Engineering organoids

Emerging biotechnologies for engineering liver organoids

The engineering construction of the liver has attracted enormous attention. Organoids, as emerging miniature three-dimensional cultivation units, hold significant potential in the biomimetic simulation of liver structure and function. Despite notable successes, organoids still face limitations such as high variability and low maturity. To overcome these challenges, engineering strategies have been established to maintain organoid stability and enhance their efficacy, laying the groundwork for the development of advanced liver organoids. The present review comprehensively summarizes the construction of engineered liver organoids and their prospective applications in biomedicine. Initially, we briefly present the latest research progress on matrix materials that maintain the three-dimensional morphology of organoids. Next, we discuss the manipulative role of engineering technologies in organoid assembly. Additionally, we outline the impact of gene-level regulation on organoid growth and development. Further, we introduce the applications of liver organoids in disease modeling, drug screening and regenerative medicine. Lastly, we overview the current obstacles and forward-looking perspectives on the future of engineered liver organoids. We anticipate that ongoing innovations in engineered liver organoids will lead to significant advancements in medical applications.

Modeling vascular dynamics at the initial stage of endochondral ossification on a microfluidic chip using a human embryonic-stem-cell-derived organoid

Vascular interactions play a crucial role in embryogenesis, including skeletal development. During endochondral ossification, vascular networks are formed as mesenchymal cells condense and later invade skeletal elements to form the bone marrow. We and other groups developed a model of endochondral ossification by implanting human embryonic stem cell (hESC)-derived sclerotome into immunodeficient mice. However, in vitro models of endochondral ossification, particularly vascular interaction with mesenchymal cells at its initial stage, are yet to be established. Therefore, we developed a method to model the initial stage of endochondral ossification using a microfluidic chip-based platform, with a particular focus on the vascular interaction. On the chip, we found that the fibrin gel helped align mCherry-expressing human umbilical vein endothelial cells (HUVECs) better than the collagen-I gel, suggesting that the fibrin gel is more suitable for the formation of a vascular-like network. The perfusability of the vascular-like networks was partially confirmed using fluorescein isothiocyanate (FITC)-dextran and fluorescent microbeads. We then mixed hESC-derived sclerotome with enhanced green fluorescent protein (EGFP)-expressing HUVECs and applied this mixture on the chip. We named this mixture of cells SH organoids. The SH organoids showed superior abilities to maintain the vascular-like network, which was formed by the mCherry-expressing HUVECs, compared with the sclerotome spheroids on the chip. The EGFP-expressing HUVECs migrated from the SH organoid, formed a vascular-like networks, and partially interacted with the mCherry-expressing vascular-like networks on the chip. Histological analysis showed that SRY-box transcription factor 9 (SOX9) and type I collagen were expressed mutually exclusively in the condensed mesenchymal cells and perichondrial-like cells, respectively. This study demonstrates that our SH organoid-on-a-chip method reproduces vascular networks that are formed at the initial stage of endochondral ossification. This model may provide insights into human endochondral ossification and has potential applications in bone disease modeling and drug screening.

CRISPR-Cas9 mediated knockout of NDUFS4 in human iPSCs: A model for mitochondrial complex I deficiency

Mitochondrial diseases, often caused by defects in complex I (CI) of the oxidative phosphorylation system, currently lack curative treatments. Human-relevant, high-throughput drug screening platforms are crucial for the discovery of effective therapeutics, with induced pluripotent stem cells (iPSCs) emerging as a valuable technology for this purpose. Here, we present a novel iPSC model of NDUFS4-related CI deficiency that displays a strong metabolic phenotype in the pluripotent state. Human iPSCs were edited using CRISPR-Cas9 to target the NDUFS4 gene, generating isogenic NDUFS4 knockout (KO) cell lines. Sanger sequencing detected heterozygous biallelic deletions, whereas no indel mutations were found in isogenic control cells. Western blotting confirmed the absence of NDUFS4 protein in KO iPSCs and CI enzyme kinetics showed a ~56 % reduction in activity compared to isogenic controls. Comprehensive metabolomic profiling revealed a distinct metabolic phenotype in NDUFS4 KO iPSCs, predominantly associated with an elevated NADH/NAD+ ratio, consistent with alterations observed in other models of mitochondrial dysfunction. Additionally, β-lapachone, a recognized NAD+ modulator, alleviated reductive stress in KO iPSCs by modifying the redox state in both the cytosol and mitochondria. Although undifferentiated iPSCs cannot fully replicate the complex cellular dynamics of the disease seen in vivo, these findings highlight the utility of iPSCs in providing a relevant metabolic milieu that can facilitate early-stage, high-throughput exploration of therapeutic strategies for mitochondrial dysfunction.

A tunable human intestinal organoid system achieves controlled balance between self-renewal and differentiation

A balance between stem cell self-renewal and differentiation is required to maintain concurrent proliferation and cellular diversification in organoids; however, this has proven difficult in homogeneous cultures devoid of in vivo spatial niche gradients for adult stem cell-derived organoids. In this study, we leverage a combination of small molecule pathway modulators to enhance the stemness of organoid stem cells, thereby amplifying their differentiation potential and subsequently increasing cellular diversity within human intestinal organoids without the need for artificial spatial or temporal signaling gradients. Moreover, we demonstrate that this balance between self-renewal and differentiation can be effectively and reversibly shifted from secretory cell differentiation to the enterocyte lineage with enhanced proliferation using BET inhibitors, or unidirectional differentiation towards specific intestinal cell types by manipulating in vivo niche signals such as Wnt, Notch, and BMP. As a result, we establish an optimized human small intestinal organoid (hSIO) system characterized by high proliferative capacity and increased cell diversity under a single culture condition. This optimization facilitates the scalability and utility of the organoid system in high-throughput applications.

Engineering organoids-on-chips for drug testing and evaluation

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

Engineered nascent living human tissues with unit programmability

Leveraging human cells as materials precursors is a promising approach for fabricating living materials with tissue-like functionalities and cellular programmability. Here we describe a set of cellular units with metabolically engineered glycoproteins that allow cells to tether together to function as macrotissue building blocks and bioeffectors. The generated human living materials, termed as Cellgels, can be rapidly assembled in a wide variety of programmable three-dimensional configurations with physiologically relevant cell densities (up to 108 cells per cm3), tunable mechanical properties and handleability. Cellgels inherit the ability of living cells to sense and respond to their environment, showing autonomous tissue-integrative behaviour, mechanical maturation, biological self-healing, biospecific adhesion and capacity to promote wound healing. These living features also enable the modular bottom-up assembly of multiscale constructs, which are reminiscent of human tissue interfaces with heterogeneous composition. This technology can potentially be extended to any human cell type, unlocking the possibility for fabricating living materials that harness the intrinsic biofunctionalities of biological systems.

