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Photo of Philip Miller's microneedle device.
Researcher Philip Miller examines a microneedle device. The new device design uses an array of needles and can extract 20 µL of interstitial fluid, compared to the 2 µL that the previous version of the device achieved. (Credit: Randy Montoya)

A technique using microneedles able to draw relatively large amounts of interstitial fluid — a liquid that lurks just under the skin — opens new possibilities. Previously, microneedles — tiny, hollow, stainless steel needles — have drained tiny amounts of interstitial fluid needed to analyze electrolyte levels but could not draw enough fluid to make more complicated medical tests practical. The new method’s larger draws could be more effective in rapidly diagnosing cancer and other diseases.

The relatively large quantities of pure interstitial fluid extracted, which have never before been achieved, make it possible to create a database of testable molecules, such as proteins, nucleotides, small molecules and other cell-to-cell signaling vesicles called exosomes. Their presence or absence in a patient’s interstitial fluid would then indicate, when an individual’s data is transmitted by electronic means to a future data center, whether bodily disorders like cancers, liver disease or other problems might be afoot.

By creating arrays of needles, the extractable amount increased from 2 microliters to up to 20 microliters in human subjects.” One microliter is about 0.000034 fluid ounces. Interstitial fluid’s advantage for patients is that it can be probed by 1.5-mm (approximately 0.06 in.) needles that are too short to reach nerves that cause pain. It also has no red blood cells to cloud the results of tests.

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