The patch is 240μm thick and stretches with strains up to 60%.
“Wearable devices have so far been limited to sensing signals either on the surface of the skin or right beneath it. But this is like seeing just the tip of the iceberg,” said Professor Sheng Xu. “By integrating ultrasound technology into wearables, we can start to capture a whole lot of other signals, biological events and activities going on way below the surface in a non-invasive manner.”
Variation in the diameter of blood vessels as deep as 40mm has been measured, according to the University. Tested on the neck, the array allowed pressure to be inferred in the carotid artery, internal jugular vein and external jugular vein. It was also tried on the forearm, wrist, neck and foot: “Tests were performed both while the subject was stationary and during exercise. Recordings collected with the patch were more consistent and precise than recordings from a commercial tonometer. The patch recordings were also comparable to those collected with a traditional ultrasound probe. And it can still get a good reading through fatty tissue.”
– A tonometer is a probe hand-held against the skin over the the blood vessel by trained medical staff.
For this part of the programme, which is described in the Nature Biomedical Engineering paper ‘Monitoring of the central blood pressure waveform via a conformal ultrasonic device‘, all processing was done externally through wires connected to the array.
Future plans include collaborating with engineers to integrating a power source, data processing units and wireless communication.
“If we want to move this from benchtop to bedside, we need to put all these components on board,” said Xu.