Long-Term Stable Flexible Strain Sensor Fabricated by Constant Hysteresis

Stable electromechanical responses are the foundation for achieving reliable health monitoring. Long-term stability, in wearable or implantable medical devices, is a key to addressing challenges such as mechanical deformation and body fluid erosion during continuous physiological activities, which seriously restricts the transformation of flexible wearable devices from laboratory prototypes to commercial products. This paper reports on a hierarchical AgNWs-P3HT/PDMS-based flexible strain sensor, having an advantage of performance characterized by constant hysteresis. Employing 80-day experimental assays, it is confirmed that the herein fabricated flexible strain sensor is long-term stable at room temperature in the laboratory environment; there is no statistical difference existing in its sensitivity described by gauge factor (GF) during the testing duration. GF-sensitivity can be improved through reducing the thickness of the composite electrode, such that it can exhibit a very high GF-sensitivity (151.1) with a thinner thickness of 0.2 mm. And it features a wide strain response range (0.1-40%) that covers the physiological deformation levels. Besides, it has good shape-plasticity that can be processed and formed according to the topological structure of the host organ, such as integrating into a contact lens with a circle configuration. Employing human corneal epithelial cells, additionally, it is evidenced that the sensor has excellent biocompatibility through the cytotoxicity assay. Furthermore, it is also confirmed that the sensor can generally realize physiological pressure monitoring and diverse movement action detecting.