Tunable Dual Temperature–Pressure Sensing and Parameter Self-Separating Based on Ionic Hydrogel via Multisynergistic Network Design

Abstract

Hydrogel-based wearable sensors have experienced an explosive development, whereas functional integration to mimic the multisignal responsiveness of skin especially for pressure and temperature remained a challenge. Herein, a functional ionic hydrogel-base flexible sensor was successfully prepared by integrating the thermal-sensitive N-isopropylacrylamide (NIPAAm) into another conductive double-network hydrogel based on polyvinyl alcohol–graphene oxide (PVA–GO) and polyacrylic acid–Fe3+ (PAA–Fe3+). Because of the multisynergistic network design, the triple-network hydrogel was endowed with excellent conductivity (∼170 Ω/mm), mechanical tolerance (1.1 MPa), and rapid recoverability (within 0.5 s), which demonstrated the potential use in pressure monitoring. Moreover, the introduction of a thermal-sensitive network allowed it to capture the changes in the human body temperature accurately simultaneously and to be further developed as a flexible temperature sensor. In particular, the unsynchronization of pressure and temperature strain (straining to stability within 0.5 s and more than 50 s, respectively) caused the two electrical signals to be automatically separated. Intuitive reading of data without involving complex parameter separation calculations allowed the hydrogel to be developed as an integrated dual temperature–pressure-sensitive flexible sensor. In addition, all above properties demonstrated that the as-prepared functional hydrogel could be extended to the practical application in human–machine interactions and personalized multisignal monitoring.

Highly Stretchable, Adhesive, and Self‐Healing Silk Fibroin‐Dopted Hydrogels for Wearable Sensors

“…[31,32] In recent years, water-rich, soft, and 3D network hydrogels have spout out in the field of flexible sensors. [33][34][35][36][37] However, some problems remain to be solved: i) the physical cross-linking networks are often fragile and cannot meet the requirements of larger deformation while the chemical cross-linking hydrogels, once the chemical bonding is destroyed, are difficult to restore the original structure. [38] ii) Due to the lack of adhesion, adhesive tapes such as 3M tape, are required to attach the hydrogel sensors to the skin, which influences the measurement process of the sensors.…”

“…[39] Zhang and co-workers prepared mechanically recoverable flexible sensors by integrating the thermal-sensitive N-isopropylacrylamide (NIPAAm) into another conductive double-network hydrogel based on polyvinyl alcohol-graphene oxide (PVA-GO) and polyacrylic acid-Fe 3+ (PAA-Fe 3+ ). [34] Inspired by nature, Shen's group combined natural sea urchin-like microcapsules with 2D MXene nanoflakes to prepare a flexible pressure sensor that was 8.69 times more sensitive than the sensor with a planar structure. [40] In this work, a ternary system hydrogel consists of silk fibroin (SF), acrylamide (AM) and acrylic acid (AA) is prepared by one-pot thermal polymerization.…”

Hydrogel: Diversity of Structures and Applications in Food Science

“…reported. For instance, multiple-network hydrogels, such as triple-network hydrogels, [482,483] DN-NC hydrogels, [484][485][486] anisotropic liquid crystalline DN hydrogels, [487,488] void-DN hydrogels, [489] and microgel-reinforced DN hydrogels. [89,490,491] Suo's group formed a type of highly stretchable and tough DN hydrogels that had combined ionically and covalently crosslinked networks.…”

Smart Composite Hydrogels with pH-Responsiveness and Electrical Conductivity for Flexible Sensors and Logic Gates

“…However, acrylic hydrogels are very brittle, which is a big problem in building smart devices [35]. Therefore, many studies have been reported on improving the mechanical properties of polyacrylic acid hydrogels to prepare smart devices, such as flexible sensors [36,37]. Herein, in the process of polymerization of acrylic acid and hydroxyethyl acrylate monomers into hydrogels, we added graphene oxide to a prehydrogel solution to prepare pH-responsive conductive hydrogels, which have high conductivity.…”