New wearable sensors can be printed directly on human skin

Engineers print wearable on-body sensors directly on human skin without heat. An international team of researchers developed a novel technique to produce precise, high-performing biometric sensors. Wearable sensors are evolving from watches and electrodes to bendable devices. Now researchers are printing sensors directly on human skin without the use of heat. Researchers developed a simple fabrication technique using a novel sintering aid layer to enable printing for on-body sensors. Researchers previously developed flexible printed circuit boards for use in wearable sensors but printing directly on skin has been an obstacle. 
The sintering process requires temperature of around 300 0C (572 0F) to bond the sensor's silver nanoparticles together. But the skin surface cannot withstand such a high temperature. To get around this limitation, researchers added a sintering aid layer that could help the material sinter together at a lower temperature. By adding a nanoparticle to the mix, the silver particles sinter at a lower temperature of about 100 0C (212 0F). 
This process can be used to print sensors on clothing and paper but it's still higher than we can stand at skin temperature. Researchers then changes the formula of the aid layer to be able to sinter at room temperature. The new sintering aid layer consists of polyvinyl alcohol paste.The layer reduces printing surface roughness. Is also allows for an ultrathin layer of metal patterns that can bend and fold while maintaining electromechanical capabilities. 
The sensors are capable of precisely capturing temperature humidity, blood oxygen levels and heart performance signals. The researchers also linked the on-body sensors into a wireless network to monitor the combination of signals as they progress. 
The sensor remains robust in slightly warm water for a few days but a hot shower will easily remove it. The process is also environmentally friendly as the device could be recycled when removed