Conductive Composite Hydrogels Research Articles

Silver nanowire-doped conductive polymer hydrogel anode for increasing electron transfer and COD removal rate simultaneously in microbial fuel cell

Microbial fuel cell (MFC) can generate electrons through microbial metabolism of organic matter in sewage. In this paper, carbon felt as base material, the conductive polymers polyaniline and polypyrrole combined with silver nanowires were doped in hydrogel, a super hydrophilicity, low electron transfer resistance, good biocompatibility hydrogel MFC anode (PANI-PPy-Ag NWs/CF) were prepared. It showed a hand-torn bread structure, this three-dimensional (3D) porous structure increased microbial attachment amount. The anode could reach a maximum voltage output of 0.66 V in only 5.5 h, and produce a maximum power density of 2196.61 mW/m3. Due to the doping of silver nanowire, a new electronic mode was explored, coulomb efficiency of 31.01 % and an ultra-high COD removal rate (96.69 %) was obtained. This study introduces a conductive composite hydrogel MFC anode, which provides a new idea for the material diversity, electrical production and sewage removal performance of MFC anode.

Ultrasound-triggerennd piezocatalytic conductive Guar gum/PEDOT: PSS/BTO composite hydrogels for bacterial-infected skin wound healing

Open skin wounds are susceptible to infections by multidrug-resistant bacteria, which can lead to delayed wound healing or worsening of symptoms. Therefore, there is an urgent need to develop a comprehensive strategy that addresses bacterial infections while simultaneously promoting wound healing for optimal clinical outcomes. In this study, we aimed to combine the benefits of antibacterial piezoelectric catalysis action and controlled electrical stimulation to promote skin tissue repair. Initially, piezoelectric catalytic BaTiO3(BTO) nanoparticles were coated with polydopamine (PDA) to improve the interface compatibility between inorganic and organic phase. Subsequently, a novel conductive composite hydrogel termed PPGSCH was synthesized by doping PDA@BTO into poly (3, 4-ethylenedioxythiophene) -poly (styrene sulfonate) (PEDOT: PSS) hydrogel. Traditional dye degradation experiments and EPR tests found that PDA@BTO nanoparticles exhibited superior piezoelectric catalytic efficiency compared with the pristine BTO. Rheological tests and electrical conductivity tests demonstrated better electrical adaptability and mechanical stability of PPGSCH. Remarkably, under the synergism of piezoelectricity and electric polarization induced by ultrasound (US), the antibacterial rate of PPGSCH exceeded 90% in vitro. Furthermore, when subjected to 0.5 W/cm2 US irradiation, it can generate moderate levels of reactive oxygen (ROS) and micro current, promoting the proliferation and migration of mouse fibroblasts. Animal experiments on infected skin wounds in mice showed that PPGSCH could reduce inflammation, accelerate angiogenesis, and ultimately expedite the infected wound healing. This work opens up new possibilities for enhancing the repair of infected skin wounds.

Antifreezing, Antidrying, and Conductive Hydrogels for Electronic Skin Applications at Ultralow Temperatures.

Although conductive hydrogel-based flexible electronic devices have superb flexibility and high conductivities, they tend to malfunction in dry or frigid areas. Herein, an ultralow-temperature tolerant, antidrying, and conductive composite hydrogel is designed for electronic skin applications on the basis of the synergy of double-cross-linked polymer networks, Hofmeister effect, and electrostatic interaction and fabricated by in situ free radical polymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid and acrylic acid in the presence of poly(vinyl alcohol) and conductive MXene sheets, followed by impregnation with LiCl. Thanks to the synergy of LiCl and the charged polar terminal groups of the synthesized polymers, the composite hydrogel can not only bear an ultralow temperature of -80 °C without freezing but also maintain its original mass. Meanwhile, the resultant hydrogel possesses satisfactory self-regeneration ability benefiting from the moisturizing effect of LiCl. The conductive network of MXene sheets greatly improves the ionic conductivity of the hydrogel at low temperatures, exhibiting an ionic conductivity of 1.4 S m-1 at -80 °C. Furthermore, the electronic skin assembled by the multifunctional hydrogel is efficient in monitoring human motions at -80 °C. The antifreezing and antidrying features along with favorable ionic conductivity, high tensile strength, and outstanding flexibility make the composite hydrogel promising for applications in frigid and dry regions.

