements in organoid technology have positioned them as promising candidates for regenerative medicine. However, current organoids still have limitations, such as the absence of internal vasculature, limited functionality, and a small size that is not commensurate with that of actual organs. These limitations hinder their survival and regenerative effects after transplantation. Another significant concern is the reliance on mouse tumor-derived matrix in organoid culture, which is unsuitable for clinical translation due to its tumor origin and safety issues. Therefore, our aim is to describe engineering strategies and alternative biocompatible materials that can facilitate the practical applications of organoids in regenerative medicine. Furthermore, we highlight meaningful progress in organoid transplantation, with a particular emphasis on the functional restoration of various organs.

Advances in cardiac tissue engineering and heart-on-a-chip

Recent advances in both cardiac tissue engineering and hearts-on-a-chip are grounded in new biomaterial development as well as the employment of innovative fabrication techniques that enable precise control of the mechanical, electrical, and structural properties of the cardiac tissues being modelled. The elongated structure of cardiomyocytes requires tuning of substrate properties and application of biophysical stimuli to drive its mature phenotype. Landmark advances have already been achieved with induced pluripotent stem cell-derived cardiac patches that advanced to human testing. Heart-on-a-chip platforms are now commonly used by a number of pharmaceutical and biotechnology companies. Here, we provide an overview of cardiac physiology in order to better define the requirements for functional tissue recapitulation. We then discuss the biomaterials most commonly used in both cardiac tissue engineering and heart-on-a-chip, followed by the discussion of recent representative studies in both fields. We outline significant challenges common to both fields, specifically: scalable tissue fabrication and platform standardization, improving cellular fidelity through effective tissue vascularization, achieving adult tissue maturation, and ultimately developing cryopreservation protocols so that the tissues are available off the shelf.

Neuropathogenesis-on-chips for neurodegenerative diseases

Developing diagnostics and treatments for neurodegenerative diseases (NDs) is challenging due to multifactorial pathogenesis that progresses gradually. Advanced in vitro systems that recapitulate patient-like pathophysiology are emerging as alternatives to conventional animal-based models. In this review, we explore the interconnected pathogenic features of different types of ND, discuss the general strategy to modelling NDs using a microfluidic chip, and introduce the organoid-on-a-chip as the next advanced relevant model. Lastly, we overview how these models are being applied in academic and industrial drug development. The integration of microfluidic chips, stem cells, and biotechnological devices promises to provide valuable insights for biomedical research and developing diagnostic and therapeutic solutions for NDs.

Modular tissue-in-a-CUBE platform to model blood-brain barrier (BBB) and brain interaction

With the advent of increasingly sophisticated organoids, there is growing demand for technology to replicate the interactions between multiple tissues or organs. This is challenging to achieve, however, due to the varying culture conditions of the different cell types that make up each tissue. Current methods often require complicated microfluidic setups, but fragile tissue samples tend not to fare well with rough handling. Furthermore, the more complicated the human system to be replicated, the more difficult the model becomes to operate. Here, we present the development of a multi-tissue chip platform that takes advantage of the modularity and convenient handling ability of a CUBE device. We first developed a blood-brain barrier-in-a-CUBE by layering astrocytes, pericytes, and brain microvascular endothelial cells in the CUBE, and confirmed the expression and function of important tight junction and transporter proteins in the blood-brain barrier model. Then, we demonstrated the application of integrating Tissue-in-a-CUBE with a chip in simulating the in vitro testing of the permeability of a drug through the blood-brain barrier to the brain and its effect on treating the glioblastoma brain cancer model. We anticipate that this platform can be adapted for use with organoids to build complex human systems in vitro by the combination of multiple simple CUBE units.

Brain organoids: A revolutionary tool for modeling neurological disorders and development of therapeutics

Brain organoids are self-organized, three-dimensional (3D) aggregates derived from pluripotent stem cells that have cell types and cellular architectures resembling those of the developing human brain. The current understanding of human brain developmental processes and neurological disorders has advanced significantly with the introduction of this in vitro model. Brain organoids serve as a translational link between two-dimensional (2D) cultures and in vivo models which imitate the neural tube formation at the early and late stages and the differentiation of neuroepithelium with whole-brain regionalization. In addition, the generation of region-specific brain organoids made it possible to investigate the pathogenic and etiological aspects of acquired and inherited brain disease along with drug discovery and drug toxicity testing. In this review article, we first summarize an overview of the existing methods and platforms used for generating brain organoids and their limitations and then discuss the recent advancement in brain organoid technology. In addition, we discuss how brain organoids have been used to model aspects of neurodevelopmental and neurodegenerative diseases, including autism spectrum disorder (ASD), Rett syndrome, Zika virus-related microcephaly, Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD).

