Implantable Wireless Sensors for Three-Node Temperature Monitoring of Artificial Knee Joints

Monitoring the temperature changes around the artificial knee joint is of great significance for diagnosing periprosthetic infection after total knee arthroplasty (TKA). A comprehensive diagnosis relies on the in situ and multinode monitoring of the key components. To achieve long-term temperature monitoring of multiple locations around the artificial knee joint, we propose an implantable passive wireless LC temperature sensor capable of achieving three-node noninterference monitoring. By interrogating the resonant frequency and Q factor of the sensor in real-time, it is beneficial to realize in situ temperature monitoring of multiple positions around the artificial knee joint. In our experiments, we fabricated a single three-node temperature sensor based on the polyimide substrate and demonstrated that the measured temperatures of the three nodes are independent of each other. The average sensitivities of the three nodes are -30 kHz/°C, -26.6kHz/°C, and
$0.078\Omega / ^{\circ }\text{C}$
, respectively, from 36 °C to 50 °C. And the resolutions of the three nodes are 0.187 °C, 0.14 °C, and 0.258 °C respectively. This method paves the way for implanting wireless multinode sensors, where multinode sensing is able to provide more reliable judgments for medical diagnosis. In addition, our proposal can be extended to the measurement of other parameters of interest.