Wearable sensors for real-time monitoring in medicine, e.g., for electrocardiograms (ECGs), need to keep in close contact with the skin to work correctly. Thus, they need to be flexible, stretchable, and adhere securely to the skin, preferably without causing skin irritation. Silicone-based polymers, for example, are biocompatible and have good mechanical properties for such apllications. However, they are electrical insulators.

Jin-Woo Park, Yonsei University, Seoul, Republic of Korea, and colleagues have developed transparent electrodes for medical applications based on an adhesive polydimethylsiloxane (a-PDMS) matrix with embedded Ag nanowire (AgNW) networks to provide the necessary electrical conductivity. The team combined a commercially available PDMS base and the corresponding crosslinker with Triton X-100, a surfactant. AgNW networks were then prepared on a glass slide, which was spin-coated with the liquid PDMS precursor mixture to embed the nanowires in the silicone. The films were then cured at 40 °C and removed from the glass slides to give the finished electrodes.

The addition of Triton X-100 allowed the researchers to optimize the mechanical properties of the electrodes. The surfactant partially inhibits the cross-linking reaction of the PDMS. The resulting mix of crosslinked and non-crosslinked PDMS forms the desired a-PDMS material. The team tested the electrodes in strain sensors and ECG sensors and found that the composite material is biocompatible, adhesive, transparent, stretchable, and conforms well to the skin, which leads to a high detection sensitivity.

• Highly Conformable, Transparent Electrodes for Epidermal Electronics,
  Jin-Hoon Kim, Seung-Rok Kim, Hye-Jun Kil, Yu-Chan Kim, Jin-Woo Park,
  Nano Lett. 2018.
  https://doi.org/10.1021/acs.nanolett.8b01743