Conductive Inks Image
A pen containing conductive ink can draw circuits on a variety of surfaces — even a loofah (shown here). (Credit: Adapted from ACS Applied Electronic Materials 2020, DOI: 10.1021/acsaelm.0c00866)

Scientists have developed inexpensive conductive inks for clog-free ballpoint pens that can allow users to “write” circuits almost anywhere — even on human skin. Flexible electronics are widely used in applications such as biosensors, electronic skin and energy storage.

The scientists developed a water-based ink containing conductive carbon particles composed of graphene nanosheets, multiwalled carbon nanotubes, and carbon black. Maleic anhydride modified rosin resin was added as a binder to reduce the ink’s solid content and viscosity, and xanthan gum was added to stabilize the dispersion so the carbon wouldn’t settle out of the ink.

The researchers optimized viscosity and the size of the conductive particles relative to the pen tip to create a system that provided stable and smooth writing performance on both flat and irregular surfaces — even a loofah. Circuits drawn on paper with the pen withstood multiple cycles of folding without deterioration.

The ink remained stable after sitting for 12 hours, released no harmful gases during use and cost much less than others reported in the literature, the researchers note. The pens could be used to draw flexible, wearable electronic devices on soft substrates or human skin.