Spatially Self-Organized Three-Dimensional Neural Concentroid as a Novel Reductionist Humanized Model to Study Neurovascular Development

Although human pluripotent stem cell (PSC)-derived brain organoids have enabled researchers to gain insight into human brain development and disease, these organoids contain solely ectodermal cells and are not vascularized as occurs during brain development. Here it is created less complex and more homogenous large neural constructs starting from PSC-derived neuroprogenitor cells (NPC), by fusing small NPC spheroids into so-called concentroids. Such concentroids consisted of a pro-angiogenic core, containing neuronal and outer radial glia cells, surrounded by an astroglia-dense outer layer. Incorporating PSC-derived endothelial cells (EC) around and/or in the concentroids promoted vascularization, accompanied by differential outgrowth and differentiation of neuronal and astroglia cells, as well as the development of ectodermal-derived pericyte-like mural cells co-localizing with EC networks. Single nucleus transcriptomic analysis revealed an enhanced neural cell subtype maturation and diversity in EC-containing concentroids, which better resemble the fetal human brain compared to classical organoids or NPC-only concentroids. This PSC-derived "vascularized" concentroid brain model will facilitate the study of neurovascular/blood-brain barrier development, neural cell migration, and the development of effective in vitro vascularization strategies of brain mimics.

Small Joint Organoids 3D Bioprinting: Construction Strategy and Application

Osteoarthritis (OA) is a chronic disease that causes pain and disability in adults, affecting ≈300 million people worldwide. It is caused by damage to cartilage, including cellular inflammation and destruction of the extracellular matrix (ECM), leading to limited self-repairing ability due to the lack of blood vessels and nerves in the cartilage tissue. Organoid technology has emerged as a promising approach for cartilage repair, but constructing joint organoids with their complex structures and special mechanisms is still challenging. To overcome these boundaries, 3D bioprinting technology allows for the precise design of physiologically relevant joint organoids, including shape, structure, mechanical properties, cellular arrangement, and biological cues to mimic natural joint tissue. In this review, the authors will introduce the biological structure of joint tissues, summarize key procedures in 3D bioprinting for cartilage repair, and propose strategies for constructing joint organoids using 3D bioprinting. The authors also discuss the challenges of using joint organoids' approaches and perspectives on their future applications, opening opportunities to model joint tissues and response to joint disease treatment.

Modeling the neuroimmune system in Alzheimer's and Parkinson's diseases

Parkinson's disease (PD) and Alzheimer's disease (AD) are neurodegenerative disorders caused by the interaction of genetic, environmental, and familial factors. These diseases have distinct pathologies and symptoms that are linked to specific cell populations in the brain. Notably, the immune system has been implicated in both diseases, with a particular focus on the dysfunction of microglia, the brain's resident immune cells, contributing to neuronal loss and exacerbating symptoms. Researchers use models of the neuroimmune system to gain a deeper understanding of the physiological and biological aspects of these neurodegenerative diseases and how they progress. Several in vitro and in vivo models, including 2D cultures and animal models, have been utilized. Recently, advancements have been made in optimizing these existing models and developing 3D models and organ-on-a-chip systems, holding tremendous promise in accurately mimicking the intricate intracellular environment. As a result, these models represent a crucial breakthrough in the transformation of current treatments for PD and AD by offering potential for conducting long-term disease-based modeling for therapeutic testing, reducing reliance on animal models, and significantly improving cell viability compared to conventional 2D models. The application of 3D and organ-on-a-chip models in neurodegenerative disease research marks a prosperous step forward, providing a more realistic representation of the complex interactions within the neuroimmune system. Ultimately, these refined models of the neuroimmune system aim to aid in the quest to combat and mitigate the impact of debilitating neuroimmune diseases on patients and their families.

Uniform cerebral organoid culture on a pillar plate by simple and reproducible spheroid transfer from an ultralow attachment well plate

Human induced pluripotent stem cell (iPSC)-derived brain organoids have potential to recapitulate the earliest stages of brain development, serving as an effectivein vitromodel for studying both normal brain development and disorders. However, current brain organoid culture methods face several challenges, including low throughput, high variability in organoid generation, and time-consuming, multiple transfer and encapsulation of cells in hydrogels throughout the culture. These limitations hinder the widespread application of brain organoids including high-throughput assessment of compounds in clinical and industrial lab settings. In this study, we demonstrate a straightforward approach of generating multiple cerebral organoids from iPSCs on a pillar plate platform, eliminating the need for labor-intensive, multiple transfer and encapsulation steps to ensure the reproducible generation of cerebral organoids. We formed embryoid bodies in an ultra-low attachment 384-well plate and subsequently transferred them to the pillar plate containing Matrigel, using a straightforward sandwiching and inverting method. Each pillar on the pillar plate contains a single spheroid, and the success rate of spheroid transfer was in a range of 95%-100%. Using this approach, we robustly generated cerebral organoids on the pillar plate and demonstrated an intra-batch coefficient of variation below 9%-19% based on ATP-based cell viability and compound treatment. Notably, our spheroid transfer method in combination with the pillar plate allows miniaturized culture of cerebral organoids, alleviates the issue of organoid variability, and has potential to significantly enhance assay throughput by allowingin situorganoid assessment as compared to conventional organoid culture in 6-/24-well plates, petri dishes, and spinner flasks.

