Giant negative thermopower of ionic hydrogel by synergistic coordination and hydration interactions

Multi-Layered Calcium Silicate Hydrate-Based Composites: A Nacre-Mimetic Design for Ultra-High Toughness

Cement-based materials are the most extensively utilized artificial material in the world. The low toughness of cementitious materials has long been a significant constraint in the development of modern concrete, limiting its performance in critical infrastructure applications. As the primary hydration product, calcium silicate hydrate (C-S-H) determines the mechanical properties of cementitious materials, in which optimizing C-S-H presents a promising avenue for toughness enhancement. In this work, a nacre-mimetic design strategy is employed to develop a high toughness C-S-H composite, achieved by the arrangement of inorganic C-S-H "brick" alternated with polyvinyl alcohol (PVA) "mortar". The unique hierarchically soft/hard structure significantly improved the mechanical properties of C-S-H composite, showcasing a substantial improvement on tensile strength, ductility and toughness by 1-2 orders of magnitude compared with fiber/polymer reinforced cementitious composites, especially reaching ultra-high toughness (20.01±3.64 MJ m-3), which outperforms nacre by a factor of over ten and exhibits the highest performance among reported C-S-H-based materials. The nacre-mimetic C-S-H composite displayed exquisite interface and toughening mechanism revealed by density functional theory (DFT), molecular dynamics (MD), and finite element method (FEM) simulations. These findings provide a prospect for toughening cement-based materials, and broaden the potential applications in advanced functional composite systems.

Thermogalvanic hydrogels for low-grade heat harvesting and health monitoring

Direct conversion of ubiquitous heat energy into electricity is crucial for the development of green and sustainable power sources and self-powered electronic devices. Compared with traditional semiconductor thermoelectric materials, emerging thermogalvanic hydrogels offer high thermopowers, excellent intrinsic flexibilities, and low manufacturing costs, making them highly promising for low-grade thermal energy harvesting, self-powered flexible electronics, and wearable health monitoring devices. This review summarizes the recent advancements in thermogalvanic hydrogels, focusing on the strategies employed to enhance their thermoelectric properties and mechanical performances and expand their operational temperature ranges. We also explore their potential applications in low-grade heat harvesting for powering electronic devices and wearable applications. This review will provide valuable insights and guidance for the development and application of high-performance thermogalvanic hydrogels by systematically analyzing the potential of thermogalvanic hydrogels for flexible energy supply systems, outlining the performance enhancement mechanisms, and further discussing the current challenges and opportunities.

P-N Series Integrated Ionic Thermoelectric Generator Based on Cation/Anion-Selective Hydrogels for Body Heat Harvesting

Low-grade heat accounts for a significant portion of the heat, but is often overlooked and not utilized. Ionic thermoelectric generators (i-TEGs) are an ideal choice for harvesting low-grade heat due to their simple design and operation. However, challenges such as ion mobility regulation and the need for series integration still hinder their performance. In this work, an interesting approach is introduced to improve the thermoelectric efficiency of i-TEG by utilizing ion-selective hydrogels containing sodium chloride (NaCl). The anionic polymer in the cation-selective hydrogel is attractive to sodium ions, while the cationic polymer in the anion-selective hydrogel is attractive to chloride ions. This regulates the thermal mobility of ions in the hydrogel without polymer modification or the addition of some additives, thus enhancing or changing the Seebeck coefficient (S). By connecting 12 pairs of the P-type and N-type i-TEGs, a voltage of 1.54 V and an output power of 21 µW can be achieved on the surface of the body skin. This work opens a new horizon for obtaining high-performance i-TEGs through ion mobility regulation by ion-selective hydrogels, and highlights the prospect of P-N series integrated i-TEGs from hydrogels for body heat harvesting.

Water Transport-Modulated Highly Compressive Hydrogel for Total Biomimetic Sensing Intervertebral Disc

Degenerative disc disease (DDD) affects millions globally, with artificial total disc replacement (A-TDR) emerging as a key surgical intervention to restore spinal function and mobility. Current implantable prostheses incorporating multi-component architectures to replicate the functional heterogeneity of natural intervertebral discs (IVD) face challenges in achieving mechanical and physiological compatibility. Inspired by the natural IVD's structure, where a soft nucleus pulposus (NP) is encased by a tough annulus fibrosus (AF), a water transport-modulated directional annealing casting (DAC) approach has been developed to construct bulk hydrogels with tunable mechanical properties (up to ≈36.69 MPa compressive strength with ≈5.35 MPa modulus). This strategy enables the fabrication of an integrated hydrogel-based IVD (H-IVD) with biomechanically gradient structures, featuring a high-strength AF region (compressive modulus ≈2.77 MPa) seamlessly transitioning to a compliant NP core (modulus ≈0.26 MPa) while maintaining physiological water content throughout. The H-IVD exhibits excellent biocompatibility and load-bearing capacity, with inherent stress-sensing capabilities enabling dynamic functional assessment of spinal biomechanics. Furthermore, this integrated design strategy demonstrates broad applicability for engineering various dimensionally-controlled biomimetic tissues, from simple 1D structures to complex 3D organs requiring precise spatial control of material properties.

High-Performance Temperature Sensors for Early Warning Utilizing Flexible All-Inorganic Thermoelectric Films

The demand for highly sensitive temperature-response materials is critical for the advancement of intelligent temperature sensing and fire warning systems. Despite notable progress in thermoelectrical (TE) materials and devices, designing TE materials suitable for wide-range temperature monitoring across diverse scenarios remains a challenge. In this study, we introduce a TE temperature sensor for fire warnings and hot object recognition, utilizing an all-inorganic TE film composite of reduced graphene oxide (rGO)/Te nanowires (Te NWs). The resulting all-inorganic TE film, annealed at a high temperature, exhibits distinct response ratios to varying temperature changes, enabling consistently sensitive thermosensation. The robust linear relationship between open circuit voltage and temperature difference establishes it as an effective thermoreceptor for enhanced temperature alerts. Furthermore, we demonstrate that the assembled TE sensor provides rapid high-temperature warnings with adjustable threshold voltages (1-7 mV), achieving an ultrafast response time of approximately 4.8 s at 1 mV threshold voltage. Additionally, this TE sensor can be integrated with the gloves to monitor high-temperature objects in various scenarios, such as the brewed milk in daily life and heating reactors in industrial applications. These results offer perspectives for future innovations in intelligent temperature monitoring.

Long-Term Serviceable Ionic Thermoelectric Hydrogel with Temperature and Moisture Dual-Driven Waste Energy Harvesting Capability

Despite the substantial progress in developing high-performance quasi-solid hydrogels based on ionic thermophoretic migration, ionic thermoelectric materials (i-TEs) show unsatisfactory long-lasting stability caused by ionic migration failures and de-electrolytes. In this work, by enriching oxygen-containing functional groups in the gel network and constructing oriented ionic transport nanochannels, an innovative approach is presented to reach long-term service and reusability for i-TEs without sacrificing their TE properties. The as-prepared hydrogel with thermopower of 17.0 ± 1.0 mV K-1 stables at 82% of its original performance when immersed in the electrolyte. Notably, even after being air-dried for 135 days, its thermopower returns to 87% of the original value through replenishing electrolyte solution and its 3D shape fully recovers. Meanwhile, the dual-driven nature for moisture and temperature as well as the pH sensitivity of this network is systematically investigated. The maximum output voltage of a single sample reaches 0.215 V at a ΔT of 3.7 K, and it works continuously for more than 26 h. This study offers a new approach to overcoming the short-term service bottleneck of i-TEs and provides a practical scheme for the multi-source drive of self-powered TE equipment.

