Engineering organoids

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.

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.

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.

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.

Bridging the gap: Innovative human-based in vitro approaches for nanomaterials hazard assessment and their role in safe and sustainable by design, risk assessment, and life cycle assessment

The application of nanomaterials in industry and consumer products is growing exponentially, which has pressed the development and use of predictive human in vitro models in pre-clinical analysis to closely extrapolate potential toxic effects in vivo. The conventional cytotoxicity investigation of nanomaterials using cell lines from cancer origin and culturing them two-dimensionally in a monolayer without mimicking the proper pathophysiological microenvironment may affect a precise prediction of in vitro effects at in vivo level. In recent years, complex in vitro models (also belonging to the new approach methodologies, NAMs) have been established in unicellular to multicellular cultures either by using cell lines, primary cells or induced pluripotent stem cells (iPSCs), and reconstituted into relevant biological dimensions mimicking in vivo conditions. These advanced in vitro models retain physiologically reliant exposure scenarios particularly appropriate for oral, dermal, respiratory, and intravenous administration of nanomaterials, which have the potential to improve the in vivo predictability and lead to reliable outcomes. In this perspective, we discuss recent developments and breakthroughs in using advanced human in vitro models for hazard assessment of nanomaterials. We identified fit-for-purpose requirements and remaining challenges for the successful implementation of in vitro data into nanomaterials Safe and Sustainable by Design (SSbD), Risk Assessment (RA), and Life Cycle Assessment (LCA). By addressing the gap between in vitro data generation and the utility of in vitro data for nanomaterial safety assessments, a prerequisite for SSbD approaches, we outlined potential key areas for future development.

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.

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.

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.

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.

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.

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.

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.

Reassessment of marker genes in human induced pluripotent stem cells for enhanced quality control

Human induced pluripotent stem cells (iPSCs) have great potential in research, but pluripotency testing faces challenges due to non-standardized methods and ambiguous markers. Here, we use long-read nanopore transcriptome sequencing to discover 172 genes linked to cell states not covered by current guidelines. We validate 12 genes by qPCR as unique markers for specific cell fates: pluripotency (CNMD, NANOG, SPP1), endoderm (CER1, EOMES, GATA6), mesoderm (APLNR, HAND1, HOXB7), and ectoderm (HES5, PAMR1, PAX6). Using these genes, we develop a machine learning-based scoring system, "hiPSCore", trained on 15 iPSC lines and validated on 10 more. hiPSCore accurately classifies pluripotent and differentiated cells and predicts their potential to become specialized 2D cells and 3D organoids. Our re-evaluation of cell fate marker genes identifies key targets for future studies on cell fate assessment. hiPSCore improves iPSC testing by reducing time, subjectivity, and resource use, thus enhancing iPSC quality for scientific and medical applications.

Establishment and Characterization of Testis Organoids with Proliferation and Differentiation of Spermatogonial Stem Cells into Spermatocytes and Spermatids

Organoids play pivotal roles in uncovering the molecular mechanisms underlying organogenesis, intercellular communication, and high-throughput drug screening. Testicular organoids are essential for exploring the genetic and epigenetic regulation of spermatogenesis in vivo and the treatment of male infertility. However, the formation of testicular organoids with full spermatogenesis has not yet been achieved. In this study, neonatal mouse testicular cells were isolated by two-step enzymatic digestion, and they were combined with Matrigel and transplanted subcutaneously into nude mice. Histological examination (H&E) staining and immunohistochemistry revealed that cell grafts assembled to form seminiferous tubules that contained spermatogonial stem cells (SSCs) and Sertoli cells, as illustrated by the co-expression of PLZF (a hallmark for SSCs) and SOX9 (a marker for Sertoli cells) as well as the co-expression of UCHL1 (a hallmark for SSCs) and SOX9, after 8 weeks of transplantation. At 10 weeks of transplantation, SSCs could proliferate and differentiate into spermatocytes as evidenced by the expression of PCNA, Ki67, c-Kit, SYCP3, γ-HA2X, and MLH1. Notably, testicular organoids were seen, and spermatids were observed within the lumen of testicular organoids after 16 weeks of transplantation, as shown by the presence of TNP1 and ACROSIN (hallmarks for spermatids). Collectively, these results implicate that we successfully established testicular organoids with spermatogenesis in vivo. This study thus provides an excellent platform for unveiling the mechanisms underlying mammalian spermatogenesis, and it might offer valuable male gametes for treating male infertility.

