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Tuesday, January 7, 2014

Continuous temperature monitoring via skin patch

Continuous temperature monitoring can be important for some medical conditions. Chad Webb and Andrew Bonifas of the University of Illinois and colleagues from the U.S., China and Singapore have developed an extremely thin electronic patch that can adhere to skin and deliver all kinds of information.

There were a couple of obstacles to overcome in designing a skin patch monitor. First, the patch can’t irritate the skin. Second, the monitor has to be able to stretch with the movement of the skin. It defeats the purpose if the patient must keep the patched body part perfectly still for hours or days. The device shouldn’t raise the temperature of the skin under it (unless you want it to do so) nor should it be shed during profuse sweating.

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a) Image of a  sensor array after application to the skin.b) Similar device, deformed by pinching the skin in a twisting motion. c) Magnified image of a related device under tensile strain. d) Infrared image of a sensor array mounted on the wrist at a location near the ulnar artery. e) Image of an Si nanomembrane diode sensor array mounted on the skin. f) Similar device as deformed by pinching the skin in a twisting motion. g) Image of a sensor array showing the ability of water to pass through readily.
Inset: magnified image of a single sensor. 
h) Infrared image of an array on the human wrist while heating the four inner-most elements.Nature materials, 12 (10), 938-44 PMID: 24037122.

The sensors developed by the team met all the criteria, plus were able to detect changes in skin temperature in the millikelvin range. That’s a thousandth of a degree. Your skin temperature changes more than that when you’re doing mental math problems.

It probably seems like this kind of precision is overkill, and it largely is. However, subtle difference in temperature can be markers for medical conditions like dehydration or blood flow problems. Future iterations could also monitor glucose levels, metabolites, or blood cell counts. Plus, versions of the skin patches could someday be used to deliver medicines.

Webb RC, Bonifas AP, Behnaz A, Zhang Y, Yu KJ, Cheng H, Shi M, Bian Z, Liu Z, Kim YS, Yeo WH, Park JS, Song J, Li Y, Huang Y, Gorbach AM, & Rogers JA (2013). Ultrathin conformal devices for precise and continuous thermal characterization of human skin. Nature materials, 12 (10), 938-44 PMID: 24037122.