Bioengineering toolkits for potentiating organoid therapeutics

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

Versatile human cardiac tissues engineered with perfusable heart extracellular microenvironment for biomedical applications

Engineered human cardiac tissues have been utilized for various biomedical applications, including drug testing, disease modeling, and regenerative medicine. However, the applications of cardiac tissues derived from human pluripotent stem cells are often limited due to their immaturity and lack of functionality. Therefore, in this study, we establish a perfusable culture system based on in vivo-like heart microenvironments to improve human cardiac tissue fabrication. The integrated culture platform of a microfluidic chip and a three-dimensional heart extracellular matrix enhances human cardiac tissue development and their structural and functional maturation. These tissues are comprised of cardiovascular lineage cells, including cardiomyocytes and cardiac fibroblasts derived from human induced pluripotent stem cells, as well as vascular endothelial cells. The resultant macroscale human cardiac tissues exhibit improved efficacy in drug testing (small molecules with various levels of arrhythmia risk), disease modeling (Long QT Syndrome and cardiac fibrosis), and regenerative therapy (myocardial infarction treatment). Therefore, our culture system can serve as a highly effective tissue-engineering platform to provide human cardiac tissues for versatile biomedical applications.

Magneto-acoustic protein nanostructures for non-invasive imaging of tissue mechanics in vivo

Measuring cellular and tissue mechanics inside intact living organisms is essential for interrogating the roles of force in physiological and disease processes. Current agents for studying the mechanobiology of intact, living organisms are limited by poor light penetration and material stability. Magnetomotive ultrasound is an emerging modality for real-time in vivo imaging of tissue mechanics. Nonetheless, it has poor sensitivity and spatiotemporal resolution. Here we describe magneto-gas vesicles (MGVs), protein nanostructures based on gas vesicles and magnetic nanoparticles that produce differential ultrasound signals in response to varying mechanical properties of surrounding tissues. These hybrid nanomaterials significantly improve signal strength and detection sensitivity. Furthermore, MGVs enable non-invasive, long-term and quantitative measurements of mechanical properties within three-dimensional tissues and in vivo fibrosis models. Using MGVs as novel contrast agents, we demonstrate their potential for non-invasive imaging of tissue elasticity, offering insights into mechanobiology and its application to disease diagnosis and treatment.

Decellularized heart extracellular matrix alleviates activation of hiPSC-derived cardiac fibroblasts

Human induced pluripotent stem cell derived cardiac fibroblasts (hiPSC-CFs) play a critical role in modeling human cardiovascular diseases in vitro. However, current culture substrates used for hiPSC-CF differentiation and expansion, such as Matrigel and tissue culture plastic (TCPs), are tissue mismatched and may provide pathogenic cues. Here, we report that hiPSC-CFs differentiated on Matrigel and expanded on tissue culture plastic (M-TCP-iCFs) exhibit transcriptomic hallmarks of activated fibroblasts limiting their translational potential. To alleviate pathogenic activation of hiPSC-CFs, we utilized decellularized extracellular matrix derived from porcine heart extracellular matrix (HEM) to provide a biomimetic substrate for improving hiPSC-CF phenotypes. We show that hiPSC-CFs differentiated and expanded on HEM (HEM-iCFs) exhibited reduced expression of hallmark activated fibroblast markers versus M-TCP-iCFs while retaining their cardiac fibroblast phenotype. HEM-iCFs also maintained a reduction in expression of hallmark genes associated with pathogenic fibroblasts when seeded onto TCPs. Further, HEM-iCFs more homogenously integrated into an hiPSC-derived cardiac organoid model, resulting in improved cardiomyocyte sarcomere development. In conclusion, HEM provides an improved substrate for the differentiation and propagation of hiPSC-CFs for disease modeling.

Advanced lung organoids for respiratory system and pulmonary disease modeling

Amidst the recent coronavirus disease 2019 (COVID-19) pandemic, respiratory system research has made remarkable progress, particularly focusing on infectious diseases. Lung organoid, a miniaturized structure recapitulating lung tissue, has gained global attention because of its advantages over other conventional models such as two-dimensional (2D) cell models and animal models. Nevertheless, lung organoids still face limitations concerning heterogeneity, complexity, and maturity compared to the native lung tissue. To address these limitations, researchers have employed co-culture methods with various cell types including endothelial cells, mesenchymal cells, and immune cells, and incorporated bioengineering platforms such as air-liquid interfaces, microfluidic chips, and functional hydrogels. These advancements have facilitated applications of lung organoids to studies of pulmonary diseases, providing insights into disease mechanisms and potential treatments. This review introduces recent progress in the production methods of lung organoids, strategies for improving maturity, functionality, and complexity of organoids, and their application in disease modeling, including respiratory infection and pulmonary fibrosis.

Predicting response to anti-EGFR antibody, cetuximab, therapy by monitoring receptor internalization and degradation

Anti-epidermal growth factor receptor (EGFR) antibody, cetuximab, therapy has significantly improved the clinical outcomes of patients with colorectal cancer, but the response to cetuximab can vary widely among individuals. We thus need strategies for predicting the response to this therapy. However, the current methods are unsatisfactory in their predictive power. Cetuximab can promote the internalization and degradation of EGFR, and its therapeutic efficacy is significantly correlated with the degree of EGFR degradation. Here, we present a new approach to predict the response to anti-EGFR therapy, cetuximab by evaluating the degree of EGFR internalization and degradation of colorectal cancer cells in vitro and in vivo. Our newly developed fluorogenic cetuximab-conjugated probe (Cetux-probe) was confirmed to undergo EGFR binding, internalization, and lysosomal degradation to yield fluorescence activation; it thus shares the action mechanism by which cetuximab exerts its anti-tumor effects. Cetux-probe-activated fluorescence could be used to gauge EGFR degradation and showed a strong linear correlation with the cytotoxicity of cetuximab in colorectal cancer cells and tumor-bearing mice. The predictive ability of Cetux-probe-activated fluorescence was much higher than those of EGFR expression or KRAS mutation status. The Cetux-probes may become useful tools for predicting the response to cetuximab therapy by assessing EGFR degradation.

