Researchers have found a way to print sensors onto skin without heat, potentially creating a more accurate way of taking biometric measurements than wearable devices.
Sensors of a number different types can now be printed on the human body without putting a person at risk of getting burned, according to new research.
Writing in ACS Applied Materials and Interfaces, researchers from Penn State University and the Harbin Institute of Technology in China said their new printing method will allow for sensors be placed directly on human skin without the need for heat. This, they said, will allow for more precise biometric measurements and comfort for users compared to wearable sensors.
The fabrication technique uses a novel sintering aid layer to enable direct printing for on-body sensors. Sintering, a bonding process for metallic components of a sensor, typically requires temperatures of around 300 degrees Celsius to bond the sensor’s silver nanoparticles together.
“The skin surface cannot withstand such a high temperature, obviously,” said Huanyu Cheng of Penn State, who led the research. “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.”
By adding a nanoparticle to the mix, the researchers were able to lower the necessary temperature to about 100 degrees Celsius, which is usable for clothing and paper. However, Huanyu noted that even at temperatures of 40 degrees Celsius, skin tissue can burn.
‘The outcome is profound’
To help lower the temperature further, researchers changed the formula of the aid layer to include polyvinyl alcohol paste – found in peelable face masks – and calcium carbonate. This not only reduced the necessary sintering temperature to room temperature, but allowed for an ultrathin layer of metal patterns that can bend and fold while maintaining electro-mechanical capabilities.
All that’s needed to apply the sensor once printed is an air blower, such as a hairdryer set on cool, to remove the water that is used as a solvent in the ink.
“The outcome is profound,” Huanyu said. “We don’t need to rely on heat to sinter.” Researchers said the sensors are capable of precisely and continuously capturing temperature, humidity, blood oxygen levels and heart performance signals. The sensors were also found to be able to transmit information wirelessly, while all that’s needed to remove it is a hot shower.
“It could be recycled, since removal doesn’t damage the device,” Huanyu said. “And, importantly, removal doesn’t damage the skin, either. That’s especially important for people with sensitive skin, like the elderly and babies. The device can be useful without being an extra burden to the person using it or to the environment.”