A Novel Multishaped Variable Stiffness Magnetic Catheter for Minimally Invasive Surgery

Magnetically controlled continuum robots enable dexterous manipulation within compact dimensions. However, their deformations are typically limited to C-shaped configurations, which restricts their practical applications such as obstacle avoidance, stable tip orientation, and navigation through anatomical channels with minimal tissue trauma. Moreover, the fixed stiffness of these robots limit its adaptability. To address these limitations, a continuum catheter must possess both multishaped deformation capability and variable stiffness. In this work, we propose a magnetically steerable catheter incorporating 2 radially magnetized magnets and a thermosetting shape memory polymer. Two variable stiffness segments that achieve a 20.8-fold stiffness variation (from 30 to 70 °C) within a compact design through shape memory polymer actuation. The distal magnet can rotate axially, while a single uniform magnetic field generates differential torques on both magnets, enabling multishaped deformation, including C-, J-, and S-shaped configurations. Large C-shaped deformation is achieved under a 15-mT uniform magnetic field, with a maximum distal bending angle of 127°. Experimental validation on the highly realistic gastrointestinal phantoms and ex vivo stomach model demonstrates the potential for clinical application. Compared with existing magnetic catheters, the proposed design exhibits enhanced deformation diversity and operational flexibility, making it adaptable to a broader range of medical procedures.