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Engineered systems that can serve as chronically stable, high-performance electronic recording and stimulation interfaces to the brain and other parts of the nervous system, with cellular-level resolution across macroscopic areas, are of broad interest to the neuroscience and biomedical communities. Challenges remain in the development of biocompatible materials and the design of flexible implants for these purposes, where ulimate goals are for performance attributes approaching those of conventional wafer-based technologies and for operational timescales reaching the human lifespan. This Review summarizes recent advances in this field, with emphasis on active and passive constituent materials, design architectures and integration methods that support necessary levels of biocompatibility, electronic functionality, long-term stable operation in biofluids and reliability for use in vivo. Bioelectronic systems that enable multiplexed electrophysiological mapping across large areas at high spatiotemporal resolution are surveyed, with a particular focus on those with proven chronic stability in live animal models and scalability to thousands of channels over human-brain-scale dimensions. Research in materials science will continue to underpin progress in this field of study. This Review provides an overview of the advances in materials and device design that are enabling the realization of implantable electronic interfaces for long-term, multiplexed recording and stimulation of the brain and nervous system.

The rigidity and relatively primitive modes of operation of catheters equipped with sensing or actuation elements impede their conformal contact with soft-tissue surfaces, limit the scope of their uses, lengthen surgical times and increase the need for advanced surgical skills. Here, we report materials, device designs and fabrication approaches for integrating advanced electronic functionality with catheters for minimally invasive forms of cardiac surgery. By using multiphysics modelling, plastic heart models and Langendorff animal and human hearts, we show that soft electronic arrays in multilayer configurations on endocardial balloon catheters can establish conformal contact with curved tissue surfaces, support high-density spatiotemporal mapping of temperature, pressure and electrophysiological parameters and allow for programmable electrical stimulation, radiofrequency ablation and irreversible electroporation. Integrating multimodal and multiplexing capabilities into minimally invasive surgical instruments may improve surgical performance and patient outcomes. Soft multilayer electronic arrays on endocardial balloon catheters allow for multiplexed high-density spatiotemporal sensing and actuation, as shown in perfused ex vivo hearts.

Thermochromic window develops as a competitive solution for carbon emissions due to comprehensive advantages of its passivity and effective utilization of energy. How to further enhance the solar modulation ( △ T sol ) of thermochromic windows while ensuring high luminous transmittance ( T lum ) becomes the latest challenge to touch the limit of energy efficiency. Here, we show a smart window combining mechanochromism with thermochromism by self-rolling of vanadium dioxide (VO 2 ) nanomembranes to enhance multi-level solar modulation. The mechanochromism is introduced by the temperature-controlled regulation of curvature of rolled-up smart window, which benefits from effective strain adjustment in VO 2 nanomembranes upon the phase transition. Under geometry design and optimization, the rolled-up smart window with high △ T sol and T lum is achieved for the modulation of indoor temperature self-adapted to seasons and climate. Furthermore, such rolled-up smart window enables high infrared reflectance after triggered phase transition and acts as a smart lens protective cover for strong radiation. This work supports the feasibility of self-rolling technology in smart windows and lens protection, which promises broad interest and practical applications of self-adapting devices and systems for smart building, intelligent sensors and actuators with the perspective of energy efficiency. In this work, authors demonstrate a smart window combining mechanochromism with thermochromism by self-rolling of VO 2 nanomembranes to modulate in-door temperature self-adapted to seasons and climate with high efficiency.

Foundry-based routes to transient silicon electronic devices have the potential to serve as the manufacturing basis for “green” electronic devices, biodegradable implants, hardware secure data storage systems, and unrecoverable remote devices. This article introduces materials and processing approaches that enable state-of-the-art silicon complementary metal-oxide-semiconductor (CMOS) foundries to be leveraged for high-performance, water-soluble forms of electronics. The key elements are (i) collections of biodegradable electronic materials (e.g., silicon, tungsten, silicon nitride, silicon dioxide) and device architectures that are compatible with manufacturing procedures currently used in the integrated circuit industry, (ii) release schemes and transfer printing methods for integration of multiple ultrathin components formed in this way onto biodegradable polymer substrates, and (iii) planarization and metallization techniques to yield interconnected and fully functional systems. Various CMOS devices and circuit elements created in this fashion and detailed measurements of their electrical characteristics highlight the capabilities. Accelerated dissolution studies in aqueous environments reveal the chemical kinetics associated with the underlying transient behaviors. The results demonstrate the technical feasibility for using foundry-based routes to sophisticated forms of transient electronic devices, with functional capabilities and cost structures that could support diverse applications in the biomedical, military, industrial, and consumer industries.

