Magnetic steering continuum robot for transluminal procedures with programmable shape and functionalities

Abstract

Millimeter-scale soft continuum robots offer safety and adaptability in transluminal procedures due to their passive compliance, but this feature necessitates interactions with surrounding lumina, leading to potential medical risks and restricted mobility. Here, we introduce a millimeter-scale continuum robot, enabling apical extension while maintaining structural stability. Utilizing phase transition components, the robot executes cycles of tip-based elongation, steered accurately through programmable magnetic fields. Each motion cycle features a solid-like backbone for stability, and a liquid-like component for advancement, thereby enabling autonomous shaping without reliance on environmental interactions. Together with clinical imaging technologies, we demonstrate the capability of navigating through tortuous and fragile lumina to transport microsurgical tools. Once it reaches larger anatomical spaces such as stomach, it can morph into functional 3D structures that serve as surgical tools or sensing units, overcoming the constraints of initially narrow pathways. By leveraging this design paradigm, we anticipate enhanced safety, multi-functionality, and cooperative capabilities among millimeter-scale continuum robots, opening new avenues for transluminal robotic surgery.

Fig. 1. Schematic of the millimeter-scale magnetic steering continuum robot for transluminal procedures.

a Overview of the proposed continuum robot. Our robot consists of a couple of phase transition components (PTCs) named “Guider” and “Follower”. The Guider is assembled coaxially in a silicone tube bonded to the Follower, and its tip has an embedded tiny permanent magnet to respond to external magnetic fields. The low melting point alloy (LMPA) and the resistive heater are encapsulated by the silicone tube, and the hydrogel coating is grown on the surfaces of the Guider and Follower to reduce the friction coefficient significantly. b Schematic of our robot’s design principle. The shapes of the Guider and Follower are interlocked. In the motion cycle, the two PTCs alternate between solid and liquid, corresponding to the states of support and movement. c Under magnetic steering, the magnetic steering continuum robot shows excellent movement performance (i, ii, iii) and functionalities (iv, v, vi) in lumina or the relatively open cavities of organs.

Fig. 2. Preparation, structure analysis, and thermal management of the robot.

a Detailed preparation process. (i) Inject the molten LMPA into a silicone tube where a heating circuit has been pre-arranged. (ii) Cool the LMPA and encapsulate both ends of the silicone tube with glue. (iii) Remelt the encapsulated LMPA and pressurize the silicone tube to maintain force on LMPA, and obtain the phase transition component (PTC). (iv) Apply the hydrogel layer for lubrication. (v) Mount the permanent magnet to PTC to obtain the Guider. Axially bond a silicone tube to PTC to obtain the Follower. (vi) Assembly of the Guider and the Follower results in the proposed magnetic steering continuum robot. b The friction coefficient is dramatically reduced by applying hydrogel to the PTC surface. The embedded image is the schematic of the friction coefficient test. c In gravitational fields, limited by the elastic modulus of the material and the application purpose, the rigid PTC should be over 1 mm in diameter to constrain the other flexible PTC and maintain its shape. d Heat transfer simulation shows that a constant heating current maintained over 0.3 A or 0.9 A allows the LMPA to rapidly reach the phase transition temperature in gas or liquid environments. e Once one PTC is heated to flexible, the temperature of the other rigid PTC may exceed the phase transition temperature due to heat conduction; hence the need to control the heating temperature. The influence of the heated Guider’s stable temperature on the Follower was obtained by numerical simulation. f The mapping between temperature and absolute resistance change is established. g The Guider and Follower’s temperatures can be proportional-integral-derivative (PID) regulated in air and water (ambient temperature = 37 °C).

Fig. 3. Numerical control of the robot.

a Schematic of the experimental equipment. b The scenario was analyzed where the effect of gravity is most prominent: the softened Guider is placed horizontally as a cantilever beam under horizontal magnetic and vertical gravity fields. c Under the constant curvature assumption, the accessible area of the Guider (l ∈^, mm) is highlighted in blue at 30 mT magnetic flux density (γ ∈ [0, π] rad). The background color represents the tip deflection angle as indicated by the color bar in rad. d Our robot navigated under a series of pre-planned magnetic fields and formed a predetermined body shape. Adv. and Mag. abbreviations for advance and magnetic Field. Scale bars, 10 mm. e Comparison of the movement of the bine and our robot. Pictures document that the continuum robot curls around the support in an aqueous environment like a natural climbing plant: bine. Scale bars, 10 mm.

Fig. 4. Magnetic navigation in a complex environment.

a Schematic of the robot performing tasks through a highly unstructured environment. b Schematic of the working environment. The first layer with barriers is in the aquatic environment, and the second layer with a set of rings and a channel is in the air environment. There is a large angle between adjacent small rings. c The robot can pass through the unstructured environment without relying on interactions with it. First, the robot passes smoothly through the barriers on the first layer (0–5 min). Then it can navigate tortuous paths 1 (5–9 min) and 2 (9–18 min) to reach the region of interest. Scale bars, 10 mm.

Fig. 5. Formation of various functional structures.

a Schematic of the robot forming large functional structures upon passing through the narrow body lumen and reaching the relatively open space. The robot can form structures such as (b) the letters ‘B’, ‘M’, ‘C’, and ‘R’, (c) a lasso, and an antenna. d The lasso formed by the robot, capable of segmented variable stiffness, can be used for object capture. e Series of optical images document that the robot can form and tie three-dimensional knot patterns tightly. All scale bars, 10 mm. f The robot can tie itself into a knot for pressure detection. In contrast to radial deformation, the resistance of the PTC is non-sensitive to axial deformation. The Guider and Follower only deform axially during regular operation, which causes no interference with resistance-based real-time condition monitoring. The knot improves the robot’s sensitivity to radial deformation, enabling this robot to act as a pressure sensor for intestinal pressure detection.

Fig. 6. Magnetic navigation of the continuum robot with ultrasound imaging in a phantom aortic arch.

a Schematic illustration shows that the robot can create a channel through the arteriae radialis to the common carotid artery for cerebral vascular intervention. b The robot follows a planned path with little environmental interaction (top). At the same time, the probe repeatedly scans along this path (middle) to reconstruct the overall shape of the robot in the vascular network (bottom). Scale bars, 20 mm.

Fig. 7. Magnetic navigation of the continuum robot with endoscopic imaging for gastric treatment ex vivo.

a The robot can act as a motion unit with functional units attached. For example, equipped with minicameras, optical fibers, and manipulation channels, this robot can deliver drugs to stomach lesions. b The experimental environment of the gastric therapy on a porcine stomach. The numbered correspondence is (1) magnetic actuation system, (2) 4-DOF platform, (3) US imaging equipment, (4) advancement unit, and (5) porcine stomach. c The robot passed through the esophagus into the stomach. Then it found and reached stomach lesions with the help of an equipped minicamera. After spraying the drug around the lesion, another region was examined in the stomach. Images were taken by the on-board camera and a fixed camera in the porcine stomach.

Fig. 8. In/ex vivo experiments assisted by X-ray imaging.

a Schematic of the robot passing through the inferior vena cava into the superior vena cava or the right atrium under magnetic navigation. The thorax of a porcine cadaver is imaged by X-ray after angiography. b Series of radiographic images document the deployment of the robot in the vena cava and heart. Scale bars, 30 mm. c The deployment of the robot in the porcine stomach in vivo. d Positioned by X-ray imaging, the robot is navigated through the esophagus into the porcine stomach and forms the shape of a hook in vivo under the applied magnetic field. Scale bars, 40 mm.