Conductive Nanocomposite Hydrogel Research Articles

Induction of polymer-grafted cellulose nanocrystals in hydrogel nanocomposites to increase anti-swelling, mechanical properties and conductive self-recovery for underwater strain sensing

Anti-swelling conductive hydrogels with simultaneous high tensile strength (>1 MPa) and fast self-recovery are promising candidates for underwater strain sensing, but their preparation remains challenging. Herein, novel anti-swelling conductive nanocomposite hydrogels were fabricated based on poly(acrylamide-co-acrylic acid) (P(AM-co-AA)), polymer-grafted cellulose nanocrystals (CNCs) and Fe3+ ions through a strategy combining nano-reinforcing and multiple physical crosslinking. Due to the presence of interfacial H-bonds, polymer-grafted cellulose nanocrystals played important role in endowing hydrogels with anti-swelling capacity and enhanced mechanical performance. The obtained nanocomposite hydrogels exhibited relatively low swelling ratio (2.9–3.3 g/g), high tensile strength (>1.5 MPa), fast self-recovery (86 % recovery of hysteresis within 5 min) and conductivities of 0.0534–0.0593 S/m. The combination of excellent tensile properties and conductivity endowed the hydrogel-based strain sensors with good sensitivity (GF ≈ 0.8) and reliable cycling repeatability in 0–100 % strain range. Notably, the nanocomposite hydrogels can maintain their mechanical and sensing performance after soaking in water for 14 days, making them applicable for human motion detection both in air and underwater. Hence, this work provided a facile method to construct highly robust and anti-swelling CNC-reinforced conductive hydrogels, which have potential applications in underwater strain sensing and beyond.

Fabrication of Uniform Anionic Polymeric Nanoplatelets as Building Blocks for Constructing Conductive Hydrogels with Enhancing Conductive and Mechanical Properties.

Conductive hydrogels play a crucial role in advancing technologies like implantable bioelectronics and wearable electronic devices, owing to their favorable conductivity and appropriate mechanical properties. Here, a novel bottom-up approach is reported for crafting conductive nanocomposite hydrogels to achieve enhancing conductive and mechanical properties. In this approach, new poly(ɛ-caprolactone)-based block copolymers with sulfonic groups are first synthesized and self-assembled into uniform polyanionic nanoplatelets. Subsequently, these negatively charged nanoplatelets, with sulfonic groups on the surface, are employed as nanoadditives for the polymerization of 3,4-ethylenedioxythiophene (EDOT), resulting in poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/nanoplatelet complex with 3.8 times enhanced electrical conductivity compared with their counterparts prepared using block copolymers (BCPs). Blending the (PEDOT:PSS)/nanoplatelet complex with calcium alginate, nanocomposite hydrogels are successfully prepared. In comparison with hydrogels with (PEDOT:PSS)/BCP complexes prepared by a top-down method, the nanocomposite hydrogels are found to show twice as strong mechanical strength and 1.6 times higher conductivity. This work provides valuable insights into the bottom-up construction of conductive hydrogels for bioelectronics using well-controlled polymeric nanoplatelets.

An Antibacterial, Conductive Nanocomposite Hydrogel Coupled with Electrical Stimulation for Accelerated Wound Healing.

Electrical stimulation (ES) can effectively promote skin wound healing; however, single-electrode-based ES strategies are difficult to cover the entire wound area, and the effectiveness of ES is often limited by the inconsistent mechanical properties of the electrode and wound tissue. The above factors may lead to ES treatment is not ideal. A multifunctional conductive hydrogel dressing containingmethacrylated gelatin (GelMA), Ti3C2and collagen binding antimicrobial peptides (V-Os) was developed to improve wound management. Ti3C2 was selected as the electrode component due to its excellent electrical conductivity, the modified antimicrobial peptide V-Os could replace traditional antibiotics to suppress bacterial infections, and GelMA hydrogel was used due to its clinical applicability in wound healing. The results showed that this new hydrogel dressing (GelMA@Ti3C2/V-Os) not only has excellent electrical conductivity and biocompatibility but also has a durable and efficient bactericidal effect. The modified antimicrobial peptides V-Os used were able to bind more closely to GelMA hydrogel to exert long-lasting antibacterial effects. The results of cell experiment showed that the GelMA@Ti3C2/V-Os hydrogel dressing could enhance the effect of current stimulation and significantly improve the migration, proliferation and tissue repair related genes expression of fibroblasts. In vitro experiments results showed that under ES, GelMA@Ti3C2/V-Os hydrogel dressing could promote re-epithelialization, enhance angiogenesis, mediate immune response and prevent wound infection. This multifunctional nanocomposite hydrogel could provide new strategies for promoting infectious wound healing.

