Conductive Organohydrogel Research Articles

Binary-1D/2D nanomaterial-functionalization toward strong, stretchable, and anti-freezing electrically conductive organohydrogels for self-powered operation monitoring of robotic hand

Machines and robots have become greatly significant in liberating human beings from heavy and repetitive physical work, which requires intelligent monitoring of their operation states. However, simultaneous realization of self-power, high mechanical strength, ultra-stretchability, and low-temperature tolerance for sensing devices remains challenging. Here, a triboelectric nanogenerator (TENG) based on anti-freezing, mechanically robust and electrically conductive organohydrogels is demonstrated via a binary-nanomaterial-functionalization and solvent-exchange approach. The organohydrogel exhibits high anti-freezing behaviors with maintained electrical conductivity (6.2 S/m) and mechanical properties (2.7 MPa and 820 %) at extreme subzero temperatures. Notably, molecular interactions and geometrical synergy of the nanophases enable the high operation durability of the TENG with at least 15,000 working cycles and a peak power density of ∼ 120 mW m−2 (loading resistance of 5 × 107 Ω and pressure of 40 N) in such harsh environments. Furthermore, the TENG is employed to create a monitoring system capable of real-time wirelessly transmitting electrical signals for identifying the sizes and textures of objects grasped by a robotic hand. Featuring these characteristics, this work may provide a new perspective for designing new strong yet tough and cold-tolerant materials for intelligent and self-powered human–machine interactive systems.

Bacterial cellulose nanofiber-reinforced PVA conductive organohydrogel for flexible strain sensors with high sensitivity and durability

Flexible strain sensors based on conductive organohydrogels have aroused wide range of interests owing to their potential utilization in human health and motion detecting. However, the mechanical performance and sensitivity of the organohydrogel sensors need to be further optimized. Herein, we have designed a dual-network organohydrogel utilizing poly(vinyl alcohol) (PVA) as raw materials, bacterial cellulose (BC) nanofibers as reinforcements, tannic acid (TA) as crosslinkers and multiwall carbon nanotubes (CNTs) as conducting fillers. The constructed C-PVA/BC/CNT organohydrogel shows good mechanical properties and high sensitivity. The resistance of the C-PVA/BC/CNT organohydrogel can be remarkably changed during deformation, demonstrating superior synchronicity between mechanical stimulus and electric signals, and thus can be used as piezoresistive strain sensors. In addition, the C-PVA/BC/CNT organohydrogel also exhibits favorable durability under different strains, and excellent cycling stability during loading/unloading processes. This C-PVA/BC/CNT organohydrogel can be used to monitor human motion and physiological activities, and has great potential applications in wearable electronic devices.

Self-Healable, Adhesive, Anti-Drying, Freezing-Tolerant, and Transparent Conductive Organohydrogel as Flexible Strain Sensor, Triboelectric Nanogenerator, and Skin Barrier.

Conductive hydrogels have attracted tremendous interest in the construction of flexible strain sensors and triboelectric nanogenerators (TENGs) owing to their good stretchability and adjustable properties. Nevertheless, how to simultaneously achieve high transparency, self-healing, adhesion, antibacterial, anti-freezing, anti-drying, and biocompatibility properties through a simple method remains a challenge. Herein, a transparent, freezing-tolerant, and multifunctional organohydrogel (PAOAM-PDO) as electrode for strain sensors and TENGs was constructed through a free radical polymerization in the 1,3-propanediol (PDO)/water binary solvent system, in which oxide sodium alginate, aminated gelatin, acrylic acid, and AlCl3 were used as raw materials. The obtained PAOAM-PDO exhibited good transparency (>90%), self-healing, adhesiveness, antibacterial property, good conductivity (1.13 S/m), and long-term environmental stability. The introduction of PDO endowed PAOAM-PDO with freezing resistance with a low freezing point of -60 °C, and PAOAM-PDO could serve as a protective skin barrier to prevent frostbite at low temperature. PAOAM-PDO could be assembled as strain sensors to monitor heterogeneous human movements with high strain sensitivity (gauge factor of 7.05, strain = 233%). Meanwhile, PAOAM-PDO could be further fabricated as a TENG with a "sandwich" structure in single electrode mode. Moreover, the resulting TENG achieved electrical outputs with simple hand tapping and served as a self-powered device to light light-emitting diodes. This work displays a feasible strategy to build environment-tolerant and multifunctional organohydrogels, which possess potential applications in the wearable electronics and self-powered devices.