Intestinal organoids: The path towards clinical application

Organoids have revolutionized the whole field of biology with their ability to model complex three-dimensional human organs in vitro. Intestinal organoids were especially consequential as the first successful long-term culture of intestinal stem cells, which raised hopes for translational medical applications. Despite significant contributions to basic research, challenges remain to develop intestinal organoids into clinical tools for diagnosis, prognosis, and therapy. In this review, we outline the current state of translational research involving adult stem cell and pluripotent stem cell derived intestinal organoids, highlighting the advances and limitations in disease modeling, drug-screening, personalized medicine, and stem cell therapy. Preclinical studies have demonstrated a remarkable functional recapitulation of infectious and genetic diseases, and there is mounting evidence for the reliability of intestinal organoids as a patient-specific avatar. Breakthroughs now allow the generation of structurally and cellularly complex intestinal models to better capture a wider range of intestinal pathophysiology. As the field develops and evolves, there is a need for standardized frameworks for generation, culture, storage, and analysis of intestinal organoids to ensure reproducibility, comparability, and interpretability of these preclinical and clinical studies to ultimately enable clinical translation.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Dynamic Diselenide Hydrogels for Controlled Tumor Organoid Culture and Dendritic Cell Vaccination

Dynamic hydrogels are emerging as advanced materials for engineering tissue-like environments that mimic cellular microenvironments. We introduce a diselenide-cross-linked hydrogel system with light-responsive properties, designed for precise control of tumor organoid growth and light-initiated radical inactivation, particularly for dendritic cell (DC) vaccines. Diselenide exchange enables stress relaxation and hydrogel remodeling, while recombination and quenching of seleno radicals (Se•) reduce cross-linking density, leading to controlled degradation. We demonstrate a 2D to 3D growth strategy, where tumor cells inoculate on the hydrogel surface, expand, and gradually form spherical organoids within the 3D hydrogel. These tumor organoids show significantly higher drug resistance compared to 2D-cultured cells. High-density light irradiation enhances diselenide exchange, inducing hydrogel degradation, tumor cell death, and release of functional antigens. This system serves as a dynamic platform for tumor organoid culture and antigen release, offering significantly advanced approaches for in vitro tumor modeling and immunological research. Our findings position diselenide-cross-linked hydrogels as versatile materials for precision cellular engineering, with broad applications in cancer research and beyond.

Proximity adjusted centroid mapping for accurate detection of nuclei in dense 3D cell systems

In the past decade, deep learning algorithms have surpassed the performance of many conventional image segmentation pipelines. Powerful models are now available for segmenting cells and nuclei in diverse 2D image types, but segmentation in 3D cell systems remains challenging due to the high cell density, the heterogenous resolution and contrast across the image volume, and the difficulty in generating reliable and sufficient ground truth data for model training. Reasoning that most image processing applications rely on nuclear segmentation but do not necessarily require an accurate delineation of their shapes, we implemented Proximity Adjusted Centroid MAPping (PAC-MAP), a 3D U-net based method that predicts the position of nuclear centroids and their proximity to other nuclei. We show that our model outperforms existing methods, predominantly by boosting recall, especially in conditions of high cell density. When trained from scratch with limited expert annotations (30 images), PAC-MAP attained an average F1 score of 0.793 for nuclei centroid prediction in dense spheroids. When pretraining using weakly supervised bulk data (>2300 images) followed by finetuning with the available expert annotations, the average F1 score could be significantly improved to 0.816. We demonstrate the utility of our method for quantifying the absolute cell content of spheroids and comprehensively mapping the infiltration pattern of patient-derived glioblastoma cells in cerebral organoids.

An integrated microfluidic device for sorting of tumor organoids using image recognition

Tumor organoids present a challenge in drug screening due to their considerable heterogeneity in morphology and size. To address this issue, we proposed a portable microfluidic device that employs image processing algorithms for specific target organoid recognition and microvalve-controlled deflection for sorting and collection. This morphology-activated organoid sorting system offers numerous advantages, such as automated classification, portability, low cost, label-free sample preparation, and gentle handling of organoids. We conducted classification experiments using polystyrene beads, F9 tumoroids and patient-derived tumor organoids, achieving organoid separation efficiency exceeding 88%, purity surpassing 91%, viability exceeding 97% and classification throughput of 800 per hour, thereby meeting the demands of clinical organoid medicine.

A High-Throughput and Logarithm-Serial-Dilution Microfluidic Chip for Combinational Drug Screening on Tumor Organoids

Tumor organoids are biological models for studying precision medicine. Microfluidic technology offers significant benefits for high throughput drug screening using tumor organoids. However, the range of concentrations achievable with traditional linear gradient generators in microfluidics is restricted, generating logarithmic drug concentration gradients by adjusting the channel ratio in the chip is confined to single-drug dilution chips, significantly restricting the application of microfluidics in drug screening. Here, we presented a microfluidic chip featuring continuous dilution capabilities, which generates logarithmic stepwise drug concentration gradients. We have devised a "mathematical-circuit-chip" model for designing such chips, and based on this model, we have developed and fabricated a device capable of providing 36 distinct drug concentration conditions for two types of drugs. The chip is composed of two structurally identical yet orthogonally arranged layers, each containing a dilution network capable of forming a 5-fold gradient and a tumor organoid culture module. Drug and culture medium delivery to the open culture chamber array is driven by syringe pumps. We have conducted drug screening experiments on patient-derived tumor organoids. This device facilitates high-throughput drug screening for patient-derived organoids, representing a significant stride toward the realization of precision medicine.

