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UBC Theses and Dissertations

Wireless heating of resonant stent with micro circuit breaker for self-regulated endovascular hyperthermia treatment Chen, Jiaxu


In-stent restenosis remains the most common complication in stent implantation. Hyperthermia treatment through moderate heating of implanted stent is expected to be an effective treatment for restenosis. Toward this goal, this thesis presents a wirelessly powered resonant-heating stent device, with a focus on design improvement, experimental analysis of power transfer and electrothermal behavior, as well as safeguarded thermal regulation of the proposed device. The stent device, configured to form a passive resonator with a capacitor-integrated inductive stent, was coated with optimized layers of gold and Parylene C to improve the quality factor and heating performance of the device. Wireless testing results of the device deployed in artificial artery has shown its promising thermal performance in physiological saline with a flow rate relevant to stenotic blood flow, while revealing clear merits of resonant-based heating with up to ~220 and ~40 times higher heating rates than off-the-resonance conditions in air and saline flow, respectively. The wireless heating efficiency, as well as the effects of saline temperature and flow rate on the device performance along with other parameters are also studied in details based on the results. Finally, for the temperature regulation of the stent device, a thermal-sensitive MEMS circuit breaker (1900 × 700 × 605 µm3) with the function of a power switch is presented. The circuit breaker is fabricated using Nitinol shape memory alloy as a micro-actuator to have a cantilever beam that forms a closed power switch at low temperatures and open switch when the temperature reaches 65 - 69 °C. After integrated with the stent device, the circuit breaker chip is able to open or close the resonant circuit to prevent the stent device from overheating. The intended functionality of the circuit breaker has been verified from the electrothermal and thermomechanical behavior of the circuit breaker measured in this study. Preliminary experimental results in the wireless heating of the stent device with circuit breaker also indicate that the circuit breaker is capable of limiting the device temperature to be below the threshold.

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