Behavior of poly(d,l-lactic-co-glycolic acid) (PLGA)-based droplets falling into a complex extraction medium simulating the prilling process.

Hypothesis: Prilling process is one of advanced techniques for manufacturing microspheres of controlled and uniform size. In this process, homogenous polymer droplets fall into an extraction medium. The aim of this study was to identify the key parameters influencing the behavior of PLGA polymer-based droplets falling into a complex extraction medium, to select appropriate conditions for prilling.

Experiments: Polymer solutions and extraction media were characterized by determining their viscosity, density and surface tension. A simple model simulating the prilling process was developed to study droplet behavior. Particle shape and velocity at the air-liquid interface and during sedimentation in the container were analyzed step by step. The correlations between the variables studied were visualized by principal component analysis (PCA).

Findings: Droplet deformation at the interface greatly affected the recovery and final particle shape. It depended on the viscosity ratio of polymer solution/extraction medium. The particle shape recovery depended on the viscosity and density of extraction media and polymer solutions. The solidification speed is also an important parameter. In media which the solvent diffused slowly, particles were able to relax and recover their shape, however, they can also deform during sedimentation and collision with the bottom of the cuvette.