Development of in vitro hair pigmentation model using hair follicle organoids

Hair color is formed through a series of processes such as melanin synthesis and storage in melanosomes, transfer from melanocytes, and reception by hair matrix cells in the hair bulb. Because gray hair is caused by the deterioration of a single or multiple of these processes, understanding the mechanisms responsible for these processes is crucial for developing therapeutic strategies. Recently, a robust approach for preparing hair follicle organoids (HFOs) was reported, in which hair follicle morphogenesis, including hair shaft elongation, was tracked in vitro. Here, we investigated whether HFOs could be used to assess genes involved in hair pigmentation. HFOs generated hair follicles and pigmented shafts during the in vitro culturing process. The knockdown of genes associated with melanosome production (Bcl2 and Mitf) and transport (MyoX, PAR2, and Rab11b) significantly increased the number of gray hairs in HFOs. This organoid model may be a promising platform for better understanding hair pigmentation and screening drugs for gray hair.

Generation and maintenance of kidney and kidney cancer organoids from patient-derived material for drug development and precision oncology

Despite significant advancements in targeted- and immunotherapies, millions of patients with cancer still succumb to the disease each year. In renal cell carcinoma, up to 25% of metastatic patients do not respond to first-line therapies. This reality underscores the urgent need for innovative or repurposed therapies to effectively treat these patients. Patient-derived organoids represent a promising model for evaluating treatment efficacy and toxicity, offering a potential breakthrough in personalized medicine. However, utilizing organoid models for drug screening presents several challenges. Our protocol aims to address these obstacles by outlining a practical approach to successfully isolate and cultivate patient-derived renal cell carcinoma and kidney organoids for treatment screening purposes.

Nascent matrix deposition supports alveolar organoid formation from aggregates in synthetic hydrogels

Human induced pluripotent stem cell (iPSC)-derived alveolar organoids have emerged as a system to model the alveolar epithelium in homeostasis and disease. However, alveolar organoids are typically grown in Matrigel, a mouse sarcoma-derived basement membrane matrix that offers poor control over matrix properties, prompting the development of synthetic hydrogels as a Matrigel alternative. Here, we develop a two-step culture method that involves pre-aggregation of organoids in hydrogel-based microwells followed by embedding in a synthetic hydrogel that supports alveolar organoid growth, while also offering considerable control over organoid and hydrogel properties. We find that the aggregated organoids secrete their own nascent extracellular matrix (ECM) both in the microwells and upon embedding in synthetic hydrogels, which supports their growth. Thus, the synthetic hydrogels described here allow us to de-couple exogenous and nascent ECM to interrogate the role of ECM in organoid formation.

Engineering the 3D structure of organoids

Organoids form through the sel f-organizing capabilities of stem cells to produce a variety of differentiated cell and tissue types. Most organoid models, however, are limited in terms of the structure and function of the tissues that form, in part because it is difficult to regulate the cell type, arrangement, and cell-cell/cell-matrix interactions within these systems. In this article, we will discuss the engineering approaches to generate more complex organoids with improved function and translational relevance, as well as their advantages and disadvantages. Additionally, we will explore how biofabrication strategies can manipulate the cell composition, 3D organization, and scale-up of organoids, thus improving their utility for disease modeling, drug screening, and regenerative medicine applications.

Effects of long-term treatment with low concentration butylparaben on prostate organoids

Endocrine-disrupting compounds (EDCs), such as butylparaben (BP), which are used as preservatives in food and cosmetics, have been shown to negatively affect male reproductive health. Organs under the control of hormones such as androgens and estrogens, such as the prostate, are vulnerable to EDC stimulation. It is well known that BP can cause hormonal imbalances in the prostate and lead to various prostate diseases. However, studies on the long-term exposure of low-dose BP, which is common in daily life, are lacking, and existing studies rely heavily on in vitro tests to assess the risk of EDCs. Therefore, in this study, we investigated the long-term exposure effects of low-dose BP using a prostate organoid model that more closely resembles the target organ. When prostate organoids were treated with BP for a long period, hormonal imbalance was confirmed through differences in the expression of hormone receptors. In addition, reactive oxygen species (ROS) production was confirmed by DCFDA staining, and the protective effect of prostate organoids against stimulation was confirmed by increased protein levels of antioxidant factors. Through transcriptome analysis, we confirmed the occurrence of reproductive toxicity caused by BP. The long-term treatment of prostate organoids with BP causes hormonal imbalance and increased ROS exhibits reproductive toxicity and exerts a protective mechanism against BP through the expression of antioxidant factors. Our results highlight the potential of prostrate organoids as an alternative to animal experimental model and the need for further research on the effects of low EDC concentrations on male reproductive function.

3D-Bioprinting for Precision Microtissue Engineering: Advances, Applications, and Prospects

Microtissues, engineered to emulate the complexity of human organs, are revolutionizing the fields of regenerative medicine, disease modelling, and drug screening. Despite the promise of traditional microtissue engineering, it has yet to achieve the precision required to fully replicate organ-like structures. Enter 3D bioprinting, a transformative approach that offers unparalleled control over the microtissue's spatial arrangement and mechanical properties. This cutting-edge technology enables the detailed layering of bioinks, crafting microtissues with tissue-like 3D structures. It allows for the direct construction of organoids and the fine-tuning of the mechanical forces vital for tissue maturation. Moreover, 3D-printed devices provide microtissues with the necessary guidance and microenvironments, facilitating sophisticated tissue interactions. The applications of 3D-printed microtissues are expanding rapidly, with successful demonstrations of their functionality in vitro and in vivo. This technology excels at replicating the intricate processes of tissue development, offering a more ethical and controlled alternative to traditional animal models. By simulating in vivo conditions, 3D-printed microtissues are emerging as powerful tools for personalized drug screening, offering new avenues for pharmaceutical development and precision medicine.

Simulating irregular symmetry breaking in gut cross sections using a novel energy-optimization approach in growth-elasticity

