Prosthetic vascular grafts are now common implants that surgeons have gotten pretty good at performing. Nevertheless, complications do arise and the newly implanted grafts often get damaged or occluded, requiring a surgical redo. Continuously knowing the condition of the graft after the patient is sutured up would provide a way to prevent serious complications and help treat any problems in the developing stages.

Researchers at A*STAR Institute for Microelectronics, Singapore have developed a tiny sensor that can be placed inside the graft to monitor blood flow. Because it is so small, an on-board battery would have been impractical as the power source. Instead, the team used an inductive system to provide battery free, wireless power to the implant. Seeing how the technology is finding use in such a tiny implant, it should be readily translatable to power other medical implants.

From the study abstract in IEEE Transactions on Biomedical Engineering:

The microsystem integrates silicon nanowire (SiNW) sensors with tunable piezoresistivity, an ultralow-power application-specific integrated circuit (ASIC), and two miniature coils that are coupled with a larger coil in an external monitoring unit to form a passive wireless link. Operating at 13.56-MHz carrier frequency, the implantable microsystem receives power and command from the external unit and backscatters digitized sensor readout through the coupling coils. The ASIC fabricated in 0.18-μm CMOS process occupies an active area of 1.5 × 1.78 mm$^2$ and consumes 21.6 μW only. The sensors based on the SiNW and diaphragm structure provide a gauge factor higher than 300 when a small negative tuning voltage (−0.5–0 V) is applied. The measured performance of the pressure sensor and ASIC has demonstrated 0.176 mmHg/√Hz sensing resolution.