Human body heat-driven thermoelectric generators as a sustainable power supply for wearable electronic devices: Recent advances, challenges, and future perspectives

Flexible Epidermal Sensor Power Systems: Innovations in Multidimensional Materials and Biomedical Applications

Epidermal sensors are pivotal components of next-generation wearable technologies. They offer transformative potential in health monitoring, motion tracking, and biomedical applications. This potential stems from their ultra-thin design, skin compatibility, and ability to continuously detect physiological signals. The long-term functionality relies on advanced power systems balancing flexibility, energy density, and environmental resilience. This review highlights four key power strategies: chemical batteries, biofuel cells, environmental energy harvesters, and wireless power transfer. Breakthroughs in multidimensional materials address challenges in ion transport, catalytic stability, and mechanical durability. Structural innovations mitigate issues like dendrite growth and enzyme degradation. These systems enable applications spanning biomarker analysis, motion sensing, and environmental monitoring. By integrating these advancements, this review concludes with a prospective outlook on future directions for epidermal sensor power systems.

Microfluidic-based redesign of a humidity-driven energy harvester

Integrating microfluidic elements onto a single chip offers many advantages, including miniaturization, portability, and multifunctionality, making such systems highly useful for biomedical, healthcare, and sensing applications. However, these chips need redesigning for compatibility with microfluidic fabrication methods such as photolithography. To address this, we integrated microfluidics technology into our previously developed humidity-driven energy harvester to create a self-powered system and redesigned it so that it could be fabricated using photolithography and printing. The device comprises stacked electrodes, cation-exchange membranes, and microchannels. The multi-element version of the device generated ten times more voltage than the single-element version. Both versions produced stable patterns of voltage output with respect to the fluctuations in humidity in both controlled and real-world environments. Their potential as humidity sensors is supported by the correlations exhibited between humidity and voltage output. The capacity of the device to respond to changes in perspiration-induced changes in humidity suggests its usefulness as a power source for wearable sensors. This novel device element, which can be easily integrated into other microfluidic devices, is expected to provide a new approach to powering microfluidic-based wearable sensors.

Towards Perfluoroalkyl and Polyfluoroalkyl Substance (PFAS)-Free Energy Harvesting: Recent Advances in Triboelectric Nanogenerators for Sports Applications

Triboelectric nanogenerators (TENGs) can convert the mechanical energy of physical activities into electricity. This is particularly useful in sports applications, where physical activity can power devices such as wearables that can provide real-time feedback on athletes' performance or health. To work, a TENG usually needs tribopositive and tribonegative materials. Currently, the vast majority of TENGs use materials containing perfluoroalkyl and polyfluoroalkyl substances (PFAS) as tribonegative materials. However, these substances pose risks to humans and the environment, which has led the European Union to consider restrictions on these compounds. For this reason, PFAS-free alternatives, such as polydimethylsiloxane (PDMS) and MXenes, need to be better explored to replace PFAS materials while aiming to achieve equal efficiency. This review will explore some of the recent advances that have been developed in the field of PFAS-free TENGs, with an emphasis on sports applications.

Self-powered biomedical devices: biology, materials, and their interfaces

Integrating biomedical electronic devices holds profound promise for advancements in healthcare and enhancing individuals' quality of life. However, the persistent challenges associated with the traditional batteries' limited lifespan and bulkiness hinder these devices' long-term functionality and consistent power supply. Here, we delve into the biology and material interfaces in self-powered medical devices by summarizing the intrinsic electric demands in humans, analyzing material and biological mechanisms for electricity generation and storage, and discussing the pathways toward self-chargeable powering. As a result, the current challenges in material designs and biological integrations emerged to shape the future directions in advancing self-powered medical devices. This paper calls on the community to integrate biology and material science to develop self-powering medical devices and improve their clinical prospects.

Electrical stimulation as an adjunctive therapy for diabetic ulcers: A systematic review and meta-analysis

Diabetic ulcers are chronic wounds that are notoriously difficult to treat, leading to significant physical and psychological distress and increased healthcare costs. Their multifactorial aetiology necessitates long-term interdisciplinary collaboration and various complementary treatment measures. While numerous studies suggest that electrical stimulation (ES) positively impacts diabetic ulcer healing, the robustness and consistency of these findings require further evaluation to optimize clinical application. We searched databases including PubMed, the Cochrane Library, Embase, Web of Science and the China National Knowledge Infrastructure (CNKI). Only randomized clinical trials (RCTs) comparing ES treatment to placebo or conventional treatment were included. Extracted information included objective healing measures and data for assessing effect sizes. Ten RCTs involving 451 patients met inclusion criteria. ES improved ulcer healing rate compared to control or placebo (MD 20.37, 95% CI: 16.89-23.85, p <0.001) and increased the number of healed ulcers (RR 1.45, 95% CI: 1.18-1.78, p <0.001), with both results being statistically significant. The observed benefits are likely due to the positive effects of ES on the vascular and neurological functions of the lower limbs in patients with diabetic ulcers. Both low-frequency, moderate-intensity alternating current and low-intensity or high-voltage direct current have demonstrated efficacy in promoting ulcer healing. The results suggest ES may be a promising approach of managing diabetic ulcers. However, the optimal method of ES application remains undetermined; therefore, high-quality and large-scale studies are essential.