Robust and sensitive conductive nanocomposite hydrogel with bridge cross-linking-dominated hierarchical structural design.

Conductive hydrogels have a remarkable potential for applications in soft electronics and robotics, owing to their noteworthy attributes, including electrical conductivity, stretchability, biocompatibility, etc. However, the limited strength and toughness of these hydrogels have traditionally impeded their practical implementation. Inspired by the hierarchical architecture of high-performance biological composites found in nature, we successfully fabricate a robust and sensitive conductive nanocomposite hydrogel through self-assembly-induced bridge cross-linking of MgB2 nanosheets and polyvinyl alcohol hydrogels. By combining the hierarchical lamellar microstructure with robust molecular B─O─C covalent bonds, the resulting conductive hydrogel exhibits an exceptional strength and toughness. Moreover, the hydrogel demonstrates exceptional sensitivity (response/relaxation time, 20 milliseconds; detection lower limit, ~1 Pascal) under external deformation. Such characteristics enable the conductive hydrogel to exhibit superior performance in soft sensing applications. This study introduces a high-performance conductive hydrogel and opens up exciting possibilities for the development of soft electronics.

Conductive nanocomposite hydrogels for flexible wearable sensors

We present a comprehensive review of the recent research advances in the field of sensors based on hydrogels with nanofillers. The characteristics and design strategies of nanofillers are highlighted and multiple properties of conductive nanocomposite hydrogels are described.

Fabrication of a tough, long-lasting adhesive hydrogel patch via the synergy of interfacial entanglement and adhesion group densification.

Adhesive hydrogels (AHs) are considered ideal materials for flexible sensors. However, the lack of effective energy dissipation networks and sparse surface polar groups in AHs lead to poor mechanical properties and interfacial adhesion, which limit their practical application. Herein, a tough, long-lasting adhesive and highly conductive nanocomposite hydrogel (PACPH) was fabricated via the synergy of interfacial entanglement and adhesion group densification. PACPH was obtained by the in situ polymerization of highly carboxylated cellulose nanocrystals (SCNCPA, surface pre-grafted polyacrylic acid chains, C-COOH = 11.5 mmol g-1) with the acrylic acid precursor. The unique tacticity of SCNCPA provides strong interface entanglement and multiple hydrogen bonds with the PACPH network, which further increases the energy dissipated during SCNCPA displacements, and enhances the mechanical properties of PACPH (tensile strength = 1.45 MPa, modulus = 332 kPa, and fracture toughness = 13.2 MJ m-3). Meanwhile, SCNCPA increases the density of surface polar groups in PAPCH and also acts as an anchor point to improve the adhesion strength (>2-3 times) of PACPH on various substrates. The combination of excellent mechanical, adhesive, and conductive properties of the PAPCH-integrated patches enables long-term monitoring of human daily activities and electrocardiogram (ECG) signals, verifying that PAPCH is a promising material platform for the further development of flexible sensors and other health management devices.