An overview of conductive composite hydrogels for flexible electronic devices

An overview of conductive composite hydrogels for flexible electronic devices

A novel smart disinfection system using 3D-printed and electrically conductive composite hydrogel

AbstractSmart materials are ushering in the era of smart and adaptable products. Hydrogels are a distinct class of smart materials that can be 3D-printed to produce smart and active structures that can be used as sensors and actuators. The development and characterization of a 3D-printable and electrically conductive composite hydrogel, as well as its application in the development of a smart disinfection system, are discussed in this article. The developed composite hydrogel has a maximum electrical conductivity of 145 S.m−1, is stable up to 200 °C, and has a 3D printable rheology. Virtuous of its electrical conductivity, the composite hydrogel was used to create a smart disinfection system. Various disinfection systems have been adopted for the disinfection of contaminated surfaces; however, most of these systems require human evacuation from the surroundings due to the hazardous nature of the virucide. The proposed system is designed to disinfect contaminated surfaces on common-use equipment and is capable of real-time activation through user interaction. It employs a thermal disinfection process at 60 °C for 5 min and becomes ready for the next user once its temperature drops below 55 °C. This system consumes 1.64 Wh of energy per disinfection cycle and is suitable for scenarios with fewer than 60 user interactions in an 8-h work shift.

Anisotropically Conductive Hydrogels with Directionally Aligned PEDOT:PSS in a PVA Matrix.

Electrical anisotropy, which is characterized by the efficient transmission of electrical signals in specific directions, is prevalent in both natural and engineered systems. However, traditional anisotropically conductive materials are often rigid and dry, thus limiting their utility in applications aiming for the seamless integration of various technologies with biological tissues. In the present study, we introduce a method for precisely controlling the microstructures of conductive and insulating polymers to create highly anisotropically conductive composite hydrogels. Our methodology involves combining aligned poly(vinyl alcohol) microfibrils, infused poly(3,4-ethylenedioxythiophene) polystyrenesulfonate, and sodium citrate precipitation to form dense, aligned conductive paths. This significantly enhances the electrical conductivity anisotropy (σ∥/σ⊥ ≈ 60.8) within these composite hydrogels.

Engineering Photo-Cross-Linkable MXene-Based Hydrogels: Durable Conductive Biomaterials for Electroactive Tissues and Interfaces.

Light-cured conductive hydrogels have attracted immense interest in the regeneration of electroactive tissues and bioelectronic interfaces. Despite the unique properties of MXene (MX), its light-blocking effect in the range of 300-600 nm hinders the efficient cross-linking of photocurable hydrogels. In this study, we investigated the photo-cross-linking process of MX-gelatin methacrylate (GelMa) composites with different types of photoinitiators and MX concentrations to prepare biocompatible, injectable, conductive, and photocurable composite hydrogels. The examined photoinitiators were Eosin Y, Irgacure 2959 (Type I), and lithium phenyl-2,4,6-trimethylbenzoyl phosphinate (Type II). The light-blocking effect of MX strongly affected the thickness, pore structure, swelling ratio, degradation, and mechanical properties of the light-cured hydrogels. Uniform distribution of MX in the hydrogel matrix was achieved at concentrations up to 0.04 wt % but the film thickness and curing times varied depending on the type of photoinitiator. It was feasible to prepare thin films (0.5 mm) by employing Type I photoinitiators under a relatively long light irradiation (4-5 min) while thick films with centimeter sizes could be rapidly cured by using Type II photoinitiator (<60 s). The mechanical properties, including elastic modulus, toughness, and stress to break for the Type II hydrogels were significantly superior (up to 300%) to those of Type I hydrogels depending on the MX concentration. The swelling ratio was also remarkably higher (648-1274%). A conductivity of about 1 mS/cm was attained at 0.1 mg/mL MX for the composite hydrogel cured by the Type I photoinitiator. In vitro cytocompatibility assays determined that the hydrogels promoted cell viability, metabolic activity, and robust proliferation of C2C12 myoblasts, which indicated their potential to support muscle cell growth during myogenesis. The developed photocurable GelMa-MX hydrogels have the potential to serve as bioactive and conductive scaffolds to modulate cellular functions and for tissue-device interfacing.

