High-Aspect-Ratio Needle-Shaped Mold Fabrication Using Rosensweig Instability in Ferrofluids

This paper reports a simple cleanroom-free fabrication technique to create high-aspect-ratio needle-like solid mold microstructures using magnetic self-assembly of ferrofluids under the Rosensweig instability of the fluids. The presented fabrication method provides precise and programmable control over the height, aspect ratio, and spatial arrangement of well-aligned and sharp microneedle structures of solidified ferrofluid formed in array on the substrate. These microneedle structures are demonstrated to have heights and aspect ratios of up to ~1.5 mm and ~5, respectively. The developed process offers an attractive path to the application for microneedle device production.