Robust conductive nanocomposite hydrogels with an interpenetrating network based on polyaniline for flexible supercapacitors

AbstractConductive polyacrylic acid/polyaniline/SiO2 (PAA/PANI/SiO2) nanocomposite hydrogels as electrolytes for a high‐performance flexible supercapacitor were prepared by combining in situ radical polymerization of anionic monomer acrylic acid, in situ sol–gel reaction of vinyltriethoxysilane (VTES), and oxidative polymerization of conductive monomer aniline (ANI). In the nanocomposite hydrogel, vinyl‐SiO2 nanoparticles served as analogous covalent crosslinkers, while the reversible noncovalent interactions (such as hydrogen bonds, electrostatic interactions, and chain entanglements) between the PAA/SiO2 and PANI networks acted as physical crosslinkers. The interconnected PANI and PAA/SiO2 networks thus constructed an interpenetrating three‐dimensional network that improved the movement of electrons and ions while also enhancing the mechanical properties of the hydrogel. At a volume ratio of ANI to VTES of 50:200, the compressive strength and conductivity of PAA/PANI/SiO2 hydrogels were as high as 1505 kPa and 4.42 S/m, respectively. Moreover, the flexible supercapacitors based on the nanocomposite hydrogel electrolyte exhibited high specific capacitance (574.7 F/g), energy density (19.6 Wh/kg), and power density (1.4 kW/kg) at a current density of 0.05 A/g. Meanwhile, these supercapacitors exhibit exceptional flexibility and mechanical stability, and can be repeatedly bent without degrading performance. This nanocomposite hydrogel has considerable potential for use in other flexible energy devices and electronics due to its excellent mechanical and electrochemical properties.Highlights Conductive nanocomposite hydrogel have good conductivity and mechanical properties. Conductive hydrogels are used as electrolytes for flexible supercapacitors. Vinyl‐SiO2 served as analogous covalent crosslinkers for the hydrogel. Noncovalent bonds between PAA/SiO2 and PANI acted as physical crosslinkers. Interconnected PANI and PAA/SiO2 networks formed an interpenetrating network.

Highly stretchable, self-healing, self-adhesive and conductive nanocomposite hydrogels based on multi-reversible interactions as multifunctional strain sensors

Construction of highly stretchable and sensitive flexible strain sensors is of great significance for wide applications in human–computer interaction, wearable devices, and electronic skins. However, it turned out to be not effortless to integrate the two seemingly contrary features of high stretchability and sensitivity into a system. Herein, we designed a nanocomposite conductive hydrogel (NCCH) composed of zwitterionic poly(HEAA-co-SBMA) polymers and lithium magnesium silicate (XLG) by means of multi-reversible molecular interactions (MRMIs) including borate ester bonds between polyHEAA and borax, hydrogen bonds, and polySBMA-XLG-based electrostatic interaction, endowing the NCCH with enhanced mechanical, self-healing, adhesive, biocompatible, and sensing performances. The MRMI method enabled NCCHs to obtain an excellent stretchability (∼1080 %)/compressibility (∼98.5 %), a tensile strength of ∼ 0.06 MPa, a good self-healing with a fracture strain recovery of 90.5 %, and a strong adhesion on various hard and soft substrates (e.g. a adhesive shear force of 60 kPa to pigskin tissues). Besides, the integration of zwitterionic polySBMA and conductive XLG promoted charge transfer.by optimal ioinic channels. Based on these outstanding strengths, the NCCHs were farther rationally fabricated as multifunctional strain sensors with remarkable sensing stability for fast and accurately detecting strain/pressure-induced deformation, joint motions, and animal heartbeats. Notably, the excellent self-healing property of NCCH sensors can facilitate their long-period usage and complete recyclability for avoiding wastes. The new MRMI-based NCCH sensor without any conductive additives is deemed to provide a new strategy for broadening their multifunctional strain sensor and healthcare monitoring applications.

Antibacterial, conductive nanocomposite hydrogel based on dextran, carboxymethyl chitosan and chitosan oligosaccharide for diabetic wound therapy and health monitoring