Phosphoric acid/glycerol-based anti-freezing organohydrogel electrolyte for flexible supercapacitor with excellent low-temperature stability

Flexible supercapacitors (SCs) have attracted much attention from researchers on account of their excellent safety, high power density, fast charging/discharging speed and long cycle life. Conventional hydrogel electrolytes will freeze when the operating temperature drops below zero degree, limiting the practical applications of SCs. Here, we proposed a strategy to prepare a highly conductive organohydrogel electrolyte (OHE) with excellent anti-freezing property and moisture retention by soaking poly(2-acrylamido-2-methypropane sulfonic acid)/poly (acrylamide) (PAMPS/PAAm) hydrogel into phosphoric acid/glycerol (PA/Gly) co-solvent. The OHE possessed favorable flexibility and excellent electrical conductivity of 9 and1.98 S/m at room temperature and −40 °C, respectively. Meanwhile, the prepared SCs obtained high specific capacitance, superior capacitance retention rate of 75.65% and excellent mechanical flexibility at −40 °C, compared with those at room temperature. Moreover, this work would provide a novel and promising approach for the development of flexible wearable electronic devices with low-temperature stability.

Organohydrogels with cellulose nanofibers enhanced supramolecular interactions toward high performance self-adhesive sensing pads

Gel materials with tailored functions and tissue-like properties have gained significant interest in emerging applications, including tissue engineering scaffolds, flexible electronics, and soft robotics. In this work, we developed a stretchable, flexible, adhesive, and conductive organohydrogel through physical cross-linking of the poly (N-[tris (hydroxymethyl) methyl] acrylamide-co-acrylamide) (denoted as P(THMA-AM)) network in the presence of cellulose nanofiber (CNF), sodium chloride, and glycerol. The gel matrix is rich in intermolecular interactions, including hydrogen bonding and ionic interactions, which contribute to a highly compact and cohesive structure without the requirement of any chemical crosslinkers. Moreover, the plasticizing effect of glycerol can mitigate the self-entanglement of CNFs, enhancing their mobility and ultimately conferring the organohydrogel with exceptional stretchability and flexibility. The resulting organohydrogel exhibited superior mechanical properties, self-adhesion, and ionic conductivity, making it an excellent candidate for strain-sensing applications, particularly in distinguishing and monitoring human movements.

High-Strength, Freeze-Resistant, Recyclable, and Biodegradable Polyvinyl Alcohol/Glycol/Wheat Protein Complex Organohydrogel for Wearable Sensing Devices.

The application of flexible wearable sensing devices based on conductive hydrogels in human motion signal monitoring has been widely studied. However, conventional conductive hydrogels contain a large amount of water, resulting in poor mechanical properties and limiting their application in harsh environments. Here, a simple one-pot method for preparing conductive hydrogels is proposed, that is, polyvinyl alcohol (PVA), wheat protein (WP), and lithium chloride (LiCl) are dissolved in an ethylene glycol (EG)/water binary solvent. The obtained PVA/EG/WP (PEW) conductive organohydrogel has good mechanical properties, and its tensile strength and elongation at break reach 1.19 MPa and 531%, respectively, which can withstand a load of more than 6000 times its own weight without breaking. The binary solvent system composed of EG/water endows the hydrogel with good frost resistance and water retention. PEW organohydrogel as a wearable strain sensor also has good strain sensitivity (GF = 2.36), which can be used to detect the movement and physiological activity signals in different parts of the human body. In addition, PEW organohydrogels exhibit good degradability, reducing the environmental footprint of the flexible sensors after disposal. This research provides a new and viable way to prepare a new generation of environmentally friendly sensors.

