Direct fabrication of flexible strain sensor with adjustable gauge factor on medical catheters

The preparation of flexible sensors on medical catheters is primarily an indirect process using certain materials as substrates. Using medical catheters as flexible substrates is beneficial for directly detecting the strain and contact force of the catheters. In this study, a strain sensor is prepared by rubbing graphite on a silicone medical catheter with a minimum inner diameter of 1 mm × 2 mm. The gauge factor (GF) of the strain sensor is adjusted by changing the resistance during preparation. By precisely controlling the composite material seepage zone, the maximum achievable GF is 121 at a low strain of 1%, which can be used to detect low forces with a resolution of 0.0013 N. Liquid glue is used to encapsulate the sensor, which barely changes the conductive network of the sensor. The response time of the strain sensor is 50 ms, and the performance of the sensor remains unchanged after 1000 cycles, which renders it suitable for intestinal shape detection. Additionally, we demonstrate the feasibility of integrating four strain sensors on the medical catheter to detect its bending direction via vector synthesis, which allows the spatial shape to be examined. The results obtained indicate the potential of the friction method for preparing strain sensors with different GFs on medical catheters to be used in different medical applications.