Tough, Healable, and Sensitive Strain Sensor Based on Multiphysically Cross-Linked Hydrogel for Ionic Skin

Abstract

Ion conductive hydrogels (ICHs) have attracted great interest in the application of ionic skin because of their superior characteristics. However, it remains a challenge for ICHs to achieve balanced properties of high strength, large fracture strain, self-healing and freezing tolerance. In this study, a strong, stretchable, selfhealing and antifreezing ICH was demonstrated by rationally designing a multiphysically cross-linked network structure consisting of the hydrophobic association, metal-ion coordination and chain entanglement among poly(acrylic acid) (PAA) polymer chains. The deliberately designed Brij S 100 acrylate (Brij-100A) micelle crosslinker can effectively dissipate energy and endow hydrogels with desirable stretchability. The self-healing ability of hydrogels originates from the reversible hydrophobic association in micelles and Fe 3+ -COO − coordination. After the addition of NaCl, the chain-entangled physical network caused by the salting-out effect can both enhance mechanical strength and promote electron transport. With the synergy of hydrophobic association, mental-ligand coordination and chain entanglement, the PAA/Brij-100A/ Fe 3+ /NaCl (PAA/BA/Fe 3+ /NaCl) hydrogels exhibited a high tensile strain of 1140%, a tensile strength of 0.93 MPa and a toughness of 3.48 MJ m −3 . Besides, the PAA/BA/Fe 3+ /NaCl hydrogels exhibited a high conductivity of 0.43 S m −1 and good freezing resistance. The ionic skin based on the PAA/BA/Fe 3+ /NaCl hydrogels showed high sensitivity (GF = 5.29), wide strain range (0− 950%), fast response time (220 ms) and good stability. Also, the self-healing ability of the ionic skin can significantly prolong its service time, and the antifreezing property can broaden its applicable temperature. This study offers new insight into the design of multifunctional ionic skin for wearable electronics.

Self-healing, self-adhesive, stretchable and flexible conductive hydrogels for high-performance strain sensors

“…32 The existence of the stretching peaks of the -OH group illustrates that there are hydrogen bonds among the network for all hydrogels. 9 The peak at 1064 cm À1 attributed to the stretching vibrations of C-O for the primary hydroxyl groups of CS and TP weakens in the hydrogel spectra, further indicating the coordination reaction of the metal ions with the hydroxyl groups. 33 The peak at 1710 cm À1 is the coordination peak of the PAA carboxyl group and the iron ion, indicating that Fe 3+ has ion coordination interactions with PAA.…”

“…6,7 These conductive materials can detect external stimuli (such as extension, bending, and expansion) and transduce them into electrical signals (e.g., resistance, current, or capacitance) just like the human skin. [8][9][10] However, traditional conductive materials generally suffered from the intrinsic stiffness, restricted stretchability, or a narrow detection range which limits their practical applications. Therefore, it remains a great challenge to fabricate ideal sensors with tunable flexibility, stable conductivity, excellent self-healing and selfadhesive properties, a wide working strain range, and high sensitivity.…”

High-Strength, Freeze-Resistant, Recyclable, and Biodegradable Polyvinyl Alcohol/Glycol/Wheat Protein Complex Organohydrogel for Wearable Sensing Devices

“…Conductive hydrogel is a three-dimensional network structure containing large amounts of water with excellent flexibility and biocompatibility . Due to the potential toxicity of some synthetic polymer organisms, the application in the medical and health field is limited .…”

“…10 Conductive hydrogel is a three-dimensional network structure containing large amounts of water with excellent flexibility and biocompatibility. 11 Due to the potential toxicity of some synthetic polymer organisms, the application in the medical and health field is limited. 12 Furthermore, synthetic polymers have the problem of difficult degradation, and with the wide application of human wearable devices, it will cause a large amount of electronic waste and seriously harm the ecological environment.…”

Cartilage-inspired terpolymer hydrogel with excellent mechanical properties and superior lubricating ability

“…11,17,18 These ionically cross-linked hydrogels have been used in wound dressings, cartilage regeneration, gas detection, catalysis, and other fields. [19][20][21][22] Carboxylate-rich hydrogels, such as poly(acrylic acid) (PAAc) [23][24][25] and alginate, 26 can be readily enhanced by multivalent ions such as Fe 3+ , [23][24][25] Zr 4+ , 17 and Zn 2+ . 27 Fe 3+ exhibits a pronounced binding affinity for carboxylate groups, making it a popular choice for enhancing the mechanical properties of hydrogels.…”