Functionally integrated conductive organohydrogel sensor for wearable motion detection, triboelectric nanogenerator and non-contact sensing

In the field of wearable devices, hydrogel has become a new material due to its excellent flexibility and adjustable multifunctionality. However, there are still many problems in practical application, which cannot meet the requirements of people for flexible electronic devices. Herein, a stretchable, self-adhesive, anti-freezing and moisturizing ion-conductive organohydrogel was successfully prepared. This organohydrogel can exhibit adjustable optical properties in different solvents, and the strain sensor based on it can exhibits excellent sensing capability and real-time responsiveness to various strains, pressures and human body. In addition, the organohydrogel exhibits excellent energy harvesting capabilities when it was assembled with Ecoflex elastomers to form a triboelectric nanogenerator (TENG). And when it was assembled with Ecoflex elastomer to form a non-contact capacitive sensor, it can achieve good proximity sensing stability. Therefore, it can be seen that the multifunctional organohydrogel provides an idea for the design and preparation of advanced versatile flexible sensors.

Highly Stretchable, Self-Adhesive, Antidrying Ionic Conductive Organohydrogels for Strain Sensors.

As flexible wearable devices, hydrogel sensors have attracted extensive attention in the field of soft electronics. However, the application or long-term stability of conventional hydrogels at extreme temperatures remains a challenge due to the presence of water. Antifreezing and antidrying ionic conductive organohydrogels were prepared using cellulose nanocrystals and gelatin as raw materials, and the hydrogels were prepared in a water/glycerol binary solvent by a one-pot method. The prepared hydrogels were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The mechanical properties, electrical conductivity, and sensing properties of the hydrogels were studied by means of a universal material testing machine and LCR digital bridge. The results show that the ionic conductive hydrogel exhibits high stretchability (elongation at break, 584.35%) and firmness (up to 0.16 MPa). As the binary solvent easily forms strong hydrogen bonds with water molecules, experiments show that the organohydrogels exhibit excellent freezing and drying (7 days). The organohydrogels maintain conductivity and stable sensitivity at a temperature range (-50 °C-50 °C) and after long-term storage (7 days). Moreover, the organohydrogel-based wearable sensors with a gauge factor of 6.47 (strain, 0-400%) could detect human motions. Therefore, multifunctional organohydrogel wearable sensors with antifreezing and antidrying properties have promising potential for human body monitoring under a broad range of environmental conditions.

Collagen-Based Organohydrogel Strain Sensor with Self-Healing and Adhesive Properties for Detecting Human Motion.

Conductive hydrogels are ideal for flexible sensors, but it is still a challenge to produce such hydrogels with combined toughness, self-adhesion, self-healing, anti-freezing, moisturizing, and biocompatibility properties. Herein, inspired by natural skin, a highly stretchable, strain-sensitive, and multi-environmental stable collagen-based conductive organohydrogel was constructed by using collagen (Col), acrylic acid, dialdehyde carboxymethyl cellulose, 1,3-propylene glycol, and AlCl3. The resulting organohydrogel exhibited excellent tensile (strain >800%), repeatable adhesion (>10 times), self-healing [self-healing efficiency (SHE) ≈ 100%], anti-freezing (-60 °C), moisturizing (>20 d), and biocompatible properties. This organohydrogel also possessed good electrical conductivity (σ = 3.4 S/m) and strain-sensitive properties [GF (gauge factor) = 13.65 with the maximal strain of 400%]. Notably, the organohydrogel had a considerable low-temperature self-healing performance (SHE = 88% at -24 °C) and rapid underwater self-healing property (SHE = 92%, self-healing time <20 min). This type of strain sensor could not only accurately and continuously monitor the large-scale motions of the human body but also provide an accurate response to the human tiny motions. This work not only proposes a development strategy for a multifunctional conductive organohydrogel with multiple environmental stability but also provides potential research value for the construction of biomimetic electronic skin.

