Epidermal Sensors\nConstructed by a Stabilized Nanosilver\nHydrogel with Self-Healing, Antimicrobial, and Temperature-Responsive\nProperties

The development of conductive hydrogels has garnered\nsignificant\nattention in the field of wearable devices and smart sensors. However,\nthe fabrication of hydrogels that possess both multifunctionality\nand structural stability remains a challenging task. In this study,\na novel hydrogel, P<sub>Ag</sub>HCB, was synthesized using a mild\nmethod and exhibited outstanding characteristics such as electrical\nconductivity, self-healing capability, antimicrobial activity, dimensional\nstability, and temperature sensitivity. The exceptional mechanical\nperformance (∼120 kPa at a strain of 450%) of P<sub>Ag</sub>HCB is attributed to the incorporation of hydroxypropylmethylcellulose\n(HPMC) and the mechanical reinforcement of the gel network by carboxylated\ncarbon nanotubes (CNT-COOH). The borate bonds between or within poly(vinyl\nalcohol) (PVA) chains confer self-healing capabilities upon P<sub>Ag</sub>HCB, with a healing efficiency of 74.1%. The in situ reduction\nof silver nanoparticles through ultraviolet irradiation imparts antimicrobial\ncharacteristics to the hydrogel [against Escherichia\ncoli, zone of inhibition (ZOI) = 3.7 mm; against Staphylococcus aureus, ZOI = 6.3 mm]. The linear\ntemperature responsiveness of the P<sub>Ag</sub>HCB hydrogel (<i>R</i> = −3.99<i>T</i> + 608.84 and COD = 0.9988)\narises from the migration of silver ions within the gel matrix and\nthe dissociation of borate bonds. Furthermore, P<sub>Ag</sub>HCB was\nseamlessly integrated into sensors designed for monitoring human motion.\nThe gel-based sensors exhibited three distinct sensing strain ranges\ncorresponding to three different gauge factors (GF<sub>1</sub> = 2.976,\nGF<sub>2</sub> = 1.063, and GF<sub>3</sub> = 2.97). Notably, P<sub>Ag</sub>HCB gel sensors demonstrated the capability to detect electrical\nsignals generated by finger and wrist joint movements and even discerned\nsignals arising from subtle deformations induced by activities such\nas speaking. Additionally, the P<sub>Ag</sub>HCB gel was utilized\nas a pressure sensor to detect external pressures applied to the skin\n(from 0.373 to 15.776 kPa). This work expands the avenues for designing\nand synthesizing multifunctional conductive hydrogels, promoting the\napplication of hydrogel sensors with comfortable wear and high sensitivity.