With the development of lithography techniques, microfluidic systems have drastically evolved in the past decades. Digital microfluidics (DMF), which enables discrete droplet actuation without any carrying liquid as opposed to the continuous-fluid-based microfluidics, emerged as the candidate for the next generation of lab-on-a-chip systems. The DMF has been applied to a wide variety of fields including electrochemical and biomedical assays, drug delivery, and point-of-care diagnosis of diseases. Most of the DMF devices are made with photolithography which requires complicated processes, sophisticated equipment, and cleanroom setting. Based on the fabrication technology being used, these DMF manipulate droplets in a planar format that limits the increase of chip density. The objective of this study is to introduce additive manufacturing (AM) into the fabrication process of DMF to design and build a 3D-structured DMF platform for droplet actuation between different planes. The creation of additively manufactured DMF is demonstrated by fabricating a planar DMF device with ion-selective sensing functions. Following that, the design of vertical DMF electrodes overcomes the barrier for droplets to move between different actuation components, and the application of AM helps to construct free-standing xylem DMF to drive the droplet upward. To form a functional system, the horizontal and xylem DMF are integrated so that a three-dimensional (3D) droplet manipulation is demonstrated. The integrated system performs a droplet actuation speed of 1 mm/s from horizontal to vertical with various droplet sizes. It is highly expected that the 3D-structured DMF open new possibilities for the design of DMF devices that can be used in many practical applications.
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Thesis advisor: Soo, Kim, Woo
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