Advances in conductive supramolecular hydrogels for applications in wearable electronics.

Stochastic dynamics of a bistable vibration energy harvesting system with bilateral barriers

Ion-track-etched membranes (ITEMs) have emerged as a distinct class of nanostructured materials and represent a versatile platform that offers precise control over pore shape, size, and areal density. These membranes offer considerable mechanical and chemical stability, making them valuable for a variety of applications, including nanoionic rectifiers, sensors, nanoiontronics devices, and energy harvesting systems. The chemical etching process of ITEMs introduces carboxylic acid groups on the surface, which serve as the sites for functionalization. Functionalization is crucial for using the ITEMs in sensor applications. ITEM-based sensors provide considerable sensitivity and selectivity. Moreover, the sensors have a low limit of detection compared to other traditional sensors. ITEMs also exhibit memristive behavior (hysteresis loop) and can perform logic gate functions. These attributes are crucial for nanoionic fluidic-based neuromorphic computing. Moreover, ITEMs can serve as efficient platforms for osmotic energy harvesting (OEH) as well as membrane-assisted cooling and dehumidification applications. This review article articulates the fundamentals of ITEMs, fabrication strategies, the origins of surface-charge-dominated ion-transport mechanisms under nanoconfinement, and chemical functionalization approaches. In addition to that, concepts of ionic rectification, hysteresis, and nonlinear functionalities related to the memristor and neuromorphic computing are also discussed. Moreover, special attention was paid to OEH systems, and power densities obtained with different membranes were also discussed and compared. The review article also provides insights into next-generation nanoionic systems by combining the concepts of nanofluidics and electrochemistry. In addition, a comprehensive analysis of the current challenges and future opportunities in developing multifunctional, scalable, and sustainable ITEM technologies is also presented.

Liquid-solid triboelectric nanogenerators (LS-TENGs) based on contact electrification and electrostatic induction effect havegarnered significantattention as apromisingrenewable energy harvesting technology. So far, the LS-TENGs still have relatively low charge density. Here, we developed a tubular structure LS-TENG with high charge density by employing a self-assembled fluoroalkyl layer and grounding water. It was found that the transferred charge of the tubular structure LS-TENG can be enhanced by grounding water, which is likely attributed to the grounded water acquiring more charges from the ground to effectively shield the dielectric surface charges. Then, applying fluorinated modification on silica (SiO2) surface to enhance surface contact electrification, the tubular LS-TENG generated a high transferred charge of 1.96 µC (charge density of 2.16 mC m-2), superior to previous LS-TENGs based on contact electrification. The electrical output performance of the tubular LS-TENGs can be precisely regulated by adjusting the motion frequency, swing angle, and liquid properties. Finally, the tubular LS-TENGs successfully realized the parallel connection of multiple devices and powered a hygrothermometer, which exhibits great potential in low-frequency mechanical energy harvesting and self-powered system applications.

Scientists have been working diligently to develop environmentally friendly piezoelectric materials that meet the growing demand for renewable, biocompatible, and flexible power sources. Common piezoelectric materials such as poly(vinylidene fluoride) and lead zirconate titanate are not practical due to their toxicity, environmental persistence, and short lifespan. Because of its inherent piezoelectricity, flexibility, biocompatibility, and biodegradability, cellulose, the most prevalent renewable biopolymer, is an excellent substitute. It is currently challenging to achieve performance optimization, environmental stability, uniform benchmarking, regeneration, and large-scale commercialization. Cellulose-derived materials possess considerable potential because they originate from renewable biomass resources, exhibit built-in piezoelectricity, are flexible, and degrade naturally. This paper provides a comprehensive examination of the fundamental principles of cellulose piezoelectricity and discusses several forms of cellulose-based piezoelectric materials, including composites. We also examine the manufacturing and processing of nanogenerators and wearable sensors, which are examples of biodegradable, flexible energy-harvesting devices, and their interactions with these devices. We provide an in-depth review of recent advances in performance, including piezoelectric constants, device output, stability, and the roles of structural engineering, alignment, recycling and regeneration and hybridization. We also explore potential avenues for future research, including scalable green processing, green composites, and additive manufacturing. At the same time, we thoroughly examine the supply chain, potential revenue streams, industry growth, and market readiness. By combining materials research, longevity evaluation, and techno-economic perspectives, this study offers a translational framework for high-performance, regenerative, and economically feasible cellulose-based piezoelectric devices. problems such as manufacturability, lower output than inorganic piezoelectrics, and sensitivity to moisture. Cellulose-based piezoelectrics hold significant potential as self-sufficient, eco-friendly electronics in fields such as the Internet of Things (IoT), biomedicine, and environmental protection.

