Cyborg Organoids: Implantation of Nanoelectronics via Organogenesis for Tissue-Wide Electrophysiology

Real-time electro-mechanical profiling of dynamically beating human cardiac organoids by coupling resistive skins with microelectrode arrays

Cardiac organoids differentiated from induced pluripotent stem cells are emerging as a promising platform for pre-clinical drug screening, assessing cardiotoxicity, and disease modelling. However, it is challenging to simultaneously measure mechanical contractile forces and electrophysiological signals of cardiac organoids in real-time and in-situ with the existing methods. Here, we present a biting-inspired sensory system based on a resistive skin sensor and a microelectrode array. The bite-like contact can be established with a micromanipulator to precisely position the resistive skin sensor on the top of the cardiac organoid while the 3D microneedle electrode array probes from underneath. Such reliable contact is key to achieving simultaneous electro-mechanical measurements. We demonstrate the use of our system for modelling cardiotoxicity with the anti-cancer drug doxorubicin. The electro-mechanical parameters described here elucidate the acute cardiotoxic effects induced by doxorubicin. This integrated electro-mechanical system enables a suite of new diagnostic options for assessing cardiac organoids and tissues.

Enhancing biocompatibility of the brain-machine interface: A review

In vivo implantation of microelectrodes opens the door to studying neural circuits and restoring damaged neural pathways through direct electrical stimulation and recording. Although some neuroprostheses have achieved clinical success, electrode material properties, inflammatory response, and glial scar formation at the electrode-tissue interfaces affect performance and sustainability. Those challenges can be addressed by improving some of the materials' mechanical, physical, chemical, and electrical properties. This paper reviews materials and designs of current microelectrodes and discusses perspectives to advance neuroprosthetics performance.

Organoid intelligence for developmental neurotoxicity testing

The increasing prevalence of neurodevelopmental disorders has highlighted the need for improved testing methods to determine developmental neurotoxicity (DNT) hazard for thousands of chemicals. This paper proposes the integration of organoid intelligence (OI); leveraging brain organoids to study neuroplasticity in vitro, into the DNT testing paradigm. OI brings a new approach to measure the impacts of xenobiotics on plasticity mechanisms - a critical biological process that is not adequately covered in current DNT in vitro assays. Finally, the integration of artificial intelligence (AI) techniques will further facilitate the analysis of complex brain organoid data to study these plasticity mechanisms.

Bipolar electrochemical growth of conductive microwires for cancer spheroid integration: a step forward in conductive biological circuitry

The field of bioelectronics is developing exponentially. There is now a drive to interface electronics with biology for the development of new technologies to improve our understanding of electrical forces in biology. This builds on our recently published work in which we show wireless electrochemistry could be used to grow bioelectronic functional circuitry in 2D cell layers. To date our ability to merge electronics with in situ with biology is 3D limited. In this study, we aimed to further develop the wireless electrochemical approach for the self-assembly of microwires in situ with custom-designed and fabricated 3D cancer spheroids. Unlike traditional electrochemical methods that rely on direct electrical connections to induce currents, our technique utilises bipolar electrodes that operate independently of physical wired connections. These electrodes enable redox reactions through the application of an external electric field. Specifically, feeder electrodes connected to a power supply generate an electric field, while the bipolar electrodes, not physically connected to the feeder electrodes, facilitate the reduction of silver ions from the solution. This process occurs upon applying a voltage across the feeder electrodes, resulting in the formation of self-assembled microwires between the cancer spheroids.Thereby, creating interlinked bioelectronic circuitry with cancer spheroids. We demonstrate that a direct current was needed to stimulate the growth of conductive microwires in the presence of cell spheroids. Microwire growth was successful when using 50 V (0.5 kV/cm) of DC applied to a single spheroid of approximately 800 µm in diameter but could not be achieved with alternating currents. This represents the first proof of the concept of using wireless electrochemistry to grow conductive structures with 3D mammalian cell spheroids.

In Situ Synthesis and Assembly of Functional Materials and Devices in Living Systems

ConspectusIntegrating functional materials and devices with living systems enables novel methods for recording, manipulating, or augmenting organisms not accessible by traditional chemical, optical, or genetic approaches. (The term "device" refers to the fundamental components of complex electronic systems, such as transistors, capacitors, conductors, and electrodes.) Typically, these advanced materials and devices are synthesized, either through chemical or physical reactions, outside the biological systems (ex situ) before they are integrated. This is due in part to the more limited repertoire of biocompatible chemical transformations available for assembling functional materials in vivo. Given that most of the assembled bulk materials are impermeable to cell membranes and cannot go through the blood-brain barrier (BBB), the external synthesis poses challenges when trying to interface these materials and devices with cells precisely and in a timely manner and at the micro- and nanoscale─a crucial requirement for modulating cellular functions. In contrast to presynthesis in a separate location, in situ assembly, wherein small molecules or building blocks are directly assembled into functional materials within a biological system at the desired site of action, has offered a potential solution for spatiotemporal and genetic control of material synthesis and assembly.In this Account, we highlight recent advances in spatially and temporally targeted functional material synthesis and assembly in living cells, tissues and animals and provide perspective on how they may enable novel probing, modulation, or augmentation of fundamental biology. We discuss several strategies, starting from the traditional nontargeted methods to targeted assembly of functional materials and devices based on the endogenous markers of the biological system. We then focus on genetically targeted assembly of functional materials, which employs enzymatic catalysis centers expressed in living systems to assemble functional materials in specific molecular-defined cell types. We introduce the recent efforts of our group to modulate membrane capacitance and neuron excitability using in situ synthesized electrically functional polymers in a genetically targetable manner. These advances demonstrate the promise of in situ synthesis and assembly of functional materials and devices, including the optogenetic polymerization developed by our lab, to interface with cells in a cellular- or subcellular-specific manner by incorporating genetic and/or optical control over material assembly. Finally, we discuss remaining challenges, areas for improvement, potential applications to other biological systems, and novel methods for the in situ synthesis of functional materials that could be elevated by incorporating genetic or material design strategies. As researchers expand the toolkit of biocompatible in situ functional material synthetic techniques, we anticipate that these advancements could potentially offer valuable tools for exploring biological systems and developing therapeutic solutions.