Fluorinated Graphene Thermally Conductive Hydrogel with a Solid-Liquid Interpenetrating Heat Conduction Network.

Hydrogels with excellent mechanical flexibility are widely used in flexible electronic devices. However, it is difficult to meet further applications of high-power integrated flexible electronics as a result of their low thermal conductivity. Herein, highly thermally conductive composite hydrogels with a solid-liquid interpenetrating thermal conductivity network are constructed by aromatic polyamide nanofibers (ANF) and fluorinated graphene (FG) reinforced poly(vinyl alcohol) (PVA) and cross-linked by tannic acid (TA) solution immersion to obtain a hydrogel with a double cross-linked network. The PVA-ANF-FG3T-11.1% composite hydrogel exhibits good mechanical properties compared to PVA-ANFT, with a tensile modulus of up to 0.89 MPa, a tensile strength of up to 1.23 MPa, and an energy of rupture of up to 3.45 MJ cm-3, which is mainly attributed to the multihydrogen bonding interactions in the composite hydrogel. In addition, the friction coefficient of the PVA-ANF-FG3T-11.1% composite hydrogel is 0.178, making it suitable for use in high-friction coefficient applications. The thermal conductivity of the PVA-ANF-FG3T-11.1% composite hydrogel is 1.42 W m-1 K-1, which is attributed to the synergistic effect of the solid thermal conductivity network and the liquid convection network, resulting in a high thermal conductivity of the composite hydrogel. The high thermal conductivity of the PVA-ANF-FG3T-11.1% composite hydrogel shows great potential for flexible wearable electronics and cooling paste applications.

Highly stretchable polyvinyl alcohol composite conductive hydrogel sensors reinforced by cellulose nanofibrils and liquid metal for information transmission

Conductive hydrogels have received widespread attention in the field of flexible sensors. However, a single network structure inside the hydrogel sensor usually makes it difficult to bear larger mechanical loadings, greatly limiting practical applications. Developing a recoverable conductive hydrogel sensor with high toughness and adaptability is still challenging. Herein, a high-performance polyvinyl alcohol (PVA)-based conductive composite hydrogel was constructed, assisted by green cellulose nanofibrils (CNFs), magnesium chloride (MgCl2), ethylene glycol (EG), and liquid metal (LM). The synergistic effects between CNFs and LM enhanced the network structure inside the recoverable hydrogel. This resulted in an excellent tensile strength of 3.86 MPa with an elongation at break of as high as 918.4 % and compressive strength of 4.04 MPa at 80 % strain. In addition, the conductive network composed of MgCl2 and LM endowed the hydrogel good electrical conductivity. Moreover, it could be used as a flexible strain sensor for various application scenarios, e.g., micro-stress monitoring (water droplet falling) and information encryption transmission of Morse code. Such uniqueness will provide a design strategy for developing a new generation of hydrogel sensors.

Chitosan/dialdehyde cellulose hydrogels with covalently anchored polypyrrole: Novel conductive, antibacterial, antioxidant, immunomodulatory, and anti-inflammatory materials

In this work, conductive composite hydrogels with covalently attached polypyrrole (PPy) nanoparticles are prepared. Hydrogels are based on partially re-acetylated chitosan soluble at physiological pH without any artificial structural modifications or need for an acidic environment, which simplifies synthesis and purification. Low-toxic and sustainable dialdehyde cellulose (DAC) was used for crosslinking chitosan and covalent anchoring of PPy colloidal particles. The condensation reaction between DAC and PPy is reported for the first time and improves not only the anchoring of PPy particles but also control over the properties of the final composite. The soluble chitosan and PPy particles are shown to act in synergy, which improves the biological properties of the materials. Prepared composite hydrogels are non-cytotoxic, non-irritating, antibacterial, can capture reactive oxygen species often related to excessive inflammation, have conductivity similar to human tissues, enhance in vitro cell growth (migration assay), and have immunomodulatory effects related to the stimulation of neutrophils and macrophages. The covalent attachment of PPy also strengthens the hydrogel network. The aldol condensation as a method for PPy covalent anchoring thus presents an interesting possibility for the development of advanced biomaterials in the future.

