Dependence of sonoporation efficiency on microbubble size: An in vitro monodisperse microbubble study

Benjamin van Elburg, Joke Deprez, Martin van den Broek, Stefaan C. De Smedt, Michel Versluis, Guillaume Lajoinie, Ine Lentacker, Tim Segers*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Sonoporation is the process where intracellular drug delivery is facilitated by ultrasound-driven microbubble oscillations. Several mechanisms have been proposed to relate microbubble dynamics to sonoporation including shear and normal stress. The present work aims to gain insight into the role of microbubble size on sonoporation and thereby into the relevant mechanism(s) of sonoporation. To this end, we measured the sonoporation efficiency while varying microbubble size using monodisperse microbubble suspensions. Sonoporation experiments were performed in vitro on cell monolayers using a single ultrasound pulse with a fixed frequency of 1 MHz while the acoustic pressure amplitude and pulse length were varied at 250, 500, and 750 kPa, and 10, 100, and 1000 cycles, respectively. Sonoporation efficiency was quantified using flow cytometry by measuring the FITC-dextran (4 kDa and 2 MDa) fluorescence intensity in 10,000 cells per experiment to average out inherent variations in the bioresponse. Using ultra-high-speed imaging at 10 million frames per second, we demonstrate that the bubble oscillation amplitude is nearly independent of the equilibrium bubble radius at acoustic pressure amplitudes that induce sonoporation (≥ 500 kPa). However, we show that sonoporation efficiency is strongly dependent on the equilibrium bubble size and that under all explored driving conditions most efficiently induced by bubbles with a radius of 4.7 μm. Polydisperse microbubbles with a typical ultrasound contrast agent size distribution perform almost an order of magnitude lower in terms of sonoporation efficiency than the 4.7-μm bubbles. We elucidate that for our system shear stress is highly unlikely the mechanism of action. By contrast, we show that sonoporation efficiency correlates well with an estimate of the bubble-induced normal stress.

Original languageEnglish
Pages (from-to)747-755
Number of pages9
JournalJournal of controlled release
Publication statusPublished - Nov 2023


  • Monodisperse microbubbles
  • Sonoporation
  • Therapy
  • Ultrasound
  • Ultrasound contrast agents


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