Geometric effects in gas vesicle buckling under ultrasound
Acoustic reporter genes based on gas vesicles (GVs) have enabled the use of ultrasound to noninvasively visualize cellular function in vivo. The specific detection of GV signals relative to background acoustic scattering in tissues is facilitated by nonlinear ultrasound imaging techniques taking advantage of the sonomechanical buckling of GVs. However, the effect of geometry on the buckling behavior of GVs under exposure to ultrasound has not been studied. To understand such geometric effects, we developed computational models of GVs of various lengths and diameters and used finite element simulations to predict their threshold buckling pressures and post-buckling deformations. We demonstrated that the GV diameter has an inverse cubic relation to the threshold buckling pressure, whereas length has no substantial effect. To complement these simulations, we experimentally probed the effect of geometry on the mechanical properties of GVs and the corresponding nonlinear ultrasound signals. The results of these experiments corroborate our computational predictions. This study provides fundamental insights into how geometry affects the sonomechanical properties of GVs, which, in turn, can inform further engineering of these nanostructures for high-contrast, nonlinear ultrasound imaging.STATEMENT OF SIGNIFICANCEGas vesicles (GVs) are an emerging class of genetically encodable and engineerable imaging agents for ultrasound whose sonomechanical buckling generates nonlinear contrast to enable sensitive and specific imaging in highly scattering biological systems. Though the effect of protein composition on GV buckling has been studied, the effect of geometry has not previously been addressed. This study reveals that geometry, especially GV diameter, significantly alters the threshold acoustic pressures required to induce GV buckling. Our computational predictions and experimental results provide fundamental understanding of the relationship between GV geometry and buckling properties and underscore the utility of GVs for nonlinear ultrasound imaging. Additionally, our results provide suggestions to further engineer GVs to enable in vivo ultrasound imaging with greater sensitivity and higher contrast.
The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. The authors are grateful to Ngozi A. Eze for the helpful editorial comments. This research was supported by the National Institutes of Health grant R01-EB018975. Related research in the Shapiro Lab is supported by the Packard Foundation, The Pew Charitable Trusts, and the Chan Zuckerberg Initiative. Cryo-electron microscopy was performed at the Beckman Institute Resource Center for Transmission Electron Microscopy at Caltech. M.G.S. is an Investigator of the Howard Hughes Medical Institute (HHMI). This article is subject to HHMI's Open Access to Publications policy. HHMI Investigators have previously granted a nonexclusive CC BY 4.0 license to the public and a sublicensable license to HHMI in their research articles. Pursuant to those licenses, the author-accepted manuscript of this article can be made freely available under a CC BY 4.0 license immediately upon publication. AUTHOR CONTRIBUTIONS. H.S., Y.Y., P.D., and M.G.S. conceived and designed the study. H.S. and E.M. developed the computational models. H.S. and E.M. performed the simulations and analyzed the simulation data. Y.Y., P. D., Z. J., and D. M. conducted in vitro experiments and analyzed the experimental data. N.N.N. was involved in planning experiments and data analysis. M.G.S., M.O., and G.J.J. supervised the research. H.S., Y.Y., P.D., and M.G.S. wrote and edited the manuscript. All authors read, edited, and confirmed the content of the manuscript. The authors have declared no competing interest.
Submitted - 2022.06.27.497663v1.full.pdf