Remote Loading of Gas Bubbles into Polylactic Acid Microcapsules Creates Acoustically Active Janus Particles

Polymeric microcapsules (MCs) are biocompatible agents used in biomedical applications such as drug delivery and in vivo imaging. We have discovered a method of remotely loading air into polylactic acid (PLA)-based MCs with an aqueous core. When the microcapsules are suspended in high content glycerol and propylene glycol solutions, changes in gas solubility cause bubbles to nucleate within the core through an "Ouzo-like" effect. The resulting bubble displaces the internal fluid of the MCs, but small molecules are retained in their interior. The residual content does not homogeneously distribute; rather, it localizes to one specific location, creating gas-filled Janus particles.