Controlled protein release from microcapsules with composite shells using high frequency ultrasound—potential for in vivo medical use

The possibility of protein release from polymeric microcapsules by means of low-power (up to a maximum of 3.2 W) high-frequency (850 kHz) ultrasound was studied. The release efficiency using these ultrasonic parameters that are close to those currently used in medical diagnostic and ultrasound treatment was compared to that achieved with a conventional 20 kHz 70 W ultrasonic probe. Microcapsules were made by polyelectrolyte multilayer assembly on 3-5 [small micro]m calcium carbonate particles with co-precipitated fluorescently labelled protein. Ultrasound induced protein release was monitored by supernatant fluorescence increase after sonication. The release efficiency is improved by the presence of gold nanoparticles in the microcapsule shell. The amount of gold nanoparticles in the shell was found to play an important role in release efficiency. The irradiation was carried out at several intensities and exposure times and evidence of microcapsule rupture after treatment was obtained by confocal and scanning electron microscopy.