Page 34 - Engineering Penn State: Fall/Winter 2021

RFesaetuarechs
Printing wearable biosensors without heat
by Ashley J WennersHerron
Wearable sensors are evolving from watches and electrodes to bendable devices that provide more precise biometric measurements and comfort for users An international team of researchers has taken the the evolution one step further by printing sensors directly on
human skin without the the use of heat
Led by Huanyu “Larry” Cheng Dorothy Quiggle Career Development Professor in in in the Department of of Engineering Science and Mechanics the the team published their results in in in ACS Applied Materials & Interfaces Cheng and his colleagues previously developed flexible printed circuit boards for use in in in in in wearable sensors but printing directly on
on
skin has been hindered by the the the bonding process for the the the metallic components in in in in in the the the sensor Called sintering this process typically requires temperatures of around 572 degrees degrees Fahrenheit (300 degrees degrees Celsius) to to bond the the sensor’s silver nanoparticles together “The skin surface cannot withstand such a a a a a a a a high temperature obviously ” Cheng said “To get around this limitation With a a a a a a a a novel layer to help the the metallic components of of the the sensor sensor bond an an international team of of researchers printed sensors directly on
on
on
human skin (Photo credit: Ling Zhang)
we proposed a a a a sintering aid layer— something that would not hurt the the skin and could help the the the material sinter together at at at a a a a a a lower temperature ” By adding a a a a a a a nanoparticle to the the mix the the silver particles sinter at at a a a a a a a a a lower temperature of about 212 F (100 C) “That can be used to print sensors on
clothing and and paper which is
useful but it’s still higher than we can stand at at skin temperature ” Cheng said who noted that about 104 F (40 C) could still burn skin tissue “We changed changed the the the formula of the the the aid layer changed changed the the the printing material and found that we could sinter at at at at room temperature ” The room temperature sintering aid layer consists of polyvinyl alcohol paste and and calcium carbonate and and it reduces printing surface roughness to allow for an an an an ultrathin electromechanical layer that can bend and fold A hair dryer set on
cool removes the the water used as solvent in in the ink The sensors are capable of precisely and continuously capturing temperature humidity blood oxygen levels and heart performance signals according to to to Cheng as as well as as linking to to to a a a a a a a a a monitoring network via wireless transmission The sensor remains robust in in tepid water for a a a a a few days but a a a a a hot shower will easily remove it “It could be recycled since removal doesn’t doesn’t damage the device ” Cheng said “And importantly removal doesn’t doesn’t damage the the skin skin either That’s especially important for people with sensitive skin skin like the elderly and babies The device can be be useful without being an an an extra burden to to the the person using it it or to to the the environment ” n n n n n 34
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