Advances in Microfluidic Technologies in Organoid Research

Organoids have emerged as major technological breakthroughs and novel organ models that have revolutionized biomedical research by recapitulating the key structural and functional complexities of their in vivo counterparts. The combination of organoid systems and microfluidic technologies has opened new frontiers in organoid engineering and offers great opportunities to address the current challenges of existing organoid systems and broaden their biomedical applications. In this review, the key features of the existing organoids, including their origins, development, design principles, and limitations, are described. Then the recent progress in integrating organoids into microfluidic systems is highlighted, involving microarrays for high-throughput organoid manipulation, microreactors for organoid hydrogel scaffold fabrication, and microfluidic chips for functional organoid culture. The opportunities in the nascent combination of organoids and microfluidics that lie ahead to accelerate research in organ development, disease studies, drug screening, and regenerative medicine are also discussed. Finally, the challenges and future perspectives in the development of advanced microfluidic platforms and modified technologies for building organoids with higher fidelity and standardization are envisioned.

Bioprinting of Stable Bionic Interfaces Using Piezoresistive Hydrogel Organoelectronics

Bionic tissues offer an exciting frontier in biomedical research by integrating biological cells with artificial electronics, such as sensors. One critical hurdle is the development of artificial electronics that can mechanically harmonize with biological tissues, ensuring a robust interface for effective strain transfer and local deformation sensing. In this study, a highly tissue-integrative, soft mechanical sensor fabricated from a composite piezoresistive hydrogel. The composite not only exhibits exceptional mechanical properties, with elongation at the point of fracture reaching up to 680%, but also maintains excellent biocompatibility across multiple cell types. Furthermore, the material exhibits bioadhesive qualities, facilitating stable cell adhesion to its surface. A unique advantage of the formulation is the compatibility with 3D bioprinting, an essential technique for fabricating stable interfaces. A multimaterial sensorized 3D bionic construct is successfully bioprinted, and it is compared to structures produced via hydrogel casting. In contrast to cast constructs, the bioprinted ones display a high (87%) cell viability, preserve differentiation ability, and structural integrity of the sensor-tissue interface throughout the tissue development duration of 10 d. With easy fabrication and effective soft tissue integration, this composite holds significant promise for various biomedical applications, including implantable electronics and organ-on-a-chip technologies.

Microinstrumentation for Brain Organoids

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

Drug Evaluation of Parkinson's Disease Patient-Derived Midbrain Organoids Using Mesoporous Au Nanodot-Patterned 3D Concave Electrode

Brain organoids are being recognized as valuable tools for drug evaluation in neurodegenerative diseases due to their similarity to the human brain's structure and function. However, a critical challenge is the lack of selective and sensitive electrochemical sensing platforms to detect the response of brain organoids, particularly changes in the neurotransmitter concentration upon drug treatment. This study introduces a 3D concave electrode patterned with a mesoporous Au nanodot for the detection of electrochemical signals of dopamine in response to drugs in brain organoids for the first time. The mesoporous Au nanodot-patterned film was fabricated using laser interference lithography and electrochemical deposition. Then, the film was attached to a polymer-based 3D concave mold to obtain a 3D concave electrode. Midbrain organoids generated from Parkinson's disease (PD) patient-derived iPSCs with gene mutations (named as PD midbrain organoid) or normal midbrain organoids were positioned on the developed 3D concave electrode. The 3D concave electrode showed a 1.4 times higher electrochemical signal of dopamine compared to the bare gold electrode. And the dopamine secreted from normal midbrain organoids or PD midbrain organoids on the 3D concave electrode could be detected electrochemically. After the treatment of PD midbrain organoids with levodopa, the drug for PD, the increase in dopamine level was detected due to the activation of dopaminergic neurons by the drug. The results suggest the potential of the proposed 3D concave electrode combined with brain organoids as a useful tool for assessing drug efficacy. This sensing system can be applied to a variety of organoids for a comprehensive drug evaluation.

Beyond 25 years of biomedical innovation in nano-bioelectronics

Nano-bioelectronics, which blend the precision of nanotechnology with the complexity of biological systems, are evolving with innovations such as silicon nanowires, carbon nanotubes, and graphene. These elements serve applications from biochemical sensing to brain-machine interfacing. This review examines nano-bioelectronics' role in advancing biomedical interventions and discusses their potential in environmental monitoring, agricultural productivity, energy efficiency, and creative fields. The field is transitioning from molecular to ecosystem-level applications, with research exploring complex cellular mechanisms and communication. This fosters understanding of biological interactions at various levels, such as suggesting transformative approaches for ecosystem management and food security. Future research is expected to focus on refining nano-bioelectronic devices for integration with biological systems and on scalable manufacturing to broaden their reach and functionality.

Electrophysiological insights with brain organoid models: a brief review

Brain organoid is a three-dimensional (3D) tissue derived from stem cells such as induced pluripotent stem cells (iPSCs) embryonic stem cells (ESCs) that reflect real human brain structure. It replicates the complexity and development of the human brain, enabling studies of the human brain in vitro. With emerging technologies, its application is various, including disease modeling and drug screening. A variety of experimental methods have been used to study structural and molecular characteristics of brain organoids. However, electrophysiological analysis is necessary to understand their functional characteristics and complexity. Although electrophysiological approaches have rapidly advanced for monolayered cells, there are some limitations in studying electrophysiological and neural network characteristics due to the lack of 3D characteristics. Herein, electrophysiological measurement and analytical methods related to neural complexity and 3D characteristics of brain organoids are reviewed. Overall, electrophysiological understanding of brain organoids allows us to overcome limitations of monolayer in vitro cell culture models, providing deep insights into the neural network complex of the real human brain and new ways of disease modeling. [BMB Reports 2024; 57(7): 311-317].

