Bulk nanobubbles in the mineral and environmental areas: Updating research and applications.

Current commercially available ultrasound contrast agents are gas-filled, lipid- or protein-stabilized microbubbles larger than 1 µm in diameter. Because the signal generated by these agents is highly dependent on their size, small yet highly echogenic particles have been historically difficult to produce. This has limited the molecular imaging applications of ultrasound to the blood pool. In the area of cancer imaging, microbubble applications have been constrained to imaging molecular signatures of tumor vasculature and drug delivery enabled by ultrasound-modulated bubble destruction. Recently, with the rise of sophisticated advancements in nanomedicine, ultrasound contrast agents, which are an order of magnitude smaller (100-500 nm) than their currently utilized counterparts, have been undergoing rapid development. These agents are poised to greatly expand the capabilities of ultrasound in the field of targeted cancer detection and therapy by taking advantage of the enhanced permeability and retention phenomenon of many tumors and can extravasate beyond the leaky tumor vasculature. Agent extravasation facilitates highly sensitive detection of cell surface or microenvironment biomarkers, which could advance early cancer detection. Likewise, when combined with appropriate therapeutic agents and ultrasound-mediated deployment on demand, directly at the tumor site, these nanoparticles have been shown to contribute to improved therapeutic outcomes. Ultrasound's safety profile, broad accessibility and relatively low cost make it an ideal modality for the changing face of healthcare today. Aided by the multifaceted nano-sized contrast agents and targeted theranostic moieties described herein, ultrasound can considerably broaden its reach in future applications focused on the diagnosis and staging of cancer.

Ultrasound imaging beyond the vasculature with new generation contrast agents

/pdf/improving-performance-of-nanoscale-ultrasound-contrast-2azl9132ha.pdf

Improving performance of nanoscale ultrasound contrast agents using N,N-diethylacrylamide stabilization.

Chemical gas-generating nanoparticles for tumor-targeted ultrasound imaging and ultrasound-triggered drug delivery

Ultrasound (US) medical technology is widely used due to its advantages of safety, speed, and low cost. With the rapid development of biomedical nanotechnology, micro/nanobubbles, as US contrast agents, are not only valuable in US imaging diagnosis but also show broad application prospects in drug delivery. Nanobubbles (NBs) have more advantages as drug delivery systems (DDSs) due to their smaller size and longer circulation time compared with microbubbles. In this review, the fundamentals of NBs, including classification, stability mechanism, and preparation methods are summarized. Then, the strategies of a DDS based on NBs, including direct delivery, codelivery, target delivery, and stimuli‐responsive delivery are reviewed and discussed. The three main applications of NBs‐based DDSs, namely tumor theranostics, brain drug delivery, and vascular disease theranostics were highlighted. The challenges and future directions of the NBs‐based DDSs are also considered and discussed.

Drug delivery system based on nanobubbles

Nanobubbles and microbubbles are non-invasive ultrasound imaging contrast agents that may potentially enhance diagnosis of tumors. However, to date, both nanobubbles and microbubbles display poor in vivo tumor-selectivity over non-targeted organs such as liver. We report here cyanine 5.5 conjugated nanobubbles (cy5.5-nanobubbles) of a biocompatible chitosan–vitamin C lipid system as a dual ultrasound-fluorescence contrast agent that achieved tumor-selective imaging in a mouse tumor model. Cy5.5-nanobubble suspension contained single bubble spheres and clusters of bubble spheres with the size ranging between 400–800 nm. In the in vivo mouse study, enhancement of ultrasound signals at tumor site was found to persist over 2 h while tumor-selective fluorescence emission was persistently observed over 24 h with intravenous injection of cy5.5-nanobubbles. In vitro cell study indicated that cy5.5-flurescence dye was able to accumulate in cancer cells due to the unique conjugated nanobubble structure. Further in vivo fluorescence study suggested that cy5.5-nanobubbles were mainly located at tumor site and in the bladder of mice. Subsequent analysis confirmed that accumulation of high fluorescence was present at the intact subcutaneous tumor site and in isolated tumor tissue but not in liver tissue post intravenous injection of cy5.5-nanobubbles. All these results led to the conclusion that cy5.5-nanobubbles with unique crosslinked chitosan–vitamin C lipid system have achieved tumor-selective imaging in vivo.

