Transparent microelectrodes have recently emerged as a promising approach for crosstalk‐free multifunctional electrical and optical biointerfacing. High‐performance flexible platforms that allow seamless integration with soft tissue systems for such applications are urgently needed. Here, silver nanowires (Ag NWs)‐based transparent microelectrode arrays (MEAs) and interconnects are designed to meet this demand. The nanowire networks exhibit a high optical transparency >90.0% at 550 nm, and superior mechanical stability up to 100,000 bending cycles at 5 mm radius. The Ag NWs microelectrodes preserve low normalized electrochemical impedance of 3.4–15 Ω cm2 at 1 kHz, and the interconnects demonstrate excellent sheet resistance (Rsh) of 4.1–25 Ω sq−1. In vivo histological analysis reveals that the Ag NWs structures are biocompatible. Studies on Langendorff‐perfused mouse and rat hearts demonstrate that the Ag NWs MEAs enable high‐fidelity real‐time monitoring of heart rhythm during co‐localized optogenetic pacing and optical mapping. This proof‐of‐concept work illustrates that the solution‐processed, transparent, and flexible Ag NWs structures are a promising candidate for the next‐generation of large‐area multifunctional biointerfaces for interrogating complex biological systems in basic and translational research.

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The two distinct TDR modes were revealed during the progression of mouse cardiac hypertrophy and failure, indicating that the remodelling of TDR depends on the stage of the disease.

Heart rhythm disorders, known as arrhythmias, cause signi cant morbidity and are one of the leading causes of mortality. Cardiac arrhythmias are primarily treated by implantable devices, such as pacemakers and de brillators, or by ablation therapy guided by electroanatomical mapping.Pharmacological treatments are mostly ineffective. Both implantable and ablation therapies require sophisticated biointerfaces for electrophysiological measurements of electrograms and delivery of therapeutic stimulation or ablation energy. In this work, we report for the rst time on graphene biointerface for in vivo cardiac electrophysiology. Leveraging sub-micrometer thick tissue-conformable graphene arrays, we demonstrate sensing and stimulation of the open mammalian heart both in vitro and in vivo. Furthermore, we demonstrate graphene pacemaker treatment of a pharmacologically-induced arrhythmia, AV block. The arrays show effective electrochemical properties, namely interface impedance down to 40 Ohm×cm 2 , charge storage capacity up to 63.7 mC/cm 2 , and charge injection capacity up to 704 µC/cm 2 . Transparency of the graphene structures allows for simultaneous optical mapping of cardiac action potentials and calcium transients while performing electrical measurements and stimulation. Our report presents evidence of the signi cant potential of graphene biointerfaces for the future clinical device-and catheter-based cardiac arrhythmias therapies.

disease arises from asynchrony and abnormalities in the complex and coordinated electro-mechanical properties over time and space. Therefore, devices that allow monitoring and controlling of the spatiotemporal dynamics of cardiac activity are crucial for unraveling the pathophysiology of heart disease and developing effective treatment therapies in clinical cardiology practice. Implantable electronic pacemakers play an essential role in treating various types of arrhythmias and heart failure and studying cardiac physiology by changing the membrane potential and triggering an action potential with an electric current. [3,4] However, electrical stimulation can lead to adverse effects on cell health and integrity due to the cell membrane electroporation and redox processes. [5,6] The electrical fields created by the stimulation electrodes will generate electrical crosstalk between stimulation and recording electrodes and result in recording artifacts. [7] Furthermore, electrical stimulation is unable to target specific subtypes of cardiac cells. Optogenetics uses light to modulate the activity of genetically targeted cell types through photosensitive ion channels and pumps. [8] Despite its initial use in neuroscience research to control neural circuits, [8,9] optogenetics has now been applied as a promising tool in cardiology for pain-free, low-energy optical pacing, and defibrillation with cell-type specificity. [10][11][12] In addition, cardiac optogenetics generally interferes less with simultaneous electrical readout of cardiac activity compared to electrical stimulation. Currently, cardiac optogenetics is primarily used in in vitro and ex vivo cardiac studies with cell cultures or explanted perfused hearts. [13][14][15][16][17] More in vivo research is crucially needed to fully exploit the unique opportunities cardiac optogenetics offers for mechanistic investigations of heart function in health and disease.Small animal models such as mice and rats are the main rodent species that could be genetically engineered for in vivo cardiac optogenetics research and their heart electrophysiology is a good approximation of the human electrophysiology. [18] Implantable cardiac devices that combine precise light delivery to targeted heart regions of small animals with electrophysiological readout capabilities remain a major technological Bioelectronic devices that allow simultaneous accurate monitoring and control of the spatiotemporal patterns of cardiac activity provide an effective means to understand the mechanisms and optimize therapeutic strategies for heart disease. Optogenetics is a promising technology for cardiac research due to its advantages such as cell-type selectivity and high space-time resolution, but its efficacy is limited by the insufficient number of modulation channels and lack of simultaneous spatiotemporal mapping capabilities in current implantable cardiac optogenetics tools available for in vivo investigations. Here, soft implantable electro-optical cardiac devices integrating multilayered highly ...