(526f) Design of Polylactide Microparticle Morphology By Internal Phase Separation

We report a facile approach to prepare monodisperse polylactide (PLA) microparticles and design their surface and internal morphology via solvent diffusion coupled with internal phase separation. With the aid of microfluidics, monodisperse oil-in-water emulsion droplets were produced, in which PLA and perfluorooctyl bromide (PFOB), non-solvent for PLA were dissolved in the dispersed oil phase. The emulsion droplets travelled towards exit of the microfluidics and then mixed with massive amount of pure water that extracted ethyl acetate (EA) from the droplets due to high solubility of EA in water, which gave rise to shrinkage of the droplets and eventually induced internal phase separation between PLA-rich phase and PFOB-rich phase within each droplet. Further removal of EA from the droplets led to precipitation of PLA on the interface and formation of monodisperse microcapsules with a liquid PFOB core and thick PLA shell. We investigated the effect of the flow rate, content of the PFOB in the dispersed phase and molecular weight of PLA on the final shape of the particles. The diameter of the microcapsules was easily controlled by the flow rates while keeping the shell thickness to volume (T/R) ratio constant. The T/R ratio was modulated by changing the PFOB concentration in the dispersed phase independent of the particle size. We found that using higher molecular weight PLA for the matrix gave rise to structural complexity of the microcapsules during the formation, resulting in the microcapsules covered with small PFOB droplets, which was similar to colloidsome. In addition, removal of the PFOB by freeze-drying provided the microcapsules with dimpled surface like golf-ball. Confocal laser scanning microscopy observation revealed that the microcapsules also had core-shell morphology. These results show that this droplet to particle technology has great advantage to produce not only compact particles but also microcapsules with complex architecture. The presentation will give an overview of the fabrication process, mechanism of the morphology transition, and further recent update.