In situbiosensing technologies for an organ-on-a-chip

Thein vitrosimulation of organs resolves the accuracy, ethical, and cost challenges accompanyingin vivoexperiments. Organoids and organs-on-chips have been developed to model thein vitro, real-time biological and physiological features of organs. Numerous studies have deployed these systems to assess thein vitro, real-time responses of an organ to external stimuli. Particularly, organs-on-chips can be most efficiently employed in pharmaceutical drug development to predict the responses of organs before approving such drugs. Furthermore, multi-organ-on-a-chip systems facilitate the close representations of thein vivoenvironment. In this review, we discuss the biosensing technology that facilitates thein situ, real-time measurements of organ responses as readouts on organ-on-a-chip systems, including multi-organ models. Notably, a human-on-a-chip system integrated with automated multi-sensing will be established by further advancing the development of chips, as well as their assessment techniques.

Adhesive Hydrogel Patch-Mediated Combination Drug Therapy Induces Regenerative Wound Healing through Reconstruction of Regenerative Microenvironment

Regenerative wound healing involves the scarless wound healing as observed in fetal skin. Multiple features of regenerative wound healing have been well studied; however, the practical application of pro-regenerative materials to recapitulate the regenerative wound healing in adult skins has not yet been achieved. In this study, the authors identified that their novel pro-regenerative material, pyrogallol-functionalized hyaluronic acid (HA-PG) patches in combination with protein transduction domain-fused Dishevelled (Dvl)-binding motif (PTD-DBM), a peptide inhibiting the CXXC-type zinc finger protein 5 (CXXC5)-Dvl interaction, promoted regenerative wound healing in mice. The HA-PG patches loaded with this competitor peptide and valproic acid (VPA), a glycogen synthase kinase 3β (GSK3β) inhibitor, significantly inhibited scar formation during wound healing. The HA-PG patches with PTD-DBM and/or VPA inhibit the expression of differentiated cell markers such as α-smooth muscle actin (α-SMA) while inducing the expression of stem cell markers such as CD105 and Nestin. Moreover, Collagen III, an important factor for regenerative healing, is critically induced by the HA-PG patches with PTD-DBM and/or VPA, as also seen in VPA-treated Cxxc5-/- mouse fibroblasts. Overall, these findings suggest that the novel regeneration-promoting material can be utilized as a potential therapeutic agent to promote both wound healing and scar attenuation.

Ferritin Nanoshuttle for Long-Lasting Self-Healing of Phenolic Hydrogels

Herein, we highlight a novel finding that ferritin can play a crucial role in the "self-healing lifetime" of soft phenolic materials. Ferritin interacts with a catechol-functionalized polymer to form a self-healable and adhesive hydrogel bidirectionally by providing and retrieving Fe³⁺. As a result of its unique role as a nanoshuttle to store and release iron, ferritin significantly increases the self-healing lifetime of the hydrogel compared with that afforded by catechol-Fe³⁺ coordination through direct Fe³⁺ addition without ferritin. Ferritin also induces stable oxidative coupling between catechol moieties following metal coordination, which contributes to double cross-linking networks of catechol-catechol adducts and catechol-Fe³⁺ coordination. Thus, ferritin-mediated cross-linking can provide phenolic hydrogels with the advantages of hydrogels prepared by both metal coordination and oxidative coupling, thereby overcoming the limitations of the current cross-linking methods of phenolic hydrogels and broadening their versatility in biomedical applications.

3D printing of mechanically tough and self-healing hydrogels with carbon nanotube fillers

Hydrogels have the potential to play a crucial role in bioelectronics, as they share many properties with human tissues. However, to effectively bridge the gap between electronics and biological systems, hydrogels must possess multiple functionalities, including toughness, stretchability, self-healing ability, three-dimensional (3D) printability, and electrical conductivity. Fabricating such tough and self-healing materials has been reported, but it still remains a challenge to fulfill all of those features, and in particular, 3D printing of hydrogel is in the early stage of the research. In this paper, we present a 3D printable, tough, and self-healing multi-functional hydrogel in one platform made from a blend of poly(vinyl alcohol) (PVA), tannic acid (TA), and poly(acrylic acid) (PAA) hydrogel ink (PVA/TA/PAA hydrogel ink). Based on a reversible hydrogen-bond (H-bond)-based double network, the developed 3D printable hydrogel ink showed excellent printability via shear-thinning behavior, allowing high printing resolution (~100 μm) and successful fabrication of 3D-printed structure by layer-by-layer printing. Moreover, the PVA/TA/PAA hydrogel ink exhibited high toughness (tensile loading of up to ~45.6 kPa), stretchability (elongation of approximately 650%), tissue-like Young's modulus (~15 kPa), and self-healing ability within 5 min. Furthermore, carbon nanotube (CNT) fillers were successfully added to enhance the electrical conductivity of the hydrogel. We confirmed the practicality of the hydrogel inks for bioelectronics by demonstrating biocompatibility, tissue adhesiveness, and strain sensing ability through PVA/TA/PAA/CNT hydrogel ink.

Engineered human cardiac tissues for modeling heart diseases

Heart disease is one of the major life-threatening diseases with high mortality and incidence worldwide. Several model systems, such as primary cells and animals, have been used to understand heart diseases and establish appropriate treatments. However, they have limitations in accuracy and reproducibility in recapitulating disease pathophysiology and evaluating drug responses. In recent years, three-dimensional (3D) cardiac tissue models produced using tissue engineering technology and human cells have outperformed conventional models. In particular, the integration of cell reprogramming techniques with bioengineering platforms (e.g., microfluidics, scaffolds, bioprinting, and biophysical stimuli) has facilitated the development of heart-ona- chip, cardiac spheroid/organoid, and engineered heart tissue (EHT) to recapitulate the structural and functional features of the native human heart. These cardiac models have improved heart disease modeling and toxicological evaluation. In this review, we summarize the cell types for the fabrication of cardiac tissue models, introduce diverse 3D human cardiac tissue models, and discuss the strategies to enhance their complexity and maturity. Finally, recent studies in the modeling of various heart diseases are reviewed. [BMB Reports 2023; 56(1): 32-42].

