Jiang, Xinyue; (2019) Microfluidic Devices with Coarse Capillaries to Fabricate Bioengineering Products: Bubbles, Scaffolds and Nanoparticles. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Microbubbles fabricated by microfluidic techniques have garnered remarkable interest in many diverse fields for various applications such as ultrasound contrast agents, tissue engineering scaffolds and nanoparticles in drug delivery. Microfluidic T-junctions were used for this purpose owing to their ease of operation and fine control over the operation parameters. This thesis consists of two main sections: (1) microfluidic-assisted production of scaffolds and nanoparticles; and (2) multiple T-junctions for the reduction of microbubble size in size-restricted applications. In section one, a single T-junction was used to produce microdroplets with pre-designed sizes for tissue-engineering applications. It was found that the scaffold structure and porosity can be tuned by altering the microdroplet size. Nanoparticles were formed by nanoprecipitation inside a microfluidic channel, inducing self-assembled polymeric particle patterns upon solvent evaporation. The processing parameters and materials properties were investigated for their effects on the sizes of microbubbles and nanoparticles. In section two, the method of using multiple T-junctions to reduce microbubble size was explored. In some applications for microbubbles, size is a design constraint with smaller microbubbles being desired To overcome the limitation, the idea of combining multiple T-junctions with coarse capillaries for size reduction has been investigated. Firstly, a double T-junction was assembled, and the effect of an additional T-junction on microbubble formation, stability and productivity has been thoroughly studied. A microbubble scaling prediction equation was proposed based on experimental data and the Garstecki equation. A triple T-junction was assembled to validate the proposed equation and to further reduce the microbubble size. Capillary number was introduced to investigate the microbubble fission regime. The critical capillary number was found experimentally to indicate the breaking and non-breaking microbubbles. Thus, the microfluidic-assisted setup described in this work offers a feasible processing method for fabricating microbubbles, scaffolds and nanoparticles with good uniformity and low polydispersity index.

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