A prototype of a device that can measure interstitial fluid uses microneedles. Credit: Mark Friedel
Key points:
- Interstitial fluid could be an alternative to blood for continuous monitoring of health and wellness.
- Interstitial fluid is easier to access and more cost-effective to process. It is also in high supply, as it makes up as much as 15% of body weight.
- The method has shown some success for diabetes monitoring thus far.
Researchers are always looking for better ways to monitor both short- and long-term health and wellness. Sweat is a very popular sample type—and effective for some readings like anxiety and stress—but it not a suitable medium for everything.
“Sweat glands are big filters that don’t allow everything to pass through,” says University of Cincinnati doctoral graduate Mark Friedel. “So, more than half of the things we want to monitor have no access to sweat at all.”
Thus, blood is the current gold standard for health monitoring; but, Friedel and his team are looking at a different type of fluid.
In a paper published in Nature Biomedical Engineering, the scientists outline the potential advantages and technological challenges of using interstitial fluid, the watery fluid found between and around cells, tissues or organs in the body, to provide early disease diagnosis and long-term health monitoring.
“Why we see it as a valuable diagnostic fluid is a continuous access. With blood, you can’t easily take continuous readings,” said Friedel, co-lead author of the study.
Interstitial fluid makes up as much as 15% of body weight and contains many of the same chemicals proportional to that in the blood, which can be an alternative to costly and time-consuming lab work.
The current study outlines the various ways doctors can sample interstitial fluid, from applying suction to the skin to deploying microdialysis. The University of Cincinnati team is developing sensors to measure hormones and other chemicals in interstitial fluid. They use microneedles less than 1 millimeter in length that pierce the skin through a tiny patch.
Thus far, the method has only been used for diabetes monitoring because, Friedel says, even if you don’t know it’s there, the body does.
“There’s a Schrödinger’s observer effect with interstitial fluid. Any 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 becomes inflamed, and your sample levels change. For continuous biomonitoring, we want to know those concentrations as they are when you’re not being poked with a tiny needle.”
Still, the scientists say interstitial fluid holds enormous promise for monitoring health through wearable technology, with more research needed to explore its full potential.