Rapid room-temperature polymerization strategy to prepare organic/inorganic hybrid conductive organohydrogel for terahertz wave responsiveness

Conductive organohydrogel with better environmental stability than conductive hydrogel, has more promising applications in the fields of soft robots, wearable electronics and electromagnetic interference shielding. However, the current organohydrogels still face the trade-off dilemma between environmental stability and conductivity, and their preparation is usually time-consuming and complicated. Here, we report a room-temperature rapid polymerization strategy to prepare conductive organohydrogel using PEDOT:PSS and MXene nanosheets as conductive fillers as well as cross-linking sites, which is applicable to a variety of binary solvent systems. The synergistic effect between PEDOT:PSS and MXene nanosheets activates the formation of abundant hydrogen bonds, chelation interaction and electrostatic interaction between different components, thus significantly shortening the polymerization time from several hours to less than five minutes. Meanwhile, the organic–inorganic hybrid network constructs efficient conductive paths and strengthens the mechanical properties. Over a wide temperature range (−18 to 70 °C), this composite organohydrogel shows excellent stretchability, self-healing, adhesion, environmental stability. More interestingly, the organohydrogel with reasonably designed binary solvent system and conductive network achieves absorption-dominated shielding performance and wireless displacement sensing in the frequency of 2–10 terahertz. The revealed contributions of binary solvent system and conductive network to the absorption and reflection of terahertz waves are conducive to promote the development of organohydrogel-based terahertz responsive materials.

Rapid self-healing, self-adhesive, anti-freezing, moisturizing, antibacterial and multi-stimuli-responsive PVA/starch/tea polyphenol-based composite conductive organohydrogel as flexible strain sensor

• A novel PVA/starch/tea polyphenol-based conductive organohydrogel is fabricated. • Organohydrogel contains dynamic borate ester bonds and reversible multiple hydrogen bonds. • Organohydrogel features its remarkable self-healing and self-adhesive properties in the air, underwater and at low temperature. • Organohydrogel exhibits anti-freezing, moisturizing, antibacterial and pH/sugar-responsive properties. • Organohydrogel as strain sensor can accurately monitor various human motions and vital signs. The complexity of application environment stimulates the development of wearable devices based on functional hydrogels. Among all the promising performances, self-healing and self-adhesion properties are ideal for hydrogel sensors, which can guarantee good accuracy, comfort and long service life. However, it is still a challenge to achieve simultaneous self-healing and self-adhesion in different environments (in the air, underwater and at low temperatures). Herein, a feasible new strategy was successfully carried out to prepare a starch-based composite conductive organohydrogel based on the reversible borate ester bonds formed by complexing starch/polyvinyl alcohol (PVA)/tea polyphenol (TP) with borax, and multiple hydrogen-bond interactions among PVA, starch, TP and ethylene glycol (EG). Silver nanoparticles (AgNPs), reduced and stabilized by TP, and MWCNTs (multi-walled carbon nanotubes) were introduced into the cross-linking networks to endow the resulting PBSTCE organohydrogel with considerable antibacterial property and conductivity, respectively. The organohydrogel possessed rapid self-healing (HE (self-healing efficiency) = 96.07% in 90 s, both in the air and underwater, also at -20 °C), considerable self-adhesion (both in the air and underwater, also at -20 °C), remarkable stretchability (814% of elongation), anti-freezing (-20 °C) and moisture-retention abilities, antibacterial activity, sensitive pH/sugar-responsiveness, and plasticity. The strain sensor formed by the PBSTCE organohydrogel can not only effectively record large-scale human motions (e.g. finger/wrist/elbow bending, walking, etc.), but also accurately capture subtle motion changes (e.g. breathing, chewing, swallowing, speaking, smiling and frowning). Moreover, the self-healed organohydrogel sensor also exhibited almost invariable mechanical, electrical and sensing behaviors. This work demonstrates a feasible strategy to construct multifunctional starch-based organohydrogels, and promotes their efficient, stable and eco-friendly application as flexible wearable devices.

