The next frontier of continuous health monitoring could be superficial.
Biomedical engineers at the University of Cincinnati say interstitial fluid, the watery fluid found between and around cells, tissues or organs in the body, could provide an excellent means of early disease diagnosis or health monitoring. long-term.
In an article published in the magazine Nature Biomedical Engineeringdescribed the potential advantages and technological challenges of using interstitial fluid.
“The reason we see it as a valuable diagnostic fluid is continuous access. With blood, you can’t easily take continuous readings,” said UC PhD Mark Friedel, co-lead author of the study.
“Can you imagine spending the day with a needle stuck in your vein all day? So we need other tools.”
Researchers are looking for alternatives to monitor a person’s health and well-being. Sweat is a good way to measure things like stress or anxiety because it contains hormones like cortisol. But the body is stingy with other chemicals that aren’t as easily released in sweat, Friedel said.
“Sweat glands are big filters that don’t let everything through,” he said. “So more than half of the things we want to monitor don’t have access to sweat.”
Blood is the gold standard for health monitoring. But people also have liters of interstitial fluid that makes up to 15% of their body weight.
“The key feature of blood that makes it so advantageous is that we understand blood very well,” Friedel said. “If you have something in your blood, we know what will happen to your heart or your liver,” he said.
The researchers said that interstitial fluid contains many of the same chemicals in the same proportions as blood, offering a potential alternative to expensive and time-consuming lab work.
The study described the various ways doctors can sample interstitial fluid, from applying suction to the skin to implementing 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 big barrier to this accessibility is that most current diagnostics are based on blood samples, which can be painful and require trained personnel to perform. Therefore, in recent years there has been increasing interest in using liquid interstitial tissue just under the skin as a diagnostic sample, which is more accessible and less painful to remove.”
In UC School of Engineering and Applied Sciences professor Jason Heikenfeld’s New Devices Laboratory, students are developing sensors to measure hormones and other chemicals in interstitial fluid. They use microneedles less than 1 millimeter long that pierce the skin through a small patch.
“If you had a splinter, it probably went deeper into the skin than our microneedles,” Friedel said. “They are usually painless. I don’t feel it most of the time. The most awkward part is removing the tape that holds the device on.”
But even if you don’t know it’s there, your body does, Friedel said. And this tiny reaction can affect the test results.
“There is a Schrödinger observer effect with interstitial fluid. Every time you try to collect and measure it, you inherently change the fluid itself,” Friedel said. “If you stick a needle in your skin, your body swells up and then your [sample] levels change. For continuous biomonitoring, we want to know those concentrations as they are when you’re not being poked with a small needle.
“That’s why it’s such a challenging liquid that it hasn’t been used outside of diabetes management.”
Still, say the researchers, interstitial fluid holds great promise for monitoring health through wearable technology. This could help doctors track the effectiveness of drugs to ensure proper dosing or provide early diagnosis of diseases by monitoring the immune system.
But Friedel said there is still a lot to learn.
“We are trying to unlock the box and read the instructions inside to understand what is in the interstitial fluid and what are the potentials to exploit it,” he said.
Friedel and Thompson worked with co-author Heikenfeld, the UC James L. Winkle College of Pharmacy, Sandia National Laboratories in New Mexico, and Southeastern Missouri State University.
The study was funded through grants from the National Science Foundation, the US Air Force Office of Scientific Research, and the US Office of Naval Research.