Growth-elasticity (also known as morphoelasticity) is a powerful model framework for understanding complex shape development in soft biological tissues. At each instant, by mapping how continuum building blocks have grown geometrically and how they respond elastically to the push-and-pull from their neighbors, the shape of the growing structure is determined from a state of mechanical equilibrium. As mechanical loads continue to be added to the system through growth, many interesting shapes, such as smooth wavy wrinkles, sharp creases, and deep folds, can form on the tissue surface from a relatively flatter geometry. Previous numerical simulations of growth-elasticity have reproduced many interesting shapes resembling those observed in reality, such as the foldings on mammalian brains and guts. In the case of mammalian guts, it has been shown that wavy wrinkles, deep folds, and sharp creases on the interior organ surface can be simulated even under a simple assumption of isotropic uniform growth in the interior layer of the organ. Interestingly, the simulated patterns are all regular along the tube's circumference, with either all smooth or all sharp indentations, whereas some undulation patterns in reality exhibit irregular patterns and a mixture of sharp creases and smooth indentations along the circumference. Can we simulate irregular indentation patterns without further complicating the growth patterning? In this paper, we have discovered abundant shape solutions with irregular indentation patterns by developing a Rayleigh-Ritz finite-element method (FEM). In contrast to previous Galerkin FEMs, which solve the weak formulation of the mechanical-equilibrium equations, the new method formulates an optimization problem for the discretized energy functional, whose critical points are equivalent to solutions obtained by solving the mechanical-equilibrium equations. This new method is more robust than previous methods. Specifically, it does not require the initial guess to be near a solution to achieve convergence, and it allows control over the direction of numerical iterates across the energy landscape. This approach enables the capture of more solutions that cannot be easily reached by previous methods. In addition to the previously found regular smooth and non-smooth configurations, we have identified a new transitional irregular smooth shape, new shapes with a mixture of smooth and non-smooth surface indentations, and a variety of irregular patterns with different numbers of creases. Our numerical results demonstrate that growth-elasticity modeling can match more shape patterns observed in reality than previously thought.

Patterned gastrointestinal monolayers with bilateral access as observable models of parasite gut infection

Organoids for modelling the physiology and pathology of gastrointestinal tissues are constrained by a poorly accessible lumen. Here we report the development and applicability of bilaterally accessible organoid-derived patterned epithelial monolayers that allow the independent manipulation of their apical and basal sides. We constructed gastric, small-intestinal, caecal and colonic epithelial models that faithfully reproduced their respective tissue geometries and that exhibited stem cell regionalization and transcriptional resemblance to in vivo epithelia. The models' enhanced observability allowed single-cell tracking and studies of the motility of cells in immersion culture and at the air-liquid interface. Models mimicking infection of the caecal epithelium by the parasite Trichuris muris allowed us to live image syncytial tunnel formation. The enhanced observability of bilaterally accessible organoid-derived gastrointestinal tissue will facilitate the study of the dynamics of epithelial cells and their interactions with pathogens.

Dynamic duo: Cell-extracellular matrix interactions in hair follicle development and regeneration

Ectodermal organs, such as hair follicles, originate from simple epithelial and mesenchymal sheets through a complex developmental process driven by interactions between these cell types. This process involves dermal condensation, placode formation, bud morphogenesis, and organogenesis, and all of these processes require intricate interactions among various tissues. Recent research has emphasized the crucial role of reciprocal and dynamic interactions between cells and the extracellular matrix (ECM), referred to as the "dynamic duo", in the development of ectodermal organs. These interactions provide spatially and temporally changing biophysical and biochemical cues within tissues. Using the hair follicle as an example, this review highlights two types of cell-ECM adhesion units-focal adhesion-type and hemidesmosome-type adhesion units-that facilitate communication between epithelial and mesenchymal cells. This review further explores how these adhesion units, along with other cell-ECM interactions, evolve during hair follicle development and regeneration, underscoring their importance in guiding both developmental and regenerative processes.

DNA microbeads for spatio-temporally controlled morphogen release within organoids

Organoids are transformative in vitro model systems that mimic features of the corresponding tissue in vivo. However, across tissue types and species, organoids still often fail to reach full maturity and function because biochemical cues cannot be provided from within the organoid to guide their development. Here we introduce nanoengineered DNA microbeads with tissue mimetic tunable stiffness for implementing spatio-temporally controlled morphogen gradients inside of organoids at any point in their development. Using medaka retinal organoids and early embryos, we show that DNA microbeads can be integrated into embryos and organoids by microinjection and erased in a non-invasive manner with light. Coupling a recombinant surrogate Wnt to the DNA microbeads, we demonstrate the spatio-temporally controlled morphogen release from the microinjection site, which leads to morphogen gradients resulting in the formation of retinal pigmented epithelium while maintaining neuroretinal cell types. Thus, we bioengineered retinal organoids to more closely mirror the cell type diversity of in vivo retinae. Owing to the facile, one-pot fabrication process, the DNA microbead technology can be adapted to other organoid systems for improved tissue mimicry.

Approaches for studying neuroimmune interactions in Alzheimer's disease

Peripheral immune cells play an important role in the pathology of Alzheimer's disease (AD), impacting processes such as amyloid and tau protein aggregation, glial activation, neuronal integrity, and cognitive decline. Here, we examine cutting-edge strategies - encompassing animal and cellular models - used to investigate the roles of peripheral immune cells in AD. Approaches such as antibody-mediated depletion, genetic ablation, and bone marrow chimeras in mouse models have been instrumental in uncovering T, B, and innate immune cell disease-modifying functions. However, challenges such as specificity, off-target effects, and differences between human and mouse immune systems underscore the need for more human-relevant models. Emerging multicellular models replicating critical aspects of human brain tissue and neuroimmune interactions increasingly offer fresh insights into the role of immune cells in AD pathogenesis. Refining these methodologies can deepen our understanding of immune cell contributions to AD and support the development of novel immune-related therapeutic interventions.

Emerging strategies to investigate the biology of early cancer

Early detection and intervention of cancer or precancerous lesions hold great promise to improve patient survival. However, the processes of cancer initiation and the normal-precancer-cancer progression within a non-cancerous tissue context remain poorly understood. This is, in part, due to the scarcity of early-stage clinical samples or suitable models to study early cancer. In this Review, we introduce clinical samples and model systems, such as autochthonous mice and organoid-derived or stem cell-derived models that allow longitudinal analysis of early cancer development. We also present the emerging techniques and computational tools that enhance our understanding of cancer initiation and early progression, including direct imaging, lineage tracing, single-cell and spatial multi-omics, and artificial intelligence models. Together, these models and techniques facilitate a more comprehensive understanding of the poorly characterized early malignant transformation cascade, holding great potential to unveil key drivers and early biomarkers for cancer development. Finally, we discuss how these new insights can potentially be translated into mechanism-based strategies for early cancer detection and prevention.

