Material selection strategies for inductive-resonant implantable bioelectronics

Implantable bioelectronic sensors enable minimally invasive and continuous monitoring of vital physiological parameters. For instance, inductive-resonance-based sensors integrated into stent grafts allow battery-free, real-time monitoring of hemodynamic conditions, offering a powerful tool for tracking the progression of diseases such as Abdominal Aortic Aneurysm, which affects over 35 million people worldwide. In such implantable sensing systems, wireless communication between an external readout circuit and the in-body sensor is typically achieved through magnetically coupled coils. Therefore, the choice of material for these coils is critical in determining key electromagnetic characteristics. Particularly, the quality factor could be used as an early indicator of coil performance and its applicability for an implantable, wireless sensing system. Copper, known for its excellent performance as coils, is commonly used during early-stage prototyping. However, its poor biocompatibility and susceptibility to oxidation make it unsuitable for long-term implantation devices. Consequently, alternative materials such as brass, stainless steel, and nitinol, each exhibiting unique electromagnetic and biocompatibility properties, must be evaluated for clinical applications. In this work, we present a comparative assessment of different metallic materials used in biomedical applications and their influence on the performance of sensors utilising inductive coils. The results provide insights into the trade-offs between electrical performance and biocompatibility and outline design strategies for optimizing inductive-resonant implantable sensors.