Enhancing regenerative medicine with self-healing hydrogels: A solution for tissue repair and advanced cyborganic healthcare devices

Considering the global burden related to tissue and organ injuries or failures, self-healing hydrogels may be an attractive therapeutic alternative for the future. Self-healing hydrogels are highly hydrated 3D structures with the ability to self-heal after breaking, this property is attributable to a variety of dynamic non-covalent and covalent bonds that are able to re-linking within the matrix. Self-healing ability specially benefits minimal invasive medical treatments with cell-delivery support. Moreover, those tissue-engineered self-healing hydrogels network have demonstrated effectiveness for myriad purposes; for instance, they could act as delivery-platforms for different cargos (drugs, growth factors, cells, among others) in tissues such as bone, cartilage, nerve or skin. Besides, self-healing hydrogels have currently found their way into new and novel applications; for example, with the development of the self-healing adhesive hydrogels, by merely aiding surgical closing processes and by providing biomaterial-tissue adhesion. Furthermore, conductive hydrogels permit the stimuli and monitoring of natural electrical signals, which facilitated a better fitting of hydrogels in native tissue or the diagnosis of various health diseases. Lastly, self-healing hydrogels could be part of cyborganics - a merge between biology and machinery - which can pave the way to a finer healthcare devices for diagnostics and precision therapies.

Promoting Human Intestinal Organoid Formation and Stimulation Using Piezoelectric Nanofiber Matrices

Human organoid model systems have changed the landscape of developmental biology and basic science. They serve as a great tool for human specific interrogation. In order to advance our organoid technology, we aimed to test the compatibility of a piezoelectric material with organoid generation, because it will create a new platform with the potential for sensing and actuating organoids in physiologically relevant ways. We differentiated human pluripotent stem cells into spheroids following the traditional human intestinal organoid (HIO) protocol atop a piezoelectric nanofiber scaffold. We observed that exposure to the biocompatible piezoelectric nanofibers promoted spheroid morphology three days sooner than with the conventional methodology. At day 28 of culture, HIOs grown on the scaffold appeared similar. Both groups were readily transplantable and developed well-organized laminated structures. Graft sizes between groups were similar. Upon characterizing the tissue further, we found no detrimental effects of the piezoelectric nanofibers on intestinal patterning or maturation. Furthermore, to test the practical feasibility of the material, HIOs were also matured on the nanofiber scaffolds and treated with ultrasound, which lead to increased cellular proliferation which is critical for organoid development and tissue maintenance. This study establishes a proof of concept for integrating piezoelectric materials as a customizable platform for on-demand electrical stimulation of cells using remote ultrasonic waveforms in regenerative medicine.

Brain implantation of tissue-level-soft bioelectronics via embryonic development

The design of bioelectronics capable of stably tracking brain-wide, single-cell, and millisecond-resolved neural activities in the developing brain is critical to the study of neuroscience and neurodevelopmental disorders. During development, the three-dimensional (3D) structure of the vertebrate brain arises from a 2D neural plate 1,2 . These large morphological changes previously posed a challenge for implantable bioelectronics to track neural activity throughout brain development 3-9 . Here, we present a tissue-level-soft, sub-micrometer-thick, stretchable mesh microelectrode array capable of integrating into the embryonic neural plate of vertebrates by leveraging the 2D-to-3D reconfiguration process of the tissue itself. Driven by the expansion and folding processes of organogenesis, the stretchable mesh electrode array deforms, stretches, and distributes throughout the entire brain, fully integrating into the 3D tissue structure. Immunostaining, gene expression analysis, and behavioral testing show no discernible impact on brain development or function. The embedded electrode array enables long-term, stable, brain-wide, single-unit-single-spike-resolved electrical mapping throughout brain development, illustrating how neural electrical activities and population dynamics emerge and evolve during brain development.

Looking both ways: Electroactive biomaterials with bidirectional implications for dynamic cell-material crosstalk

Cells exist in natural, dynamic microenvironmental niches that facilitate biological responses to external physicochemical cues such as mechanical and electrical stimuli. For excitable cells, exogenous electrical cues are of interest due to their ability to stimulate or regulate cellular behavior via cascade signaling involving ion channels, gap junctions, and integrin receptors across the membrane. In recent years, conductive biomaterials have been demonstrated to influence or record these electrosensitive biological processes whereby the primary design criterion is to achieve seamless cell-material integration. As such, currently available bioelectronic materials are predominantly engineered toward achieving high-performing devices while maintaining the ability to recapitulate the local excitable cell/tissue microenvironment. However, such reports rarely address the dynamic signal coupling or exchange that occurs at the biotic-abiotic interface, as well as the distinction between the ionic transport involved in natural biological process and the electronic (or mixed ionic/electronic) conduction commonly responsible for bioelectronic systems. In this review, we highlight current literature reports that offer platforms capable of bidirectional signal exchange at the biotic-abiotic interface with excitable cell types, along with the design criteria for such biomaterials. Furthermore, insights on current materials not yet explored for biointerfacing or bioelectronics that have potential for bidirectional applications are also provided. Finally, we offer perspectives aimed at bringing attention to the coupling of the signals delivered by synthetic material to natural biological conduction mechanisms, areas of improvement regarding characterizing biotic-abiotic crosstalk, as well as the dynamic nature of this exchange, to be taken into consideration for material/device design consideration for next-generation bioelectronic systems.

Conducting polymer scaffolds: a new frontier in bioelectronics and bioengineering

Conducting polymer (CP) scaffolds have emerged as a transformative tool in bioelectronics and bioengineering, advancing the ability to interface with biological systems. Their unique combination of electrical conductivity, tailorability, and biocompatibility surpasses the capabilities of traditional nonconducting scaffolds while granting them access to the realm of bioelectronics. This review examines recent developments in CP scaffolds, focusing on material and device advancements, as well as their interplay with biological systems. We highlight applications for monitoring, tissue stimulation, and drug delivery and discuss perspectives and challenges currently faced for their ultimate translation and clinical implementation.

