3D-Printed Variable-Length Magnetically Steered Catheter Tip for Enhanced Access in Aneurysm Interventions

Recent catheter designs have considered the use of magnetically active soft continuum robots controlled via external magnetic actuation systems. These have proven effective for minimally invasive applications due to their soft structure, high dexterity, and wireless actuation, all at small scales. Single and multiple magnetic segment configurations have been proposed to allow tip-only control or full shape-forming, respectively. However, these approaches utilize fixed-length magnetic segments, which require advancement from the proximal end to enhance the reachability and workspace coverage of the steerable tip. To address this limitation, we propose a dual-actuated catheter tip design comprising a 3D-printed soft tendon-driven helical body for length adaptability coupled with a tip-mounted permanent magnet for steering. We achieve a compact design of 2.4 mm outer diameter and 18 mm nominal length, suitable for carotid artery aneurysm intervention. An existing analytical model based on the Euler-Bernoulli beam theory is adapted to predict tip deflection and tip angle under magnetic actuation at three different actuation lengths: contracted, normal, and extended. We demonstrate tip length actuation spanning from a 37.2% reduction to a 35.6% extension, corresponding to 11.3 mm and 24.4 mm when fully contracted and extended, respectively. The experimental magnetic actuation shows a maximum deflection angle of 89.5° with >68° achievable across all length configurations. We subsequently demonstrate how the proposed hybrid tendon and magnetic actuation approach enables enhanced workspace access when compared to a fixed-length design, improving access within simple and more complex aneurysm phantoms.