Collaborative Research: Magnetically Actuated Black Silicon Ratchet Surfaces for Digital Microfluidics

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Since most of the sensitive and standardized bio-analytical techniques work in the liquid medium, the lab-on-a-chip system should be able to efficiently handle liquid solutions in micro/nano scale. To date, most of these systems have been developed based on the continuous flow system which lacks device reconfigurability. Consequently, much attention has been drawn to droplet-based lab-on-a-chip systems, namely, digital micro fluidic systems based on electrowetting that manipulate discrete liquid droplets rather than continuous liquid streams. Nevertheless, the electrowetting-based approach suffers from limitations such as high voltage requirement and biofouling, hampering many real applications. This project provides a straightforward pathway to a new digital micro fluidic platform without electrowetting-related limitations. The proposed platform exploits a purely mechanical means to drive discrete liquid droplets in a rapid, flexible, programmable, and reconfigurable manner. This project will also generate information and demonstration materials that can be directly used to promote both classroom teaching and general public's interest in materials, microfluidics, interfacial science, micro/nanotechnology. The project aims to explore the dynamically tunable surface morphology and consequential interfacial wettability using a black silicon ratchet surface in order to seek a new strategy to manipulate liquid droplets for the advancement of digital microfluidics. The proposed ratchet surface involves superhydrophobic black silicon scales on elastomer micropillars such that individual signals actuate individual scales and change the entire surface morphology forming a black silicon ratchet surface that drives liquid droplets. Consequently, droplets are essentially driven mechanically, not electrically. In addition, it is expected that conical nanostructures on the black silicon surface and/or slippery liquid infused porous surfaces to be integrated will significantly reduce biofouling. The proposed approach cannot be realized without elucidating underlying principles and establishing necessary techniques. Two principal investigators’ expertise encompassing mechanics, materials, manufacturing and microfluidics will be combined in order to achieve those understanding and knowledge, and finally open up a new interdisciplinary research area across smart composite materials and digital microfluidics. During the project, three objectives will be systematically pursued to towards the project goal. First, the mechanical characteristics involved in the proposed superhydrophobic ratchet surface will examined, Second, the interaction between liquid droplets and the superhydrophobic ratchet surface will be characterized and associated forces to manipulate liquid droplets on it will be investigated. Finally, droplet manipulations including droplet transporting, merging, and splitting along with the reduced biofouling will be demonstrated.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.