Resistance Increase of Only About 16% After 10 Hours in Water — A Transparent Electrode That Works Even in Bodily Fluids (RIKEN)

Explanation

Transparent conductive films—thin films that are transparent yet conduct electricity—are widely used in smartphone touch panels and similar devices. However, conventional films are weak against water, and their performance degrades in salt-containing liquids such as bodily fluids. They have not been suitable for electrodes used on or inside the body.

On August 20, 2026, a RIKEN research group announced the development of a transparent conductive film that remains stable even in water. The achievement was made by Research Scientist Lulu Sun and Senior Research Scientist Takao Someya, in collaboration with Yonsei University in South Korea, Huazhong University of Science and Technology in China, and Osaka University.

The film created was named "Biphasic Percolation Network (BIPIN)." It has a structure in which silver nanowires (extremely thin metal wires) are enveloped by a conductive polymer and a fluorine-containing ionomer (a polymer bearing ionic groups). The polymer phase surrounds the metal nanowires, preserving the electrical pathways while preventing water from penetrating. The film is only about 200 nanometers thick (roughly 1/5000 of a millimeter).

The numbers make the performance clear. The water contact angle is 94.6 degrees, indicating water-repellent properties. After 600 minutes (10 hours) of immersion in water, the increase in electrical resistance was only 15.8±5.1 percent. The sheet resistance is about 20 ohms per square, and the visible light transmittance exceeds 90 percent. The survival rate of cells cultured on the film was 92.77±1.78 percent, confirming that it is not harmful to cells when placed on living tissue.

Transparency has practical significance. Using this film, the research group created a 9-channel (each 300×300 micrometers) electrode array for the brain surface. The overall thickness is 5.5 micrometers. Because the electrodes are transparent, it is possible to optically observe blood vessels in the same location while recording electrical activity in the brain. Conventional metal electrodes are opaque, making it impossible to see what lies beneath them.

Other applications mentioned include electromyography measurement during water sports and wearable devices that can be used even when sweating.

The concept behind this film is reflected in its name, "biphasic." If metal nanowires alone are arranged, electricity flows well, but water seeps in through the gaps. With a water-repellent polymer alone, electricity does not flow. The film combines the two phases with separate roles: the metal phase remains connected as an electrical pathway, while the polymer phase covers the whole and blocks water intrusion. Percolation refers to a phenomenon in which fine particles or wires connect to form pathways throughout a material, and in this film, that "connectivity" is established on both the metal side and the polymer side.

The paper was published online in Nature Communications on August 7, 2026.

Source: RIKEN, "Successful development of a transparent conductive film resistant to water and bodily fluids" (August 20, 2026)
https://www.riken.jp/press/2026/20260820_2/index.html