Recent Advances in Brain Organoid Technology for Human Brain Research

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

Engineered human cardiac tissues for modeling heart diseases

Heart disease is one of the major life-threatening diseases with high mortality and incidence worldwide. Several model systems, such as primary cells and animals, have been used to understand heart diseases and establish appropriate treatments. However, they have limitations in accuracy and reproducibility in recapitulating disease pathophysiology and evaluating drug responses. In recent years, three-dimensional (3D) cardiac tissue models produced using tissue engineering technology and human cells have outperformed conventional models. In particular, the integration of cell reprogramming techniques with bioengineering platforms (e.g., microfluidics, scaffolds, bioprinting, and biophysical stimuli) has facilitated the development of heart-ona- chip, cardiac spheroid/organoid, and engineered heart tissue (EHT) to recapitulate the structural and functional features of the native human heart. These cardiac models have improved heart disease modeling and toxicological evaluation. In this review, we summarize the cell types for the fabrication of cardiac tissue models, introduce diverse 3D human cardiac tissue models, and discuss the strategies to enhance their complexity and maturity. Finally, recent studies in the modeling of various heart diseases are reviewed. [BMB Reports 2023; 56(1): 32-42].

Three-dimensional heart extracellular matrix enhances chemically induced direct cardiac reprogramming

Direct cardiac reprogramming has emerged as a promising therapeutic approach for cardiac regeneration. Full chemical reprogramming with small molecules to generate cardiomyocytes may be more amenable than genetic reprogramming for clinical applications as it avoids safety concerns associated with genetic manipulations. However, challenges remain regarding low conversion efficiency and incomplete cardiomyocyte maturation. Furthermore, the therapeutic potential of chemically induced cardiomyocytes (CiCMs) has not been investigated. Here, we report that a three-dimensional microenvironment reconstituted with decellularized heart extracellular matrix can enhance chemical reprogramming and cardiac maturation of fibroblasts to cardiomyocytes. The resultant CiCMs exhibit elevated cardiac marker expression, sarcomeric organization, and improved electrophysiological features and drug responses. We investigated the therapeutic potential of CiCMs reprogrammed in three-dimensional heart extracellular matrix in a rat model of myocardial infarction. Our platform can facilitate the use of CiCMs for regenerative medicine, disease modeling, and drug screening.

Photoswitchable Microgels for Dynamic Macrophage Modulation

Dynamic manipulation of supramolecular self-assembled structures is achieved irreversibly or under non-physiological conditions, thereby limiting their biomedical, environmental, and catalysis applicability. In this study, microgels composed of azobenzene derivatives stacked via π-cation and π-π interactions are developed that are electrostatically stabilized with Arg-Gly-Asp (RGD)-bearing anionic polymers. Lateral swelling of RGD-bearing microgels occurs via cis-azobenzene formation mediated by near-infrared-light-upconverted ultraviolet light, which disrupts intermolecular interactions on the visible-light-absorbing upconversion-nanoparticle-coated materials. Real-time imaging and molecular dynamics simulations demonstrate the deswelling of RGD-bearing microgels via visible-light-mediated trans-azobenzene formation. Near-infrared light can induce in situ swelling of RGD-bearing microgels to increase RGD availability and trigger release of loaded interleukin-4, which facilitates the adhesion structure assembly linked with pro-regenerative polarization of host macrophages. In contrast, visible light can induce deswelling of RGD-bearing microgels to decrease RGD availability that suppresses macrophage adhesion that yields pro-inflammatory polarization. These microgels exhibit high stability and non-toxicity. Versatile use of ligands and protein delivery can offer cytocompatible and photoswitchable manipulability of diverse host cells.

Multimodal Characterization of Cardiac Organoids Using Integrations of Pressure-Sensitive Transistor Arrays with Three-Dimensional Liquid Metal Electrodes

Herein, we present an unconventional method for multimodal characterization of three-dimensional cardiac organoids. This method can monitor and control the mechanophysiological parameters of organoids within a single device. In this method, local pressure distributions of human-induced pluripotent stem-cell-derived cardiac organoids are visualized spatiotemporally by an active-matrix array of pressure-sensitive transistors. This array is integrated with three-dimensional electrodes formed by the high-resolution printing of liquid metal. These liquid-metal electrodes are inserted inside an organoid to form the intraorganoid interface for simultaneous electrophysiological recording and stimulation. The low mechanical modulus and low impedance of the liquid-metal electrodes are compatible with organoids' soft biological tissue, which enables stable electric pacing at low thresholds. In contrast to conventional electrophysiological methods, this measurement of a cardiac organoid's beating pressures enabled simultaneous treatment of electrical therapeutics using a single device without any interference between the pressure signals and electrical pulses from pacing electrodes, even in wet organoid conditions.

pH-Universal Catechol-Amine Chemistry for Versatile Hyaluronic Acid Bioadhesives

Catechol, a major mussel-inspired underwater adhesive moiety, has been used to develop functional adhesive hydrogels for biomedical applications. However, oxidative catechol chemistry for interpolymer crosslinking and adhesion is exclusively effective under alkaline conditions, with limited applications in non-alkaline conditions. To overcome this limitation, pH-universal catechol-amine chemistry to recapitulate naturally occurring biochemical events induced by pH variation in the mussel foot is suggested. Aldehyde moieties are introduced to hyaluronic acid (HA) by partial oxidation, which enables dual-mode catechol tethering to the HA via both stable amide and reactive secondary amine bonds. Because of the presence of additional reactive amine groups, the resultant aldehyde-modified HA conjugated with catechol (AH-CA) is effectively crosslinked in acidic and neutral pH conditions. The AH-CA hydrogel exhibits not only fast gelation via active crosslinking regardless of pH conditions, but also strong adhesion and excellent biocompatibility. The hydrogel enables rapid and robust wound sealing and hemostasis in neutral and alkaline conditions. The hydrogel also mediates effective therapeutic stem cell and drug delivery even in dynamic and harsh environments, such as a motile heart and acidic stomach. Therefore, the AH-CA hydrogel can serve as a versatile biomaterial in a wide range of pH conditions in vivo.

In situ diagnosis and simultaneous treatment of cardiac diseases using a single-device platform

The in situ diagnosis of cardiac activities with simultaneous therapeutic electrical stimulation of the heart is key to preventing cardiac arrhythmia. Here, we present an unconventional single-device platform that enables in situ monitoring even in a wet condition and control of beating heart motions without interferences to the recording signal. This platform consists of the active-matrix array of pressure-sensitive transistors for detecting cardiac beatings, biocompatible, low-impedance electrodes for cardiac stimulations, and an alginate-based hydrogel adhesive for attaching this platform conformally to the epicardium. In contrast to conventional electrophysiological sensing using electrodes, the pressure-sensitive transistors measured mechanophysiological characteristics by monitoring the spatiotemporal distributions of cardiac pressures during heart beating motions. In vivo tests show mechanophysiological readings having good correlation with electrocardiography and negligible interference with the electrical artifacts caused during cardiac stimulations. This platform can therapeutically synchronize the rhythm of abnormal heartbeats through efficient pacing of cardiac arrhythmia.