Mechanically Strong, Freeze-Resistant, and Ionically Conductive Organohydrogels for Flexible Strain Sensors and Batteries.

Conductive hydrogels as promising material candidates for soft electronics have been rapidly developed in recent years. However, the low ionic conductivity, limited mechanical properties, and insufficient freeze-resistance greatly limit their applications for flexible and wearable electronics. Herein, aramid nanofiber (ANF)-reinforced poly(vinyl alcohol) (PVA) organohydrogels containing dimethyl sulfoxide (DMSO)/H2 O mixed solvents with outstanding freeze-resistance are fabricated through solution casting and 3D printing methods. The organohydrogels show both high tensile strength and toughness due to the synergistic effect of ANFs and DMSO in the system, which promotes PVA crystallization and intermolecular hydrogen bonding interactions between PVA molecules as well as ANFs and PVA, confirmed by a suite of characterization and molecular dynamics simulations. The organohydrogels also exhibit ultrahigh ionic conductivity, ranging from 1.1 to 34.3Sm-1 at -50 to 60°C. Building on these excellent material properties, the organohydrogel-based strain sensors and solid-state zinc-air batteries (ZABs) are fabricated, which have a broad working temperature range. Particularly, the ZABs not only exhibit high specific capacity (262mAhg-1 ) with ultra-long cycling life (355cycles, 118h) even at -30°C, but also can work properly under various deformation states, manifesting their great potential applications in soft robotics and wearable electronics.

Preparation and applications of flexible conductive organohydrogels with ultrahigh gas permeability

Flexible conductive organohydrogels with ultrahigh gas permeability for wearable electronic device applications.

A robust conductive organohydrogel with adhesive and low-hysteresis properties for all-weather human motion and wireless electrocardiogram sensing

A strain sensor based on OH-PLT organohydrogel is reported and characterized by low hysteresis, high sensitivity, and high adhesion for the stable monitoring of human movement in all-weather environments and the wireless monitoring of ECG signals.

Chestnut-Tannin-Crosslinked, Antibacterial, Antifreezing, Conductive Organohydrogel as a Strain Sensor for Motion Monitoring, Flexible Keyboards, and Velocity Monitoring

Flexible sensing devices (FSDs) fabricated using conductive hydrogels have attracted researchers' extensive enthusiasm in recent years due to their versatility. Considering the complexity of their application environments, the integration of various functional characteristics (e.g., excellent mechanical, antibacterial, and antifreezing properties) is an important guarantee for FSDs to stably perform their applications in different environments. Herein, we developed a multifunctional conductive polyvinyl alcohol (PVA) organohydrogel PVA-CT-Ag-Al-Gly (PCAAG) by using a green, natural, and cheap biomass, chestnut tannin (CT), as a crosslinking agent, nano-silver particles (AgNPs) as an antimicrobial agent, aluminum trichloride (AlCl3) as a conducting medium, and the mixed water-glycerol as the solvent system. In this organohydrogel system, CT acted not only as the reducing and stabilizing agent for the preparation of antibacterial AgNPs but also as the crosslinking agent owing to its strong multiple hydrogen bonding interactions with PVA, realizing its multifunctional application. The PCAAG organohydrogel possessed outstanding physical and mechanical properties (350.54% of the maximum fracture strain and 1.55 MPa of the maximum tensile strength), considerable bacteriostatic effects against both Escherichia coli and Staphylococcus aureus, and excellent freeze resistance (it could function normally at -20 °C). The motion-monitoring sensor based on the PCAAG organohydrogel exhibited excellent specificity recognition for both large-amplitude (e.g., elbow bending, wrist bending, finger bending, running and walking, etc.) and small-amplitude (frowning and swallowing) human movements. The flexible keyboard constructed by using the PCAAG organohydrogel could easily achieve the transformation between digital signals and electrical signals, and the signal output had both specificity and stability. The velocity-monitoring sensor fabricated by using the PCAAG organohydrogel could accurately measure the speed of the object movement (less than 3% of relative error). In short, the present PCAAG organohydrogel solves the problems of the single application environment and a few application scenarios of traditional conductive hydrogels and possesses remarkable application potential as a multifunctional FSD in many fields such as artificial intelligence, sport management, soft robots, and human-computer interface.