Xenotransplantation - a shortcut to construct tissue complexity in organoids

Our knowledge of human biology is mainly originated from studies using animal models. However, interspecies differences between human and model organisms may lead to imprecise extrapolation of results obtained from model organisms. Organoids are three-dimensional cell clusters derived from pluripotent or adult stem cells that self-organize into organ-like structures reminiscent of the cognate organ. The establishment of human organoids makes it possible to study organ or tissue pathophysiology that is specific to human beings. However, most organoids do not have organ-specific vasculature, neurons, and immune cells, hence limiting their utility in emulating complex pathophysiological phenotypes. Among the various approaches to address these limitations, xenotransplantation represents a promising 'shortcut'. We will discuss recent advance in constructing tissue complexity in organoids, with a special focus on xenotransplantation.

Cellular Architects at Work: Cells Building their Own Microgel Houses

Microporous annealed particle (MAP) scaffolds are investigated for their application as injectable 3D constructs in the field of regenerative medicine and tissue repair. While available MAP scaffolds provide a stable interlinked matrix of microgels for cell culture, the infiltration depth and space for cells to grow inside the scaffolds is pre-determined by the void fraction during the assembly. In the case of MAP scaffolds fabricated from interlinked spherical microgels, a cellularity gradient can be observed with the highest cell density on the scaffold surface. Additionally, the interlinked microgel network limits the ability of cells to remodel their environment, which contradicts native tissue dynamics. In this work, a cell-induced interlinking method for MAP scaffold formation is established, which avoids the necessity of chemical crosslinkers and pre-engineered pores to achieve micro- or macropores in these 3D frameworks. This method enables cells to self-organize with microgels into dynamic tissue constructs, which can be further controlled by altering the microgel properties, the cell/microgel ratio, and well shape. To form a cell-induced interlinked scaffold, the cells are mixed with dextran-based microgels and function as a glue between the microgels, resulting in a more homogenous cell distribution throughout the scaffold with efficient cell-cell interactions.

Bioprinting of Cells, Organoids and Organs-on-a-Chip Together with Hydrogels Improves Structural and Mechanical Cues

The 3D bioprinting technique has made enormous progress in tissue engineering, regenerative medicine and research into diseases such as cancer. Apart from individual cells, a collection of cells, such as organoids, can be printed in combination with various hydrogels. It can be hypothesized that 3D bioprinting will even become a promising tool for mechanobiological analyses of cells, organoids and their matrix environments in highly defined and precisely structured 3D environments, in which the mechanical properties of the cell environment can be individually adjusted. Mechanical obstacles or bead markers can be integrated into bioprinted samples to analyze mechanical deformations and forces within these bioprinted constructs, such as 3D organoids, and to perform biophysical analysis in complex 3D systems, which are still not standard techniques. The review highlights the advances of 3D and 4D printing technologies in integrating mechanobiological cues so that the next step will be a detailed analysis of key future biophysical research directions in organoid generation for the development of disease model systems, tissue regeneration and drug testing from a biophysical perspective. Finally, the review highlights the combination of bioprinted hydrogels, such as pure natural or synthetic hydrogels and mixtures, with organoids, organoid-cell co-cultures, organ-on-a-chip systems and organoid-organ-on-a chip combinations and introduces the use of assembloids to determine the mutual interactions of different cell types and cell-matrix interferences in specific biological and mechanical environments.

Light-field tomographic fluorescence lifetime imaging microscopy

Fluorescence lifetime imaging microscopy (FLIM) is a powerful imaging technique that enables the visualization of biological samples at the molecular level by measuring the fluorescence decay rate of fluorescent probes. This provides critical information about molecular interactions, environmental changes, and localization within biological systems. However, creating high-resolution lifetime maps using conventional FLIM systems can be challenging, as it often requires extensive scanning that can significantly lengthen acquisition times. This issue is further compounded in three-dimensional (3D) imaging because it demands additional scanning along the depth axis. To tackle this challenge, we developed a computational imaging technique called light-field tomographic FLIM (LIFT-FLIM). Our approach allows for the acquisition of volumetric fluorescence lifetime images in a highly data-efficient manner, significantly reducing the number of scanning steps required compared to conventional point-scanning or line-scanning FLIM imagers. Moreover, LIFT-FLIM enables the measurement of high-dimensional data using low-dimensional detectors, which are typically low cost and feature a higher temporal bandwidth. We demonstrated LIFT-FLIM using a linear single-photon avalanche diode array on various biological systems, showcasing unparalleled single-photon detection sensitivity. Additionally, we expanded the functionality of our method to spectral FLIM and demonstrated its application in high-content multiplexed imaging of lung organoids. LIFT-FLIM has the potential to open up broad avenues in both basic and translational biomedical research.