Optimization of Vascularized Intestinal Organoid Model

Vasculature is crucial for maintaining organ homeostasis and metabolism. Although 3D organoids can mimic organ structures and patterns, they still lack vascular systems, limiting the recapitulation of physiological complexities. Although vascularization of organoids has been demonstrated by mixing Matrigel in fibrin, how the mixed gel niche affects endothelial cells (ECs) and organoids remains unclear. Existing protocols rely on fibroblasts to promote vascular network formation. This study explores how varying the ratio of Matrigel in fibrin-Matrigel co-gel affects vascular network formation and intestinal organoid growth. A fine-tuned hydrogel is developed by adding aprotinin and 15% Matrigel in fibrin. Medium for co-culturing ECs and organoids is modified with basic fibroblast growth factor (bFGF) and heparin. In combination with fine-tuned hydrogel and modified medium, vascular network formation and organoid vascularization are successfully generated in the absence of fibroblast. Furthermore, structural cues and pore architectures are critical for angiogenesis and vascularization. By incorporating engineered thick collagen fiber bundles into the system, vascular network formation is guided by bundle architectures, enhancing interactions between vascular networks and organoids. The results demonstrate an optimized system that advances tissue and organoid vascularization by combining fiber bundles with fine-tuned hydrogel and modified medium.

The organoid modeling approach to understanding the mechanisms underlying neurodegeneration: A comprehensive review

Neurodegenerative diseases (NDs) are severe disorders of the nervous system, and their causes are still not completely understood. Modeling the complex pathological mechanisms underlying NDs has long posed a significant challenge, as traditional in vitro and animal models often fail to accurately recapitulate the disease phenotypes observed in humans; however, the rise of organoid technology has opened new approaches for developing innovative disease models that can better capture the nuances of the human nervous system. Organoid platforms hold promise for contributing to the design of future clinical trials and advancing our understanding of these devastating neurological conditions and accelerate the discovery of effective, personalized therapies. This comprehensive review discusses the recent advancements in neural organoid technology and explores the potential of patient-derived organoids for modeling NDs conditions and presents findings related to the mechanisms of their development or progress.

Engineering immune organoids to regenerate host immune system

Recent advances in immunotherapy have underscored the potential of harnessing the immune system to treat disorders associated with immune dysregulation, such as primary and secondary immunodeficiencies, cancer, transplantation rejection, and aging. Owing to the cellular and structural complexity and the dynamic nature of immune responses, engineering immune organoids that replicate the function and key features of their corresponding immune organs continues to be a formidable challenge. In this overview, we will discuss the recent progress in bioengineering organoids of key primary and secondary immune organs and tissues, focusing particularly on their contributions to the host's immune system in animal models and highlighting their potential roles in regenerative medicine.

Development of Novel 3D Spheroids for Discrete Subaortic Stenosis

In this study, we propose a new method for bioprinting 3D Spheroids to study complex congenital heart disease known as discrete subaortic stenosis (DSS). The bioprinter allows us to manipulate the extrusion pressure to change the size of the spheroids, and the alginate porosity increases in size over time. The spheroids are composed of human umbilical vein endothelial cells (HUVECs), and we demonstrated that pressure and time during the bioprinting process can modulate the diameter of the spheroids. In addition, we used Pluronic acid to maintain the shape and position of the spheroids. Characterization of HUVECs in the spheroids confirmed their uniform distribution and we demonstrated cell viability as a function of time. Compared to traditional 2D cell cultures, the 3D spheroids model provides more relevant physiological environments, making it valuable for drug testing and therapeutic applications.

Targeting the Complexity of In Vitro Skin Models: A Review of Cutting-Edge Developments

Skin in vitro models offer much promise for research, testing drugs, cosmetics, and medical devices, reducing animal testing and extensive clinical trials. There are several in vitro approaches to mimicking human skin behavior, ranging from simple cell monolayer to complex organotypic and bioengineered 3-dimensional models. Some have been approved for preclinical studies in cosmetics, pharmaceuticals, and chemicals. However, development of physiologically reliable in vitro human skin models remains in its infancy. This review reports on advances in in vitro complex skin models to study skin homeostasis, aging, and skin disease.

Bioengineered human arterial equivalent and its applications from vascular graft to in vitro disease modeling

Arterial disorders such as atherosclerosis, thrombosis, and aneurysm pose significant health risks, necessitating advanced interventions. Despite progress in artificial blood vessels and animal models aimed at understanding pathogenesis and developing therapies, limitations in graft functionality and species discrepancies restrict their clinical and research utility. Addressing these issues, bioengineered arterial equivalents (AEs) with enhanced vascular functions have been developed, incorporating innovative technologies that improve clinical outcomes and enhance disease progression modeling. This review offers a comprehensive overview of recent advancements in bioengineered AEs, systematically summarizing the bioengineered technologies used to construct these AEs, and discussing their implications for clinical application and pathogenesis understanding. Highlighting current breakthroughs and future perspectives, this review aims to inform and inspire ongoing research in the field, potentially transforming vascular medicine and offering new avenues for preclinical and clinical advances.

Validation of non-destructive morphology-based selection of cerebral cortical organoids by paired morphological and single-cell RNA-seq analyses

Organoids, self-organized cell aggregates, contribute significantly to developing disease models and cell-based therapies. Organoid-to-organoid variations, however, are inevitable despite the use of the latest differentiation protocols. Here, we focused on the morphology of organoids formed in a cerebral organoid differentiation culture and assessed their cellular compositions by single-cell RNA sequencing analysis. The data revealed that organoids primarily composed of non-neuronal cells, such as those from the neural crest and choroid plexus, showed unique morphological features. Moreover, we demonstrate that non-destructive morphological analysis can accurately distinguish organoids composed of cerebral cortical tissues from other cerebral tissues, thus enhancing experimental accuracy and reliability to ensure the safety of cell-based therapies.

Design and Applications of Supramolecular Peptide Hydrogel as Artificial Extracellular Matrix

Supramolecular peptide hydrogels (SPHs) consist of peptides containing hydrogelators and functional epitopes, which can first self-assemble into nanofibers and then physically entangle together to form dynamic three-dimensional networks. Their porous structures, excellent bioactivity, and high dynamicity, similar to an extracellular matrix (ECM), have great potential in artificial ECM. The properties of the hydrogel are largely dependent on peptides. The noncovalent interactions among hydrogelators drive the formation of assemblies and further transition into hydrogels, while bioactive epitopes modulate cell-cell and cell-ECM interactions. Therefore, SPHs can support cell growth, making them ideal biomaterials for ECM mimics. This Review outlines the classical molecular design of SPHs from hydrogelators to functional epitopes and summarizes the recent advancements of SPHs as artificial ECMs in nervous system repair, wound healing, bone and cartilage regeneration, and organoid culture. This emerging SPH platform could provide an alternative strategy for developing more effective biomaterials for tissue engineering.