Diabetic severe wound healing is challenging and also carries a high risk of bacterial infection and may be accompanied by serious complications. Electrical stimulation (ES) can effectively promote wound healing, but its effectiveness is often limited by incomplete contact between the electrodes and the wound site. In order to improve the efficiency of electrical stimulation utilization and to avoid wound infection, a multi-dynamically crosslinked nanocomposite hydrogel was prepared from dextran modified with aldehyde groups and phenylboronic acid esters (Dex-FA-BA), carboxymethyl chitosan (CMCS), polyaniline grafted chitosan oligosaccharide (CP), and Epigallocatechin Gallate/Ca2+ modified melanin-like nanoparticles (CEMNPs), based on dynamic Schiff base bonds, phenylboronic acid/diol interactions, and hydrogen bonding. The CEMNPs have good photothermal conversion properties and antioxidant activity and can also enhance the mechanical properties of the hydrogel system. The CP endows the hydrogel with good electrical conductivity and sensing properties and can record the respiratory and heart rate of rats in real time. Based on the convolutional neural networks (CNN) algorithm constructed by ResNet9, the respiratory and heart rate signals can be distinguished with 93.9 % accuracy. This multifunctional nanocomposite hydrogel can provide a new strategy to promote chronic wound healing and achieve health monitoring effectively.

Copolymer-grafted cellulose nanocrystal induced nanocomposite hydrogels with enhanced strength, high elasticity and adhesiveness for flexible strain and pressure sensors

Recently, the application of cellulose nanocrystals (CNCs) in the field of hydrogel sensors has attracted much attention. However, it remains challenging to construct CNC-reinforced conductive hydrogels with a combination of enhanced strength, low hysteresis, high elasticity and remarkable adhesiveness. Herein, we present a facile method to prepare conductive nanocomposite hydrogels with the above-mentioned properties by reinforcing chemically crosslinked poly(acrylic acid) (PAA) hydrogel with rational-designed copolymer-grafted CNCs. The copolymer-grafted CNCs interact with PAA matrix to form carboxyl-amide conventional hydrogen bonds and carboxyl-amino ionic hydrogen bonds, among which the ionic hydrogen bonds with rapid recovery capability are critical to the low hysteresis and high elasticity of hydrogel. The introduction of copolymer-grafted CNCs endowed the hydrogels with enhanced tensile/compressive strength, high resilience (>95 %) during tensile cyclic loading, rapid self-recovery during compressive cyclic loading and improved adhesiveness. Thanks to the high elasticity and durability of hydrogel, the assembled hydrogel sensors exhibited good cycling repeatability and durability in detecting various strains, pressures and human motions. The hydrogel sensors also showed satisfying sensitivity. Hence, the proposed preparation method and the obtained CNC-reinforced conductive hydrogels would open new avenues in flexible strain and pressure sensors for human motion detection and beyond.

Enhancement of Self-Healing Efficacy of Conductive Nanocomposite Hydrogels by Polysaccharide Modifiers.

The proper design of a polysaccharide/hydrocolloid modifier significantly affects the conductivity, self-healing, and viscoelastic properties of nanocomposite hydrogels. Due to the presence of different functional groups, these hydrogels can participate in the covalent, hydrogen and dynamic bonding of a system. The improvement of interactions in this system can lead to the development of high-performance nanocomposite hydrogels. In this study, resilient, self-healing and self-adhesive conductive nanocomposite hydrogels were produced by multiple and diverse coordination connections between various polysaccharide-based modifiers (Arabic gum, sodium carboxymethyl cellulose, and xanthan), the poly(vinyl alcohol) (PVA) network and different graphene-based fillers. Graphene nanoplatelets (GNP), activated carbon black (ACB), and reduced graphene oxide (rGO) have distinct functionalized surfaces, which were analyzed by X-ray photoelectron spectroscopy (XPS). Furthermore, the introduction of fillers balanced the hydrogels' viscoelastic properties and electrical conductivity, providing the hydrogels with resilience, improved electrical conductivity, and extreme stretchability (5000%). The self-healing properties were analyzed using time-dependent measurements in a shear strain mode using an RSO Rheometer. The improvement in electrochemical and conductivity properties was confirmed by electrochemical impedance spectroscopy (EIS). The obtained conductive nanocomposite hydrogels design opens new possibilities for developing high-performance polysaccharide-based hydrogels with wearable electrical sensors and healthcare monitoring applications.