The development of advanced solar energy harvesting systems requires metamaterial absorbers that overcome the limitations of conventional noble-metal designs, particularly their insufficient thermal stability and significant optical losses. This study introduces a stepped-height concentric dual-ring metamaterial absorber (SHCDR-MA) based on titanium nitride (TiN), which achieves an average absorptivity of 99.27% across an ultra-broadband spectrum from 150 to 3000nm. The structure employs a vertically graded dual-ring configuration, atop a silicon dioxide (SiO2) dielectric spacer and a TiN substrate, enabling multi-resonance coupling and impedance matching. Absorption originates from the synergistic interplay of several mechanisms: a vertical impedance gradient created by the concentric ring height difference, coherent transition from TiN interband transitions and localized surface plasmon resonances at shorter wavelengths to propagating surface plasmon resonances and dielectric-guided modes at longer wavelengths, and efficient energy dissipation through magnetic hotspots and Poynting vector convergence. The absorber exhibits excellent angular independence (up to 60°) and maintains near-ideal, temperature-invariant blackbody-like emission across a wide temperature range (373-1500K). By leveraging the refractory properties of TiN, this design provides a feasible strategy for advanced applications in solar energy harvesting and high-temperature solar thermophotovoltaics.

This paper addresses the problem of efficient federated learning in energy-harvesting AIoT systems, where time-varying energy availability may lead to device blackouts and unstable learning performance. To address this issue, we propose an energy-adaptive multi-dimensional learning control framework that jointly determines model complexity and training intensity based on the real-time energy state of each device. This method integrates multiple control dimensions, including model pruning, quantization, knowledge distillation, and adaptive local training, into a unified decision mechanism under an energy constraint. Each device determines its participation in federated learning based on its residual energy relative to an energy threshold. When participating, the device selects a feasible learning configuration that jointly considers training intensity (e.g., epoch size and batch size) and lightweight learning operations to maximize learning effectiveness while preventing energy depletion. The proposed framework was implemented on a real-world testbed using NVIDIA Jetson Orin Nano devices under solar-energy-harvesting conditions. Our experimental results demonstrate that the proposed method significantly reduces device blackout while maintaining competitive model accuracy with respect to energy-unconstrained scenarios. These results highlight that joint control of multiple learning-cost factors is essential for achieving stable and efficient federated learning in energy-harvesting AIoT environments.

Marine biofouling represents a persistent threat to sustainable ocean industries, elevating operational costs and accelerating infrastructure degradation. While conventional biocide-releasing coatings demonstrate antifouling efficacy, their environmental toxicity necessitates the development of eco-friendly alternatives. Herein, we present a mechanical energy-harvesting piezo-biocatalytic system for sustainable marine antifouling, leveraging a CeO2-BaTiO3 (Ce-BTO) heterojunction with a synergistic triple-catalytic mechanism. The integration of piezoelectric BaTiO3 and CeO2 nanozyme not only enhances charge separation and suppresses recombination to boost piezocatalytic reactive oxygen species (ROS) generation, but also exploits an electron injection effect to augment haloperoxidase-like activity, enabling in situ production of biocidal hypobromous acid (HOBr) in seawater. Furthermore, Ce-BTO exhibits DNA hydrolase-like activity that specifically degrades extracellular DNA (eDNA)-a key structural component of extracellular polymeric substances-thereby disrupting biofilm integrity. This concerted action of ROS/HOBr-mediated biocidal effects and eDNA hydrolysis confers Ce-BTO with potent, broad-spectrum anti-microbial and anti-algal performance, while remaining non-toxic to non-target marine organisms. In a six-month marine field test, coatings incorporating Ce-BTO achieved superior antifouling performance, markedly surpassing a commercial Cu2O-based antifouling paint. By harnessing renewable ocean mechanical energy and green catalytic chemistry, this piezo-biocatalytic strategy offers a promising and sustainable pathway for next-generation antifouling technologies.

