Fabrication and Patterning of Magnetic Polymer Micropillar Structures Using a Dry-Nanoparticle Embedding Technique

Previously, solvent casting techniques have been used for the fabrication of magnetic polymer micropillar structures. These techniques provide very limited control over magnetic-particle placement, and particle agglomeration limits their use with highly viscous polymers such as polydimethylsiloxane. We report a new technique for the fabrication of magnetic polymer micropillars to overcome the aforementioned limitations. In this technique, magnetic micro-/nanoparticles are applied to a mold in their dry particulate state, omitting the need for the use of solvents. We demonstrate magnetic micropillars with uniform properties using high-viscosity polymers and iron nanoparticles. We show that simple modifications to the dry-nanoparticle embedding technique allow the embedding of other functional (nonmagnetic) particles inside the polymer micropillars, and we demonstrate patterning of the device. We present experimental results for the material composition, the magnetic properties, and the bending performance of our magnetic micropillar arrays. Compared to previously fabricated magnetic micropillars of similar dimensions and using lower magnitudes of externally applied magnetic fields and magnetic field gradients (286 mT, 41.45 mT/mm), our 8-mu m-diameter 18-mu m-high pillars produce an estimated maximum horizontal tip force of 0.33 +/- 0.08 mu N, larger than the values previously reported.