In situ microenvironment remodeling using a dual-responsive system: photodegradable hydrogels and gene activation by visible light

A 3D microenvironment with dynamic cell-biomaterial interactions was developed using a dual-responsive system for in situ microenvironment remodeling and control of cellular function. A visible-light-responsive polymer was utilized to prepare a hydrogel with photodegradation properties, enabling in situ microenvironment remodeling. Additionally, a vascular endothelial growth factor (VEGF) gene activation unit that was responsive to the same wavelength of light was incorporated to support the potential application of the system in regenerative medicine. Following light exposure, the mechanical properties of the photodegradable hydrogel gradually deteriorated, and product analysis confirmed the degradation of the hydrogel, and thereby, 3D microenvironment remodeling. In situ microenvironment remodeling influenced stem cell proliferation and enlargement within the hydrogel. Furthermore, stem cells engineered to express light-activated VEGF and incorporated into the dual-responsive system were applied to wound healing and an ischemic hindlimb model, proving their potential application in regenerative medicine.

Blood-brain barrier-on-a-chip for brain disease modeling and drug testing

The blood-brain barrier (BBB) is an interface between cerebral blood and the brain parenchyma. As a gate keeper, BBB regulates passage of nutrients and exogeneous compounds. Owing to this highly selective barrier, many drugs targeting brain diseases are not likely to pass through the BBB. Thus, a large amount of time and cost have been paid for the development of BBB targeted therapeutics. However, many drugs validated in in vitro models and animal models have failed in clinical trials primarily due to the lack of an appropriate BBB model. Human BBB has a unique cellular architecture. Different physiologies between human and animal BBB hinder the prediction of drug responses. Therefore, a more physiologically relevant alternative BBB model needs to be developed. In this review, we summarize major features of human BBB and current BBB models and describe organ-on-chip models for BBB modeling and their applications in neurological complications.

Blood-brain barrier-on-a-chip for brain disease modeling and drug testing

The blood-brain barrier (BBB) is an interface between cerebral blood and the brain parenchyma. As a gate keeper, BBB regulates passage of nutrients and exogeneous compounds. Owing to this highly selective barrier, many drugs targeting brain diseases are not likely to pass through the BBB. Thus, a large amount of time and cost have been paid for the development of BBB targeted therapeutics. However, many drugs validated in in vitro models and animal models have failed in clinical trials primarily due to the lack of an appropriate BBB model. Human BBB has a unique cellular architecture. Different physiologies between human and animal BBB hinder the prediction of drug responses. Therefore, a more physiologically relevant alternative BBB model needs to be developed. In this review, we summarize major features of human BBB and current BBB models and describe organ-on-chip models for BBB modeling and their applications in neurological complications. [BMB Reports 2022; 55(5): 213-219].

Hybrid skin chips for toxicological evaluation of chemical drugs and cosmetic compounds

Development of drugs and cosmetics for topical application require safety tests in skin models. However, current skin models, such as skin cell sheets and artificial tissue-engineered skin, do not allow sophisticated toxicological evaluations (e.g., sensory irritation, hepatotoxicity). Animal models are prohibited worldwide for testing cosmetics. Therefore, reliable human skin models that recapitulate physiological events in skin tissue need to be established under in vitro settings. In this study, hybrid human skin models that enable delicate toxicological evaluations of drugs and cosmetic compounds are demonstrated. To recapitulate skin cornification, keratinocytes in the top layer of a vertical microfluidic chip were cultured at the air-liquid interface. For the skin-nerve hybrid model, differentiated neural stem cells in 3D collagen were positioned adjacent to and right below the skin layer. This model enables real-time quantitative skin sensitization analysis following chemical treatments by detecting alterations in neuronal activity in combination with a calcium imaging technique. For the skin-liver model, hepatic cells derived from pluripotent stem cells were cultured in 3D collagen distant from the skin layer. Potential hepatotoxicity of cutaneously applied chemicals in this model can be evaluated by quantification of glutathione and reactive oxygen species. Our study suggests that 3D hybrid skin chips would provide useful human skin models in pharmaceutical and cosmetic industries.

Organoid engineering with microfluidics and biomaterials for liver, lung disease, and cancer modeling

As life expectancy improves and the number of people suffering from various diseases increases, the need for developing effective personalized disease models is rapidly rising. The development of organoid technology has led to better recapitulation of the in vivo environment of organs, and can overcome the constraints of existing disease models. However, for more precise disease modeling, engineering approaches such as microfluidics and biomaterials, that aid in mimicking human physiology, need to be integrated with the organoid models. In this review, we introduce key elements for disease modeling and recent engineering advances using both liver and lung organoids. Due to the importance of personalized medicine, we also emphasize patient-derived cancer organoid models and their engineering approaches. These organoid-based disease models combined with microfluidics, biomaterials, and co-culture systems will provide a powerful research platform for understanding disease mechanisms and developing precision medicine; enabling preclinical drug screening and drug development. STATEMENT OF SIGNIFICANCE: The development of organoid technology has led to better recapitulation of the in vivo environment of organs, and can overcome the constraints of existing disease models. However, for more precise disease modeling, engineering approaches such as microfluidics and biomaterials, that aid in mimicking human physiology, need to be integrated with the organoid models. In this review, we introduce liver, lung, and cancer organoids integrated with various engineering approaches as a novel platform for personalized disease modeling. These engineered organoid-based disease models will provide a powerful research platform for understanding disease mechanisms and developing precision medicine.

Bioengineering platforms for cell therapeutics derived from pluripotent and direct reprogramming

Pluripotent and direct reprogramming technologies hold great potential for tissue repair and restoration of tissue and organ function. The implementation of induced pluripotent stem cells and directly reprogrammed cells in biomedical research has resulted in a significant leap forward in the highly promising area of regenerative medicine. While these therapeutic strategies are promising, there are several obstacles to overcome prior to the introduction of these therapies into clinical settings. Bioengineering technologies, such as biomaterials, bioprinting, microfluidic devices, and biostimulatory systems, can enhance cell viability, differentiation, and function, in turn the efficacy of cell therapeutics generated via pluripotent and direct reprogramming. Therefore, cellular reprogramming technologies, in combination with tissue-engineering platforms, are poised to overcome current bottlenecks associated with cell-based therapies and create new ways of producing engineered tissue substitutes.

