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Conductive hydrogels usually suffer from weak mechanical properties and are easily destroyed, resulting in limited applications in flexible electronics. Concurrently, adding conductive additives to the hydrogel solution increases the probability of agglomeration and uneven dispersion issues. In this study, the biocompatible natural polymer chitosan was used as the network substrate. The rigid network employed was the Cit 3- ion crosslinked chitosan (CS) network, and the MBA chemically crosslinked polyacrylamide (PAM) network was used as the flexible network. Tannic acid-reduced graphene oxide (TA-rGO), which has excellent conductivity and dispersibility, is used as a conductive filler. Thus, a CS/TA-rGO/PAM double network conductive hydrogel with excellent performance, high toughness, high conductivity, and superior sensing sensitivity was prepared. The prepared CS/TA-rGO/PAM double network conductive hydrogels have strong tensile properties (strain and toughness as high as 2009 % and 1045 kJ/cm 3 ), excellent sensing sensitivity (GF value was 4.01), a wider strain detection range, high cycling stability and durability, good biocompatibility, and antimicrobial properties. The hydrogel can be assembled into flexible wearable devices that can not only dynamically detect human movements, such as joint bending, facial expression changes, swallowing, and saying, but also recognize handwriting and enable human-computer interaction., Competing Interests: Declaration of competing interest I declare that the funded projects and funds of this study have no conflicts of interest., (Copyright © 2023. Published by Elsevier B.V.)

Hydrogels have been widely used for adsorbing heavy metal ions in wastewater treatment. Herein, a calcium alginate/poly‐N‐isopropylacrylamide double‐network hydrogel with photothermal responsiveness was prepared for adsorbing heavy metal ions in aqueous solution. The chemical composition, micromorphology, swelling properties, photothermal responsiveness, adsorption properties, and adsorption mechanism of gel microspheres were studied, respectively. The gel microspheres had an interpenetrating three‐dimensional porous structure, and their high porosity morphology and high specific surface area could ensure the adequate exposure of active adsorption sites. The gel microspheres showed excellent selective adsorption of Cr(III), and the theoretical maximum adsorption capacity of 146.16 mg/g was calculated according to the Langmuir model. Besides, its excellent photothermal conversion ability enhanced the resistance to external interference after the adsorption. Our work has provided an innovative approach to solar water purification while optimizing the preparation process. [ABSTRACT FROM AUTHOR]

Conductive hydrogels are promising flexible conductors for human motion monitoring. However, this kind of wearable strain sensor has often shown weak mechanical properties. To overcome the inherent mechanical weakness and improve the electrical conductivity, CNT-Br/PEDOT:PSS/PAAS triple-network penetrating conductive hydrogels (CBP) are fabricated. The n-butylimidazolium bromide salt-functionalized MWCNTs (CNT-Br) as conductive fillers form a three-dimensional conductive path through the crosslinking agent XR-100, penetrating with the skeleton of crosslinking sodium polyacrylate. The conductive liquid PEDOT:PSS is further evenly dispersed in the penetrating double network to further enhance the electrical conductivity of the hydrogels. CNT-Br without obvious agglomeration significantly improved the thermal stability and mechanical properties of CBP. Moreover, CNT-Br enabled the PEDOT:PSS components to be more evenly dispersed in the PAAS matrix. Due to the good conductive paths inside the hydrogels, the maximum electrical conductivity (CBP10) increases to 10.35 mS cm−1, which is 415% higher than that of pure P1. Our work provides a method to prepare conductive hydrogels with high electrical conductivity and excellent mechanical properties, which can be used for human joint motion detection. [ABSTRACT FROM AUTHOR]

