A novel technique to fabricate magnetic polydimethylsiloxane micropillar

Abstract

In past decades, polymeric micropillars have been employed in many complex functional micro-devices, such as micro-fluids, micro-sensors, tunable wetting surfaces, and substrate structures. This paper presents a novel technique to fabricate high-aspect-ratio magnetic polydimethylsiloxane (PDMS) micropillars that can move under gradient magnetic fields. First, a drop of Fe3O4 superparamagnetic nanoparticles was dispersed in acetone solution, sonicated, and poured over a pre-etch silicon mold with deep micro-holes. Second, we quickly attracted Fe3O4 nanoparticles in micro-holes with a strong permanent magnet at the silicon mold's backside. Third, we used a soft lithography process to force the PDMS liquid to flow into the micro-holes by sequencing the air in a vacuum chamber, baked in a hot plate, and then peeled off in ethanol solution and dried in a CO2 dryer machine. The diameters of PDMS magnetic micropillars were from 1 μm, 2 μm to 10 μm, and the heights were 30 μm and 50 μm. We observed 1 μm micropillar with 50 aspect ratio could deflect its end up to 12 μm under a gradient magnetic field of 5 mT/mm. The magnetic micropillar end movement in an ethanol solution was validated, which broads the application to micro-fluidics and other liquid microdevices. The energy-dispersive X-ray spectroscopy also examined the iron percentage in PDMS micropillars. They were in a range of 42% to 81.4%; with the median value was 59.6% that is the highest value reported in the literature, to our best knowledge.