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The aberrant mechanical microenvironment in degenerated tissues induces misdirection of cell fate, making it challenging to achieve efficient endogenous regeneration. Herein, a hydrogel microsphere-based synthetic niche with integrated cell recruitment and targeted cell differentiation properties via mechanotransduction is constructed . Through the incorporation of microfluidics and photo-polymerization strategies, fibronectin (Fn) modified methacrylated gelatin (GelMA) microspheres are prepared with the independently tunable elastic modulus (1-10Kpa) and ligand density (2 and 10 µg mL -1 ), allowing a wide range of cytoskeleton modulation to trigger the corresponding mechanobiological signaling. The combination of the soft matrix (2Kpa) and low ligand density (2 µg mL -1 ) can support the nucleus pulposus (NP)-like differentiation of intervertebral disc (IVD) progenitor/stem cells by translocating Yes-associated protein (YAP), without the addition of inducible biochemical factors. Meanwhile, platelet-derived growth factor-BB (PDGF-BB) is loaded onto Fn-GelMA microspheres (PDGF@Fn-GelMA) via the heparin-binding domain of Fn to initiate endogenous cell recruitment. In in vivo experiments, hydrogel microsphere-niche maintained the IVD structure and stimulated matrix synthesis. Overall, this synthetic niche with cell recruiting and mechanical training capabilities offered a promising strategy for endogenous tissue regeneration., (© 2023 Wiley-VCH GmbH.)

Soft hydrogel materials can be applied for use in biosensors, wearable electronics, artificial skin, soft robots, and so on. Practical applications require the materials to have various properties such as high conductivity, toughness, self-healing, stretchability, and so on. However, achieving all these features in a single material remains challenging at present. Herein, the fabrication of novel composite carboxymethylcellulose/poly(acrylic acid)/polypyrrole/Al(III) (CMC/PAA/PPy/Al(III)) multifunctional hydrogels using a simple method is described. The mechanical and electrical self-healing properties are attained by multiple dynamic coordinations between Al 3+ ions and carboxyl groups from CMC and PAA together with the hydrogen bonding between PPy and the -OH of CMC and/or the -COOH of PAA. The electrical conductivity is achieved by the conductive polymer PPy, free ions, and the synergistic effect between the PPy particles and the free ions. Moreover, desirable mechanical properties, such as stretchability (1344%), toughness, and mouldability are realized by establishing a balance between the chemical and physical crosslinking networks, and the nanostructure of PPy. Thus, the resultant hydrogels have potential applications in electronic skin, biomedical implants, and wearable electronic devices in the future.

In recent years, hydrogels with self-healing capability and conductivity have become ideal materials for the design of electrodes, soft robotics, electronic skin, and flexible wearable devices. However, it is still a critical challenge to achieve the synergistic characteristics of high conductivity, excellent self-healing efficiency without any stimulations, and decent mechanical properties. Herein, we developed a ferric-ion (Fe 3+ ) crosslinked acrylic acid and chitosan polymer hydrogel using embedded polypyrrole particles with features of high conductivity (2.61S·m -1 ) and good mechanical performances (a tensile strength of 628%, a stress of 0.33 MPa, an elastic modulus of 0.146 MPa, and a toughness of 1.14 MJ·m -3 ). In addition, the self-healing efficiency achieved 93% in tensile strength after healing in the air for 9 h without any external stimuli. Therefore, with these outstanding mechanical, self-healing, and conductive abilities all in one, it is possible to fabricate a new kind of soft material with wide applications.

