Hysteresis-Free Double-Network Hydrogel-Based Strain Sensor for Wearable Smart Bioelectronics.

Hydrogel-based electronics have attracted substantial attention in the field of biological engineering, energy storage devices, and soft actuators due to their resemblance to living tissues, biocompatibility, tunable softness, and consolidated structures. However, combining the properties of quick resilience, hysteresis-free, and robust mechanical properties in physically cross-linked hydrogels is still a great challenge. Herein, we present a vinyl hybrid silica nanoparticle (VSNPs)/polyacrylamide (PAAm)/alginate double-network hydrogel-based strain sensor with the characteristics of quick resilience, hysteresis-free, and a low limit of detection (LOD). The physical cross-linking among PAAm chains and covalent cross-linking between PAAm, alginate, and N,N-methylenebisacrylamide chains promotes excellent mechanical properties. Moreover, the incorporation of VSNPs reinforces the mechanical strength by the dynamic cross-linking of the PAAm network to maintain the integrity of the hydrogel and works as a stress buffer to dissipate energy. The as-prepared hydrogel-based sensor exhibits a strain sensitivity (i.e., gauge factor) of 1.73 (up to 100% strain), a response time of 0.16 s, an ultra-low electrical hysteresis of 2.43%, and a low LOD of 0.4%. The outstanding properties of the hydrogel are further used to illustrate the utility of the sensor in e-skin, ranging from low-strain applications, such as carotid pulse and artificial sound detection, to large bending applications, such as sign language translations. In addition, an efficient and cost-effective synthesis of double-network hydrogel that can overcome the bottleneck of the electromechanical properties of single network hydrogel has potential prospects in soft actuators, tissue engineering, and various biomedical applications.