Sessile drops, interfaces, and fluid walls: microfluidic approaches to studying single cells

Thesis

Microfluidic technologies are advancing rapidly and have been implemented across a wide range of biological applications, offering reduced reagent consumption, high-throughput screening, and in vitro modelling of cellular microenvironments. These systems have provided valuable insights into cellular behaviour and processes, yet adoption of microfluidic technologies by biologists remains limited. This is commonly attributed to complex device fabrication methods and restricted access to cells within enclosed microchannels. A promising new method to overcome these limitations is to replace solid plastic walls with fluid-fluid interfaces. In this approach, microfluidic environments are fabricated using cell-culture medium and immiscible oil, with the oilmedium interface forming fluid walls which confine the medium to any two-dimensional pattern. Such environments are fabricated in seconds within standard tissue-cultureware and are fully accessible through fluid-fluid interfaces. However, this presents significant engineering challenges; 1) interface curvatures and heights change in response to local pressures and volumes; 2) dynamic interfacial tension associated with adsorption and desorption of amphiphilic molecules to interfaces; 3) the need to create microchambers to isolate cells of interest. Combined, these challenges make characterisation and operation of fluid-walled microfluidics inherently complex. 

This thesis investigates both static and dynamic microfluidic systems with fluid walls and explores applications in single-cell isolation and manipulation. First, use of a static system – a sessile drop – is developed and validated as a method to confirm monoclonality within a singlecell cloning workflow. Next, fluid walls are used to connect two drops (chambers) via a conduit to form a ‘dumbbell.’ This established design is applied to model metastasis of cancer cells as they are introduced to one chamber and their migration to the other is quantified. Fluid walls are reconfigured to isolate and retrieve the most migratory cells and machine learning is used to assess cell morphology during migration. Finally, the influence of dynamic changes in oil-medium interfacial tension on flow rates and equilibration times between connected chambers is characterised to provide a model to predict fluid-walled chamber behaviour with biological fluids. Together, this work broadens the possible applications of microfluidics with fluid walls and enhances understanding of the dynamic behaviour of such systems.

Authors: Morgan, JAE

• DOI: 10.5287/ora-nrg8pn458
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: fluid walls; microfluidics
• Subjects: Biology; Biomedical engineering; Engineering