RF-Powered Stent With Integrated Circuit Breaker for Safeguarded Wireless Hyperthermia Treatment

This paper presents a wireless, electrothermally active stent with an integrated temperature limiter toward the application to endohyperthermia treatment of restenosis, a major post-stenting complication. A stent-based resonant circuit serves as a frequency selective wireless heater controlled using a tuned radio-frequency (RF) electromagnetic field radiated externally, applying local thermal stress to the stented site to suppress in-stent restenosis. A biocompatible 1.5 × 2 × 0.6-mm
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chip of micro circuit breaker with an embedded capacitor is developed and integrated with the stent to establish the resonant circuitry with a series-connected micro breaker. A micromachined shape-memory-alloy cantilever serves as a thermoresponsive switch in the chip that opens/closes the circuit depending on the stent temperature, automatically preventing the stent from overheating in a fully passive manner. Wireless heating tests of the prototypes deployed into artificial artery using commercial balloon catheters demonstrate the designed function of the circuit breaker, regulating the stent temperature within 50 °C-66 °C when excited in air at an output RF power of 320 mW, which heats the device to 78 °C without the breaker. Their performance in physiological saline is also tested and discussed in detail. The experimental results validate the device concept and approach toward enabling reliable and safeguarded hyperthermia treatment through wireless stents.