Robust super-structured porous hydrogel enables bioadaptive repair of dynamic soft tissue

Well-orchestrated integration of multiple contradictory properties into a single material is crucial for dynamic soft tissue defect repair but remains challenging. Bioinspired by diaphragm, we have successfully developed a robust super-structured porous hydrogel with anisotropic skeleton and asymmetric porous surfaces via integrated molding. Thanks to synergistic toughening of anisotropic structure and Hofmeister effect of amino acid, our hydrogel achieves high tensile strength (22.2 MPa) and elastic modulus (32.4 MPa) for strong mechanical support, while maintaining excellent toughness (61.9 MJ m-3) and fatigue threshold (5.6 kJ m-2) against dynamic stretching during the early healing phase. The mechanical properties of hydrogel gradually decrease during the late healing phase, minimizing its restriction on physiological movements. In addition, diaphragm defect repair models on female rabbits demonstrate asymmetric porous surfaces can simultaneously prevent visceral adhesion and promote defect healing. Therefore, our hydrogel opens an attractive avenue for the construction of biomimetically hierarchical materials to address the stringent requirements of dynamic tissue defect repair.

Recent Progress in Polymer Gel-Based Ionic Thermoelectric Devices: Materials, Methods, and Perspectives

Polymer gel-based ionic thermoelectric (i-TE) devices, including thermally chargeable capacitors and thermogalvanic cells, represent an innovative approach to sustainable energy harvesting by converting waste heat into electricity. This review provides a comprehensive overview of recent advancements in gel-based i-TE materials, focusing on their ionic Seebeck coefficients, the mechanisms underlying the thermodiffusion and thermogalvanic effects, and the various strategies employed to enhance their performance. Gel-based i-TE materials show great promise due to their flexibility, low cost, and suitability for flexible and wearable devices. However, challenges such as improving the ionic conductivity and stability of redox couples remain. Future directions include enhancing the efficiency of ionic-electronic coupling and developing more robust electrode materials to optimize the energy conversion efficiency in real-world applications.

Bio-inspired thermoelectric cement with interfacial selective immobilization towards self-powered buildings

Buildings and infrastructure significantly contribute to global energy consumption and CO2 emissions. Transforming cement, the most widely used construction material, into a functional medium for heat harvesting presents a promising avenue to offset the energy demands of buildings. The disparity in diffusion rate between cations and anions within cement pore solution due to variations in interactions with pore walls, endows cement with inherent ionic thermoelectric properties. However, the isolation of pores by the dense cement matrix hinders the rapid transportation of ions with superior diffusion rates, impeding the enhancement of mobility difference between ions and limiting the enhancement of Seebeck coefficient. Inspired by the stem structure of plants, we present a cement-polyvinyl alcohol (PVA) composite (CPC) featuring aligned cement and PVA hydrogel layers. While PVA hydrogel layers provide ion diffusion highways for OH- ions, cement-PVA interfaces establish strong coordination bonds with Ca2+ ions and weaker interactions with OH- ions, enabling selective immobilization, which amplifies the diffusion rate disparity between Ca2+ and OH-. The CPC's multilayer structure yields abundant interfaces, providing ample interaction sites that maximize the contribution of cement ions to thermoelectric performance. The as-prepared composite achieves an impressive Seebeck coefficient of -40.5 mV/K and a figure of merit (ZT) of 6.6 × 10-2. Due to the engineered multilayer structure, the CPC also demonstrates superior mechanical strength and intrinsic energy storage potential, which has been assembled into a self-powered architecture. The biomimetic structure and interfacial selective immobilization mechanism may pave the way for the design and fabrication of high-performance ionic thermoelectric materials.

Fatigue-resistant and super-tough thermocells

Wearable thermocells offer a sustainable energy solution for wearable electronics but are hindered by poor fatigue resistance, low fracture energy, and thermal inefficiencies. In this study, we present a high-strength, fatigue-resistant thermocell with enhanced thermoelectric performance through solvent exchange-assisted annealing and chaotropic effect-enhanced thermoelectric properties. The mechanical strength and toughness are improved by forming macromolecular crystal domains and entangling polymer chains. Guanidine ions, with strong chaotropic properties, optimize the solvation layer of redox ion couple, boosting thermoelectric efficiency. Compared to existing anti-fatigue thermocells, the current design exhibits a 20-fold increase in mechanical toughness (368 kJ m-2) and a 3-fold increase in Seebeck coefficient (5.4 mV K-1). With an ultimate tensile strength of 12 MPa, a fatigue threshold of 4.1 kJ m-2, and a specific output power density of 714 μW m-2 K-2, this thermocell outperforms existing designs, enabling more reliable and efficient wearable electronics and stretchable devices.

Recent Advances in Self-Powered Sensors Based on Ionic Hydrogels

After years of research and development, flexible sensors are gradually evolving from the traditional "electronic" paradigm to the "ionic" dimension. Smart flexible sensors derived from the concept of ion transport are gradually emerging in the flexible electronics. In particular, ionic hydrogels have increasingly become the focus of research on flexible sensors as a result of their tunable conductivity, flexibility, biocompatibility, and self-healable capabilities. Nevertheless, the majority of existing sensors based on ionic hydrogels still mainly rely on external power sources, which greatly restrict the dexterity and convenience of their applications. Advances in energy harvesting technologies offer substantial potential toward engineering self-powered sensors. This article reviews in detail the self-powered mechanisms of ionic hydrogel self-powered sensors (IHSSs), including piezoelectric, triboelectric, ionic diode, moist-electric, thermoelectric, potentiometric transduction, and hybrid modes. At the same time, structural engineering related to device and material characteristics is discussed. Additionally, the relevant applications of IHSS toward wearable electronics, human-machine interaction, environmental monitoring, and medical diagnostics are further reviewed. Lastly, the challenges and prospective advancement of IHSS are outlined.

A Multifunctional MXene/PVA Hydrogel as a Continuous Ionic Thermoelectric Generator and a Strain/Temperature Sensor

This research reports a continuous output ionic thermoelectric (i-TE) system based on MXene/PVA (polyvinyl alcohol) hydrogel, by utilizing thermo-diffusion of Cu2+ and Cl- ions and the redox reaction involving Cu/Cu2+ at the electrode interfaces. The thermopower of the i-TE system can be independently tuned to a value of -3.13 mVK-1 by adjusting the ion diffusivity via MXene (Ti3C2Tx). The i-TE system demonstrates a rapid response time of less than 100 s, outperforming any other polyelectrolyte-based system. Crucially, the i-TE system achieves continuous current output when equipped with copper electrodes, facilitated by the redox reaction involving Cu/Cu2+, and maintains stable long-term outputs across a range of resistances from 1 kΩ to 1 MΩ. A three-serial-connected i-TE module demonstrates an output voltage of 26 mV with 6 °C temperature difference, confirming the feasibility of creating an array of i-TE devices for substantial energy output. Beyond energy harvesting, the MXene/PVA hydrogel serves as multifunctional strain/temperature sensors, capable of detecting mechanical strains via the piezoresistive effect and locating finger contact points via the ionic thermoelectric effect.