ST-CellSeg: Cell segmentation for imaging-based spatial transcriptomics using multi-scale manifold learning

Spatial transcriptomics has gained popularity over the past decade due to its ability to evaluate transcriptome data while preserving spatial information. Cell segmentation is a crucial step in spatial transcriptomic analysis, as it enables the avoidance of unpredictable tissue disentanglement steps. Although high-quality cell segmentation algorithms can aid in the extraction of valuable data, traditional methods are frequently non-spatial, do not account for spatial information efficiently, and perform poorly when confronted with the problem of spatial transcriptome cell segmentation with varying shapes. In this study, we propose ST-CellSeg, an image-based machine learning method for spatial transcriptomics that uses manifold for cell segmentation and is novel in its consideration of multi-scale information. We first construct a fully connected graph which acts as a spatial transcriptomic manifold. Using multi-scale data, we then determine the low-dimensional spatial probability distribution representation for cell segmentation. Using the adjusted Rand index (ARI), normalized mutual information (NMI), and Silhouette coefficient (SC) as model performance measures, the proposed algorithm significantly outperforms baseline models in selected datasets and is efficient in computational complexity.

Advancing Intelligent Organ-on-a-Chip Systems with Comprehensive In Situ Bioanalysis

In vitro models are essential to a broad range of biomedical research, such as pathological studies, drug development, and personalized medicine. As a potentially transformative paradigm for 3D in vitro models, organ-on-a-chip (OOC) technology has been extensively developed to recapitulate sophisticated architectures and dynamic microenvironments of human organs by applying the principles of life sciences and leveraging micro- and nanoscale engineering capabilities. A pivotal function of OOC devices is to support multifaceted and timely characterization of cultured cells and their microenvironments. However, in-depth analysis of OOC models typically requires biomedical assay procedures that are labor-intensive and interruptive. Herein, the latest advances toward intelligent OOC (iOOC) systems, where sensors integrated with OOC devices continuously report cellular and microenvironmental information for comprehensive in situ bioanalysis, are examined. It is proposed that the multimodal data in iOOC systems can support closed-loop control of the in vitro models and offer holistic biomedical insights for diverse applications. Essential techniques for establishing iOOC systems are surveyed, encompassing in situ sensing, data processing, and dynamic modulation. Eventually, the future development of iOOC systems featuring cross-disciplinary strategies is discussed.

Cyborg islets: implanted flexible electronics reveal principles of human islet electrical maturation

Flexible electronics implanted during tissue formation enable chronic studies of tissue-wide electrophysiology. Here, we integrate tissue-like stretchable electronics during organogenesis of human stem cell-derived pancreatic islets, stably tracing single-cell extracellular spike bursting dynamics over months of functional maturation. Adapting spike sorting methods from neural studies reveals maturation-dependent electrical patterns of α and β-like (SC-α and β) cells, and their stimulus-coupled dynamics. We identified two major electrical states for both SC-α and β cells, distinguished by their glucose threshold for action potential firing. We find that improved hormone stimulation capacity during extended culture reflects increasing numbers of SC-α/β cells in low basal firing states, linked to energy and hormone metabolism gene upregulation. Continuous recording during further maturation by entrainment to daily feeding cycles reveals that circadian islet-level hormone secretion rhythms reflect sustained and coordinate oscillation of cell-level SC-α and β electrical activities. We find that this correlates with cell-cell communication and exocytic network induction, indicating a role for circadian rhythms in coordinating system-level stimulus-coupled responses. Cyborg islets thus reveal principles of electrical maturation that will be useful to build fully functional in vitro islets for research and therapeutic applications.

Graphene-integrated mesh electronics with converged multifunctionality for tracking multimodal excitation-contraction dynamics in cardiac microtissues

Cardiac microtissues provide a promising platform for disease modeling and developmental studies, which require the close monitoring of the multimodal excitation-contraction dynamics. However, no existing assessing tool can track these multimodal dynamics across the live tissue. We develop a tissue-like mesh bioelectronic system to track these multimodal dynamics. The mesh system has tissue-level softness and cell-level dimensions to enable stable embedment in the tissue. It is integrated with an array of graphene sensors, which uniquely converges both bioelectrical and biomechanical sensing functionalities in one device. The system achieves stable tracking of the excitation-contraction dynamics across the tissue and throughout the developmental process, offering comprehensive assessments for tissue maturation, drug effects, and disease modeling. It holds the promise to provide more accurate quantification of the functional, developmental, and pathophysiological states in cardiac tissues, creating an instrumental tool for improving tissue engineering and studies.

Heart-on-a-chip systems with tissue-specific functionalities for physiological, pathological, and pharmacological studies

Recent advances in heart-on-a-chip systems hold great promise to facilitate cardiac physiological, pathological, and pharmacological studies. This review focuses on the development of heart-on-a-chip systems with tissue-specific functionalities. For one thing, the strategies for developing cardiac microtissues on heart-on-a-chip systems that closely mimic the structures and behaviors of the native heart are analyzed, including the imitation of cardiac structural and functional characteristics. For another, the development of techniques for real-time monitoring of biophysical and biochemical signals from cardiac microtissues on heart-on-a-chip systems is introduced, incorporating cardiac electrophysiological signals, contractile activity, and biomarkers. Furthermore, the applications of heart-on-a-chip systems in intelligent cardiac studies are discussed regarding physiological/pathological research and pharmacological assessment. Finally, the future development of heart-on-a-chip toward a higher level of systematization, integration, and maturation is proposed.

