Effect of Temperature on Stability of Lipid Microbubbles

Year 2019, , 439 - 450, 20.10.2019

Sevgi Kilic

https://doi.org/10.18596/jotcsa.594219

Abstract

The effect of temperature on
stability of lipid microbubble shell containing polyethyleneoxide-40-stearate
(PEG₄₀St) as emulsifier was investigated. Microbubbles at 4 °C were
subjected to different temperatures up to 48 ºC
(down-to-up) and it was found that both the number and the size of microbubbles
remained unchanged in the population up to a certain time, so called “onset
time”. The onset time was about 6 hrs at 10 °C, 2 hrs at 20 °C and shorter at
elevated temperatures, exhibiting an exponential decrease with increasing
temperature. Once the onset time was reached, the number of microbubbles
started to decrease and the average size of the population started to increase.
Observation of single microbubbles on a constant temperature heating stage exhibited
that each microbubble had its own onset time, with the smaller microbubbles
vanishing earlier than the larger ones. The Langmuir monolayer studies showed
that hydration degree of the emulsifier PEG chains decreased with temperature, causing
them go through conformational changes and subsequently destabilization of the
shell. By subjecting the freshly produced microbubbles directly to the desired
temperatures in up-to-down fashion, more stable microbubbles were able to be
produced, with their onset time increased 40% at 10 °C to 500% at 38 °C.
Overall, the results suggest that the new strategies need to be developed to
control the collapse process in the microbubble shell resulting from the
conformational changes in the PEG chains of the emulsifier for the design of
more stable microbubbles.

Keywords

Langmuir monolayers, phosholipids, PEG conformations, emulsifier, Microbubble, ultrasound contrast agent

Supporting Institution

Tubitak

Project Number

109M494

Thanks

The author would like to thank The Scientific and Technological Research Council of Turkey (TUBITAK) for the financial support through the project number of 109M494.

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