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Ion channels transduce external stimuli into ion-transport-mediated signaling, which has received considerable attention in diverse fields such as sensors, energy harvesting devices, and desalination membrane. In this work, we present a photosensitive ion channel based on plasmonic gold nanostars (AuNSs) and cellulose nanofibers (CNFs) embedded in layered MXene nanosheets. The MXene/AuNS/CNF (MAC) membrane provides subnanometer-sized ionic pathways for light-sensitive cationic flow. When the MAC nanochannel is exposed to NIR light, a photothermal gradient is formed, which induces directional photothermo-osmotic flow of nanoconfined electrolyte against the thermal gradient and produces a net ionic current. MAC membrane exhibits enhanced photothermal current compared with pristine MXene, which is attributed to the combined photothermal effects of plasmonic AuNSs and MXene and the widened interspacing of the MAC composite via the hydrophilic nanofibrils. The MAC composite membranes are envisioned to be applied in flexible ionic channels with ionogels and light-controlled ionic circuits. Artificial ion channels are in demand for ionotronic devices. Here, the authors use layered MXene membranes modified with plasmonic gold nanostars and cellulose nanofibers to convert a thermal gradient into an ion current for photosensitive ion channeling.

Biodegradable artificial synapses hold great promise for sustainable neuromorphic electronics, yet combining long-term memory, ultralow energy consumption, and mechanical robustness remains challenging. Here, we report a fully biodegradable multilayer artificial synapse (M-AS) composed of crosslinked chitosan–guar gum (CS–GG) ion-active layers (IALs) and a cellulose acetate (CA) ion-binding layer (IBL). This trilayer architecture enhances ion trapping via ion-dipole coupling (IDC) at the IAL–IBL interface, while hydrogen-bonded crosslinking within the CS–GG matrix enhances mechanical and environmental stability. Sodium chloride, embedded in the IALs, serves as a mobile ionic species analogous to biological neurotransmitters, enabling low-voltage ion migration. Upon electrical stimulation, ion migration and dipole alignment induce IDC, leading to partial ion retention and cascade-like postsynaptic current responses that support memory formation. The M-AS supports key synaptic functionalities—including paired-pulse facilitation, short-term and long-term plasticity, multilevel memory encoding, and bidirectional modulation—under sub-millivolt operation. It achieves the longest long-term memory time (5944 s) reported among biodegradable artificial synapses and an energy consumption (0.85 fJ/event) lower than that of biological synapses. Integration with a thermistor and robotic actuator enables a bioinspired reflexive system capable of adaptive, stimulus-dependent learning and reflex-like behaviors. These results demonstrate the potential of M-AS for low-power, intelligent human–machine interfaces. Artificial synapses for wearable and implantable applications are limited in widespread use due to environmental instability, limited ion-trapping capabilities and high energy consumption. Here, the authors present a biodegradable multilayer artificial synapse achieving 0.85 fJ per synaptic event.

Over the past decade, stereotactically placed electrodes have become the gold standard for deep brain recording and stimulation for a wide variety of neurological and psychiatric diseases. Current electrodes, however, are limited in their spatial resolution and ability to record from small populations of neurons, let alone individual neurons. Here, we report on an innovative, customizable, monolithically integrated human-grade flexible depth electrode capable of recording from up to 128 channels and able to record at a depth of 10 cm in brain tissue. This thin, stylet-guided depth electrode is capable of recording local field potentials and single unit neuronal activity (action potentials), validated across species. This device represents an advance in manufacturing and design approaches which extends the capabilities of a mainstay technology in clinical neurology. Electrodes available for deep brain recording and stimulation have a number of limitations. Here the authors describe a thin-film depth electrode that may offer improved spatial and temporal resolution for recording brain activity.

