血管壁复杂边界约束下的包膜微气泡动力学特性分析

Encapsulated microbubbles (EMBs) are widely used in medical ultrasound applications. When injected into the bloodstream, EMBs can travel to all organs of the body within blood vessels. Therefore, the confinement of blood vessel plays an important role in the dynamics of EMBs. There was considerable study on a gas bubble under confinement and an EMB in unbounded field. We propose to study the dynamics of EMBs under confinement of elastic and complex blood vessel in an ultrasound field.. In the theoretical study, we will establish the dynamic equations of the radial oscillations, translations and shape oscillations of EMBs under confined boundary. The difficulties will be the setting of simplified confinement and its validity and feasibility. We will derive the expressions of natural frequencies of different modes combining the effects of confined boundary. The influence of ultrasound parameters, such as frequency, amplitude and waveform, is of our interest. The condition of the stability of shape modes will be derived.. In the numerical study, we will couple the flow field with the membrane mechanics. The encapsulating membrane is considered as viscoelastic material. The blood vessel is considered as an elastic wall. Using the immersed boundary method, we will investigate the microstreaming near an EMB during oscillations, focusing on the no-slip condition at the EMB interface. The effects on the shear tension at the blood vessel will be studied. Using the 3D boundary integral method, we will model the unsteady shape oscillation and the subsequent jet formation, especially the topological change of the interface. The code is to model the behavior of one EMB, the interaction of EMBs, and the interaction between EMBs and cells or particles. We will investigate the type and direction of jet near the blood vessel. The effects of elastic modulus of the blood vessel, the complex geometry of vessel and the shear flow near blood vessel will be studied.. In the experimental study, we will generate EMBs with different sizes and elastic moduli using microfluidic chip, observe their behavior including jet formation near elastic wall using microscopy and measure the velocity field of microstreaming near the EMBs using Micro-PIV. The experimental results will be used to validate the theoretical and numerical models.. Our study will develop the dynamics of bubbles in complex physical confined condition. The developments will have important and timely applications in improving the efficiency and safety of sonography. We will address fundamental questions of immediate significance relating the mechanisms of drug delivery and sonoporation in terms of shape mode oscillation and bubble jetting.

血管壁的复杂边界是医疗超声应用中包膜微气泡(EMB)动力学问题必不可少的约束条件。目前对边界约束下气泡动力学的研究多针对非包膜气泡，而关于EMB动力学的研究多基于无界流场。本项目拟采用数学建模、数值模拟和微流道实验相结合的方法，研究超声场中受复杂几何和弹性血管壁约束的EMB动力学特性。建立边界约束下EMB动力学模型，分析界面稳定性；采用浸入边界法模拟EMB与管壁间的微流，关注粘弹性界面的影响，采用Micro-PIV校验速度场，计算壁面切应力评价微流对细胞通透性的影响；采用边界积分法模拟EMB在血管壁附近发生坍塌射流导致界面拓扑变化的过程，结合显微镜观察，分析决定射流类型和方向的条件；考察EMB与细胞间相互作用。本项目旨在深入认识复杂物理约束下的气泡动力学行为，为EMB的医疗应用提供机理支持，指导针对不同血管壁特点，通过控制超声波和包膜参数，延长造影时间、提高药物运输和声致穿孔的准确度。

包膜微气泡在医疗超声中有着广泛应用，血管壁的复杂边界是应用中必不可少的约束条件。为了有效地控制包膜气泡界面的稳定性、辅助医疗应用中的超声参数设定和造影剂的选择，本项目研究超声场中受弹性血管壁约束的包膜气泡动力学特性，从力学的角度揭示约束、超声波、粘弹性膜等参数与包膜气泡动力学响应之间的关系。. 主要研究成果有：(1)建立气泡动力学与薄膜力学耦合的数学物理模型，计入弹性壁的约束，提出快速预报约束条件下包膜气泡径向振荡模态和各阶形状模态固有频率的方法，明确激发气泡界面模态共振的参数，阐明引起气泡界面变形的Mathieu不稳定和Rayleigh-Taylor不稳定两种机制，为通过超声波参数控制气泡界面稳定性提供了机理支持；(2)实现气泡动力学与多物理场的耦合建模，揭示超声激励、振荡电场、血管壁约束、血液流动中的气泡动力学特征，阐明流体粘性对包膜气泡动力学的重要作用，为结合真实流动和约束环境研究气泡动力学响应提供了可靠的手段。. 本项目以研究包膜气泡界面稳定性的控制机理作为出发点，建立气泡动力学、薄膜力学与超声波场互相耦合的理论与数值模型，揭示包膜气泡发生界面不稳定的机理，及其与超声波参数和包膜参数的关系，为包膜微气泡在医疗超声中的应用提供理论参考和基础性技术支持，指导针对不同部位的血管壁特点，通过控制超声波参数和包膜参数，提高超声成像效率、进行精准的药物运输和提高细胞膜通透性。

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