Soft Bidirectional Shape Memory Alloy Actuators for Robotic Catheters

Abstract

In this paper, we present a robotic catheter consisting of a steerable tip driven by a novel soft shape memory alloy (SMA) actuator. The SMA actuator is a continuum body made of silicone hosting a U-shaped SMA bending wire and a pre-stretched elastic band. Through Joule heating, the temperature and recovery force of the SMA wire can be adjusted to control the bidirectional bending of the actuator between positive and negative curvatures. The SMA wire is specially designed and trained to contain serially connected parallel segments to obtain sufficient motion stability and range. This paper presents the methods on how to design and fabricate the SMA wire and soft actuator, and integrate the SMA actuator into a catheter, as well as the modeling, characterization, and testing results of the SMA actuator and the catheter. The bending range of the SMA actuator is about 120<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> with a maximum surface temperature of 46 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula>C. A feasibility study demonstrated that the SMA-actuated catheter can be navigated through a vasculature phantom into different arteries smoothly within 30 s by manipulating the catheter tip.