Magnetically Actuated Catheter for Bronchoscopic InterventionsFollow project
|4||Bright Zinc Plated Steel Plain Washer, 0.8mm Thickness, M4||525-925|
|5||RS PRO, M6 Countersunk Head, 60mm Steel Pozidriv Bright Zinc Plated||908-7567|
|7||18mm Bright Zinc Plated Steel Coupling Nut, M6||276-522|
|7||Bright Zinc Plated Steel Plain Washer, 1.6mm Thickness, M6||525-947|
|1||Wurth Elektronik Ferrite, Rubber Shielding Sheet, 330mm x 210mm x 0.5mm||736-2140|
|4||RS PRO, M4 Pan Head, 16mm Steel Pozidriv Bright Zinc Plated||553-554|
|4||RS PRO Steel Hex Nut, Zinc Plated, M4||201-0850|
|7||RS PRO Steel Hex Nut, Zinc Plated, M6||201-0852|
|2||M6 Countersunk Head, 16mm Steel Pozidriv Bright Zinc Plated||-|
|1||Suction Catheter 16f 53cm Funnel Type (Single) Orange - Sterile||-|
|1||5mm dia x 20mm thick N42 Neodymium Magnet - 1.1kg Pull|
|8||40 x 20 x 5mm thick Ultra High Performance N52 Grade Neodymium Magnet - 15.1kg Pull|
|1||50 x 50 x 25mm Ultra high Performance N52 Neodymium Magnet - 116kg Pull|
Catheters are used in various clinical applications, and being able to steer the catheter to the target location is very important to the procedure's clinical outcome. Steerable catheters allow clinicians to reach the target organ without damaging surrounding tissue, particularly vascular bundles and major vessels. We hypothesized that a new catheter actuation method based on three magnetic couples would enable catheter steering in clinical procedures. Our method is simple, based on three magnets interacting with each other to create two-dimensional motions. A proof-of-concept prototype is presented in this manuscript along with an analysis of the catheter’s position and force during steering. Tests of the proposed actuation method demonstrate the possibility of manipulating a catheter wirelessly with the desired manoeuvrability for different clinical applications and manufacturing a catheter with this three magnet couples method is possible. Follow-up studies will include investigating the presented mechanism's kinematics and developing a closed-form solution for catheter steering regardless of different design parameters.
Concept and Design
Our idea was inspired by the "tractor beam,” a fictitious gadget used to move items from a long distance in E.E. Smith's 1931 science fiction book Spacehounds of IPC.
A tractor beam magnet, also called an inverter magnet, consists of an array of magnets. A single magnetic field is created in this system, and another magnet called the follower magnet is placed at a predetermined distance. As the name implies, the follower magnet follows the movement of the inverter magnet. A simple experiment can be conducted to test this phenomenon. First, place an inverter magnet and another magnet (which will be the follower magnet) on opposite sides of a table. Then bring the inverter magnet closer to the follower magnet until the follower magnet begins to move. Normally, two magnets would either repel each other or collide depending on their orientation. In contrast, the inverter magnet and follower magnet maintain a steady spacing. When the inverter magnet is moved over the table’s surface, the follower magnet follows as if they were connected with a hard chain even though the magnets are only coupled by magnetic forces.
Figure 1: New arrangement idea of the inverter magnet.
Based on the existing design of the inverter magnet, which uses a cylinder shape magnet, we formed an idea of how we could alter the arrangement to be suitable for catheter actuation (Figure 1). We hypothesized that if we moved the co-lead magnets closer together, the follower magnet would move further, and if we moved the co-lead magnets further apart, the follower magnet would move closer to the inverter magnet. We believed that with this arrangement, we would be able to control the distance of the follower magnet. To prove the idea, we placed three magnets on a table, used tape to stick the lead magnet to the table, and moved the two co-lead magnets by hand. This test can be found in Figure 2.
Figure 2: First idea verification.
After this test, we designed and constructed the first simple prototype. The prototype consisted of an acrylic sheet, chopstick, shielding sheet, and magnets. First, we cut the acrylic sheet into pieces and stuck them to the magnet using a glue gun. Next, we stuck the shielding sheet to two acrylic sheets, which we attached to the co-lead magnets to reduce the magnetic strength while moving the magnets by hand. The follower magnet was attached to the tip of a chopstick to mimic a catheter during surgery. We then tested whether the follower magnet could move upward and downward on the y-axis. The prototype was successful because the follower magnet and chopstick moved up and down through the y-axis.
Figure 3: First prototype.
Then, we designed the second prototype in SolidWorks, as seen in Figure 4. Our goal for this prototype was for it to move the follower magnet in both the x-axis and y-axis. We printed each part of the model using a 3D printer and assembled the parts to hold the magnets. We inserted a small magnet into a 5 mm catheter and placed it above the prototype (Figure 5).
Figure 4: SolidWorks design of the second prototype. (a) Front view. (b) Side view.
Figure 5: Second prototype. (a)Front view. (b)Side view.
When we moved the two co-lead magnets closer to each other and farther away from each other, the lead magnet controlled the follower magnet to move in the x-axis and y-axis and to levitate 7–10 cm in the air (Figure 6).
Figure 6: Distance between Co-Lead Magnets vs. Distance between lead and follower magnets graph
Conclusion and Future Works
This project proves that the inverter magnet has the potential to be used in medical applications. According to our idea verification, a catheter attached to a magnet can move in both the x-axis and y-axis. In future works, a better and more robust version of the prototype will be designed. Furthermore, we have already printed out a lung airway model using a 3D printer (Figure 6) to test the inverter magnet’s ability to manipulate a catheter for lung interventions.
Figure 7: 3D printed lung airway model (a) CAD drawing and (b) 3D printed prototype.