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Device Technologies and Biomedical Robotics

Device Technologies and Biomedical Robotics - Poster Session A

Poster I15 - An esophageal stent with an integrated wireless peristaltic pump for preventing aspiration

Thursday, October 24, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  The transport of viscous fluids and solids plays a pivotal role in various biological processes facilitated by peristalsis within structures like the esophagus, small intestine, and fallopian tube. Peristalsis is a wave-like motion of the muscles in the human lumen that efficiently transports fluid and solid cargo. The impairment of peristalsis in various diseases can result in luminal occlusion. Particularly, esophageal tumors can obstruct the lumen, hindering the passage of food and liquids. Treatment often involves metal esophageal stents which maintain an open passage in the narrowed portion of the esophagus. However, food particles or other materials may accumulate around the stent, leading to blockages, and in some cases aspiration when the food enters the airway causing inflammation. Compact and wirelessly actuated soft robotic pumps designed for transporting cargoes can be integrated in medical stents to potentially overcome these challenges. Soft robotic pumps, powered by various soft actuators have been shown before but have not been successfully integrated into medical stents due to the extensive size of external compressors and/or batteries, as well as the demand for flexible circuits sufficient for the compact luminal space. We propose a magnetically actuated soft robotic pump that can restore peristalsis through magnetically actuated sheets within a stent. Wireless actuation using external magnetic fields eliminates the need for bulky on-board components, ensuring the safe interaction of the soft robotic structure with esophageal tissue. Finally, we demonstrate this device in a modular, 3D-printed esophageal phantom to mimic in vivo pressure conditions and potential for aspiration.

Materials and

Methods:  Fabrication of Magnetic Sheets on a Metal Mesh Esophageal Stent
Ecoflex 00-30 was combined with NdFeB particles at a weight ratio of 1:2. This mixture was spread onto an acrylic substrate with PET tape boundaries and cured at 70 °C. Using a UV laser cutter, a 12 x 6 array of magnetic modules was prepared. One of the 12-module strips were isolated, wrapped around a cylindrical fixture, and placed in an impulse magnetizer for a magnetic field impulse of 2.3 T and a maximum discharging voltage of 300 V. To create one magnetic soft sheet, twelve modules were adhered to an existing Ecoflex 00-30 back layer with 1 mm spacing. The back layer was then margined to a 0.5 mm fin length and a 4 mm anchor. After preparing n=10 such magnetic sheets, the fin of each was adhered to a separate 0.2 mm thick Ecoflex 00-30 substrate. This substrate was then rolled cylindrically, lubricated with glycerol, and deployed into a metal mesh stent with additional Ecoflex 00-30 for bonding.

Preparation of an Esophagus Phantom
An esophagus phantom designed in Autodesk MeshMixer and Fusion360 (Autodesk Research) from a modified human upper gastrointestinal model. UV curable resin (Elastic 50A, Formlabs Inc.) was used to 3D print segmented parts of the phantom. These parts were later united with additional UV-curable resin and UV exposure.

Results, Conclusions, and Discussions: Single Magnetic Sheet Achieves Undulating Motion
Magnetic torque through the long axis of the sheet bends the magnetic modules. An applied rotating magnetic field (B = 55 mT, avg; f = 2 Hz) induced an undulating motion in a single sheet. Extracting the undulating sheet kinematics, the peak of the curve was found to shift along the sheet each period, indicating a propagating wave of modules that bends sequentially with the fully-programmable phase lag.

Pairwise Sheets Pumping Liquids and Solids
A pair of magnetic sheets were induced to have coordinated, peristaltic-like motion. A 3π/4 phase difference between the two sheets allowed for these mechanics. Extracted kinematics show a narrow stricture traveling vertically within the rotating magnetic field. The maximum flow rate for both liquid and solid pumping ( < 30 s traversal) was achieved with a 3π/4 phase difference.

Integrating Magnetic Sheets Inside a Medical Stent for Pumping
Integrating a circular array of n=9 magnetic sheets into a medical mesh stent, the sheets were shown to provide radial support and achieve solid and liquid pumping. Point-of-care X-ray imaging was used to monitor the sheets in a phantom. An endoscope and hydrogel beads were used to demonstrate clearance of a simulated food blockage, a common issue with previous esophageal stents.

Conclusion
This work presents a novel soft robotic medical stent, which achieves a peristalsis-like motion by coordinating magnetically-actuated sheets. The resulting undulation, which is fully programmable, has been shown to coordinate pairwise pumping in just 30 s. Additionally, a 3D-printed esophageal phantom was developed to characterize the wireless peristaltic pump in the metal stent. Finally, an esophageal stent with solid pumping ability was demonstrated to clear simulated food blockages for preventing aspiration when the blocked food goes into the airway causing inflammation.

Discussion
Advanced fabrication methods may scale down the wireless pump for narrower medical stents, such as for tubal cannulation of the female oviduct. To improve the esophageal phantom, composite materials of various rigidities may more accurately model the variegated tissue properties in the human esophagus. Finally, a wearable magnetic actuation system could offer long-term, at-home control of the esophageal stent.

Acknowledgements (Optional):