Surgical rolling joint optimization to maximize payload capability and its application to flexible endoscopic manipulator

Abstract

This study was motivated by the idea that tissue traction by adding an additional flexible surgical instrument that can be attached to and controlled by a conventional flexible endoscope to overcome the complications of endoscopic submucosal dissection procedures, such as difficulty in complex movement due to the limited degree of freedom (DOF) of commercial instruments and obstruction of the field of view of a cut tissue. The desired features of flexible surgical instruments include flexibility and miniature structure for easy insertion into natural openings such as the mouth and anus and to reach the lesion through torturous paths such as the stomach or large intestine as well as have sufficient payload to lift tissues or organs. However, when the diameter of the surgical joint decreases, the payload decreases due to a decrease in the moment arm, and when the flexibility increases, the stiffness decreases and the payload decreases. As such, they have a trade-off relationship

thus, study on a flexible and miniature surgical instrument with enhanced payload is indispensable. In this study, the payload of surgical instruments was analyzed from two perspectives, i.e., a: actively lifting organs or tissues and b: passively withstanding the weight of the organs and tissues. In the `a' perspective, the moment equilibrium equation was used to calculate the output force for a given wire tension at the tip of the surgical instrument, and in the `b' perspective, stiffness was calculated from the deflection against an external force (weight of organ or tissue). It was found that the payload (output force and stiffness) is expressed as joint design parameters, and the effect of each design parameter on the payload was analyzed. In addition, a method of maximizing the payload through design parameter optimization has been proposed. As a result of the optimization, a flexible surgical tool consisting of three joints was developed, and it was confirmed that a weight of up to 300g could be lifted. To overcome the problems of the endoscopic procedures, the idea of a flexible endoscopic platform including the proposed surgical instrument was suggested, and experiments and analysis were conducted to determine the composition of required/effective DOF of the surgical instrument for tissue pulling to increase the effectiveness of the endoscopic procedures. Through tissue traction experiments, 2 DOF (2 DOF bending or 1 DOF bending + rotation) were sufficient for the traction tissue. In order to overcome the hand-eye coordination mismatch problem due to the relative rotation between the endoscope and the surgical instrument, it was most effective to have two DOF bending and rotation. In addition, the conventional procedure method and the method using the proposed platform were compared through in-vivo animal experiments, and the procedure speed and dissection speed were significantly higher, and the blind dissection rate was significantly lowered. Therefore, it has been verified through the proposed platform can overcome complex movements and obstruction of vision of resected tissues, which are limitations of conventional endoscopic procedures. In addition, the number of tool replacements was significantly reduced, maximizing the efficiency of the procedure.