Multi-Objective Design Optimization of a Shape Memory Alloy Actuated Robotic Catheter

In this paper, we present a method for optimizing the design of a shape memory alloy (SMA) actuated robotic catheter. The robotic catheter is designed for use in endocardial ablation procedures, where “trackability” (bending flexibility) and “pushability” are desirable but conflicting catheter traits, leading to a multi-objective optimization problem. The catheter uses SMA tendons for internal actuation, which create a bending moment about a central structure. The design of SMA actuators is often non-intuitive and complicated due to the material’s hysteretic dependence on stress and temperature. The modeling and design difficulties increase when considering antagonistic SMA actuation, which is the case for the robotic catheter. The catheter is optimized using a genetic algorithm coupled with COMSOL Multiphysics Modeling and Simulation software. The objective functions are formulated in order to improve bending flexibility and pushability. Bending flexibility is quantified by radius of curvature. Pushability is a more subjective characteristic that depends on axial stiffness and friction, but for optimization purposes, it is quantified using axial stiffness and the surface area of the catheter. Several design variables that affect the catheter behavior are considered; these include the SMA tendon diameter and its pre-strain, the offset of the SMA tendon from the neutral axis of the central structure, and the central structure’s diameter and elastic modulus.