Neural patterning of human induced pluripotent stem cells in 3-D cultures for studying biomolecule-directed differential cellular responses

3D bioprinting of human neural tissues with functional connectivity

Probing how human neural networks operate is hindered by the lack of reliable human neural tissues amenable to the dynamic functional assessment of neural circuits. We developed a 3D bioprinting platform to assemble tissues with defined human neural cell types in a desired dimension using a commercial bioprinter. The printed neuronal progenitors differentiate into neurons and form functional neural circuits within and between tissue layers with specificity within weeks, evidenced by the cortical-to-striatal projection, spontaneous synaptic currents, and synaptic response to neuronal excitation. Printed astrocyte progenitors develop into mature astrocytes with elaborated processes and form functional neuron-astrocyte networks, indicated by calcium flux and glutamate uptake in response to neuronal excitation under physiological and pathological conditions. These designed human neural tissues will likely be useful for understanding the wiring of human neural networks, modeling pathological processes, and serving as platforms for drug testing.

3D Bioprinting of Human Neural Tissues with Functional Connectivity

Probing how the human neural networks operate is hindered by the lack of reliable human neural tissues amenable for dynamic functional assessment of neural circuits. We developed a 3D bioprinting platform to assemble tissues with defined human neural cell types in a desired dimension using a commercial bioprinter. The printed neuronal progenitors differentiate to neurons and form functional neural circuits in and between tissue layers with specificity within weeks, evidenced by the cortical-to-striatal projection, spontaneous synaptic currents and synaptic response to neuronal excitation. Printed astrocyte progenitors develop into mature astrocytes with elaborated processes and form functional neuron-astrocyte networks, indicated by calcium flux and glutamate uptake in response to neuronal excitation under physiological and pathological conditions. These designed human neural tissues will likely be useful for understanding the wiring of human neural networks, modeling pathological processes, and serving as platforms for drug testing.

Engineering Extracellular Matrix-Bound Nanovesicles Secreted by Three-Dimensional Human Mesenchymal Stem Cells

Extracellular matrix (ECM) in the human tissue contains vesicles, which are defined as matrix-bound nanovesicles (MBVs). MBVs serve as one of the functional components in ECM, recapitulating part of the regulatory roles and in vivo microenvironment. In this study, extracellular vesicles from culture supernatants (SuEVs) and MBVs are isolated from the conditioned medium or ECM, respectively, of 3D human mesenchymal stem cells. Nanoparticle tracking analysis shows that MBVs are smaller than SuEVs (100-150 nm). Transmission electron microscopy captures the typical cup shape morphology for both SuEVs and MBVs. Western blot reveals that MBVs have low detection of some SuEV markers such as syntenin-1. miRNA analysis of MBVs shows that 3D microenvironment enhances the expression of miRNAs such as miR-19a and miR-21. In vitro functional analysis shows that MBVs can facilitate human pluripotent stem cell-derived forebrain organoid recovery after starvation and promote high passage fibroblast proliferation. In macrophage polarization, 2D MBVs tend to suppress the pro-inflammatory cytokine IL-12β, while 3D MBVs tend to enhance the anti-inflammatory cytokine IL-10. This study has the significance in advancing the understanding of the bio-interface of nanovesicles with human tissue and the design of cell-free therapy for treating neurological disorders such as ischemic stroke.

Inflammatory Response and Exosome Biogenesis of Choroid Plexus Organoids Derived from Human Pluripotent Stem Cells

The choroid plexus (ChP) is a complex structure in the human brain that is responsible for the secretion of cerebrospinal fluid (CSF) and forming the blood-CSF barrier (B-CSF-B). Human-induced pluripotent stem cells (hiPSCs) have shown promising results in the formation of brain organoids in vitro; however, very few studies to date have generated ChP organoids. In particular, no study has assessed the inflammatory response and the extracellular vesicle (EV) biogenesis of hiPSC-derived ChP organoids. In this study, the impacts of Wnt signaling on the inflammatory response and EV biogenesis of ChP organoids derived from hiPSCs was investigated. During days 10-15, bone morphogenetic protein 4 was added along with (+/-) CHIR99021 (CHIR, a small molecule GSK-3β inhibitor that acts as a Wnt agonist). At day 30, the ChP organoids were characterized by immunocytochemistry and flow cytometry for TTR (~72%) and CLIC6 (~20%) expression. Compared to the -CHIR group, the +CHIR group showed an upregulation of 6 out of 10 tested ChP genes, including CLIC6 (2-fold), PLEC (4-fold), PLTP (2-4-fold), DCN (~7-fold), DLK1 (2-4-fold), and AQP1 (1.4-fold), and a downregulation of TTR (0.1-fold), IGFBP7 (0.8-fold), MSX1 (0.4-fold), and LUM (0.2-0.4-fold). When exposed to amyloid beta 42 oligomers, the +CHIR group had a more sensitive response as evidenced by the upregulation of inflammation-related genes such as TNFα, IL-6, and MMP2/9 when compared to the -CHIR group. Developmentally, the EV biogenesis markers of ChP organoids showed an increase over time from day 19 to day 38. This study is significant in that it provides a model of the human B-CSF-B and ChP tissue for the purpose of drug screening and designing drug delivery systems to treat neurological disorders such as Alzheimer's disease and ischemic stroke.

Modelling hyperexcitability in human cerebral cortical organoids: Oxygen/glucose deprivation most effective stimulant

Epilepsy is a common neurological disorder that affects 1% of the global population. The neonatal period constitutes the highest incidence of seizures. Despite the continual developments in seizure modelling and anti-epileptic drug development, the mechanisms involved in neonatal seizures remain poorly understood. This leaves infants with neonatal seizures at a high risk of death, poor prognosis of recovery and risk of developing neurological disorders later in life. Current in vitro platforms for modelling adult and neonatal epilepsies - namely acute cerebral brain slices or cell-derived cultures, both derived from animals-either lack a complex cytoarchitecture, high-throughput capabilities or physiological similarities to the neonatal human brain. Cerebral organoids, derived from human embryonic stem cells (hESCs), are an emerging technology that could better model neurodevelopmental disorders in the developing human brain. Herein, we study induced hyperexcitability in human cerebral cortical organoids - setting the groundwork for neonatal seizure modelling - using electrophysiological techniques and pharmacological manipulations. In neonatal seizures, energy failure - specifically due to deprivation of oxygen and glucose - is a consistent and reliable seizure induction method that has been used to study the underlying cellular and molecular mechanisms. Here, we applied oxygen-glucose deprivation (OGD) as well as common chemoconvulsants in 3-7-month-old cerebral organoids. Remarkably, OGD resulted in hyperexcitability, with increased power and spontaneous events compared to other common convulsants tested at the population level. These findings characterize OGD as the stimulus most capable of inducing hyperexcitable changes in cerebral organoid tissue, which could be extended to future modelling of neonatal epilepsies in cerebral organoids.

