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Cardiovascular Engineering

Cardiovascular Engineering - Poster Session B

Poster H15 - Energy Harvesters: A Novel Approach to Leadless Pacemaker Battery Life​ Improvement

Thursday, October 24, 2024
2:45 PM - 3:45 PM EST
Location: Exhibit Hall E, F & G

Introduction:  One of the most crucial limiting factors of modern leadless pacemakers today is their battery life. Due to size constraints, their current battery life is around 8-13 years [1], forcing some patients to undergo repeated replacement procedures throughout their lives [2]. Our proposed device aims to house the pacemaker within a stent and utilize the deformations on the stent via expansion and contraction of the heart to recharge the pacemaker, increasing its lifespan. We would generate small voltages via electromagnetic induction, then condition this harvested energy and recharge the battery. Our team has created coupled electromagnetic fields and mechanical simulations to investigate the energy transfer and fatigue characteristics of various stent designs. We can confirm these findings with our benchtop mechanical and electrical test setup. Preliminary simulation data suggests that ring and bridge stent designs are better than unit cell stents to dissipate the radial stresses resulting from the expansion and crimping test. Our electrical simulations and circuit design indicated that a 10-millivolt peak-to-peak voltage cycle was sufficient to power our pacemaker and was confirmed with initial feasibility studies.

Materials and

Methods:  Several energy conditioning circuits were created with KiCAD and simulated with LTSpice. The assembled circuits were then tested with a function generator to simulate the generated input energy. Electrical signals were taken with an oscilloscope at various nodes of the circuits.

To further investigate the feasibility of inducing energy electromagnetically, we used ANSYS Maxwell for 3D dynamic simulations. Neodymium ring magnet models were created with a circular surface (loop of wire) moving between them. A parametric study was performed to calculate how the voltage changes as the loop moves from bottom to top.

For experimental verification of the mechanical transduction of energy, we employed 3D printing to create the test fixture and several scaled-up models of various stent designs. Two stepper motors were used to generate linear and torsional motions respectively to achieve coupled cyclical linear and rotational motions on the stent in a manner detailed by M. Lang [3].

We used ANSYS Workbench to conduct static structural simulations to test stent expansion and crimping parameters. The traditional multi-cell simulation setup was modified into a two-step, single-cell orientation to combine expansion and crimping into one seamless test. The one-cell approach would allow us to conduct stent fatigue analysis, which was not feasible in the multi-cell setup. Stent flat patterns were designed as surfaces in SolidWorks and fully processed in ANSYS SpaceClaim for meshing, contact definition, and physics setup. Two main types of stents were explored: ring & bridge stents and unit cell stents [4].

Results, Conclusions, and Discussions: The amplifier circuit was tested with physical components and achieved an output of 20V DC. The input voltage was a 10 Hz sine wave with a peak-to-peak amplitude of 10 mV. The +/- output ports of a triple output DC power supply at approximately 9V emulated the pacemaker battery and voltage inverter component.

Our electromagnetic simulations yielded a peak-to-peak voltage of approximately 43 millivolts. The calculation was based on a 100-turn coil, a conservative number, with the magnets moving a total distance of 10mm.

The development of our expansion & crimping simulations test allowed for initial stent design verification. Our main high-level test compared Ring & Bridge versus Unit Cell stents. The U-Ring and V-Ring stents were successfully expanded and crimped and produced similar principal stress values, which was expected. The Reentrant Auxetic unit cell stent failed the test, despite attempts to restructure the stent.

Our benchtop mechanical testing model employs both linear and rotational movement to mimic the contortion of the heart, allowing us to capture more acute stent behaviors impossible with simulations.

For electrical, we have demonstrated the feasibility of the project through the 43mV generation in our electrical simulation which is greater than the 10milivolt requirement we set within our actual circuit design to be able to power the pacemaker continually.

Preliminary testing data leads to the high-level favorability of Ring & Bridge stent designs over Unit Cell designs for their ability to withstand the radial forces of expansion and crimping. Furthermore, by modifying conventional stent simulation parameters, our model is also capable of performing fatigue analysis; a crucial component in determining overall stent design.

Our findings are extremely favorable for the future development of a rechargeable pacemaker. As we continue to develop testing methods, we have thus far demonstrated the viability of such a device. Its impact can result in future patients undergoing only a single operation, a life-changing development considering the edge cases of pediatric pacemaker cases. Additionally, for general pacemaker design, it allows for the slimming of the device by reducing necessary battery space allowing for easier surgical implantation and reduced blood flow disruption.

Acknowledgements (Optional):  

References:

1. Medtronic. (n.d.). *Micra pacing system*. Retrieved from https://www.medtronic.com/us-en/healthcare-professionals/products/cardiac-rhythm/pacemakers/micra-pacing-system.html



2. City Labs. (n.d.). *Pacemaker batteries*. Retrieved from https://citylabs.net/applications/pacemaker-batteries/#:~:text=Leadless%20pacemakers%20are%20typically%20not,take%20a%20couple%20of%20hours



3. Lang, R. M., Badano, L. P., Mor-Avi, V., Afilalo, J., Armstrong, A., Ernande, L., ... & Voigt, J.-U. (2015). Recommendations for cardiac chamber quantification by echocardiography in adults: An update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging. *Journal of the American Society of Echocardiography, 28*(1), 1-39.



4. Pan, C., Han, Y., & Lu, J. (2021). Structural design of vascular stents: A review. *Micromachines, 12*(7), 770. https://doi.org/10.3390/mi12070770