Liquid crystal elastomers (LCEs) with reversible thermal actuation are promising platforms for multifunctional flexible electronics. Herein, we present a PVDF/LM-LCE (PVDF, polyvinylidene fluoride; LM, liquid metal) composite in which PVDF is polymerized in situ within the LCE matrix to achieve seamless mechanical coupling and efficient stress transfer. LM nanodroplets enhance mechanical robustness, charge transport, and photothermal conversion, enabling LCEs to serve as photothermally driven transducers that amplify the piezoelectric and pyroelectric outputs in these flexible systems. The optimized composite achieves a pyroelectric coefficient of -4.81 nC·cm- 2·K- 1, 1.8 times higher than conventional PVDF films. Furthermore, the composite device powers two LEDs and digital sensors using low-grade photothermal fluctuations. This LCE-based light-driven thermomechanical-to-electrical conversion strategy offers a generalizable pathway for high-performance, flexible pyroelectric and piezoelectric energy-harvesting materials.

A high-efficiency inductor-less solar energy harvesting system for IoT end nodes

Advances in electrical stimulation-based therapeutic technologies for sarcopenia prevention and treatment.

A novel energy-harvesting interface (EHI) circuit that employs a continuously scalable-conversion-ratio (CSCR) switched-capacitor (SC) DC-DC converter is introduced in this paper. CSCR converters inherently sustain high power conversion efficiency across a wide voltage conversion ratio (VCR), making them well suited for EHI applications. Realizing wide-range maximum-power-point tracking (MPPT) with a hill climbing algorithm, however, demands accurate on-chip power estimation. Recent EHI works failed to provide such estimation, neglecting the unit step voltages in the internal flying-capacitor network, hence constraining the attainable MPPT range. To overcome this limitation, a compact power monitor that explicitly accounts for the unit step voltages in the internal flying-capacitor network is introduced. The monitor employs a capacitive divider and is tightly coupled to an exponential digitally controlled oscillator (DCO), yielding precise power measurements over a broad frequency span. Fabricated in a 180 nm CMOS process, the prototype delivers up to 6.05 mW while achieving 90.4% end-to-end efficiency. It sustains ≥ 97% MPPT efficiency over a 14.6× dynamic-power range (130 μW – 1.9 mW), 3.4× wider than previously reported CSCR-based harvesters. The proposed architecture thus offers an efficient and scalable solution for next-generation energy-harvesting systems.

