Self-powered patch for painless biomarker monitoring

Researchers have developed a self-powered microneedle patch to monitor a range of health biomarkers without drawing blood or relying on batteries or external devices. In proof-of-concept testing with synthetic skin, the researchers demonstrated that the patches could collect biomarker samples over periods ranging from 15 minutes to 24 hours.

“Biomarkers are measurable indicators of biological processes, which can help us monitor health and diagnose medical conditions,” said Michael Daniele, corresponding author of a paper on the work. “The vast majority of conventional biomarker testing relies on taking blood samples. In addition to being unpleasant for most people, blood samples also pose challenges for health professionals and technology developers. That’s because blood is a complex system, and you need to remove the platelets, red blood cells, and so on before you can test the relevant fluid.

“The patch we’ve developed uses microneedles to sample the fluid that surrounds cells in the dermal and epidermal layers just below the very top layer of cells that make up your skin,” Daniele said. “This is called dermal interstitial fluid (ISF) and it contains almost all of the same biomarkers found in blood. What’s more, ISF makes for a ‘cleaner’ sample – it doesn’t need to be processed the way blood does before you can test it. Essentially, it streamlines the biomarker testing process.”

Specifically, Daniele and his collaborators have made a fully passive microneedle patch that doesn’t rely on either batteries or external energy sources to take or store ISF samples. Here’s how it works.

The patch consists of four layers: a polymer ‘housing’ — which is effectively the part of the patch you can see; a layer of gel; a layer of paper; and the microneedles themselves. The microneedles are made of a material that swells when it touches the ISF. The ISF wicks through the microneedle — like water through a paper towel — until it comes into contact with the paper. As the paper begins absorbing the ISF, the fluid comes into contact with the gel that is on the other side of the paper. That gel contains a high concentration of glycerol. The imbalance of glycerol between the gel and the ISF creates osmotic pressure that pulls more ISF through the paper until the paper is saturated.

“The paper is where the ISF is stored,” Daniele said. “When you take the patch off, you remove the paper strip and analyse the sample.”

The researchers tested the patch on two synthetic skin models.

“It worked well. The patches collected measurable results in as little as 15 minutes and were capable of storing the biomarker samples for at least 24 hours,” Daniele said.

For the proof-of-concept testing, the researchers monitored for cortisol — which is a biomarker for stress that fluctuates over the course of the day.

“That means it’s something people may want to monitor multiple times a day without having to draw blood repeatedly,” Daniele said. “And there’s no reason the patch wouldn’t work for many of the biomarkers found in ISF.”

Another attractive aspect of the patches is that they’re made from relatively inexpensive materials that are widely available.

“The highest cost of the patches would be manufacturing the microneedles, but we think the price would be competitive with the costs associated with blood testing,” Daniele said. “Drawing blood requires vials, needles and — usually — a phlebotomist. The patch doesn’t require any of those things.”

The researchers have already begun human testing with the patches and are developing electronic devices to ‘read’ the paper strip from the microneedle patch.

“We’ve already developed an electronic device that can ‘read’ cortisol levels from the paper strip and are working on another device that evaluates a different biomarker,” Daniele said.

“We’re now looking for industry partners on two fronts. We’d love to talk with companies in the diagnostic space to explore additional applications, and we’d also like to talk with potential partners about scaling up production.”

The research findings have been published in the journal Lab on a Chip.

Image credit: North Carolina State University