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• The asymmetric hydrogel is adjusted and assembled by lignin and cellulose derivatives. • The hydrogel exhibits completely asymmetric adhesion, strength, and electriferous. • The hydrogel-based sensor has excellent skin adaptability and application stability. • The hydrogel can be applied to self-adhesive bioelectrodes and self-powered sensors. Mechanical adaptability, great wearability, application stability, and self-powered sensing characteristics are important requirements for hydrogel-based strain sensors. In this study, a novel double-layer hydrogel was fabricated with asymmetrical adhesion, strength, and electriferous properties. Wherein, the lignosulfonate sodium (LS)-borax mediated bottom hydrogel layer exhibits excellent softness (Young's modulus: ~14.2 kPa) and skin-adhesion (Adhesive strength: ~18.7 kPa) while the quaternary hydroxyethyl cellulose (QHEC) mediated top hydrogel layer demonstrates great mechanical strength (Young's modulus: ~101.3 kPa) and non-adhesive (Adhesive strength: ~2.2 kPa) properties. These complementary asymmetrical adhesion and strength properties endow the hydrogel-based sensor with exceptionally stable sensing performance and adaptive wearability; moreover, the lignocellulosic materials utilization plays a significant role in the designability, antibacterial and biodegradable properties. In addition, the synergy of negative LS (-) and positive QHEC (+) particles enables the double-layer hydrogel great self-powered sensing because of the directional movement of free ions initiated by the external mechanical stimulus. This study presents a hierarchical design idea of wearable electronics, which will have potential applications in many fields from wearable bioelectrodes to self-powered sensors. [ABSTRACT FROM AUTHOR]

• MXene can catalyze the ultrafast preparation of hydrogels by redox reaction. • MXene can regulate the internal structure and properties of the hydrogel. • Composite hydrogel has great stretchability (1400%) and recoverability. • Composite hydrogel can be used as a bioelectronic with adjustable adhesion. Re-stacking of 2D Ti 3 C 2 T X (MXene) nanosheets seriously limits their applications and development of effective strategies to overcome this issue remains challenging. Thus, an efficient method was proposed to rapidly fabricate (<20 min) a MXene nanosheets-catalyzed self-assembled, poly-acrylic acid (PAA) hydrogel with excellent conductivity, stretchability (~1400%), and anti-aggregation (>60 d) properties. In the proposed strategy, in-situ growth of TiO 2 nanoparticles (NPs) on MXene surfaces could effectively overcome the nanosheets restacking in solvents. Moreover, the reductive TiO 2 @MXene nanosheets not only catalyze the dissociation of the initiator generating sufficient radicals by redox reaction to initiate the ultrafast polymerization of AA monomers without heating, but also cross-link polymer chains (via chemical bonding) to produce hydrogel in a time scale of minutes instead of hours. Therefore, the MXene-catalyzed ultrafast self-assembly design effectively overcame the problem associated with the re-aggregation of nanosheets in hydrogels. More importantly, the structural, mechanical, swelling, adhesive, and conductive performances of the hydrogel could be adjusted by altering the TiO 2 @MXene contents. This strategy should be extended to almost all types of MXene-radical polymerized hydrogels with tunable structures and performances that have potential applications in the field of wearable bioelectronics. [ABSTRACT FROM AUTHOR]

• The redox SL-Fe3+ chelates can shorten the hydrogel gelation time by 99.67%. • The hydrogel obtained stretchable, conductive, adhesive, and UV-blocking properties. • The green SL-Fe3+ chelates imparts excellent self-healing properties of the hydrogel. • The rapid preparation of soft multifunctional coatings electronics was proposed. Developing an ecological and economical method for fabrication and application of polymer hydrogels is important for the hydrogel/coating electronics. Here, a dynamic oxidation and coordination system composed of sulfonated lignin (SL) and Fe3+ was introduced to assemble multifunctional Fe-SL-g-polyacrylic acid (PAA) hydrogel at 20 ℃ in a time scale of minutes instead of hours. The SL-Fe3+ system can rapidly activate the ammonium persulfate (APS, initiator), and then it instantaneously provides abundant semiquinone and hydroxyl radicals to accelerate the formation of polymer chains. Moreover, the functional SL-Fe3+ chelates can also reversibly crosslink the polymer chains to form multifunctional hydrogels. Surprisingly, the resultant hydrogel obtained charming extension ratio (up to 1680%), conductivity (up to 7.0 × 10-2 S·m−1), and adhesive strength (up to 36.4 kPa). This technology was also applied to rapidly fabricate a transparent (up to 81%, thickness: 2 mm), UV-blocking (up to 99.7%, thickness: 2 mm), adhesive, and conductive hydrogel coating on substrates. Besides, the dynamic coordination inside the hydrogel imparts desirable self-healing capabilities to damaged network, with up to 98.5% recovery in conductivity and 85.7% in extension ratio. In short, this technology based on the sustainable SL-Fe3+ system greatly facilitates the rapid and low-cost preparation of multifunctional hydrogel/coatings, which have promising industrial applications in human–machine electronics. [ABSTRACT FROM AUTHOR]