Conducting polymers with inherently good flexibility and conductivity are good candidates for stretchable conductor applications, such as wearable electronics and healthcare devices. In this article, the crosslinked PAA (polyacrylic acid, n-PAA) hydrogels were fabricated via the reaction between hydrophilic groups of polymers in the presence of the water-based silicone crosslinking agent. By using the PEDOT:PSA (poly(3,4-ethylenedioxythiophene):polystyrene sulfonate-co-acrylic acid) as a conducting component, the conductive hydrogels prepared by this method are highly conductive with a value of 2.00 S cm−1, highly stretchable with 800% strain and exceedingly stable in ambient air for a long time; also they possess superior properties to similar crosslinking methods. The resistance change with stretching is almost strain-insensitive up to 50% strain after 1000 fatigue cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anti-freezing conductive semi-IPN hydrogel was constructed by PAM, SA and LiCl. • Sodium alginate enhanced mechanical toughness (elongation at break ∼2100%). • LiCl contributed to sensitivity (GF = 17.45 in high strain) and anti-freezing property. • PAM/SA/3M LiCl hydrogel could maintain stretchable and conductive at −30 °C. As an ideal material for flexible sensors, electrically conductive hydrogels (ECHs) has been faced with water loss and easy freezing, which affects the conductive and tensile properties. Polyacrylamide/sodium alginate/LiCl (PAM/SA/LiCl) hydrogel was constructed to enhance the anti-freezing property without deficiencies of tensile and electrical performance. A semi-interpenetrating network (semi-IPN) was formed by PAM and SA through hydrogen bonding, which performed excellent mechanical property (fracture strain 2100%, fracture stress 110 KPa). LiCl contributed to the high ionic conductivity (up to 21.7 S/m) and sensitivity (Gauge Factor (GF) = 17.45). Double hydrogen bonding of SA and PAM, hydration of LiCl and ion interaction between SA and lithium ion improved the anti-freezing performance and mechanical property of the hydrogel together. The proportion of non-freezing water in system was proved to be significantly increased. The comprehensive properties of the hydrogels were evaluated and PAM/SA/3M LiCl hydrogel kept conductive without obvious loss of stretchability at −30 °C. The PAM/SA/LiCl hydrogel integrates remarkable toughness, conductivity, sensitivity and anti-freezing property, which is a suitable choice in smart wearable devices, soft robots and medical monitoring. [ABSTRACT FROM AUTHOR]

Recently, wearable services that are flexible and based on conductive hydrogels have rapidly evolved and found numerous applications. These conductive hydrogels must possess remarkable mechanical strength, electrical conductivity, and sensing stability, while also being able to withstand low temperatures. However, creating hydrogels that meet all these requirements can be a lengthy and complicated process. Herein, we quickly (10 s) generated a double network conductive hydrogels (PHTF@DNH) using the double autocatalytic system consisting of TA (Tannic acid) and Fe3+. Due to the hydrogen bonding interactions between polyacrylamide (PAM), chitosan quaternary ammonium salt (HACC), TA, cross-linking of N, N′-methylene-bis-acrylamide (MBA), and ionic conduction of sodium citrate (Na 3 Cit), the hydrogel exhibit excellent tensile property (stress of 177.40 kPa, elongation at break of 788%), compressive performance (compressive strength of 1.1 MPa at 80% deformation), desirable toughness (702.60 kJ/m3), and exceptional cyclic compression and swelling properties. The hydrogel-based sensors show exceptional electrical conductivity (59.02 mS/cm), sensitivity (GF value of 1.13 at 100–550% strain), broad detection range and good signal stability. Even at −30 °C, the hydrogels still maintained stable. Eventually, it is harmless to human skin. We believe that the PHTF@DNH offer a new approach to the manufacture of sensitive wearable electronic devices. [Display omitted] • Double network conductive hydrogels (PHTF@DNH) were prepared under double autocatalytic conditions. • The hydrogel showed exceptional electrical conductivityand sensitivity. • The hydrogel exhibited excellent mechanical and swelling properties. • At a very low temperature (−30 °C), the hydrogel could maintain stable. [ABSTRACT FROM AUTHOR]

In recent years, hydrogels have attracted extensive attention due to their unique properties. More and more studies have added new functions to hydrogels through modification, but the modified hydrogels only show unique properties in a specific aspect, which limits the application of hydrogels. Therefore, how to endow hydrogels with two or more functions at the same time has become a research hotspot. In this study, polyacrylamide and chitosan quaternary ammonium salt were used as the matrix of the hydrogel. The surface of magnetic ferric oxide nanoparticles (Fe 3 O 4 NPs) was modified by tannic acid (TA). TA and Fe 3 O 4 NPs were connected by coordination bonds to improve the surface properties of Fe 3 O 4 NPs. Then aniline molecules were coated on the surface of Fe 3 O 4 -TA NPs by the electrostatic attraction through in-situ chemical polymerization under the action of sulfuric acid doping to obtain composite Fe 3 O 4 NPs with electromagnetic dual functions. The electromagnetic bifunctional hydrogel was prepared by introducing the composite Fe 3 O 4 NPs into the hydrogel through physical doping. The results showed that the hydrogel had excellent mechanical properties (the tensile strength was 113.3 kPa, the elongation was 1070%). Due to the existence of polyaniline, the hydrogel showed outstanding electrical properties (the conductivity was up to 24.3 mS/cm and the gauge factor was up to 9.43). In addition, Fe 3 O 4 NPs gave the hydrogel good magnetism, and the hydrogel underwent a certain deformation in the switching magnetic field, which further expanded the application field of the hydrogel. Synthesis process and structure of electromagnetic bifunctional hydrogel. [Display omitted] • Tannic acid used as coupling agent to connect Fe 3 O 4 with polyaniline. • Fe 3 O 4 composite particles act as physical cross-linking points in the hydrogel. • Hydrogels have electromagnetic dual functions and high sensing sensitivity. [ABSTRACT FROM AUTHOR]

