Shape-Shifting Ultrasound Stickers to Monitor Post-Surgical Complications

Northwestern University, Cook County, IL

Three variations of the ultrasound sticker displayed on a fingertip for scale. (Image: Northwestern University)

Researchers led by Northwestern University and Washington University School of Medicine in St. Louis have developed a first-of-its-kind sticker that enables clinicians to monitor the health of patients’ organs and deep tissues with a simple ultrasound device.

When attached to an organ, the soft, tiny sticker changes in shape in response to the body’s changing pH levels, which can serve as an early warning sign for post-surgery complications such as anastomotic leaks. Clinicians then can view these shape changes in real time through ultrasound imaging.

Currently, no existing methods can reliably and non-invasively detect anastomotic leaks — a life-threatening condition that occurs when gastrointestinal fluids escape the digestive system. By revealing the leakage of these fluids with high sensitivity and high specificity, the non-invasive sticker can enable earlier interventions than previously possible. Then, when the patient has fully recovered, the biocompatible, bioresorbable sticker simply dissolves away — bypassing the need for surgical extraction.

The study was published in the journal Science. The paper outlines evaluations across small and large animal models to validate three different types of stickers made of hydrogel materials tailored for the ability to detect anastomotic leaks from the stomach, the small intestine and the pancreas.

“These leaks can arise from subtle perforations in the tissue, often as imperceptible gaps between two sides of a surgical incision,” said Northwestern’s John A. Rogers, who led device development with postdoctoral fellow Jiaqi Liu. “These types of defects cannot be seen directly with ultrasound imaging tools. They also escape detection by even the most sophisticated CT and MRI scans. We developed an engineering approach and a set of advanced materials to address this unmet need in patient monitoring. The technology has the potential to eliminate risks, reduce costs and expand accessibility to rapid, non-invasive assessments for improved patient outcomes.”

Rogers’ team devised an approach to use tiny sensor devices designed to be readable by ultrasound imaging. Specifically, they created a small, tissue-adhesive sticker out of a flexible, chemically responsive, soft hydrogel material. Then, they embedded tiny, paper-thin metal disks into the thin layers of this hydrogel. When the sticker encounters acidic fluids, such as stomach acid, it swells. When the sticker encounters caustic fluids, such as pancreatic fluids, it contracts. As the hydrogel swells or shrinks in response to changing pH, the metal disks either move apart or closer together, respectively. Then, the ultrasound can view these subtle changes in placement.

Rogers team constructed stickers of varying sizes. The largest sticker measures 12 mm in diameter, while the smallest is just 4 mm in diameter. Considering that the metal disks are each 1 mm or smaller, Rogers realized that it might be difficult for radiologists to assess the images manually. To overcome this challenge, his team also developed software that can automatically analyze the images to detect with high accuracy any relative movement of the disks.

“Right now, there is no good way whatsoever to detect these kinds of leaks,” said gastrointestinal surgeon Dr. Chet Hammill, who led the clinical evaluation and animal model studies at Washington University with collaborator Dr. Matthew MacEwan, an Assistant Professor of Neurosurgery. “The majority of operations in the abdomen — when you have to remove something and sew it back together — carry a risk of leaking. We can’t fully prevent those complications, but maybe we can catch them earlier to minimize harm. Even if we could detect a leak 24- or 48-hours earlier, we could catch complications before the patient becomes really sick. This new technology has potential to completely change the way we monitor patients after surgery.”

Rogers and Hammill imagine that the device could be implanted at the end of a surgical procedure. Or, because it’s small and flexible, the device also fits (rolled up) inside a syringe, which clinicians can use to inject the tag into the body.

“It’s obviously an early prototype, but I can envision the final product where, at the end of surgery, you just place these little patches for monitoring,” Hammill said. “It does its job and then completely disappears. This could have a huge impact on patients, their recovery time and, ultimately, their quality of life.”

Next, Rogers and his team are exploring similar tags that could detect internal bleeding or temperature changes. “Detecting changes in pH is a good starting point,” Rogers said. “But this platform can extend to other types of applications by use of hydrogels that respond to other changes in local chemistry, or to temperature or other properties of clinical relevance.”

For more information, contact Amanda Morris at This email address is being protected from spambots. You need JavaScript enabled to view it.; 847-467-6790.