Microbubbles have potential for applications as drug and gene carriers, and ultrasonication can induce bubble vibration, facilitating the release of molecules adsorbed on the bubble surface. This paper examined the impact of continuous ultrasonic irradiation on the absorption and desorption of surfactant molecules on a single microbubble. The behavior of molecules under continuous ultrasonic irradiation was investigated through optical observation system consisted of a high-speed camera with a jong-distance microscope and an ultrasound observation cell. Pluronic F-127 was used as a surfactant, and lipid-shelled microbubbles were fabricated. The molecular density on the bubble surface was measured using an optical observation system to determine the contact angle of bubbles adhering to a glass plate placed in a cell filled with a Pluronic F-127 solution. Continuous ultrasonic irradiations were conducted for 1800 s at 39 kHz. Continuous ultrasound reduced the molecular adsorption on the bubble surface, and a larger bubble vibration enhanced this tendency. These findings imply that the terminal molecular density on the bubble surface is dependent on the balance between molecular adsorption from the ambient medium and desorption by bubble vibration.
Kanayama et al. (2025) studied this question.