Multilayer Polymer Shell Perfluoropentane Nanodroplets for Multimodal Ultrasound, Magnetic Resonance, and Optoacoustic Imaging

Abstract

Multimodal imaging increases the value of stand‐alone modalities by enabling simultaneous multiparametric characterization of biological tissues in vivo. Particularly, optoacoustic (OA) tomography has enabled bringing optical imaging advantages to previously unattainable depths and is currently being hybridized with other imaging technologies for enhanced performance. The full potential of these multimodal imaging approaches can only be achieved with dedicated contrast agents ensuring simultaneous measurements and accurate co‐registration of the information provided. Herein, perfluoropentane‐filled nanodroplets are modified, providing excellent contrast in ultrasound imaging, by introducing shell‐embedded additives offering strong contrast in magnetic resonance and OA imaging. Magnetite nanoparticles and indocyanine green (ICG) dye are simultaneously deposited as a multilayer shell on the droplets with the layer‐by‐layer method. This results in sufficiently high amounts of magnetite (0.54 ± 0.08 mg mL−1) and ICG (0.30 ± 0.08 mg mL−1) for efficient magnetic resonance and OA detection, respectively. The high sensitivity achieved with the developed trimodal nanodroplets is first demonstrated in phantom experiments, after which their potential toxic effects, biodistribution, and clearance are examined in vitro and in vivo. Taken together, the obtained results indicate that the developed multilayer polymer shell nanodroplets are efficient hybrid contrast agents for multimodal biomedical imaging applications.

Ultrasound-Based Micro-/Nanosystems for Biomedical Applications

“…Although polymer-based microbubbles offer only moderate ultrasound contrast in comparison to lipid-based counterparts, they are still detectable in clinical ultrasound imaging settings. Recent advancements have led to polymeric nanodroplets with fluorocarbon liquid cores that transform into gas-filled microbubbles upon acoustic evaporation. − However, these nanodroplets may necessitate higher acoustic pressures for vaporization, tend to enlarge significantly, and burst at certain thresholds, in contrast to microbubbles which maintain stable cavitation at lower acoustic pressures. Another innovative design is the nanocup, a solid polymeric nanoparticle comprising polystyrene beads coated with a layer of cross-linked poly­(methacrylic acid) (Figure a) .…”

Polymeric materials for ultrasound imaging and therapy

“…In addition, recently described polymeric nanodroplets with heavy liquid fluorocarbon-filled cores can convert into gas-filled MB upon acoustic or optical evaporation. 61–65 However, nanodroplets may require high acoustic pressures to vaporize, tend to grow significantly in size (up to several hundred microns), and burst at a certain diameter threshold, whereas MB are capable of stable cavitation at low acoustic pressures.…”