/pdf/cyanine-5-5-conjugated-nanobubbles-as-a-tumor-selective-iqa087wcpy.pdf

Cyanine 5.5 Conjugated Nanobubbles as a Tumor Selective Contrast Agent for Dual Ultrasound-Fluorescence Imaging in a Mouse Model

Recent literatures have reported that the targeted nanoscale ultrasound contrast agents are becoming more and more important in medical application, like ultrasound imaging, detection of perfusion, drug delivery and molecular imaging and so on. In this study, we fabricated an uniform nanoscale bubbles (257 nm with the polydispersity index of 0.458) by incorporation of antibody targeted to vascular endothelial growth factor receptor 2 (VEGFR2) into the nanobubbles membrane by using avidin-biotin interaction. Some fundamental characterizations such as nanobubble suspension, surface morphology, particle size distribution and zeta potential were investigated. The concentration and time-intensity curves (TICs) were obtained with a self-made ultrasound experimental setup in vitro evaluation. In addition, in order to evaluate the contrast enhancement ability and the potential tumor-targeted ability in vivo, normal Wistar rats and nude female BALB/c mice were intravascular administration of the nanobubbles via tail vein injection, respectively. Significant contrast enhancement of ultrasound imaging within liver and tumor were visualized. These experiments demonstrated that the targeted nanobubbles is efficient in ultrasound molecular imaging by enhancement of the contrast effect and have potential capacity for targeted tumor diagnosis and therapy in the future.

Development and evaluation of a novel VEGFR2-targeted nanoscale ultrasound contrast agents

Ultrasound contrast agents (UCAs) such as SonoVue or Optison have been used widely in clinic
for contrast-enhanced vascular imaging. However, microbubbles UCAs display limitations in
tumor-targeted imaging due to the large sizes, nanoscaled UCAs has consequently attracted increasing
attentions. In this work, we synthesized nanobubbles (NBs) by ultrasonic cavitation method, then a
fluorescent marker of Alexa Fluor 680 was conjugated to the shell in order to observe the localization
of NBs in tumor tissue. Measurement of fundamental characteristics showed that the NBs had
homogeneous distribution of mean diameter of 267.9 ± 19.2 nm and polydispersity index of 0.410 ±
0.056. To assess in vivo tumor-selectivity of NBs, we established the rabbits VX2 hepatocellular
carcinoma model though surgical implantation method. After the rabbits were intravenous administered
of NBs, contrast-enhanced sonograms was observed in the surrounding of VX2 tumor, which showed
there are rich capillaries in the tumor periphery. We additionally investigated the toxic of the NBs by
hematoxylin-eosin staining. The results indicated that the NBs is a biocompatible non-toxic lipid
system. Furthermore, the VX2 tumors and major organs were analyzed using ex vivo fluorescence
imaging to confirm the targeted selectivity of NBs, and the results verified that the NBs were capable
of targeting VX2 tumor. Confocal laser scanning microscopy examination showed that the NBs can
traverse the VX2 tumor capillaries and target to the hepatocellular carcinoma tumor cells. All these
results suggested that the newly prepared NBs have a potential application in molecular imaging and
tumor-targeting therapy.

Novel fluorescence nanobubbles for contrast-enhanced ultrasound imaging in rabbit VX2 hepatocellular carcinoma model

In this paper, the relationship between image intensity and ultrasound contrast agent (UCA) concentration is investigated. Experiments are conducted in water bath using a silicon tube filled with UCA (SonoVue) at different concentrations (100μl/l to 6000μl/l) at around 37 °C to simulate the temperature in human body. The mean gray-scale intensity within the region of interest (ROI) is calculated to obtain the plot of signal intensity to UCA concentration. The results show that the intensity firstly exhibits a linear increase to the peak at approximately 1500μl/l then appears a downward trend due to the multiple scattering (MS) effects.

Relationship of ultrasound signal intensity with SonoVue concentration at body temperature in vitro

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Papers

Cyanine 5.5 Conjugated Nanobubbles as a Tumor Selective Contrast Agent for Dual Ultrasound-Fluorescence Imaging in a Mouse Model

Development and evaluation of a novel VEGFR2-targeted nanoscale ultrasound contrast agents

Novel fluorescence nanobubbles for contrast-enhanced ultrasound imaging in rabbit VX2 hepatocellular carcinoma model

Relationship of ultrasound signal intensity with SonoVue concentration at body temperature in vitro