Redox‐Active Iron‐Citrate Complex Regulated Robust Coating‐Free Hydrogel Microfiber Net with High Environmental Tolerance and Sensitivity

Abstract

Stretchable hydrogel microfibers as a novel type of ionic conductors are promising in gaining skin‐like sensing applications in more diverse scenarios. However, it remains a great challenge to fabricate coating‐free but water‐retaining conductive hydrogel microfibers with a good balance of spinnability and mechanical strength. Here the old yet significant redox chemistry of Fe‐citrate complex is employed to solve this issue in the continuous draw‐spinning process of poly(acrylamide‐co‐sodium acrylate) hydrogel microfibers and microfiber nets from a water/glycerol solution. The resultant microfibers are ionically conductive, highly stretchable, and uniform with tunable diameters. Furthermore, the presence of redox‐reversible Fe‐citrate complex and glycerol endows the fibers with good anti‐freezing, water‐retaining, and environmentally intelligent properties. Humidity and UV light can finely mediate the stiffness of hydrogel microfibers; conversely, the ionic conductance of microfibers is also responsive to light, humidity, and strain, which enables the highly sensitive perception of environmental changes. The present draw‐spinning strategy provides more possibilities for coating‐free conductive hydrogel microfibers with a variety of responsive and sensing applications.

Skin-like hydrogel devices for wearable sensing, soft robotics and beyond

“…Alternatively, organic solvents such as glycerol ( Chen et al., 2018 ; Han et al., 2018 ; Ju et al., 2020 ; Liu et al., 2019a ; Qin et al., 2019 ; Yang et al., 2019 ), EG ( Chen et al., 2019 ; Liao et al., 2019 ; Rong et al., 2017 , 2018b ), DMSO ( Nian et al., 2019 ), sorbitol ( Chen et al., 2018 ), and the combination thereof ( Chen et al., 2018 ) have been incorporated into both regular and tough hydrogels to enhance the water retention capacity and decrease the freeze point of water-based devices for applications such as batteries ( Nian et al., 2019 ), flexible solid-state supercapacitors ( Rong et al., 2018b ), flexible wearable devices ( Chen et al., 2019 ; Liao et al., 2019 ; Yang et al., 2019 ) operating under extreme environments. In addition, the anti-freezing and anti-dehydration capabilities of hydrogels as well as their mechanical and electrical properties can be altered by adjusting the concentrations of organic contents.…”

Adaptive Ionogel Paint from Room‐Temperature Autonomous Polymerization of α‐Thioctic Acid for Stretchable and Healable Electronics

“…In addition, the intrinsic opacity of conductive fillers also limits their transparent applications. To challenge the paradigm, soft ionic conductors with small ions as charge carriers and polymer network as the matrix, mainly sorted into hydrogels, [ 12,13 ] organohydrogels, [ 14 ] and ionogels, [ 15,16 ] may partially circumvent the above compliance and transparency limitations. Nevertheless, challenging issues still persist for ionic conductors as a conducting paint.…”

A mechanical, electrical dual autonomous self-healing multifunctional composite hydrogel

“…Thereby, the aqueous solution of glycerol is in more stable state than the aggregation state of water molecules. Second, hydrogen bonding between hydroxyl groups and water molecules reduces the interactions between water molecules (hydrogen bonds), whereas hydrogen bonding between water and glycerol increases the nucleation barrier for ice crystallization, thus reducing the number of ‘free water’ molecules and preventing the formation of ice crystals [ [38] , [39] , [40] , [41] , [42] , [43] ]. Third, the aggregation of the hydrophobic residues of the glycerol will disturb the three-dimensional H-bond network [ 44 ], thus restraining the formation of ice crystals.…”