A Life-Saving Sticker

Image courtesy of Kiera Suh.

Diagnosing diseases can be tricky. How can doctors tell if a headache stems from a lack of sleep or something more serious? How can they see what is happening inside a patient? Peering inside the body can provide valuable, life-saving information for clinicians. Among the different imaging techniques, ultrasound—a non-invasive, risk-free diagnostic tool—stands out as a leading option. Researchers at the Massachusetts Institute of Technology (MIT) have developed a small, adhesive device that may revolutionize ultrasound technology.

Ultrasound devices use sound waves to create a picture of internal organs and tissues. An ultrasound probe emits high-frequency waves, which can travel through soft tissues but bounce off harder structures. An image is then created by a computer using these echoes. Thanks to its lack of radiation, ultrasound is the safest imaging tool, making it an ideal choice for continuous monitoring. However, current ultrasound devices are bulky and require an experienced clinician to operate the handheld probe. The clinician can only obtain a few images or videos in a regular ultrasound appointment, which typically lasts less than thirty minutes. Continuous imaging to monitor internal changes as the body moves on a day-to-day basis is not an option.

The team at MIT was able to transform the standard bulky, handheld ultrasound into a simple sticker by developing a brand-new bioadhesive that can comfortably attach a small ultrasound probe to the skin. The resulting bioadhesive ultrasound (BAUS) device can be attached to the body for up to forty-eight hours at a time to take high-quality images and videos of our body’s activities—blood vessels contracting, lungs expanding, stomachs digesting, and hearts pumping. The BAUS device can comfortably move with the person and capture the human body’s natural dynamism.

“Wearable ultrasound equipment can potentially revolutionize medical imaging,” said Xuanhe Zhao, professor of mechanical engineering and civil and environmental engineering at MIT, who co-authored the Science paper that describes the BAUS device. “Medical imaging is very important for diagnostic purposes. However, with existing medical imaging, the timescale is short. It’s usually a few seconds or minutes—just a snapshot.” Continuous and frequent imaging of internal organs, over days or even months, could help clinicians more effectively monitor the health of patients and observe how diseases progress. It could also provide invaluable new data about the human body and lead to discoveries in medicine and biology.

The biggest challenge has been comfortably attaching an ultrasound probe to the body. “It’s really [about] how you can integrate the ultrasound device with the body so it can give you long-term continuous imaging over days even under dynamic body motion,” Zhao said. Previous wearable ultrasound devices were designed to be stretchable and move with the skin. However, this design sacrificed image quality and resolution despite the improved wearability. Moreover, sound transmission is vital to reach deep organs, such as the heart or stomach, and accurately image them. When using traditional ultrasound devices, clinicians apply a gel layer to prevent air pockets that can block the transmission of sound waves through the skin. However, these gels are not designed for prolonged use. “The liquid gel, if you put it in contact with the body, it can potentially cause acidification in a few hours,” Zhao explained. Wearable ultrasound devices have used hydrogels––a water-rich, goo-like substance––in the past to solve this problem, but they get dehydrated and detach after only a couple of hours. Other devices use a rubbery material called an elastomer to attach the device to the skin. However, pure elastomer adhesives dampen sound waves, preventing them from reaching deep organs. 

The beauty of the BAUS device comes from a newly developed bioadhesive that combines the adhesion capabilities of an elastomer with the sound transmission abilities of a hydrogel. “For the bioadhesive part, we really spent lots of effort to develop a hydrogel-elastomer hybrid. It’s very different from existing liquid hydrogels that can easily flow away,” Zhao said. The new material consists of a hydrogel encapsulated by an elastomer to form a soft solid that can adhere robustly and comfortably to the skin, doubling as an adhesive and a gel to improve sound transmission. The researchers then embedded a thin high-performance probe in the hydrogel-elastomer to complete the BAUS. 

They tested its performance over forty-eight hours by imaging the various organs and tissues of fifteen test subjects. The BAUS device showed everything from how blood vessels’ diameter increased as a subject stood up to how blood flow rate increased after thirty minutes of exercise to how the stomach emptied over two hours after a subject drank a glass of juice. It can also image the heart’s four chambers and show how they change in size under continuous body motion. Furthermore, its success in imaging the lungs and the diaphragm means that the BAUS could potentially be used to monitor respiratory diseases, including COVID-19, and prevent further complications.

“I would say it’d be easier for clinicians and maybe even patients to [use] this. It’s like [adhering] a bandaid on the skin. And our lab is currently working to further simplify this process,” Zhao said. Traditional handheld ultrasound requires qualified personnel and can be relatively expensive. Apart from continuous imaging, the BAUS device provides a simplified imaging process that could eliminate the need for an experienced operator and possibly even give patients the option of adhering the device by themselves. Hence, the BAUS could help increase the accessibility of ultrasounds.

Clinicians and healthcare professionals alike are excited about the broad medical potential of the BAUS device. Continuous imaging is essential for monitoring and tracking tumor growth and for early detection and treatment of cancer. Diagnoses for conditions that involve muscles, joints, and bones often require dynamic tests that cannot be performed using traditional ultrasound techniques. Cardiovascular diseases, which affect the performance of blood vessels and the heart, can lead to dangerous heart attacks that require ultrasound technology for diagnosis. A wearable ultrasound device could help alert those at higher risk for heart attacks of changes in their blood pressure in time to save lives. Ultimately, the BAUS opens up a world of possibilities in diagnostic practices and the continuous monitoring of patient health. 

However, more steps must be taken before the BAUS device can be widely used and implemented. The existing device still needs to plug into a computer that collects and analyzes data. Zhao’s team is working on making a portable wireless version that can truly move with a patient and be used even when there is no access to a computer. Zhao also describes that while the image quality of the BAUS probes is superior to other wearable devices, his team is still working on obtaining higher image resolution to match traditional ultrasound devices. Clinical trials must also be conducted before FDA approval. “In the first paper, we only tested healthy people. Now, we are applying this system to patients to study various diseases,” Zhao said.

The development of the BAUS device is only the latest project that Zhao’s team at MIT has been working on as part of their mission to advance science and technology at the interface of humans and machines. The team’s expertise centers around materials science, mechanics, and biotechnology, but they regularly collaborate with experts in other fields and engage in intersectional projects. “We are really focused on addressing multidisciplinary challenges in health and sustainability. I believe we are solving some of the most important questions facing society, and I hope we can contribute to their solution,” Zhao said.