Gold nanomesh enables ultra-breathable skin electronics
Trying to solve this issue, a team of Japanese researchers led by Prof. Takao Someya from the University of Tokyo have managed to remove the substrate altogether, creating a highly stretchable and breathable gold nanomesh to support or connect various sensing functions directly on the patient’s skin, without adverse effects.
Published in Nature under the title “Inflammation-free, gas-permeable, lightweight, stretchable on-skin electronics with nanomeshes”, their paper reports touch, temperature and pressure sensors directly implemented onto the skin and able to withstand hundreds of flexing and stretching cycles.
Key to breathability is the nanomesh structure. First, the researchers made nanofibres (300 to 500nm in diameter) by electrospinning a polyvinyl alcohol (PVA) solution. Those fibres were then intertwined to form a mesh-like sheet, electrodeposited with a 70 to 100nm-thick layer of gold on top. When applied to the skin and sprayed with water, the nanomesh’s PVA nanofibres easily get dissolved and a highly conductive gold nanomesh remains, adhering to the skin and conforming to its most minute details (including ridges and creases).
The dissolved PVA nanofibres act as a super-thin adhesion layer, only tens of nanometres thick and the nanomesh conductor is so conformable and stretchable that the wearer does not even feel it. What’s more, the porous overlapping spaghetti-like structure of the nanomesh conductor exhibits excellent water vapour permeability, facilitating skin breathing. The resistivity of the gold nanomesh was estimated to 5.3×10−7 Ω m, conductance changed sharply under elongation, but gradually recovered to its initial value during shrinking, which could be harnessed to form a stretchable sensor.
In an experiment, the researchers created a touch sensor consisting of a simple nanomesh conductor array applied to a fingertip. The resistance between the nanomesh conductor strips decreases when a conductive object creates a shortcut. Such electrode arrays were also used to create a thermal and a pressure sensor, by applying a strip of positive temperature coefficient (PTC) polymer and pressure-sensitive rubber across them, respectively.
In another implementation, the nanomesh conductors were used as on-skin electrophysiology electrodes for electromyography (EMG) recording and yielded good signals comparable to today’s gel electrodes.
The researchers also tested a gold nanomesh skin patch for one week to prove the breathability and the very low risk of skin-inflammation, recording electromyograms with minimal discomfort to the user.
University of Tokyo – www.ntech.t.u-tokyo.ac.jp
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