A Novel Robotic Guiding Sheath With Variable Stiffness Capability Based on Conductive Graphene and Thermoplastic Polymer

In robot-assisted endoscopic procedures, a guiding sheath must be flexibly advanced through anatomic paths via natural orifices, while maintaining sufficient rigidity to serve as a base for the surgical instruments used in dexterous diagnostic and therapeutic tasks. Therefore, developing a guiding sheath with the capacity of both flexible access and variable stiffness is imperative and challenging. To address these challenges, we have developed a novel robotic guiding sheath. Its stiffness can be managed using the innovatively-manufactured variable stiffness coating layer (VSCL), which has a thickness of only 1 mm and is composed of polycaprolactone (PCL) and conductive graphene. An active water heating and cooling mechanism was designed to regulate the temperature of the VSCL, thereby controlling the stiffness of the guiding sheath. Through detailed performance evaluation, the guiding sheath achieved a fixed-end bending stiffness gain of 25.76 and a mid-span bending stiffness gain of 25.01, reaching a fixed-end bending stiffness of 739.63 N/m and a mid-span bending stiffness of 5779.33 N/m. The fast switching between the rigid and flexible states was realized with switching times of 6.5 s (from rigid state to flexible state) and 10.0 s (from flexible state to rigid state). The sheath was also validated with phantom and ex-vivo experiments. The capability of this guiding sheath to traverse the tortuous digestive tract in a flexible state was proved. Additionally, the guiding sheath in a rigid state can significantly improve instrument manipulation stability during the ex-vivo trials. The experimental results demonstrated the potential clinical value of this system.