Wireless blood flow sensor wraps around arteries, self-resorbs

January 14, 2019 // By Julien Happich
Using exclusively bio-compatible and bio-degradable materials, researchers from the University of Stanford have devised a capacitive-based artery blood-flow sensor which can be read out wirelessly once implanted, and which does not require removal as it self-resorbs after a few months of operation.

The thin flexible device described in a paper titled "Biodegradable and flexible arterial-pulse sensor for the wireless monitoring of blood flow" published in Nature Biomedical Engineering was designed to locally monitor blood flow after complex reconstructive surgeries involving "anastomosis", the suturing of blood vessels, such as would be the case in cardiovascular, vascular and transplantation operations.

So far, commercially existing sensor require careful fixation and also need to be removed after use, which presents an additional surgical risk. The paper describes a thin and flexible pressure sensor made entirely of biodegradable materials, which can be wrapped around arteries as small as 1mm in diameter.

Arterial pulsations affect vessel diameter which can
measured by the biodegradable capacitive pulse sensor
wrapped around the artery. Changes in capacitance
result in a shift of the fundamental frequency of the LCR circuit,
which can be interpreted as blood flow measurements.

Measuring only a few square millimetres, the whole device consists of a layered fringe-field capacitive sensor sensitive in both contact (the sensor is put in contact with the artery) and non-contact modes, connected to a bilayer coil structure (made of magnesium) used for data transmission through radio-frequency coupling with an external reader coil.

Close-up illustration of the sensor with an exposed view
of the bilayer coil structure for wireless data transmission
and the cuff-type pulse sensor wrapped around the artery.

Here, blood flow is indirectly measured through pulse detection as the monitored artery experiences pulsatile changes of vessel diameter which can measured by the capacitive sensor. The change in capacitance results in a shift of the resonant frequency in an inductor–capacitor–resistor circuit, which is monitored wirelessly through the skin via inductive coupling, enabling battery-free operation.

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