Humanized brain organoids-on-chip integrated with sensors for screening neuronal activity and neurotoxicity

The complex structure and function of the human central nervous system that develops from the neural tube made in vitro modeling quite challenging until the discovery of brain organoids. Human-induced pluripotent stem cells-derived brain organoids offer recapitulation of the features of early human neurodevelopment in vitro, including the generation, proliferation, and differentiation into mature neurons and micro-macroglial cells, as well as the complex interactions among these diverse cell types of the developing brain. Recent advancements in brain organoids, microfluidic systems, real-time sensing technologies, and their cutting-edge integrated use provide excellent models and tools for emulation of fundamental neurodevelopmental processes, the pathology of neurological disorders, personalized transplantation therapy, and high-throughput neurotoxicity testing by bridging the gap between two-dimensional models and the complex three-dimensional environment in vivo. In this review, we summarize how bioengineering approaches are applied to mitigate the limitations of brain organoids for biomedical and clinical research. We further provide an extensive overview and future perspectives of the humanized brain organoids-on-chip platforms with integrated sensors toward brain organoid intelligence and biocomputing studies. Such approaches might pave the way for increasing approvable clinical applications by solving their current limitations.

Application of patient-derived induced pluripotent stem cells and organoids in inherited retinal diseases

Inherited retinal diseases (IRDs) can induce severe sight-threatening retinal degeneration and impose a considerable economic burden on patients and society, making efforts to cure blindness imperative. Transgenic animals mimicking human genetic diseases have long been used as a primary research tool to decipher the underlying pathogenesis, but there are still some obvious limitations. As an alternative strategy, patient-derived induced pluripotent stem cells (iPSCs), particularly three-dimensional (3D) organoid technology, are considered a promising platform for modeling different forms of IRDs, including retinitis pigmentosa, Leber congenital amaurosis, X-linked recessive retinoschisis, Batten disease, achromatopsia, and best vitelliform macular dystrophy. Here, this paper focuses on the status of patient-derived iPSCs and organoids in IRDs in recent years concerning disease modeling and therapeutic exploration, along with potential challenges for translating laboratory research to clinical application. Finally, the importance of human iPSCs and organoids in combination with emerging technologies such as multi-omics integration analysis, 3D bioprinting, or microfluidic chip platform are highlighted. Patient-derived retinal organoids may be a preferred choice for more accurately uncovering the mechanisms of human retinal diseases and will contribute to clinical practice.

Modular 3D printed platform for fluidically connected human brain organoid culture

Brain organoid technology has transformed both basic and applied biomedical research and paved the way for novel insights into developmental processes and disease states of the human brain. While the use of brain organoids has been rapidly growing in the past decade, the accompanying bioengineering and biofabrication solutions have remained scarce. As a result, most brain organoid protocols still rely on commercially available tools and culturing platforms that had previously been established for different purposes, thus entailing suboptimal culturing conditions and excessive use of plasticware. To address these issues, we developed a 3D printing pipeline for the fabrication of tailor-made culturing platforms for fluidically connected but spatially separated brain organoid array culture. This all-in-one platform allows all culturing steps-from cellular aggregation, spheroid growth, hydrogel embedding, and organoid maturation-to be performed in a single well plate without the need for organoid manipulation or transfer. Importantly, the approach relies on accessible materials and widely available 3D printing equipment. Furthermore, the developed design principles are modular and highly customizable. As such, we believe that the presented technology can be easily adapted by other research groups and fuel further development of culturing tools and platforms for brain organoids and other 3D cellular systems.

Uniform cerebral organoid culture on a pillar plate by simple and reproducible spheroid transfer from an ultralow attachment well plate

Human induced pluripotent stem cell (iPSCs)-derived brain organoids have potential to recapitulate the earliest stages of brain development, serving as an effective in vitro model for studying both normal brain development and disorders. However, current brain organoid culture methods face several challenges, including low throughput, high variability in organoid generation, and time-consuming, multiple transfer and encapsulation of cells in hydrogels throughout the culture. These limitations hinder the widespread application of brain organoids including high-throughput assessment of compounds in clinical and industrial lab settings. In this study, we demonstrate a straightforward approach of generating multiple cerebral organoids from iPSCs on a pillar plate platform, eliminating the need for labor-intensive, multiple transfer and encapsulation steps to ensure the reproducible generation of cerebral organoids. We formed embryoid bodies (EBs) in an ultra-low attachment (ULA) 384-well plate and subsequently transferred them to the pillar plate containing Matrigel, using a straightforward sandwiching and inverting method. Each pillar on the pillar plate contains a single spheroid, and the success rate of spheroid transfer was in a range of 95 - 100%. By differentiating the EBs on the pillar plate, we achieved robust generation of cerebral organoids with a coefficient of variation (CV) below 19%. Notably, our spheroid transfer method in combination with the pillar plate allows miniaturized culture of cerebral organoids, alleviates the issue of organoid variability, and has potential to significantly enhance assay throughput by allowing in situ organoid assessment as compared to conventional organoid culture in 6-/24-well plates, petri dishes, and spinner flasks.