In the domains of wearable electronics, robotics, and the Internet of Things, there is a demand for devices with low power consumption and the capability of multiplex sensing, memory, and learning. Triboelectric nanogenerators (TENGs) offer remarkable versatility in this regard, particularly when integrated with synaptic transistors that mimic biological synapses. However, conventional TENGs, generating only two spikes per cycle, have limitations when used in synaptic devices requiring repetitive high‐frequency gating signals to perform various synaptic plasticity functions. Herein, a multi‐layered micropatterned TENG (M‐TENG) consisting of a polydimethylsiloxane (PDMS) film and a composite film that includes 1H,1H,2H,2H‐perfluorooctyltrichlorosilane/BaTiO3/PDMS are proposed. The M‐TENG generates multiple spikes from a single touch by utilizing separate triboelectric charges at the multiple friction layers, along with a contact/separation delay achieved by distinct spacers between layers. This configuration allows the maximum triboelectric output charge of M‐TENG to reach up to 7.52 nC, compared to 3.69 nC for a single‐layered TENG. Furthermore, by integrating M‐TENGs with an organic electrochemical transistor, the spike number multiplication property of M‐TENGs is leveraged to demonstrate an artificial synaptic device with low energy consumption. As a proof‐of‐concept application, a robotic hand is operated through continuous memory training under repeated stimulations, successfully emulating long‐term plasticity. Three‐layered triboelectric nanogenerator (3‐TENG) generates multiple spikes from a single touch and its integration with an organic electrochemical transistor (OECT) to accomplish a highly efficient artificial synaptic device. These multiple spikes not only enhance the triboelectric performance of the TENG but can also be utilized to successfully emulate neural functions by delivering high‐frequency gate voltage to the OECT.

Iontronic bioelectronics provides a powerful framework for bridging the mismatch between conventional electronic systems and soft, ion‐mediated biological tissues. By harnessing mobile ions as charge carriers and functional mediators, iontronic devices enable biocompatible, conformal, and low‐impedance interfaces that support both signal acquisition and therapeutic delivery. Recent advances in ionic materials, such as hydrogels, ion gels, and ionic liquids, have facilitated high‐fidelity physiological sensing, wound monitoring, and programmable drug and ion release. In addition to passive sensing and delivery, emerging iontronic platforms integrate real‐time biosignal monitoring with adaptive, AI‐guided feedback to enable closed‐loop therapeutic control. This review highlights the multifunctional role of ions in sensing, modulation, and stimulation across diverse applications, including skin‐interfaced electronics, neural and cardiac interfaces, and wound therapy. Key challenges such as operational stability, signal specificity, and long‐term biocompatibility are further examined, and material, structural, and system‐level innovations that are paving the way toward intelligent, responsive, and clinically viable iontronic bioelectronic platforms are discussed.

Internet of Things (IoT) is becoming pervasive in our daily lives. Wearable technologies will expand the connectivity of IoT and will increase the interaction between technology and human body. Micro Electro-Mechanical Systems (MEMS) microfabrication techniques that involve bulk Si micromachining and thin film processing have allowed us to develop electronic systems that are based on Si and other advanced materials that are flexible, wearable, and implantable. Wearable and implantable electronics equipped with sensors enable us to perform real-time health monitoring from above and below the skin, respectively, and can replace conventional bulky electrophysiological monitoring devices and systems. Research efforts in wearables and implantables have intensified in the last decade tackling several aspects of the sensor technology, embedded signal processing and conditioning, energy harvesting, connectorization, functionality, longevity and reliability. However, there are still technical challenges that impose restrictions for their widespread adoption. On top of these challenges is the power source for the wearable or implantable device. Energy harvesting is expected to replace conventional battery systems that power wearables and implantables. In this dissertation, we focus on solar energy as an energy source for self-powered electronics. In Chapter 1, the motivation of the dissertation together with a brief survey of state of the art in flexible and wearable electronics with energy harvesting system and implantable medical devices are discussed. In Chapter 2, we disclose our parametric studies on solar cells with different microwire surface and array morphologies to understand the effect of surface passivation, surface crystal orientation on surface recombination and carrier collection on SiMW solar cells with radial p-n junctions as well as their emitter series resistances with an overall goal of maximizing their power conversion efficiencies. In Chapter 3, we present an approach for self-powered wearable electronics by means of the monolithic integration of SiMW solar cells with Si MOSFETs on a Silicon on Insulator (SOI) wafer that is subsequently transferred to flexible substrates. The fabrication details and its application to a voltage-controlled oscillator and electrophysiological monitoring are discussed. In Chapter 4, we discuss the details of the novel fabrication processes for the development of a stylet guided depth/laminar probe and of a surface electrocorticography (ECoG) grid that is fabricated with bio-compatible polymers (Polyimide and Parylene C) including their electrochemical characterization and their use in vivo for electrophysiological recordings in rats.