Advancing cancer research through organoid technology

The complexity of tumors and the challenges associated with treatment often stem from the limitations of existing models in accurately replicating authentic tumors. Recently, organoid technology has emerged as an innovative platform for tumor research. This bioengineering approach enables researchers to simulate, in vitro, the interactions between tumors and their microenvironment, thereby enhancing the intricate interplay between tumor cells and their surroundings. Organoids also integrate multidimensional data, providing a novel paradigm for understanding tumor development and progression while facilitating precision therapy. Furthermore, advancements in imaging and genetic editing techniques have significantly augmented the potential of organoids in tumor research. This review explores the application of organoid technology for more precise tumor simulations and its specific contributions to cancer research advancements. Additionally, we discuss the challenges and evolving trends in developing comprehensive tumor models utilizing organoid technology.

Human brain organoids for understanding substance use disorders

Substance use disorders (SUDs) are complex mental health conditions involving a problematic pattern of substance use. Challenges remain in understanding its neural mechanisms, which are likely to lead to improved SUD treatments. Human brain organoids, brain-like 3D in vitro cultures derived from human stem cells, show unique potential in recapitulating the response of a developing human brain to substances. Here, we review the recent progress in understanding SUD using human brain organoid models focusing on neurodevelopmental perspectives. We first summarize the background of SUD in humans. Moreover, we introduce the development of various human brain organoid models and then discuss current progress and findings underlying the abuse of substances like nicotine, alcohol, and other addictive drugs using organoid models. Furthermore, we review efforts to develop organ chips and microphysiological systems to engineer better human brain organoids for advancing SUD studies. Lastly, we conclude by elaborating on the current challenges and future directions of SUD studies using human brain organoids.

Ex Vivo Tools and Models in MASLD Research

Metabolic dysfunction-associated fatty liver disease (MASLD) presents a growing global health challenge with limited therapeutic choices. This review delves into the array of ex vivo tools and models utilized in MASLD research, encompassing liver-on-a-chip (LoC) systems, organoid-derived tissue-like structures, and human precision-cut liver slice (PCLS) systems. Given the urgent need to comprehend MASLD pathophysiology and identify novel therapeutic targets, this paper aims to shed light on the pivotal role of advanced ex vivo models in enhancing disease understanding and facilitating the development of potential therapies. Despite challenges posed by the elusive disease mechanism, these innovative methodologies offer promise in reducing the utilization of in vivo models for MASLD research while accelerating drug discovery and biomarker identification, thereby addressing critical unmet clinical needs.

Coumarin-Based Photodegradable Hydrogels Enable Two-Photon Subtractive Biofabrication at 300 mm s-1

Spatiotemporally controlled two-photon photodegradation of hydrogels has gained increasing attention for high-precision subtractive tissue engineering. However, conventional photolabile hydrogels often have poor efficiency upon two-photon excitation in the near-infrared (NIR) region and thus require high laser dosage that may compromise cell activity. As a result, high-speed two-photon hydrogel erosion in the presence of cells remains challenging. Here we introduce the design and synthesis of efficient coumarin-based photodegradable hydrogels to overcome these limitations. A set of photolabile coumarin-functionalized polyethylene glycol linkers are synthesized through a Passerini multicomponent reaction. After mixing these linkers with thiolated hyaluronic acid, semi-synthetic photodegradable hydrogels are formed in situ via Michael addition crosslinking. The efficiency of photodegradation in these hydrogels is significantly higher than that in nitrobenzyl counterparts upon two-photon irradiation at 780 nm. A complex microfluidic network mimicking the bone microarchitecture is successfully fabricated in preformed coumarin hydrogels at high speeds of up to 300 mm s-1 and low laser dosage down to 10 mW. Further, we demonstrate fast two-photon printing of hollow microchannels inside a hydrogel to spatiotemporally direct cell migration in 3D. Collectively, these hydrogels may open new avenues for fast laser-guided tissue fabrication at high spatial resolution.

Regenerative human liver organoids (HLOs) in a pillar/perfusion plate for hepatotoxicity assays

Human liver organoids (HLOs) differentiated from embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and adult stem cells (ASCs) can recapitulate the structure and function of human fetal liver tissues, thus being considered as a promising tissue model for liver diseases and predictive compound screening. However, the adoption of HLOs in drug discovery faces several technical challenges, which include the lengthy differentiation process with multiple culture media leading to batch-to-batch variation, short-term maintenance of hepatic functions post-maturation, low assay throughput due to Matrigel dissociation and HLO transfer to a microtiter well plate, and insufficient maturity levels compared to primary hepatocytes. To address these issues, expandable HLOs (Exp-HLOs) derived from human iPSCs were generated by optimizing differentiation protocols, which were rapidly printed on a 144-pillar plate with sidewalls and slits (144PillarPlate) and dynamically cultured for up to 20 days into differentiated HLOs (Diff-HLOs) in a 144-perfusion plate with perfusion wells and reservoirs (144PerfusionPlate) for in situ organoid culture and analysis. The dynamically cultured Diff-HLOs exhibited greater maturity and reproducibility than those cultured statically, especially after a 10-day differentiation period. In addition, Diff-HLOs in the pillar/perfusion plate were tested with acetaminophen and troglitazone for 3 days to assess drug-induced liver injury (DILI) and then incubated in an expansion medium for 10 days to evaluate liver recovery from DILI. The assessment of liver regeneration post-injury is critical to understanding the mechanism of recovery and determining the threshold drug concentration beyond which there will be a sharp decrease in the liver's regenerative capacity. We envision that bioprinted Diff-HLOs in the pillar/perfusion plate could be used for high-throughput screening (HTS) of hepatotoxic compounds due to the short-term differentiation of passage-able Exp-HLOs, stable hepatic function post-maturation, high reproducibility, and high throughput with capability of in situ organoid culture, testing, staining, imaging, and analysis.

