State Key Laboratory of Ultrasound in Medicine and Engineering, College of Biomedical Engineering, Chongqing Medical University, Chongqing, 400016, China.
Chongqing Key Laboratory of Biomedical Engineering, Chongqing Medical University, Chongqing, 400016, China.
Biomed Microdevices. 2021 Dec 29;24(1):7. doi: 10.1007/s10544-021-00608-6.
Acoustofluidics inside the microchannel has already found its wide applications recently. Acoustic streaming and radiation force are two underlying mechanisms that determine the trajectory of microparticles and cells in the manipulation. Critical particle size of viscous effects is found to be about 1.6 µm in the conventional rectangular microchannel (W × H = 380 m × 160 m) at the frequency of 2 MHz, below which the acoustic streaming dominants, and is independent of the driving voltage. In order to effectively adjust such a critical size, a approach is proposed and evaluated numerically to enhance the acoustic streaming by adding some protrusions (i.e., in the shape of a wedge, rod, half-ellipse) to the middle of the top or bottom wall. It is found that the resonant frequency and acoustic pressure will decrease and the acoustic streaming velocity will increase significantly, respectively, with the increase of protrusion height (up to 30 µm while keeping the width the same as 8 µm). Subsequently, trajectory motion patterns of microparticles have apparent changes in comparison to those inside the rectangular microchannel, and acoustic streaming can even dominate the motion of large microparticles (i.e., 10 µm). As a result, the critical particle size could be increased up to 72.5 µm. Furthermore, different protrusion shapes (i.e., wedge, rod, half-ellipse) on the top wall were compared. The sharpness of protrusion at its tip seems to determine the acoustic streaming velocity. The wedge attached to the bottom wall had higher resonant frequency and lower acoustic streaming velocity compared with the top wedge in the same dimension. The patterns of acoustic streaming and microparticle trajectory motion in the microchannel with dual wedges on the top and bottom walls are not the superposition of those of the top and bottom wedge individually. In summary, the geometry of the microchannel has a significant effect on the induced acoustofluidics by the bulk acoustic waves. A much larger acoustic streaming velocity is produced at the tip of the protrusion to change the critical size of microparticles between acoustic streaming and radiation force. It suggests that more applications of acoustofluidics (i.e., mixing and sonoporation) to microparticles and cells in various sizes are feasible by designing an appropriate geometry of the microchannel.
近年来，微通道内的声流已得到广泛应用。声流和辐射力是决定微粒子和细胞在操控中运动轨迹的两个基本机制。在频率为 2MHz 的常规矩形微通道（W×H=380μm×160μm）中，粘性效应的临界粒子尺寸约为 1.6μm，此时声流占主导地位，且与驱动电压无关。为了有效调整这种临界尺寸，提出并数值评估了一种方法，即在微通道的顶壁或底壁中间添加一些突起（如楔形、棒状、半椭圆形）来增强声流。研究发现，随着突起高度的增加（突起高度增加到 30μm 时保持宽度为 8μm），共振频率和声压会显著降低，而声流速度会显著增加。随后，与矩形微通道相比，微粒子的运动轨迹模式发生了明显变化，甚至可以控制大微粒子（即 10μm）的运动。结果，临界粒子尺寸增加到 72.5μm。此外，还比较了顶壁上不同的突起形状（如楔形、棒状、半椭圆形）。在尖端的突起尖锐度似乎决定了声流速度。与相同尺寸的顶楔形相比，附着在底壁上的楔形具有更高的共振频率和更低的声流速度。在顶壁和底壁上有两个楔形的微通道中的声流和微粒子运动轨迹模式不是顶壁和底壁楔形各自模式的叠加。总之，微通道的几何形状对体声波诱导的声流有显著影响。在突起的尖端产生更大的声流速度，从而改变声流和辐射力之间的微粒子临界尺寸。这表明通过设计适当的微通道几何形状，可以实现对各种尺寸的微粒子和细胞的更多声流应用（如混合和超声穿孔）。
