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

由于大多数敏感和标准化的生物分析技术都是在液体介质中工作的，因此芯片实验室系统应该能够有效地处理微/纳米尺度的液体溶液。迄今为止，这些系统大多是基于连续流系统开发的，缺乏设备可重构性。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体系统，它可以操纵离散的液滴而不是连续的液体流。然而，基于电润湿的方法受到诸如高电压要求和生物污垢等限制，阻碍了许多实际应用。这个项目提供了一个没有电润湿相关限制的新型数字微流体平台的直接途径。提出的平台利用纯机械手段以快速、灵活、可编程和可重构的方式驱动离散液滴。该项目还将产生信息和示范材料，可直接用于促进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。该项目旨在探索黑硅棘轮表面的动态可调表面形态和相应的界面润湿性，以寻求一种新的策略来操纵液滴，以促进数字微流体的发展。所提出的棘轮表面涉及弹性体微柱上的超疏水黑硅鳞片，这样单个信号驱动单个鳞片并改变整个表面形态，形成驱动液滴的黑硅棘轮表面。因此，液滴本质上是机械驱动的，而不是电驱动的。此外，预计黑硅表面的锥形纳米结构和/或光滑的液体注入多孔表面的集成将显著减少生物污染。如果不阐明基本原则和建立必要的技术，所建议的方法就无法实现。两位主要研究人员将结合力学、材料、制造和微流体的专业知识，以实现这些理解和知识，最终开辟智能复合材料和数字微流体的跨学科研究新领域。在项目期间，将系统地追求三个目标，以实现项目目标。首先，研究了所提出的超疏水棘轮表面的力学特性，其次，表征了液滴与超疏水棘轮表面之间的相互作用，并研究了操纵液滴的相关力。最后，液滴操作包括液滴运输，合并和分裂随着减少的生物污染将被证明。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.