Enhanced drug classification using machine learning with multiplexed cardiac contractility assays

Cardiac screening of newly discovered drugs remains a longstanding challenge for the pharmaceutical industry. While therapeutic efficacy and cardiotoxicity are evaluated through preclinical biochemical and animal testing, 90 % of lead compounds fail to meet safety and efficacy benchmarks during human clinical trials. A preclinical model more representative of the human cardiac response is needed; heart tissue engineered from human pluripotent stem cell derived cardiomyocytes offers such a platform. In this study, three functionally distinct and independently validated engineered cardiac tissue assays are exposed to increasing concentrations of known compounds representing 5 classes of mechanistic action, creating a robust electrophysiology and contractility dataset. Combining results from six individual models, the resulting ensemble algorithm can classify the mechanistic action of unknown compounds with 86.2 % predictive accuracy. This outperforms single-assay models and offers a strategy to enhance future clinical trial success aligned with the recent FDA Modernization Act 2.0.

Targeting ALDH1A1 to enhance the efficacy of KRAS-targeted therapy through ferroptosis

KRAS is among the most commonly mutated oncogenes in human malignancies. Although the advent of sotorasib and adagrasib, has lifted the "undruggable" stigma of KRAS, the resistance to KRAS inhibitors quickly becomes a major issue. Here, we reported that aldehyde dehydrogenase 1 family member A1 (ALDH1A1), an enzyme in retinoic acid biosynthesis and redox balance, increases in response to KRAS inhibitors and confers resistance in a range of cancer types. KRAS inhibitors' efficacy is significantly improved in sensitive or drug-resistant cells, patient-derived organoids (PDO), and xenograft models by ALDH1A1 knockout, loss of enzyme function, or inhibitor. Furthermore, we discovered that ALDH1A1 suppresses the efficacy of KRAS inhibitors by counteracting ferroptosis. ALDH1A1 detoxicates deleterious aldehydes, boosts the synthesis of NADH and retinoic acid (RA), and improves RARA function. ALDH1A1 also activates the CREB1/GPX4 pathway, stimulates the production of lipid droplets in a pH-dependent manner, and subsequently prevents ferroptosis induced by KRAS inhibitors. Meanwhile, we established that GTF2I is dephosphorylated at S784 via ERK by KRAS inhibitors, which hinders its nuclear translocation and mediates ALDH1A1's upregulation in response to KRAS inhibitors. In summary, the results offer valuable insights into targeting ALDH1A1 to enhance the effectiveness of KRAS-targeted therapy through ferroptosis in cancer treatment.

Engineering next generation vascularized organoids

Organoids are self-organizing 3D cell culture models that are valuable for studying the mechanisms underlying both development and disease in multiple species, particularly, in humans. These 3D engineered tissues can mimic the structure and function of human organs in vitro. Methods to generate organoids have substantially improved to better resemble, in various ways, their in vivo counterpart. One of the major limitations in current organoid models is the lack of a functional vascular compartment. Here we discuss methodological approaches to generating perfusable blood vessel networks in organoid systems. Inclusion of perfused vascular compartments markedly enhances the physiological relevance of organoid systems and is a critical step in the establishment of next generation, higher-complexity in vitro systems for use in developmental, clinical, and drug-development settings.

Microphysiological systems to advance human pathophysiology and translational medicine

Microphysiological systems (MPS) or "organ-on-a-chip" models are sophisticated tools that harness techniques from cell biology, tissue engineering, and microengineering to recapitulate human physiology. Typically, MPS are biofabricated three-dimensional (3-D) tissue constructs integrated into platforms designed to mimic the tissue microenvironment and provide functional outputs. Over the past decade, researchers have endeavored to manufacture high-throughput, high-fidelity MPS models of all major human organs. By incorporating patient-derived cells, researchers have produced biomimetic models of tissues with disease-linked genetic mutations capable of exhibiting patient heterogeneity. This work has demonstrated that MPS more closely model organotypic function and pathophysiology than traditional two-dimensional (2-D) culture systems. Moreover, investigators have shown that human MPS are better predictors of drug efficacy and toxicity than animal models. Thus, MPS have emerged as a promising candidate to improve the efficacy and safety of preclinical trials. In this mini-review, we provide an overview of current advances in MPS models, their applications in mechanistic research, and relevance to drug screening. Finally, we discuss current investments in MPS development by the United States federal government and research institutions around the world to advance translational medicine.

Robust tissue pattern formation by coupling morphogen signal and cell adhesion

Morphogens, locally produced signaling molecules, form a concentration gradient to guide tissue patterning. Tissue patterns emerge as a collaboration between morphogen diffusion and responsive cell behaviors, but the mechanisms through which diffusing morphogens define precise spatial patterns amidst biological fluctuations remain unclear. To investigate how cells respond to diffusing proteins to generate tissue patterns, we develop SYMPLE3D, a 3D culture platform. By engineering gene expression responsive to artificial morphogens, we observe that coupling morphogen signals with cadherin-based adhesion is sufficient to convert a morphogen gradient into distinct tissue domains. Morphogen-induced cadherins gather activated cells into a single domain, removing ectopically activated cells. In addition, we reveal a switch-like induction of cadherin-mediated compaction and cell mixing, homogenizing activated cells within the morphogen gradient to form a uniformly activated domain with a sharp boundary. These findings highlight the cooperation between morphogen gradients and cell adhesion in robust tissue patterning and introduce a novel method for tissue engineering to develop new tissue domains in organoids.

Scalable production of uniform and mature organoids in a 3D geometrically-engineered permeable membrane

The application of organoids has been limited by the lack of methods for producing uniformly mature organoids at scale. This study introduces an organoid culture platform, called UniMat, which addresses the challenges of uniformity and maturity simultaneously. UniMat is designed to not only ensure consistent organoid growth but also facilitate an unrestricted supply of soluble factors by a 3D geometrically-engineered, permeable membrane-based platform. Using UniMat, we demonstrate the scalable generation of kidney organoids with enhanced uniformity in both structure and function compared to conventional methods. Notably, kidney organoids within UniMat show improved maturation, showing increased expression of nephron transcripts, more in vivo-like cell-type balance, enhanced vascularization, and better long-term stability. Moreover, UniMat's design offers a more standardized organoid model for disease modeling and drug testing, as demonstrated by polycystic-kidney disease and acute kidney injury modeling. In essence, UniMat presents a valuable platform for organoid technology, with potential applications in organ development, disease modeling, and drug screening.

