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

由于大多数灵敏和标准化的生物分析技术都在液体介质中工作，芯片实验室系统应该能够有效地处理微米/纳米级的液体溶液。到目前为止，这些系统大多是基于连续流系统开发的，缺乏设备的可重构性。因此，基于液滴的芯片实验室系统引起了人们的极大关注，即基于电润湿的数字微流控系统，它操纵离散的液滴而不是连续的液流。然而，基于电润湿的方法受到高电压要求和生物污垢等限制，阻碍了许多实际应用。该项目提供了一条通向新型数字微流控平台的直接途径，没有与电润湿相关的限制。所提出的平台利用一种纯粹的机械手段，以快速、灵活、可编程和可重构的方式驱动离散的液滴。该项目还将产生可直接用于课堂教学和公众对材料、微流体、界面科学、微/纳米技术的兴趣的信息和演示材料。该项目旨在利用黑色硅棘轮表面探索动态可调的表面形貌和相应的界面润湿性，以寻求一种新的策略来操纵液滴，以促进数字微流控技术的发展。所提出的棘轮表面包括弹性体微柱上的超疏水黑色硅鳞片，以便单个信号驱动单独的鳞片并改变整个表面形态，形成驱动液体液滴的黑色硅棘轮表面。因此，液滴基本上是机械驱动的，而不是电力驱动的。此外，预计在黑色硅表面和/或光滑的液体注入的多孔表面上的锥形纳米结构将显著减少生物污垢。如果不阐明基本原则和建立必要的技术，拟议的办法就无法实现。两位首席研究人员涵盖机械、材料、制造和微流体的专业知识将结合在一起，以实现这些理解和知识，并最终开辟一个横跨智能复合材料和数字微流体的新的跨学科研究领域。在项目期间，将系统地追求三个目标，以实现项目目标。首先，将研究所提出的超疏水棘轮表面所涉及的机械特性，其次，将表征液滴与超疏水棘轮表面之间的相互作用，并将研究操纵其上的液滴的相关作用力。最后，将展示液滴的操作，包括液滴的运输、合并和分裂，以及减少生物污垢。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.