Factors affecting the size and uniformity of hollow poly(lactic acid) microcapsules fabricated from microbubble templates.

Hollow microcapsules of poly(lactic acid) (PLA) were fabricated using the bubble template method, which involves the nucleation of bubbles inside droplets of a dichloromethane solution of PLA prepared in a continuum medium of an aqueous solution of poly(vinyl alcohol) (PVA). PLA-covered microbubbles are formed by PLA adsorbing onto the microbubble surface and then spontaneously released from the dichloromethane droplets into the surrounding aqueous solution. Thereby, hollow PLA microcapsules are formed. In the present study, we focus on the effects of the initial PLA concentration, addition of PVA to the aqueous medium, and PLA molecular weight on the radius distribution of the hollow PLA microcapsules. Results show that a low initial concentration of PLA, the addition of PVA, and low molecular weight PLA are required to form uniform hollow microcapsules. It is suggested that these factors reduce the energy barrier at the liquid-liquid interface, which allows the PLA-covered microbubbles to pass smoothly through the interface. Furthermore, we observed the release of the microbubbles from the dichloromethane droplets through a microscope and clarified the relationship between the uniformity of the hollow PLA microcapsules and the bubble-release mechanism.