Self-healing conductive composite hydrogel for human motion and 3D cell culture monitoring

Self-healing conductive composite hydrogel for human motion and 3D cell culture monitoring

Robust and stretchable Ti3C2Tx MXene/PEI conductive composite dual-network hydrogels for ultrasensitive strain sensing

The development of high-performance hydrogels with superior strength, stretchability, and conductivity is critical to the practical application of flexible sensors. In this study, we employed a strategy that involves introducing physical cross-linking points, creating a double network, and adding nanofillers. By utilizing a two-step method that involves thermal cross-linking and post-immersion cross-linking, and using two common metal ions to crosslink different polymer networks, we successfully developed a conductive composite dual-network hydrogel. In addition, the incorporation of modified MXene has significantly improved the strength and toughness of the hydrogel. The resulting hydrogel exhibits impressive mechanical properties, including a tensile strength of 2.64 MPa and elongation at break of 689%, as well as high toughness of 10.25 MJ·m−3 and conductivity of 1.89 S/m. When applied as a flexible sensor in electronic skin, the sensor demonstrates a wide operating range (>300%), high sensitivity (GF = 4.64), and excellent linear detection ability (R2 = 0.99).

Anti-freezing conductive zwitterionic composite hydrogels for stable multifunctional sensors

Zwitterionic conductive hydrogels have shown potential application in wearable strain and pressure sensors. However, there are still fundamental challenges to achieve zwitterionic hydrogels with excellent mechanical properties, able to keep flexibility at sub-zero temperatures. To overcome these limitations, a zwitterionic conductive hydrogel was fabricated in this work by in-situ polymerization of aniline (ANI) monomer in a copolymer of sulfobetaine methacrylate (SBMA) and acrylic acid (AA) matrix. The obtained hydrogel possesses outstanding anti-freezing performance (without obvious loss of stretchability at −18 °C) and water-retaining properties, due to the introduction of LiCl on the zwitterionic polymer matrix. The synergy of chemical and physical crosslinking between poly (SBMA-co-AA) and polyaniline (PANI) networks enhance the mechanical performance of the zwitterionic hydrogel, that exhibits a fracture tensile strength of 470 kPa, and a fracture strain up to 600 %. Additionally, the integration of PANI confers stable conductivity (2.23 S m−1, maintained at 1.89 S m−1 even at −18 °C), high sensitivity (GF = 1.74), and short response and recovery times (223 ms and 191 ms, respectively). The hydrogel can be applied as a flexible sensor to accurately detect various human motions. This work provides a feasible strategy for developing wearable multifunctional sensors in a wide working temperature range.

Mechanical robust and highly conductive composite hydrogel reinforced by a combination of cellulose nanofibrils/polypyrrole toward high-performance strain sensor

Although conductive and elastic materials are increasingly required for strain or stress sensing application in wearable electronic devices, it remains a great challenge to achieve outstanding and balanced mechanical performance while retaining high conductivity. Herein, the development of an ionic/electronic conductive hydrogel with mechanically robustness for strain sensors is reported. A covalently cross-linked polymer network is highly enhanced by a synergy of nano-enhancement (cellulose nanofibrils) and dynamic interactions containing hydrogen bonding and ionic coordination, which is used to support the mechanical structure of the hydrogel. By decorating with polypyrrole molecules via Fe3+ induced in-situ polymerization, the integrity of network structure is further improved by constructing physical interactions and chain entanglement. Therefore, compared to virgin poly(acrylamide-co-acrylic acid) hydrogel, the obtained hydrogel exhibits prominent mechanical performance containing high tensile strength (2.54 MPa) and ultra-high toughness (17.71 MJ m−3) along with remarkable stretchability (925%). Apart from Establishing a fair balance among mechanical parameters, a hybrid conductive path composed of ionic and electronic mechanism is also constructed simultaneously that results in an improved conductivity (995 mS m−1), wide working range (≈873%) and high sensitivity (maximum gauge factor: 25.6). Thus, the combination of outstanding mechanical performance and sensitive strain response makes the conductive hydrogel prepared herein apply for mechanically reliable and flexible strain sensor that can monitor diverse mechanical deformation (e.g., human joint movement) reflected by real-time resistance variation. Clearly, this work provides a new perspective for the design and fabrication of advanced gel-based materials aiming at high performance in human motion detection.

