Silver Nano-Inks Synthesized with Biobased Polymers for High-Resolution Electrohydrodynamic Printing Toward In-Space Manufacturing

Electrohydrodynamic (EHD) printing is an additive manufacturing technique capable of producing micro/nanoscale features by precisely jetting ink under an electric field. However, as a new technique compared to more conventional methods, commercially available inks designed and optimized for EHD are currently very limited. To address this challenge, a new silver nanoink platform was developed by synthesizing silver nanoparticles in situ with biobased polymer 2-hydroxyethyl cellulose (HEC). Typically used as a thickening agent, HEC is cost-effect, biocompatible, and versatile in developing inks that meet the rheology criteria for high-resolution EHD jetting. This approach significantly outperforms the traditional use of polyvinylpyrrolidone (PVP), enabling the stabilization of high solids content (>50 wt %) nanoinks for over 10 months with an HEC dosage 20 times lower than that required by PVP. The HEC-synthesized silver ink displays excellent electrical properties, yielding resistivities as low as 2.81 μΩ cm upon sintering, less than twice that of pure silver. Additionally, the capability to sinter at low temperatures (<200 °C) enables the use of this ink on polymer substrates for flexible devices. The synthesized nanoinks were also found to be capable of producing precise, high-resolution features by EHD printing with smooth lines narrower than 5 μm printed using a 100 μm nozzle. Additionally, a semiempirical model was developed to reveal the relationship between printing resolution, ink properties, and printing parameters, enabling precise printing control. Moreover, for the first time, the unique ability of EHD to achieve precise fabrication under microgravity was conclusively demonstrated through a parabolic flight test utilizing the HEC-based nanoinks. The study greatly expands the potential of printing thin films for the on-demand manufacturing of electronic devices in space.