Facile microfluidic production of composite polymer core-shell microcapsules and crescent-shaped microparticles

Hypothesis Core-shell microcapsules and crescent-shaped microparticles can be used as picolitre bioreactors for cell culture and microwells for cell trapping/immobilisation, respectively. Results Monodisperse polylactic acid (PLA) core-shell microcapsules with a diameter above 200 μm, a shell thickness of 10 μm, and 96% water entrapment efficiency were produced by solvent evaporation from microfluidically generated W/O/W emulsion drops with core-shell structure, and used to encapsulate Saccharomyces cerevisiae yeast cells in their aqueous cores. The morphological changes of the capsules stained with Nile red were studied over 14 days under different osmotic pressure and pH gradients. Findings The shell retained its integrity under isotonic conditions, but buckling and particle crumbling occurred in a hypertonic solution. When the capsules containing 5 wt% aqueous Eudragit® S 100 solution in the core were incubated in 10⁻⁴ M HCl solution, H⁺ diffused through the PLA film into the core causing an ionic gelation of the inner phase and its phase separation into polymer-rich and water-rich regions, due to the transition of Eudragit from a hydrophilic to hydrophobic state. Crescent-shaped composite microparticles with Eudragit cores and PLA shells were fabricated by drying core-shell microcapsules with gelled cores, due to the collapse of PLA shells encompassing water-rich crescent regions.