Multifunctional small biomolecules as key building blocks in the development of hydrogel-based strain sensors

Hydrogels are three-dimensional polymer networks that are considered a promising option for developing strain sensors due to their stretchability, mechanical robustness, and high water content. These attributes make hydrogel-based sensors suitable for various applications, such as wearable electronics, human-machine interfaces, health monitoring, and soft robotics. Small biomolecules, which are biologically derived and possess attributes such as renewability, eco-friendliness, and multifunctionality, have been consistently explored for use in hydrogel-based strain sensors to improve their multifunctional properties and strain-sensing performance. This review offers a comprehensive overview of incorporating small biomolecules in developing hydrogel-based strain sensors, with a focus on enhancing their multifunctional properties and strain-sensing performance. Firstly, the representative applications and strain-sensing mechanisms of hydrogel-based strain sensors are introduced. Subsequently, the status of the functional properties of the hydrogels and the performance indicators of their strain-sensing abilities are outlined. Finally, multifunctional small biomolecules are described, followed by a comprehensive discussion concerning recent developments regarding their role in enhancing various functional properties and the performance of hydrogel-based strain sensors. Furthermore, the latest trends and perspectives on the future of hydrogel-based strain sensors are also reported.