De Lora Jacqueline A, Aubermann Florian, Frey Christoph, Jahnke Timotheus, Wang Yuanzhen, Weber Sebastian, Platzman Ilia, Spatz Joachim P
Department of Cellular Biophysics, Max Planck Institute for Medical Research, Jahnstraße 29, 69120 Heidelberg, Germany.
Institute for Molecular Systems Engineering (IMSE), Heidelberg University, Im Neuenheimer Feld 225, 69120 Heidelberg, Germany.
ACS Omega. 2024 Mar 28;9(14):16097-16105. doi: 10.1021/acsomega.3c09881. eCollection 2024 Apr 9.
Acoustophoretic forces have been successfully implemented into droplet-based microfluidic devices to manipulate droplets. These acoustophoretic forces in droplet microfluidic devices are typically generated as in acoustofluidic devices through transducer actuation of a piezoelectric substrate such as lithium niobate (LiNbO), which is inherently accompanied by the emergence of electrical fields. Understanding acoustophoretic versus dielectrophoretic forces produced by electrodes and transducers within active microfluidic devices is important for the optimization of device performance during design iterations. In this case study, we design microfluidic devices with a droplet injection module and report an experimental strategy to deduce the respective contribution of the acoustophoretic versus dielectrophoretic forces for the observed droplet injection. Our PDMS-based devices comprise a standard oil-in-water droplet-generating module connected to a T-junction injection module featuring actuating electrodes. We use two different electrode geometries produced within the same PDMS slab as the droplet production/injection channels by filling low-melting-point metal alloy into channels that template the electrode geometries. When these electrodes are constructed on LiNbO as the substrate, they have a dual function as a piezoelectric transducer, which we call embedded liquid metal interdigitated transducers (elmIDTs). To decipher the contribution of acoustophoretic versus dielectrophoretic forces, we build the same devices on either piezoelectric LiNbO or nonpiezo active glass substrates with different combinations of physical device characteristics (i.e., elmIDT geometry and alignment) and operate in a range of phase spaces (i.e., frequency, voltage, and transducer polarity). We characterize devices using techniques such as laser Doppler vibrometry (LDV) and infrared imaging, along with evaluating droplet injection for our series of device designs, constructions, and operating parameters. Although we find that LiNbO device designs generate acoustic fields, we demonstrate that droplet injection occurs only due to dielectrophoretic forces. We deduce that droplet injection is caused by the coupled dielectrophoretic forces arising from the operation of elmIDTs rather than by acoustophoretic forces for this specific device design. We arrive at this conclusion because equivalent droplet injection occurs without the presence of an acoustic field using the same electrode designs on nonpiezo active glass substrate devices. This work establishes a methodology to pinpoint the major contributing force of droplet manipulation in droplet-based acoustomicrofluidics.
声泳力已成功应用于基于液滴的微流控装置中以操控液滴。液滴微流控装置中的这些声泳力通常与声流体装置中一样，通过诸如铌酸锂（LiNbO）等压电基板的换能器驱动产生，而这必然伴随着电场的出现。了解有源微流控装置中电极和换能器产生的声泳力与介电泳力对于在设计迭代过程中优化装置性能很重要。在本案例研究中，我们设计了带有液滴注入模块的微流控装置，并报告了一种实验策略，以推断观察到的液滴注入中声泳力与介电泳力各自的贡献。我们基于聚二甲基硅氧烷（PDMS）的装置包括一个标准的水包油液滴生成模块，该模块连接到一个具有驱动电极的T型结注入模块。我们通过将低熔点金属合金填充到形成电极几何形状模板的通道中，在与液滴产生/注入通道相同的PDMS平板内制作了两种不同的电极几何形状。当这些电极构建在LiNbO作为基板上时，它们具有作为压电换能器的双重功能，我们将其称为嵌入式液态金属叉指换能器（elmIDTs）。为了解释声泳力与介电泳力的贡献，我们在具有不同物理装置特性组合（即elmIDT几何形状和排列）的压电LiNbO或非压电有源玻璃基板上构建相同的装置，并在一系列相空间（即频率、电压和换能器极性）中运行。我们使用激光多普勒振动测量法（LDV）和红外成像等技术对装置进行表征，同时评估我们一系列装置设计、构造和操作参数下的液滴注入情况。尽管我们发现LiNbO装置设计会产生声场，但我们证明液滴注入仅由于介电泳力而发生。我们推断，对于这种特定的装置设计，液滴注入是由elmIDTs操作产生的耦合介电泳力引起的，而不是由声泳力引起的。我们得出这个结论是因为在非压电有源玻璃基板装置上使用相同的电极设计，在没有声场的情况下也会发生等效的液滴注入。这项工作建立了一种方法，以确定基于液滴的声微流控中液滴操控的主要作用力。