Cortical spheroid on perfusable microvascular network in a microfluidic device

Human induced pluripotent stem cell (hiPSC)-derived brain spheroids can recapitulate the complex cytoarchitecture of the brain, as well as the genetic/epigenetic footprint of human brain development. However, hiPSC-derived 3D models such as spheroid and organoids does not have a perfusable microvascular network, which plays a vital role in maintaining homeostasis in vivo. With the critical balance of positive and negative angiogenic modulators, 3D microvascular network can be achieved by angiogenesis. This paper reports on a microfluidic-based three-dimensional, cortical spheroid grafted on the vascular-network. Vascular network was formed by inducing angiogenic sprouting using concentration gradient-driven angiogenic factors in the microfluidic device. We investigate critical factors for angiogenic vascular network formation with spheroid placement, including 1) a PKCα activator, phorbol-12-myristate-13-acetate (PMA); 2) orientation of endothelial cells under perfusion and permeability of vascular network; 3) effect of extracellular matrix (ECM) types and their densities on angiogenesis; and 4) integration with cortical spheroid on vascular network. This paper demonstrates proof of concept for the potential utility of a membrane-free in vitro cortical spheroid tissue construct with perfusable microvascular network that can be scaled up to a high throughput platform. It can provide a cost-effective alternative platform to animal testing by modeling brain diseases and disorders, and screening drugs.

Brain organoids for hypoxic-ischemic studies: from bench to bedside

Our current knowledge regarding the development of the human brain mostly derives from experimental studies on non-human primates, sheep, and rodents. However, these studies may not completely simulate all the features of human brain development as a result of species differences and variations in pre- and postnatal brain maturation. Therefore, it is important to supplement the in vivo animal models to increase the possibility that preclinical studies have appropriate relevance for potential future human trials. Three-dimensional brain organoid culture technology could complement in vivo animal studies to enhance the translatability of the preclinical animal studies and the understanding of brain-related disorders. In this review, we focus on the development of a model of hypoxic-ischemic (HI) brain injury using human brain organoids to complement the translation from animal experiments to human pathophysiology. We also discuss how the development of these tools provides potential opportunities to study fundamental aspects of the pathophysiology of HI-related brain injury including differences in the responses between males and females.

Modeling development using microfluidics: bridging gaps to foster fundamental and translational research

In vitro stem cell-derived embryo and organ models, termed embryoids and organoids, respectively, provide promising experimental tools to study physiological and pathological processes in mammalian development and organ formation. Most of current embryoid and organoid systems are developed using conventional three-dimensional cultures that lack controls of spatiotemporal extracellular signals. Microfluidics, an established technology for quantitative controls and quantifications of dynamic chemical and physical environments, has recently been utilized for developing next-generation embryoids and organoids in a controllable and reproducible manner. In this review, we summarize recent progress in constructing microfluidics-based embryoids and organoids. Development of these models demonstrates the successful applications of microfluidics in establishing morphogen gradients, accelerating medium transport, exerting mechanical forces, facilitating tissue coculture studies, and improving assay throughput, thus supporting using microfluidics for building next-generation embryoids and organoids for fundamental and translational research.

Biomimetic Gland Models with Engineered Stratagems

As extensively distributed tissues throughout the human body, glands play a critical role in various physiological processes. Therefore, the construction of biomimetic gland models in vitro has aroused great interest in multiple disciplines. In the biological field, the researchers focus on optimizing the cell sources and culture techniques to reconstruct the specific structures and functions of glands, such as the emergence of organoid technology. From the perspective of biomedical engineering, the generation of biomimetic gland models depends on the combination of engineered scaffolds and microfluidics, to mimic the in vivo environment of glandular tissues. These engineered stratagems endowed gland models with more biomimetic features, as well as a wide range of application prospects. In this review, we first describe the biomimetic strategies for constructing different in vitro gland models, focusing on the role of microfluidics in promoting the structure and function development of biomimetic glands. After summarizing several common in vitro models of endocrine and exocrine glands, the applications of gland models in disease modelling, drug screening, regenerative medicine, and personalized medicine are enumerated. Finally, we conclude the current challenges and our perspective of these biomimetic gland models.

Organoid-on-a-chip: Current challenges, trends, and future scope toward medicine

In vitro organoid models, typically defined as 3D multicellular aggregates, have been extensively used as a promising tool in drug screening, disease progression research, and precision medicine. Combined with advanced microfluidics technique, organoid-on-a-chip can flexibly replicate in vivo organs within the biomimetic physiological microenvironment by accurately regulating different parameters, such as fluid conditions and concentration gradients of biochemical factors. Since engineered organ reconstruction has opened a new paradigm in biomedicine, innovative approaches are increasingly required in micro-nano fabrication, tissue construction, and development of pharmaceutical products. In this Perspective review, the advantages and characteristics of organoid-on-a-chip are first introduced. Challenges in current organoid culture, extracellular matrix building, and device manufacturing techniques are subsequently demonstrated, followed by potential alternative approaches, respectively. The future directions and emerging application scenarios of organoid-on-a-chip are finally prospected to further satisfy the clinical demands.

