A STUDY OF A MODULAR MICROFLUIDIC STABILISER SYSTEM USING FLUIDIC CIRCUIT ANALOGY

The thesis presents my PhD study about a novel flow-control solution for typical lab-on-a-chip systems. The design, fabrication, and analysis of a Legolike modular microfluidic stabiliser system are discussed. This system can provide controllable, amplitude-adjustable features for microfluidic systems and offer steady and accurate flow control solutions. The study has three main contributions: (1) it provided a generalised and standardised stabiliser system with adjustable working curves; (2) it established a simplified fluid circuit analogy to present a prediction model for all stabiliser systems; and (3) it improved the universality of microfluidic systems for different applications.
For contribution (1), the thesis presents a Lego-like modular stabiliser system. Inspired by Lego toys, the devices are standardised, pluggable and exchangeable. With a simplified design iteration, the 3D-printed modular microfluidic stabiliser system can be quickly assembled with twelve adjustable working states and tunable resistance and capacitance constants (RCconstants) ranging from 3.24 s to 12.57 s. The Lego-like design can enlarge the working range of stabilisers and provide more generalised design iterations for microfluidic stabilisers.
For contribution (2), by studying the deflection of membranes, this work uses a recursive method to summarise a simplified circuit model for microfluidic stabiliser systems. By borrowing the transfer function and amplitude response law from the digital circuit analogy, the established model has an R-square value of 0.95, which proves the model's accuracy.
For contribution (3), to evaluate the system's effectiveness and improve the universality of all microfluidic chips with a common flow-control solution, the stabiliser system is tested when working with typical fluid providers such as gas pumps, piezoelectric pumps, and syringe pumps. The Lego-like system can provide controllable working curves with an optimal stabilisation ratio of less than 1%. The amplitude feature can be controlled numerically by linking different combinations of devices. Furthermore, droplet generation experiments coupled with the proposed system are conducted and discussed.
By using the novel flow-control solution, the polydispersity of droplets reduced from 0.13 to 0.07 by using a typical cross-junction droplet generator. The standard deviation of the droplet distribution reduced by over 40% when compared with its original working state without stabilisers.
In summary, this thesis presents a novel flow-control solution based on a Lego-like microfluidic stabiliser system with a predictable working curve. The system's adjustability and universality, combined with the simplified prediction model established in this study, make it a valuable tool for a wide range of microfluidic applications.

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