Silver nanowires have drawn significant interest in recent years for use in many applications ranging from prosthetic devices to wearable health sensors due to their flexibility, stretchability, and conductive properties. While proof-of-concept experiments have been promising, there have been significant challenges to printing highly integrated circuits using silver nano-wires. Silver nanoparticles can be used to print circuits, but the nanoparticles produce circuits that are more brittle and less conductive than silver nano-wires. Conventional techniques for printing circuits don't work well with silver nanowires; the nanowires often clog the printing nozzles.
A new technique was developed that allows circuits to be printed on flexible, stretchable substrates using silver nano-wires. The advance makes it possible to integrate the material into a wide array of electronic devices.
The approach uses electrohydrodynamic printing, which relies on electrostatic force to eject the ink from the nozzle and draw it to the appropriate site on the substrate. This allows use of a very wide nozzle, which prevents clogging while retaining very fine printing resolution.
The “ink” consists of a solvent containing silver nanowires that are typically more than 20 micrometers long. The resulting circuits have the desired conductivity, flexibility, and stretchability. In addition, the solvent is both nontoxic and water-soluble; once the circuit is printed, the solvent can simply be washed off.
The size of the printing area is limited only by the size of the printer, meaning the technique could be easily scaled up. The new technique was used to create prototypes that make use of the silver nanowire circuits, including a glove with an internal heater and a wearable electrode for use in electrocardiography.