Covalently Attached Slippery Surface Coatings to Reduce Protein Adsorptions on Poly(dimethylsiloxane) Planar Surfaces and 3D Microfluidic Channels

Silicone elastomers, such as poly(dimethylsiloxane) (PDMS), have a broad range of applications in basic biomedical research and clinical medicine, ranging from the preparation of microfluidic devices for organs-on-chips and ventriculoperitoneal shunts for the treatment of hydrocephalus to implantable neural probes for neuropharmacology. Despite the importance, the protein adsorptions on silicone elastomers in these application environments represent a significant challenge. Surface coatings with slippery lubricants, inspired by the Nepenthes pitcher plants, have recently received much attention for reducing protein adsorptions. Nevertheless, the depletion of the physically infused lubricants limits their broad applications. In this study, we report a covalently attached slippery surface coating to reduce protein adsorptions on PDMS surfaces. As demonstrations, we show that the adsorption of serum proteins, human fibrinogen and albumin, can be significantly reduced by the slippery surface coating in both planar PDMS surfaces and 3D microfluidic channels. The preparation of slippery surface coatings relies on the acid-catalyzed polycondensation reaction of dimethyldimethoxysilane, which utilizes a low-cost and scalable dip-coating method. Furthermore, cell metabolic activity and viability studies demonstrate the biocompatibility of the surface coating. These results suggest the potential applications of slippery surface coatings to reduce protein adsorptions for implantable medical devices, organs-on-chips, and many others.

Human Forebrain Organoid-Derived Extracellular Vesicle Labeling with Iron Oxides for In Vitro Magnetic Resonance Imaging

The significant roles of extracellular vesicles (EVs) as intracellular mediators, disease biomarkers, and therapeutic agents, make them a scientific hotspot. In particular, EVs secreted by human stem cells show significance in treating neurological disorders, such as Alzheimer’s disease and ischemic stroke. However, the clinical applications of EVs are limited due to their poor targeting capabilities and low therapeutic efficacies after intravenous administration. Superparamagnetic iron oxide (SPIO) nanoparticles are biocompatible and have been shown to improve the targeting ability of EVs. In particular, ultrasmall SPIO (USPIO, <50 nm) are more suitable for labeling nanoscale EVs due to their small size. In this study, induced forebrain neural progenitor cortical organoids (iNPCo) were differentiated from human induced pluripotent stem cells (iPSCs), and the iNPCo expressed FOXG1, Nkx2.1, α-catenin, as well as β-tubulin III. EVs were isolated from iNPCo media, then loaded with USPIOs by sonication. Size and concentration of EV particles were measured by nanoparticle tracking analysis, and no significant changes were observed in size distribution before and after sonication, but the concentration decreased after labeling. miR-21 and miR-133b decreased after sonication. Magnetic resonance imaging (MRI) demonstrated contrast visualized for the USPIO labeled EVs embedded in agarose gel phantoms. Upon calculation, USPIO labeled EVs exhibited considerably shorter relaxation times, quantified as T2 and T2* values, reducing the signal intensity and generating higher MRI contrast compared to unlabeled EVs and gel only. Our study demonstrated that USPIO labeling was a feasible approach for in vitro tracking of brain organoid-derived EVs, which paves the way for further in vivo examination.

Microplastics exposure affects neural development of human pluripotent stem cell-derived cortical spheroids

Plastics have been part of our ecosystem for about a century and their degradation by different environmental factors produce secondary microplastics (MPs). To date, the impact of MPs on human health has not been well investigated. To understand the possible effects of polystyrene-MPs (PS-MPs) on the human brain, a 3D model of human forebrain cortical spheroids has been derived, which mimics early development of human cerebral cortex. The spheroids were exposed to 100, 50, and 5 µg/mL of 1 µm and 10 µm PS-MPs during day 4-10 and day 4-30. The short-term MP exposure showed the promoted proliferation and high gene expression of Nestin, PAX6, ATF4, HOXB4 and SOD2. For long-term exposure, reduced cell viability was observed. Moreover, changes in size and concentration of PS-MPs altered the gene expression of DNA damage and neural tissue patterning. In particular, β-tubulin III, Nestin, and TBR1/TBR2 gene expression decreased in PS-MP treated conditions compare to the untreated control. The results of this study suggest that the size- and concentration-dependent exposure to PS-MPs can adversely affect embryonic brain-like tissue development in forebrain cerebral spheroids. This study has significance in assessing environmental factors in neurotoxicity and degeneration in human.

Synthetic developmental biology: Engineering approaches to guide multicellular organization

Multicellular organisms of various complexities self-organize in nature. Organoids are in vitro 3D structures that display important aspects of the anatomy and physiology of their in vivo counterparts and that develop from pluripotent or tissue-specific stem cells through a self-organization process. In this review, we describe the multidisciplinary concept of “synthetic developmental biology” where engineering approaches are employed to guide multicellular organization in an experimental setting. We introduce a novel classification of engineering approaches based on the extent of microenvironmental manipulation applied to organoids. In the final section, we discuss how engineering tools might help overcome current limitations in organoid construction.

Studying the Inflammatory Responses to Amyloid Beta Oligomers in Brain-Specific Pericyte and Endothelial Co-culture from Human Stem Cells

Background

Recently, the in vitro blood brain barrier (BBB) models derived from human pluripotent stem cells have been given extensive attention in therapeutics due to the implications it has with the health of the central nervous system. It is essential to create an accurate BBB model in vitro in order to better understand the properties of the BBB and how it can respond to inflammatory stimulation and be passed by targeted or non-targeted cell therapeutics, more specifically extracellular vesicles.

Methods

Brain-specific pericytes (iPCs) were differentiated from iPSK3 cells using dual SMAD signaling inhibitors and Wnt activation plus fibroblast growth factor 2 (FGF-2). The derived cells were characterized by immunostaining, flow cytometry and RT-PCR. In parallel, blood vessels organoids were derived using Wnt activation, BMP4, FGF2, VEGF and SB431542. The organoids were replated and treated with retinoic acid to enhance the blood brain barrier (BBB) features in the differentiated brain endothelial cells (iECs). Co-culture was performed for the iPCs and iECs in transwell system and 3-D microfluidics channels.