Compressible, anti-freezing, and ionic conductive cellulose/polyacrylic acid composite hydrogel prepared via AlCl3/ZnCl2 aqueous system as solvent and catalyst

From the perspective of environmental sustainability, introducing cellulose into ionic conductive hydrogel is an inevitable trend for the development of flexible conductive materials. We report a double-network cellulose/polyacrylic acid (Cel/PAA) composite hydrogel based on the dissolving of cellulose by AlCl3/ZnCl2 aqueous system. The Cel/PAA composite hydrogel consists of rigid cellulose chains and flexible polyacrylic acid, which synergistically realize the improvement of the mechanical properties. The AlCl3/ZnCl2 aqueous system not only serves as the green solvent for cellulose, but also the Al3+ and Zn2+ metal ions can be served as a catalyst to activate the initiator for polymerization of acrylic acid. Compared with pure cellulose hydrogel, the compression strain of the Cel/PAA composite hydrogel was significantly improved to 80 %, and its conductivity increased by 28.1 %. In addition, its compression stress was enhanced over 2 times than pure PAA hydrogel. The Cel/PAA composite hydrogel exhibits excellent anti-freezing (−45 °C), weight retention (90 %), and conductivity (2.70 S/m) properties, still maintaining transparency and storage stability in the extreme environment. This work presents a facile strategy to develop an ionic conductive cellulose-based composite hydrogel with good conductivity and mechanical properties, which shows potential for the application fields of flexible sensors and 3D-printing functional materials.

Self-strengthening and conductive cellulose composite hydrogel for high sensitivity strain sensor and flexible triboelectric nanogenerator

Triboelectric nanogenerators (TENGs) as promising energy harvesting devices have gained increasing attention. However, the fabrication of TENG simultaneously meets the requirements of green start feedstock, flexible, stretchable, and environmentally friendly remains challenging. Herein, the hydroxyethyl cellulose macromonomer (HECM) simultaneously bearing acrylate and hydroxyl groups was first synthesized and used as a crosslinker to prepare the chemically and physically dual-crosslinked cellulose composite hydrogel for an electrode material of stretchable TENG. Meanwhile, the in-situ polymerization of pyrrole endowed the hydrogel with satisfactory conductivity of 0.40 S/m. More impressively, the synergies of the cellulose rigid skeleton and the construction of the dual-crosslinking network significantly improved the mechanical toughness, and the hydrogel exhibited excellent self-strengthening through cyclic compression mechanical training, the self-strengthening efficiency reached 124.7 % after 10 compression cycles. Given these features, the hydrogel was used as wearable strain sensors with extremely high sensitivity (GF = 3.95) for real-time monitoring human motions. Additionally, the hydrogel showed practical applications in stretchable H-TENG for converting mechanical energy into electric energy to light LEDs and power a digital watch, and in self-powered wearable sensors to distinguish human motions and English letters. This work provided a promising strategy for fabricating sustainable, eco-friendly energy harvesting and self-powered electronic devices.

Triple-cross-linked composite hydrogels based on EGaIn liquid metal with controllable degradability for flexible strain sensors

Conductive hydrogels with intrinsic flexibility, high sensitivity, antibacterial activity, and repeatability are used in wearable devices. The development of conductive hydrogels with simultaneously high conductivity, reliability, and controllable degradability remains a challenge. Therefore, conductive composite hydrogel polyvinyl alcohol (PVA)-stabilized eutectic gallium and indium (EGaIn)/polyacrylamide (PAAm)/polyacrylic acid (PAA)@FeCl3@polyprrole (PPy) (PVA-EGaIn-x@PAAm/PAA@FeCl3@PPy, where x represents EGaIn content) was employed to fabricate a multi-cross-linked network and interpenetrating hydrogel with high conductivity, mechanical properties, and controllable degradability. Ga3+/Fe3+–carboxyl group coordination bonds can act as a dynamic cross-linking network to promote controllable degradability. Meanwhile, EGaIn liquid metal and PPy, as electronic conductors, conferred the composite hydrogel with good conductivity. The effects of EGaIn liquid metal content on mechanical properties and conductivity were investigated in detail. A simple strain sensor fabricated by using PVA-EGaIn-5@PAAm/PAA@FeCl3@PPy achieved the detection of the current signal of human motions. The conductive composite hydrogel had good conductivity (8.1 S m−1), acceptable sensitivity (gauge factor of 0.28), and reliability (500 cycles at 200% strain). Furthermore, the prepared composite can be degraded in acid and base solutions for environmental preservation. This work provides a feasible method for the construction of multifunctional robust hydrogel strain sensors to facilitate the practical development of sensors for monitoring human motions.

