Implantable Blood Sensor With Wirelessly Powered Microchip Developed

Scientists in Singapore developed a microscale electronic sensor that can be implanted under the skin and is connected by wireless data and power to continously monitor blood flow through artificial blood vessels. The prototype device, constructed by researchers at A*STAR Institute of Microelectronics in Singapore, measures the blood-pressure with piezoresistive silicon nanowires and eliminates the need to recharge or replace a battery, and would of course reduce the number of necessary check-ups and clinic visits for patients.

The device would be especially important to monitor prosthetic (blood vessel) grafts, which are implanted by surgeons to bypass diseased or clogged blood vessels in patients experiencing restricted blood supply, for example. Over time, however, the graft can also become blocked. To avoid complete failure, blood flow through the graft must be monitored regularly, but existing techniques are slow and costly.

Monitoring blood flow rate inside prosthetic vascular grafts enables early detection of graft degradation and prevention of graft failure.

The new implantable device will be powered by a handheld external reader, which wirelessly transfers the data but at the same time also uses inductive coupling to wirelessly transfer energy. The scientists developed an ultralow-power application-specific integrated circuit (ASIC) for the implant designed for low-power (21.6 μW) use, to make the sensor system compatible with the low power density available in such a compact device supplied by inductive electricity within the body.

The actual sensor works by blood flowing over piezoresistive silicon nanowires. The associated mechanical stresses induce a measurable increase in electrical resistance, proportional to the flow pressure.

"Our flow sensor system achieves an ultra-low power consumption of 12.6 microwatts," said A*STAR's Jia Hao Cheong, who heads the project. To achieve that the sensor transmits its data to the handheld reader passively, similar to the now common RFID chips integrated in many products and devices, by backscattering some of the incoming energy. "We have tested our system with 50-millimeter-thick tissue between the external coil and implantable coil, and it successfully extracted the pressure data from the implantable device."

"The next step of the project is to integrate the system and embed it inside a graft for an experimental animal," Cheong said.

Paper:

Cheong, J. H. et al., An inductively powered implantable blood flow sensor microsystem for vascular grafts, IEEE Transactions on Biomedical Engineering, 2013, DOI: 10.1109/TBME.2012.2203131