Extrusion: A New Method for Rapid Formulation of High‐Yield, Monodisperse Nanobubbles

Abstract

Shell‐stabilized gas microbubbles (MB) and nanobubbles (NB) are frequently used for biomedical ultrasound imaging and therapeutic applications. While it is widely recognized that monodisperse bubbles can be more effective in these applications, the efficient formulation of uniform bubbles at high concentrations is difficult to achieve. Here, it is demonstrated that a standard mini‐extruder setup, commonly used to make vesicles or liposomes, can be used to quickly and efficiently generate monodisperse NBs with high yield. In this highly reproducible technique, the NBs obtained have an average diameter of 0.16 ± 0.05 µm and concentration of 6.2 ± 1.8 × 1010 NBs mL−1 compared to 0.32 ± 0.1 µm and 3.2 ± 0.7 × 1011 mL−1 for NBs made using mechanical agitation. Parameters affecting the extrusion and NB generation process including the temperature, concentration of the lipid solution, and the number of passages through the extruder are also examined. Moreover, it is demonstrated that extruded NBs show a strong acoustic response in vitro and a strong and persistent US signal enhancement under nonlinear contrast enhanced ultrasound imaging in mice. The extrusion process is a new, efficient, and scalable technique that can be used to easily produce high yield smaller monodispersed nanobubbles.

Microfluidic Generation of Bulk Nanobubbles

“…In contrast, when 𝐷i > 𝐷i,c, MBs shrink by the amount predicted by previous literature. 162 Specifically, when MB 𝐷i < 𝐷i,c ,MBs appear to always shrink to a diameter 𝐷f = 150 -250 nm, using the lipid concentrations in our experiments. I observe that the critical initial diameter, 𝐷i,c ranges between 13.0 -15.0 µm, for lipid concentrations of 0.30 -0.75 mg/mL, respectively.…”

Real-time imaging of nanobubble ultrasound contrast agent flow, extravasation, and diffusion through an extracellular matrix using a microfluidic model

“…35,36 S-NB morphology has been previously investigated using SEM, TEM, and cryo-EM. 31,36–39 S-NB lipid structure, shell morphology, and zeta potential have also been previously characterized. 35,40…”

“…35,36 S-NB morphology has been previously investigated using SEM, TEM, and cryo-EM. 31,[36][37][38][39] S-NB lipid structure, shell morphology, and zeta potential have also been previously characterized. 35,40 Large diameter nanobubble preparation Large diameter NBs (L-NBs) with the same lipid shell composition as the S-NBs were prepared according to Abenojar et al 39 Briefly, the L-NBs were isolated by diluting the bubble solution obtained after mechanical agitation with a VialMix with 10% vol/vol glycerol/propylene glycol in PBS.…”

Microfluidic nanobubbles: observations of a sudden contraction of microbubbles into nanobubbles

“…1C shows, we secondly utilize transmission electron microscopy (TEM, Hitachi HT7800, Japan) to capture images of the BNBs after shrinkage. 21 The bubbles are kept inside a plastic vial for 1 hour before TEM imaging. To start the TEM imaging, first we plasma clean the TEM grid before each imaging session.…”