Odderon Exchange from Elastic Scattering Differences between pp and pp[over ¯] Data at 1.96 TeV and from pp Forward Scattering Measurements

We describe an analysis comparing the pp[over ¯] elastic cross section as measured by the D0 Collaboration at a center-of-mass energy of 1.96 TeV to that in pp collisions as measured by the TOTEM Collaboration at 2.76, 7, 8, and 13 TeV using a model-independent approach. The TOTEM cross sections, extrapolated to a center-of-mass energy of sqrt[s]=1.96  TeV, are compared with the D0 measurement in the region of the diffractive minimum and the second maximum of the pp cross section. The two data sets disagree at the 3.4σ level and thus provide evidence for the t-channel exchange of a colorless, C-odd gluonic compound, also known as the odderon. We combine these results with a TOTEM analysis of the same C-odd exchange based on the total cross section and the ratio of the real to imaginary parts of the forward elastic strong interaction scattering amplitude in pp scattering for which the significance is between 3.4σ and 4.6σ. The combined significance is larger than 5σ and is interpreted as the first observation of the exchange of a colorless, C-odd gluonic compound.

Microfluidic device with brain extracellular matrix promotes structural and functional maturation of human brain organoids

Brain organoids derived from human pluripotent stem cells provide a highly valuable in vitro model to recapitulate human brain development and neurological diseases. However, the current systems for brain organoid culture require further improvement for the reliable production of high-quality organoids. Here, we demonstrate two engineering elements to improve human brain organoid culture, (1) a human brain extracellular matrix to provide brain-specific cues and (2) a microfluidic device with periodic flow to improve the survival and reduce the variability of organoids. A three-dimensional culture modified with brain extracellular matrix significantly enhanced neurogenesis in developing brain organoids from human induced pluripotent stem cells. Cortical layer development, volumetric augmentation, and electrophysiological function of human brain organoids were further improved in a reproducible manner by dynamic culture in microfluidic chamber devices. Our engineering concept of reconstituting brain-mimetic microenvironments facilitates the development of a reliable culture platform for brain organoids, enabling effective modeling and drug development for human brain diseases.

Fungal brain infection modelled in a human-neurovascular-unit-on-a-chip with a functional blood-brain barrier

The neurovascular unit, which consists of vascular cells surrounded by astrocytic end-feet and neurons, controls cerebral blood flow and the permeability of the blood-brain barrier (BBB) to maintain homeostasis in the neuronal milieu. Studying how some pathogens and drugs can penetrate the human BBB and disrupt neuronal homeostasis requires in vitro microphysiological models of the neurovascular unit. Here we show that the neurotropism of Cryptococcus neoformans-the most common pathogen causing fungal meningitis-and its ability to penetrate the BBB can be modelled by the co-culture of human neural stem cells, brain microvascular endothelial cells and brain vascular pericytes in a human-neurovascular-unit-on-a-chip maintained by a stepwise gravity-driven unidirectional flow and recapitulating the structural and functional features of the BBB. We found that the pathogen forms clusters of cells that penetrate the BBB without altering tight junctions, suggesting a transcytosis-mediated mechanism. The neurovascular-unit-on-a-chip may facilitate the study of the mechanisms of brain infection by pathogens, and the development of drugs for a range of brain diseases.

Vertical Nanowire Electrode Array for Enhanced Neurogenesis of Human Neural Stem Cells via Intracellular Electrical Stimulation

Extracellular electrical stimulation (ES) can provide electrical potential from outside the cell membrane, but it is often ineffective due to interference from external factors such as culture medium resistance and membrane capacitance. To address this, we developed a vertical nanowire electrode array (VNEA) to directly provide intracellular electrical potential and current to cells through nanoelectrodes. Using this approach, the cell membrane resistivity and capacitance could be excluded, allowing effective ES. Human fetal neural stem cells (hfNSCs) were cultured on the VNEA for intracellular ES. Combining the structural properties of VNEA and VNEA-mediated ES, transient nanoscale perforation of the electrode was induced, promoting cell penetration and delivering current to the cell. Intracellular ES using VNEA improved the neuronal differentiation of hfNSCs more effectively than extracellular ES and facilitated electrophysiological functional maturation of hfNSCs because of the enhanced voltage-dependent ion-channel activity. The results demonstrate that VNEA with advanced nanoelectrodes serves as a highly effective culture and stimulation platform for stem-cell neurogenesis.

Diving beetle-like miniaturized plungers with reversible, rapid biofluid capturing for machine learning-based care of skin disease

Recent advances in bioinspired nano/microstructures have received attention as promising approaches with which to implement smart skin-interfacial devices for personalized health care. In situ skin diagnosis requires adaptable skin adherence and rapid capture of clinical biofluids. Here, we report a simple, all-in-one device consisting of microplungers and hydrogels that can rapidly capture biofluids and conformally attach to skin for stable, real-time monitoring of health. Inspired by the male diving beetle, the microplungers achieve repeatable, enhanced, and multidirectional adhesion to human skin in dry/wet environments, revealing the role of the cavities in these architectures. The hydrogels within the microplungers instantaneously absorb liquids from the epidermis for enhanced adhesiveness and reversibly change color for visual indication of skin pH levels. To realize advanced biomedical technologies for the diagnosis and treatment of skin, our suction-mediated device is integrated with a machine learning framework for accurate and automated colorimetric analysis of pH levels.

Functional Skeletal Muscle Regeneration with Thermally Drawn Porous Fibers and Reprogrammed Muscle Progenitors for Volumetric Muscle Injury

Skeletal muscle has an inherent capacity for spontaneous regeneration. However, recovery after severe injuries such as volumetric muscle loss (VML) is limited. There is therefore a need to develop interventions to induce functional skeletal muscle restoration. One suggested approach includes tissue-engineered muscle constructs. Tissue-engineering treatments have so far been impeded by the lack of reliable cell sources and the challenges in engineering of suitable tissue scaffolds. To address these challenges, muscle extracellular matrix (MEM) and induced skeletal myogenic progenitor cells (iMPCs) are integrated within thermally drawn fiber based microchannel scaffolds. The microchannel fibers decorated with MEM enhance differentiation and maturation of iMPCs. Furthermore, engraftment of these bioengineered hybrid muscle constructs induce de novo muscle regeneration accompanied with microvessel and neuromuscular junction formation in a VML mouse model, ultimately leading to functional recovery of muscle activity.