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.

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.

Protocol for in vitro co-culture, proliferation, and cell cycle analyses of patient-derived leukemia cells

Leukemia niche impacts quiescence; however, culturing patient-derived samples ex vivo is technically challenging. Here, we present a protocol for in vitro co-culture of patient-derived xenograft acute lymphoblastic leukemia (PDX-ALL) cells with human mesenchymal stem cells (MSCs). We describe steps for labeling PDX-ALL cells with CellTrace Violet dye to demonstrate MSC-primed PDX-ALL cycling. We then detail procedures to identify MSC-primed G0/quiescent PDX-ALL cells via Hoechst-33342/Pyronin Y live cell cycle analysis. For complete details on the use and execution of this protocol, please refer to Pal et al.1,2.

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.

Unveiling senescence-associated ocular pathogenesis via lacrimal gland organoid magnetic bioassembly platform and HMGB1-Box A gene therapy

Dry eye disease (DED) is a multifactorial aging disorder leading to tear film insufficiency and instability. Yet, an important knowledge gap lingers in understanding senescence-associated ocular pathogenesis, due to limited in vitro translational lacrimal gland (LG) models. Consequently, this remains a major roadblock to discover effective therapies for the restoration of tear film secretion. Herein, the authors reported the magnetic bioassembly of two LG organoid platforms to recapitulate functional and aging states. Using a proof-of-concept approach, porcine primary LG cells were assembled into organoids via a magnetic 3D bioprinting (M3DB) platform. This platform could form reproducible LG organoids with epithelial hallmarks (AQP5+) and exhibit epithelial secretory functions (lysozyme activity). DNA damage-induced senescence and cell death was induced with etoposide, and LG organoid hypofunction and senescence-associated pathogenesis were observed. To confer DNA protection against aging, a novel gene therapy with Box A domain of high-mobility group box-1 (HMGB1-Box A) previously established by our group, was applied here to prevent LG cellular senescence for the first time. HMGB1-Box A transfection prevented LG organoids from senescence-associated pathogenesis at the transcriptomic, metabolomic and proteomic levels. Thus, M3DB platforms could generate functional and DNA damage-induced senescence LG organoids, and this latter damage could be prevented with HMGB1-Box A gene therapy.

Revolutionizing immune research with organoid-based co-culture and chip systems

The intertwined interactions various immune cells have with epithelial cells in our body require sophisticated experimental approaches to be studied. Due to the limitations of immortalized cell lines and animal models, there is an increasing demand for human in vitro model systems to investigate the microenvironment of immune cells in normal and in pathological conditions. Organoids, which are self-renewing, 3D cellular structures that are derived from stem cells, have started to provide gap-filling tissue modelling solutions. In this review, we first demonstrate with some of the available examples how organoid-based immune cell co-culture experiments can advance disease modelling of cancer, inflammatory bowel disease, and tissue regeneration. Then, we argue that to achieve both complexity and scale, organ-on-chip models combined with cutting-edge microfluidics-based technologies can provide more precise manipulation and readouts. Finally, we discuss how genome editing techniques and the use of patient-derived organoids and immune cells can improve disease modelling and facilitate precision medicine. To achieve maximum impact and efficiency, these efforts should be supported by novel infrastructures such as organoid biobanks, organoid facilities, as well as drug screening and host-microbe interaction testing platforms. All these together or in combination can allow researchers to shed more detailed, and often patient-specific, light on the crosstalk between immune cells and epithelial cells in health and disease.

Spheroid-Hydrogel-Integrated Biomimetic System: A New Frontier in Advanced Three-Dimensional Cell Culture Technology

BACKGROUND

Despite significant advances in three-dimensional (3D) cell culture technologies, creating accurate in vitro models that faithfully recapitulate complex in vivo environments remains a major challenge in biomedical research. Traditional culture methods often fail to simultaneously facilitate critical cell-cell and cell-extracellular matrix (ECM) interactions while providing control over mechanical and biochemical properties.