Engineering the Physical Microenvironment into Neural Organoids for Neurogenesis and Neurodevelopment

Understanding the signals from the physical microenvironment is critical for deciphering the processes of neurogenesis and neurodevelopment. The discovery of how surrounding physical signals shape human developing neurons is hindered by the bottleneck of conventional cell culture and animal models. Notwithstanding neural organoids provide a promising platform for recapitulating human neurogenesis and neurodevelopment, building neuronal physical microenvironment that accurately mimics the native neurophysical features is largely ignored in current organoid technologies. Here, it is discussed how the physical microenvironment modulates critical events during the periods of neurogenesis and neurodevelopment, such as neural stem cell fates, neural tube closure, neuronal migration, axonal guidance, optic cup formation, and cortical folding. Although animal models are widely used to investigate the impacts of physical factors on neurodevelopment and neuropathy, the important roles of human stem cell-derived neural organoids in this field are particularly highlighted. Considering the great promise of human organoids, building neural organoid microenvironments with mechanical forces, electrophysiological microsystems, and light manipulation will help to fully understand the physical cues in neurodevelopmental processes. Neural organoids combined with cutting-edge techniques, such as advanced atomic force microscopes, microrobots, and structural color biomaterials might promote the development of neural organoid-based research and neuroscience.

Nanoscale surface coatings and topographies for neural interfaces

With the lack of minimally invasive tools for probing neuronal systems across spatiotemporal scales, understanding the working mechanism of the nervous system and limited assessments available are imperative to prevent or treat neurological disorders. In particular, nanoengineered neural interfaces can provide a solution to this technological barrier. This review covers recent surface engineering approaches, including nanoscale surface coatings, and a range of topographies from the microscale to the nanoscale, primarily focusing on neural-interfaced biosystems. Specifically, the immobilization of bioactive molecules to fertilize the neural cell lineage, topographical engineering to induce mechanotransduction in neural cells, and enhanced cell-chip coupling using three-dimensional structured surfaces are highlighted. Advances in neural interface design will help us understand the nervous system, thereby achieving the effective treatments for neurological disorders. STATEMENT OF SIGNIFICANCE: • This review focuses on designing bioactive neural interface with a nanoscale chemical modification and topographical engineering at multiscale perspective. • Versatile nanoscale surface coatings and topographies for neural interface are summarized. • Recent advances in bioactive materials applicable for neural cell culture, electrophysiological sensing, and neural implants are reviewed.

Materials-Driven Soft Wearable Bioelectronics for Connected Healthcare

In the era of Internet-of-things, many things can stay connected; however, biological systems, including those necessary for human health, remain unable to stay connected to the global Internet due to the lack of soft conformal biosensors. The fundamental challenge lies in the fact that electronics and biology are distinct and incompatible, as they are based on different materials via different functioning principles. In particular, the human body is soft and curvilinear, yet electronics are typically rigid and planar. Recent advances in materials and materials design have generated tremendous opportunities to design soft wearable bioelectronics, which may bridge the gap, enabling the ultimate dream of connected healthcare for anyone, anytime, and anywhere. We begin with a review of the historical development of healthcare, indicating the significant trend of connected healthcare. This is followed by the focal point of discussion about new materials and materials design, particularly low-dimensional nanomaterials. We summarize material types and their attributes for designing soft bioelectronic sensors; we also cover their synthesis and fabrication methods, including top-down, bottom-up, and their combined approaches. Next, we discuss the wearable energy challenges and progress made to date. In addition to front-end wearable devices, we also describe back-end machine learning algorithms, artificial intelligence, telecommunication, and software. Afterward, we describe the integration of soft wearable bioelectronic systems which have been applied in various testbeds in real-world settings, including laboratories that are preclinical and clinical environments. Finally, we narrate the remaining challenges and opportunities in conjunction with our perspectives.

Transparent Intracellular Sensing Platform with Si Needles for Simultaneous Live Imaging

Vertically ordered Si needles are of particular interest for long-term intracellular recording owing to their capacity to infiltrate living cells with negligible damage and minimal toxicity. Such intracellular recordings could greatly benefit from simultaneous live cell imaging without disrupting their culture, contributing to an in-depth understanding of cellular function and activity. However, the use of standard live imaging techniques, such as inverted and confocal microscopy, is currently impeded by the opacity of Si wafers, typically employed for fabricating vertical Si needles. Here, we introduce a transparent intracellular sensing platform that combines vertical Si needles with a percolated network of Au-Ag nanowires on a transparent elastomeric substrate. This sensing platform meets all prerequisites for simultaneous intracellular recording and imaging, including electrochemical impedance, optical transparency, mechanical compliance, and cell viability. Proof-of-concept demonstrations of this sensing platform include monitoring electrical potentials in cardiomyocyte cells and in three-dimensionally engineered cardiovascular tissue, all while conducting live imaging with inverted and confocal microscopes. This sensing platform holds wide-ranging potential applications for intracellular research across various disciplines such as neuroscience, cardiology, muscle physiology, and drug screening.

Scalable Electrophysiology of Millimeter-Scale Animals with Electrode Devices

Millimeter-scale animals such as Caenorhabditis elegans, Drosophila larvae, zebrafish, and bees serve as powerful model organisms in the fields of neurobiology and neuroethology. Various methods exist for recording large-scale electrophysiological signals from these animals. Existing approaches often lack, however, real-time, uninterrupted investigations due to their rigid constructs, geometric constraints, and mechanical mismatch in integration with soft organisms. The recent research establishes the foundations for 3-dimensional flexible bioelectronic interfaces that incorporate microfabricated components and nanoelectronic function with adjustable mechanical properties and multidimensional variability, offering unique capabilities for chronic, stable interrogation and stimulation of millimeter-scale animals and miniature tissue constructs. This review summarizes the most advanced technologies for electrophysiological studies, based on methods of 3-dimensional flexible bioelectronics. A concluding section addresses the challenges of these devices in achieving freestanding, robust, and multifunctional biointerfaces.

Cell Replacement Therapy for Brain Repair: Recent Progress and Remaining Challenges for Treating Parkinson's Disease and Cortical Injury

Neural transplantation represents a promising approach to repairing damaged brain circuitry. Cellular grafts have been shown to promote functional recovery through "bystander effects" and other indirect mechanisms. However, extensive brain lesions may require direct neuronal replacement to achieve meaningful restoration of function. While fetal cortical grafts have been shown to integrate with the host brain and appear to develop appropriate functional attributes, the significant ethical concerns and limited availability of this tissue severely hamper clinical translation. Induced pluripotent stem cell-derived cells and tissues represent a more readily scalable alternative. Significant progress has recently been made in developing protocols for generating a wide range of neural cell types in vitro. Here, we discuss recent progress in neural transplantation approaches for two conditions with distinct design needs: Parkinson's disease and cortical injury. We discuss the current status and future application of injections of dopaminergic cells for the treatment of Parkinson's disease as well as the use of structured grafts such as brain organoids for cortical repair.