Stretchable, transparent, self-adhesive, anti-freezing and ionic conductive nanocomposite hydrogels for flexible strain sensors

Conductive hydrogels have attracted considerable attentions due to their great potential in the field of flexible strain sensors. However, the low stretchability, poor adhesiveness as well as the lack of freezing-resistant capacity of conventional conductive hydrogels greatly limited their practical applications. Herein, a stretchable, transparent, self-adhesive and anti-freezing conductive nanocomposite hydrogel (PAHS gel) was fabricated via a one-step in situ free-radical polymerization of sulfobetaine methacrylate (SBMA), acrylic acid (AA) and 2-hydroxyethyl methacrylate (HEMA) in the presence of alumina nanoparticles (Al2O3 NPs) and lithium chloride (LiCl) as the inorganic cross-linkers and conductive substance, respectively. The obtained PAHS gels displayed high transparency (higher than 85 % at 550 nm), excellent stretchability (up to 800 %) and good ionic conductivity (2.25 S/m) and could keep flexible and conductive at the temperature at −18 ℃. Furthermore, the various types of functional groups on the polymer chains endow the PAHS gels with strong self-adhesiveness to different substrates such as glass, rubber, skin, etc. In addition, the PAHS gels also revealed superior strain sensitivity (GF = 2.69) in the strain of 0 ∼ 100 %, which can be assembled into wearable strain sensors to monitor various human activity. Based on these combined merits, it is believed that this newly developed conductive nanocomposite hydrogel would have prospective applications in the field of wearable strain sensors and other flexible electronics.

A multifunctional conductive nanocomposite hydrogel for high-performance strain sensors

A tannic acid-coated graphitized carbon hydrogel possesses high tensile strength, self-adhesion, conductivity, and strain sensitivity. It adheres well to various surfaces and functions as a responsive strain sensor for human motion.

Ultra stretchable, tough, elastic and transparent hydrogel skins integrated with intelligent sensing functions enabled by machine learning algorithms

Hydrogel-based ionic skins are ionic conductive artificial skin-like materials that are promising for a broad range of applications such as wearable sensory devices, soft robotics and machines, and bioelectronics. However, fabricating hydrogel skins with satisfying mechanical performance and intelligent sensing functions is still a significant challenge. Herein, we have developed an ionic conductive nanocomposite hydrogel with ultra stretchability and self-evolving sensing functions. By leveraging the dynamic feature of synergetic interfacial ionic interactions, a trace amount of carbon nanotubes endows the hydrogel networks with excellent mechanical performances (i.e., tensile strength, stretchability and toughness up to 1.09 MPa, 4075 % and 12.8 MJ/m3, respectively). Additionally, the hydrogel is soft, elastic, transparent and self-healing. The rational combination of the mechanical and electrical properties renders the as-prepared hydrogel with excellent sensing performances and cycling stability, and therefore enables it to perform as a sensory unit of a complete platform for the recognition of some complicated human behaviors, outperforming the previously reported hydrogels due to its intelligent sensing functions. Specifically, with the integration of machine learning module, the hydrogel-based platform exhibits great recognition accuracies to human handwriting motions from single letters to words, phrases, and short sentences after proper training. The combination of superior mechanical performances and self-evolving sensing functions within this hydrogel-based ionic skin unlocks its potential as the intelligent human-device interface, which promotes the application of artificial intelligence in customized electronic devices.

Tough, highly resilient and conductive nanocomposite hydrogels reinforced with surface-grafted cellulose nanocrystals and reduced graphene oxide for flexible strain sensors

Conductive hydrogels have drawn much attention in the field of flexible strain sensors. However, it remains challenging to fabricate conductive hydrogels with simultaneous high toughness and high resilience. Herein, we present a facile method to fabricate tough, highly resilient and conductive nanocomposite hydrogels, i.e. introducing poly(N-vinylpyrrolidone) grafted cellulose nanocrystal (CNC-g-PVP) and poly(acrylic acid) grafted reduced graphene oxide (rGO-g-PAA) into chemically crosslinked polyacrylamide (PAM) hydrogel networks through in-situ free radical polymerization. The synergistic reinforcement effect of CNC-g-PVP and rGO-g-PAA brings the nanocomposite hydrogels high toughness under stretching, and low hysteresis and high resilience (＞95%) during cyclic tensile loading-unloading. The well-dispersed rGO-g-PAA endows the nanocomposite hydrogels with satisfactory electrical conductivity (5.3–8.3 × 10−4 S/m) and obvious resistance change under stretching. The hydrogel-based strain sensors exhibit good cycling stability and repeatability because of the high resilience of hydrogels. The combination of conductivity, toughness and high resilience makes the nanocomposite hydrogels good choice for flexible strain sensors.