Immunomodulatory Scaffolds Derived from Lymph Node Extracellular Matrices

Immunomodulation in the local tissue microenvironment is pivotal for the determination of macrophage phenotypes and regulation of functions necessary for pro-healing effects. Herein, we demonstrate that a lymph node extracellular matrix (LNEM) prepared by the decellularization of lymph node tissues can mimic lymph node microenvironments for immunomodulation in two-dimensional (2D) and three-dimensional (3D) formats. The LNEM exhibits strengthened immunomodulatory effects in comparison to conventional collagen-based platforms. A 3D LNEM hydrogel is more effective than the 2D LNEM coating in inducing M2 macrophage polarization. The 3D LNEM induces macrophage elongation and enhances the M2-type marker expression and the secretion of anti-inflammatory cytokines. Additionally, the phagocytic function of macrophages is improved upon exposure to the intricate 3D LNEM environment. We demonstrate the reduced susceptibility of liver organoids to a hepatotoxic drug when co-cultured with macrophages in a 3D LNEM. This effect could be attributed to the enhanced anti-inflammatory functions and indicates its potential as a drug-testing platform that enables drug responses similar to those observed in vivo. Finally, the implantation of an LNEM hydrogel in a mouse volumetric muscle loss model facilitates the recruitment of host macrophages to the site of injury and enhances macrophage polarization toward the M2 phenotype for tissue healing in vivo. Therefore, 3D immune system-mimicking biomaterials could serve as useful platforms for tissue modeling and regenerative medicine development.

Tissue-Adhesive Chondroitin Sulfate Hydrogel for Cartilage Reconstruction

Chondroitin sulfate (CS), the main component of cartilage extracellular matrix, has attracted attention as a biomaterial for cartilage tissue engineering. However, current CS hydrogel systems still have limitations for application in successful cartilage tissue engineering owing to their unsuitable degradation kinetics, insufficient mechanical similarity, and lack of integration with the native cartilage tissue. In this study, using mussel adhesive-inspired catechol chemistry, we developed a functional CS hydrogel that exhibits tunable physical and mechanical properties as well as excellent tissue adhesion for efficient integration with native tissues. Various properties of the developed catechol-functionalized CS (CS-CA) hydrogel, including swelling, degradation, mechanical properties, and adhesiveness, could be tailored by varying the conjugation ratio of the catechol group to the CS backbone and the concentration of the CS-CA conjugates. CS-CA hydrogels exhibited significantly increased modulus (∼10 kPa) and superior adhesive properties (∼3 N) over conventional CS hydrogels (∼hundreds Pa and ∼0.05 N). In addition, CS-CA hydrogels incorporating decellularized cartilage tissue dice promoted the chondrogenic differentiation of human adipose-derived mesenchymal stem cells by providing a cartilage-like microenvironment. Finally, the transplantation of autologous cartilage dice using tissue-adhesive CS-CA hydrogels enhanced cartilage integration with host tissue and neo-cartilage formation owing to favorable physical, mechanical, and biological properties for cartilage formation. In conclusion, our study demonstrated the potential utility of the CS-CA hydrogel system in cartilage tissue reconstruction.

Regeneration of irradiation-damaged esophagus by local delivery of mesenchymal stem-cell spheroids encapsulated in a hyaluronic-acid-based hydrogel

Radiation therapy (RT) is a typical treatment for head and neck cancers. Generally, prolonged irradiation of the esophagus causes esophageal fibrosis due to increased reactive oxygen species and proinflammatory cytokines. This study was designed to determine whether catechol-functionalized hyaluronic acid (HA-CA) hydrogel-encapsulated human mesenchymal stem-cell spheroids (MSC-SPs) could ameliorate damage to the esophagus in a mouse model of radiation-induced esophageal fibrosis. MSC-SPs were cultured in concave microwells 600 μm in diameter at a cell density of 1 × 10⁶ cells per mL. Most cells formed spheroids with a 100-300 μm size distribution in concave microwells. MSC-SPs were well maintained in the HA gel, and live-dead staining confirmed that most cells survived. The HA gel containing the MSC-SPs was then injected into the damaged esophageal layer. Inflammatory signs or adverse tissue reactions were not observed after esophageal injection of HA-gel-encapsulated MSC-SPs. Based on Masson's trichrome staining at 4 and 12 weeks postinjection, the inner esophageal layer (IEL) was significantly thinner in the MSC-SP + HA gel group compared to those in the other experimental groups. While the saline and HA gel treatments made the esophageal muscles loose and thick, the MSC-SP + HA gel group showed bundles of tightly packed esophageal muscles, as assayed by desmin immunostaining. qPCR analysis showed that epithelial genes tended to increase over time in the MSC-SP + HA gel group, and the expression of most fibrosis-related genes decreased. This study proposes the potential of using HA-CA-hydrogel-encapsulated MSC-SPs as a promising therapy against radiation-induced esophageal fibrosis.

NEUROD1 Intrinsically Initiates Differentiation of Induced Pluripotent Stem Cells into Neural Progenitor Cells

Cell type specification is a delicate biological event in which every step is under tight regulation. From a molecular point of view, cell fate commitment begins with chromatin alteration, which kickstarts lineage-determining factors to initiate a series of genes required for cell specification. Several important neuronal differentiation factors have been identified from ectopic over-expression studies. However, there is scarce information on which DNA regions are modified during induced pluripotent stem cell (iPSC) to neuronal progenitor cell (NPC) differentiation, the cis regulatory factors that attach to these accessible regions, or the genes that are initially expressed. In this study, we identified the DNA accessible regions of iPSCs and NPCs via the Assay for Transposase-Accessible Chromatin sequencing (ATACseq). We identified which chromatin regions were modified after neuronal differentiation and found that the enhancer regions had more active histone modification changes than the promoters. Through motif enrichment analysis, we found that NEUROD1 controls iPSC differentiation to NPC by binding to the accessible regions of enhancers in cooperation with other factors such as the Hox proteins. Finally, by using Hi-C data, we categorized the genes that directly interacted with the enhancers under the control of NEUROD1 during iPSC to NPC differentiation.

