A Double-Walled Flexible Friction-Based Locomotion and Transport Mechanism

Abstract

Background: The goal of minimally invasive surgery (MIS) is to perform surgery by minimal damaging the body. Compared to traditional open surgery MIS results in faster recovery and lower mortality, and is therefore the preferred method for performing a biopsy. Natural Orifice Transluminal Endoscopic Surgery (NOTES) is a type of MIS where an instrument enters the body through a natural orifice to reach the target. During NOTES an instrument enters the body through a natural orifice to reach the target. Upon entering the body via a natural orifice, first the target area needs to be reached and second, the targeted tissue needs to be transported out of the body for further examination. Currently used instruments for NOTES are suboptimal for transport through tubular organs due to damaging the tissue. In this study, a friction-based transport mechanism, inspired by eggs of parasitic wasps, was developed as an improved tool for NOTES. Additionally, the possibility to steer this instrument was examined as well. Methods: State of the art mechanisms were analysed and selected based on their potential for being used as a flexible system for locomotion through a tubular organ and tissue transport. Requirements of this instrument were determined which were divided into requirements for the flexible shaft and for the actuation of the locomotion and transport mechanism. Requirements were also determined for the additional wish for the instrument to be steerable. Based on these requirements a final design of a flexible shaft and actuation was developed. The design process for steerability of the flexible shaft is described as well, resulting in a tip that can be added to the flexible shaft to add steerability. Performance of the flexible shaft was evaluated based on locomotion through a tube, tissue transport and steerability in a simulated setting. The flexible shaft was tested if it is possible to locomote through a tube, transport tissue and can be steered. Results: The developed instrument was able to locomote in a straight direction and three different configurations: with a bending radius of 80 mm, 105 mm and 130mm and a bending angle of 45°, 30° and 15°, respectively. The locomotion rate in the straight direction was 6.17±0.27 mm/cycle and was 5.21±0.21 mm/cycle in the maximum bent direction (bending radius of 80 mm). The instrument was adequate for the intended use: (1) insertion into a tube, (2) locomote through the tube, and (3) transport tissue out of the tube using the flexible shaft. Adding the tip and attached steering wire ropes with manual operation allowed the shaft to be steered up to an angle of 90° with a bending radius of 58 mm. Discussion and conclusion: A flexible shaft instrument was developed that was able to locomote and transport tissue through a tube. Additionally, a steering tip was designed that allowed to steer the instrument from outside the body/tube. While lower locomotion rates were observed for lower bending radii, the developed design shows great potential for an instrument to perform NOTES with minimal burden for the patient.