Department of Mechanical Engineering, Chonnam National University, Yongbong-ro 77, Buk-gu, Gwangju 61186, Republic of Korea.
Department of Mechanical Engineering, Chonnam National University, Yongbong-ro 77, Buk-gu, Gwangju 61186, Republic of Korea.
Ultrason Sonochem. 2023 Feb;93:106305. doi: 10.1016/j.ultsonch.2023.106305. Epub 2023 Jan 18.
In droplet-based microfluidic platforms, precise separation of microscale droplets of different chemical composition is increasingly necessary for high-throughput combinatorial chemistry in drug discovery and screening assays. A variety of droplet sorting methods have been proposed, in which droplets of the same kind are translocated. However, there has been relatively less effort in developing techniques to separate the uniform-sized droplets of different chemical composition. Most of the previous droplet sorting or separation techniques either rely on the droplet size for the separation marker or adopt on-demand application of a force field for the droplet sorting or separation. The existing droplet microfluidic separation techniques based on the in-droplet chemical composition are still in infancy because of the technical difficulties. In this study, we propose an acoustofluidic method to simultaneously separate microscale droplets of the same volume and dissimilar acoustic impedance using ultrasonic surface acoustic wave (SAW)-induced acoustic radiation force (ARF). For extensive investigation on the SAW-induced ARF acting on both cylindrical and spherical droplets, we first performed a set of the droplet sorting experiments under varying conditions of acoustic impedance of the dispersed phase fluid, droplet velocity, and wave amplitude. Moreover, for elucidation of the underlying physics, a new dimensionless number AR was introduced, which was defined as the ratio of the ARF to the drag force acting on the droplets. The experimental results were comparatively analyzed by using a ray acoustics approach and found to be in good agreement with the theoretical estimation. Based on the findings, we successfully demonstrated the simultaneous separation of uniform-sized droplets of the different acoustic impedance under continuous application of the acoustic field in a label-free and detection-free manner. Insomuch as on-chip, precise separation of multiple kinds of droplets is critical in many droplet microfluidic applications, the proposed acoustofluidic approach will provide new prospects for microscale droplet separation.
在基于液滴的微流控平台中，为了在药物发现和筛选测定中进行高通量组合化学，越来越需要精确分离不同化学成分的微尺度液滴。已经提出了各种液滴分选方法，其中同种液滴被转移。然而，开发用于分离不同化学成分的均匀尺寸液滴的技术相对较少。以前的大多数液滴分选或分离技术要么依赖于液滴尺寸作为分离标记，要么采用按需施加力场的方法进行液滴分选或分离。由于技术上的困难，基于液滴内化学成分的现有液滴微流控分离技术仍处于起步阶段。在这项研究中，我们提出了一种基于声流的方法，使用超声表面声波（SAW）诱导的声辐射力（ARF）同时分离相同体积和不同声阻抗的微尺度液滴。为了广泛研究 SAW 诱导的 ARF 对圆柱和球形液滴的作用，我们首先在不同的分散相流体声阻抗、液滴速度和波幅条件下进行了一组液滴分选实验。此外，为了阐明潜在的物理机制，引入了一个新的无量纲数 AR，它定义为 ARF 与作用在液滴上的阻力之比。通过使用射线声学方法对实验结果进行了比较分析，发现与理论估计吻合较好。基于这些发现，我们成功地在连续施加声场的情况下，以无标记和无检测的方式，同时分离不同声阻抗的均匀尺寸液滴。在片上，精确分离多种液滴对于许多液滴微流控应用至关重要，所提出的声流方法将为微尺度液滴分离提供新的前景。
