Saito Makoto, Arai Fumihito, Yamanishi Yoko, Sakuma Shinya
Department of Mechanical Engineering, Faculty of Engineering, Kyushu University, Fukuoka 819-0395, Japan.
Department of Mechanical Engineering, Graduate School of Engineering, The University of Tokyo, Bunkyo-ku 113-8656, Japan.
Proc Natl Acad Sci U S A. 2024 Aug 13;121(33):e2306182121. doi: 10.1073/pnas.2306182121. Epub 2024 Aug 5.
Microvortices are emerging components that impart functionality to microchannels by exploiting inertia effects such as high shear stress, effective fluid diffusion, and large pressure loss. Exploring the dynamic generation of vortices further expands the scope of microfluidic applications, including cell stimulation, fluid mixing, and transport. Despite the crucial role of vortices' development within sub-millisecond timescales, previous studies in microfluidics did not explore the modulation of the Reynolds number (Re) in the range of several hundred. In this study, we modulated high-speed flows (54 < [Formula: see text] < 456) within sub-millisecond timescales using a piezo-driven on-chip membrane pump. By applying this method to microchannels with asymmetric geometries, we successfully controlled the spatiotemporal development of vortices, adjusting their behavior in response to oscillatory flow directions. These different vortices induced different pressure losses, imparting the microchannels with direction-dependent flow resistance, mimicking a diode-like behavior. Through precise control of vortex development, we managed to regulate this direction-dependent resistance, enabling the rectification of oscillatory flow resembling a diode and the ability to switch its rectification direction. This component facilitated bidirectional flow control without the need for mechanical valves. Moreover, we demonstrated its application in microfluidic cell pipetting, enabling the isolation of single cells. Consequently, based on modulating high-speed flow, our approach offers precise control over the spatiotemporal development of vortices in microstructures, thereby introducing innovative microfluidic functionalities.
微涡旋是新兴的组件，通过利用诸如高剪切应力、有效流体扩散和大压力损失等惯性效应，赋予微通道功能。探索涡旋的动态生成进一步扩展了微流体应用的范围，包括细胞刺激、流体混合和传输。尽管涡旋在亚毫秒时间尺度内的发展起着关键作用，但以前在微流体方面的研究并未探索数百范围内雷诺数（Re）的调制。在本研究中，我们使用压电驱动的片上膜泵在亚毫秒时间尺度内调制高速流动（54 < [公式：见原文] < 456）。通过将此方法应用于具有不对称几何形状的微通道，我们成功地控制了涡旋的时空发展，根据振荡流动方向调整它们的行为。这些不同的涡旋引起不同的压力损失，赋予微通道与方向相关的流动阻力，类似于二极管的行为。通过精确控制涡旋发展，我们设法调节这种与方向相关的阻力，实现类似于二极管的振荡流整流以及切换其整流方向的能力。该组件无需机械阀即可实现双向流动控制。此外，我们展示了其在微流体细胞移液中的应用，能够分离单个细胞。因此，基于调制高速流动，我们的方法提供了对微结构中涡旋时空发展的精确控制，从而引入了创新的微流体功能。