Asteroid impact: the potential of astrocytes to modulate human neural networks within organoids

Astrocytes are a vital cellular component of the central nervous system that impact neuronal function in both healthy and pathological states. This includes intercellular signals to neurons and non-neuronal cells during development, maturation, and aging that can modulate neural network formation, plasticity, and maintenance. Recently, human pluripotent stem cell-derived neural aggregate cultures, known as neurospheres or organoids, have emerged as improved experimental platforms for basic and pre-clinical neuroscience compared to traditional approaches. Here, we summarize the potential capability of using organoids to further understand the mechanistic role of astrocytes upon neural networks, including the production of extracellular matrix components and reactive signaling cues. Additionally, we discuss the application of organoid models to investigate the astrocyte-dependent aspects of neuropathological diseases and to test astrocyte-inspired technologies. We examine the shortcomings of organoid-based experimental platforms and plausible improvements made possible by cutting-edge neuroengineering technologies. These advancements are expected to enable the development of improved diagnostic strategies and high-throughput translational applications regarding neuroregeneration.

Recent advances in tailoring stimuli-responsive hybrid scaffolds for cardiac tissue engineering and allied applications

To recapitulate bio-physical properties and functional behaviour of native heart tissues, recent tissue engineering-based approaches are focused on developing smart/stimuli-responsive materials for interfacing cardiac cells. Overcoming the drawbacks of the traditionally used biomaterials, these smart materials portray outstanding mechanical and conductive properties while promoting cell-cell interaction and cell-matrix transduction cues in such excitable tissues. To date, a large number of stimuli-responsive materials have been employed for interfacing cardiac tissues alone or in combination with natural/synthetic materials for cardiac tissue engineering. However, their comprehensive classification and a comparative analysis of the role played by these materials in regulating cardiac cell behaviour and in vivo metabolism are much less discussed. In an attempt to cover the recent advances in fabricating stimuli-responsive biomaterials for engineering cardiac tissues, this review details the role of these materials in modulating cardiomyocyte behaviour, functionality and surrounding matrix properties. Furthermore, concerns and challenges regarding the clinical translation of these materials and the possibility of using such materials for the fabrication of bio-actuators and bioelectronic devices are discussed.

A snapshot review on materials enabled multimodal bioelectronics for neurological and cardiac research

Seamless integration of the body and electronics toward the understanding, quantification, and control of disease states remains one of the grand scientific challenges of this era. As such, research efforts have been dedicated to developing bioelectronic devices for chemical, mechanical, and electrical sensing, and cellular and tissue functionality modulation. The technologies developed to achieve these capabilities cross a wide range of materials and scale (and dimensionality), e.g., from micrometer to centimeters (from 2-dimensional (2D) to 3-dimensional (3D) assemblies). The integration into multimodal systems which allow greater insight and control into intrinsically multifaceted biological systems requires careful design and selection. This snapshot review will highlight the state-of-the-art in cellular recording and modulation as well as the material considerations for the design and manufacturing of devices integrating their capabilities.

Combining PEDOT:PSS Polymer Coating with Metallic 3D Nanowires Electrodes to Achieve High Electrochemical Performances for Neuronal Interfacing Applications

This study presents a novel approach to improve the performance of microelectrode arrays (MEAs) used for electrophysiological studies of neuronal networks. The integration of 3D nanowires (NWs) with MEAs increases the surface-to-volume ratio, which enables subcellular interactions and high-resolution neuronal signal recording. However, these devices suffer from high initial interface impedance and limited charge transfer capacity due to their small effective area. To overcome these limitations, the integration of conductive polymer coatings, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) is investigated as a mean of improving the charge transfer capacity and biocompatibility of MEAs. The study combines platinum silicide-based metallic 3D nanowires electrodes with electrodeposited PEDOT:PSS coatings to deposit ultra-thin (<50 nm) layers of conductive polymer onto metallic electrodes with very high selectivity. The polymer-coated electrodes were fully characterized electrochemically and morphologically to establish a direct relationship between synthesis conditions, morphology, and conductive features. Results show that PEDOT-coated electrodes exhibit thickness-dependent improved stimulation and recording performances, offering new perspectives for neuronal interfacing with optimal cell engulfment to enable the study of neuronal activity with acute spatial and signal resolution at the sub-cellular level.

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.

Perspectives on tissue-like bioelectronics for neural modulation

Advances in bioelectronic implants have been offering valuable chances to interface and modulate neural systems. Potential mismatches between bioelectronics and targeted neural tissues require devices to exhibit "tissue-like" properties for better implant-bio integration. In particular, mechanical mismatches pose a significant challenge. In the past years, efforts were made in both materials synthesis and device design to achieve bioelectronics mechanically and biochemically mimicking biological tissues. In this perspective, we mainly summarized recent progress of developing "tissue-like" bioelectronics and categorized them into different strategies. We also discussed how these "tissue-like" bioelectronics were utilized for modulating in vivo nervous systems and neural organoids. We concluded the perspective by proposing further directions including personalized bioelectronics, novel materials design and the involvement of artificial intelligence and robotic techniques.

A mesh microelectrode array for non-invasive electrophysiology within neural organoids

Organoids are emerging in vitro models of human physiology. Neural models require the evaluation of functional activity of single cells and networks, which is commonly measured by microelectrode arrays. The characteristics of organoids clash with existing in vitro or in vivo microelectrode arrays. With inspiration from implantable mesh electronics and growth of organoids on polymer scaffolds, we fabricated suspended hammock-like mesh microelectrode arrays for neural organoids. We have demonstrated the growth of organoids enveloping these meshes and the culture of organoids on meshes for up to one year. Furthermore, we present proof-of-principle recordings of spontaneous electrical activity across the volume of an organoid. Our concept enables a new class of microelectrode arrays for in vitro models of three-dimensional electrically active tissue.