SUMMARY

This review introduces the spheroid-hydrogel-integrated biomimetic system (SHIBS), a groundbreaking approach that synergistically combines spheroid culture with tailored hydrogel technologies. SHIBS uniquely bridges the gap between traditional culture methods and physiological conditions by offering unprecedented control over both cellular interactions and environmental properties. We explore how SHIBS is revolutionizing fields ranging from drug discovery and disease modeling to regenerative medicine and basic biological research. The review discusses current challenges in SHIBS technology, including reproducibility, scalability, and high-resolution imaging, and outlines ongoing research addressing these issues. Furthermore, we envision the future evolution of SHIBS into more sophisticated organoid-hydrogel-integrated biomimetic systems and its integration with cutting-edge technologies such as microfluidics, 3D bioprinting, and artificial intelligence.

KEY MESSAGES

SHIBS represents a paradigm shift in 3D cell culture technology, offering a unique solution to recreate complex in vivo environments. Its potential to accelerate the development of personalized therapies across various biomedical fields is significant. While challenges persist, the ongoing advancements in SHIBS technology promise to overcome current limitations, paving the way for more accurate and reliable in vitro models. The future integration of SHIBS with emerging technologies may revolutionize biomimetic modeling, potentially reducing the need for animal testing and expediting drug discovery processes. This comprehensive review provides researchers and clinicians with a holistic understanding of SHIBS technology, its current capabilities, and its future prospects in advancing biomedical research and therapeutic innovations.

A 3D Bio-Printed-Based Model for Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a disease with a very poor prognosis, characterized by incidence rates very close to death rates. Despite the efforts of the scientific community, preclinical models that faithfully recreate the PDAC tumor microenvironment remain limited. Currently, the use of 3D bio-printing is an emerging and promising method for the development of cancer tumor models with reproducible heterogeneity and a precisely controlled structure. This study presents the development of a model using the extrusion 3D bio-printing technique. Initially, a model combining pancreatic cancer cells (Panc-1) and cancer-associated fibroblasts (CAFs) encapsulated in a sodium alginate and gelatin-based hydrogel to mimic the metastatic stage of PDAC was developed and comprehensively characterized. Subsequently, efforts were made to vascularize this model. This study demonstrates that the resulting tumors can maintain viability and proliferate, with cells self-organizing into aggregates with a heterogeneous composition. The utilization of 3D bio-printing in creating this tumor model opens avenues for reproducing tumor complexity in the future, offering a versatile platform for improving anti-cancer therapy models.

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.

Thymic epithelial organoids mediate T-cell development

Although the advent of organoids has opened unprecedented perspectives for basic and translational research, immune system-related organoids remain largely underdeveloped. Here, we established organoids from the thymus, the lymphoid organ responsible for T-cell development. We identified conditions enabling mouse thymic epithelial progenitor cell proliferation and development into organoids with diverse cell populations and transcriptional profiles resembling in vivo thymic epithelial cells (TECs) more closely than traditional TEC cultures. In contrast to these two-dimensional cultures, thymic epithelial organoids maintained thymus functionality in vitro and mediated physiological T-cell development upon reaggregation with T-cell progenitors. The reaggregates showed in vivo-like epithelial diversity and the ability to attract T-cell progenitors. Thymic epithelial organoids are the first organoids originating from the stromal compartment of a lymphoid organ. They provide new opportunities to study TEC biology and T-cell development in vitro, paving the way for future thymic regeneration strategies in ageing or acute injuries.

Current status and new avenues of stem cell-based preclinical and therapeutic approaches in amyotrophic lateral sclerosis

INTRODUCTION

Cell therapy development represents a critical challenge in amyotrophic lateral sclerosis (ALS) research. Despite more than 20 years of basic and clinical research, no definitive safety and efficacy results of cell-based therapies for ALS have been published.

AREAS COVERED

This review summarizes advances using stem cells (SCs) in pre-clinical studies to promote clinical translation and in clinical trials to treat ALS. New technologies have been developed and new experimental in vitro and animal models are now available to facilitate pre-clinical research in this field and to determine the most promising approaches to pursue in patients. New clinical trial designs aimed at developing personalized SC-based treatment with biological endpoints are being defined.

EXPERT OPINION

Knowledge of the basic biology of ALS and on the use of SCs to study and potentially treat ALS continues to grow. However, a consensus has yet to emerge on how best to translate these results into therapeutic applications. The selection and follow-up of patients should be based on clinical, biological, and molecular criteria. Planning of SC-based clinical trials should be coordinated with patient profiling genetically and molecularly to achieve personalized treatment. Much work within basic and clinical research is still needed to successfully transition SC therapy in ALS.

