Design of injectable agar/NaCl/polyacrylamide ionic hydrogels for high performance strain sensors.

High performance strain sensors have recently attracted immense interest because of their potential applications in wearable devices. However, it remains a challenge in achieving critical feature combinations (e.g., high sensitivity, high mechanical properties, and easy fabrication) for soft wearable sensors. Herein, we fabricated new ionic strain sensors based on agar/NaCl/polyacrylamide double network hydrogels. By taking the advantage of the electric neutrality of agar, we can easily combine the sensitivity and mechanical properties into same ionic hydrogel by tuning the chemical compositions of the hydrogels. Moreover, thanks to the thermoreversible sol-gel properties of agar, the pregel can be injected into various complex shapes. The ionic hydrogels exhibit high strain sensitivity and many superior mechanical properties. The ionic sensor can monitor human motions such as joint motions, slight wrist pulse and subtle muscle movements of throat. Thus, this study demonstrates that the ionic hydrogels have potential applications as high performance strain sensors.