Programmable droplet manipulation by combining a superhydrophobic magnetic film and an electromagnetic pillar array

In this paper, we present a novel magnetic digital microfluidic platform that combines a superhydrophobic magnetic film (SHMF) with an electromagnetic pillar array (EMPA) for droplet manipulation. Upon dynamic excitation of the EMPA under the SHMF, the surface topography of the SHMF was programmatically changed, which can direct and control the motion of aqueous droplets efficiently and accurately by utilizing gravitational force. Using this platform, we demonstrated the following droplet operations: path-programmable transportation of droplets, parallel transportation of multiple droplets, merging and mixing of multiple droplets. In particular, a rapid and efficient mixing was easily achieved by oscillating the coalesced droplets with the frequent switching of magnetic actuation of the EMPA (e.g., by applying AC current). We also demonstrated the applicability of this platform as a new type of open-surface digital microfluidic device using a simple crystallization experiment. We believe that this platform is appealing for biological microanalyses and chemical microreactions because it provides a means for pure droplet manipulation without any additives (e.g., magnetic particles), and allows better scalability and programmability of droplet manipulation. (C) 2018 Elsevier B.V. All rights reserved.