Developed a 3 mm diameter fully soft robotic catheter tip that combined independent hydraulic bending and torsion to improve branch access and local tip control without relying on base shaft rotation. The system achieved up to 90° bending, 360° axial rotation, 53.8 mN bending force, and 1.3 mN·m torsional torque, then demonstrated navigation through an aortic arch phantom into multiple branches using localized tip motion rather than shaft twisting.
Assembled soft robotic catheter tip.
Soft Robotic Catheter with Independent Bending and Torsion
Problem
Conventional endovascular catheters are typically built from semi-rigid polymers and steered largely through shaft manipulation and base rotation. That makes maneuvering through tortuous vasculature difficult, increases reliance on advanced catheter maneuvers by the operator, and raises the risk of vessel wall trauma or perforation when the shaft must be rotated or pushed aggressively to achieve the right tip orientation. Existing robotic catheters improve steerability, but many still rely on mechanically coupled actuation, bulky external systems, or partially rigid structures that limit conformability around delicate anatomy. The key challenge in this project was to create a millimeter-scale catheter tip that could deliver localized multi-DOF steering and orientation control at the tip itself, while remaining soft enough to reduce contact risk against vessel walls.
Solution
Designed a modular soft catheter composed of a passive flexible shaft and two hydraulically actuated soft modules: one for bending and one for torsion. By independently pressurizing the two modules through coaxial PTFE supply tubes, the catheter could bend and rotate at the tip in a decoupled way, allowing the user to orient the tip locally instead of transmitting rotational inputs through the entire shaft. Because both distal modules were built from hyperelastic silicone with fiber and fabric reinforcement, the tip remained compliant during contact, helping it conform to vessel walls instead of behaving like a rigid probing element. The result was a soft catheter architecture aimed at both safer vessel interaction and more controllable branch navigation through localized articulation and on-tip orientation.
Series integrated catheter design showing the C-shaped bending actuator, cylindrical torsional actuator, and coaxial tubing used for independent hydraulic control.
Design and Fabrication
The system was built around two custom soft actuators, each 20 mm long, integrated into a 3 mm OD catheter-scale platform. The bending actuator used a C-shaped silicone body with an internal lumen, reinforced by two counter wound polyester fibers at ±15° and an inextensible fabric layer on the flat side to suppress expansion and drive predictable directional curvature. The torsional actuator used a cylindrical silicone body reinforced by three evenly spaced helical fibers at 30°, converting hydraulic pressurization into axial rotation while limiting radial ballooning. Arranging the two modules in series created a compact, fully soft tip capable of independent bending and torsion, giving the catheter advanced motion capability without introducing rigid steering joints at the distal end.
Fabrication was organized as a repeatable molding workflow designed for small-scale soft actuator construction. A 3D printed positive mold was used to create a rigid negative mold, and the actuator bodies were cast around a 1 mm fiberglass core to form internal channels. The bending module used a 70/30 Dragon Skin 10 SLOW and Ecoflex mixture, while the torsional module used Dragon Skin 10 SLOW. To improve repeatability, custom 3D printed winding fixtures with preset fiber grooves were developed so reinforcement strings could be placed consistently across builds. The two actuators were then integrated in series with concentric PTFE tubing, bonded and sealed to create independently addressable hydraulic lines.
Repeatable manufacturing process using 3D-printed molds, fiberglass cores, and custom string-wrapping fixtures to cast and reinforce the soft actuators.
Validation followed a progression from actuator level characterization to integrated navigation. Motion characterization with a motorized syringe setup and vision tracking confirmed that the bending actuator could reach about 90° at 0.25 mL and the torsional actuator could reach 360° at 0.30 mL, establishing that the two soft architectures produced the intended decoupled motions. Force testing then showed up to 53.8 mN bending force and 1.3 mN·m torsional torque, demonstrating that the catheter tip could generate meaningful output in addition to large motion. Integrated demonstrations showed that the assembled catheter could achieve decoupled tip articulation and local orientation control with mounted tools, directly supporting the design goal of steering and aligning the tip without base rotation.
Benchtop test setup used vision markers and a motorized syringe system to measure bending angle, torsion angle, and repeatability.
Two catheter layouts demonstrated independent bending and axial rotation for on-tip orientation and multi-DOF articulation.
The final validation step focused on practical applicability in a vascular task. In a 3D printed aortic arch phantom, the catheter was successfully navigated into the left subclavian, left common carotid, and brachiocephalic arteries. During these trials, local bending and torsion were used to align and enter branches without base shaft rotation, and the soft tip conformed to the vessel wall during contact rather than resisting it rigidly.
The catheter was guided into three branches of a 3D printed aortic arch phantom using local bending and torsion without relying on base shaft rotation.
Related Publication
Soft robotic catheters enabled by miniaturized bending and torsional hydraulic soft actuators.
AfshariNejad, P., Lee, K., Vu, S., Penchala, A., Sevic, S., Manian, V., & Sheng, J. (2026).
2026 International Symposium on Medical Robotics (In press).