High-frequency (20 to 40 MHz) acoustic response of liquid-filled nanocapsules

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

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 19F 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 19F MRI and fluorescence imaging, demonstrating their potential for long-term in vivo multimodal imaging.

Thin-Shelled PEGylated Perfluorooctyl Bromide Nanocapsules for Tumor-Targeted Ultrasound Contrast Agent

Shell thickness determines the acoustic response of polymer-based perfluorooctyl bromide (PFOB) nanocapsule ultrasound contrast agents. PEGylation provides stealth property and arms for targeting moieties. We investigated a modulation in the polymer formulation of carboxy-terminated poly(d,l-lactide-co-glycolide) (PLGA) and poly(d,l-lactide-co-glycolide)-block-polyethylene glycol (PLGA-b-PEG) to produce thin-shelled PFOB nanocapsules while keeping its echogenicity, stealth property, and active targeting potential. Polymer formulation contains 40% PLGA-PEG that yields the PEGylated PFOB nanocapsules of approximately 150 nm size with average thickness-to-radius ratio down to 0.15, which adequately hindered phagocytosis. Functionalization with antibody enables in vitro tumor-specific targeting. Despite the acoustic response improvement, the in vivo tumor accumulation was inadequate to generate an observable acoustic response to the ultrasound power at the clinical level. The use of PLGA and PLGA-PEG polymer blend allows the production of thin-shelled PFOB nanocapsules with echogenicity improvement while maintaining its potential for specific targeting.

Perfluorooctylbromide nanoparticles for ultrasound imaging and drug delivery

Perfluorooctylbromide nanoparticles (PFOB NPs) are a type of multifunctional nanotechnology that has been studied for various medical applications. Commercial ultrasound contrast agents (UCAs) suffer from the following limitations: short half-lives in vivo, high background signal and restricted distribution in the vascular circulation due to their micrometer dimensions. PFOB NPs are new potential UCAs that persist for long periods in the circulatory system, possess a relatively stable echogenic response without increasing the background signal and exhibit lower acoustic attenuation than commercial UCAs. Furthermore, PFOB NPs may also serve as drug delivery vehicles in which drugs are dissolved in the outer lipid or polymer layer for subsequent delivery to target sites in site-targeted therapy. The use of PFOB NPs as carriers has the potential advantage of selectively delivering payloads to the target site while improving visualization of the site using ultrasound (US) imaging. Unfortunately, the application of PFOB NPs to the field of ultrasonography has been limited because of the low intensity of US reflection. Numerous researchers have realized the potential use of PFOB NPs as UCAs and thus have developed alternative approaches to apply PFOB NPs in ultrasonography. In this article, we review the latest approaches for using PFOB NPs to enhance US imaging in vivo. In addition, this article emphasizes the application of PFOB NPs as promising drug delivery carriers for cancer and atherosclerosis treatments, as PFOB NPs can transport different drug payloads for various applications with good efficacy. We also note the challenges and future study directions for the application of PFOB NPs as both a delivery system for therapeutic agents and a diagnostic agent for ultrasonography.

Diagnostic and therapeutic research on ultrasound microbubble/nanobubble contrast agents (Review)

The contrast enhanced imaging function of ultrasound contrast agents (UCAs) has been extensively investigated using physical acoustic signatures. It has a number of novel applications, including tissue‑specific molecular imaging and multi‑modal imaging. In addition there are numerous other therapeutic applications of UCAs, for example as vehicles for drug or gene delivery. These uses are discussed, as well as the acoustically‑induced biological effects, including ultrasound targeted microbubble destruction (UTMD). This review also explores the considerations for the safe use of UCA from an acoustic standpoint. The scope of the application of UCA has markedly expanded in recent years, and it is a rapidly growing field of medical research. The current article reviews recent advances in the diagnostic and therapeutic applications of ultrasound microbubble/nanobubble contrast agents.