Electrochemistry-Triggered Microscopic Wrinkle Patterns That Improve the Sensitivity of Hydrogel Sensors

To improve the signal-to-noise ratio of strain sensors, a critical factor involves improving the change ratio of resistance in response to an external force. Traditional methods such as templating, prestretching, or asymmetric swelling can construct wrinkles on hydrogel but do not alter its conductive characteristics and improve the change ratio of resistance. Herein, we report an electrochemical protocol that can trigger homogeneous hydrogel to form the gradient distribution of mechanical strength and induce microscopic wrinkle patterns at the surface of hydrogel. The electrode reactions produce metal ions (Fe3+) inside the hydrogel, in which the electric field-driven ion migration results in the gradient distribution of Fe3+ ions, the closer to the wrinkle patterning surface of hydrogel, the higher content of Fe3+ ions. Large amounts of Fe3+ ions concentrate at the wrinkle surface, which improves the conductive characteristics of hydrogel. Therefore, upon compression at the wrinkle surface, the hydrogel sensor shows the higher change ratio of resistance. We demonstrate this feature by testing the weak vibration such as motion of soft brush and rolling of glass rods at the wrinkle surface of hydrogel, which shows the wrinkle patterns can improve the signal intensity of hydrogel sensor by two times. These results highlight the potential of our method for the construction of microscopic wrinkle structures to improve the sensitivity of hydrogel sensors.