Giant Power Output from Ionic/electronic Hybrid Nanocomposite Thermoelectric Converter Under Constant Temperature Gradient

Thermoelectric (TE) materials that directly convert heat to electricity are of great significance for sustainable development. However, TE generators (TEGs) made from electronic TE materials suffer from low Seebeck coefficient (10-2-100 mV K-1). While ionic TE capacitors based on ionic conductors exhibit high thermovoltage (100-102 mV K-1), ionic TE capacitors provide power discontinuously only under variation of temperature gradient as ions cannot transport across electrodes to external circuits. Herein, an ionic/electronic hybrid nanocomposite TE converter (NCTEC) by integrating carbon nanotube/polylactic acid nanofibrous fabrics (CPNF) with gelatin ionogel is reported. The resulting NCTEC exhibits a record-high output power density normalized by squared temperature gradient (Pave/ΔT2) of 1.72 mW m-2 K-2 and realizes continuous power output (over 12 h) at a constant temperature gradient, which is among the highest reported power output for TE converters and can be attributed to the combination of substantial increase in interfacial capacitive effect between ionogel and CPNF and an optimized electrical property of the CPNF. The work provides an effective strategy to overcome the limitations of both TEGs and ionic TE capacitors.

Thermoelectric Materials and Devices for Advanced Biomedical Applications

Thermoelectrics (TEs), enabling the direct conversion between heat and electrical energy, have demonstrated extensive application potential in biomedical fields. Herein, the mechanism of the TE effect, recent developments in TE materials, and the biocompatibility assessment of TE materials are provided. In addition to the fundamentals of TEs, a timely and comprehensive review of the recent progress of advanced TE materials and their applications is presented, including wearable power generation, personal thermal management, and biosensing. In addition, the new-emerged medical applications of TE materials in wound healing, disease treatment, antimicrobial therapy, and anti-cancer therapy are thoroughly reviewed. Finally, the main challenges and future possibilities are outlined for TEs in biomedical fields, as well as their material selection criteria for specific application scenarios. Together, these advancements can provide innovative insights into the development of TEs for broader applications in biomedical fields.

Enhanced treatment of acute organophosphorus pesticide poisoning using activated charcoal-embedded sodium alginate-polyvinyl alcohol hydrogel

BACKGROUND

The adsorption of activated charcoal is currently a major clinical treatment for acute organophosphorus pesticide poisoning (AOPP). However, the adsorption duration and efficiency of this method is unstable.

OBJECTIVE

In this study, a hydrogel embedding activated charcoal was prepared and its alleviating effects on AOPP were investigated.

METHODS

A composite hydrogel using sodium alginate and polyvinyl alcohol (SA-PVA) hydrogel was prepared in this study. The structural properties of the SA-PVA hydrogel were characterized via multiple analysis including FTIR, TGA, XRD, SEM, tensile strength and expansion rate. Based on these, activated charcoal (AC) was embedded within the SA-PVA hydrogel (SA-PVA-AC) and it was used for the treatment of AOPP.

RESULTS

Structural characterization indicated SA-PVA hydrogel possesses excellent mechanical properties and biocompatibility. The in vivo study demonstrated that SA-PVA-AC significantly alleviated the inflammation and oxidative damage in the liver, as evidenced by reduced levels of IL-6, TNF-α, and, IL-1β, SOD, and MDA. Furthermore, SA-PVA-AC treatment effectively re-regulated the activities of serum AST and ALT, exhibiting an improved effect on liver function.

CONCLUSION

The findings suggest that activated charcoal embedded within SA-PVA hydrogel has significant potential as a therapeutic agent in treating AOPP, and offering a novel approach to managing pesticide-induced toxicity.

Multi-crosslinked gelatin-based composite hydrogel featuring high thermoelectric performance and excellent flame retardancy for intelligent fire-warning system

The frequency occurrence of building fires necessitates response materials with high flame retardancy and temperature sensitivity. Herein, we synthesized a gelatin/poly(acrylamide-co-acrylic acid)/lithium bromide/sodium phytate/glycerol hydrogel (Gly-GAPL) using in situ radical polymerization and solvent exchange techniques. Gly-GAPL exhibits notable thermoelectric performance (the Seebeck coefficient: 8.66 mV/K), temperature sensitivity, commendable mechanical properties and flame retardancy. Remarkably, Gly-GAPL features a rapid response time, triggering an alarm within 2 s upon exposure to flame. Gly-GAPL is highly resistant to ignition and significantly enhances the fire resistance of wood coated with it. Furthermore, its high transparency, impressive water retention and adhesion further underscore its potential as a flame-retardant coating for various inflammable materials. Given its outstanding thermoelectric performance and temperature sensitivity, an early fire-warning system is rapidly activated, promptly sending alerts to smart devices. This work introduces a novel strategy for developing smart flame retardancy materials and advances the applications of ionic hydrogels in early fire-warning systems.

Molecular Chain Rearrangement-Induced In Situ Formation of Nanofibers for Improving the Strength and Toughness of Hydrogels

Although poly(vinyl alcohol) (PVA) hydrogel has high elasticity and is suitable for cartilage tissue engineering, it is difficult to have both high strength and toughness. In this study, a simple and universal strategy is proposed to prepare strong and tough PVA hydrogels by in situ forming nanofibers on the original network structure induced by a molecular chain rearrangement. Quenching-tempering alteratively in ethanol and water several times is carried out to strengthen PVA hydrogels (PVA-Etn hydrogels) due to the advantages of noncovalent bonds in adjustability and reversibility. The results show that, after three quenching-tempering cycles, PVA-Et3 hydrogel with water content up to 79 wt % shows comprehensive improved mechanical properties. The compression modulus, tensile modulus, fracture strength, tensile strain, and tear energy of the PVA-Et3 hydrogel are 270, 250, 260, 130, and 180% of the initial PVA hydrogel, respectively. The improved mechanical properties of the PVA-Et3 hydrogel are attributed to the strong cross-linked PVA chains and hydrogen bond-reinforced nanofibers. This study not only provides a simple and efficient solution for the preparation of strong and tough polymer scaffolds in tissue engineering but also provides new insights for understanding the mechanism of improving the mechanical properties of polymer hydrogels by adjusting the molecular structure.

