Ultrasound Chip Beneath the Skin Tracks Blood Pressure in Real Time

Blood pressure changes constantly throughout the day, spiking during a stressful meeting, dipping during sleep, surging during exercise. Yet most people with hypertension only catch a glimpse of those shifts when they strap on a cuff at home or sit in a clinic. Now researchers have built a device small enough to slip under the skin and watch an artery flex with every heartbeat, reconstructing blood pressure waveforms that rival the precision of intensive care monitoring.

The implant, described in Microsystems & Nanoengineering, uses ultrasound to measure how much a blood vessel expands and contracts as pressure rises and falls. In tests on a freely moving sheep, the 5-by-5-millimeter sensor array tracked systolic pressure within 1.2 mmHg and diastolic pressure within 2.9 mmHg of a gold-standard arterial line. The device picked up features like the dicrotic notch, the small dip in the waveform that marks the closing of the heart’s aortic valve.

At its core sits a dense grid of piezoelectric micromachined ultrasonic transducers, or PMUTs. These tiny sensors emit high-frequency sound waves and listen for echoes bouncing off the front and back walls of an artery. Because blood and arterial tissue reflect sound differently, the chip can pinpoint both surfaces. As the vessel swells with each pulse of blood, the time between echoes shifts slightly. That timing difference is the signal the device translates into pressure.

Why Placement Under the Skin Matters

Wearable ultrasound patches already exist, but they struggle with a persistent problem: if the sensor shifts by even a millimeter, signal strength can plummet by 60 percent. Implanting the array just beneath the skin keeps it locked in position above the artery. During the sheep trial, surgeons coated the chip in a 4-millimeter layer of polydimethylsiloxane, a soft, biocompatible polymer that protects the electronics from moisture and movement. They even flushed the implant site with saline to remove air bubbles that could interfere with ultrasound transmission.

The subcutaneous approach also sidesteps a common failure mode for long-term implants. As the body’s immune system deposits tissue around foreign objects, many sensors lose accuracy. This device measures the interval between echoes, which remains stable even if a thin layer of tissue develops over the transducers. In practice, that means the implant could keep working for months or years without recalibration.

“The study shows that ultrasound-based implants can achieve the stability and precision required for continuous blood pressure monitoring without the drawbacks of cuffs or fragile wearables,” Liwei Lin explains.

Continuous Data, Silent Operation

The sheep walked freely during testing, allowing researchers to validate the system under real-world conditions rather than on an anesthetized animal strapped to a table. The implant captured clear waveforms that matched the arterial line’s readings across multiple sessions. Because it monitors silently, the device could eventually help doctors spot dangerous spikes that occur during sleep or physical activity, moments when patients rarely check their blood pressure.

The team emphasized that further trials are needed before the technology moves to humans, but the sheep data suggest clinical-grade accuracy is achievable. If the implant translates successfully, it could give clinicians hour-by-hour feedback on how medications are working, reveal patterns that periodic cuff readings miss, and help patients understand what their cardiovascular system is doing when no one is watching. For now, the device offers a proof of concept: blood pressure monitoring can be continuous, precise, and nearly invisible.

Microsystems & Nanoengineering: 10.1038/s41378-025-01019-w