Bidirectional in-silico clearing approach for deep refractive-index tomography using a sparsely sampled transmission matrix

Optical diffraction tomography (ODT) enables the label-free volumetric imaging of biological specimens by mapping their three-dimensional refractive index (RI) distribution. However, the depth of imaging achievable is restricted due to spatially inhomogeneous RI distributions that induce multiple scattering. In this study, we introduce a novel ODT technique named bidirectional in-silico clearing RI tomography. This method incorporates both forward and reversed in-silico clearing. For the reversed in-silico clearing, we have integrated an ODT reconstruction framework with a transmission matrix approach, which enables RI reconstruction and wave backpropagation from the illumination side without necessitating modifications to the conventional ODT setup. Furthermore, the framework employs a sparsely sampled transmission matrix, significantly reducing the requisite number of measurements and computational expenses. Employing this proposed technique, we successfully imaged a spheroid with a thickness of 263 µm, corresponding to 11.4 scattering mean free paths. This method was successfully applied to various biological specimens, including liver and colon spheroids, demonstrating consistent imaging performance across samples with varied morphologies.

Nanoplasmonic Single-Tumoroid Microarray for Real-Time Secretion Analysis

Organoid tumor models have emerged as a powerful tool in the fields of biology and medicine as such 3D structures grown from tumor cells recapitulate better tumor characteristics, making these tumoroids unique for personalized cancer research. Assessment of their functional behavior, particularly protein secretion, is of significant importance to provide comprehensive insights. Here, a label-free spectroscopic imaging platform is presented with advanced integrated optofluidic nanoplasmonic biosensor that enables real-time secretion analysis from single tumoroids. A novel two-layer microwell design isolates tumoroids, preventing signal interference, and the microarray configuration allows concurrent analysis of multiple tumoroids. The dual imaging capability combining time-lapse plasmonic spectroscopy and bright-field microscopy facilitates simultaneous observation of secretion dynamics, motility, and morphology. The integrated biosensor is demonstrated with colorectal tumoroids derived from both cell lines and patient samples to investigate their vascular endothelial growth factor A (VEGF-A) secretion, growth, and movement under various conditions, including normoxia, hypoxia, and drug treatment. This platform, by offering a label-free approach with nanophotonics to monitor tumoroids, can pave the way for new applications in fundamental biological studies, drug screening, and the development of therapies.

Applications of Organoids in Advancing Drug Discovery and Development

Organoids are small, self-organizing three-dimensional cell cultures that are derived from stem cells or primary organs. These cultures replicate the complexity of an organ, which cannot be achieved by single-cell culture systems. Organoids can be used in testing of new drugs instead of animals. Development and validation of organoids is thus important to reduce the reliance on animals for drug testing. In this review, we have discussed the developmental and regulatory aspects of organoids and highlighted their importance in drug development. We have first summarized different types of culture-based organoid systems such as submerged Matrigel, micro-fluidic 3D cultures, inducible pluripotent stem cells, and air-liquid interface cultures. These systems help us understand the intricate interplay between cells and their surrounding milieu for identifying functions of target receptors, soluble factors, and spatial interactions. Further, we have discussed the advances in humanized severe-combined immunodeficiency mouse models and their applications in the pharmacology of immune-oncology. Since regulatory aspects are important in using organoids for drug development, we have summarized FDA and EMA regulations on organoid research to support pre-clinical studies. Finally, we have included some unique studies highlighting the use of organoids in studying infectious diseases, cancer, and fundamental biology. These studies also exemplify the latest technological advances in organoid development resulting in improved efficiency. Overall, this review comprehensively summarizes the applications of organoids in early drug development during discovery and pre-clinical studies.

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.

Patient-derived induced pluripotent stem cells: Tools to advance the understanding and drug discovery in Major Depressive Disorder

Major Depressive Disorder (MDD) is a pleomorphic disease with substantial patterns of symptoms and severity with mensurable deficits in several associated domains. The broad spectrum of phenotypes observed in patients diagnosed with depressive disorders is the reflection of a very complex disease where clusters of biological and external factors (e.g., response/processing of life events, intrapsychic factors) converge and mediate pathogenesis, clinical presentation/phenotypes and trajectory. Patient-derived induced pluripotent stem cells (iPSCs) enable their differentiation into specialised cell types in the central nervous system to explore the pathophysiological substrates of MDD. These models may complement animal models to advance drug discovery and identify therapeutic approaches, such as cell therapy, drug repurposing, and elucidation of drug metabolism, toxicity, and mechanisms of action at the molecular/cellular level, to pave the way for precision psychiatry. Despite the remarkable scientific and clinical progress made over the last few decades, the disease is still poorly understood, the incidence and prevalence continue to increase, and more research is needed to meet clinical demands. This review aims to summarise and provide a critical overview of the research conducted thus far using patient-derived iPSCs for the modelling of psychiatric disorders, with a particular emphasis on MDD.

