Fabrication of Crescent Shaped Microparticles for Particle Templated Droplet Formation

Crescent‐shaped hydrogel microparticles are 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 followed by photopolymerization of the curable precursor. In this work, the phase separation of poly(ethylene glycol) diacrylate (PEGDA, Mw 700) and dextran (Mw 40 000) for tunable manufacturing of crescent‐shaped particles is investigated. The particles’ morphology is precisely tuned by following a phase diagram, varying the UV intensity, and adjusting the flow rates of various streams. The fabricated particles with variable dimensions encapsulate uniform aqueous droplets upon mixing with an oil phase. The particles are fluorescently labeled with red and blue emitting dyes at variable concentrations to produce six color‐coded particles. The blue fluorescent dye shows a moderate response to the pH change. The fluorescently labeled particles are able to tolerate an extremely acidic solution (pH 1) but disintegrate within an extremely basic solution (pH 14). The particle‐templated droplets are able to effectively retain the disintegrating particle and the fluorescent signal at pH 14. The fabrication of crescent‐shaped particles is reported by selectively polymerizing photocurable hydrogel inside a microfluidic droplet generation device. The particles are encoded by introducing two fluorescent dyes into the hydrogel network separately. The crescent‐shaped particles with variable sizes and fluorescent codes are used as a template to form particle‐templated droplets by a simple pipetting operation.