Biphasic Electrical Pulse by a Micropillar Electrode Array Enhances Maturation and Drug Response of Reprogrammed Cardiac Spheroids

Direct reprogramming is an efficient strategy to produce cardiac lineage cells necessary for cardiac tissue engineering and drug testing for cardiac toxicity. However, functional maturation of reprogrammed cardiomyocytes, which is of great importance for their regenerative potential and drug response, still remains challenging. In this study, we propose a novel electrode platform to promote direct cardiac reprogramming and improve the functionality of reprogrammed cardiac cells. Nonviral cardiac reprogramming was improved via a three-dimensional spheroid culture of chemically induced cardiomyocytes exposed to a small-molecule cocktail. A micropillar electrode array providing biphasic electrical pulses mimicking the heartbeat further enhanced maturation and electrophysiological properties of reprogrammed cardiac spheroids, leading to proper responses and increased sensitivity to drugs. On the basis of our results, we conclude that our device may have a wider application in the generation of functional cardiac cells for regenerative medicine and screening of novel drugs.

Chromatin Interaction Changes during the iPSC-NPC Model to Facilitate the Study of Biologically Significant Genes Involved in Differentiation

Given the difficulties of obtaining diseased cells, differentiation of neurons from patient-specific human induced pluripotent stem cells (iPSCs) with neural progenitor cells (NPCs) as intermediate precursors is of great interest. While cellular and transcriptomic changes during the differentiation process have been tracked, little attention has been given to examining spatial re-organization, which has been revealed to control gene regulation in various cells. To address the regulatory mechanism by 3D chromatin structure during neuronal differentiation, we examined the changes that take place during differentiation process using two cell types that are highly valued in the study of neurodegenerative disease - iPSCs and NPCs. In our study, we used Hi-C, a derivative of chromosome conformation capture that enables unbiased, genome-wide analysis of interaction frequencies in chromatin. We showed that while topologically associated domains remained mostly the same during differentiation, the presence of differential interacting regions in both cell types suggested that spatial organization affects gene regulation of both pluripotency maintenance and neuroectodermal differentiation. Moreover, closer analysis of promoter-promoter pairs suggested that cell fate specification is under the control of cis-regulatory elements. Our results are thus a resourceful addition in benchmarking differentiation protocols and also provide a greater appreciation of NPCs, the common precursors from which required neurons for applications in neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, schizophrenia and spinal cord injuries are utilized.

A Phenol-Amine Superglue Inspired by Insect Sclerotization Process

Exoskeletons of insects formed by sclerotization processes exhibit superstrong properties in moduli. Here, it is demonstrated that mimicking the sclerotization process using phenol and polyamine molecules unexpectedly results in a 100% ecofriendly, biocompatible waterborne superglue. Oxygen presented in air and dissolved in water acts as an initiator producing phenolic radical/quinone for superglue curing. Despite synthesis-free uses of water, phenol, and polyamine, its adhesion strength is comparable to commercial epoxy glue showing >6 MPa in lap shear strength. The phenol-amine superglue bonds to various substrates including ceramics, woods, fabrics, plastics, metals, and importantly biological tissues. Due to strong adhesion, the superglue effectively seals wounds within a few seconds, and, due to its waterborne nature, no harmful respiratory effect is observed because of any release of volatile organic compounds. The easy, cost-effective preparation of the phenol-amine superglue can revolutionize varieties of industrial, biomedical, daily life processes.

DNA Methylation of Intragenic CpG Islands are Required for Differentiation from iPSC to NPC

The effects of gene body DNA methylation on gene regulation still remains highly controversial. In this study, we generated whole genome bisulfite sequencing (WGBS) data with high sequencing depth in induced pluripotent stem cell (iPSC) and neuronal progentior cell (NPC), and investigated the relationship between DNA methylation changes in CpG islands (CGIs) and corresponding gene expression during NPC differentiation. Interestingly, differentially methylated CGIs were more abundant in intragenic regions compared to promoters and these methylated intragenic CGIs (iCGIs) were associated with neuronal development-related genes. When we compared gene expression level of methylated and unmethylated CGIs in intragenic regions, DNA methylation of iCGI was positively correlated with gene expression in contrast with promoter CGIs (pCGIs). To gain insight into regulatory mechanism mediated by iCGI DNA methylation, we executed motif searching in hypermethylated iCGIs and found NEUROD1 as a hypermethylated iCGI binding transcription factor. This study highlights give rise to possibility of activating role of hypermethylation in iCGIs and involvement of neuronal development related TFs. Graphical Abstract The relationship between iCGI DNA methylation and expression of associated genes in neuronal developmental process. During iPSC to NPCdifferentiation, iCGI containing neural developmental genes show iCGI's DNA hypermethylation which is accompanied by gene activation and NEUROD1which is one of the core neuronal TFs interacts with hypermethylated iCGI regions.

Evolutionarily conserved sequence motif analysis guides development of chemically defined hydrogels for therapeutic vascularization

Biologically active ligands (e.g., RGDS from fibronectin) play critical roles in the development of chemically defined biomaterials. However, recent decades have shown only limited progress in discovering novel extracellular matrix-protein-derived ligands for translational applications. Through motif analysis of evolutionarily conserved RGD-containing regions in laminin (LM) and peptide-functionalized hydrogel microarray screening, we identified a peptide (a1) that showed superior supports for endothelial cell (EC) functions. Mechanistic studies attributed the results to the capacity of a1 engaging both LM- and Fn-binding integrins. RNA sequencing of ECs in a1-functionalized hydrogels showed ~60% similarities with Matrigel in "vasculature development" gene ontology terms. Vasculogenesis assays revealed the capacity of a1-formulated hydrogels to improve EC network formation. Injectable alginates functionalized with a1 and MMPQK (a vascular endothelial growth factor-mimetic peptide with a matrix metalloproteinase-degradable linker) increased blood perfusion and functional recovery over decellularized extracellular matrix and (RGDS + MMPQK)-functionalized hydrogels in an ischemic hindlimb model, illustrating the power of this approach.

Spen links RNA-mediated endogenous retrovirus silencing and X chromosome inactivation

The Xist lncRNA mediates X chromosome inactivation (XCI). Here we show that Spen, an Xist-binding repressor protein essential for XCI , binds to ancient retroviral RNA, performing a surveillance role to recruit chromatin silencing machinery to these parasitic loci. Spen loss activates a subset of endogenous retroviral (ERV) elements in mouse embryonic stem cells, with gain of chromatin accessibility, active histone modifications, and ERV RNA transcription. Spen binds directly to ERV RNAs that show structural similarity to the A-repeat of Xist, a region critical for Xist-mediated gene silencing. ERV RNA and Xist A-repeat bind the RRM domains of Spen in a competitive manner. Insertion of an ERV into an A-repeat deficient Xist rescues binding of Xist RNA to Spen and results in strictly local gene silencing in cis. These results suggest that Xist may coopt transposable element RNA-protein interactions to repurpose powerful antiviral chromatin silencing machinery for sex chromosome dosage compensation.