Gastric Cancer Assembloids Derived from Patient-Derived Xenografts: A Preclinical Model for Therapeutic Drug Screening

The construction of reliable preclinical models is crucial for understanding the molecular mechanisms involved in gastric cancer and for advancing precision medicine. Currently, existing in vitro tumor models often do not accurately replicate the human gastric cancer environment and are unsuitable for high-throughput therapeutic drug screening. In this study, droplet microfluidic technology is employed to create novel gastric cancer assembloids by encapsulating patient-derived xenograft gastric cancer cells and patient stromal cells in Gelatin methacryloyl (GelMA)-Gelatin-Matrigel microgels. The usage of GelMA-Gelatin-Matrigel composite hydrogel effectively alleviated cell aggregation and sedimentation during the assembly process, allowing for the handling of large volumes of cell-laden hydrogel and the uniform generation of assembloids in a high-throughput manner. Notably, the patient-derived xenograft assembloids exhibited high consistency with primary tumors at both transcriptomic and histological levels, and can be efficiently scaled up for preclinical drug screening efforts. Furthermore, the drug screening results clearly demonstrated that the in vitro assembloid model closely mirrored in vivo drug responses. Thus, these findings suggest that gastric cancer assembloids, which effectively replicate the in vivo tumor microenvironment, show promise for enabling more precise high-throughput drug screening and predicting the clinical outcomes of various drugs.

Improving human cardiac organoid design using transcriptomics

Cardiovascular disease (CVD) is the leading cause of death worldwide. To this end, human cardiac organoids (hCOs) have been developed for improved organotypic CVD modeling over conventional in vivo animal models. Utilizing human cells, hCOs hold great promise to bridge key gaps in CVD research pertaining to human-specific conditions. hCOs are multicellular 3D models which resemble heart structure and function. Varying hCOs fabrication techniques leads to functional and phenotypic differences. To investigate heterogeneity across hCO platforms, we performed a transcriptomic analysis utilizing bulk RNA-sequencing from four previously published unique hCO studies. We further compared selected hCOs to 2D and 3D hiPSC-derived cardiomyocytes (hiPSC-CMs), as well as fetal and adult human myocardium bulk RNA-sequencing samples. Upon investigation utilizing Principal Component Analysis, K-means clustering analysis of key genes, and further downstream analyses such as Gene Set Enrichment (GSEA), Gene Set Variation (GSVA), and GO term enrichment, we found that hCO fabrication method influences maturity and cellular heterogeneity across models. Thus, we propose that adjustment of fabrication method will result in an hCO with a defined maturity and transcriptomic profile to facilitate its specified applications, in turn maximizing its modeling potential.

Programming mammalian cell behaviors by physical cues

In recent decades, the field of synthetic biology has witnessed remarkable progress, driving advances in both research and practical applications. One pivotal area of development involves the design of transgene switches capable of precisely regulating specified outputs and controlling cell behaviors in response to physical cues, which encompass light, magnetic fields, temperature, mechanical forces, ultrasound, and electricity. In this review, we delve into the cutting-edge progress made in the field of physically controlled protein expression in engineered mammalian cells, exploring the diverse genetic tools and synthetic strategies available for engineering targeting cells to sense these physical cues and generate the desired outputs accordingly. We discuss the precision and efficiency limitations inherent in these tools, while also highlighting their immense potential for therapeutic applications.

AUTS2 disruption causes neuronal differentiation defects in human cerebral organoids through hyperactivation of the WNT/β-catenin pathway

