| Summary: | A buoyancy-assisted microfluidic approach is introduced for facile production and collection of uniform drops within a wide range of sizes, particularly on a millimetre scale, which is not easily achievable via conventional microfluidic approach. The proposed methodology, characterised by vertical orientation and non-confined quiescent outer phase of the device used, was also applied to droplet-in-droplet and droplet-in-fibre encapsulation using a co-axial glass microcapillary arrangement, to obtain millimetric capsules and multi-compartmental fibres. The shell thickness of double emulsions was tuned, via altering flow rates and formulations, to produce millimetric ultrathin shelled capsules. Alginate fibres with different oil-encapsulate geometries were fabricated, via simultaneous oil-droplet formation and encapsulation, and characterised and analysed for their encapsulation volume, surface roughness, spillage ratio and mechanical strength. Furthermore, the size and locations of oil encapsulates were manipulated to obtain asymmetric fibres with parallel oil streams. An asymmetric encapsulation approach was designed and used to fabricate dehydration-responsive fibres, which demonstrated a benign and facile dehydration-triggered core-release mechanism. This core-release response was also demonstrated for fibres with parallel oil-encapsulates with multiple cargos. The fibre morphology was also tuned to provide an enhanced response to its mechanical failure, marked by a simultaneous release of potentially reactive components at the point of fracture. Such fibres, can behave as fibres with self-repairing properties. The buoyancy-assisted microfluidics was also used to produce microfibres containing gas encapsulates with tuneable morphology. The buoyancy force, driven by the trapped microbubbles, was utilised for stretching the gelling alginate fibres to fabricate ultrathin alginate microfibres, a feature not possible via conventional horizontally-oriented microfluidic techniques. The collected bubble-filled fibres were also morphed to produce new varieties of fibres, such as beaded fibres and fibres with segmented aqueous cores.
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