Conductive hydrogels have been widely studied in many fields, such as wearable electronic materials, soft robotics, and human medical monitoring, due to their good water retention, elasticity, softness, flexibility, and sensory properties. However, it is still a great challenge to make all-in-one hydrogels with good mechanical properties, rapid self-healing ability, self-adhesion, and sensitive sensing abilities like natural skin. Thus, a multifunctional ionic conductive hydrogel containing hydroxypropyl methylcellulose/acrylic acid/acrylamide/tea polyphenol and Al3+ (HPMC/AA/AM/TP/Al3+) was prepared by a simple method. Owing to multiple dynamic noncovalent interactions, such as hydrogen bonds, electrostatic interactions, and metal coordination, in the ionic conductive hydrogel network, the hydrogel exhibited excellent mechanical properties (breaking stress: 0.032 MPa, toughness: 0.689 MJ m−3), skin-like elastic modulus (0.065 kPa), and stretchability (2225%). The electric conductivity could rapidly self-heal in a dramatically short period of time (5.1 s). Stress and strain self-healing efficiencies reached 93.8% and 99.4% in 60 min, respectively. Its adhesion strengths on wood and pigskin were as high as 13.12 kPa and 9.98 kPa, respectively, due to phenolic hydroxyl groups in TP. Moreover, the hydrogel exhibits good conductivity (3.03 S m−1). Hence, the hydrogel was assembled as a human motion sensor and high sensitivity (GF: 5.13) was obtained over the strain range of 200–1000% with a fast response/recovery time (response time: 0.4 s; recovery time: 0.75 s). Furthermore, the hydrogel sensor can monitor various human movements, including joint movement and vocal cord vibration. The as-prepared hydrogel achieved multiple functions in a single hydrogel system (all-in-one) and has great potential for application in flexible wearable sensors. [ABSTRACT FROM AUTHOR]

Conductive hydrogels have attracted the attention of researchers due to their similarity to biological tissues and potential application in flexible wearable electronic devices. However, fabrication of hydrogels with high sensitivity in combination with mechanical stretchability and biocompatibility via a simple method remains a great challenge. Here, a novel multifunctional hydrogel with high tensile properties, self-adhesion, strain sensitivity and conductivity is prepared by introducing tannic acid (TA) coated graphitized carbon nanotubes (CNTs) into the network structure composed of polyacrylic acid (PAA) and carboxymethyl cellulose (CMC). The chemical cross-linking constructed the framework for the network of the hydrogel. The dynamic physical cross-linking of the multiple hydrogen bonding among TA, CMC, and PAA together with the π–π stacking between CNTs could dissipate energy effectively. The hybrid of chemical and physical cross-linking endowed the hydrogel with excellent toughness, high stretchability, and self-adhesion. The strain reached 1385% of its original length and self-adhesion force on the wood can reach 16.65 kPa. When the carbon nanotube content was 0.6 wt%, the conductivity of the hydrogel reached 5.13 S m−1. Furthermore, the resultant hydrogel as a strain sensor to detect various physiological human movements was investigated in detail. The results indicated that the multifunctional hydrogel has high strain sensitivity and fast response ability. Therefore, the resultant hydrogel has potential application as a strain sensor for human movement monitoring. [ABSTRACT FROM AUTHOR]

Given the poor mechanical properties of traditional adhesive hydrogels, many pieces of research have been focused on the preparation of adhesive hydrogels with good mechanical properties and expanded their application. In this study, a novel multifunctional adhesive hydrogel acrylated adenine/chitosan/polyacrylamide/ Fe(III)(Aa/CS/PAM/Fe(III)) hydrogels were prepared by a chemical and physical hybrid crosslinking strategy. The hydrogels can adhere to various solid substrate surfaces and show good mechanical properties. The highest adhesion strength of the hydrogel to wood reached 11.17 kPa with the fracture stress being 0.11 MPa and the toughness 0.84 MJ/m3. The hydrogels can be stretched to more than 1400% of their original length without breaking. Additionally, the hydrogels also have good repetitive adhesion and fatigue resistance. Due to the presence of Fe3+ and Cl−, hydrogels also have certain electrical conductivity, which can be used in human motion detection. [ABSTRACT FROM AUTHOR]

