Nobody likes having blood samples taken, which is why it's always good to hear about possible alternatives. One of the latest takes the form of a self-powered skin patch that painlessly gathers biomarker chemicals for up to 24 hours at a time.
Not only is the blood-sample-drawing process painful – and "icky," for many people – it also only shows which tell-tale biomarkers are present in the bloodstream at the time the sample is taken.
If doctors want to see all of the biomarkers that may come and go throughout the day, they have to draw multiple samples over a 24-hour period. What's more, analyzing those samples can be a complex affair, as it involves separating blood components such as platelets and red blood cells.
That's where the experimental new microneedle patch comes in. It's being developed by scientists from North Carolina State University, and the University of North Carolina at Chapel Hill.
The device consists of a polymer housing with three stacked layers of material inside – there's a layer of glycerol-loaded polyacrylamide hydrogel on top, a strip of absorbent paper in the middle, and an array of tiny sharp-stud-like microneedles on the bottom. When the patch is adhered to the skin and pressed against it, the needles painlessly pierce only the top layer of the skin, not reaching the nerve endings below.
Upon coming into contact with the interstitial fluid (ISF) that surrounds the skin cells, the microneedles – which are made of methacrylated hyaluronic acid – swell up and start wicking the ISF into the paper. Biomarker concentrations in the fluid correspond to those in the bloodstream.
When the ISF passes through microfluidic channels in the paper and comes into contact with the layer of hydrogel, the glycerol imbalance between that gel and the ISF creates what is known as osmotic pressure. That pressures draws more ISF up from the skin into the paper, until the latter is saturated.
In a final step, the patch is removed from the skin, the paper strip is removed from the patch, and the interstitial fluid in the paper is quickly and easily analyzed. "ISF makes for a 'cleaner' sample – it doesn’t need to be processed the way blood does before you can test it," says lead scientist Prof. Michael Daniele, who is affiliated with both universities. "Essentially, it streamlines the biomarker testing process."
In lab tests performed on synthetic skin models, the patch was found to collect measurable amounts of ISF within 15 minutes, and it could continue to draw and store the fluid for up to 24 hours. The scientists were able to accurately measure levels of cortisol in the ISF, and have developed an electronic patch-paper-processing device that does the job automatically. Other devices for measuring other biomarkers are now in the works.
"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," say Daniele. "Drawing blood requires vials, needles and – usually – a phlebotomist. The patch doesn’t require any of those things."
Human testing of the technology is now underway. A paper on the research was recently published in the journal Lab on a Chip.
Source: North Carolina State University
