Alternating Follow-the-Leader Medical Device with Pneumatically Actuated Shape Locks

Abstract

Developments in minimally invasive surgery such as natural orifice transluminal endoscopic surgery and single port laparoscopic surgery have pushed medical devices to be higher articulated and more dexterous. These surgery methods have proven to greatly decrease bleeding, scar tissue, hospital time, and cost. The procedures involve the navigation of flexible instruments through tortuous anatomical pathways. To reduce chances of tissue damage it is desired to reduce the interaction with anatomical structures during the trajectory. To realize this aspect a so-called Follow-the-Leader (FTL) motion has been adapted as a design feature for medical devices. This motion allows for the shaft of the instrument to conform to the shape taken by its end-effector without relying on anatomical reaction forces. One strategy to achieve FTL motion is the so-called alternating advancement where two shafts subsequently switch from flexible to stiff in order to conserve the configuration of the shaft. These devices have been shown to possess relatively many degrees of freedom for a small number of actuators which can greatly reduce the cost of the device. A state-of-the-art analysis has shown that, despite the kinetic advantages, there are no alternating FTL devices that use pneumatically actuated shape locks to constrain the flexibility of the shaft. In this work an alternating FLT medical device with pneumatically actuated shape locks was designed, produced, and tested. The device has a diameter of 40 mm and nine degrees of freedom. The total bending angle is 90 degrees with a bending radius of 85 mm. The device leaves room for improvement but does show that two concentric shafts can be shape locked pneumatically to perform an alternating FTL motion.