Researchers say interstitial fluid could replace blood to monitor health and well-being – ScienceDaily

The next frontier for continuous health monitoring may be skin deep.

Biomedical engineers at the University of Cincinnati say interstitial fluid, the watery fluid found between and around cells, tissues or organs in the body, can provide an excellent medium for early disease diagnosis or long-term health monitoring.

In an article published in the journal Nature Biomedical Engineeringthey described the potential advantages and technical challenges of using interstitial fluid.

“Why we see it as a valuable diagnostic fluid is continuous availability. With blood, you can’t easily take continuous readings,” said UC graduate student Mark Friedel, co-author of the study.

“Can you imagine going about your day with a needle in your vein all day? So we need other tools.”

Researchers are looking for options to monitor a person’s health and well-being. Sweat is a good medium to measure certain things like stress or anxiety because it contains hormones like cortisol. But the body is stingy with other chemicals that aren’t so easily released in sweat, Friedel said.

“Sweat glands are big filters that don’t let everything pass,” he said. “So more than half of the things we want to monitor don’t have access to sweat at all.”

Blood is the gold standard for health monitoring. But humans also have liters of interstitial fluid that makes up as much as 15% of their body weight.

“The key feature of blood that makes it so beneficial is that we understand blood really well,” Friedel said. “If you have something in your blood, we know what’s going to happen to your heart or your liver,” he said.

Researchers said interstitial fluid contains many of the same chemicals in the same proportions as blood, offering a potential alternative to costly and time-consuming lab work.

The study described the different ways doctors can sample interstitial fluid, from applying suction to the skin to using microdialysis.

“As biomedical engineers, one of our biggest goals is to help people better manage their health by making diagnostics more accessible,” said co-lead author Ian Thompson of Stanford University.

“A major barrier to this availability is that most current diagnostics rely on blood sampling, which can be painful and requires trained personnel to perform. Thus, in recent years there has been growing interest in using interstitial fluid just under the skin as a diagnostic prov. which is more accessible and less painful to extract.”

In UC College of Engineering and Applied Science professor Jason Heikenfeld’s Novel Devices Lab, students are developing sensors to measure hormones and other chemicals in interstitial fluid. They use microneedles less than 1 millimeter long that penetrate the skin through a tiny spot.

“If you had a chip, it probably went deeper into the skin than our microneedles,” Friedel said. “They’re generally painless. I don’t feel it most of the time. The most uncomfortable part is removing the tape that holds the device down.”

But even if you don’t know it’s there, your body does, Friedel said. And this minute reaction can affect the test results.

“There’s a Schrödinger observer effect with interstitial fluid. Every time you try to collect and measure it, you’re inherently changing the fluid itself,” Friedel said. “If you stick a needle in your skin, your body becomes inflamed and then yours [sample] the levels change. For continuous biomonitoring, we want to know these concentrations as they are when you are not poked with a small needle.

“That’s why it’s such a challenging fluid that hasn’t been used outside of diabetes monitoring.”

Still, researchers say, interstitial fluid holds enormous promise for monitoring health through wearable technology. This can help doctors track the effect of drugs to ensure proper dosing or provide early diagnosis of disease by monitoring the immune system.

But Friedel said there is still much to learn.

“We’re trying to unlock the box and read the instructions inside to understand what’s in interstitial fluid and what the potential is for harnessing it,” he said.

Friedel and Thompson worked with co-author Heikenfeld, UC’s James L. Winkle College of Pharmacy, Sandia National Laboratories in New Mexico and Southeast Missouri State University.

The study was funded by grants from the National Science Foundation, the US Air Force Office of Scientific Research and the US Office of Naval Research.

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