The removal of dye pollutants from dyeing and printing industrial wastewater is a very important issue, and different methods have developed for this purpose. Here, a hydrogel adsorbent gelatin/chitosan/β-cyclodextrin/sodium humate (GEL/CS/β-CD/SH) was developed by a simple method for removal of the reactive dyes in aqueous solutions. The hydrogel used as an adsorbent had a good adsorption to different kinds of organic dyes. In this work, we focused on the adsorption process of GEL/CS/β-CD/SH hydrogels to the cationic dyes methylene blue (MB) and anionic dyes acid fuchsin (AF), which are commonly used in the printing and dyeing industry. The effects of dye solution pH, ionic strength, temperature, and contact time were investigated in a batch system. The adsorption thermodynamic and dynamic behaviors towards AF and MB were investigated in detail. The adsorption process could occur spontaneously at environmental temperature. The results indicated that the maximum adsorption capacity of AF and MB reached 1666.7 mg/g and 714.3 mg/g, respectively. Moreover, the GEL/CS/β-CD/SH hydrogel could be degraded completely by microorganisms in the soil. Therefore, GEL/CS/β-CD/SH hydrogel has a potential application as an effective adsorbent for the treatment of dyeing wastewater. [ABSTRACT FROM AUTHOR]

A novel biodegradable porous hydrogel (gelatin/chitosan/β-cyclodextrin, GEL/CS/β-CD) was prepared via a simple one-pot polymerization of gelatin, chitosan, and β-cyclodextrin. The chemical structure, morphology, and thermal stability were characterized by Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), and thermogravimetric (TG) analysis, respectively. Due to a great number of active groups, such as amino groups, hydroxyl groups, and carboxyl groups of the hydrogel providing enough adsorption active sites, the hydrogel had excellent adsorption performances. Various organic dyes, such as malachite green (MG), crystalline violet (CV), congo red (CR), methylene blue (MB), acid fuchsin (AF), and methyl orange (MO), could be effectively removed. For 30 mg /L of MB and AF, the removal rate was between 80.0 and 93.3%. At 298 K, the adsorption capacities of AF and MB were as high as 1111 mg/g and 667 mg/g, respectively. Adsorption thermodynamics study indicated that the adsorption was a spontaneous process with a negative ΔG. The adsorption process followed the pseudo-second-order kinetic model and the Langmuir isotherm model. Moreover, the GEL/CS/β-CD hydrogel had good biodegradability and it degraded completely in soil extract solution for 30 days. Herein, the prepared GEL/CS/β-CD hydrogel has potential application as a green and environmentally friendly adsorbent for the effective removal of organic dyes in printing and dyeing wastewater. [ABSTRACT FROM AUTHOR]

Herein, a porous, biodegradable and recyclable Gelatin/Chitosan hydrogel was fabricated as an effective adsorbent for organic pollutant. The synthesized Gelatin/Chitosan hydrogel composite was utilized in the removal of multiple dyes from aqueous solution using batch adsorption experiments. Among them, the Gelatin/Chitosan hydrogel had excellent adsorption capacity for various dyes. The maximum adsorption capacities for crystalline violet, methyl orange, acid fuchsin, congo red, malachite green, and methylene blue were 233.4 mg/g, 294.1 mg/g, 454.5 mg/g, 221.2 mg/g, 186.7 mg/g, and 209.2 mg/g, respectively. Moreover, the adsorption process could be well described by the Langmuir isotherm model and pseudo-second-order kinetic model. The dye removal efficiency was still more than 50% after five consecutive cycles of dye adsorption–desorption. Therefore, the Gelatin/Chitosan hydrogel composite is a potential candidate towards dye pollution remediation owing to its environment friendliness, high adsorption potential and regeneration capability. [ABSTRACT FROM AUTHOR]

Adsorptive removal of dyes from industrial wastewater has attracted intensive interests in recent years. Hydrogels is a kind of promising adsorbent in dyes removal owing to the simple synthesis and convenient application. A biodegradable and recyclable gelatin hydrogel (GH) was synthesized by a convenient approach in this work. The as-prepared GH was used to remove dyes in aqueous solution. The results indicated that the GH had excellent adsorption capacity for various dyes and the maximum adsorption capacities of crystalline violet (CV), methyl orange (MO), acid fuchsin (AF), congo red (CR), malachite green (MG), and methylene blue (MB) were 138.89 mg/g, 72.63 mg/g, 66.29 mg/g, 64.84 mg/g, 64.64 mg/g, and 60.32 mg/g, respectively. Moreover, the dye removal efficiency was still more than 60% after five consecutive adsorption–desorption cycles and the shape of the GH kept well. Therefore, GH can be used as an environmentally friendly and effective adsorbent to remove virous dyes from printing and dyeing wastewater. [ABSTRACT FROM AUTHOR]