Stretchable electronics that prevalently adopt chemically inert metals as sensing layers and interconnect wires have enabled high-fidelity signal acquisition for on-skin applications. However, the weak interfacial interaction between inert metals and elastomers limit the tolerance of the device to external friction interferences. Here, we report an interfacial diffusion-induced cohesion strategy that utilizes hydrophilic polyurethane to wet gold (Au) grains and render them wrapped by strong hydrogen bonding, resulting in a high interfacial binding strength of 1017.6 N/m. By further constructing a nanoscale rough configuration of the polyurethane (RPU), the binding strength of Au-RPU device increases to 1243.4 N/m, which is 100 and 4 times higher than that of conventional polydimethylsiloxane and styrene-ethylene-butylene-styrene-based devices, respectively. The stretchable Au-RPU device can remain good electrical conductivity after 1022 frictions at 130 kPa pressure, and reliably record high-fidelity electrophysiological signals. Furthermore, an anti-friction pressure sensor array is constructed based on Au-RPU interconnect wires, demonstrating a superior mechanical durability for concentrated large pressure acquisition. This chemical modification-free approach of interfacial strengthening for chemically inert metal-based stretchable electronics is promising for three-dimensional integration and on-chip interconnection. Stretchable electronics require high interfacial strength between the inert metal and elastomer components for durable interconnection applications. Cao et al. show a chemical modification-free interfacial diffusion-induced cohesion strategy, using hydrophilic polyurethane to induce hydrogen bonding of gold grains.

Dynamically controlling electromagnetic waves at will is highly desired in many applications, but most previously realized mechanically reconfigurable metasurfaces are of restricted wave-control capabilities due to the limited tuning ranges of structural properties (e.g., lattice constant or meta-atoms). Here, we present mechanically reconfigurable metasurfaces in which both lattice constants and local reflection phases of constitutional meta-atoms can be synchronously controlled based on the kirigami rotation transformation, thereby exhibiting extended tuning ranges and thus wave-control capabilities. In particular, such metasurfaces can exhibit continuously varied and even re-formed reflection-phase profiles along with the kirigami rotation transformation, serving as ideal platforms to achieve reconfigurable beam steering in pre-designed manners. Using this concept, we design and fabricate two kirigami metasurfaces, working as a beam flipper and as a beam splitter for microwaves, respectively, and experimentally characterize their wave-manipulation functionalities. Experimental results are in good agreement with full-wave simulations. The proposed idea is so general that it can be applied to realize reconfigurable metasurfaces with different materials/configurations or in high frequency regimes, for controlling electromagnetic waves and other classical waves (e.g., acoustic waves). Jiang et al. propose a kirigami-based, mechanically reconfigurable metasurface that utilizes simple uniform stretching to achieve unexpected and dynamic beam steering functions. This unique approach modifies the geometric phase and lattice constant synchronously based on the rotation of anisotropic meta-atoms, exhibiting extended degree of freedom and wave-tuning ranges.

Advanced capabilities in electrical recording are essential for the treatment of heart-rhythm diseases. The most advanced technologies use flexible integrated electronics; however, the penetration of biological fluids into the underlying electronics and any ensuing electrochemical reactions pose significant safety risks. Here, we show that an ultrathin, leakage-free, biocompatible dielectric layer can completely seal an underlying array of flexible electronics while allowing for electrophysiological measurements through capacitive coupling between tissue and the electronics, without the need for direct metal contact. The resulting current-leakage levels and operational lifetimes are, respectively, four orders of magnitude smaller and between two and three orders of magnitude longer than those of other flexible-electronics technologies. Systematic electro­physiological studies with normal, paced and arrhythmic conditions in Langendorff hearts highlight the capabilities of the capacitive-coupling approach. These advances provide realistic pathways towards the broad applicability of biocompatible, flexible electronic implants. Capacitive coupling between tissue and flexible integrated electronics through a sealing dielectric layer facilitates long-term electrophysiology measurements, as demonstrated in ex vivo Langendorff heart models.

