Variable stiffness catheter makes cover page of Advanced Science

In minimally invasive surgery, such as cardiac ablation, magnetically steered catheters made of variable-stiffness materials can enable higher dexterity and higher force application to human tissue. However, the long transition time between soft and rigid states leads to a significant increase in procedure duration.

In the new article published in Advanced Science, we present a fast-response, multisegmented catheter for minimally invasive surgery made of a fast-response variable-stiffness thread (FRVST) that encapsulates a helical cooling channel. The rapid stiffness change in the FRVST, which is composed of a nontoxic shape memory polymer, is achieved by an active cooling system that pumps water through the helical channel. An integrated active cooling mechanism allows the shortening of the stiffening process from 117 to 4.4 s. The FRVST displays a stiffness change of 66 times with a 26 times faster cooling rate when the active cooling system is used.

The FRVST is composed of an outer SMP tube with an encapsulated copper electrode serving as a heater to warm up the SMP tube and change its stiffness from a rigid to a soft state. A helical channel is placed inside the SMP tube to form a microchannel and guide the water flow when active cooling is turned on. The helical channel is wound around an inner tube, which is used as the second independent cooling system to cool the tip of the catheter during ablation surgery.

We demonstrated the selective bending of a multisegmented catheter to achieve complicated bending curvatures in different planes. The multisegmented catheter was placed in a 3D phantom of the human heart underwater at body temperature to demonstrate an ablation procedure.

Our catheter design has a 20 times faster cooling rate, 30° larger actuation stroke angle, and, at the same time, 1.7 times higher stiffness change factor than existing proof-of-concept multisegmented VS catheters for cardiac ablation.