Self-oscillating polymer gels driven by the Belousov–Zhabotinsky (BZ) chemical reaction are a new class of functional gels that have a wide range of potential applications (e.g., in autonomously functioning membranes and as artificial muscle actuators). However, their use in areas such as robotics and soft wearable electrical devices is currently limited because of their poor mechanical strength and electrical conductivity. In general, double network (DN) hydrogels that feature electrically conductive nanoparticles have been investigated with the aim of improving the toughness of gel materials. Herein, we have developed a novel "self-oscillating" gel with electrical conductivity and mechanical toughness using reduced graphene oxide (RGO). To prepare the gels, 5-acrylamido-1,10-phenanthroline bis(1,10-phenanthroline)iron(II) (Fe(phen)3) was used as a catalyst in the BZ reaction to induce self-oscillating behavior, whereas RGO was used to improve the toughness and electrical conductivity via physical cross-linking. The electrical conductivity of a gel with 0.35 wt% RGO content was found to be up to 15.58 S m−1, with a tensile strength of 80 kPa, 870% tensile strain and a toughness of 0.99 MJ m−3. The prepared gels exhibit autonomous mechanical oscillation without the need for any external stimuli and their oscillating amplitude was increased upon adding RGO. These characteristics of the prepared gels make them suitable for use in further applications in wearable flexible electronic devices and biomimetic materials. [ABSTRACT FROM AUTHOR]

Conventional hydrogels are extremely brittle, fragile and poorly conductive, which limits their applications in a variety of aspects. In this study, we fabricated a novel kind of nanocomposite self‐oscillating hydrogel poly(AA‐co‐Fe(phen)3)/PVA/RGO with high conductivity and good mechanical strength by dispersing reduced graphene oxide (RGO). Due to the synergetic effect of RGO dispersed in the hydrogels or dry gels and Fe metal which is the reduction product of the Fe(phen)3 moiety by RGO, the hydrogels have a high conductivity of 18.2 S m−1 with 0.67 wt% RGO content. The dispersed RGO in the hydrogels combined with the network structure by means of hydrogen bonding, π–π stacking and electrostatic interaction and was demonstrated to enhance the mechanical properties of the hydrogels. The elastic modulus achieves 65.2 kPa (1020% of the tensile strength) and 236.4 kPa (with 70% compression), respectively. In addition, the prepared hydrogels exhibit a self‐oscillating behavior in a Belousov–Zhabotinsky solution free of catalyst. These results can be broadly applied in the future in the development of an autonomous on–off switching, flexible/stretchable, graphene‐based soft electronic device. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: In this work, an acrylic acid/vermiculite (AA/VMT) hydrogel was prepared by glow‐discharge‐electrolysis plasma initiated graft copolymerization, in which N,N′‐methylenebisacrylamide was used as a cross‐linker. The structure, thermal stability, morphology and surface area of AA/VMT hydrogel were characterized by FT‐IR, TG, SEM, and automated porosimeter. Cationic dyes such as Crystal violet (CV) and Methylene blue (MB) were used for testing the adsorption property. Factors influencing adsorption such as pH, contact time, concentration were investigated by batch experiments. Adsorption kinetics and adsorption isotherms were employed to illustrate the hydrogel‐dye interaction. The results showed that the best parameters for the adsorption of dyes were pH = 6 and contact time 2 h. The adsorption kinetic followed the pseudo‐second‐order model with multi‐step diffusion process. Both Langmuir and Redlich‐Peterson isotherms were well agreed with the experimental data. The maximum adsorption capacities of CV and MB on AA/VMT hydrogel were 2575.2 and 2674.0 mg g−1, respectively. [ABSTRACT FROM AUTHOR]

