Abstract: Systems, methods, and sensor devices for identifying one or more changes in a stimulus-responsive hydrogel include a sensor device having (i) a sensing structure and (ii) a stimulus-responsive hydrogel associated with a first side of the sensing structure. The sensing structure includes a flexible thin film polymer and an electric sensing element capable of electric impedance change, and the hydrogel is configured to dimensionally change in response to predefined stimuli such that a dimensional change of the hydrogel causes a change in an impedance property of the electric sensing element. Systems including such a sensor device can additionally include a meter in electrical communication with the sensor device to identify changes in the impedance properties of the structure and/or a catheter sheath configured for placement within an in vivo environment and is sized and shaped to receive the sensor device within a lumen thereof.