Results

The derived iPCs expressed common markers PDGFRb and NG2, as well as brain-specific genes FOXF2, ABCC9, KCNJ8, and ZIC1. The derived iECs expressed common endothelial cell markers CD31, VE-cadherin, as well as BBB-associated genes BRCP, GLUT-1, PGP, ABCC1, OCLN, SLC2A1. The co-culture of the two cell types responded to the stimulation of amyloid β42 oligomers by the upregulation of expression of TNFa, IL6, NFKB, Casp3, SOD2 and TP53. The co-culture also showed the property of trans-endothelial electrical resistance. The proof-of-concept vascularization strategy was demonstrated in a 3-D microfluidics-based device.

Conclusion

The derived iPCs and iECs have brain-specific properties and the co-culture of iPCs and iECs provides an in vitro BBB model that show inflammatory response. This study has significance in establishing micro-physiological systems for neurological disease modeling and drug screening.

Glutamatergic Neurons Differentiated from Embryonic Stem Cells: An Investigation of Differentiation and Associated Diseases

Neurons that have been derived from various types of stem cells have recently undergone significant study due to their potential for use in various aspects of biomedicine. In particular, glutamatergic neurons differentiated from embryonic stem cells (ESCs) potentially have many applications in both basic research and regenerative medicine. This review summarized the literatures published thus far and focused on two areas related to these applications. Firstly, these neurons can be used to investigate neuronal signal transduction during differentiation and this means that the genes/proteins/markers involved in this process can be identified. In this way, the dynamic spatial and temporal changes associated with neuronal morphology can be investigated relatively easily. Such an in vitro system can also be used to study how neurons during neurogenesis integrate into normal tissue. At the same time, the integration, regulation and functions of extracellular matrix secretion, various molecular interactions, various ion channels, the neuronal microenvironment, etc., can be easily traced. Secondly, the disease-related aspects of ESC-derived glutamatergic neurons can also be studied and then applied therapeutically. In the future, greater efforts are needed to explore how ESC-differentiated glutamatergic neurons can be used as a neuronal model for the study of Alzheimer’s disease (AD) mechanistically, to identify possible therapeutic strategies for treating AD, including tissue replacement, and to screen for drugs that can be used to treat AD patients. With all of the modern technology that is available, translational medicine should begin to benefit patients soon.

Biogenesis of Extracellular Vesicles Produced from Human-Stem-Cell-Derived Cortical Spheroids Exposed to Iron Oxides

Stem-cell-derived extracellular vesicles (EVs) are promising tools for therapeutic delivery and imaging in the medical research fields. EVs that arise from endosomal compartments or plasma membrane budding consist of exosomes and microvesicles, which range between 30 and 200 nm and 100-1000 nm, respectively. Iron oxide nanoparticles can be used to label stem cells or possibly EVs for magnetic resonance imaging. This could be a novel way to visualize areas in the body that are affected by neurological disorders such as stroke. Human induced pluripotent stem cells (iPSK3 cells) were plated on low-attachment plates and treated with SB431542 and LDN193189 during the first week for the induction of cortical spheroid formation and grown with fibroblast growth factor 2 and cyclopamine during the second week for the neural progenitor cell (iNPC) differentiation. iNPCs were then grown on attachment plates and treated with iron oxide (Fe₃O₄) nanoparticles at different sizes (8, 15, and 30 nm in diameter) and concentrations (0.1, 10, and 100 μM). The spheroids and media collected from these cultures were used for iron oxide detection as well as EV isolation and characterizations, respectively. MTT assay demonstrated that the increased size and concentration of the iron oxide nanoparticles had little effect on the metabolic activity of iNPCs. In addition, the Live/Dead assay showed high viability in all the nanoparticle treated groups and the untreated control. The EVs isolated from these culture groups were analyzed and displayed similar or higher EV counts compared with control. The observed EV size averaged 200-250 nm, and electron microscopy revealed the expected exosome morphology for EVs from all groups. RT-PCR analysis of EV biogenesis markers (CD63, CD81, Alix, TSG101, Syntenin1, ADAM10, RAB27b, and Syndecan) showed differential expression between the iron-oxide-treated cultures and nontreated cultures, as well as between adherent and nonadherent 3D cultures. Iron oxide nanoparticles were detected inside the cortical spheroid cells but not EVs by MRI. The addition of iron oxide nanoparticles does not induce significant cytotoxic effects to cortical spheroids. In addition,, nanoparticles may stimulate the biogenesis of EVs when added to cortical spheroids in vitro.

Alix and Syntenin-1 direct amyloid precursor protein trafficking into extracellular vesicles

BACKGROUND

Endosomal trafficking and amyloidogenic cleavage of amyloid precursor protein (APP) is believed to play a role in the neurodegeneration observed in Alzheimer's disease (AD). Recent evidence has suggested that packaging and secretion of APP and its amyloidogenic cleaved products into small extracellular vesicles (EVs) may facilitate uptake of these neurotoxic factors during disease progression. However, the molecular mechanisms underlying trafficking of APP into EVs are poorly understood.

RESULTS

In this study, the mechanism and impact of APP trafficking into extracellular vesicles (EVs) were assessed by a series of inducible gene knockdowns. We demonstrate that vesicle-associated proteins Alix and Syntenin-1 are essential for proper subcellular localization and efficient EV secretion of APP via an endosomal sorting complexes required for transport (ESCRT)-independent pathway. The neurotoxic C-terminal fragment (CTFβ) of APP is similarly secreted in association with small vesicles. These mechanisms are conserved in terminally differentiated neuron-like cells. Furthermore, knockdown of Alix and Syntenin-1 alters the subcellular localization of APP, sequestering the precursor protein to endoplasmic reticulum and endolysosomal compartments, respectively. Finally, transfer of small EVs containing mutant APP confers an increase in reactive oxygen species production and neurotoxicity to human induced pluripotent stem cell-derived cortical neurons and naïve primary neurons, an effect that is ameliorated by Alix and Syntenin-1 depletion.

CONCLUSIONS

Altogether these findings elucidate a novel mechanism for understanding the intracellular trafficking of APP and CTFβ into secreted extracellular vesicles, and the resultant potential impact on neurotoxicity in the context of Alzheimer's disease amyloidopathy.