Highly swelling P(2-acrylamido-2-methyl-1-propanesulfonic acid- co-acrylic acid) (P(AMPS- co-AAc)) superabsorbent hydrogel was synthesized in aqueous solution by a simple one-step using glow-discharge electrolysis plasma technique, in which N,N'-methylenebisacrylamide was used as a crosslinking agent. The structure, thermal stability and morphology of P(AMPS- co-AAc) superabsorbent hydrogel were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. A mechanism for synthesis of P(AMPS- co-AAc) superabsorbent hydrogel was proposed. The reaction parameters affecting the equilibrium swelling (i.e., discharge voltage, discharge time, macroscopic temperature of the liquid phase, mass ratio of AMPS to AAc, and content of crosslinker) were systematically optimized to achieve a superabsorbent hydrogel with a maximum swelling capacity. The hydrogel formed which absorbed about 1,685 g HO/g dry hydrogel of the optimized product was used to study the influence of various pH values and salts solutions (NaCl, KCl, MgCl, and CaCl) on the equilibrium swelling. In addition, swelling kinetics in distilled water and on-off switching behavior were preliminarily investigated. The results showed that superabsorbent hydrogel was responsive to the pH and salts. [ABSTRACT FROM AUTHOR]

Recently, conductive hydrogels have shown great promise in flexible electronics and are ideal materials for the preparation of wearable strain sensors. However, developing a simple method to produce conductive hydrogels with excellent mechanical properties, self-adhesion, transparency, anti-freezing, and UV resistance remains a significant challenge. A novel sodium lignosulfonate/xanthan gum/sodium alginate/polyacrylamide/Zn2+/DMSO (SLS/XG/SA/PAM/Zn2+/DMSO) ionic conductive hydrogel was developed using a one-pot method. The resulting ionic conductive hydrogels have excellent mechanical properties (stress: 0.13 MPa, strain: 1629 %), high anti-fatigue properties, self-adhesion properties (iron: 7.37 kPa, pigskin: 4.74 kPa), anti-freezing (freezing point: −33.49 °C) and UV resistance by constructing a chemical and physical hybrid cross-linking network. In particular, the conductivity of G hydrogel reached 6.02 S/m at room temperature and 5.52 S/m at −20 °C. Thus, the hydrogel was assembled into a flexible sensor that could distinguish a variety of large and small scales human movements, such as joint bending, swallowing and speaking in real time with high stability and sensitivity. Moreover, the hydrogel could be used as electronic skin just like human skin and touch screen pen to write. [ABSTRACT FROM AUTHOR]

Due to the flexibility, ductility and tensile properties, hydrogel is considered as promising candidates for the new generation of wearable flexible devices. However, it is still a challenge to endow multiple functions such as excellent conductivity, high stretchability, self-healing, self-adhesion, and biocompatibility in one hydrogel network. Herein, a two-step method was used to prepare multifunctional transparent tannic acid/sodium alginate/polyacrylic acid/carboxymethyl cellulose/aluminum trichloride (SA/TA/PAA/CMC/Al(III)) hydrogels with high stretchability, toughness, adhesion, and conductivity. This hydrogel can adhere to various substrates both organic and inorganic materials. The highest adhesion strength of the hydrogels to the iron sheet reaches 22.33 kPa with the fracture stress being 0.16 MPa and the toughness 1.01 MJ/m3. Moreover, the hydrogel exhibited repeatable and durable adhesion to human skin and could be peeled off completely without any residual, irritation or allergic reactions. Additionally, the hydrogels also have good repetitive adhesion and strain sensitivity. It was demonstrated that both large-scale and small-scale movements of the human body could be monitored by directly attached to various parts of the human body by the self-adhesion. This work provides a new prospect for the design of the biocompatible hydrogels with transparent, stretchable, self-adhesive, and strain-sensitive properties for potential applications in wearable electronic sensors. [Display omitted] [ABSTRACT FROM AUTHOR]