Harmonic response from microscopic antibubbles

Abstract

An antibubble is a gas bubble containing a liquid droplet core. Both the droplet and the gas bubble are typically surrounded by stabilising shells. Owing to electrostatic forces exerted by these shells, core droplets of micrometer diameter do not readily coalesce with the surrounding liquid medium. Owing to the incompressibility of the liquid droplet core, antibubbles will oscillate asymmetrically, i.e., the radial excursion amplitude of the surface is greater during expansion than during contraction, when subjected to diagnostic ultrasound. Consequently, the harmonic content of the ultrasound signal radiated from antibubbles must be higher that that from identical bubbles without a liquid core. Whether the harmonic signal component generated by physical antibubbles is higher than the harmonic component of identical bubbles without a core has been studied here. We subjected prefabricated antibubbles and identical bubbles without core droplets to 1-MHz ultrasound and to a commercial ultrasound system, and recorded the spectra with a broadband transducer oriented perpendicularly to the transmitter. Normalised by the acoustic response from the medium, the antibubble signal shows stronger higher harmonics than the reference signal, and negligible fundamental response. In conclusion, antibubbles are suitable candidates for harmonic imaging. The generation of higher harmonics without fundamental has been attributed to asymmetric antibubble expansion.

Controlling the lifetime of antibubbles

“…Noticeably, it has recently been suggested that leaks from subsea hydrocarbon production facilities contain antibubbles with a specific acoustic signature [5]. Nowadays, benefiting from the development of microfluidics, several potential applications have arisen, such as using antibubbles as contrast agent for enhancing ultrasonic imaging [6,7] or loading the antibubble core with a ferrofluid to serve as a vehicle for magneto-controlled drug delivery [8].…”

Asymmetric oscillations of endoskeletal antibubbles

“…The silica particles on the outer interface have been reported to form a single elastic layer. 22) The same batch of the antibubbles used to create Figure 1 has been used for the experiments described in this paper.…”

“…Two media containing (anti)bubbles were prepared for evaluation, as previously published. 18,22) For stabilisation, Aerosil ® R972 hydrophobised silica particles (Evonik Industries AG, Essen, Germany) were used. 22) For the first medium, hereafter referred to as AB, the aqueous cores were replaced by 2 vol% of hydrophobically modified Zano 10 Plus zinc oxide nanoparticles (Umicore, Brussel, Belgium).…”

“…18,22) For stabilisation, Aerosil ® R972 hydrophobised silica particles (Evonik Industries AG, Essen, Germany) were used. 22) For the first medium, hereafter referred to as AB, the aqueous cores were replaced by 2 vol% of hydrophobically modified Zano 10 Plus zinc oxide nanoparticles (Umicore, Brussel, Belgium). Instead of the formation of just droplets inside antibubbles, adding nanoparticles creates an endoskeletal structure with one or multiple voids that can be liquid-filled.…”

Acoustic bubbles in therapy: Recent advances with medical microbubbles, clouds, and harmonic antibubbles

“…The session on bubbles, antibubbles, and droplets was chaired by Christine Contino-Pépin from the University of Avignon and Charles Sennoga from the University of Tours. Invited speaker Albert Poortinga from Eindhoven University of Technology lectured on a new kind of acoustic bubble, called the antibubble [15,16]. Steven Wrenn from Drexel University presented a voltage-activated ultrasound contrast agent for myocardial perfusion imaging [17].…”