Slap it on

This ultrasound ‘sticker’ may revolutionize health care

One day, you might see your insides right from the comfort of your own home.

If you were a 90s kid growing up in the post-Christoper Reeves Superman heyday, maybe your coveted superpower was the ability to fly. Or maybe you wanted something with a little less turbulence and arguably a little more practicality, like x-ray vision. Well, now you can… sort of.

In a paper published in the journal Science on Thursday, researchers at MIT have taken ultrasound – a technology commonly used in health care that directs sound waves into the body to see what’s inside — and miniaturized it in the form of a sticker. No bigger than your average postage stamp, this innovative ultrasound sticker may revolutionize the way we do health care by providing greater support to people with chronic medical conditions or pregnancy, and may even help finetune fitness and wellness.

Here’s the background - If you’ve ever had an ultrasound, you’re probably familiar with the rather hefty machine-on-wheels bearing a slight, albeit oversized resemblance to Wall-E.

A clinician or ultrasound technician typically applies a layer of bone-chilling hydrogel on the body. This hydrogel acts as a conductive medium for sound waves emitted by the ultrasound probe, also known as a transducer, that’s pressed against the skin or inside the body, such as the vagina or rectum. The sound waves enter the body and collide into structures – whether it be an organ, blood vessel, bone, or other tissues – before being promptly reflected back to the probe. These echoes are then translated into visual images by a computer, like a beating heart or a cancerous growth.

Since the 1940s and 50s, when ultrasound was first proposed and used for medical purposes, the technology has grown immensely powerful, becoming a much relied-on diagnostic and treatment tool. However, there is the question of accessibility: Conventional ultrasounds aren’t portable, which can prevent them from being used in resource-limited areas. They can also be tiring to operate if someone needs to be imaged over an extended period of time (imagine having to be a living statue holding an ultrasound probe in place). In that scenario, there’s also the issue of the hydrogel drying up, which means it would have to be constantly reapplied.

There have been efforts to address all those challenges by miniaturizing ultrasound devices or making probes that are stretchy and can move with the body, Sheng Xu, a professor of nanoengineering at the University of California San Diego Jacobs School of Engineering, who was not involved in the new study, tells Inverse. But a problem engineers run into is having to sacrifice some device performance like resolution quality, which, for such essential technology as ultrasound, isn’t ideal.

This innovative, postage stamp-sized ultrasound ‘sticker’ is made up of layers of rubbery elastomer, watery hydrogel, and an array of tiny ultrasound probes.Xuanhe Zhao/MIT

How they did it - With their ultrasound sticker, the MIT researchers were able to leap over those design hurdles.

First matter of business: Preventing the hydrogel from drying out. Xuanhe Zhao, a professor of mechanical engineering and of civil and environmental engineering at MIT who led the study, tells Inverse the sticker’s construction took inspiration from the human body, where skin acts as a tough but flexible barrier to the outside world keeping our internal fluids.

Instead of using actual skin, of course, Zhao and his team thickened the consistency of the hydrogel to resemble jello than its usual toothpaste. They then sandwiched the hydro-jello in a very, very thin case of a material called elastomer about 40 micrometers, or 0.04 millimeters thick. This rubbery material keeps the watery gel from drying out while also still allowing sound waves to propagate through.

Next comes the array of ultrasound probes, which sit right on top of the elastomer-hydrogel sammie. Unlike other ultrasound patches that have used stretchable probes, this one is rigid but also very thin. This is important because once the sticker is placed in the desired area to be imaged (which Zhao says may initially need some calibration by moving around the sticker to find just the right spot), the probes stay focused even if the body moves or skin contorts. The ultrasound sticker barely budged when volunteers wore it while performing different physical activities like jogging or biking, producing pretty clear images of underlying body structures despite all the commotion.

The final touch is a bioadhesive layer along the sticker’s underbelly. Zhao and his team designed it to allow the sticker to adhere to skin for up to two days, whether in dry or wet environments and without leaving any gunky residue.

The size is also pretty unobtrusive: Only about two centimeters across and three millimeters thick, so about the size of a postage stamp.

Why it matters - Continuous ultrasound imaging can be very crucial for people with severe medical conditions that require clinicians to closely monitor and see how everything unfolds over time wherever a patient is located, what’s called point-of-care ultrasound, says Zhao. This can include diseases affecting the heart, cancer, and conditions like pregnancy (ultrasound is the only way to make sure a growing baby is developing normally).

An ultrasound sticker could be used by healthy people for personal use such as monitoring fitness or muscle growth if you’re on a journey to get swole.

“Ultrasound can image the muscle and now we have the capability to do long-term continuous muscle imaging,” says Zhao. “The image can tell if you’ve done [a sufficient amount of exercise] and you should stop at this point. I can imagine the potential impact of this technology on sports and [muscle] strength.”

Digging into the details - The ultrasound sticker still needs to be connected to an external device called a data acquisition box that collects the incoming sound waves and converts them into an image. That is obviously still a major sticking point.

“We’re working very hard to fully integrate everything into an integrated wireless device that you can use this [ultrasound] patch wirelessly to image the internal organs,” says Zhao.

And while its image quality is pretty decent, Zhao and his team hope to up the resolution their ultrasound sticker can achieve to be on par with conventional, standalone machines.

“So currently the highest resolution we can achieve is around 100 to 200 micrometers,” he says. “We want to get that higher, especially for deeper organs like the heart and lungs, the resolution currently is a few millimeters but we want that to be even higher. Basically, we want to reach the state of art ultrasound imaging.”

What’s next - Zhao and his team are currently collaborating with hospitals and clinicians in the Boston area to test their ultrasound stickers in a broader patient setting. They’re hopeful that one day their device will be something anyone will be able to easily get their hands on and use in their everyday lives, whether they are healthy, pregnant, or have a condition that needs around-the-clock medical attention.

The MIT researchers also want to potentially integrate an artificial intelligence that could analyze the ultrasound images, and interpret and make diagnoses much like having a built-in radiologist.

“Now we’ve entered the age of wearable imaging,” he says. In the day and age of superhero comics, advanced technology is as close to a superpower as any.

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