Alignment behavior of nerve, vascular, muscle, and intestine cells in two- and three-dimensional strategies

By harnessing structural hierarchical insights, plausibly simulate better ones imagination to figure out the best choice of methods for reaching out the unprecedented developments of the tissue engineering products as a next level. Constructing a functional tissue that incorporates two-dimensional (2D) or higher dimensions requires overcoming technological or biological limitations in order to orchestrate the structural compilation of one-dimensional and 2D sheets (microstructures) simultaneously (in situ). This approach enables the creation of a layered structure that can be referred to as an ensemble of layers or, after several days of maturation, a direct or indirect joining of layers. Here, we have avoided providing a detailed methodological description of three-dimensional and 2D strategies, except for a few interesting examples that highlight the higher alignment of cells and emphasize rarely remembered facts associated with vascular, peripheral nerve, muscle, and intestine tissues. The effective directionality of cells in conjunction with geometric cues (in the range of micrometers) is well known to affect a variety of cell behaviors. The curvature of a cell's environment is one of the factors that influence the formation of patterns within tissues. The text will cover cell types containing some level of stemness, which will be followed by their consequences for tissue formation. Other important considerations pertain to cytoskeleton traction forces, cell organelle positioning, and cell migration. An overview of cell alignment along with several pivotal molecular and cellular level concepts, such as mechanotransduction, chirality, and curvature of structure effects on cell alignments will be presented. The mechanotransduction term will be used here in the context of the sensing capability that cells show as a result of force-induced changes either at the conformational or the organizational levels, a capability that allows us to modify cell fate by triggering downstream signaling pathways. A discussion of the cells' cytoskeleton and of the stress fibers involvement in altering the cell's circumferential constitution behavior (alignment) based on exposed scaffold radius will be provided. Curvatures with size similarities in the range of cell sizes cause the cell's behavior to act as if it was in an in vivo tissue environment. The revision of the literature, patents, and clinical trials performed for the present study shows that there is a clear need for translational research through the implementation of clinical trial platforms that address the tissue engineering possibilities raised in the current revision. This article is categorized under: Infectious Diseases > Biomedical Engineering Neurological Diseases > Biomedical Engineering Cardiovascular Diseases > Biomedical Engineering.

3D bio-printed hydrogel inks promoting lung cancer cell growth in a lab-on-chip culturing platform

The results of a lab-on-chip (LOC) platform fabrication equipped with a hydrogel matrix is reported. A 3D printing technique was used to provide a hybrid, "sandwiched" type structure, including two microfluidic substrates of different origins. Special attention was paid to achieving uniformly bio-printed microfluidic hydrogel layers of a unique composition. Six different hydrogel inks were proposed containing sodium alginate, agar, chitosan, gelatin, methylcellulose, deionized water, or 0.9% NaCl, varying in proportions. All of them exhibited appropriate mechanical properties showing, e.g., the value of elasticity modulus as similar to that of biological tissues, such as skin. Utilizing our biocompatible, entirely 3D bio-printed structure, for the first time, a multi-drug-resistant lung cancer cell line (H69AR) was cultured on-chip. Biological validation of the device was performed qualitatively and quantitatively utilizing LIVE/DEAD assays and Presto blue staining. Although all bio-inks exhibited acceptable cell viability, the best results were obtained for the hydrogel composition including 3% sodium alginate + 7% gelatin + 90% NaCl (0.9%), reaching approximately 127.2% after 24 h and 105.4% after 48 h compared to the control group (100%). Further research in this area will focus on the microfluidic culture of the chosen cancer cell line (H69AR) and the development of novel drug delivery strategies towards appropriate in vivo models for chemotherapy and polychemotherapy treatment.

Transformative Materials to Create 3D Functional Human Tissue Models In Vitro in a Reproducible Manner

Recreating human tissues and organs in the petri dish to establish models as tools in biomedical sciences has gained momentum. These models can provide insight into mechanisms of human physiology, disease onset, and progression, and improve drug target validation, as well as the development of new medical therapeutics. Transformative materials play an important role in this evolution, as they can be programmed to direct cell behavior and fate by controlling the activity of bioactive molecules and material properties. Using nature as an inspiration, scientists are creating materials that incorporate specific biological processes observed during human organogenesis and tissue regeneration. This article presents the reader with state-of-the-art developments in the field of in vitro tissue engineering and the challenges related to the design, production, and translation of these transformative materials. Advances regarding (stem) cell sources, expansion, and differentiation, and how novel responsive materials, automated and large-scale fabrication processes, culture conditions, in situ monitoring systems, and computer simulations are required to create functional human tissue models that are relevant and efficient for drug discovery, are described. This paper illustrates how these different technologies need to converge to generate in vitro life-like human tissue models that provide a platform to answer health-based scientific questions.