The development of flexible, high-performance thermoelectric materials is necessary due to the growing demand for sustainable energy conversion from waste heat sources. In this work, we present higher manganese silicide/polyaniline (HMS/PANI) composite thin films that exhibit a hierarchical interface design, which partially decouples the typically interrelated thermoelectric parameters for waste heat recovery from working 3D printers. Structural characterization studies - XRD and SEM - confirm the well-dispersed HMS network with good interfacial quality. Through systematic composition optimization, we achieved enhanced electrical conductivity, 438 S m-1, and a simultaneous increase in the Seebeck coefficient of 72 μV K-1 at 80% HMS content. This enhancement results from hierarchical composite engineering, achieved by percolation-driven charge transfer at HMS/PANI interfaces and energy filtering effects, which also increase carrier concentration. The optimized composition exhibits an enhanced power factor of 2.3 μW (mK2)-1. Phonon engineering suppresses the lattice thermal conductivity relative to pure PANI, thereby maximizing the thermoelectric performance of composites. I-V characterization confirms the ohmic transport behaviour across all compositions. Device output characterization demonstrates a maximum power generation of 0.33 nW at ΔT = 70 K. Real-time application demonstration on an operating 3D printer reveals stable performance by generating 6-8 mV output, validating its functionality for autonomous IoT energy harvesting systems. This work establishes HMS/PANI composites as a flexible thermoelectric material where sophisticated composite design transcends individual phase limitations, paving the way for practical thermoelectric energy harvesting from diverse waste heat sources.

Hydrovoltaic technology generates electricity directly via interactions between nanomaterials and water, demonstrating significant promise for sustainable energy harvesting. However, its widespread application is hindered by insufficient power output and poorly understood underlying mechanisms. Here, we develop a two-dimensional nanofluidic hydrovoltaic device using a MXene/silk nanoparticle composite membrane that leverages ion-electron coupling to enhance electricity generation. Upon deposition of deionized water droplets, an ionization-induced proton gradient generates a maximum open-circuit voltage of 496 mV and a peak short-circuit current of nearly 8 µA. Notably, replacing deionized water with 10-4 M NaCl elevates the output to 593 mV, which is further boosted to 622 mV under infrared irradiation-sufficient to power microelectronic circuits. Mechanism investigations reveal that this enhancement arises from ion-electron Coulomb drag interactions at the solid-liquid interface. This study provides fundamental insights into nanofluidic energy conversion and demonstrates potential applications in self-powered wearable electronics and all-weather energy harvesting systems.

The increasing development of ingestible medical devices for gastrointestinal diagnostics, drug delivery, and physiological monitoring has created a growing demand for reliable and long-lasting power sources. Conventional batteries limit device lifetime, increase capsule size, and raise safety concerns, making biomechanical energy harvesting from gastrointestinal motility a promising alternative for self-powered ingestible systems. This review aims to provide a comprehensive overview of biomechanical energy harvesting from gastrointestinal mechanical activity for powering ingestible biomedical devices, with emphasis on energy sources, transduction mechanisms, materials, system integration, limitations, and future research directions. Recent literature on gastrointestinal biomechanics and energy harvesting technologies was analyzed, focusing on major transduction mechanisms such as piezoelectric, triboelectric, and electromagnetic generators. The review also evaluates material selection, device architectures, encapsulation strategies, and power management circuits from a system-level integration perspective. Piezoelectric, triboelectric, and electromagnetic energy harvesters demonstrate the ability to convert low-frequency gastrointestinal mechanical energy into electrical energy suitable for ultra-low-power biomedical devices. Hybrid energy harvesting systems improve energy reliability and output performance. However, several challenges remain, including low energy density, variability in gastrointestinal mechanical forces, miniaturization constraints, material durability, electrical conversion losses, and lack of standardized testing protocols. Biomechanical energy harvesting has significant potential to enable battery-free ingestible biomedical devices. Future developments in hybrid energy systems, ultra-low-power electronics, biodegradable materials, and adaptive power management are expected to support the development of fully autonomous self-powered ingestible medical devices.

Energy-harvesting (EH) AIoT systems enable long-term autonomous operation but suffer from time-varying energy availability, which makes stable learning difficult. In such environments, federated learning (FL) is prone to energy depletion (blackout), while continual learning is required to handle evolving data distributions, leading to a trade-off between energy stability and catastrophic forgetting. In this paper, we propose a stability-controlled continual federated learning framework that jointly regulates local training intensity and rehearsal usage based on the residual energy state. The proposed method is derived from a Lyapunov drift-plus-penalty formulation and implemented as a lightweight mode-based control policy. Simulation results using real solar energy traces show that the proposed method significantly reduces blackout while improving accuracy and mitigating forgetting compared to existing approaches. These results demonstrate the effectiveness of energy-aware joint control for stable continual federated learning in EH-AIoT systems.

