Univ Lyon, Université Claude Bernard Lyon 1, Centre Léon Bérard, INSERM, UMR 1032, LabTAU, France;
Univ Lyon, Ecole Centrale de Lyon, INSA de Lyon, CNRS, LMFA UMR 5509, France.
J Vis Exp. 2021 May 9(171). doi: 10.3791/62044.
When located near biological barriers, oscillating microbubbles may increase cell membrane permeability, allowing for drug and gene internalization. Experimental observations suggest that the temporary permeabilization of these barriers may be due to shear stress that is exerted on cell tissues by cavitation microstreaming. Cavitation microstreaming is the generation of vortex flows which arise around oscillating ultrasound microbubbles. To produce such liquid flows, bubble oscillations must deviate from purely spherical oscillations and include either a translational instability or shape modes. Experimental studies of bubble-induced flows and shear stress on nearby surfaces are often restricted in their scope due to the difficulty of capturing shape deformations of microbubbles in a stable and controllable manner. We describe the design of an acoustic levitation chamber for the study of symmetry-controlled nonspherical oscillations. Such control is performed by using a coalescence technique between two approaching bubbles in a sufficiently intense ultrasound field. The control of nonspherical oscillations opens the way to a controlled cavitation microstreaming of a free surface-oscillating microbubble. High-frame rate cameras allow investigating quasi-simultaneously the nonspherical bubble dynamics at the acoustic timescale and the liquid flow at a lower timescale. It is shown that a large variety of fluid patterns may be obtained and that they are correlated to the modal content of the bubble interface. We demonstrate that even the high-order shape modes can create large-distance fluid patterns if the interface dynamics contain several modes, highlighting the potential of nonspherical oscillations for targeted and localized drug delivery.
当微泡位于生物屏障附近时，其振动可能会增加细胞膜的通透性，从而使药物和基因内流。实验观察表明，这些屏障的暂时通透性可能是由于空化微流对细胞组织施加的剪切力所致。空化微流是在超声微泡振动时产生的涡旋流。为了产生这种液体流动，气泡振动必须偏离纯球形振动，并包括平移失稳或形状模式。由于难以以稳定和可控的方式捕捉微泡的形状变形，因此，关于气泡诱导的流动和附近表面剪切力的实验研究通常受到限制。我们描述了一种用于研究对称控制非球形振动的声悬浮腔的设计。通过在足够强的超声场中使两个接近的气泡合并来实现这种控制。非球形振动的控制为自由表面振动微泡的受控空化微流开辟了道路。高帧率相机允许在声学时间尺度上同时研究非球形气泡动力学和较低时间尺度上的液体流动。结果表明，可以获得多种流体图案，并且它们与气泡界面的模态内容相关。我们证明，如果界面动力学包含多个模态，即使是高阶形状模式也可以产生远距离的流体图案，突出了非球形振动在靶向和局部药物输送方面的潜力。
