An international team of scientists has figured out how to print biometric sensors directly onto a person’s body. The sensors can be printed without any heat, offer wireless connectivity, and can read a range of different vital signs, including blood oxygen levels, heart rate, humidity, and body temperature.
The breakthrough was accomplished through a series of improvements to the sintering process that is used to bond the silver nanoparticles in a metallic sensor. The researchers had previously created flexible printed circuit boards that could be deployed in wearable devices, but could not print directly to the skin because sintering required temperatures of 300 degrees Celsius (or 572 degrees Fahrenheit).
The researchers lowered those thresholds to 100 degrees Celsius (and 212 degrees Fahrenheit) by adding a new nanoparticle to the sintering mixture. The improved compound could be printed on cloth or paper, but was still too hot to print to skin, which can burn at 40 Celsius and 104 Fahrenheit.
With that in mind, the researchers changed their formula one more time to get over the final hurdle. They devised a sintering aid layer that consists of calcium carbonate (which is found in egg shells) and polyvinyl alcohol paste (which is used in peelable face masks) to create a product that could sinter at room temperature.
The printed sensors can withstand tepid water, but will come off in a hot shower. Doing so does not damage the sensor itself, so that same sensor can be reused on future occasions. After printing, the researchers used a blow dryer on the cool setting to get rid of the water that they used as a solvent in the ink.
The results of the study were published in ACS Applied Materials & Interfaces, while the study itself took place under the guidance of Huanyu “Larry” Cheng, a Professor in the Penn State Department of Engineering Science and Mechanics. Ling Zhang, a researcher in the Harbin Institute of Technology in China, acted as the first author for the paper.
The new technology allows manufacturers to sinter sensors without the use of heat, and could eventually replace more traditional electrodes. Moving forward, the researchers plan to modify the technology for more specific applications, such as the detection of COVID-19 symptoms.
October 14, 2020 – by Eric Weiss