Engineering Design of Concentric Amphiphilic Microparticles for Spontaneous Formation of Picoliter to Nanoliter Droplet Volumes.

Simple mixing of aqueous and oil solutions with amphiphilic particles leads to the spontaneous formation of uniform reaction volumes (dropicles) that can enable numerous applications in the analysis of biological entities (e.g., cells and molecules). Approaches to manufacture such amphiphilic particles are just starting to be investigated. Here, we investigate the tunable manufacturing of concentric amphiphilic particles, with outer hydrophobic and inner hydrophilic layers, fabricated by flowing reactive precursor streams through a 3D printed device with coaxial microfluidic channels, and curing the structured flow by UV exposure through a photomask. The dimensions of the engineered amphiphilic particles, including height, inner and outer diameters, and thicknesses of the hydrophobic and hydrophilic layers, are precisely controlled by modulating the UV exposure time, the precursor flow rate ratios, and the size of the channel in the exposure region. The particle design is systematically engineered to hold a wide range of droplet volumes, that is, from a few hundred picoliters to several nanoliters. We show that the particle size can be significantly reduced from previous reports to not only hold subnanoliter drops but the shape can also be tuned to increase the seeding density and orientation of dropicles within a well plate for imaging and analysis.