Conductive nanocomposite hydrogel and mesenchymal stem cells for the treatment of myocardial infarction and non-invasive monitoring via PET/CT.

BackgroundInjectable hydrogels have great promise in the treatment of myocardial infarction (MI); however, the lack of electromechanical coupling of the hydrogel to the host myocardial tissue and the inability to monitor the implantation may compromise a successful treatment. The introduction of conductive biomaterials and mesenchymal stem cells (MSCs) may solve the problem of electromechanical coupling and they have been used to treat MI. In this study, we developed an injectable conductive nanocomposite hydrogel (GNR@SN/Gel) fabricated by gold nanorods (GNRs), synthetic silicate nanoplatelets (SNs), and poly(lactide-co-glycolide)-b-poly (ethylene glycol)-b-poly(lactide-co-glycolide) (PLGA-PEG-PLGA). The hydrogel was used to encapsulate MSCs and 68Ga3+ cations, and was then injected into the myocardium of MI rats to monitor the initial hydrogel placement and to study the therapeutic effect via 18F-FDG myocardial PET imaging.ResultsOur data showed that SNs can act as a sterically stabilized protective shield for GNRs, and that mixing SNs with GNRs yields uniformly dispersed and stabilized GNR dispersions (GNR@SN) that meet the requirements of conductive nanofillers. We successfully constructed a thermosensitive conductive nanocomposite hydrogel by crosslinking GNR@SN with PLGA2000-PEG3400-PLGA2000, where SNs support the proliferation of MSCs. The cation-exchange capability of SNs was used to adsorb 68Ga3+ to locate the implanted hydrogel in myocardium via PET/CT. The combination of MSCs and the conductive hydrogel had a protective effect on both myocardial viability and cardiac function in MI rats compared with controls, as revealed by 18F-FDG myocardial PET imaging in early and late stages and ultrasound; this was further validated by histopathological investigations.ConclusionsThe combination of MSCs and the GNR@SN/Gel conductive nanocomposite hydrogel offers a promising strategy for MI treatment.Graphical Supplementary InformationThe online version contains supplementary material available at 10.1186/s12951-022-01432-7.

Super-stretchable and adhesive cellulose Nanofiber-reinforced conductive nanocomposite hydrogel for wearable Motion-monitoring sensor

Conductive hydrogel has been considered as a promising material for wearable sensors, constructing a flexible conductive hydrogel sensor with super stretchability, adhesion, and sensing stability is essential, but still challenging. Herein, A super-stretchable, adhesive, and conductive nanocomposite hydrogel was successfully constructed by a facile and one-pot process in conjunction with ball milling and blending. The resulting hydrogel exhibited super-stretchable ability (2795%), excellent tensile stress (128.6 kPa), good fatigue resistance, and self-recovery ability due to multiple cross-linked network structures, including physical hybrid networks (hydrogen bonds and ionic coordination bonds) and flexible polyacrylamide networks. Moreover, the nanocomposite hydrogel showed outstanding conductivity stability, fast response, durability, and repeatability. And it displayed excellent adhesion on various materials. Strain sensors based on hydrogels showed high sensitivity, stability, and action recognition ability. In summary, this work provides a simple strategy for preparing conductive hydrogel sensors with high stretchability, adhesion, and stability, and has potential application prospects in the field of wearable sensors for human body motion detection.

Highly conductive thermoresponsive silver nanowire PNIPAM nanocomposite for reversible electrical switch.