Environmentally Stable, Stretchable, Adhesive, and Conductive Organohydrogels with Multiple Dynamic Interactions as High-Performance Strain and Temperature Sensors.

Nowadays, with the rapid development of artificial intelligence, conductive hydrogel-based sensors play an increasingly vital role in health monitoring and temperature sensing. However, the perfect integration of the environmental stability and applied performance of the hydrogel has always been a challenging and significant problem. Herein, we report an environmentally tolerant, stretchable, adhesive, self-healing conductive gel through multiple dynamic interactions in the water/glycerol/ionic liquids medium, which can be used as a high-performance strain and temperature sensor. The random copolymer poly(acrylic acid-co-acetoacetoxyethyl methacrylate) interacts with the branched poly(ethylene imine) (PEI) and Zr4+ ions via the dynamic covalent enamine bonds, coordinations, and electrostatic interactions to improve stretchable (1300%), compressible, fatigue-resistant (1000 cycles at 50% strain), and self-healing performance (95%, 24 h). The combination of water/glycerol/ionic liquids imparts the resulting gel with excellent electrical conductivity, anti-drying, and anti-freezing performance. By means of the above excellent performance, the gel could be used as the flexible strain or pressure sensor with high sensitivity and stability for the detection of the movement, expression, handwriting, pronouncing, and electrocardiogram (ECG) signals in various models. Meanwhile, the resulting gel can be assembled as the temperature sensor to trace the change of temperature accurately and steadily, which has a wide operating window (0 to 100 °C), an ultralow detection limit (0.2 °C), and high sensitivity (2.1% °C-1). It is believed that the strategy for the multifunction and high-performance gel will blaze a new trail for the smart device in health management, temperature detection, and information transmission under various environmental conditions.

Intrinsically adhesive, conductive organohydrogel with high stretchable, moisture retention, anti-freezing and healable properties for monitoring of human motions and electrocardiogram

A novel self-adhesive conductive organohydrogel without catechol adhesive components is developed for long-term, continuous monitoring of human motions and electrocardiogram. The organohydrogel is achieved by covalent cross-linking polymerization of acrylamide, N-acryloylglycinamide, and reduced graphene oxide, followed by soaking into ethylene glycol-water mixture. The organohydrogel exhibits intrinsic adhesion to various substances, excellent healing ability of nearly 100% conductivity repair rate, long-lasting moisture retention (about 30 days), extreme temperature tolerance (–20–60 °C), stable conductivity and extraordinary mechanical properties with a maximum tensile strength of 300 kPa, high stretchability over 1700%, compressive stress over 5 MPa. This organohydrogel can adhere to human skin without other fixture for human motions monitoring, such as the bending of wrist, finger, elbow and knee, and throat actions. Moreover, the organohydrogel can achieve long-term, continuous monitoring of human ECG signals in various daily activities, such as a night of sleep, standing, walking, performing leg curls and leg presses, and using an elliptical machine. This research offers a new strategy to develop self-adhesive conductive organohydrogel for long-term, continuous, and imperceptible monitoring of human health signals.

