Structure and acoustical properties control of magnetite/PLA composite microbubbles

Abstract

Poly(lactic acid) (PLA) microbubbles and magnetite/PLA composite microbubbles with various structures and controllable average size were prepared by a modified double emulsion–solvent evaporation process, and sound attenuation spectrum was performed to investigate the influence of size, composite structure, and magnetite loading on the acoustical properties of microbubbles. With the increase of time or energy of the emulsification, the inner structure of composite microbubbles changed continuously from honeycomb to solid structure, accompanied by the change of surface morphology and the decrease of average particle size. The sound attenuation and resonance frequency of concentric microbubbles were higher than those of other structures, while microbubbles with multicavities had the lowest sound attenuation and resonance frequency. The difference in the acoustical properties was related to their different structures and water permeability. In vitro ultrasonography of composite microbubbles showed a higher video intensity than that of PLA microbubbles, which was consistent with their sound attenuation spectra.