Giant gateable thermoelectric conversion by tuning the ion linkage interactions in covalent organic framework membranes

Efficient energy conversion using ions as carriers necessitates membranes that sustain high permselectivity in high salinity conditions, which presents a significant challenge. This study addresses the issue by manipulating the linkages in covalent-organic-framework membranes, altering the distribution of electrostatic potentials and thereby influencing the short-range interactions between ions and membranes. We show that a charge-neutral covalent-organic-framework membrane with β-ketoenamine linkages achieves record permselectivity in high salinity environments. Additionally, the membrane retains its permselectivity under temperature gradients, providing a method for converting low-grade waste heat into electrical energy. Experiments reveal that with a 3 M KCl solution and a 50 K temperature difference, the membrane generates an output power density of 5.70 W m-2. Furthermore, guided by a short-range ionic screening mechanism, the membrane exhibits adaptable permselectivity, allowing reversible and controllable operations by finely adjusting charge polarity and magnitude on the membrane's channel surfaces via ion adsorption. Notably, treatment with K3PO4 solutions significantly enhances permselectivity, resulting in a giant output power density of 20.22 W m-2, a 3.6-fold increase over the untreated membrane, setting a benchmark for converting low-grade heat into electrical energy.

3D-Printed Hydrogels with Engineered Nanocrystalline Domains as Functional Vascular Constructs

Three-dimensionally printed (3DP) hydrogel-based vascular constructs have been investigated in response to the impaired function of blood vessels or organs by replicating exactly the 3D structural geometry to approach their function. However, they are still challenged by their intrinsic brittleness, which could not sustain the suture piercing and enable the long-term structural and functional stability during the direct contact with blood. Here, we reported the high-fidelity digital light processing (DLP) 3D printing of hydrogel-based vascular constructs from poly(vinyl alcohol)-based inks, followed by mechanical strengthening through engineering the nanocrystalline domains and subsequent surface modification. The as-prepared high-precision hydrogel vascular constructs were imparted with highly desirable mechanical robustness, suture tolerance, swelling resistance, antithrombosis, and long-term patency. Notably, the hydrogel-based bionic vein grafts, with precise valve structures, exhibited excellent control over the unidirectional flow and successfully fulfilled the biological functionalities and patency during a 4-week implantation within the deep veins of beagles, thus corroborating the promising potential for treating chronic venous insufficiency.

Control nucleation for strong and tough crystalline hydrogels with high water content

Hydrogels, provided that they integrate strength and toughness at desired high content of water, promise in load-bearing tissues such as articular cartilage, ligaments, tendons. Many developed strategies impart hydrogels with some mechanical properties akin to natural tissues, but compromise water content. Herein, a strategy deprotonation-complexation-reprotonation is proposed to prepare polyvinyl alcohol hydrogels with water content as high as ~80% and favorable mechanical properties, including tensile strength of 7.4 MPa, elongation of around 1350%, and fracture toughness of 12.4 kJ m-2. The key to water holding yet improved mechanical properties lies in controllable nucleation for refinement of crystalline morphology. With nearly constant water content, mechanical properties of as-prepared hydrogels are successfully tailored by tuning crystal nuclei density via deprotonation degree and their distribution uniformity via complexation temperature. This work provides a nucleation concept to design robust hydrogels with desired water content, holding implications for practical application in tissue engineering.

Unveiling Gating Behavior in Piezoionic Effect: toward Neuromimetic Tactile Sensing

The human perception system's information processing is intricately linked to the nonlinear response and gating effect of neurons. While piezoionics holds potential in emulating the pressure sensing capability of biological skin, the incorporation of information processing functions seems neglected. Here, ionic gating behavior in piezoionic hydrogels is uncovered as a notable extension beyond the previously observed linear responses. The hydrogel can generate remarkably high voltages (700 mV) and currents (7 mA) when indentation forces surpass the threshold. Through a comprehensive analysis involving simulations and experimental investigations, it is proposed that the gating behavior emerges due to significant diffusion differences between cations and anions. To showcase the practical implications of this breakthrough, the piezoionic hydrogels are successfully integrated with prostheses and robot hands, demonstrating that the gating effect enables accurate discrimination between gentle and harsh touch. The advancement in neuromimetic tactile sensing has significant potential for emerging applications such as humanoid robotics and biomedical engineering, offering valuable opportunities for further development of embodied neuromorphic intelligence.

Research on the Thermal Aging Mechanism of Polyvinyl Alcohol Hydrogel

Polyvinyl alcohol (PVA) hydrogels find applications in various fields, including machinery and tissue engineering, owing to their exceptional mechanical properties. However, the mechanical properties of PVA hydrogels are subject to alteration due to environmental factors such as temperature, affecting their prolonged utilization. To enhance their lifespan, it is crucial to investigate their aging mechanisms. Using physically cross-linked PVA hydrogels, this study involved high-temperature accelerated aging tests at 60 °C for 80 d and their performance was analyzed through macroscopic mechanics, microscopic morphology, and microanalysis tests. The findings revealed three aging stages, namely, a reduction in free water, a reduction in bound water, and the depletion of bound water, corresponding to volume shrinkage, decreased elongation, and a "tough-brittle" transition. The microscopic aging mechanism was influenced by intermolecular chain spacing, intermolecular hydrogen bonds, and the plasticizing effect of water. In particular, the loss of bound water predominantly affected the lifespan of PVA hydrogel structural components. These findings provide a reference for assessing and improving the lifespan of PVA hydrogels.

Intricate Ionic Behaviors in High-Performance Self-Powered Hydrothermal Chemical Generator Using Water and Iron (III) Gate

Utilizing the ionic flux to generate voltage output has been confirmed as an effective way to meet the requirements of clean energy sources. Different from ionic thermoelectric (i-TE) and hydrovoltaic devices, a new hydrothermal chemical generator is designed by amorphous FeCl3 particles dispersing in MWCNT and unique ferric chloride or water gate. In the presence of gate, the special ion behaviors enable the cell to present a constant voltage of 0.60 V lasting for over 96 h without temperature difference. Combining the differences of cation concentration, humidity and temperature between the right and left side of sample, the maximum short-circuit current and power output can be obtained to 168.46 µA and 28.11 µW, respectively. The generator also can utilize the low-grade heat to produce electricity wherein Seebeck coefficient is 6.79 mV K-1. The emerged hydrothermal chemical generator offers a novel approach to utilize the low-grade heat, water and salt solution resources, which provides a simple, sustainable and low-cost strategy to realize energy supply.

A pH-Sensitive Stretchable Zwitterionic Hydrogel with Bipolar Thermoelectricity

Amid growing interest in using body heat for electricity in wearables, creating stretchable devices poses a major challenge. Herein, a hydrogel composed of two core constituents, namely the negatively-charged 2-acrylamido-2-methylpropanesulfonic acid and the zwitterionic (ZI) sulfobetaine acrylamide, is engineered into a double-network hydrogel. This results in a significant enhancement in mechanical properties, with tensile stress and strain of up to 470.3 kPa and 106.6%, respectively. Moreover, the ZI nature of the polymer enables the fabrication of a device with polar thermoelectric properties by modulating the pH. Thus, the ionic Seebeck coefficient (Si) of the ZI hydrogel ranges from -32.6 to 31.7 mV K-1 as the pH is varied from 1 to 14, giving substantial figure of merit (ZTi) values of 3.8 and 3.6, respectively. Moreover, a prototype stretchable ionic thermoelectric supercapacitor incorporating the ZI hydrogel exhibits notable power densities of 1.8 and 0.9 mW m-2 at pH 1 and 14, respectively. Thus, the present work paves the way for the utilization of pH-sensitive, stretchable ZI hydrogels for thermoelectric applications, with a specific focus on harvesting low-grade waste heat within the temperature range of 25-40 °C.

