Hydrodynamically Formed Uniform Thick Coatings on Microspheres

: Forming uniform thick coatings on microspheres remains a significant challenge in various surface modification and drug delivery applications. In this work, a hydrodynamic method is demonstrated for centering microspheres in droplets with sizes ranging from tens to hundreds of micrometers. The core microspheres stay at the center of the droplets due to the hydrodynamic pressure generated in the surrounding liquid shells, despite the significant density difference between the core microsphere and the liquid shell. Therefore, by using polymerizable liquids that can be solidified thermally or by illumination as the shell layer, core-shell particles with gas, liquid, or solid cores can be surrounded with uniform coatings using the present method.