Real-time sensing and processing of tactile information are essential to enhance the capability of artificial electronic skins (e-skins), enabling unprecedented intelligent applications in tactile exploration and object manipulation. However, conventional tactile e-skin systems typically execute redundant data transfer and conversion for decision making due to their physical separation between sensors and processing units, leading to high transmission latency and power consumption. Here, we report an in-sensor tactile computing system based on a flexible capacitive pressure sensor array. This system utilizes multiple connected sensor networks to execute in-situ analog multiplication and accumulation operations, achieving both tactile sensing and computing functionalities. We experimentally implemented the in-sensor tactile computing system for low-level tactile sensory processing tasks including noise reduction and edge detection. The consumed power for single sensing-computing operation is over 22 times lower than that of a conventional mixed electronic system. These results demonstrate that our capacitive in-sensor computing system paves a promising way for power-constrained applications such as robotics and human-machine interfaces. Traditional tactile systems suffer from the physical separation between sensing and processing units, causing latency and power issues. Here, Chen et al. report a capacitive in-sensor tactile computing system, using sensor networks to execute in-situ multiplication and accumulation operations.

Vivid haptic feedback remains a challenge in truly immersive virtual reality and augmented reality. As the tactile sensitivity among different individuals and different parts of the hand within a person varies widely, a universal method to encode tactile information into faithful feedback in hands according to sensitivity features is urgently needed. In addition, existing haptic interfaces worn on the hand are usually bulky, rigid and tethered by cables, which is a hurdle for accurately and naturally providing haptic feedbacks. Here we report a soft, ultrathin, miniaturized and wireless electrotactile system (WeTac) that delivers current through the hand to induce tactile sensations as the skin-integrated haptic interface. With a relatively high pixel density over the whole hand area, the WeTac can provide tactile stimulation and measure the sensation thresholds of users in a flexible way. By mapping the thresholds for different electrical parameters, personalized threshold data can be acquired to reproduce virtual touching sensations on the hand with optimized stimulation intensity and avoid causing pain. With an accurate control of sensation level, temporal and spatial perception, it allows providing personalized feedback when users interact with virtual objects. This technique is promising for a more vivid touching experience in the virtual world and in human–machine interactions. The haptic interface is an essential part of human–machine interfaces where tactile information is delivered between human and machine. Yao et al. develop a soft, ultrathin, miniaturized and wireless electrotactile system that allows virtual tactile information to be reproduced over the hand.

A critical challenge lies in the development of the next‐generation neural interface, in mechanically tissue‐compatible fashion, that offer accurate, transient recording electrophysiological (EP) information and autonomous degradation after stable operation. Here, an ultrathin, lightweight, soft and multichannel neural interface is presented based on organic‐electrochemical‐transistor‐(OECT)‐based network, with capabilities of continuous high‐fidelity mapping of neural signals and biosafety active degrading after performing functions. Such platform yields a high spatiotemporal resolution of 1.42 ms and 20 µm, with signal‐to‐noise ratio up to ≈37 dB. The implantable OECT arrays can well establish stable functional neural interfaces, designed as fully biodegradable electronic platforms in vivo. Demonstrated applications of such OECT implants include real‐time monitoring of electrical activities from the cortical surface of rats under various conditions (e.g., narcosis, epileptic seizure, and electric stimuli) and electrocorticography mapping from 100 channels. This technology offers general applicability in neural interfaces, with great potential utility in treatment/diagnosis of neurological disorders. The ultrasoft, multichannel, biodegradable OECT‐based neural interfaces are developed, which not only monitor the μ‐ECoG signals in high fidelity, but also autonomous degradation without any trigger events. Arrays with 100 channels, temporal/spatial resolution of 1.42 ms and 20 µm, and great signal‐to‐noise ratio of 37 dB, are achieved, demonstrating a facile and efficient tool for diagnostic purposes and neuroscience research.