Human 3D brain organoids: steering the demolecularization of brain and neurological diseases

Understanding of human brain development, dysfunction and neurological diseases has remained limited and challenging due to inability to recapitulate human brain-specific features in animal models. Though the anatomy and physiology of the human brain has been understood in a remarkable way using post-mortem, pathological samples of human and animal models, however, modeling of human brain development and neurological diseases remains a challenge owing to distinct complexity of human brain. In this perspective, three-dimensional (3D) brain organoids have shown a beam of light. Tremendous growth in stem cell technologies has permitted the differentiation of pluripotent stem cells under 3D culture conditions into brain organoids, which recapitulate the unique features of human brain in many ways and also offer the detailed investigation of brain development, dysfunction and neurological diseases. Their translational value has also emerged and will benefit the society once the protocols for the upscaling of brain organoids are in place. Here, we summarize new advancements in methods for generation of more complex brain organoids including vascularized and mixed lineage tissue from PSCs. How synthetic biomaterials and microfluidic technology is boosting brain organoid development, has also been highlighted. We discuss the applications of brain organoids in studying preterm birth associated brain dysfunction; viral infections mediated neuroinflammation, neurodevelopmental and neurodegenerative diseases. We also highlight the translational value of brain organoids and current challenges that the field is experiencing.

Recent Advances on Cell Culture Platforms for In Vitro Drug Screening and Cell Therapies: From Conventional to Microfluidic Strategies

The clinical translations of drugs and nanomedicines depend on coherent pharmaceutical research based on biologically accurate screening approaches. Since establishing the 2D in vitro cell culture method, the scientific community has improved cell-based drug screening assays and models. Those advances result in more informative biochemical assays and the development of 3D multicellular models to describe the biological complexity better and enhance the simulation of the in vivo microenvironment. Despite the overall dominance of conventional 2D and 3D cell macroscopic culture methods, they present physicochemical and operational challenges that impair the scale-up of drug screening by not allowing a high parallelization, multidrug combination, and high-throughput screening. Their combination and complementarity with microfluidic platforms enable the development of microfluidics-based cell culture platforms with unequivocal advantages in drug screening and cell therapies. Thus, this review presents an updated and consolidated view of cell culture miniaturization's physical, chemical, and operational considerations in the pharmaceutical research scenario. It clarifies advances in the field using gradient-based microfluidics, droplet-based microfluidics, printed-based microfluidics, digital-based microfluidics, SlipChip, and paper-based microfluidics. Finally, it presents a comparative analysis of the performance of cell-based methods in life research and development to achieve increased precision in the drug screening process.

Microfluidics and Organoids, the Power Couple of Developmental Biology and Oncology Studies

Organoids are an advanced cell model that hold the key to unlocking a deeper understanding of in vivo cellular processes. This model can be used in understanding organ development, disease progression, and treatment efficacy. As the scientific world embraces the model, it must also establish the best practices for cultivating organoids and utilizing them to the greatest potential in assays. Microfluidic devices are emerging as a solution to overcome the challenges of organoids and adapt assays. Unfortunately, the various applications of organoids often depend on specific features in a device. In this review, we discuss the options and considerations for features and materials depending on the application and development of the organoid.

Unlocking Neural Function with 3D In Vitro Models: A Technical Review of Self-Assembled, Guided, and Bioprinted Brain Organoids and Their Applications in the Study of Neurodevelopmental and Neurodegenerative Disorders

Understanding the complexities of the human brain and its associated disorders poses a significant challenge in neuroscience. Traditional research methods have limitations in replicating its intricacies, necessitating the development of in vitro models that can simulate its structure and function. Three-dimensional in vitro models, including organoids, cerebral organoids, bioprinted brain models, and functionalized brain organoids, offer promising platforms for studying human brain development, physiology, and disease. These models accurately replicate key aspects of human brain anatomy, gene expression, and cellular behavior, enabling drug discovery and toxicology studies while providing insights into human-specific phenomena not easily studied in animal models. The use of human-induced pluripotent stem cells has revolutionized the generation of 3D brain structures, with various techniques developed to generate specific brain regions. These advancements facilitate the study of brain structure development and function, overcoming previous limitations due to the scarcity of human brain samples. This technical review provides an overview of current 3D in vitro models of the human cortex, their development, characterization, and limitations, and explores the state of the art and future directions in the field, with a specific focus on their applications in studying neurodevelopmental and neurodegenerative disorders.

The applications and techniques of organoids in head and neck cancer therapy

Head and neck cancer (HNC) is one of the most common cancers on the planet, with approximately 600,000 new cases diagnosed and 300,000 deaths every year. Research into the biological basis of HNC has advanced slowly over the past decades, which has made it difficult to develop new, more effective treatments. The patient-derived organoids (PDOs) are made from patient tumor cells, resembling the features of their tumors, which are high-fidelity models for studying cancer biology and designing new precision medicine therapies. In recent years, considerable effort has been focused on improving "organoids" technologies and identifying tumor-specific medicine using head and neck samples and a variety of organoids. A review of improved techniques and conclusions reported in publications describing the application of these techniques to HNC organoids is presented here. Additionally, we discuss the potential application of organoids in head and neck cancer research as well as the limitations associated with these models. As a result of the integration of organoid models into future precision medicine research and therapeutic profiling programs, the use of organoids will be extremely significant in the future.