A high-power plantar energy harvester with LSTM-KAN adaptive damping control

Thermoelectric (TE) energy conversion, which directly transforms waste heat into usable electricity, presents a crucial technology for sustainable power generation and energy efficiency enhancement. The emergence of two-dimensional (2D) materials has profoundly impacted this field by providing an atomically thin platform for unprecedented control over electronic and thermal transport properties. This comprehensive review critically analyzes the latest progress, persistent challenges, and future opportunities of 2D materials for advanced TE applications. We begin by systematically evaluating the synthesis and processing toolkit, correlating techniques from top-down exfoliation to bottom-up chemical vapor deposition with their specific impacts on microstructure and final device performance. Subsequently, we provide a critical assessment of the fundamental TE performance of key 2D families, including graphene, transition metal dichalcogenides (TMDs), MXenes, black phosphorus (BP), and hexagonal boron nitride (h-BN). The discussion details how advanced engineering strategies, such as strain modulation, layer number control, chemical doping, and heterostructure (HS) design, can dramatically enhance the power factor (PF) while simultaneously suppressing lattice thermal conductivity (κL). Finally, we showcase the successful translation of these materials into practical applications, encompassing flexible and wearable TE generators (WTEGs), self-powered sensors, and integrated energy harvesting systems.

Three-dimensional (3D) hydrogel membranes offer great potential for harvesting osmotic energy from salinity gradients, yet their practical application remains limited by the lack of an autonomous self-healing capability, which is critical for long-term operational stability. Here, we report a self-healing 3D hydrogel membrane engineered via physical metal coordination interactions that enables efficient osmotic energy conversion with autonomous repair functionality. Combined experimental and theoretical investigations reveal that the space-charged 3D network facilitates highly efficient permselective ion transport. Beyond its excellent self-healing capability, the membrane delivers a high power density of 6.35 W m-2 for osmotic energy harvesting from seawater-river water mixing, significantly outperforming most macroscopic porous nanofluidic membranes. This work not only underscores the potential of interconnected 3D hydrogels for high-performance osmotic energy conversion but also provides a practical strategy to achieve durable and sustainable energy harvesting systems.

Abstract Thermoelectric materials enable direct heat-to-electricity conversion. They have gained increasing interest in sustainable and wearable energy-harvesting systems. However, progress in flexible thermoelectric devices remains limited by the shortage of high-performance n-type organic materials, hindering the development of efficient p–n complementary modules. Laser-induced graphene (LIG) has attracted considerable attention for thermoelectric applications due to its high electrical conductivity, scalable fabrication, and compatibility with flexible substrates. However, LIG produced from polyimide typically exhibits p-type behavior, which limits its applicability in thermoelectric modules requiring complementary n-type materials. In this study, we address this limitation by introducing a simple and scalable urea-assisted strategy to convert p-type LIG into n-type LIG through nitrogen doping during the laser-induced graphitization process. First, we have fabricated LIG by direct laser writing on polyimide and subsequently treated with 5 and 10 wt% urea solutions, followed by mild annealing. Subsequent structural and chemical characterizations confirmed effective nitrogen incorporation, dominated by graphitic-N species, while preserving the porous 3D LIG network. Thermoelectric measurements revealed enhanced electrical conductivity (up to 1120 S/m) and a clear p-to-n transition, as evidenced by negative Seebeck coefficients in urea-treated films. The optimized LIG-10 N sample delivered the highest thermoelectric performance, reaching a power factor of 0.136 µW m⁻¹ K⁻² at 60 °C. Overall, this work provides a practical route for engineering n-type LIG, supporting the development of flexible thermoelectric modules for wearable and low-power energy-harvesting applications. Graphical Abstract