Expanding 3D geometry for enhanced on-chip microbubble production and single step formation of liposome modified microbubbles

Abstract

Micron sized, lipid stabilized bubbles of gas are of interest as contrast agents for ultra-sound (US) imaging and increasingly as delivery vehicles for targeted, triggered, therapeutic delivery. Microfluidics provides a reproducible means for microbubble production and surface functionalisation. In this study, microbubbles are generated on chip using flow-focussing microfluidic devices that combine streams of gas and liquid through a nozzle a few microns wide and then subjecting the two phases to a downstream pressure drop. While microfluidics has successfully demonstrated the generation of monodisperse bubble populations, these approaches inherently produce low bubble counts. We introduce a new micro-spray flow regime that generates consistently high bubble concentrations that are more clinically relevant compared to traditional monodisperse bubble populations. Final bubble concentrations produced by the micro-spray regime were up to 10(10) bubbles mL(-1). The technique is shown to be highly reproducible and by using multiplexed chip arrays, the time taken to produce one millilitre of sample containing 10(10) bubbles mL(-1) was ∼10 min. Further, we also demonstrate that it is possible to attach liposomes, loaded with quantum dots (QDs) or fluorescein, in a single step during MBs formation.

Increasing the sonoporation efficiency of targeted polydisperse microbubble populations using chirp excitation

“…Microfluidic techniques for manufacturing monodisperse microbubble populations are in use, but the concentrations generated from these techniques are low when compared with available agents currently in clinical use [31]. Nevertheless, there are efforts to address this problem through generation in situ [32] or multiplexed devices [33].…”

Ultrasound assisted particle and cell manipulation on-chip

“…The techniques have also been demonstrated for the fabrication of liposome functionalised microbubbles [122] and in some cases the intention is that this sort of technology could be used to deliver microbubbles from an intrasvascular catheter directly to the treatment location [123].…”

“…Finally, in addition to the employment of microbubbles in on-chip devices, novel techniques for microbubble fabrication [121] have been adapted to miniaturised platforms [122,123] enabling lab-on-chip microbubble fabrication for drug delivery applications and the control of microbubble diameter to yield monodisperse microbubble suspensions. The techniques have also been demonstrated for the fabrication of liposome functionalised microbubbles [122] and in some cases the intention is that this sort of technology could be used to deliver microbubbles from an intrasvascular catheter directly to the treatment location [123].…”

Quantitative Ultrasound Molecular Imaging in Large Blood Vessel Environments

“…This distortion might lead to a build-up in liquid pressure, which again could overcome gas pressure leading to the cessation of MB production. However, by massively parallelizing MB production [191], [197], [225], [226] -either through FFMDs with multiple nozzles or multiple…”

“…The diameter distribution of the resulting MB population is highly polydisperse (i.e. polydispersity index or standard deviation/mean, up to 150%) [189], however, resulting in reduced image contrast compared to monodisperse populations of MBs [184], [190], [191]. Various size separating techniques [192]- [194] have been developed to sort polydisperse MBs into sub-populations with narrower size distributions, but this adds complexity and reduces overall yield.…”