A Surface-Tailoring Method for Rapid Non-Thermosensitive Cell-Sheet Engineering via Functional Polymer Coatings

Cell sheet engineering, a technique utilizing a monolayer cell sheet, has recently emerged as a promising technology for scaffold-free tissue engineering. In contrast to conventional tissue-engineering approaches, the cell sheet technology allows cell harvest as a continuous cell sheet with intact extracellular matrix proteins and cell-cell junction, which facilitates cell transplantation without any other artificial biomaterials. A facile, non-thermoresponsive method is demonstrated for a rapid but highly reliable platform for cell-sheet engineering. The developed method exploits the precise modulation of cell-substrate interactions by controlling the surface energy of the substrate via a series of functional polymer coatings to enable prompt cell sheet harvesting within 100 s. The engineered surface can trigger an intrinsic cellular response upon the depletion of divalent cations, leading to spontaneous cell sheet detachment under physiological conditions (pH 7.4 and 37 °C) in a non-thermoresponsive manner. Additionally, the therapeutic potential of the cell sheet is successfully demonstrated by the transplantation of multilayered cell sheets into mouse models of diabetic wounds and ischemia. These findings highlight the ability of the developed surface for non-thermoresponsive cell sheet engineering to serve as a robust platform for regenerative medicine and provide significant breakthroughs in cell sheet technology.

Gastrointestinal tract modeling using organoids engineered with cellular and microbiota niches

The recent emergence of organoid technology has attracted great attention in gastroenterology because the gastrointestinal (GI) tract can be recapitulated in vitro using organoids, enabling disease modeling and mechanistic studies. However, to more precisely emulate the GI microenvironment in vivo, several neighboring cell types and types of microbiota need to be integrated into GI organoids. This article reviews the recent progress made in elucidating the crosstalk between GI organoids and components of their microenvironment. We outline the effects of stromal cells (such as fibroblasts, neural cells, immune cells, and vascular cells) on the gastric and intestinal epithelia of organoids. Because of the important roles that microbiota play in the physiology and function of the GI tract, we also highlight interactions between organoids and commensal, symbiotic, and pathogenic microorganisms and viruses. GI organoid models that contain niche components will provide new insight into gastroenterological pathophysiology and disease mechanisms.

Magnetic Control of Axon Navigation in Reprogrammed Neurons

While neural cell transplantation represents a promising therapy for neurodegenerative diseases, the formation of functional networks of transplanted cells with host neurons constitutes one of the challenging steps. Here, we introduce a magnetic guidance methodology that controls neurite growth signaling via magnetic nanoparticles (MNPs) conjugated with antibodies targeting the deleted in colorectal cancer (DCC) receptor (DCC-MNPs). Activation of the DCC receptors by clusterization and subsequent axonal growth of the induced neuronal (iN) cells was performed in a spatially controlled manner. In addition to the directionality of the magnetically controlled axon projection, axonal growth of the iN cells assisted the formation of functional connections with pre-existing primary neurons. Our results suggest magnetic guidance as a strategy for improving neuronal connectivity by spatially guiding the axonal projections of transplanted neural cells for synaptic interactions with the host tissue.

Hydrogel Skin-Covered Neurons Self-Assembled with Gustatory Cells for Selective Taste Stimulation

Many technical challenges exist in the co-culture of multiple types of cells, including medium optimization, cell-to-cell connection, and selective data acquisition of cellular responses. Particularly, mixed cellular responses limit the precise interpretation of intercellular signal transduction. Here, we report the formation of an agarose gel skin on neurons closely assembled with gustatory cells to selectively stimulate gustatory cells by retarding the diffusion of tastants to neurons. The signal transmission, triggered by denatonium benzoate, from gustatory cells to neurons was monitored using intracellular calcium ion concentrations. The agarose gel skin efficiently suppressed the direct transfer of tastants to neurons, decreasing the number of responsive neurons from 56 to 13% and the number of calcium ion signals per neuron from multiple to single. The assembly of neurons with gustatory cells induced the high level of neuronal responses through taste signal transduction from gustatory cells to neurons. However, the calcium ion signal peaks of free neurons coated with agarose gel were much shorter and weaker than those of neurons closely assembled with gustatory cells. This work demonstrated that agarose gel skin is a simple, fast, and effective means to increase the signal selectivity of cellular responses in the co-culture of multiple types of cells.

Aligned Brain Extracellular Matrix Promotes Differentiation and Myelination of Human-Induced Pluripotent Stem Cell-Derived Oligodendrocytes

Myelination by oligodendrocytes (OLs) is a key developmental milestone in terms of the functions of the central nervous system (CNS). Demyelination caused by defects in OLs is a hallmark of several CNS disorders. Although a potential therapeutic strategy involves treatment with the myelin-forming cells, there is no readily available source of these cells. OLs can be differentiated from pluripotent stem cells; however, there is a lack of efficient culture systems that generate functional OLs. Here, we demonstrate biomimetic approaches to promote OL differentiation from human-induced pluripotent stem cells (iPSCs) and to enhance the maturation and myelination capabilities of iPSC-derived OL (iPSC-OL). Functionalization of culture substrates using the brain extracellular matrix (BEM) derived from decellularized human brain tissue enhanced the differentiation of iPSCs into myelin-expressing OLs. Co-culture of iPSC-OL with induced neuronal (iN) cells on BEM substrates, which closely mimics the in vivo brain microenvironment for myelinated neurons, not only enhanced myelination of iPSC-OL but also improved electrophysiological function of iN cells. BEM-functionalized aligned electrospun nanofibrous scaffolds further promoted the maturation of iPSC-OLs, enhanced the production of myelin sheath-like structures by the iPSC-OL, and enhanced the neurogenesis of iN cells. Thus, the biomimetic strategy presented here can generate functional OLs from stem cells and facilitate myelination by providing brain-specific biochemical, biophysical, and structural signals. Our system comprising stem cells and brain tissue from human sources could help in the establishment of human demyelination disease models and the development of regenerative cell therapy for myelin disorders.