Considerations for modelling diffuse high-grade gliomas and developing clinically relevant therapies

Diffuse high-grade gliomas contain some of the most dangerous human cancers that lack curative treatment options. The recent molecular stratification of gliomas by the World Health Organisation in 2021 is expected to improve outcomes for patients in neuro-oncology through the development of treatments targeted to specific tumour types. Despite this promise, research is hindered by the lack of preclinical modelling platforms capable of recapitulating the heterogeneity and cellular phenotypes of tumours residing in their native human brain microenvironment. The microenvironment provides cues to subsets of glioma cells that influence proliferation, survival, and gene expression, thus altering susceptibility to therapeutic intervention. As such, conventional in vitro cellular models poorly reflect the varied responses to chemotherapy and radiotherapy seen in these diverse cellular states that differ in transcriptional profile and differentiation status. In an effort to improve the relevance of traditional modelling platforms, recent attention has focused on human pluripotent stem cell-based and tissue engineering techniques, such as three-dimensional (3D) bioprinting and microfluidic devices. The proper application of these exciting new technologies with consideration of tumour heterogeneity and microenvironmental interactions holds potential to develop more applicable models and clinically relevant therapies. In doing so, we will have a better chance of translating preclinical research findings to patient populations, thereby addressing the current derisory oncology clinical trial success rate.

Novel model of cortical-meningeal organoid co-culture system improves human cortical brain organoid cytoarchitecture

Human cortical organoids (hCOs), derived from human induced pluripotent stem cells (iPSCs), provide a platform to interrogate mechanisms of human brain development and diseases in complex three- dimensional tissues. However, current hCO development methods lack important non-neural tissues, such as the surrounding meningeal layer, that have been shown to be essential for normal corticogenesis and brain development. Here, we first generated hCOs from a single rosette to create more homogenous organoids with consistent size around 250 µm by day 5. We then took advantage of a 3D co-culture system to encapsulate brain organoids with a thin layer of meningeal cells from the very early stages of cortical development. Immunostaining analysis was performed to display different cortical layer markers during different stages of development. Real-time monitoring of organoid development using IncuCyte displayed enhanced morphology and increased growth rate over time. We found that meningeal-encapsulated organoids illustrated better laminar organization by exhibiting higher expression of REELIN by Cajal-Retzius neurons. Presence of meningeal cells resulted in a greater expansion of TBR2 intermediate progenitor cells (IPCs), the deep cortical layer (CTIP2) and upper cortical layer (BRN2). Finally, meningeal-encapsulated organoids enhanced outer radial glial and astrocyte formation illustrated by stronger expression of HOPX and GFAP markers, respectively. This study presents a novel 3D co-culture platform to more closely mimic the in vivo cortical brain structure and enable us to better investigating mechanisms underlying the neurodevelopmental disorders during embryonic development.

Engineered Vasculature for Cancer Research and Regenerative Medicine

Engineered human tissues created by three-dimensional cell culture of human cells in a hydrogel are becoming emerging model systems for cancer drug discovery and regenerative medicine. Complex functional engineered tissues can also assist in the regeneration, repair, or replacement of human tissues. However, one of the main hurdles for tissue engineering, three-dimensional cell culture, and regenerative medicine is the capability of delivering nutrients and oxygen to cells through the vasculatures. Several studies have investigated different strategies to create a functional vascular system in engineered tissues and organ-on-a-chips. Engineered vasculatures have been used for the studies of angiogenesis, vasculogenesis, as well as drug and cell transports across the endothelium. Moreover, vascular engineering allows the creation of large functional vascular conduits for regenerative medicine purposes. However, there are still many challenges in the creation of vascularized tissue constructs and their biological applications. This review will summarize the latest efforts to create vasculatures and vascularized tissues for cancer research and regenerative medicine.

Emerging strategies of engineering retinal organoids and organoid-on-a-chip in modeling intraocular drug delivery: current progress and future perspectives

Retinal diseases are a rising concern as major causes of blindness in an aging society; therapeutic options are limited, and the precise pathogenesis of these diseases remains largely unknown. Intraocular drug delivery and nanomedicines offering targeted, sustained, and controllable delivery are the most challenging and popular topics in ocular drug development and toxicological evaluation. Retinal organoids (ROs) and organoid-on-a-chip (ROoC) are both emerging as promising in-vitro models to faithfully recapitulate human eyes for retinal research in the replacement of experimental animals and primary cells. In this study, we review the generation and application of ROs resembling the human retina in cell subtypes and laminated structures and introduce the emerging engineered ROoC as a technological opportunity to address critical issues. On-chip vascularization, perfusion, and close inter-tissue interactions recreate physiological environments in vitro, whilst integrating with biosensors facilitates real-time analysis and monitoring during organogenesis of the retina representing engineering efforts in ROoC models. We also emphasize that ROs and ROoCs hold the potential for applications in modeling intraocular drug delivery in vitro and developing next-generation retinal drug delivery strategies.

Transplantation Strategies to Enhance Maturity and Cellular Complexity in Brain Organoids

Human brain organoids are 3-dimensional cell aggregates that are generated from pluripotent stem cells and recapitulate features of the early developing human brain. Brain organoids mainly consist of cells from the neural lineage, such as neural progenitor cells, neurons, and astrocytes. However, current brain organoid systems lack functional vasculature as well as other non-neuronal cells that are indispensable for oxygen and nutrient supply to the organoids, causing cell stress and formation of a necrotic center. Attempts to utilize intracerebral transplantation approaches have demonstrated successful vascularization of brain organoids and robust neurodifferentiation. In this review, we summarize recent progress and discuss ethical considerations in the field of brain organoid transplantation.

