Continuous Detection of Fluid Leaks Into the Body by Means of Partially Dissolvable Antennas

Internal fluid leaks in the human body can be caused by underlying medical disorders. Leakage may also be relevant to implanted stent grafts for the treatment of abdominal aneurysms. Indeed, blood may leak through the stent into the aneurysm sac with the risk of rupture due to increased internal pressure. As standard screenings cannot be performed frequently enough, this paper proposes wireless monitoring of fluid leaks into human body regions exploiting an implanted antenna partially coated by an engineered material and an auto-tuning IC in the UHF RFID band. The presence of fluid modifies the antenna impedance in a controlled way by the hydrolysis of the coating. An indication of this change can be obtained through radiofrequency interrogation from an external reader even when the antenna is implanted at 6 cm. Simulations and tests with a mock-up demonstrated the ability to distinguish the degradation of the bioresorbable coating. The sensor is responsive to up to 3.5 mm
$^{3}$
of dissolved coating, with a sensitivity of more 10 units
$/$
mm
$^{3}$
. Provided that the size of the coating has been properly engineered, the response of the sensor is robust w.r.t. the unpredictable interaction with the fluid.