Spider-silk-inspired strong and tough hydrogel fibers with anti-freezing and water retention properties

Ideal hydrogel fibers with high toughness and environmental tolerance are indispensable for their long-term application in flexible electronics as actuating and sensing elements. However, current hydrogel fibers exhibit poor mechanical properties and environmental instability due to their intrinsically weak molecular (chain) interactions. Inspired by the multilevel adjustment of spider silk network structure by ions, bionic hydrogel fibers with elaborated ionic crosslinking and crystalline domains are constructed. Bionic hydrogel fibers show a toughness of 162.25 ± 21.99 megajoules per cubic meter, comparable to that of spider silks. The demonstrated bionic structural engineering strategy can be generalized to other polymers and inorganic salts for fabricating hydrogel fibers with broadly tunable mechanical properties. In addition, the introduction of inorganic salt/glycerol/water ternary solvent during constructing bionic structures endows hydrogel fibers with anti-freezing, water retention, and self-regeneration properties. This work provides ideas to fabricate hydrogel fibers with high mechanical properties and stability for flexible electronics.

Bismuth-Based Perovskite Derivates with Thermal Voltage Exceeding 40 mV/K

Heat is an inexhaustible source of energy, and it can be exploited by thermoelectronics to produce electrical power or electrical responses. The search for a low-cost thermoelectric material that could achieve high efficiencies and can also be straightforwardly scalable has turned significant attention to the halide perovskite family. Here, we report the thermal voltage response of bismuth-based perovskite derivates and suggest a path to increase the electrical conductivity by applying chalcogenide doping. The films were produced by drop-casting or spin coating, and sulfur was introduced in the precursor solution using bismuth triethylxanthate. The physical-chemical analysis confirms the substitution. The sulfur introduction caused resistivity reduction by 2 orders of magnitude, and the thermal voltage exceeded 40 mV K-1 near 300 K in doped and undoped bismuth-based perovskite derivates. X-ray diffraction, Raman spectroscopy, and grazing-incidence wide-angle X-ray scattering were employed to confirm the structure. X-ray photoelectron spectroscopy, elemental analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were employed to study the composition and morphology of the produced thin films. UV-visible absorbance, photoluminescence, inverse photoemission, and ultraviolet photoelectron spectroscopies have been used to investigate the energy band gap.

Implantable celecoxib nanofibers made by electrospinning: fabrication and characterization

Background: Osteoarthritis causes tremendous damage to the joints, reducing the quality of life and imposing significant financial burden. An implantable drug-delivery system can improve the symptomatic manifestations with low doses and frequencies. However, the free drug has short retention in the joint cavity. Materials & methods: This study used electrostatic spinning technology to create an implantable drug-delivery system loaded with celecoxib (celecoxib nanofibers [Cel-NFs]) to improve retention and bioavailability. Results: Cel-NFs exhibited good formability, hydrophilicity and tensile properties. Cel-NFs were able to continuously release drugs for 2 weeks and increase the uptake capacity of Raw 264.7 cells, ultimately ameliorating symptoms in osteoarthritis rats. Conclusion: These results suggest that Cel-NFs can effectively ameliorate cartilage damage, reduce joint pain and alleviate osteoarthritis progression.

Chaotropic Effect-Boosted Thermogalvanic Ionogel Thermocells for All-Weather Power Generation

Ionic thermocells convert heat into electricity and are promising power sources for electronic devices. However, discontinuous and small electricity output limits practical use under varying environmental conditions. Here, a thermogalvanic ionogel with a high Seebeck coefficient (32.4 mV K-1) is designed. Thermocells that combine thermogalvanic ionogel-based thermocells, which realize all-weather power generation via passive radiative cooling, are also developed. These thermocells generate electricity continuously under varying weather conditions and over a wide temperature range (-40 to 90 °C), with a normalized power density of 25.84 mW m-2 K-2. Advanced characterization shows that the chaotropic effect enhances the Seebeck coefficient, while the self-supplying temperature difference given the radiative cooling structure enables all-weather power generation. These results provide an effective strategy for developing practical thermocells suitable for diverse daily and seasonal variations.

Solid-state, liquid-free ion-conducting elastomers: rising-star platforms for flexible intelligent devices

Soft ionic conductors have emerged as a powerful toolkit to engineer transparent flexible intelligent devices that go beyond their conventional counterparts. Particularly, due to their superior capacities of eliminating the evaporation, freezing and leakage issues of the liquid phase encountered with hydrogels, organohydrogels and ionogels, the emerging solid-state, liquid-free ion-conducting elastomers have been largely recognized as ideal candidates for intelligent flexible devices. However, despite their extensive development, a comprehensive and timely review in this emerging field is lacking, particularly from the perspective of design principles, advanced manufacturing, and distinctive applications. Herein, we present (1) the design principles and intriguing merits of solid-state, liquid-free ion-conducting elastomers; (2) the methods to manufacture solid-state, liquid-free ion-conducting elastomers with preferential architectures and functions using advanced technologies such as 3D printing; (3) how to leverage solid-state, liquid-free ion-conducting elastomers in exploiting advanced applications, especially in the fields of flexible wearable sensors, bioelectronics and energy harvesting; (4) what are the unsolved scientific and technical challenges and future opportunities in this multidisciplinary field. We envision that this review will provide a paradigm shift to trigger insightful thinking and innovation in the development of intelligent flexible devices and beyond.

Ionic Peltier effect in Li-ion electrolytes

The coupled transport of charge and heat provide fundamental insights into the microscopic thermodynamics and kinetics of materials. We describe a sensitive ac differential resistance bridge that enables measurements of the temperature difference on two sides of a coin cell with a resolution of better than 10 μK. We use this temperature difference metrology to determine the ionic Peltier coefficients of symmetric Li-ion electrochemical cells as a function of Li salt concentration, solvent composition, electrode material, and temperature. The Peltier coefficients Π are negative, i.e., heat flows in the direction opposite to the drift of Li ions in the applied electric field, large, -Π > 30 kJ mol-1, and increase with increasing temperature at T > 300 K. The Peltier coefficient is approximately constant on time scales that span the characteristic time for mass diffusion across the thickness of the electrolyte, suggesting that heat of transport plays a minor role in comparison to the changes in partial molar entropy of Li at the interface between the electrode and electrolyte. Our work demonstrates a new platform for studying the non-equilibrium thermodynamics of electrochemical cells and provides a window into the transport properties of electrochemical materials through measurements of temperature differences and heat currents that complement traditional measurements of voltages and charge currents.

