A wearable ultrasound “sticker” that enables high-quality, continuous medical imaging of internal organs and tissues for up to 48 hours has been developed by researchers from MIT. The stickers may lead to improved diagnostic and monitoring technologies for various diseases and provide new insights into developmental biology.

The work was led by Xuanhe Zhao, PhD, professor of mechanical engineering and civil and environmental engineering at MIT, and was published in Science (“Bioadhesive ultrasound for long-term continuous imaging of diverse organs”).

“The current paradigm . . . is to make [wearable ultrasound] devices thin and stretchable for conformal attachment on the body,” the researchers wrote. Although stretchable ultrasound imaging devices are comfortable to wear, they still suffer from limitations, including low imaging resolution, unstable image quality during body movement, short imaging duration (~1 hour), and susceptibility to device failure.

“Here, we propose a different paradigm for biointegration: to robustly adhere thin and rigid devices on the body via a soft, tough, and bioadhesive couplant,” they continued.

Their sticker, which they call a bioadhesive ultrasound (BAUS) device, overcomes many of these limitations. It consists of a thin and rigid probe that adheres to the skin with a durable, stretchy material that is also soft and comfortable.

 “This combination enables the device to conform to the skin while maintaining the relative location of transducers to generate clearer and more precise images,” said Chonghe Wang, a graduate student at MIT and the first author on the paper.

The device’s adhesive layer is made from two thin layers of elastomer that encapsulate a middle layer of solid hydrogel, a mostly water-based material that easily transmits sound waves. Unlike traditional ultrasound gels, the MIT team’s hydrogel is elastic and stretchy.

“The elastomer prevents dehydration of hydrogel,” explained Xiaoyu Chen, PhD, an MIT postdoc and co-author on the study. “Only when hydrogel is highly hydrated can acoustic waves penetrate effectively and give high-resolution imaging of internal organs.”

The bottom elastomer layer is designed to stick to skin, while the top layer adheres to a rigid array of transducers that the team also designed and fabricated. The entire ultrasound sticker measures about 2 cm2 across and 3 mm thick.

The team of researchers tested the devices on volunteers, who wore the stickers on various parts of their bodies, including the neck, chest, abdomen, and arms. The devices produced live, high-resolution images of major blood vessels and deeper organs such as the heart, lungs, and stomach. They maintained strong adhesion and captured changes under various environmental conditions and for different patient movements, including jogging, drinking fluids, and lifting weights.

From the stickers’ images, the team was able to observe the changing diameter of major blood vessels when seated versus standing. The stickers also captured details of deeper organs, such as how the heart changes shape as it exerts during exercise. The researchers were also able to watch the stomach distend, then shrink back as volunteers drank then later passed juice out of their system. And as some volunteers lifted weights, the team could detect bright patterns in underlying muscles, signaling temporary microdamage.

The current design requires connecting the devices to instruments that translate the reflected sound waves into images. But if the devices can be made to operate wirelessly—a goal the team is currently working toward—they could be made into wearable imaging products that patients could take home from a doctor’s office.

“We envision a few patches adhered to different locations on the body, and the patches would communicate with your cellphone, where AI algorithms would analyze the images on demand,” said Zhao. “We believe we’ve opened a new era of wearable imaging: With a few patches on your body, you could see your internal organs.”

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