Opportunities and challenges for the use of induced pluripotent stem cells in modelling neurodegenerative disease

Adult-onset neurodegenerative diseases are among the most difficult human health conditions to model for drug development. Most genetic or toxin-induced cell and animal models cannot faithfully recapitulate pathology in disease-relevant cells, making it excessively challenging to explore the potential mechanisms underlying sporadic disease. Patient-derived induced pluripotent stem cells (iPSCs) can be differentiated into disease-relevant neurons, providing an unparalleled platform for in vitro modelling and development of therapeutic strategies. Here, we review recent progress in generating Alzheimer's, Parkinson's and Huntington's disease models from patient-derived iPSCs. We also describe novel discoveries of pathological mechanisms and drug evaluations that have used these patient iPSC-derived neuronal models. Additionally, current human iPSC technology allows researchers to model diseases with 3D brain organoids, which are more representative of tissue architecture than traditional neuronal cultures. We discuss remaining challenges and emerging opportunities for the use of three-dimensional brain organoids in modelling brain development and neurodegeneration.

Human Stem Cell-derived Aggregates of Forebrain Astroglia Respond to Amyloid Beta Oligomers

Astrocytes are vital components in neuronal circuitry and there is increasing evidence linking the dysfunction of these cells to a number of central nervous system diseases. Studying the role of these cells in human brain function in the past has been difficult due to limited access to the human brain. In this study, human induced pluripotent stem cells were differentiated into astrospheres using a hybrid plating method, with or without dual SMAD inhibition. The derived cells were assessed for astrocytic markers, brain regional identity, phagocytosis, calcium-transient signaling, reactive oxygen species production, and immune response. Neural degeneration was modeled by stimulation with amyloid-β (Aβ) 42 oligomers. Finally, co-culture was performed for the derived astrospheres with isogenic neurospheres. Results indicate that the derived astroglial cells express astrocyte markers with forebrain dorsal cortical identity, secrete extracellular matrix, and are capable of phagocytosing iron oxide particles and responding to Aβ42 stimulation (higher oxidative stress, higher TNF-α, and IL-6 expression). RNA-sequencing results reveal the distinct transcriptome of the derived cells responding to Aβ42 stimulation for astrocyte markers, chemokines, and brain regional identity. Co-culture experiments show the synaptic activities of neurons and the enhanced neural protection ability of the astroglial cells. This study provides knowledge about the roles of brain astroglial cells, heterotypic cell-cell interactions, and the formation of engineered neuronal synapses in vitro. The implications lie in neurological disease modeling, drug screening, and studying progression of neural degeneration and the role of stem cell microenvironment. Impact Statement Human pluripotent stem cell-derived astrocytes are a powerful tool for disease modeling and drug screening. However, the properties regarding brain regional identity and the immune response to neural degeneration stimulus have not been well characterized. Results of this study indicate that the derived astroglial cells express astrocyte markers with forebrain dorsal cortical identity, secrete extracellular matrix (ECM), and are capable of phagocytosing iron oxide particles and responding to amyloid-β oligomers, showing the distinct transcriptome in astrocyte markers, chemokines, and brain regional identity. This study provides knowledge about the roles of brain astroglial cells, heterotypic cell-cell interactions, and engineering neural tissues in vitro.

Wnt-Notch Signaling Interactions During Neural and Astroglial Patterning of Human Stem Cells

The human brain formation involves complicated processing, which is regulated by a gene regulatory network influenced by different signaling pathways. The cross-regulatory interactions between elements of different pathways affect the process of cell fate assignment during neural and astroglial tissue patterning. In this study, the interactions between Wnt and Notch pathways, the two major pathways that influence neural and astroglial differentiation of human induced pluripotent stem cells (hiPSCs) individually, were investigated. In particular, the synergistic effects of Wnt-Notch pathway on the neural patterning processes along the anterior-posterior or dorsal-ventral axis of hiPSC-derived cortical spheroids were explored. The human cortical spheroids derived from hiPSCs were treated with Wnt activator CHIR99021 (CHIR), Wnt inhibitor IWP4, and Notch inhibitor (N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester [DAPT]) individually, or in combinations (CHIR + DAPT, IWP4 + DAPT). The results suggest that CHIR + DAPT can promote Notch signaling, similar or higher than CHIR alone, whereas IWP4 + DAPT reduces Notch activity compared to IWP4 alone. Also, CHIR + DAPT promoted hindbrain marker HOXB4 expression more consistently than CHIR alone, while IWP4 + DAPT promoted Olig2 expression, indicating the synergistic effects distinctly different from that of the individual small molecule. In addition, IWP4 simultaneously promoted dorsal and ventral identity. The patterned neural spheroids can be switched for astroglial differentiation using bone morphogenetic protein 4. This study should advance the derivations of neurons, astroglial cells, and brain region-specific organoids from hiPSCs for disease modeling, drug screening, as well as for hiPSC-based therapies. Impact Statement Wnt signaling plays a central role in neural patterning of human pluripotent stem cells. It can interact with Notch signaling in defining dorsal-ventral and rostral-caudal (or anterior-posterior) axis of brain organoids. This study investigates novel Wnt and Notch interactions (i.e., Wntch) in neural patterning of dorsal forebrain spheroids or organoids derived from human induced pluripotent stem cells. The synergistic effects of Wnt activator or inhibitor with Notch inhibitor were observed. This study should advance the derivations of neurons, astroglial cells, and brain region-specific organoids from human stem cells for disease modeling and drug screening, as well as for stem cell-based therapies. The results can be used to establish better in vitro culture methods for efficiently mimicking in vivo structure of central nervous system.

Genomics Analysis of Metabolic Pathways of Human Stem Cell-Derived Microglia-Like Cells and the Integrated Cortical Spheroids

Brain spheroids or organoids derived from human pluripotent stem cells (hiPSCs) are still not capable of completely recapitulating in vivo human brain tissue, and one of the limitations is lack of microglia. To add built-in immune function, coculture of the dorsal forebrain spheroids with isogenic microglia-like cells (D-MG) was performed in our study. The three-dimensional D-MG spheroids were analyzed for their transcriptome and compared with isogenic microglia-like cells (MG). Cortical spheroids containing microglia-like cells displayed different metabolic programming, which may affect the associated phenotype. The expression of genes related to glycolysis and hypoxia signaling was increased in cocultured D-MG spheroids, indicating the metabolic shift to aerobic glycolysis, which is in favor of M1 polarization of microglia-like cells. In addition, the metabolic pathways and the signaling pathways involved in cell proliferation, cell death, PIK3/AKT/mTOR signaling, eukaryotic initiation factor 2 pathway, and Wnt and Notch pathways were analyzed. The results demonstrate the activation of mTOR and p53 signaling, increased expression of Notch ligands, and the repression of NF-κB and canonical Wnt pathways, as well as the lower expression of cell cycle genes in the cocultured D-MG spheroids. This analysis indicates that physiological 3-D microenvironment may reshape the immunity of in vitro cortical spheroids and better recapitulate in vivo brain tissue function for disease modeling and drug screening.