A high-current hydrogel generator with engineered mechanoionic asymmetry

Mechanoelectrical energy conversion is a potential solution for the power supply of miniaturized wearable and implantable systems; yet it remains challenging due to limited current output when exploiting low-frequency motions with soft devices. We report a design of a hydrogel generator with mechanoionic current generation amplified by orders of magnitudes with engineered structural and chemical asymmetry. Under compressive loading, relief structures in the hydrogel intensify net ion fluxes induced by deformation gradient, which synergize with asymmetric ion adsorption characteristics of the electrodes and distinct diffusivity of cations and anions in the hydrogel matrix. This engineered mechanoionic process can yield 4 mA (5.5 A m-2) of peak current under cyclic compression of 80 kPa applied at 0.1 Hz, with the transferred charge reaching up to 916 mC m-2 per cycle. The high current output of this miniaturized hydrogel generator is beneficial for the powering of wearable devices, as exemplified by a controlled drug-releasing system for wound healing. The demonstrated mechanisms for amplifying mechanoionic effect will enable further designs for a variety of self-powered biomedical systems.

Tricarboxylic Acid Cycle Metabolite-Coordinated Biohydrogels Augment Cranial Bone Regeneration Through Neutrophil-Stimulated Mesenchymal Stem Cell Recruitment and Histone Acetylation-Mediated Osteogenesis

Cranial bone defects remain a major clinical challenge, increasing patients' life burdens. Tricarboxylic acid (TCA) cycle metabolites play crucial roles in facilitating bone tissue regeneration. However, the development of TCA cycle metabolite-modified biomimetic grafts for skull bone regeneration still needs to be improved. The mechanism underlying the release of TCA cycle metabolites from biomaterials in regulating immune responses and mesenchymal stem cell (MSC) fate (migration and differentiation) remains unknown. Herein, this work constructs biomimetic hydrogels composed of gelatin and chitosan networks covalently cross-linked by genipin (CGG hydrogels). A series of TCA cycle metabolite-coordinated CGG hydrogels with strong mechanical and antiswelling performances are subsequently developed. Remarkably, the citrate (Na3Cit, Cit)-coordinated CGG hydrogels (CGG-Cit hydrogels) with the highest mechanical modulus and strength significantly promote skull bone regeneration in rat and murine cranial defects. Mechanistically, using a transgenic mouse model, bulk RNA sequencing, and single-cell RNA sequencing, this work demonstrates that CGG-Cit hydrogels promote Gli1+ MSC migration via neutrophil-secreted oncostatin M. Results also indicate that citrate improves osteogenesis via enhanced histone H3K9 acetylation on osteogenic master genes. Taken together, the immune microenvironment- and MSC fate-regulated CGG-Cit hydrogels represent a highly efficient and facile approach toward skull bone tissue regeneration with great potential for bench-to-bedside translation.

Highly Antifreezing Thermogalvanic Hydrogels for Human Heat Harvesting in Ultralow Temperature Environments

Thermogalvanic hydrogels have been quickly developed and are widely used in thermal energy harvesting. However, the freezing behaviors of thermogalvanic hydrogels at subzero temperatures greatly limit their practical applications. Herein, we design an antifreezing thermogalvanic hydrogel based on [Fe(CN)6]3-/4- ions for thermoelectric power generation in ultralow temperature environments. The antifreezing thermogalvanic hydrogels show excellent flexibility at -80 °C owing to the hydrogen bonding between ethylene glycol and water molecules. Even after 500 cyclic tensile strains, the thermogalvanic hydrogels can still maintain excellent mechanical stability, and the Seebeck coefficient is as high as 1.43 mV/K, corresponding to a large retention rate of ∼95%. Moreover, we demonstrate a wearable thermoelectric shoe based on antifreezing thermogalvanic hydrogels for harvesting human thermal energy in a simulated winter environment of -30 °C, and the electricity can drive a green LED. This work provides important guidance for the design and optimization of antifreezing thermogalvanic hydrogels.

Exceptional n-type thermoelectric ionogels enabled by metal coordination and ion-selective association

Ionic liquid-based ionogels emerge as promising candidates for efficient ionic thermoelectric conversion due to their quasi-solid state, giant thermopower, high flexibility, and good stability. P-type ionogels have shown impressive performance; however, the development of n-type ionogels lags behind. Here, an n-type ionogel consisting of polyethylene oxide (PEO), lithium salt, and ionic liquid is developed. Strong coordination of lithium ion with ether oxygen and the anion-rich clusters generated by ion-preferential association promote rapid transport of the anions and boost Eastman entropy change, resulting in a huge negative ionic Seebeck coefficient (-15 millivolts per kelvin) and a high electrical conductivity (1.86 millisiemens per centimeter) at 50% relative humidity. Moreover, dynamic and reversible interactions among the ternary mixtures endow the ionogel with fast autonomous self-healing capability and green recyclability. All PEO-based ionic thermoelectric modules are fabricated, which exhibits outstanding thermal responses (-80 millivolts per kelvin for three p-n pairs), demonstrating great potential for low-grade energy harvesting and ultrasensitive thermal sensing.

Gigantic and Continuous Output Power in Ionic Thermo-Electrochemical Cells by Using Electrodes with Redox Couples

The main obstacle of ionic thermo-electrochemical cells (TECs) in continuous power supply lies in a low heat-to-electricity energy conversion efficiency because most TECs work in thermodiffusion mode in which the ions are confined in a liquid/electrolyte media. The introduction of the redox couple onto the electrode surface may overcome the obstacle by resolving the low mass transport rate of ions caused by the redox process occurring near but not on the electrode surface. Herein, the authors demonstrate enhancement of TECs by integrating the redox couple directly onto the electrode surface to maximize the mass transport efficiency. A discontinuous interfacial modification strategy is developed by using a carbon cloth/iron (II/III) phytate as the symmetric electrodes. The gelled electrolyte consisting of a polyacrylamide matrix and phytic acid is shown to promote selective ion diffusion. A synergistic combination consisting of the thermodiffusion effect and redox reactions on the electrode is established in a pre-treated layout. Such TEC affords a high output voltage of 0.4 V, an excellent instantaneous output power density (20.26 mW m-2 K-2 ) and a record-high 2 h output energy density (2451 J m-2 ) under TH = 30 °C with TC = 15 °C, with an ultrahigh Carnot-relative efficiency of 1.12%.

Ultrasensitive Flexible Thermal Sensor Arrays based on High-Thermopower Ionic Thermoelectric Hydrogel

Ionic circuits using ions as charge carriers have demonstrated great potential for flexible and bioinspired electronics. The emerging ionic thermoelectric (iTE) materials can generate a potential difference by virtue of selective thermal diffusion of ions, which provide a new route for thermal sensing with the merits of high flexibility, low cost, and high thermopower. Here, ultrasensitive flexible thermal sensor arrays based on an iTE hydrogel consisting of polyquaternium-10 (PQ-10), a cellulose derivative, as the polymer matrix and sodium hydroxide (NaOH) as the ion source are reported. The developed PQ-10/NaOH iTE hydrogel achieves a thermopower of 24.17 mV K-1 , which is among the highest values reported for biopolymer-based iTE materials. The high p-type thermopower can be attributed to thermodiffusion of Na+ ions under a temperature gradient, while the movement of OH- ions is impeded by the strong electrostatic interaction with the positively charged quaternary amine groups of PQ-10. Flexible thermal sensor arrays are developed through patterning the PQ-10/NaOH iTE hydrogel on flexible printed circuit boards, which can perceive spatial thermal signals with high sensitivity. A smart glove integrated with multiple thermal sensor arrays is further demonstrated, which endows a prosthetic hand with thermal sensation for human-machine interaction.

