分叉双层微流控系统中液滴分裂机理与乳化制备微粒性能的研究

Emulsions are ubiquitous in our daily life and widely involved in industries related with drugs, foods, cosmetics, and oil products. Emulsions can be formed by microfluidic technologies, which enable spatial and temporal control over size, shape, and concentration of droplets. The formed emulsions can act as template to prepare monodispersed functional materials for applications ranging from biochemical assays to pharmaceutical industry. Droplet fission is indispensable microfluidic emulsification operation, as it leads to formation of emulsion with a large number of droplets, this is particularly important when large-scale complex biological and chemical assays are needed. However, full exploitation of microfluidic production and control of emulsion is challenged by (1) lack of thorough understanding of the stability and break-up of individual emulsions as they flow through constrictions or pores, especially when the interactions among the emulsions are important; and (2) limited number of different dosages of droplets produced by existing technology. Specifically, we focus on constrictions with bifurcated junction because the encapsulated drugs must go through such complex structures in blood capillaries or the porous tissue material during drug delivery process. Therefore, understanding of the unique phenomena in such a microscale systems is urgently needed. In this project, we aim to devise a new microfluidic droplet fission and emulsification approach to address the challenge. We will characterize the droplet fission and associated breakup dynamics in bilayer microchannels with constrictions formed by bifurcated junction, in which droplets can deform significantly on account of the confining geometric boundaries, and the flow of the surrounding viscous liquid, both of which control the speed, trajectory, deformation, buckling and breakup of each droplet. The physics of droplet breakup dynamics behind this novel microstructure is highly fascinating, and will lead to different physical phenomena, which will be investigated numerically and experimentally. The mechanism of droplet fission, fluid structure interaction, and release kinetics will be investigated and applied in fabrication of higher order emulsions, which will be used to synthesize microparticles for drug delivery applications. The understanding of the droplet fission and emulsification in the novel microstructure will enable more versatile control over the emulsion formation, and the release kinetics in the emulsion-templated microparticles involved applications. Our study will provide model systems to understand how the drug delivery can be controlled precisely in media with complex constrictions, such as blood capillaries or the porous material of a tissue structure. The higher order emulsions with custom-made volume and shape formed by our novel approach can be widely used in biomedical and industrial applications, and inspire novel opportunities in these applications.

乳状液在我们生活和生产中有着重要的应用价值。由微流控形成乳状液，具有良好单分散性，可作为模板制备各种功能材料如微粒，应用于生物化学分析和制药等领域。微液滴分裂是微流控乳化中核心支撑技术，而相关领域日益涉及复杂结构如收缩分叉及多孔介质，这对微粒合成及其在给药体系的应用提出新挑战。分析研究在该微型系统内微液滴分裂机理及其对乳化影响，尤为迫切和重要。在这个项目中，我们提出一种新颖分叉双层微通道设计，形成缩颈结构，采用实验和数值模拟相结合的方法，对微液滴分裂机理开展研究。并以此为平台，研究液滴速度，轨迹，变形，屈曲和分裂。我们将形成高阶乳状液，制备满足不同剂量需要的单分散微粒，通过流固耦合分析，研究微粒释放动力特性,并应用于给药体系。我们将提供模型系统，以了解药物在毛细血管或生物组织多孔介质内如何实现精确递送。这些研究将对我们以乳状液液滴为平台在生物医学、能源方面的应用有着重要的价值和意义。

乳状液在生产生活中有重要应用价值。微液滴分裂是微流控乳化中核心支撑技术，而相关领域日益涉及复杂结构如收缩分叉及多孔介质，这对微粒合成及其在给药体系的应用提出新挑战。我们使用xurography工艺制备分叉双层微流控通道，对分叉双层微流控通道内单乳状液分裂机理进行了研究。同单层分叉微流控通道相比，双层分叉结构可产生对角线方向切割，形成父液滴不对称分裂，但每层形成子液滴尺寸具有良好的单分散性。新系统总压差较单层分叉微流控系统小。明确了收缩分叉结构处液滴分裂临界条件。定量研究了毛细数，以及上下层微通道因流阻差异带来的流量差异，对分裂后产生的子液滴的体积和形态所产生的影响。其次对双层微流控通道内以油水体系为代表的牛顿/牛顿体系和以羧甲基纤维素钠溶液／硅油为代表的剪切变稀／牛顿体系中，单乳状液成形及其分裂动力学进行了数值模拟、分析和对比。在相同的韦伯数和毛细数下（韦伯数在0.000035-0.00032之间；毛细数在0.0056-0.017之间），比较了两种体系的液滴体积和生成速率。明确了在微流控多相流体系中非牛顿流变特性对乳液形成及其稳定机理的影响，这将有助于当使用具有非牛顿流变特性的流体时，更灵活地控制乳状液形成和分裂变形。研究了当双乳液液滴流经分叉收缩结构处的分裂动力学。马伦哥尼效应作用下，内核释放率显著提高。使用针管微流控体系，可生成粒径分布均匀的单乳液液滴，和双重乳状液，以此为模板，制备具有核-壳结构的微胶囊。生成液滴过程中不需要对微通道表面进行亲、疏水性处理。开发了针管微流控装置并行生成微液滴的新方法，液滴生成速率可达每分钟535粒，粒径分布均匀，大小可通过调整针间距离或流量，实现控制。结合离心微流控平台，实现微液滴分离。我们开发的分叉双层微流控系统可作为平台，研究以乳状液为模板制备功能性微胶囊通过复杂多孔介质结构如毛细血管或生物组织多孔介质内的流动现象、释放机理。这些研究将对微流控乳化技术在生物医学、能源、环保等方面应用有较重要的价值和意义。