Active catheter driven by a thermo-hydraulic actuation

Catheters and flexible endoscopes are usually steered by mechanical wires that are driven from their base. Due to friction and buckling there is a need to place the driving actuator of the catheter at the catheter´s tip. Such active catheter´s manoeuvrability is much higher than wire-driven ones. A problem with active catheters is the difficulty to create high enough bending using micro-actuators placed at the catheter´s tip. Our actuation method is an attempt to overcome this difficulty by using a novel thermo-hydraulic actuation method. The magnitude of the bending torque of our actuator is created by internal hydraulic pressure in the tube and the steering direction is controlled by the thermal micro-actuator embedded in the wall of the tube. In this paper we present the modelling, optimization, design and testing of an initial prototype of such an actuator. We found that a 4 mm OD actuator made of TPU can bend to ±12°.