Thermoelectric Characteristics of Self-Supporting WSe2-Nanosheet/PEDOT-Nanowire Composite Films

Conducting polymer poly(3,4-ethylenedioxythiophene) nanowires (PEDOT NWs) were synthesized by a modified self-assembled micellar soft-template method, followed by fabrication by vacuum filtration of self-supporting exfoliated WSe₂-nanosheet (NS)/PEDOT-NW composite films. The results showed that as the mass fractions of WSe₂ NSs increased from 0 to 20 wt % in the composite films, the electrical conductivity of the samples decreased from ∼1700 to ∼400 S cm^-1, and the Seebeck coefficient increased from 12.3 to 23.1 μV K^-1 at 300 K. A room-temperature power factor of 44.5 μW m^-1 K^-2 was achieved at 300 K for the sample containing 5 wt % WSe₂ NSs, and a power factor of 67.3 μW m^-1 K^-2 was obtained at 380 K. The composite film containing 5 wt % WSe₂ NSs was mechanically flexible, as shown by its resistance change ratio of 7.1% after bending for 500 cycles at a bending radius of 4 mm. A flexible thermoelectric (TE) power generator containing four TE legs could generate an output power of 52.1 nW at a temperature difference of 28.5 K, corresponding to a power density of ∼0.33 W/m². This work demonstrates that the fabrication of inorganic nanosheet/organic nanowire TE composites is an approach to improve the TE properties of conducting polymers.

Mechanically Adaptative and Environmentally Stable Ionogels for Energy Harvest

Converting building and environment heat into electricity is a promising strategy for energy harvest to tackle global energy and environmental problems. The processing challenges, mechanical brittleness, and low environmental tolerance of typical thermoelectric materials, however, prevent them from realizing their full potential when employed in outdoor building systems. Herein, a general concept based on synergistic ionic associations to significantly improve the mechanical properties and harsh environment stability for high-performance ionic-type thermoelectric (i-TE) gels is explored. They demonstrate extraordinarily high stretchability (1300-2100%), fast self-healing (120 s), temperature insensitivity, and great water-proof performance, and could be painted on a variety of surfaces. The n-type ionic Seebeck coefficient is up to -8.8 mV K-1 and the ionic conductivity is more than 0.14 mS cm-1 . Both exhibit remarkable thermal and humidity stability (293-333 K, 20-100 RH%), which are rarely achieved in previous studies. Even on a cloudy day, the open-circuit thermovoltage for a painted i-TE array with an area of about 8.5 × 10-3 m2 is above 2 V. This research offers a promising approach for gathering significant waste heat and even solar energy on outside building surfaces in an effective and sustainable manner.

Integrated Moist-Thermoelectric Generator for Efficient Waste Steam Energy Utilization

Industrial waste steam is one of the major sources of global energy losses. Therefore, the collection and conversion of waste steam energy into electricity have aroused great interest. Here, a "two-in-one" strategy is reported that combines thermoelectric and moist-electric generation mechanisms for a highly efficient flexible moist-thermoelectric generator (MTEG). The spontaneous adsorption of water molecules and heat in the polyelectrolyte membrane induces the fast dissociation and diffusion of Na⁺ and H⁺ , resulting in the high electricity generation. Thus, the assembled flexible MTEG generates power with a high open-circuit voltage (V_oc ) of 1.81 V (effective area = 1cm² ) and a power density of up to 4.75±0.4 µW cm^-2 . With efficient integration, a 12-unit MTEG can produce a V_oc of 15.97 V, which is superior to most known TEGs and MEGs. The integrated and flexible MTEGs reported herein provide new insights for harvesting energy from industrial waste steam.

Giant Negative Thermopower Enabled by Bidirectionally Anchored Cations in Multifunctional Polymers

The lack of high-quality ionic thermoelectric materials with negative thermopowers has stimulated scientists' broad research interest. The effective adjustment of the interaction between ions and a polymer network is an important way to achieve high-quality ion thermoelectric properties. Integrating different types of ion-polymer interactions into the same thermoelectric device seems to lead to unexpected gains. In this work, we propose a strategy for bidirectionally anchoring cations to synergistically generate a giant negative thermopower and high ionic conductivity. This is mainly achieved through synergistic ion-polymer coordination and Coulomb interactions. An ionic thermoelectric material was prepared by infiltrating a polycation electrolyte [poly(diallyldimethylammonium chloride)] with CuCl₂ into the poly(vinyl alcohol)-chitosan aerogel. The confinement effect of copper-coordinated chitosan on cations, the repulsive property of the polycationic electrolyte on cations, and the unique chemical configuration of a transition metal chloride anion ([CuCl₄]^2-) are the fundamental guarantees for achieving a thermopower of -28.4 mV·K^-1. Moreover, benefiting from the high charge density of the polycationic electrolyte, we obtain an ionic conductivity of 40.5 mS·cm^-1. These findings show the application prospect of synergistic different types of ion-polymer interactions in designing multifunctional ionic thermoelectric materials.

Near-Infrared Light-Responsive Hydrogels for Highly Flexible Bionic Photosensors

Soft biological tissues perform various functions. Sensory nerves bring sensations of light, voice, touch, pain, or temperature variation to the central nervous system. Animal senses have inspired tremendous sensors for biomedical applications. Following the same principle as photosensitive nerves, we design flexible ionic hydrogels to achieve a biologic photosensor. The photosensor allows responding to near-infrared light, which is converted into a sensory electric signal that can communicate with nerve cells. Furthermore, with adjustable thermal and/or electrical signal outputs, it provides abundant tools for biological regulation. The tunable photosensitive performances, high flexibility, and low cost endow the photosensor with widespread applications ranging from neural prosthetics to human-machine interfacing systems.

Solvent-Exchange-Assisted Wet Annealing: A New Strategy for Superstrong, Tough, Stretchable, and Anti-Fatigue Hydrogels

Hydrogels are widely used in tissue engineering, soft robots, wearable electronics, etc. However, it remains a great challenge to develop hydrogels possessing simultaneously high strength, large stretchability, great fracture energy, and good fatigue threshold to suit different applications. Herein, a novel solvent-exchange-assisted wet-annealing strategy is proposed to prepare high performance poly(vinyl alcohol) hydrogels by extensively tuning the macromolecular chain movement and optimizing the polymer network. The reinforcing and toughening mechanisms are found to be "macromolecule crystallization and entanglement". These hydrogels have large tensile strengths up to 11.19 ± 0.27 MPa and extremely high fracture strains of 1879 ± 10%. In addition, the fracture energy and fatigue threshold can reach as high as 25.39 ± 6.64 kJ m^-2 and ≈1233 J m^-2 , respectively. These superb mechanical properties compare favorably to those of other tough hydrogels, organogels, and even natural tendons and synthetic rubbers. This work provides a new and effective method to fabricate superstrong, tough, stretchable, and anti-fatigue hydrogels with potential applications in artificial tendons and ligaments.

