非牛顿流体中包膜气泡在超声作用下的振动特性与破裂机理研究

Encapsulated bubbles have been commonly used as a kind of contrast agent in medical ultrasonic diagnosis for many years, and they are now increasingly applied in the field of ultrasound therapy，especially as drug-loaded microbubbles in ultrasonic targeted therapy. Encapsulated bubbles usually exist in non-Newtonian fluid environments (blood, tissue fluid, etc.), which makes it difficult to evaluate the real dynamical behavior of those bubbles, as extant theoretical models and experimental observations of the dynamics of encapsulated bubbles under ultrasound are confined to Newtonian fluids. The dynamical behavior of bubbles in non-Newtonian fluids is more complex than that in Newtonian fluids, leading to a more difficult theoretical analysis. Therefore, the research of bubble dynamics has become a frontier and a key scientific question of the application of encapsulated bubbles in ultrasonic diagnosis and therapy. In this project, experimental observation via high-speed photography, theoretical analysis and numerical simulation are used to compare, analyze and synthetically study the oscillations and fragmentation of encapsulated bubbles in a non-Newtonian fluid under the action of ultrasound. The dynamic model of encapsulated bubbles in a non-Newtonian fluid will be established. The effect of rheological characteristics of non-Newtonian fluid on the dynamical behavior of encapsulated bubbles will be explored, and the mechanism of encapsulated bubble fragmentation will be revealed. The results of this project will grow deeper understandings of the dynamics of encapsulated bubbles and provide theoretical guidance for the application of encapsulated bubbles in ultrasonic diagnosis and therapy.

包膜气泡作为造影剂在超声诊断中应用已久，近些年在超声治疗方面也渐受重视，特别是利用包膜气泡作为载药体，通过控制超声使气泡大幅振动破裂精准释放药物的靶向给药技术。包膜气泡使用时常处在非牛顿流体（如血液、组织液等）环境中，然而现有包膜气泡在超声作用下的动力学理论模型和实验观测还局限于牛顿流体中。非牛顿流体中气泡动力学行为相比在牛顿流体中更复杂，理论分析更困难，是气泡动力学前沿问题，也是包膜气泡用于超声诊疗技术的关键科学问题。本项目拟采用高速摄影技术观测非牛顿流体中包膜气泡在超声作用下的振动及破裂特性，从理论上建立非牛顿流体中包膜气泡动力学模型并利用数值计算方法分析泡的振动。通过比较、分析、综合研究非牛顿流体中包膜气泡在超声作用下振动特性及破裂机理，探索非牛顿流体环境流变特性对包膜气泡动力学行为的影响规律。本项目研究结果将扩充对包膜气泡动力学的认知，为包膜气泡在超声诊疗方面的应用提供理论指导。

本项目进行了非牛顿流体中空化实验观测表征和空化泡动力学理论建模分析。具体地：研究了空化强度和空化泡尺寸分布、超声参数、液体环境参数之间的关系；基于空化泡动力学过程中的能量守恒，给出了空化强度和空化泡尺寸分布、超声参数、液体环境参数之间的理论关系式，结果显示，对于一定声压振幅的超声和同样的液体环境及气核状况，存在一个特定的超声频率使得空化强度最大，而不是通常认为的越低频空化强度越高；研究了空化的观测表征方法，针对MHz超声空化泡动力学高速摄影观测难题，基于相似律，用低频驱动大泡代替高频驱动小泡，以空间换时间，提出了非牛顿流体中包膜气泡在超声作用下的动态特性观测分析思路。研究了非牛顿流体中超声空化特性以及超声空化对非牛顿流体流变特性影响规律，发现超声空化能降低粘弹性流体的粘度，而粘度降低又能增强粘弹性流体中的空化效应，揭示了非牛顿流体中超声空化特性以及超声空化对非牛顿流体流变特性影响机理。