Multimodal charting of molecular and functional cell states via in situ electro-sequencing

Paired mapping of single-cell gene expression and electrophysiology is essential to understand gene-to-function relationships in electrogenic tissues. Here, we developed in situ electro-sequencing (electro-seq) that combines flexible bioelectronics with in situ RNA sequencing to stably map millisecond-timescale electrical activity and profile single-cell gene expression from the same cells across intact biological networks, including cardiac and neural patches. When applied to human-induced pluripotent stem-cell-derived cardiomyocyte patches, in situ electro-seq enabled multimodal in situ analysis of cardiomyocyte electrophysiology and gene expression at the cellular level, jointly defining cell states and developmental trajectories. Using machine-learning-based cross-modal analysis, in situ electro-seq identified gene-to-electrophysiology relationships throughout cardiomyocyte development and accurately reconstructed the evolution of gene expression profiles based on long-term stable electrical measurements. In situ electro-seq could be applicable to create spatiotemporal multimodal maps in electrogenic tissues, potentiating the discovery of cell types and gene programs responsible for electrophysiological function and dysfunction.

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

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

Biosensors integrated 3D organoid/organ-on-a-chip system: A real-time biomechanical, biophysical, and biochemical monitoring and characterization

As a full-fidelity simulation of human cells, tissues, organs, and even systems at the microscopic scale, Organ-on-a-Chip (OOC) has significant ethical advantages and development potential compared to animal experiments. The need for the design of new drug high-throughput screening platforms and the mechanistic study of human tissues/organs under pathological conditions, the evolving advances in 3D cell biology and engineering, etc., have promoted the updating of technologies in this field, such as the iteration of chip materials and 3D printing, which in turn facilitate the connection of complex multi-organs-on-chips for simulation and the further development of technology-composite new drug high-throughput screening platforms. As the most critical part of organ-on-a-chip design and practical application, verifying the success of organ model modeling, i.e., evaluating various biochemical and physical parameters in OOC devices, is crucial. Therefore, this paper provides a logical and comprehensive review and discussion of the advances in organ-on-a-chip detection and evaluation technologies from a broad perspective, covering the directions of tissue engineering scaffolds, microenvironment, single/multi-organ function, and stimulus-based evaluation, and provides a more comprehensive review of the progress in the significant organ-on-a-chip research areas in the physiological state.

Technology Roadmap for Flexible Sensors

Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

Tissue-embedded stretchable nanoelectronics reveal endothelial cell-mediated electrical maturation of human 3D cardiac microtissues

Clinical translation of stem cell therapies for heart disease requires electrical integration of transplanted cardiomyocytes. Generation of electrically matured human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) is critical for electrical integration. Here, we found that hiPSC-derived endothelial cells (hiPSC-ECs) promoted the expression of selected maturation markers in hiPSC-CMs. Using tissue-embedded stretchable mesh nanoelectronics, we achieved a long-term stable map of human three-dimensional (3D) cardiac microtissue electrical activity. The results revealed that hiPSC-ECs accelerated the electrical maturation of hiPSC-CMs in 3D cardiac microtissues. Machine learning-based pseudotime trajectory inference of cardiomyocyte electrical signals further revealed the electrical phenotypic transition path during development. Guided by the electrical recording data, single-cell RNA sequencing identified that hiPSC-ECs promoted cardiomyocyte subpopulations with a more mature phenotype, and multiple ligand-receptor interactions were up-regulated between hiPSC-ECs and hiPSC-CMs, revealing a coordinated multifactorial mechanism of hiPSC-CM electrical maturation. Collectively, these findings show that hiPSC-ECs drive hiPSC-CM electrical maturation via multiple intercellular pathways.

First Organoid Intelligence (OI) workshop to form an OI community

The brain is arguably the most powerful computation system known. It is extremely efficient in processing large amounts of information and can discern signals from noise, adapt, and filter faulty information all while running on only 20 watts of power. The human brain's processing efficiency, progressive learning, and plasticity are unmatched by any computer system. Recent advances in stem cell technology have elevated the field of cell culture to higher levels of complexity, such as the development of three-dimensional (3D) brain organoids that recapitulate human brain functionality better than traditional monolayer cell systems. Organoid Intelligence (OI) aims to harness the innate biological capabilities of brain organoids for biocomputing and synthetic intelligence by interfacing them with computer technology. With the latest strides in stem cell technology, bioengineering, and machine learning, we can explore the ability of brain organoids to compute, and store given information (input), execute a task (output), and study how this affects the structural and functional connections in the organoids themselves. Furthermore, understanding how learning generates and changes patterns of connectivity in organoids can shed light on the early stages of cognition in the human brain. Investigating and understanding these concepts is an enormous, multidisciplinary endeavor that necessitates the engagement of both the scientific community and the public. Thus, on Feb 22-24 of 2022, the Johns Hopkins University held the first Organoid Intelligence Workshop to form an OI Community and to lay out the groundwork for the establishment of OI as a new scientific discipline. The potential of OI to revolutionize computing, neurological research, and drug development was discussed, along with a vision and roadmap for its development over the coming decade.

Biosensor integrated tissue chips and their applications on Earth and in space

The development of space exploration technologies has positively impacted everyday life on Earth in terms of communication, environmental, social, and economic perspectives. The human body constantly fluctuates during spaceflight, even for a short-term mission. Unfortunately, technology is evolving faster than humans' ability to adapt, and many therapeutics entering clinical trials fail even after being subjected to vigorous in vivo testing due to toxicity and lack of efficacy. Therefore, tissue chips (also mentioned as organ-on-a-chip) with biosensors are being developed to compensate for the lack of relevant models to help improve the drug development process. There has been a push to monitor cell and tissue functions, based on their biological signals and utilize the integration of biosensors into tissue chips in space to monitor and assess cell microenvironment in real-time. With the collaboration between the Center for the Advancement of Science in Space (CASIS), the National Aeronautics and Space Administration (NASA) and other partners, they are providing the opportunities to study the effects of microgravity environment has on the human body. Institutions such as the National Institute of Health (NIH) and National Science Foundation (NSF) are partnering with CASIS and NASA to utilize tissue chips onboard the International Space Station (ISS). This article reviews the endless benefits of space technology, the development of integrated biosensors in tissue chips and their applications to better understand human biology, physiology, and diseases in space and on Earth, followed by future perspectives of tissue chip applications on Earth and in space.