Building Complex Life Through Self-Organization

Cells are inherently conferred with the ability to self-organize into the tissues and organs comprising the human body. Self-organization can be recapitulated in vitro and recent advances in the organoid field are just one example of how we can generate small functioning elements of organs. Tissue engineers can benefit from the power of self-organization and should consider how they can harness and enhance the process with their constructs. For example, aggregates of stem cells and tissue-specific cells benefit from the input of carefully selected biomolecules to guide their differentiation toward a mature phenotype. This can be further enhanced by the use of technologies to provide a physiological microenvironment for self-organization, enhance the size of the constructs, and enable the long-term culture of self-organized structures. Of importance, conducting self-organization should be limited to fine-tuning and should avoid over-engineering that could counteract the power of inherent cellular self-organization. Impact Statement Self-organization is a powerful innate feature of cells that can be fine-tuned but not over-engineered to create new tissues and organs.

Differential Effects of Extracellular Vesicles of Lineage-Specific Human Pluripotent Stem Cells on the Cellular Behaviors of Isogenic Cortical Spheroids

Extracellular vesicles (EVs) contribute to a variety of signaling processes and the overall physiological and pathological states of stem cells and tissues. Human induced pluripotent stem cells (hiPSCs) have unique characteristics that can mimic embryonic tissue development. There is growing interest in the use of EVs derived from hiPSCs as therapeutics, biomarkers, and drug delivery vehicles. However, little is known about the characteristics of EVs secreted by hiPSCs and paracrine signaling during tissue morphogenesis and lineage specification. Methods: In this study, the physical and biological properties of EVs isolated from hiPSC-derived neural progenitors (ectoderm), hiPSC-derived cardiac cells (mesoderm), and the undifferentiated hiPSCs (healthy iPSK3 and Alzheimer’s-associated SY-UBH lines) were analyzed. Results: Nanoparticle tracking analysis and electron microscopy results indicate that hiPSC-derived EVs have an average size of 100–250 nm. Immunoblot analyses confirmed the enrichment of exosomal markers Alix, CD63, TSG101, and Hsc70 in the purified EV preparations. MicroRNAs including miR-133, miR-155, miR-221, and miR-34a were differently expressed in the EVs isolated from distinct hiPSC lineages. Treatment of cortical spheroids with hiPSC-EVs in vitro resulted in enhanced cell proliferation (indicated by BrdU+ cells) and axonal growth (indicated by β-tubulin III staining). Furthermore, hiPSC-derived EVs exhibited neural protective abilities in Aβ42 oligomer-treated cultures, enhancing cell viability and reducing oxidative stress. Our results demonstrate that the paracrine signaling provided by tissue context-dependent EVs derived from hiPSCs elicit distinct responses to impact the physiological state of cortical spheroids. Overall, this study advances our understanding of cell‒cell communication in the stem cell microenvironment and provides possible therapeutic options for treating neural degeneration.

Functionalization of Brain Region-specific Spheroids with Isogenic Microglia-like Cells

Current brain spheroids or organoids derived from human induced pluripotent stem cells (hiPSCs) still lack a microglia component, the resident immune cells in the brain. The objective of this study is to engineer brain region-specific organoids from hiPSCs incorporated with isogenic microglia-like cells in order to enhance immune function. In this study, microglia-like cells were derived from hiPSCs using a simplified protocol with stage-wise growth factor induction, which expressed several phenotypic markers, including CD11b, IBA-1, CX3CR1, and P2RY12, and phagocytosed micron-size super-paramagnetic iron oxides. The derived cells were able to upregulate pro-inflammatory gene (TNF-α) and secrete anti-inflammatory cytokines (i.e., VEGF, TGF-β1, and PGE2) when stimulated with amyloid β42 oligomers, lipopolysaccharides, or dexamethasone. The derived isogenic dorsal cortical (higher expression of TBR1 and PAX6) and ventral (higher expression of NKX2.1 and PROX1) spheroids/organoids displayed action potentials and synaptic activities. Co-culturing the microglia-like cells (MG) with the dorsal (D) or ventral (V) organoids showed differential migration ability, intracellular Ca2+ signaling, and the response to pro-inflammatory stimuli (V-MG group had higher TNF-α and TREM2 expression). Transcriptome analysis exhibited 37 microglia-related genes that were differentially expressed in MG and D-MG groups. In addition, the hybrid D-MG spheroids exhibited higher levels of immunoreceptor genes in activating members, but the MG group contained higher levels for most of genes in inhibitory members (except SIGLEC5 and CD200). This study should advance our understanding of the microglia function in brain-like tissue and establish a transformative approach to modulate cellular microenvironment toward the goal of treating various neurological disorders.

Assembly of Human Stem Cell-Derived Cortical Spheroids and Vascular Spheroids to Model 3-D Brain-like Tissues

Human cerebral organoids derived from induced pluripotent stem cells (iPSCs) provide novel tools for recapitulating the cytoarchitecture of human brain and for studying biological mechanisms of neurological disorders. However, the heterotypic interactions of neurovascular units, composed of neurons, pericytes, astrocytes, and brain microvascular endothelial cells, in brain-like tissues are less investigated. The objective of this study is to investigate the impacts of neural spheroids and vascular spheroids interactions on the regional brain-like tissue patterning in cortical spheroids derived from human iPSCs. Hybrid neurovascular spheroids were constructed by fusion of human iPSC-derived cortical neural progenitor cell (iNPC) spheroids, endothelial cell (iEC) spheroids, and the supporting human mesenchymal stem cells (MSCs). Single hybrid spheroids were constructed at different iNPC: iEC: MSC ratios of 4:2:0, 3:2:1 2:2:2, and 1:2:3 in low-attachment 96-well plates. The incorporation of MSCs upregulated the secretion levels of cytokines VEGF-A, PGE2, and TGF-β1 in hybrid spheroid system. In addition, tri-cultured spheroids had high levels of TBR1 (deep cortical layer VI) and Nkx2.1 (ventral cells), and matrix remodeling genes, MMP2 and MMP3, as well as Notch-1, indicating the crucial role of matrix remodeling and cell-cell communications on cortical spheroid and organoid patterning. Moreover, tri-culture system elevated blood-brain barrier gene expression (e.g., GLUT-1), CD31, and tight junction protein ZO1 expression. Treatment with AMD3100, a CXCR4 antagonist, showed the immobilization of MSCs during spheroid fusion, indicating a CXCR4-dependent manner of hMSC migration and homing. This forebrain-like model has potential applications in understanding heterotypic cell-cell interactions and novel drug screening in diseased human brain.

