Liquid Metal-Doped Conductive Hydrogel for Construction of Multifunctional Sensors

Abstract

Interest in wearable and stretchable multifunctional sensors has grown rapidly in recent years. The sensing elements must accurately detect external stimuli to expand their applicability as sensors. However, the sensor's self-healing and adhesion to a target object have been major challenges in developing such practical and versatile devices. In this study, we prepared a hydrogel (LM-SA-PAA) composed of liquid metal (LM), sodium alginate (SA), and poly(acrylic acid) (PAA) with ultrastretchable, excellent self-healing, self-adhesive, and high-sensitivity sensing capabilities that enable the conformal contact between the sensor and skin even during dynamic movements. The excellent selfhealing performance of the hydrogel stems from its double cross-linked networks, including physical and chemical cross-linked networks. The physical cross-link formed by the ionic interaction between the carboxyl groups of PAA and gallium ions provide the hydrogel with reversible autonomous repair properties, whereas the covalent bond provides the hydrogel with a stable and strong chemical network. Alginate forms a microgel shell around LM nanoparticles via the coordination of its carboxyl groups with Ga ions. In addition to offering exceptional colloidal stability, the alginate shell has sufficient polar groups, ensuring that the hydrogel adheres to diverse substrates. Based on the efficient electrical pathway provided by the LM, the hydrogel exhibited strain sensitivity and enabled the detection of various human motions and electrocardiographic monitoring. The preparation method is simple and versatile and can be used for the low-cost fabrication of multifunctional sensors, which have broad application prospects in human− machine interface compatibility and medical monitoring.

Ultra-robust, high-adhesive, self-healing, and photothermal zwitterionic hydrogels for multi-sensory applications and solar-driven evaporation

“…At elevated temperatures, the Ga 3+ ions may dissociate due to the weakened interaction between Ga 3+ ions and the catechol groups on the PDA layer, resulting in an increased concentration of charge carriers. 55 Also, higher temperatures boost the ion migration facilitation from the zwitterionic groups on PSBMA chains. 56 Therefore, rising temperatures enhanced the migrating rate of both electrons and Ga 3+ ions, i.e., improved conductivity in our PSBMA-LM@PDA-5 hydrogel.…”

Liquid metal–hydrogel composites for flexible electronics

“…7a and b), and the electrodes can continuously and stably record the heart rate during exercise, reducing the risk of heart attack. 154 In addition, the impedance of the LM–hydrogel electrodes can be reduced by adjusting the chemical composition of the hydrogel, making it more favorable for ECG signal acquisition. 155 There have been several reports demonstrating that LMs can be applied directly on human skin and easily wiped off without significant irritation.…”

Challenges and Advances of Hydrogel-Based Wearable Electrochemical Biosensors for Real-Time Monitoring of Biofluids: From Lab to Market. A Review

“…3 Moreover, their synthetic versatility enables precise control over the chemistry of gels, offering high specificity to different stimuli. 7 While hydrogels offer a wide range of responsiveness to different stimuli, effective signal transduction mechanisms are required to convert their responses into detectable signals for sensing. 8,9 Among different types of developed devices, electrochemical biosensors have emerged as the most versatile and widely used class for multipurpose applications.…”

“…Besides, they mimic the properties of hydrated biological tissues, thus making them suitable for in vivo applications . Moreover, their synthetic versatility enables precise control over the chemistry of gels, offering high specificity to different stimuli …”