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.

Intersection of nanomaterials and organoids technology in biomedicine

Organoids are stem cell-derived, self-organizing, 3D structures. Compared to the conventional 2D cell culture method, 3D cultured organoids contain a variety of cell types that can form functional "micro-organs" and can be used to simulate the occurrence process and physiological pathological state of organ tissues more effectively. Nanomaterials (NMs) are becoming indispensable in the development of novel organoids. Understanding the application of nanomaterials in organoid construction can, therefore, provide researchers with ideas for the development of novel organoids. Here, we discuss the application status of NMs in various organoid culture systems and the research direction of NMs combined with organoids in the biomedical field.

Engineering approaches for cardiac organoid formation and their characterization

Cardiac organoids are 3-dimensional (3D) structures composed of tissue or niche-specific cells, obtained from diverse sources, encapsulated in either a naturally derived or synthetic, extracellular matrix scaffold, and include exogenous biochemical signals such as essential growth factors. The overarching goal of developing cardiac organoid models is to establish a functional integration of cardiomyocytes with physiologically relevant cells, tissues, and structures like capillary-like networks composed of endothelial cells. These organoids used to model human heart anatomy, physiology, and disease pathologies in vitro have the potential to solve many issues related to cardiovascular drug discovery and fundamental research. The advent of patient-specific human-induced pluripotent stem cell-derived cardiovascular cells provide a unique, single-source approach to study the complex process of cardiovascular disease progression through organoid formation and incorporation into relevant, controlled microenvironments such as microfluidic devices. Strategies that aim to accomplish such a feat include microfluidic technology-based approaches, microphysiological systems, microwells, microarray-based platforms, 3D bioprinted models, and electrospun fiber mat-based scaffolds. This article discusses the engineering or technology-driven practices for making cardiac organoid models in comparison with self-assembled or scaffold-free methods to generate organoids. We further discuss emerging strategies for characterization of the bio-assembled cardiac organoids including electrophysiology and machine-learning and conclude with prospective points of interest for engineering cardiac tissues in vitro.

A soft and ultrasensitive force sensing diaphragm for probing cardiac organoids instantaneously and wirelessly

Time-lapse mechanical properties of stem cell derived cardiac organoids are important biological cues for understanding contraction dynamics of human heart tissues, cardiovascular functions and diseases. However, it remains difficult to directly, instantaneously and accurately characterize such mechanical properties in real-time and in situ because cardiac organoids are topologically complex, three-dimensional soft tissues suspended in biological media, which creates a mismatch in mechanics and topology with state-of-the-art force sensors that are typically rigid, planar and bulky. Here, we present a soft resistive force-sensing diaphragm based on ultrasensitive resistive nanocracked platinum film, which can be integrated into an all-soft culture well via an oxygen plasma-enabled bonding process. We show that a reliable organoid-diaphragm contact can be established by an 'Atomic Force Microscope-like' engaging process. This allows for instantaneous detection of the organoids' minute contractile forces and beating patterns during electrical stimulation, resuscitation, drug dosing, tissue culture, and disease modelling.

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.

A Novel 3D Helical Microelectrode Array for In Vitro Extracellular Action Potential Recording

Recent advances in cell and tissue engineering have enabled long-term three-dimensional (3D) in vitro cultures of human-derived neuronal tissues. Analogous two-dimensional (2D) tissue cultures have been used for decades in combination with substrate integrated microelectrode arrays (MEA) for pharmacological and toxicological assessments. While the phenotypic and cytoarchitectural arguments for 3D culture are clear, 3D MEA technologies are presently inadequate. This is mostly due to the technical challenge of creating vertical electrical conduction paths (or 'traces') using standardized biocompatible materials and fabrication techniques. Here, we have circumvented that challenge by designing and fabricating a novel helical 3D MEA comprised of polyimide, amorphous silicon carbide (a-SiC), gold/titanium, and sputtered iridium oxide films (SIROF). Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) testing confirmed fully-fabricated MEAs should be capable of recording extracellular action potentials (EAPs) with high signal-to-noise ratios (SNR). We then seeded induced pluripotent stems cell (iPSC) sensory neurons (SNs) in a 3D collagen-based hydrogel integrated with the helical MEAs and recorded EAPs for up to 28 days in vitro from across the MEA volume. Importantly, this highly adaptable design does not intrinsically limit cell/tissue type, channel count, height, or total volume.

Mucosa-interfacing electronics

The surface mucosa that lines many of our organs houses myriad biometric signals and, therefore, has great potential as a sensor-tissue interface for high-fidelity and long-term biosensing. However, progress is still nascent for mucosa-interfacing electronics owing to challenges with establishing robust sensor-tissue interfaces; device localization, retention and removal; and power and data transfer. This is in sharp contrast to the rapidly advancing field of skin-interfacing electronics, which are replacing traditional hospital visits with minimally invasive, real-time, continuous and untethered biosensing. This Review aims to bridge the gap between skin-interfacing electronics and mucosa-interfacing electronics systems through a comparison of the properties and functions of the skin and internal mucosal surfaces. The major physiological signals accessible through mucosa-lined organs are surveyed and design considerations for the next generation of mucosa-interfacing electronics are outlined based on state-of-the-art developments in bio-integrated electronics. With this Review, we aim to inspire hardware solutions that can serve as a foundation for developing personalized biosensing from the mucosa, a relatively uncharted field with great scientific and clinical potential.