Highly conductive nanocomposite hydrogels have been challenging to produce due to their high water volumes inhibiting the incorporation of an essential amount of conductive nanofillers. Furthermore, the most common fillers used, typically for easy integration, display small aspect ratios. Thus, the formation of interparticle pathways for electronic travel is limited, resulting in low conductivities. Here, we introduce ultralong silver nanowires (ULAgNWs) into a thermoresponsive, volume changing PNIPAM gel to form a nanocomposite that shows switchable electronic performance. The produced nanocomposite surpasses other PNIPAM nanocomposites by expressing the largest electrical switch ratio and the highest peak conductivity. The PNIPAM matrix possesses an interconnected microporous structure that offers a spacious network for the dispersion of nanowires while still maintaining a high volume switch ratio and excellent elastic behavior under extreme compression cycles (98% compression). The ULAgNWs significantly enhance the probability of more numerous connections forming during shrinking cycles. The high swellability displayed by the PNIPAM gel provides the ability to separate the embedded nanowires by many lengths. Together, they form a nanocomposite that can thermo-modulate its electrical properties. Moreover, the conductive PNIPAM maintains the electrical switch of 4.3-4.4 orders of magnitude with thermo-responsive cycles. Because of their high electrical conductivity and outstanding elastic behavior, these stimuli-responsive nanocomposite hydrogels may expand the prospects for conductive hydrogel applications and provide greater performance in their applications.

Thermoresponsive, magnetic, adhesive and conductive nanocomposite hydrogels for wireless and non-contact flexible sensors

Hydrogel sensors are increasingly investigated and applied in emerging flexible electronics, but the exploration of hydrogel sensors with multiple functionalities remains a challenge. In this work, thermoresponsive, magnetic, adhesive and conductive nanocomposite hydrogels are developed and further applied in fabricating multi-functional flexible sensors. In such nanocomposite hydrogels, poly(N-isopropyl acrylamide-co-acrylamide) (P(NIPAAm-co-Am)) and Fe3O4 nanoparticles are designed as the thermoresponsive and magnetic component respectively, poly(vinyl alcohol) (PVA) is introduced in a semi-interpenetrating way to enhance the adhesiveness and mechanical property, and potassium chloride (KCl) works as the conductive component. Interestingly, the adhesion property is switchable by temperature based on the thermoresponsiveness of the nanocomposite hydrogels. Resistive strain sensors assembled from the nanocomposite hydrogels achieve a gauge factor (GF) of 4.21, a response time of 140 ms, stability of 2000 sensing cycles and excellent reversibility. Such nanocomposite hydrogel sensors are used as wearable sensors for monitoring diverse human motions and further integrated with Bluetooth signal transmission and reception system to fabricate wireless wearable sensors. Because of the deformation of nanocomposite hydrogels in switching magnetic field, the nanocomposite hydrogel sensors also have the ability to respond in a non-contact way to switching magnetic fields.

Healable, Adhesive, and Conductive Nanocomposite Hydrogels with Ultrastretchability for Flexible Sensors.

In recent years, conductive hydrogels have generated tremendous attention in biomedicals and bioelectronics fields due to their excellent physiochemical properties. In this study, a physically cross-linked conducting hydrogel has been designed in combination with cellulose nanocrystalline (CNC), polyacrylic acid (PAA) chains, laurel methacrylate, and sodium dodecyl sulfate. The obtained result shows that the hydrogel prepared is ultrastretchable, mechanically robust, transparent, biocompatible, conductive, and self-healing. The mechanical property of the prepared hydrogel is optimized through variation of the CNC content. The optimal hydrogel (CNC-1/PAA) exhibits an impressive mechanics, including high stretchability (∼1800%) and compressibility, good elasticity, and fatigue resistance. Furthermore, the conductivity of the hydrogel enables tensile strain- and pressure-sensing capabilities. The CNC/PAA-based flexible sensors are successfully designed, which shows high sensitivity, fast response (290 ms), and excellent cycle stability as well as the pressure sensing capability. As a result, the designed hydrogel has the ability to sense and detect diverse human motion, including elbow/finger/wrist bending and speaking, which demonstrates that the designed self-healing conductive hydrogels have significant potential for applications in flexible electronics.