<title>Three-dimensional active microcatheter combining shape memory alloy actuators and direct-drive tubular electrostatic micromotors</title>

Abstract

This paper investigates 3D active microcatheters having millimeter size outer diameters. The proposed architectures combine mechanical cells which involve new direct-drive tubular electrostatic micromotors and conventional shape memory alloy actuators. The tubular electrostatic motors are actuated by silicon surface micromachined flexible stators. The polysilicon stators integrate up to several thousands of direct-drive electrostatic microactuators. However, they have been designed in order to provide a gap compensation at the rotor/motor frame interface. Multiple stator/rotor contact interactions involve a significant speed reduction that allow a large torque amplification, as a consequence of the torque/speed duality. These mechanical interactions allow the rotor to be moved with respect to the motor frame through direct-drive contact mechanisms, therefore allowing high torque/low speed characteristics to be performed. In such a way to get a 3D behavior, the microcatheter combines tubular electrostatic motors having flexible rotors. The rotors integrate Ti-Ni shape memory alloy wires which actuate a 2D bending motion on each mechanical cell. The 3D global behavior of the catheter is provided by the relative rotation of each cell, with respect to the other ones. The proposed architecture is particularly convenient with respect to the electric power supply which is, usually, the major problem in designing active microcatheters. A (Phi) 1 mm 3D active catheter is given as an example, but external diameters less than one millimeter can be easily expected, opening therefore numerous applications in the near future.