Sensors printed directly onto human skin without heat

The team, led by by Huanyu "Larry" Cheng, Dorothy Quiggle Career Development Professor in the Penn State Department of Engineering Science and Mechanics, published their results in ACS Applied Materials & Interfaces.

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"In this article, we report a simple yet universally applicable fabrication technique with the use of a novel sintering aid layer to enable direct printing for on-body sensors," said first author Ling Zhang, a researcher in the Harbin Institute of Technology, China and Cheng's laboratory.

Cheng and his colleagues previously developed flexible printed circuit boards for use in wearable sensors but printing directly on skin has been hindered by the bonding process for the metallic components in the sensor. The sintering process typically requires temperatures of around 572^oF (300^oC) to bond the sensor's silver nanoparticles together.

"The skin surface cannot withstand such a high temperature, obviously," Cheng said in a statement. "To get around this limitation, we proposed a sintering aid layer - something that would not hurt the skin and could help the material sinter together at a lower temperature."