Individuals with the Autism Susceptibility Candidate 2 (AUTS2) gene disruptions exhibit symptoms such as intellectual disability, microcephaly, growth retardation, and distinct skeletal and facial differences. The role of AUTS2 in neurodevelopment has been investigated using animal and embryonic stem cell models. However, the precise molecular mechanisms of how AUTS2 influences neurodevelopment, particularly in humans, are not thoroughly understood. Our study employed a 3D human cerebral organoid culture system, in combination with genetic, genomic, cellular, and molecular approaches, to investigate how AUTS2 impacts neurodevelopment through cellular signaling pathways. We used CRISPR/Cas9 technology to create AUTS2-deficient human embryonic stem cells and then generated cerebral organoids with these cells. Our transcriptomic analyses revealed that the absence of AUTS2 in cerebral organoids reduces the populations of cells committed to the neuronal lineage, resulting in an overabundance of cells with a transcription profile resembling that of choroid plexus (ChP) cells. Intriguingly, we found that AUTS2 negatively regulates the WNT/β-catenin signaling pathway, evidenced by its overactivation in AUTS2-deficient cerebral organoids and in luciferase reporter cells lacking AUTS2. Importantly, treating the AUTS2-deficient cerebral organoids with a WNT inhibitor reversed the overexpression of ChP genes and increased the downregulated neuronal gene expression. This study offers new insights into the role of AUTS2 in neurodevelopment and suggests potential targeted therapies for neurodevelopmental disorders.

Inflammasome-Inhibiting Nanoligomers Are Neuroprotective against Space-Induced Pathology in Healthy and Diseased Three-Dimensional Human Motor and Prefrontal Cortex Brain Organoids

The microgravity and space environment has been linked to deficits in neuromuscular and cognitive capabilities, hypothesized to occur due to accelerated aging and neurodegeneration in space. While the specific mechanisms are still being investigated, spaceflight-associated neuropathology is an important health risk to astronauts and space tourists and is being actively investigated for the development of appropriate countermeasures. However, such space-induced neuropathology offers an opportunity for accelerated screening of therapeutic targets and lead molecules for treating neurodegenerative diseases. Here, we show a proof-of-concept high-throughput target screening (on Earth), target validation, and mitigation of microgravity-induced neuropathology using our Nanoligomer platform, onboard the 43-day SpaceX CRS-29 mission to the International Space Station. First, comparing 3D healthy and diseased prefrontal cortex (PFC, for cognition) and motor neuron (MN, for neuromuscular function) organoids, we assessed space-induced pathology using biomarkers relevant to Alzheimer's disease (AD), frontotemporal dementia (FTD), and amyotrophic lateral sclerosis (ALS). Both healthy and diseased PFC and MN organoids showed significantly enhanced neurodegeneration in space, as measured through relevant disease biomarkers, when compared to their respective Earth controls. Second, we tested the top two lead molecules, NI112 that targeted NF-κB and NI113 that targeted IL-6. We observed that these Nanoligomers significantly mitigate the AD, FTD, and ALS relevant biomarkers like amyloid beta-42 (Aβ42), phosphorylated tau (pTau), Kallikrein (KLK-6), Tar DNA-binding protein 43 (TDP-43), and others. Moreover, the 43-day Nanoligomer treatment of these brain organoids did not appear to cause any observable toxicity or safety issues in the target organoid tissue, suggesting good tolerability for these molecules in the brain at physiologically relevant doses. Together, these results show significant potential for both the development and translation of NI112 and NI113 molecules as potential neuroprotective countermeasures for safer space travel and demonstrate the usefulness of the space environment for rapid, high-throughput screening of targets and lead molecules for clinical translation. We assert that the use of microgravity in drug development and screening may ultimately benefit millions of patients suffering from debilitating neurodegenerative diseases on Earth.

Long-working-distance high-collection-efficiency three-photon microscopy for in vivo long-term imaging of zebrafish and organoids

Zebrafish and organoids, crucial for complex biological studies, necessitate an imaging system with deep tissue penetration, sample protection from environmental interference, and ample operational space. Traditional three-photon microscopy is constrained by short-working-distance objectives and falls short. Our long-working-distance high-collection-efficiency three-photon microscopy (LH-3PM) addresses these challenges, achieving a 58% fluorescence collection efficiency at a 20 mm working distance. LH-3PM significantly outperforms existing three-photon systems equipped with the same long working distance objective, enhancing fluorescence collection and dramatically reducing phototoxicity and photobleaching. These improvements facilitate accurate capture of neuronal activity and an enhanced detection of activity spikes, which are vital for comprehensive, long-term imaging. LH-3PM's imaging of epileptic zebrafish not only showed sustained neuron activity over an hour but also highlighted increased neural synchronization and spike numbers, marking a notable shift in neural coding mechanisms. This breakthrough paves the way for new explorations of biological phenomena in small model organisms.