Development of in vitro cardiovascular tissue models within capillary circuit microfluidic devices fabricated with 3D Stereolithography printing

Human cardiovascular tissue and diseases are difficult to study for novel drug discovery and fundamental cellular/molecular processes due to limited availability of physiologically-relevant models in vitro.[1-3] Animal models may resemble human heart structure, however there are significant differences from human cardiovascular physiology including biochemical signaling, and gene expression.[4-6] In vitro microfluidic tissue models provide a less expensive, more controlled, and reproducible platform for better quantification of isolated cellular processes in response to biochemical or biophysical stimulus.[6-12] The capillary driven-flow microfluidic device in this study was manufactured with a 3D stereolithography (SLA) printed mold and is a closed circuit system operating on principles of capillary action allowing continuous fluid movement without external power supply. Human umbilical vein endothelial cells (HUVECs) and human cardiomyocytes (AC16) were encapsulated into a fibrin hydrogel to form vascular (VTM) and cardiac (CTM) tissue models respectively. To determine response to biophysical stimulus, the 3D cardiovascular tissue was directly loaded into the device tissue culture chambers that either had no microposts (DWoP) or microposts (DWPG) for 1, 3 and 5 days. The tissues were analyzed with fluorescent microscopy for morphological differences, average tube length, and cell orientation between tissues cultured in both conditions. In DWPG VTMs displayed capillary-like tube formation with visible cell alignment and orientation, while AC16s continued to elongate around microposts by day 5. VTM and CTM models in devices with posts (DWPG) displayed cell alignment and orientation after 5 days, indicated the microposts induced biophysical cues to guide cell structure and specific organization.

Advanced Nanomaterials-Based Electrochemical Biosensors for Catecholamines Detection: Challenges and Trends

Catecholamines, including dopamine, epinephrine, and norepinephrine, are considered one of the most crucial subgroups of neurotransmitters in the central nervous system (CNS), in which they act at the brain's highest levels of mental function and play key roles in neurological disorders. Accordingly, the analysis of such catecholamines in biological samples has shown a great interest in clinical and pharmaceutical importance toward the early diagnosis of neurological diseases such as Epilepsy, Parkinson, and Alzheimer diseases. As promising routes for the real-time monitoring of catecholamine neurotransmitters, optical and electrochemical biosensors have been widely adopted and perceived as a dramatically accelerating development in the last decade. Therefore, this review aims to provide a comprehensive overview on the recent advances and main challenges in catecholamines biosensors. Particular emphasis is given to electrochemical biosensors, reviewing their sensing mechanism and the unique characteristics brought by the emergence of nanotechnology. Based on specific biosensors' performance metrics, multiple perspectives on the therapeutic use of nanomaterial for catecholamines analysis and future development trends are also summarized.

Microfluidics for diagnosis and treatment of cardiovascular disease

Cardiovascular disease (CVD), a type of circulatory system disease related to the lesions of the cardiovascular system, has become one of the main diseases that endanger human health. Currently, the clinical diagnosis of most CVDs relies on a combination of imaging technology and blood biochemical test. However, the existing technologies for diagnosis of CVDs still have limitations in terms of specificity, detection range, and cost. In order to break through the current bottleneck, microfluidic with the advantages of low cost, simple instruments and easy integration, has been developed to play an important role in the early prevention, diagnosis and treatment of CVDs. Here, we have reviewed the recent various applications of microfluidic in the clinical diagnosis and treatment of CVDs, including microfluidic devices for detecting CVD markers, the cardiovascular models based on microfluidic, and the microfluidic used for CVDs drug screening and delivery. In addition, we have briefly looked forward to the prospects and challenges of microfluidics in diagnosis and treatment of CVDs.

Recent Advances in Brain Organoid Technology for Human Brain Research

Brain organoids are self-assembled three-dimensional aggregates with brain-like cell types and structures and have emerged as new model systems that can be used to investigate human neurodevelopment and neurological disorders. However, brain organoids are not as mature and functional as real human brains due to limitations of the culture system with insufficient developmental patterning signals and a lack of components that are important for brain development and function, such as the non-neural population and vasculature. In addition, establishing the desired brain-like environment and monitoring the complex neural networks and physiological functions of the brain organoids remain challenging. The current protocols to generate brain organoids also have problems with heterogeneity and batch variation due to spontaneous self-organization of brain organoids into complex architectures of the brain. To address these limitations of current brain organoid technologies, various engineering platforms, such as extracellular matrices, fluidic devices, three-dimensional bioprinting, bioreactors, polymeric scaffolds, microelectrodes, and biochemical sensors, have been employed to improve neuronal development and maturation, reduce structural heterogeneity, and facilitate functional analysis and monitoring. In this review, we provide an overview of the latest engineering techniques that overcome these limitations in the production and application of brain organoids.