Low hysteresis, anti-freezing and conductive organohydrogel prepared by thiol-ene click chemistry for human-machine interaction

Hydrogels are arousing increasing research interesting due to their potential application in the fields of motion detection and human-machine interaction. But the problems of high hysteresis, difficulty in preservation, and inadaptability to extreme conditions are still challenges nowadays. Herein, a multi-crosslinked PVA/EG/CNT-OH click-organohydrogel was prepared by photoinitiated thiol-ene click chemistry. Due to the presence of strong C–S bonds obtained by click chemistry, the click-gel has a dense structure with very low hysteresis at tensile strains of 200% and compressive strains of 50%, exhibiting a minimum dissipation energy of 0.0046 MJ m−3 and 0.00089 MJ m−3, respectively. On account of the synergistic effect of various crosslinks, it also has a tensile strength of 206 kPa, elongation at break of 408%, and compressive strength of 576 kPa at 80% compressive strain. Therefore, the click-gel has high fidelity for high-frequency motion detection as well as excellent self-recovery and anti-fatigue performances under a wide range of strain and pressure. Furthermore, the outstanding anti-freezing and moisture retention performance allow it to adapt to extreme environments. The click-gel paves a way for the development of sensors that can be used not only for human motions detection, but also as input devices of intelligent machine recognition systems for human-machine interaction.

Anti-bacterial and multi-functional smart wearable sensor based on organo-hydrogel for diagnosis of the anterior cruciate ligament injuries, and sensing glove for rehabilitation of joints motion

Stretchable multi-functional electronic skin devices capable of interface with parts of human body and/or internal organs to diagnose the anterior cruciate ligament (ACL) injuries and rehabilitation of human joint motion are attractive candidates for next-generation wearables biomedical devices, soft robots, and the Internet of Things (IoT). Such devices need to be of excellent mechanical property, anti-freezing, antibacterial, biocompatible to be comfortable to wear for long term usage and accommodate strains from repeated movement and prevent skin irritation. To address this need, we introduced conductive organo-hydrogels based on silver quantum dots (COH@AgQDs) as multi-functional stretchable sensor with outstanding high-performance diagnostic capabilities. We demonstrated a prototype from the developed sensors integrated into a wirelessly Arduino board and a smartphone was selected to transmit data which offers promising wireless system for rehabilitation after surgeries. Additionally, the developed device has ability to differentiate between ACL injury and healthy knee with different pattern shapes and high sensitivity. Moreover, the flexible sensor can inhibit the growth of bacteria (Escherichia coli (E-coli)) and Staphylococcus aureus (S. aureus) and protect human health for long-term use. It exhibited outstanding anti-freezing property (−53 °C), antibacterial, self-healing, robust mechanical property (strain 420% at stress 96 kPa), and high linearity.

Tannic acid modified antifreezing gelatin organohydrogel for low modulus, high toughness, and sensitive flexible strain sensor

Current hydrogel strain sensors have met assorted essential requirements of wearing comfort, mechanical toughness, and strain sensitivity. However, an increment in the toughness of a hydrogel usually leads to an increase in elastic moduli that could be unfavorable for wearing comfort. In addition, traits of biofriendly and sustainability require synthesis of the hydrogels from natural polymer-based networks. We propose a novel strategy to fabricate an ionic conductive organohydrogel from natural biological macromolecule “gelatin” and polyacid “tannic acid” to resolve these challenges. Tannic acid modified the structure of the gelatin network in the ionic conductive organohydrogels, that not only led to an increase in toughness accompanying a decrease in elastic moduli but also headed to higher strain sensitivity and tunability. The proposed methodology exhibited tunable tensile modulus from 27 to 13 kPa, tensile strength from 287 to 325 kPa, elongation at fracture from 510 to 620%, toughness from 500 to 550 kJ/m3, conductivity from 0.29 to 0.8 S/m, and strain sensitivity (GF = 1.4–6.5). Moreover, the proposed organohydrogel exhibited excellent freezing tolerance. This study provides a facile yet powerful strategy to tune the mechanical and electrical properties of organohydrogels which can be adapted to various wearable sensors.