27-10-2020 | | By Sam Brown
Recently, researchers from the US and China have developed biosensors that can be directly printed onto skin while not requiring high sintering temperatures. What challenges do wearable electronics currently face, how have the researchers been able to print to the skin directly, and what applications will it allow for in the future?
Of all electronics industries, one that has taken a particularly long time to develop are wearable electronics, and it is one industry that could have one of the largest impacts on daily life. Currently, the closest to practical commercial wearable electronics comes in the form of smartwatches, but even these are ridged and uncomfortable to wear at times. The reason for impractical wearable electronics comes from the underlying technology used to create them; inflexible electronics built on inflexible substrates powered by inflexible battery technology. The result is that wearable electronics cannot stretch and morph to the wearer, thus being uncomfortable to wear.
One solution to the issues faced by traditional electronic components is printable electronics; those that can be printed onto a surface. While different printing technologies exist, many printed components often have an element of flexibility, and depending on the end application the right printable material can be chosen. Some printed electronics can be as simple as graphite, while others can consist of complex organic and thin-film compounds to construct transistors and displays.
While there are many printable electronics technologies, those that utilise metal nanoparticles require sintering; the heating of the particles to metallically fuse. Such electronics make for good sensors and conductors, but cannot be applied to human skin as they require high temperatures to fuse.
Researchers from the US and China have recognised the importance of directly printing electronics to users, and thus have developed a method for doing so using metallic nanoparticles that can be sintered at very low temperatures. While the researchers were able to lower the sintering temperature by adding nanoparticles, it was still too high for use with human skin (100°C). Instead, the lowered sintering temperature was combined with an aid consisting of PVA paste and calcium carbonate, and the result is sintering at room temperature that does not burn or hurt the skin. The developed technique allows for the printed design to remain adhered to the skin when wetted and removed easily when rinsed under hot water.
To demonstrate the capabilities of the technology, the researchers created multiple sensors, including temperature, humidity, blood oxygen, and heart performance. The sensors were then linked to a wireless transmission system to allow for remote monitoring of vital signs, and the sensors were able to produce precise and continuous readings.
One of the biggest applications for skin-printed electronics is medical equipment; such electronics can allow patients to be monitored remotely without discomfort to the patient. The same electronics are also ideal for those with sensitive skin such as the elderly and the young, thus not causing itching or other severe reactions. Printed electronics will also be highly advantageous in long term health monitoring; individuals could be fitted with such sensors to study long term effects of their area of employment or to detect and prevent conditions from getting worse. AI systems can then read from the sensory data, and predictive health monitoring can not only prevent illnesses but provide valuable data for others.