Breathable nanomesh conductors on skin with no discomfort
An inflammation-free, highly gas-permeable, ultrathin, lightweight and stretchable skin sensor with a conductive nanomesh to detect touch, temperature and pressure.
“The sensor continuously monitors users’ health, and because it is both ultrathin and ultralight the users cannot even feel the device when worn, and there is no discomfort,” I used to tell my relatives when discussing my work. My aunt and uncle would simply answer “yes, great” and told me “you should continue to improve it, because it is a necessary thing”. I spent a great deal of time researching scientific papers, and pursuing the ultimate goal of producing a wearable device. The ERATO Someya Bio-Harmonized Electronics Project started in 2013, and two years into the project, in December 2015, I became involved as a research staff scientist and engaged in researching nanomesh conductors to be applied directly to skin for touch, temperature and pressure, and also electromyogram.
At that time, the most pressing issues in the project were the handling of a nanomesh sheet (due to its softness, it was difficult to handle and to fabricate devices with), its elastic durability, and the sensing mechanism, as well as the need for demonstration of a prototype device. Although the issues yet to be resolved in the project were numerous, it was already discovered that a gold nanomesh could work as a conductor with gas permeability in such devices.
Further into the project, there were two hurdles that we needed to overcome. First, the handling needed to be improved, so that anyone could easily laminate the nanomesh conductors on skin. Second, the device’s mechanical durability after repeated bending and stretching of nanomesh conductors attached to a finger needed to be demonstrated. To solve the first problem, I controlled the thickness and surface and/or structure of the nanomesh sheet by heating and applying pressure. For the second problem, I attached the nanomesh to my own forefinger and bent and stretched it 10,000 times; that is repeating opening and closing of the hand for at least 3 hours, similar to grip training. The nanomesh conductors maintained functionality even after all those repetitive movements, showing excellent reliability of the conductors on skin. With these improvements and investigation of durability, I believed I could solve the problems facing the project. Additionally, for practical, real-world applications of the nanomesh sensor in the future, I worked on improving the usability of the device. Finally, I improved the lamination process of applying the nanomesh conductors onto skin, by adopting moisture with humidifier instead of spraying with water. As a result of these efforts, it takes only around 10 seconds to install the device on a finger (Figure 1).
The nanomesh remains attached even when exposed to a humid environment or to sweat, but can be easily removed by rubbing the finger. Our next objectives are to further improve the mechanical durability of nanomesh sensors without sacrificing comfort during wear, and to perform long-term monitoring of patient vital signs without causing any stress or discomfort.
Our paper: Miyamoto, A. et al. Inflammation-free, gas-permeable, lightweight, stretchable on-skin electronics with nanomeshes. Nat. Nanotechnol. https://doi.org/10.1038/nnano.2017.125 (2017).