Hollow poly(Lactic Acid) (PLA) microcapsules were fabricated using the bubble template method. In this method, microbubbles nucleated inside droplets of a dichloromethane solution of PLA which were located in a continuous phase of poly(vinyl alcohol). PLA-covered microbubbles formed when PLA adsorbed to the bubble surface by physisorption. Then, the coated microbubbles were spontaneously released from the droplet´s interior into the continuous phase. To increase the production yield of hollow microcapsules in this method, ultrasound was applied to enhance bubble nucleation inside the droplets. Thus to attain uniform hollow PLA microcapsules, the optimum PLA concentration with ultrasound was 30 g L-1, which is higher than that without ultrasound (2 g L-1). At the optimum concentration, the average radius was 0.54 μm, with a polydispersity index of 21.2%. It was found that the equilibrium size of the microbubble template radius was the same with and without ultrasound. The production yield had a tenfold increase when ultrasound was employed.
FE-SEM images of hollow PLA microcapsules fabricated using Method B from 2 kDa PLA solutions with cPLA = 30 g L−1. The scale bars represent 0.5 μm.