The Use of Pluripotent Stem Cell-Derived Organoids to Study Extracellular Matrix Development during Neural Degeneration

The mechanism that causes the Alzheimer's disease (AD) pathologies, including amyloid plaque, neurofibrillary tangles, and neuron death, is not well understood due to the lack of robust study models for human brain. Three-dimensional organoid systems based on human pluripotent stem cells (hPSCs) have shown a promising potential to model neurodegenerative diseases, including AD. These systems, in combination with engineering tools, allow in vitro generation of brain-like tissues that recapitulate complex cell-cell and cell-extracellular matrix (ECM) interactions. Brain ECMs play important roles in neural differentiation, proliferation, neuronal network, and AD progression. In this contribution related to brain ECMs, recent advances in modeling AD pathology and progression based on hPSC-derived neural cells, tissues, and brain organoids were reviewed and summarized. In addition, the roles of ECMs in neural differentiation of hPSCs and the influences of heparan sulfate proteoglycans, chondroitin sulfate proteoglycans, and hyaluronic acid on the progression of neurodegeneration were discussed. The advantages that use stem cell-based organoids to study neural degeneration and to investigate the effects of ECM development on the disease progression were highlighted. The contents of this article are significant for understanding cell-matrix interactions in stem cell microenvironment for treating neural degeneration.

Cell population balance of cardiovascular spheroids derived from human induced pluripotent stem cells

Stem cell-derived cardiomyocytes and vascular cells can be used for a variety of applications such as studying human heart development and modelling human disease in culture. In particular, protocols based on modulation of Wnt signaling were able to produce high quality of cardiomyocytes or vascular cells from human pluripotent stem cells (hPSCs). However, the mechanism behind the development of 3D cardiovascular spheroids into either vascular or cardiac cells has not been well explored. Hippo/Yes-associated protein (YAP) signaling plays important roles in the regulation of organogenesis, but its impact on cardiovascular differentiation has been less evaluated. In this study, the effects of seeding density and a change in YAP signaling on 3D cardiovascular spheroids patterning from hPSCs were evaluated. Compared to 2D culture, 3D cardiovascular spheroids exhibited higher levels of sarcomeric striations and higher length-to-width ratios of α-actinin⁺ cells. The spheroids with high seeding density exhibited more α-actinin⁺ cells and less nuclear YAP expression. The 3D cardiovascular spheroids were also treated with different small molecules, including Rho kinase inhibitor (Y27632), Cytochalasin D, Dasatinib, and Lysophosphatidic acid to modulate YAP localization. Nuclear YAP inhibition resulted in lower expression of active β-catenin, vascular marker, and MRTF, the transcription factor mediated by RhoGTPases. Y27632 also promoted the gene expression of MMP-2/-3 (matrix remodeling) and Notch-1 (Notch signaling). These results should help our understanding of the underlying effects for the efficient patterning of cardiovascular spheroids after mesoderm formation from hPSCs.

Differential Effects of Heparin and Hyaluronic Acid on Neural Patterning of Human Induced Pluripotent Stem Cells

A lack of well-established animal models that can efficiently represent human brain pathology has led to the development of human induced pluripotent stem cell (hiPSC)-derived brain tissues. Brain organoids have enhanced our ability to understand the developing human brain and brain disorders (e.g., Schizophrenia, microcephaly), but the organoids still do not accurately recapitulate the anatomical organization of the human brain. Therefore, it is important to evaluate and optimize induction and signaling factors in order to engineer the next generation of brain organoids. In this study, the impact of hyaluronic acid (HA), a major brain extracellular matrix (ECM) component that interacts with cells through ligand-binding receptors, on the patterning of brain organoids from hiPSCs was evaluated. To mediate HA- binding capacity of signaling molecules, heparin was added in addition to HA or conjugated to HA to form hydrogels (with two different moduli). The neural cortical spheroids derived from hiPSCs were treated with either HA or heparin plus HA (Hep- HA) and were analyzed for ECM impacts on neural patterning. The results indicate that Hep-HA has a caudalizing effect on hiPSC-derived neural spheroids, in particular for stiff Hep-HA hydrogels. Wnt and Hippo/Yes-associated protein (YAP) signaling was modulated (using Wnt inhibitor IWP4 or actin disruption agent Cytochalasin D respectively) to understand the underlying mechanism. IWP4 and cytochalasin D promote forebrain identity. The results from this study should enhance the understanding of influence of biomimetic ECM factors for brain organoid generation.

Teratogen screening with human pluripotent stem cells

Birth defects are a common occurrence in the United States and worldwide. Currently, evaluation of potential developmental toxicants (i.e., teratogens) relies heavily on animal-based models which do not always adequately mimic human development. In order to address this, researchers are developing in vitro human-based models which utilize human pluripotent stem cells (hPSCs) to assess the teratogenic potential of chemical substances. The field of human developmental toxicity assays includes a variety of platforms including monolayer, micropattern, embryoid body, and 3D organoid cultures. In this review, we will overview the field of human teratogenic assays, detail the most recent advances, and discuss current limitations and future perspectives.

Neuroprotective Activities of Heparin, Heparinase III, and Hyaluronic Acid on the Aβ42-Treated Forebrain Spheroids Derived from Human Stem Cells

Extracellular matrix (ECM) components of the brain play complex roles in neurodegenerative diseases. The study of microenvironment of brain tissues with Alzheimer's disease revealed colocalized expression of different ECM molecules such as heparan sulfate proteoglycans (HSPGs), chondroitin sulfate proteoglycans (CSPGs), matrix metal-loproteinases (MMPs), and hyaluronic acid. In this study, both cortical and hippocampal populations were generated from human-induced pluripotent stem cell-derived neural spheroids. The cultures were then treated with heparin (competes for Aβ affinity with HSPG), heparinase III (digests HSPGs), chondroitinase (digests CSPGs), hyaluronic acid, and an MMP-2/9 inhibitor (SB-3CT) together with amyloid β (Aβ42) oligomers. The results indicate that inhibition of HSPG binding to Aβ42 using either heparinase III or heparin reduces Aβ42 expression and increases the population of β-tubulin III+ neurons, whereas the inhibition of MMP2/9 induces more neurotoxicity. The results should enhance our understanding of the contribution of ECMs to the Aβ-related neural cell death.

