Engineers at MIT in the US have developed a wearable ultrasound patch that can easily monitor patients for up to two days.
The stamp-sized patch uses a rigid array of piezoelectric transducers on a flexible adhesive substrate.
This acoustically transparent hydrogel elastomer layer is the key to using ultrasound for the patch. It 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 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 2cm2 and is 3mm thick and follows on from work in 2018:
The researchers ran the ultrasound sticker through a battery of tests with healthy volunteers, who wore the stickers on various parts of their bodies, including the neck, chest, abdomen, and arms. The stickers stayed attached to the skin and produced clear images of underlying structures for up to 48 hours. During this time, volunteers performed a variety of activities in the lab, from sitting and standing, to jogging, biking, and lifting weights.
From the 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 devices currently need a wired connection for monitoring, but could be applied to patients in the hospital, similar to heart-monitoring EKG stickers, and could continuously image internal organs without requiring a technician to hold a probe in place for long periods of time.
“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,” says the study’s senior author, Xuanhe Zhao, professor of mechanical engineering and civil and environmental engineering at MIT. “We believe we’ve opened a new era of wearable imaging: With a few patches on your body, you could see your internal organs.”
The study also includes lead authors Chonghe Wang and Xiaoyu Chen, and co-authors Liu Wang, Mitsutoshi Makihata, and Tao Zhao at MIT, along with Hsiao-Chuan Liu of the Mayo Clinic in Rochester, Minnesota.
“Wearable ultrasound imaging tool would have huge potential in the future of clinical diagnosis. However, the resolution and imaging duration of existing ultrasound patches is relatively low, and they cannot image deep organs,” says Chonghe Wang, an MIT graduate student.
The MIT team’s new ultrasound sticker produces higher resolution images over a longer duration by pairing a stretchy adhesive layer with a rigid array of transducers. “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 Wang.
“The elastomer prevents dehydration of hydrogel,” says Chen, an MIT postdoc. “Only when hydrogel is highly hydrated can acoustic waves penetrate effectively and give high-resolution imaging of internal organs.”
“With imaging, we might be able to capture the moment in a workout before overuse, and stop before muscles become sore,” says Chen. “We do not know when that moment might be yet, but now we can provide imaging data that experts can interpret.”
The team is working on a wireless connection to turn the ultrasound stickers into wearable imaging sensors that patients could take home from a doctor’s office or even buy at a pharmacy.
They are also developing software algorithms based on artificial intelligence that can better interpret and diagnose the stickers’ images. Then, Zhao envisions ultrasound stickers could be packaged and purchased by patients and consumers, and used not only to monitor various internal organs, but also the progression of cancer tumours, as well as the development of fetuses in the womb.
“We imagine we could have a box of stickers, each designed to image a different location of the body,” Zhao says. “We believe this represents a breakthrough in wearable devices and medical imaging.”
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