Batteryless, Wireless Stent Sensor Warns of Blockages in Bile Duct

Bile duct blockages can lead to jaundice, liver damage, and potentially life-threatening infections. Conditions that result in the narrowing and closure of bile ducts, such as pancreatic and liver cancers, may be treated by inserting stents to keep the ducts open. However, these stents can themselves become obstructed by bacterial sludge or gallstones, requiring urgent treatment with antibiotics and replacement of the stent. Currently, healthcare providers monitor biliary stent blockages using blood tests, which means that the issue must reach a significant level for the body to signal its presence. Researchers have now developed a new sensor for stents used in the bile duct that could help physicians detect and address stent blockages early, thereby improving patient health. This sensor can inform doctors of accumulating bacterial sludge and allow for intervention before the patient shows signs of illness.

Developed by researchers at the University of Michigan (Ann Arbor, MI, USA), the sensor measures 8 millimeters long—approximately half the diameter of a penny—and is 1 millimeter wide. It is housed in a protective, 3D-printed plastic structure that attaches to plastic stents. During a checkup, the patient would wear a belt-like detector around their waist that emits an alternating magnetic field, changing its sign at various frequencies to induce maximum, or resonant, vibration in the sensor. As the sensor vibrates, any masses adding weight to it are indicated by a lowered resonant frequency. One significant challenge was detecting this resonant frequency, which appears as a responding magnetic field emitted by the sensor, even through nearly 7 inches of fluid-rich abdominal tissue. Through careful hardware design and digital signal processing, the team achieved a signal-to-noise ratio of one million to one during their tests.

The design also enhances the communication range while minimizing signal feedthrough, ensuring that the sensor’s signaling and receiving ends do not interfere with each other. This is accomplished through time domain decoupling, where one end is suspended while the other operates and vice versa. Moving forward, the researchers plan to develop a version compatible with metal stents. In the long term, they aim to further miniaturize the sensor, allowing multiple sensors to be distributed along the stent, each with a different resonant frequency. This would facilitate localized detection of sludge buildup. Additionally, the team intends to create more affordable electronics for the belt-like detector, setting the stage for human clinical trials. As this technology evolves, magnetoelastic sensors could also be applied in other areas of the body, including peripheral vascular stents, long-term coronary stents, and ureteral stents.

"This novel stent sensor provides the opportunity to detect impending biliary stent obstructions without waiting for clinical symptoms, blood tests or imaging tests, all of which delay intervention," said Richard Kwon, a clinical professor of internal medicine and gastroenterology at the U-M Medical School and co-author of the study in Nature Microsystems & Nanoengineering.

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