Vascular differentiation from pluripotent stem cells in 3-D auxetic scaffolds

Auxetic scaffolds, that is, scaffolds that can display negative Poisson's ratio, have unique physical properties and can expand transversally when axially strained or contract under compression. Auxetic materials have been used for bioprostheses and artery stents due to the enhanced compressive strength and shear stiffness. In vascular tissue engineering, auxetic scaffolds allow the widening of blood vessels when blood flows through (creating compressive stress) to prevent the blockage. However, the influence of auxetic materials on the cellular fate decision in local environment is unclear. In this study, auxetic polyurethane foams were used to support vascular differentiation from pluripotent stem cells. The expression of alkaline phosphatase, Oct-4, and Nanog was lower after 4 days of differentiation for the cells grown in auxetic scaffolds. Higher expression of vascular markers CD31 and VE-cadherin was observed for the cells from auxetic scaffolds compared with those from the scaffolds before auxetic conversion. Little influence on the expression of cardiac marker α-actinin was observed. The vascular cells secreted extracellular matrix proteins vitronectin and laminin and expressed membrane-bound matrix metalloproteinase 9. The examination of Yes-associated protein expression indicated more cytoplasmic retention in the cells from auxetic scaffolds compared with those from regular scaffolds, suggesting that the auxetic scaffolds may affect cellular contraction. This study demonstrates a novel 3-D culture based on auxetic scaffolds for vascular differentiation and provides a platform to study the influence of biophysical microenvironments on differentiation of pluripotent stem cells. The outcome of this study has implications for regenerative medicine and drug discovery.

Wnt/Yes-Associated Protein Interactions During Neural Tissue Patterning of Human Induced Pluripotent Stem Cells

Human induced pluripotent stem cells (hiPSCs) have special ability to self-assemble into neural spheroids or mini-brain-like structures. During the self-assembly process, Wnt signaling plays an important role in regional patterning and establishing positional identity of hiPSC-derived neural progenitors. Recently, the role of Wnt signaling in regulating Yes-associated protein (YAP) expression (nuclear or cytoplasmic), the pivotal regulator during organ growth and tissue generation, has attracted increasing interests. However, the interactions between Wnt and YAP expression for neural lineage commitment of hiPSCs remain poorly explored. The objective of this study is to investigate the effects of Wnt signaling and YAP expression on the cellular population in three-dimensional (3D) neural spheroids derived from hiPSCs. In this study, Wnt signaling was activated using CHIR99021 for 3D neural spheroids derived from human iPSK3 cells through embryoid body formation. Our results indicate that Wnt activation induces nuclear localization of YAP and upregulates the expression of HOXB4, the marker for hindbrain/spinal cord. By contrast, the cells exhibit more rostral forebrain neural identity (expression of TBR1) without Wnt activation. Cytochalasin D was then used to induce cytoplasmic YAP and the results showed the decreased HOXB4 expression. In addition, the incorporation of microparticles in the neural spheroids was investigated for the perturbation of neural patterning. This study may indicate the bidirectional interactions of Wnt signaling and YAP expression during neural tissue patterning, which have the significance in neurological disease modeling, drug screening, and neural tissue regeneration.

Design and validation of an ontology-driven animal-free testing strategy for developmental neurotoxicity testing

Developmental neurotoxicity entails one of the most complex areas in toxicology. Animal studies provide only limited information as to human relevance. A multitude of alternative models have been developed over the years, providing insights into mechanisms of action. We give an overview of fundamental processes in neural tube formation, brain development and neural specification, aiming at illustrating complexity rather than comprehensiveness. We also give a flavor of the wealth of alternative methods in this area. Given the impressive progress in mechanistic knowledge of human biology and toxicology, the time is right for a conceptual approach for designing testing strategies that cover the integral mechanistic landscape of developmental neurotoxicity. The ontology approach provides a framework for defining this landscape, upon which an integral in silico model for predicting toxicity can be built. It subsequently directs the selection of in vitro assays for rate-limiting events in the biological network, to feed parameter tuning in the model, leading to prediction of the toxicological outcome. Validation of such models requires primary attention to coverage of the biological domain, rather than classical predictive value of individual tests. Proofs of concept for such an approach are already available. The challenge is in mining modern biology, toxicology and chemical information to feed intelligent designs, which will define testing strategies for neurodevelopmental toxicity testing.

Modeling Neurodegenerative Microenvironment Using Cortical Organoids Derived from Human Stem Cells

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders and causes cognitive impairment and memory deficits of the patients. The mechanism of AD is not well known, due to lack of human brain models. Recently, mini-brain tissues called organoids have been derived from human induced pluripotent stem cells (hiPSCs) for modeling human brain development and neurological diseases. Thus, the objective of this research is to model and characterize neural degeneration microenvironment using three-dimensional (3D) forebrain cortical organoids derived from hiPSCs and study the response to the drug treatment. It is hypothesized that the 3D forebrain organoids derived from hiPSCs with AD-associated genetic background may partially recapitulate the extracellular microenvironment in neural degeneration. To test this hypothesis, AD-patient derived hiPSCs with presenilin-1 mutation were used for cortical organoid generation. AD-related inflammatory responses, matrix remodeling and the responses to DAPT, heparin (completes with heparan sulfate proteoglycans [HSPGs] to bind Aβ42), and heparinase (digests HSPGs) treatments were investigated. The results indicate that the cortical organoids derived from AD-associated hiPSCs exhibit a high level of Aβ42 comparing with healthy control. In addition, the AD-derived organoids result in an elevated gene expression of proinflammatory cytokines interleukin-6 and tumor necrosis factor-α, upregulate syndecan-3, and alter matrix remodeling protein expression. Our study demonstrates the capacity of hiPSC-derived organoids for modeling the changes of extracellular microenvironment and provides a potential approach for AD-related drug screening.

