Wearable sensors have come a long way, indeed – from smart watches and electrodes to bendable devices for precise tracking and comfort. Now, taking the technology a step further, an international team of researchers introduce a technique that makes it possible to print sensors directly on human skin without applying any heat.
“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,” the researchers wrote in a recent paper for ACS Applied Materials & Interfaces.
Up until now, the key issue with printing sensors directly on the skin was the requirement for using high temperatures, necessary to induce nanoparticle bonding (sintering). To circumvent the problem, the research team changed the printing material and developed a special aid layer that enables printing at room temperature.
The aid layer – comprised of polyvinyl alcohol paste (commonly used in peelable face masks) and calcium carbonate – reduces printing surface roughness and thereby allows for the printing of an ultrathin layer of metal patterns that maintain their electromechanical properties even when bent or folded.
Upon printing, the researchers used a simple hair dryer, set on cool, to remove the water used as a solvent in the ink. According to lead researcher Huanyu “Larry” Cheng, Dorothy Quiggle Career Development Professor in the Penn State Department of Engineering Science and Mechanics, the main achievement here is the removal of heat from the sintering process.
When linked into a network, the on-body sensors can precisely and continuously monitor temperature, humidity, blood oxygen levels and heart performance, and wirelessly transmit the signals for processing. Once the sensor grid is no longer needed, it can be easily removed by entering a hot shower.
“It could be recycled, since removal doesn’t damage the device,” Cheng 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.”
Up next, the team has plans to adapt the technology for the seamless tracking of symptoms associated with COVID-19.