Uniform Drug Loading into Prefabricated Microparticles by Freeze-Drying

Microparticle-based drug delivery is a promising technology for small volume bioassay platforms. The general utilization of the drug-loaded microparticles in the in vitro bioassay platforms requires the drug loading method, which should impregnate the general drug types (e.g., water insoluble) with high payload into the variously designed microparticles. Loading the drug into the prefabricated microparticles using solvent evaporation satisfies the requirement. However, similar to the "coffee-ring effect," drugs are loaded in a seriously nonuniform manner, caused by the capillary flow during the evaporation process. Here, it is presented that the freeze-drying is an efficient way to load uniform and high amount of the drug into the prefabricated microparticles. It is demonstrated that freezing solvent can block the capillary flow during the solvent removal process, improving the loading uniformity. The delivered amount of drugs is linearly proportional to the initial loading amount of drugs. Also, this drug loading method is shown to be applied to the various drug types and the prefabricated microparticles with different properties. Considering many challenges to suppress the "coffee-ring effect" that induces nonuniform impregnation/deposition, the proposed concept can be applied not only for microparticle-based drug delivery but also for uniform coating applications (e.g., thin-film coating, DNA/protein microarray).