Catalysts play a significant role in clean renewable hydrogen fuel generation through water splitting reaction as the surface of most semiconductors proper for water splitting has poor performance for hydrogen gas evolution. The catalytic performance strongly depends on the atomic arrangement at the surface, which necessitates the correlation of the surface structure to the catalytic activity in well-controlled catalyst surfaces. Herein, we report a novel catalytic performance of simple-synthesized porous NiO nanowires (NWs) as catalyst/co-catalyst for the hydrogen evolution reaction (HER). The correlation of catalytic activity and atomic/surface structure is investigated by detailed high resolution transmission electron microscopy (HRTEM) exhibiting a strong dependence of NiO NW photo- and electrocatalytic HER performance on the density of exposed high-index-facet (HIF) atoms, which corroborates with theoretical calculations. Significantly, the optimized porous NiO NWs offer long-term electrocatalytic stability of over one day and 45 times higher photocatalytic hydrogen production compared to commercial NiO nanoparticles. Our results open new perspectives in the search for the development of structurally stable and chemically active semiconductor-based catalysts for cost-effective and efficient hydrogen fuel production at large scale.

Over the past decade, stereotactically placed electrodes have become the gold standard for deep brain recording and stimulation for a wide variety of neurological and psychiatric diseases. Current electrodes, however, are limited in their spatial resolution and ability to record from small populations of neurons, let alone individual neurons. Here, we report on a novel, reconfigurable, monolithically integrated human-grade flexible depth electrode capable of recording from up to 128 channels and able to record at a depth of 10 cm in brain tissue. This thin, stylet-guided depth electrode is capable of recording local field potentials and single unit neuronal activity (action potentials), validated across species. This device represents a major new advance in manufacturing and design approaches which extends the capabilities of a mainstay technology in clinical neurology.Competing Interest StatementThe authors declare the following competing interests: KL, YGR, and SAD and the University of California San Diego filed a patent application for the manufacture of the novel depth electrodes. YT, AMR, and SAD have competing interests not related to this work including equity in Precision Neurotek Inc. and SAD in FeelTheTouch LLC. SAD was a paid consultant to MaXentric Technologies. AMR has an equity and is a cofounder of CerebroAI. AMR received consulting fees from Abbott Inc and Biotronik Inc. The MGH Translational Research Center has clinical research support agreements with Neuralink, Paradromics, and Synchron, for which SSC provide consultative input. The other authors declare that they have no competing interests.Footnotes* Figure 2 had an update.

Abstract Despite ongoing advancements in our understanding of the local single-cellular and network-level activity of neuronal populations in the human brain, extraordinarily little is known about their ‘intermediate’ microscale local circuit dynamics. Here, we utilized ultrahigh density microelectrode arrays and a rare opportunity to perform intracranial recordings across multiple cortical areas in human participants to discover three distinct classes of cortical activity that are not locked to ongoing natural brain rhythmic activity. The first included fast waveforms similar to extracellular single unit activity. The other two types were discrete events with slower waveform dynamics and were found preferentially in upper layers of the grey matter. They were also observed in rodents, non-human primates, and semi-chronic recordings in humans via laminar and Utah array microelectrodes. The rates of all three events were selectively modulated by auditory and electrical stimuli, pharmacological manipulation, and cold saline application and had small causal co-occurrences. These results suggest that with the proper combination of high resolution microelectrodes and analytic techniques it is possible to capture neuronal dynamics that lay between somatic action potentials and aggregate population activity and that understanding these intermediate microscale dynamics may reveal important details of the full circuit behavior in human cognition. Competing Interest Statement The authors have declared no competing interest. Footnotes * To address questions of regarding these microscale events on microelectrodes, we demonstrate we can find these events in laminar microelectrode array (N=9) and Utah array recordings (N=8) from semi-chronic human studies. For this reason, we have changed the title of the original submission as well as the writing to reflect a focus on these events detected on or near the cortical surface of the brain. We have added several more coauthors to the manuscript to reflect their hard work in gathering these data. In addition, we have included further spectral analyses in the Supplemental files and included more gathered data and further analyses.