Multicore Liquid Perfluorocarbon‐Loaded Multimodal Nanoparticles for Stable Ultrasound and ¹⁹F MRI Applied to In Vivo Cell Tracking

Abstract

Ultrasound is the most commonly used clinical imaging modality. However, in applications requiring cell-labeling, the large size and short active lifetime of ultrasound contrast agents limit their longitudinal use. Here, 100 nm radius, clinically applicable, polymeric nanoparticles containing a liquid perfluorocarbon, which enhance ultrasound contrast during repeated ultrasound imaging over the course of at least 48 h, are described. The perfluorocarbon enables monitoring the nanoparticles with quantitative 19 F magnetic resonance imaging, making these particles effective multimodal imaging agents. Unlike typical core-shell perfluorocarbon-based ultrasound contrast agents, these nanoparticles have an atypical fractal internal structure. The nonvaporizing highly hydrophobic perfluorocarbon forms multiple cores within the polymeric matrix and is, surprisingly, hydrated with water, as determined from small-angle neutron scattering and nuclear magnetic resonance spectroscopy. Finally, the nanoparticles are used to image therapeutic dendritic cells with ultrasound in vivo, as well as with 19 F MRI and fluorescence imaging, demonstrating their potential for long-term in vivo multimodal imaging.

Continuous-Flow Production of Perfluorocarbon-Loaded Polymeric Nanoparticles: From the Bench to Clinic

“…In contrast, a typical deviation of the PFCE content between different batches prepared with conventional sonication is larger, typically around 10%. 9 Scanning electron microscopy (SEM) further confirmed that the NPs were spherical in shape and displayed some polydispersity, which is generally typical for PLGA particles. The majority of NPs had a radius between 100 and 200 nm, similar to DLS results.…”

“… 21 , 25 , 43 As a starting point for our study, we used the composition of our conventional batch formulation of PFCE–PLGA-NPs that were approved for a clinical trial. 9 , 24 At the beginning, we kept all main parameters, such as the concentration of the surfactant [poly(vinyl alcohol) (PVA)] and PLGA, the same as in the batch method, with dichloromethane (DCM) as a solvent for the organic phase, focusing on the effect of flow parameters. 22 − 24 The ratios between the three phases, which correspond to the volumes used in the conventional method, can be adjusted directly in the microfluidic system by changing the flow rates.…”

“… 21 , 45 , 46 In this application, PFCE–PLGA NPs made with the conventional batch method can act not just as imaging agents for 19 F MRI but also as multimodal imaging agents for ultrasound and optical methods. 9 , 22 , 24 On the therapeutic side, PFC-based colloids show promising results in the transportation of oxygen for the treatment of cancer 1 − 3 , 5 , 6 or stroke. 7 Therefore, in the current study, after basic toxicity testing, we focused on imaging applications and the oxygen loading in vitro .…”

“…Usually, NPs are too small to be detected with ultrasound. 9 Oppositely, we have recently shown that PFCE–PLGA NPs made with the conventional method can be imaged with ultrasound and are long-term stable in the acoustic field. 9 Both properties appeared to be related to the multicore structure of PFCE–PLGA NPs.…”

“… 7 , 8 Additionally, they act as multimodal imaging agents for 19 F magnetic resonance imaging ( 19 F MRI) and ultrasound. 9 − 12 PFCs, however, have already seen a long and much more varied history of clinical use. They were first used in the 1980s as blood substitutes because of their ability to dissolve oxygen.…”