Stiffness Optimization for Concentrated Bending in Magnetically Actuated Catheters: Maintaining Steerability under Gradient Stiffness

2026-05-24

AI Summary

This study addresses the inherent trade-off between efficient thrust transmission and controllable proximal bending in existing magnetically actuated soft catheters, which arises from the conflicting requirements of stiffness and steerability. To overcome this limitation, the authors propose a stiffness-optimized multi-segment magnetic actuation catheter (SO-MAC) that decouples steering from propulsion through a gradient-stiffness architecture. This design localizes bending at a stable proximal pivot point while enabling passive self-straightening of the distal segment for effective force transmission. The approach innovatively integrates gradient stiffness distribution, spring-reinforced elastic recovery, and vision-based feedback navigation to jointly achieve buckling resistance and precise steering. Experimental results demonstrate that the 1.5 mm-diameter catheter achieves a 3 mm bending radius across a 0–180° steering range, with an average shape error of 1.39 ± 0.56 mm and a pivot-point localization error of only 0.35 ± 0.10 mm, successfully navigating complex bronchial pathways.

Abstract

Achieving both efficient pushability (propulsion transmission) and proximally concentrated bending for steerability is challenging for magnetically actuated soft catheters: higher axial/bending stiffness improves force transmission but reduces steerability, whereas lower stiffness enables large, proximally concentrated bending yet increases kinking/buckling risk under compressive push loads. To address this trade-off, we propose a stiffness-optimized multi-segment magnetically actuated catheter (SO-MAC) that integrates a decoupled steering-advancement mechanism with a gradient-stiffness architecture. The SO-MAC concentrates bending about a stable proximal pivot during advancement while the distal section passively self-straightens to transmit propulsion, aided by the optimized stiffness distribution and elastic recovery of the spring backbone against friction-induced kinking/buckling. Over $0{-}180^{\circ}$ combined steering and advancement, the pivot remained stable and the distal tip advanced near-straight toward the target direction. A 1.5 mm-diameter SO-MAC achieved up to $180^{\circ}$ steering with a 3 mm bending radius at its 10 mm tip, with an average shape error of $1.39 \pm 0.56$ mm and a steering-pivot error of $0.35 \pm 0.10$ mm. Visual feedback control in a bronchial phantom further confirmed robust navigation through highly curved, bifurcating paths.

Problem

• stiffness optimization
• magnetically actuated catheters
• steerability
• pushability
• bending concentration

Innovation

• gradient stiffness
• magnetically actuated catheter
• concentrated bending
• steerability
• buckling resistance