Self-Assembly Determines Sign of Seebeck Coefficient in Tunneling Junctions Comprising Monolayers and Bilayers of Fullerenes

We measured the Seebeck coefficient for junctions comprising self-assembled monolayers and bilayers of the fullerene moiety PTEG-1 on Au using eutectic Ga-In in a controlled anhydrous atmosphere by varying the temperature gradient from -12 to 12 °C, observing a linear response in thermovoltage across the range. The sign of the coefficient was positive for monolayers of PTEG-1, (195 ± 8) μV K-1 and negative for bilayers of PTEG-1, (-209 ± 14) μV K-1, indicating a change from HOMO-mediated to LUMO-mediated charge-transport. Charge-transport is nonresonant tunneling for both monolayers and bilayers, but the former self-assembles with the fullerene cage at the chemisorbed interface while the latter includes a fullerene cage at the physisorbed interface, demonstrating that the physical position of the fullerene cage determines the energetic position of the frontier molecular orbitals of PTEG-1.

Thermoelectric bismuth telluride nanostructures fabricated by electrodeposition within flexible templates

Bismuth telluride, a highly efficient thermoelectric material, stands out for applications around room temperature in wearable devices. By harnessing the thermal gradient established between the human body and ambient temperature, we can generate useable electricity. Notably, bismuth telluride nanostructures exhibit significantly lower thermal conductivities compared to their bulk counterparts. As a result, the thermoelectric efficiency achieved is notably higher. Our research focuses on developing efficient nanostructured materials based on bismuth telluride inside a flexible substrate made of polyester. We employ scalable methods, such as template-assisted electrochemical deposition, to fabricate these nanostructures. In this study, we present an approach to the development of flexible nanostructured thermoelectric materials. Despite using a reduced quantity of active material, our electrochemically deposited nanostructures inside a flexible template demonstrate a remarkable performance. They exhibit 24 % of the Power Factor reported for conventional electrochemically fabricated Bi2Te3 thin films, and notably, they even surpass the Power Factor reported for flexible Bi2Te3-based inks used in the creation of flexible generators. This achievement underscores the potential of our method in the advancement of efficient, flexible thermoelectric devices.

Self-Powered Water Splitting of Ni3FeN@Fe24N10 Bifunctional Catalyst Improved Catalytic Activity and Durability by Forming Fe24N10 on Catalyst Surface via the Kirkendall Effect

Highly efficient water splitting electrocatalyst for producing hydrogen as a renewable energy source offers potential to achieve net-zero. However, it has significant challenges in using transition metal electrocatalysts as alternatives to noble metals due to their low efficiency and durability, furthermore, the reliance on electricity generation for electrocatalysts from fossil fuels leads to unavoidable carbon emissions. Here, a highly efficient self-powered water splitting system integrated is designed with triboelectric nanogenerator (TENG) and Ni3FeN@Fe24N10 catalyst with improved catalytic activity and durability. First, the durability of the Ni3FeN catalyst is improved by forming N, P carbon shell using melamine, polyetherimide, and phytic acid. The catalyst activity is improved by generating Fe24N10 in the carbon shell through the Kirkendall effect. The synthesized Ni3FeN@Fe24N10 catalyst exhibited excellent bifunctional catalytic activity (ηOER = 261.8 mV and ηHER = 151.8 mV) and remarkable stability (91.7% in OER and 90.5% in HER) in 1 m KOH. Furthermore, to achieve ecofriendly electricity generation, a rotation-mode TENG that sustainably generate high-performance is realized using butylated melamine formaldehyde. As a result, H2 is successfully generated using the integrated system composed of the designed TENG and catalyst. The finding provides a promising approach for energy generation to achieve net-zero.

Advancements in Bio-inspired Self-Powered Wireless Sensors: Materials, Mechanisms, and Biomedical Applications

The rapid maturation of smart city ecosystems is intimately linked to advances in the Internet of Things (IoT) and self-powered sensing technologies. Central to this evolution are battery-less sensors that are critical for applications such as continuous health monitoring through blood metabolites and vital signs, the recognition of human activity for behavioral analysis, and the operational enhancement of humanoid robots. The focus on biosensors that exploit the human body for energy-spanning wearable, attachable, and implantable variants has intensified, driven by their broad applicability in areas from underwater exploration to biomedical assays and earthquake monitoring. The heart of these sensors lies in their diverse energy harvesting mechanisms, including biofuel cells, and piezoelectric, triboelectric, and pyroelectric nanogenerators. Notwithstanding the wealth of research, the literature still lacks a holistic review that integrates the design challenges and implementation intricacies of such sensors. Our review seeks to fill this gap by thoroughly evaluating energy harvesting strategies from both material and structural perspectives and assessing their roles in powering an array of sensors for myriad uses. This exploration offers a comprehensive outlook on the state of self-powered sensing devices, tackling the nuances of their deployment and highlighting their potential to revolutionize data gathering in autonomous systems. The intent of this review is to chart the current landscape and future prospects, providing a pivotal reference point for ongoing research and innovation in self-powered wireless sensing technologies.

Design and Optimization Strategies for Flexible Quasi-Solid-State Thermo-Electrochemical Cells

Currently, efficient utilization of low-grade thermal energy is a great challenge. Thermoelectricity is an extremely promising method of generating electrical energy from temperature differences. As a green energy conversion technology, thermo-electrochemical cells (TECs) have attracted much attention in recent years for their ability to convert thermal energy directly into electricity with high thermal power. Within TECs, anions and cations gain and lose electrons, respectively, at the electrodes, using the potential difference between the hot and cold terminals of the electrodes by redox couples. Additionally, the anions and cations therein are constantly circulating and mobile via concentration diffusion and thermal diffusion, providing an uninterrupted supply of power to the exterior. This review article focuses mainly on the operation of TECs and recent advances in redox couples, electrolytes, and electrodes. The outlook for optimization strategies regarding TECs is also outlined in this paper.