Langmuir Trough Study of Surfactant Mixtures Used in the Production of a New Ultrasound Contrast Agent Consisting of Stabilized Microbubbles

Abstract

Span-type surfactants (sorbitan fatty acid esters) and Tween-type surfactants (sorbitan polyoxyethylene fatty acid esters) are employed by us to generate stabilized microbubbles for use in diagnostic ultrasound. After sonication of an aqueous surfactant solution, only some mixtures of Span-type and Tween-type surfactants at certain conditions can form stable microbubbles. This work investigated the stability of the surfactant-stabilized microbubbles by using a Langmuir trough to measure the π-A isotherms of the surfactant monolayer. The experimental results, which agreed with a theoretical analysis of the microbubble stability, indicate that the surfactant-stabilized microbubbles have a solid-condensed monolayer "skin" which functions to reduce the surface tension, prevent coalescence between microbubbles, and increase their aqueous compatibility. The higher surface pressure obtained for the case of a microbubble preparation, compared with that of unsonicated mixtures, indicates that sonication enhances the structure of surfactant monolayer and makes the microbubbles extremely stable.

Novel preparation techniques for controlling microbubble uniformity: a comparison

“…There are thought to be several reasons for this. First, as above, previous studies have indicated that sonication may produce a chemical change in the coating material, which improves stability [48]. Second, a much higher concentration of microbubbles was produced and the dissolved gas concentration in the liquid would also have been higher on account of the entrainment of gas throughout the processing volume during sonication.…”

“…In addition, the high temperatures and pressures generated by inertial cavitation in the liquid may result in chemical modification of the coating material that further enhances stability, although this depends upon the individual surfactant [48]. The size distribution of the microbubbles produced depends upon the frequency, power and pulse regime of the ultrasound, although there is no simple theoretical relationship between these variables and fabrication protocols are developed empirically [20].…”

Effects of encapsulation elasticity on the stability of an encapsulated microbubble

“…An encapsulation stabilizes a bubble by various mechanisms; Wang et al suggested three-reduced surface tension, increased resistance to gas permeation and surface hardening [12,13]. The first two effects have been modeled [10].…”

Small Phospholipid‐Coated Gas Bubbles Can Last Longer than Larger Ones

“…[7,15] Previous papers have reported dissolution rates of bubbles several tens of micrometers in radius using optical microscopy. [10,16] In these studies, the bubbles were immobilized on a surface or at the extremity of a pipet, which can influence the shedding of the phospholipid's wall significantly.…”