The interaction between an acoustically driven microbubble and a surface is of interest for a variety of applications, such as ultrasound imaging and therapy. Prior investigations have mainly focused on acoustic effects of a rigid boundary, where it was generally observed that the wall increases inertia and reduces the microbubble resonance frequency. Here we investigate the response of a lipid-coated microbubble adherent to a rigid wall. Firm adhesion between the microbubble and a glass surface was achieved through either specific (biotin/avidin) or nonspecific (lipid/glass) interactions. Total internal reflection fluorescence microscopy was used to verify conditions leading to either adhesion or non-adhesion of the bubble to a glass or rigid polymer surface. Individual microbubbles were driven acoustically to sub-nanometer-scale radial oscillations using a photoacoustic technique. Remarkably, adherent microbubbles were shown to have a higher resonance frequency than non-adherent microbubbles resting against the wall. Analysis of the resonance curves indicates that adhesion stiffens the bubble by an apparent increase in the shell elasticity term and decrease in the shell viscosity. Based on these results, we conclude that surface adhesion is dominant over acoustic effects for low-amplitude microbubble oscillations.

中文翻译：

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粘附到固体表面后微泡动力学的变化

声学驱动的微泡和表面之间的相互作用对各种应用感兴趣，例如超声成像和治疗。先前的研究主要集中在刚性边界的声学效应上，通常观察到壁会增加惯性并降低微泡共振频率。在这里，我们研究了附着在刚性壁上的脂质涂层微泡的反应。通过特异性（生物素/抗生物素蛋白）或非特异性（脂质/玻璃）相互作用实现微泡和玻璃表面之间的牢固粘附。全内反射荧光显微镜用于验证导致气泡粘附或不粘附到玻璃或刚性聚合物表面的条件。使用光声技术将单个微气泡声学驱动到亚纳米级径向振荡。值得注意的是，粘附的微泡显示出比靠壁休息的非粘附微泡具有更高的共振频率。共振曲线的分析表明，通过壳弹性项的明显增加和壳粘度的降低，粘附力使气泡变硬。基于这些结果，我们得出结论，对于低振幅微泡振荡，表面粘附力优于声学效应。共振曲线的分析表明，通过壳弹性项的明显增加和壳粘度的降低，粘附力使气泡变硬。基于这些结果，我们得出结论，对于低振幅微泡振荡，表面粘附力优于声学效应。共振曲线的分析表明，通过壳弹性项的明显增加和壳粘度的降低，粘附力使气泡变硬。基于这些结果，我们得出结论，对于低振幅微泡振荡，表面粘附力优于声学效应。