A solar-driven hydrogel composed of photothermal polydopamine (PDA) nanocoating, linear chitosan (CTS), and thermoresponsive poly(N-isopropyl acrylamide) (PNIPAM) crosslinking network was successfully synthesized to remove heavy metal ions from contaminated water. The as-prepared PDA/CTS/PNIPAM (DCN) hydrogel can achieve hydrophilic/hydrophobic phase transition driven by solar energy when the volume phase transition temperature (VPTT) was reached. The micromorphology, wetting behavior, swelling behavior, compression properties, photothermal responsiveness, and adsorption properties of hydrogels were studied one by one. The cross-linking of the controllable active nanogel (ANG) along with the modification of PDA endowed DCN hydrogel with a regular and interpenetrating porous structure, which enabled DCN to have excellent elasticity and withstand up to 80 % compressive deformation. And the hydrophilic groups of CTS and PDA reduced the water contact angle of DCN hydrogel to 13°, which was conducive to resisting the erosion of oil substances. The excellent photothermal conversion enabled DCN hydrogel to reach VPTT in only about 11 min under a simulated sunlight source. In addition, DCN hydrogel had excellent selective adsorption for Pb2+ and Cu2+, and the maximum theoretical adsorption capacities were 42.63 mg/g and 38.55 mg/g, respectively. It was also found that the volume phase transformation of hydrogel significantly enhanced its ability to resist external interference and effectively prevented the loss of heavy metal ions. [Display omitted] [ABSTRACT FROM AUTHOR]

In recent years, electrically conductive hydrogels (ECHs) have attracted extensive attention for their potential applications in flexible wearable sensors and human motion monitoring. However, many ECHs are prone to damage during use, limiting their application. In this study, a quick and simple one-pot in situ copolymerization method was used to introduce the double network (DN) structure with good mechanical properties into the conductive hydrogel, providing a new method for preparing the multi-function DN hydrogel. A novel conductive hydrogel was prepared by introducing sodium carboxymethyl cellulose (CMCNa) and polydopamine (PDA) reduced graphene oxide (D-rGO) into polyacrylamide (PAM) hydrogel. Among them, the well-dispersed D-rGO nanofillers provided a good electron conduction pathway. CMCNa/PAM matrix was physically and chemically crosslinked with Fe3+ and N, N′-methylene- bis -acrylamide (MBA), which made the hydrogel had better mechanical properties and pH sensitivity than pure PAM hydrogel. The conductive hydrogel designed by us had better sensitivity (gauge factor (GF) value was 6.44), wider strain detection range (0–500%), better cycle stability and durability compared with other conductive hydrogels by using a composite conductive mechanism of electron and ion conductivity. More notably, D-rGO/CMCNa/PAM hydrogel could detect large-scale changes in human movement (such as bending of fingers and wrists) and sensitive signals without obvious allergic reactions to human skin, which offered great possibilities for practical applications as flexible strain sensors. [Display omitted] [ABSTRACT FROM AUTHOR]

Chitosan(CTS) has excellent adsorption capacity for heavy metal ions, the combination of chitosan with hydrogels provides a new development direction for chitosan-based adsorbents, and further improvement of adsorption can be achieved by modifying the chitosan on this basis. A semi-interpenetrating polymer network(semi-IPN) hydrogel was successfully synthesized for the removal of heavy metal ions by combining α-ketoglutaric acid grafting chitosan (KCTS) with polyacrylamide(PAM) cross-linked by N,N-methylenebis(acrylamide). This semi-IPN hydrogel had the porous structure with high specific surface area, which can expose more active sites and provide an interface for chitosan to fully contact waste water. And it had excellent selective adsorption for Cu(II), Pb(II), and Zn(II) in a mixture of five heavy metal ions. Many influencing factors affecting adsorption have been investigated, such as initial concentration of metal ions, adsorption time, pH of solution, ionic strength, and adsorbent dosage. The adsorption data were simulated well by the pseudo-second-order kinetic and adsorption isotherms were fitted well Langmuir isotherm model. At 30 °C and pH 5.0, the theoretical maximum adsorption capacities of Cu(II), Pb(II), and Zn(II) by KCTS/PAM hydrogel were 72.39, 61.41, and 51.89 mg/g, respectively. After five adsorption-desorption cycles, the adsorption capacity of Cu(II), Pb(II), and Zn(II) still maintained above 90% of initial adsorption capacity. XPS analysis illustrated that the adsorption mechanism of heavy metal ions was mainly due to coordination and ion exchange. [Display omitted] [ABSTRACT FROM AUTHOR]