Parallel Photothermal Coalescence of Biocompatible Photocurable PEGDA Droplets

Droplet microfluidics is a powerful tool for high-throughput experimentation, and droplet coalescence is necessary for mixing and chemical reactions. Droplet merging and polymerization will release the limits on particle synthesis and widen the technical potential of droplet microfluidics. Previously, a focused laser beam has been used to induce the coalescence of droplets. This paper reports the parallel photothermal coalescence of biocompatible photocurable polyethylene glycol diacrylate (PEGDA) droplets using a 2D image for developing a more efficient coalescence process. PEGDA droplets with diameters of 18 µm to 50 µm were generated in a microfluidic flow-focusing device and stored in a microchannel. A 2D image of violet light induced the parallel coalescence of PEGDA droplets with diameters of around 30 µm. When continuous-phase oil was replaced with nitrogen, PEGDA droplets were photopolymerized.