Applications, Limitations, and Considerations of Clinical Trials in a Dish

Recent advancements in biotechnology forged the path for clinical trials in dish (CTiDs) to advance as a popular method of experimentation in biomedicine. CTiDs play a fundamental role in translational research through technologies such as induced pluripotent stem cells, whole genome sequencing, and organs-on-a-chip. In this review, we explore advancements that enable these CTiD biotechnologies and their applications in animal testing, disease modeling, and space radiation technologies. Furthermore, this review dissects the advantages and disadvantages of CTiDs, as well as their regulatory considerations. Lastly, we evaluate the challenges that CTiDs pose and the role of CTiDs in future experimentation.

The YTHDF Proteins Shape the Brain Gene Signatures of Alzheimer's Disease

The gene signatures of Alzheimer's Disease (AD) brains reflect an output of a complex interplay of genetic, epigenetic, epi-transcriptomic, and post-transcriptional regulations. To identify the most significant factor that shapes the AD brain signature, we developed a machine learning model (DEcode-tree) to integrate cellular and molecular factors explaining differential gene expression in AD. Our model indicates that YTHDF proteins, the canonical readers of N6-methyladenosine RNA modification (m6A), are the most influential predictors of the AD brain signature. We then show that protein modules containing YTHDFs are downregulated in human AD brains, and knocking out YTHDFs in iPSC-derived neural cells recapitulates the AD brain gene signature in vitro . Furthermore, eCLIP-seq analysis revealed that YTHDF proteins influence AD signatures through both m6A-dependent and independent pathways. These results indicate the central role of YTHDF proteins in shaping the gene signature of AD brains.

Aligning with the 3Rs: alternative models for research into muscle development and inherited myopathies

Inherited and acquired muscle diseases are an important cause of morbidity and mortality in human medical and veterinary patients. Researchers use models to study skeletal muscle development and pathology, improve our understanding of disease pathogenesis and explore new treatment options. Experiments on laboratory animals, including murine and canine models, have led to huge advances in congenital myopathy and muscular dystrophy research that have translated into clinical treatment trials in human patients with these debilitating and often fatal conditions. Whilst animal experimentation has enabled many significant and impactful discoveries that otherwise may not have been possible, we have an ethical and moral, and in many countries also a legal, obligation to consider alternatives. This review discusses the models available as alternatives to mammals for muscle development, biology and disease research with a focus on inherited myopathies. Cell culture models can be used to replace animals for some applications: traditional monolayer cultures (for example, using the immortalised C2C12 cell line) are accessible, tractable and inexpensive but developmentally limited to immature myotube stages; more recently, developments in tissue engineering have led to three-dimensional cultures with improved differentiation capabilities. Advances in computer modelling and an improved understanding of pathogenetic mechanisms are likely to herald new models and opportunities for replacement. Where this is not possible, a 3Rs approach advocates partial replacement with the use of less sentient animals (including invertebrates (such as worms Caenorhabditis elegans and fruit flies Drosophila melanogaster) and embryonic stages of small vertebrates such as the zebrafish Danio rerio) alongside refinement of experimental design and improved research practices to reduce the numbers of animals used and the severity of their experience. An understanding of the advantages and disadvantages of potential models is essential for researchers to determine which can best facilitate answering a specific scientific question. Applying 3Rs principles to research not only improves animal welfare but generates high-quality, reproducible and reliable data with translational relevance to human and animal patients.

Organoids-On-a-Chip for Personalized Precision Medicine

The development of personalized precision medicine has become a pivotal focus in modern healthcare. Organoids-on-a-Chip (OoCs), a groundbreaking fusion of organoid culture and microfluidic chip technology, has emerged as a promising approach to advancing patient-specific treatment strategies. In this review, the diverse applications of OoCs are explored, particularly their pivotal role in personalized precision medicine, and their potential as a cutting-edge technology is highlighted. By utilizing patient-derived organoids, OoCs offer a pathway to optimize treatments, create precise disease models, investigate disease mechanisms, conduct drug screenings, and individualize therapeutic strategies. The emphasis is on the significance of this technological fusion in revolutionizing healthcare and improving patient outcomes. Furthermore, the transformative potential of personalized precision medicine, future prospects, and ongoing advancements in the field, with a focus on genomic medicine, multi-omics integration, and ethical frameworks are discussed. The convergence of these innovations can empower patients, redefine treatment approaches, and shape the future of healthcare.

Tissue-Engineered Three-Dimensional Platforms for Disease Modeling and Therapeutic Development

Three-dimensional (3D) tissue-engineered models are under investigation to recapitulate tissue architecture and functionality, thereby overcoming limitations of traditional two-dimensional cultures and preclinical animal models. This review highlights recent developments in 3D platforms designed to model diseases in vitro that affect numerous tissues and organs, including cardiovascular, gastrointestinal, bone marrow, neural, reproductive, and pulmonary systems. We discuss current technologies for engineered tissue models, highlighting the advantages, limitations, and important considerations for modeling tissues and diseases. Lastly, we discuss future advancements necessary to enhance the reliability of 3D models of tissue development and disease.

MAGIC matrices: freeform bioprinting materials to support complex and reproducible organoid morphogenesis

Organoids are powerful models of tissue physiology, yet their applications remain limited due to their relatively simple morphology and high organoid-to-organoid structural variability. To address these limitations we developed a soft, composite yield-stress extracellular matrix that supports optimal organoid morphogenesis following freeform 3D bioprinting of cell slurries at tissue-like densities. The material is designed with two temperature regimes: at 4 °C it exhibits reversible yield-stress behavior to support long printing times without compromising cell viability. When transferred to cell culture at 37 °C, the material cross-links and exhibits similar viscoelasticity and plasticity to basement membrane extracts such as Matrigel. We first characterize the rheological properties of MAGIC matrices that optimize organoid morphogenesis, including low stiffness and high stress relaxation. Next, we combine this material with a custom piezoelectric printhead that allows more reproducible and robust self-organization from uniform and spatially organized tissue "seeds." We apply MAGIC matrix bioprinting for high-throughput generation of intestinal, mammary, vascular, salivary gland, and brain organoid arrays that are structurally similar to those grown in pure Matrigel, but exhibit dramatically improved homogeneity in organoid size, shape, maturation time, and efficiency of morphogenesis. The flexibility of this method and material enabled fabrication of fully 3D microphysiological systems, including perfusable organoid tubes that experience cyclic 3D strain in response to pressurization. Furthermore, the reproducibility of organoid structure increased the statistical power of a drug response assay by up to 8 orders-of-magnitude for a given number of comparisons. Combined, these advances lay the foundation for the efficient fabrication of complex tissue morphologies by canalizing their self-organization in both space and time.