Inhibited astrocytic differentiation in neural stem cell-laden 3D bioprinted conductive composite hydrogel scaffolds for repair of spinal cord injury

The emergence of three-dimensional (3D) bioprinting technology has attracted ever-increasing attention in engineered tissue fabrication for stem cell-based tissue repair. However, the in vivo performance of transplanted stem cells in the tissue engineering scaffolds is still a major concern for regenerative medicine researches. Especially for neural stem cell (NSC) transplantation, the uncontrollable differentiation of the NSCs in host often leads to a poor therapeutic effect in nerve tissue repair, such as spinal cord injury (SCI) repair. To address this issue, we have fabricated a conductive composite hydrogel (CCH) scaffold loading with NSCs by 3D bioprinting, for delivering the NSCs to injured spinal cord and repairing the propriospinal nerve circuit. In our strategy, a novel conductive polymer (PEDOT:CSMA,TA) was synthesized and introduced into a photocrosslinkable gelatin/polyethylene glycol physical-gel matrix, thereby forming a composite bioink with well shear-thinning and self-healing properties. The composite bioink we prepared was then printed into the NSC-laden CCH scaffold with high shape fidelity and similar physicochemical properties to native spinal cord tissues. The NSCs encapsulated in the bioprinted CCH scaffold extended their neurites to form superior physical contact with the neighboring cells as well as the electroconductive matrix, and maintained a predominant in vivo neuronal differentiation, accompanying with few astrocytic production in the lesion area after transplantation into the SCI sites. As a result, the removal of glial scar tissues and the regeneration of well-developed nerve fibres sequentially happened, which not only facilitated nerve tissue development, but also accelerated locomotor function recovery in the SCI rats. By exploring the application of conductive biomaterials in stem cell-based SCI therapy, this work represents a feasible, new approach to precisely construct tissue engineering scaffolds for stem cell-based therapy in traumatic SCI and other nervous system diseases.

Conductive and Thermo-Responsive Composite Hydrogels with Poly(N-isopropylacrylamide) and Carbon Nanotubes Fabricated by Two-Step Photopolymerization.

Biocompatible and conductive polymer hydrogels are the subject of intensive research in the bioengineering field because of their use in bioelectronic devices and for the fabrication of electro-responsive tissues and drug delivery systems. In this study, we report the synthesis of conductive composite hydrogels consisting of a poly(N-isopropylacrylamide) (PNIPAM) matrix embedding carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH) using a two-step photopolymerization method. Thermo-responsive hydrogels with controlled hydrophilicity and conductivity were prepared by varying the carbon nanotube concentration in the range 0.5-3 wt%. The thermal response of the PNIPAM-based composite hydrogels was measured by differential scanning calorimetry with both ultrapure water and PBS solution as swelling liquid. Results show that the endothermic peak associated with the temperature-induced volume phase transition (VPT) shifts to higher temperatures upon increasing the concentration of the nanotubes, indicating that more energy is required to dissociate the hydrogen bonds of the polymer/filler network. In PBS solution, the swelling ratios and the VPT temperatures of the composite hydrogels are reduced because of salt-induced screening of the oppositely charged polymer/filler assembly, and the electrical resistivity decreases by a factor of 10 with respect to the water-swollen hydrogels.

A photothermal and conductive composite hydrogel membrane for solar-driven synchronous desalination and salinity power generation

A calcium alginate hydrogel and nickel foam composite membrane (CHN) can achieve desalination and salinity gradient power generation by solar energy. The CHN membrane can be used as a universal solar conversion platform to obtain blue energy.