Fabrication of Crescent Shaped Microparticles for Particle Templated Droplet Formation

Abstract

Crescent-shaped hydrogel microparticles have been shown to template uniform volume aqueous droplets upon simple mixing with aqueous and oil media for various bioassays. This emerging "lab on a particle" technique requires hydrogel particles with tunable material properties and dimensions. The crescent shape of the particles is attained by aqueous two-phase separation of polymers inside a spherical droplet followed by photopolymerization of the curable precursor. In this work, we have investigated the phase separation of photo-curable poly(ethylene glycol) diacrylate (PEGDA, Mw 700) and dextran (Mw 40,000) for tunable manufacturing of crescent-shaped particles. The particles morphology was precisely tuned by following a phase diagram, varying the UV intensity, and adjusting the flow rate ratio between the three streams, containing PEGDA, dextran, and oil, within a microfluidic droplet generation device. The fabricated particles with variable cavity sizes and outer diameters encapsulated uniform aqueous droplets upon mixing with a continuous oil phase. The particles were fluorescently labeled with red and blue emitting dyes at variable concentrations to produce six color-coded particles. The blue fluorescent dye showed a moderate response to the pH change from 1 to 7 in terms of an increase in emitted intensity. The fluorescently labeled particles were able to tolerate an extremely acidic solution (pH 1) but disintegrated within an extremely basic solution (pH 14). The particle-templated droplets were able to effectively retain the disintegrating particle and the fluorescent signal at pH 14, indicating completely segregated compartments.