Amylopectin/poly(acrylamide-acrylic acid)/deep eutectic solvent hydrogels with good mechanical property, conductivity, freezing/fatigue resistance and biocompatibility for wearable sensors

Conductive hydrogels have great potential for applications in flexible wearable sensors. Recently, biopolymer-based hydrogels have attracted much attention due to the growing demand for sustainability and eco-friendliness. Among the biopolymers, starch has been used for the sensing materials due to its low-cost, biocompatibility and biodegradability. Nevertheless, it is still a challenge to develop multifunctional starch-based hydrogels with good mechanical properties, high conductivity and sensitivity. In this work, a physicochemical dual-crosslinked hydrogel was developed by combining a deep eutectic solvent (DES), amylopectin and poly(acrylamide-acrylic acid). The internal structure of the hydrogel was studied by multi-scale characterizations, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Moreover, density functional theory (DFT) calculation was applied to analyze the relationship between the structure and properties of the hydrogel. Finally, a wearable sensor was finally constructed based on the optimized hydrogel with a sensitivity (gauge factor) up to 12.08 and used for acquiring reliable data from detecting subtle expressions, swallowing and human joint motions. Furthermore, the wearable sensor demonstrated good sensitivity to compression and temperature. This study provides a novel starch-based hydrogel as a candidate for advanced wearable electronics and lays a theoretical foundation for versatile applications of DESs in the development of high-performance biopolymer-based materials.