Effect of leukocyte inhibitory factor on neuron differentiation from human induced pluripotent stem cell-derived neural precursor cells

Direct derivation of human induced pluripotent stem cells into neural precursor cells and differentiation of these into neurons holds great promise in the cell therapy of neuro-degenerative diseases. However, the availability and survival rate of neurons requires improvement. In the present study, it was found that the addition of 5 ng/ml leukocyte inhibitory factor (LIF) during the process of differentiation significantly improved the expression of neuron-specific class III β-tubulin (TUJ1) and microtubule-associated protein 2 (MAP2), as detected by immunofluorescence and western blotting. In addition, LIF improved the cell viability, increased the expression of phosphorylated-protein kinase B (AKT), downregulated the expression of proinflammatory cytokines, including interleukin-1α (IL-1α) and tumor necrosis factor-α (TNF-α), and upregulated the expression of anti-inflammatory cytokines, including interleukin-10 (IL-10) and transforming growth factor-β (TGF-β). After adding the phosphatidylinositol 3-kinase (PI3K)/AKT signaling inhibitor LY294002 or wortmannin to the LIF differentiation group, LIF-induced changes in the protein expression of TUJ1 and MAP2 were reversed, but this effect could not be prevented by rapamycin, a mechanistic target of rapamycin signaling inhibitor. The expression of cytokines associated with inflammation and cell viability was reversed by LY294002 and wortmannin, but not by rapamycin. In conclusion, LIF could improve neuronal differentiation and survival through the activation of PI3K/AKT signaling and the anti-inflammatory effect. The anti-inflammatory effect may be mediated by the activation of PI3K/AKT.

Neural Differentiation of Spheroids Derived from Human Induced Pluripotent Stem Cells-Mesenchymal Stem Cells Coculture

Organoids, the condensed three-dimensional (3D) tissues emerged at the early stage of organogenesis, are a promising approach to regenerate functional and vascularized organ mimics. While incorporation of heterotypic cell types, such as human mesenchymal stem cells (hMSCs) and human induced pluripotent stem cells (hiPSCs)-derived neural progenitors aid neural organ development, the interactions of secreted factors during neurogenesis have not been well understood. The objective of this study is to investigate the impact of the composition and structure of 3D hybrid spheroids of hiPSCs and hMSCs on dorsal cortical differentiation and the secretion of extracellular matrices and trophic factors in vitro. The hybrid spheroids were formed at different hiPSC:hMSC ratios (100:0, 75:25, 50:50, 25:75, 0:100) using direct mixing or pre-hiPSC aggregation method, which generated dynamic spheroid structure. The cellular organization, proliferation, neural marker expression, and the secretion of extracellular matrix proteins and the cytokines were characterized. The incorporation of MSCs upregulated Nestin and β-tubulin III expression (the dorsal cortical identity was shown by Pax6 and TBR1 expression), matrix remodeling proteins, and the secretion of transforming growth factor-β1 and prostaglandin E2. This study indicates that the appropriate composition and structure of hiPSC-MSC spheroids promote neural differentiation and trophic factor and matrix secretion due to the heterotypic cell-cell interactions.

Derivation of Cortical Spheroids from Human Induced Pluripotent Stem Cells in a Suspension Bioreactor

Human induced pluripotent stem cells (hiPSCs) emerge as a promising source to construct human brain-like tissues, spheroids, or organoids in vitro for disease modeling and drug screening. A suspension bioreactor can be used to generate large size of brain organoids from hiPSCs through enhanced diffusion, but the influence of a dynamic bioreactor culture environment on neural tissue patterning from hiPSCs has not been well understood. The objective of this study is to assess the influence of a suspension bioreactor culture on cortical spheroid (i.e., forebrain-like aggregates) formation from hiPSCs. Single undifferentiated hiPSK3 cells or preformed embryoid bodies were inoculated into the bioreactor. Aggregate size distribution, neural marker expression (e.g., Nestin, PAX6, β-tubulin III, and MAP-2), and cortical tissue patterning markers (e.g., TBR1, BRN2, SATB2, and vGlut1) were evaluated with static control. Bioreactor culture was found to promote the expression of TBR1, a deep cortical layer VI marker, and temporally affect SATB2, a superficial cortical layer II-IV marker that appears later according to inside-out cortical tissue development. Prolonged culture after 70 days showed layer-specific cortical structure in the spheroids. Differential expression of matrix metalloproteinase-2 and -3 was also observed for bioreactor and static culture. The altered expression of cortical markers by a suspension bioreactor indicates the importance of culture environment on cortical tissue development from hiPSCs.

Pluripotent stem cell expansion and neural differentiation in 3-D scaffolds of tunable Poisson's ratio

Biophysical properties of the scaffolds such as the elastic modulus, have been recently shown to impact stem cell lineage commitment. On the other hand, the contribution of the Poisson's ratio, another important biophysical property, to the stem cell fate decision, has not been studied. Scaffolds with tunable Poisson's ratio (ν) (termed as auxetic scaffolds when Poisson's ratio is zero or negative) are anticipated to provide a spectrum of unique biophysical 3-D microenvironments to influence stem cell fate. To test this hypothesis, in the present work we fabricated auxetic polyurethane scaffolds (ν=0 to -0.45) and evaluated their effects on neural differentiation of mouse embryonic stem cells (ESCs) and human induced pluripotent stem cells (hiPSCs). Compared to the regular scaffolds (ν=+0.30) before auxetic conversion, the auxetic scaffolds supported smaller aggregate formation and higher expression of β-tubulin III upon neural differentiation. The influences of pore structure, Poisson's ratio, and elastic modulus on neural lineage commitment were further evaluated using a series of auxetic scaffolds. The results indicate that Poisson's ratio may confound the effects of elastic modulus, and auxetic scaffolds with proper pore structure and Poisson's ratio enhance neural differentiation. This study demonstrates that tuning the Poisson's ratio of the scaffolds together with elastic modulus and microstructure would enhance the capability to generate broader, more diversified ranges of biophysical 3-D microenvironments for the modulation of cellular differentiation.

STATEMENT OF SIGNIFICANCE

Biophysical signaling from the substrates and scaffolds plays a critical role in neural lineage commitment of pluripotent stem cells. While the contribution of elastic modulus has been well studied, the influence of Poisson's ratio along with microstructure of the scaffolds remains unknown largely due to the lack of technology to produce materials with tailorable Poisson's ratio. This study fabricated auxetic polyurethane scaffolds with different elastic modulus, Poisson's ratio and microstructure and evaluated neural differentiation of pluripotent stem cells. The findings add a novel angle to understand the impact of biophysical microenvironment on stem cell fate decisions.