Strategies to decouple cell micro-scale and macro-scale environments for designing multifunctional biomimetic tissues

The regulation of cellular behavior within a three-dimensional (3D) environment to execute a specific function remains a challenge in the field of tissue engineering. In native tissues, cells and matrices are arranged into 3D modular units, comprising biochemical and biophysical signals that orchestrate specific cellular activities. Modular tissue engineering aims to emulate this natural complexity through the utilization of functional building blocks with unique stimulation features. By adopting a modular approach and using well-designed biomaterials, cellular microenvironments can be effectively decoupled from their macro-scale surroundings, enabling the development of engineered tissues with enhanced multifunctionality and heterogeneity. We overview recent advancements in decoupling the cellular micro-scale niches from their macroenvironment and evaluate the implications of this strategy on cellular and tissue functionality.

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.

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.

Liver organoids: updates on generation strategies and biomedical applications

The liver is the most important metabolic organ in the body. While mouse models and cell lines have further deepened our understanding of liver biology and related diseases, they are flawed in replicating key aspects of human liver tissue, particularly its complex structure and metabolic functions. The organoid model represents a major breakthrough in cell biology that revolutionized biomedical research. Organoids are in vitro three-dimensional (3D) physiological structures that recapitulate the morphological and functional characteristics of tissues in vivo, and have significant advantages over traditional cell culture methods. In this review, we discuss the generation strategies and current advances in the field focusing on their application in regenerative medicine, drug discovery and modeling diseases.

Robust and customizable spheroid culture system for regenerative medicine

Three-dimensional cell spheroids show promise for the reconstruction of native tissues. Herein, we report a sophisticated, uniform, and highly reproducible spheroid culture system for tissue reconstruction. A mesh-integrated culture system was designed to precisely control the uniformity and reproducibility of spheroid formation. Furthermore, we synthesized hexanoyl glycol chitosan, a material with ultralow cell adhesion properties, to further improve spheroid formation efficiency and biological function. Our results demonstrate improved biological function in various types of cells and ability to generate spheroids with complex structures composed of multiple cell types. In conclusion, our spheroid culture system offers a highly effective and widely applicable approach to generating customized spheroids with desired structural and biological features for a variety of biomedical applications.

The Efficiency of In Vitro Differentiation of Primate iPSCs into Cardiomyocytes Depending on Their Cell Seeding Density and Cell Line Specificity

A thorough characterization of induced pluripotent stem cells (iPSCs) used with in vitro models or therapeutics is essential. Even iPSCs derived from a single donor can exhibit variability within and between cell lines, which can lead to heterogeneity in results and hinder the promising future of cell replacement therapies. In this study, the cell seeding density of human and rhesus monkey iPSCs was tested to maximize the cell line-specific yield of the generated cardiomyocytes. We found that, despite using the same iPSC generation and differentiation protocols, the cell seeding density for the cell line-specific best differentiation efficiency could differ by a factor of four for the four cell lines used here. In addition, the cell lines showed differences in the range of cell seeding densities that they could tolerate without the severe loss of differentiation efficiency. Overall, our data show that the cell seeding density is a critical parameter for the differentiation inefficiency of primate iPSCs to cardiomyocytes and that iPSCs generated with the same episomal approach still exhibit considerable heterogeneity. Therefore, individual characterization of iPSC lines is required, and functional comparability with in vivo processes must be ensured to warrant the translatability of in vitro research with iPSCs.

The mechanical effects of chemical stimuli on neurospheres

The formulation of more accurate models to describe tissue mechanics necessitates the availability of tools and instruments that can precisely measure the mechanical response of tissues to physical loads and other stimuli. In this regard, neuroscience has trailed other life sciences owing to the unavailability of representative live tissue models and deficiency of experimentation tools. We previously addressed both challenges by employing a novel instrument called the cantilevered-capillary force apparatus (CCFA) to elucidate the mechanical properties of mouse neurospheres under compressive forces. The neurospheres were derived from murine stem cells, and our study was the first of its kind to investigate the viscoelasticity of living neural tissues in vitro. In the current study, we demonstrate the utility of the CCFA as a broadly applicable tool to evaluate tissue mechanics by quantifying the effect that oxidative stress has on the mechanical properties of neurospheres. We treated mouse neurospheres with non-cytotoxic levels of hydrogen peroxide and subsequently evaluated the storage and loss moduli of the tissues under compression and tension. We observed that the neurospheres exhibit viscoelasticity consistent with neural tissue and show that elastic modulus decreases with increasing size of the neurosphere. Our study yields insights for establishing rheological measurements as biomarkers by laying the groundwork for measurement techniques and showing that the influence of a particular treatment may be misinterpreted if the size dependence is ignored.

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.