Water-Resistant Thermoelectric Ionogel Enables Underwater Heat Harvesting

The energy crisis is one of the most critical and urgent problems in modern society; thus, harvesting energy from ubiquitous low-grade heat energy with thermoelectric (TE) materials has become an available strategy in sustainable development. Recently, emerging ionic TE materials have been widely used to harvest low-grade heat energy, owing to their excellent performance in high ionic Seebeck coefficient, low thermal conductivity, and mechanical flexibility. However, the instability of ionic conductive materials in the underwater environment seriously suppresses underwater energy-harvesting, resulting in a waste of underwater low-grade heat energy. Herein, we developed a water-resistant TE ionogel (TEIG) with excellent long-term underwater stability utilizing a hydrophobic structure. Due to the hydrophobic polymer network and hydrophobic ionic liquid (IL), the TEIG exhibits high hydrophobicity and antiswelling capacity, which meets the requirement of environment stability for underwater thermoelectric application. Furthermore, the water resistance endows the TEIG with great thermoelectric performances in the underwater environment, including satisfactory ionic Seebeck coefficient, outstanding durability, and superior salt tolerance. Therefore, this investigation provides a promising strategy to design water-resistant TE materials, enabling a remarkable potential in harvesting low-grade heat energy under water.

Preparation and Study of Polyvinyl Alcohol Gel Structures with Acrylamide and 2-Acrylamido-2-methyl-1-propanesulfonic Acid for Application in Saline Oil Reservoirs for Profile Modification

Polymer gels can be effectively applied to plug fractured reservoirs and carbonate cave strata. Herein, polyvinyl alcohol (PVA), acrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) were used as raw materials to prepare interpenetrating three-dimensional network polymer gels using formation saltwater in the Tahe oilfield (Tarim Basin, NW China) as a solvent. The effect of AMPS concentration on the gelation properties of PVA in high-temperature formation saltwater was analyzed. Further, the effect of PVA concentration on the strength and viscoelastic properties of polymer gel was studied. The polymer gel could retain stable continuous entanglement at 130 °C and exhibited satisfactory thermal stability. Continuous step oscillation frequency tests showed that it exhibited an excellent self-healing performance. Scanning electron microscopy images of the simulated core by gel plugging showed that the polymer gel could firmly fill the porous media, indicating that the polymer gel exhibits excellent application prospects in oil and gas reservoirs under high-temperature and high-salinity conditions.

Reversible bipolar thermopower of ionic thermoelectric polymer composite for cyclic energy generation

The giant thermopower of ionic thermoelectric materials has attracted great attention for waste-heat recovery technologies. However, generating cyclic power by ionic thermoelectric modules remains challenging, since the ions cannot travel across the electrode interface. Here, we reported a reversible bipolar thermopower (+20.2 mV K-1 to -10.2 mV K-1) of the same composite by manipulating the interactions of ions and electrodes. Meanwhile, a promising ionic thermoelectric generator was proposed to achieve cyclic power generation under a constant heat course only by switching the external electrodes that can effectively realize the alternating dominated thermodiffusion of cations and anions. It eliminates the necessity to change the thermal contact between material and heat, nor does it require re-establish the temperature differences, which can favor improving the efficiency of the ionic thermoelectrics. Furthermore, the developed micro-thermal sensors demonstrated high sensitivity and responsivity in light detecting, presenting innovative impacts on exploring next-generation ionic thermoelectric devices.

Solid state ionics enabled ultra-sensitive detection of thermal trace with 0.001K resolution in deep sea

The deep sea remains the largest uncharted territory on Earth because it's eternally dark under high pressure and the saltwater is corrosive and conductive. The harsh environment poses great difficulties for the durability of the sensing method and the device. Sea creatures like sharks adopt an elegant way to detect objects by the tiny temperature differences in the seawater medium using their extremely thermo-sensitive thermoelectric sensory organ on the nose. Inspired by shark noses, we designed and developed an elastic, self-healable and extremely sensitive thermal sensor which can identify a temperature difference as low as 0.01 K with a resolution of 0.001 K. The sensor can work reliably in seawater or under a pressure of 110 MPa without any encapsulation. Using the integrated temperature sensor arrays, we have constructed a model of an effective deep water mapping and detection device.

Structural Color Ionic Hydrogel Patches for Wound Management

Ionic hydrogels have attracted extensive attention because of their wide applicability in electronic skins, biosensors, and other biomedical areas. Tremendous effort is dedicated to developing ionic hydrogels with improved detection accuracy and multifunctionality. Herein, we present an inverse opal scaffold-based structural color ionic hydrogel with the desired features as intelligent patches for wound management. The patches were composed of a polyacrylamide-poly(vinyl alcohol)-polyethylenimine-lithium chloride (PAM-PVA-PEI-LiCl) inverse opal scaffold and a vascular endothelial growth factor (VEGF) mixed methacrylated gelatin (GelMA) hydrogel filler surface. The scaffold imparted the composite patches with brilliant structural color, conductive property, and freezing resistance, while the VEGF-GelMA surface could not only prevent the ionic hydrogel from the interference of complex wound conditions but also contribute to the cell proliferation and tissue repair in the wounds. Thus, the hydrogel patches could serve as electronic skins for in vivo wound healing and monitoring with high accuracy and reliability. These features indicate that the proposed structural color ionic hydrogel patches have great potential for clinical applications.

Thermoelectric energy harvesting for personalized healthcare

In recent decades, there has been increased research interest in miniaturizing and decentralizing diagnostic platforms to enable continuous personalized healthcare and free patients from long-term hospitalization. However, the lack of reliable and portable power supplies has limited the working time of the personalized healthcare platform. Compared with the current power supplies (e.g., batteries and supercapacitors) that require manual intervention, thermoelectric devices promise to continuously harvest waste heat from the human body to satisfy the energy consumption of personalized healthcare platforms. Herein, this review discusses thermoelectric energy harvesting for personalized healthcare. It begins with the fundamental concepts of different thermoelectric materials, including electron thermoelectric generators (TEGs), ionic thermogalvanic cells (TGCs), and ionic thermoelectric capacitors (TECs). Then, the wearable and implantable applications of thermoelectric devices are presented. Finally, future directions of next-generation thermoelectric devices for personalized healthcare are discussed. It is hoped that developing high-performance thermoelectric devices will change the landscape of personalized healthcare in the future.

Soret Effect of Ionic Liquid Gels for Thermoelectric Conversion

Cations and anions can accumulate at the two ends of an ionic conductor under temperature gradient, which is the so-called Soret effect. This can generate a voltage between the two electrodes, and the thermopower can be higher than that of the electronic conductors because of the Seebeck effect by 1-2 orders in magnitude. The thermoelectric properties of ionic conductors depend on the ionic thermopower, ionic conductivity, and thermal conductivity. Compared with other ionic conductors, like liquid electrolytes and hydrogels, ionogels made of an ionic liquid and a gelator can have the advantages of high thermopower and high stability. Great progress was recently made to improve the ionic conductivity and/or ionic thermopower of ionogels. They can be used in ionic thermoelectric capacitors (ITECs) to harvest heat. In addition, they can be integrated with electronic thermoelectric materials to harvest heat from both temperature gradient and temperature fluctuation, which can be caused by waste heat.