Dual-Sensing, Stretchable, Fatigue-Resistant, Adhesive, and Conductive Hydrogels Used as Flexible Sensors for Human Motion Monitoring

Abstract

Hydrogel-based sensors serve as an ideal platform for developing personalized wearable electronics due to their high flexibility and conformability. However, the weak stretchability and inferior conductivity of hydrogels have severely restricted their large-scale application. Herein, a natural polymer-based conductive hydrogel integrated with favorable mechanical properties, good adhesive performance, and excellent fatigue resistance was fabricated via interpenetrating tannic acid (TA) into a chitosan (CS) cross-linked network in an acidic aqueous solution. The hydrogel was composed of a regular hierarchical porous structure, which was built by the hydrogen bonding between TA and CS. In addition, the hydrogels exhibited adjustable mechanical properties (maximum yield stress of 7000 Pa) and good stretchability (strain up to 320%). Benefiting from the abundant catechol groups of TA, the proposed hydrogels could repeatedly adhere to various material surfaces and could be easily peeled off without residue. Moreover, the hydrogel exhibited stable conductivity, high stretching sensitivity (gauge factor of 2.956), rapid response time (930 ms), and excellent durability (>300 cycles), which can be assembled as a strain sensor to attach to the human body for precise monitoring of human exercise behavior, distinguishing physiological signals, and recognizing speech. Furthermore, the prepared hydrogels also exhibited stable sensing performance to temperature. As a result, the hydrogels exhibited dual sensory performance for both temperature and strain deformation. It is anticipated that the incorporation of strain sensors and thermal sensors will provide theoretical guidance for developing multifunctional conductive hydrogels and pave a way for the versatile application of hydrogel-based flexible sensors in wearable devices and soft actuators.

A κ-Carrageenan-Containing Organohydrogel with Adjustable Transmittance for an Antifreezing, Nondrying, and Solvent-Resistant Strain Sensor

“…These results indicated that the as-prepared κ-CG/p­(HEMA-AA-AAm)/Al 3+ organohydrogels possess excellent self-adhesive function, which could effectively eliminate the interface gap between the substrate and organohydrogel in sensing tests and ensure that the various mechanical deformations were accurately translated into electronic signals. The adhesion mechanism may ascribe to the existing vast carboxyl and amino groups in organohydrogels that can form strong noncovalent bond interactions with functional groups on the various material surfaces (Figure f). − Moreover, due to the high transparency of κ-CG/p­(HEMA-AA-AAm)/Al 3+ organohydrogels in the wavelength range of 400–700 nm, the picture behind the organohydrogel film could be clearly observed (Figure g). The outstanding optical transparency provides potential feasibility for the design of visual flexible sensors and electronics.…”

Wearable Dual-Signal NH3 Sensor with High Sensitivity for Non-invasive Diagnosis of Chronic Kidney Disease

“…Therefore, it is an optimal choice to effectively combine the breath analysis technology with wearable devices . A wearable sensor is a real-time, non-invasive, and automatic monitoring device of human physiological parameters. − …”

Carbon Nanotubes and Silica@polyaniline Core–Shell Particles Synergistically Enhance the Toughness and Electrical Conductivity in Hydrophobic Associated Hydrogels

“…Strain sensors based on hydrogel flexibility can monitor human health in real time by sensing the body’s breathing, − heartbeat, − external vibration, − and body temperature − and converting them into visual electrical signals, demonstrating its great potential for applications in human–computer interaction, artificial sensor skin, and flexible sensors. , Conductive hydrogels with excellent mechanical flexibility, strain sensitivity, long-term stable sensing, and multistimulus responsiveness are candidates for the manufacture of strain sensors. However, the poor mechanical properties of hydrogels are due to their small internal forces and difficulty in energy dissipation .…”